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DUNE Phase II:
Scientific Opportunities, Detector Concepts, Technological Solutions
The DUNE Collaboration∗
August 26, 2024
∗Editors: Sowjanya Gollapinni, Anne Heavey, Stefan S¨oldner-Rembold, Michel Sorel
1
arXiv:2408.12725v1 [physics.ins-det] 22 Aug 2024
Authors
A. Abed Abud,35 B. Abi,156 R. Acciarri,66 M. A. Acero,12 M. R. Adames,193 G. Adamov,72 M. Adamowski,66
D. Adams,20 M. Adinolfi,19 C. Adriano,30 A. Aduszkiewicz,81 J. Aguilar,126 F. Akbar,175 K. Allison,43 S. Alonso
Monsalve,35 M. Alrashed,119 A. Alton,13 R. Alvarez,39 T. Alves,88 H. Amar,84 P. Amedo,85, 84 J. Anderson,8
C. Andreopoulos,128 M. Andreotti,94, 67 M. P. Andrews,66 F. Andrianala,5S. Andringa,127 N. Anfimov ,
A. Ankowski,184 D. Antic,19 M. Antoniassi,193 M. Antonova,84 A. Antoshkin , A. Aranda-Fernandez,42
L. Arellano,135 E. Arrieta Diaz,180 M. A. Arroyave,66 J. Asaadi,197 A. Ashkenazi,194 D. M. Asner,20 L. Asquith,191
E. Atkin,88 D. Auguste,160 A. Aurisano,40 V. Aushev,124 D. Autiero,110 M. B. Azam,87 F. Azfar,156 A. Back,91
H. Back,157 J. J. Back,209 I. Bagaturia,72 L. Bagby,66 N. Balashov , S. Balasubramanian,66 P. Baldi,24
W. Baldini,94 J. Baldonedo,206 B. Baller,66 B. Bambah,82 R. Banerjee,216 F. Barao,127, 112 D. Barbu,21
G. Barenboim,84 P. Barham Alz´as,35 G. J. Barker,209 W. Barkhouse,148 G. Barr,156 J. Barranco Monarca,77
A. Barros,193 N. Barros,127, 61 D. Barrow,156 J. L. Barrow,143 A. Basharina-Freshville,203 A. Bashyal,8V. Basque,66
C. Batchelor,57 L. Bathe-Peters,156 J.B.R. Battat,210 F. Battisti,156 F. Bay,4M. C. Q. Bazetto,30 J. L. L. Bazo
Alba,169 J. F. Beacom,154 E. Bechetoille,110 B. Behera,186 E. Belchior,130 G. Bell,52 L. Bellantoni,66
G. Bellettini,103, 167 V. Bellini,93, 31 O. Beltramello,35 N. Benekos,35 C. Benitez Montiel,84, 10 D. Benjamin,20
F. Bento Neves,127 J. Berger,44 S. Berkman,139 J. Bernal,10 P. Bernardini,97, 179 A. Bersani,96 S. Bertolucci,92, 17
M. Betancourt,66 A. Betancur Rodr´ıguez,58 A. Bevan,172 Y. Bezawada,23 A. T. Bezerra,62 T. J. Bezerra,191
A. Bhat,37 V. Bhatnagar,159 J. Bhatt,203 M. Bhattacharjee,89 M. Bhattacharya,66 S. Bhuller,19 B. Bhuyan,89
S. Biagi,105 J. Bian,24 K. Biery,66 B. Bilki,15, 108 M. Bishai,20 A. Bitadze,135 A. Blake,125 F. D. Blaszczyk,66
G. C. Blazey,149 E. Blucher,37 A. Bodek,175 J. Bogenschuetz,197 J. Boissevain,129 S. Bolognesi,34 T. Bolton,119
L. Bomben,98, 107 M. Bonesini,98, 140 C. Bonilla-Diaz,32 F. Bonini,20 A. Booth,172 F. Boran,91 S. Bordoni,35
R. Borges Merlo,30 A. Borkum,191 N. Bostan,108 R. Bouet,131 J. Boza,44 J. Bracinik,16 B. Brahma,90
D. Brailsford,125 F. Bramati,98 A. Branca,98 A. Brandt,197 J. Bremer,35 C. Brew,178 S. J. Brice,66 V. Brio,93
C. Brizzolari,98, 140 C. Bromberg,139 J. Brooke,19 A. Bross,66 G. Brunetti,98, 140 M. Brunetti,209 N. Buchanan,44
H. Budd,175 J. Buergi,14 A. Bundock,19 D. Burgardt,211 S. Butchart,191 G. Caceres V.,23 I. Cagnoli,92, 17 T. Cai,216
R. Calabrese,100 R. Calabrese,94, 67 J. Calcutt,155 L. Calivers,14 E. Calvo,39 A. Caminata,96 A. F. Camino,168
W. Campanelli,127 A. Campani,96, 71 A. Campos Benitez,207 N. Canci,100 J. Cap´o,84 I. Caracas,134 D. Caratelli,27
D. Carber,44 J. M. Carceller,35 G. Carini,20 B. Carlus,110 M. F. Carneiro,20 P. Carniti,98 I. Caro Terrazas,44
H. Carranza,197 N. Carrara,23 L. Carroll,119 T. Carroll,213 A. Carter,176 E. Casarejos,206 D. Casazza,94
J. F. Casta˜no Forero,7F. A. Casta˜no,6A. Castillo,182 C. Castromonte,106 E. Catano-Mur,212 C. Cattadori,98
F. Cavalier,160 F. Cavanna,66 S. Centro,158 G. Cerati,66 C. Cerna,131 A. Cervelli,92 A. Cervera Villanueva,84
K. Chakraborty,166 S. Chakraborty,86 M. Chalifour,35 A. Chappell,209 N. Charitonidis,35 A. Chatterjee,166
H. Chen,20 M. Chen,24 W. C. Chen,199 Y. Chen,184 Z. Chen-Wishart,176 D. Cherdack,81 C. Chi,45 F. Chiapponi,92
R. Chirco,87 N. Chitirasreemadam,103, 167 K. Cho,122 S. Choate,108 D. Chokheli,72 P. S. Chong,164 B. Chowdhury,8
D. Christian,66 A. Chukanov , M. Chung,202 E. Church,157 M. F. Cicala,203 M. Cicerchia,158 V. Cicero,92, 17
R. Ciolini,103 P. Clarke,57 G. Cline,126 T. E. Coan,188 A. G. Cocco,100 J. A. B. Coelho,161 A. Cohen,161
J. Collazo,206 J. Collot,76 E. Conley,55 J. M. Conrad,136 M. Convery,184 S. Copello,96 A. F. V. Cortez,217
P. Cova,99, 162 C. Cox,176 L. Cremaldi,144 L. Cremonesi,172 J. I. Crespo-Anad´on,39 M. Crisler,66 E. Cristaldo,98, 10
J. Crnkovic,66 G. Crone,203 R. Cross,209 A. Cudd,43 C. Cuesta,39 Y. Cui,26 F. Curciarello,95 D. Cussans,19
J. Dai,76 O. Dalager,66 R. Dallavalle,161 W. Dallaway,199 R. D’Amico,94, 67 H. da Motta,33 Z. A. Dar,212
R. Darby,191 L. Da Silva Peres,65 Q. David,110 G. S. Davies,144 S. Davini,96 J. Dawson,161 R. De Aguiar,30 P. De
Almeida,30 P. Debbins,108 I. De Bonis,51 M. P. Decowski,146, 3 A. de Gouvˆea,150 P. C. De Holanda,30 I. L. De
Icaza Astiz,191 P. De Jong,146, 3 P. Del Amo Sanchez,51 A. De la Torre,39 G. De Lauretis,110 A. Delbart,34
D. Delepine,77 M. Delgado,98, 140 A. Dell’Acqua,35 G. Delle Monache,95 N. Delmonte,99, 162 P. De Lurgio,8
R. Demario,139 G. De Matteis,97, 179 J. R. T. de Mello Neto,65 D. M. DeMuth,205 S. Dennis,29 C. Densham,178
P. Denton,20 G. W. Deptuch,20 A. De Roeck,35 V. De Romeri,84 J. P. Detje,29 J. Devine,35 R. Dharmapalan,79
M. Dias,201 A. Diaz,28 J. S. D´ıaz,91 F. D´ıaz,169 F. Di Capua,100, 145 A. Di Domenico,181, 104 S. Di Domizio,96, 71
S. Di Falco,103 L. Di Giulio,35 P. Ding,66 L. Di Noto,96, 71 E. Diociaiuti,95 C. Distefano,105 R. Diurba,14
M. Diwan,20 Z. Djurcic,8D. Doering,184 S. Dolan,35 F. Dolek,207 M. J. Dolinski,54 D. Domenici,95 L. Domine,184
S. Donati,103, 167 Y. Donon,35 S. Doran,109 D. Douglas,184 T.A. Doyle,189 A. Dragone,184 F. Drielsma,184
L. Duarte,201 D. Duchesneau,51 K. Duffy,156 K. Dugas,24 P. Dunne,88 B. Dutta,195 H. Duyang,185 D. A. Dwyer,126
A. S. Dyshkant,149 S. Dytman,168 M. Eads,149 A. Earle,191 S. Edayath,109 D. Edmunds,139 J. Eisch,66 P. Englezos,177
A. Ereditato,37 T. Erjavec,23 C. O. Escobar,66 J. J. Evans,135 E. Ewart,91 A. C. Ezeribe,183 K. Fahey,66 L. Fajt,35
2
A. Falcone,98, 140 M. Fani’,143, 129 C. Farnese,101 S. Farrell,174 Y. Farzan,111 D. Fedoseev , J. Felix,77 Y. Feng,109
E. Fernandez-Martinez,133 D. Fern´andez-Posada,85 G. Ferry,160 E. Fialova,50 L. Fields,151 P. Filip,49 A. Filkins,192
F. Filthaut,146, 173 R. Fine,129 G. Fiorillo,100, 145 M. Fiorini,94, 67 S. Fogarty,44 W. Foreman,87 J. Fowler,55
J. Franc,50 K. Francis,149 D. Franco,37 J. Franklin,56 J. Freeman,66 J. Fried,20 A. Friedland,184 S. Fuess,66
I. K. Furic,68 K. Furman,172 A. P. Furmanski,143 R. Gaba,159 A. Gabrielli,92, 17 A. M Gago,169 F. Galizzi,98
H. Gallagher,200 N. Gallice,20 V. Galymov,110 E. Gamberini,35 T. Gamble,183 F. Ganacim,193 R. Gandhi,78
S. Ganguly,66 F. Gao,27 S. Gao,20 D. Garcia-Gamez,73 M. ´
A. Garc´ıa-Peris,84 F. Gardim,62 S. Gardiner,66
D. Gastler,18 A. Gauch,14 J. Gauvreau,153 P. Gauzzi,181, 104 S. Gazzana,95 G. Ge,45 N. Geffroy,51 B. Gelli,30
S. Gent,187 L. Gerlach,20 Z. Ghorbani-Moghaddam,96 T. Giammaria,94, 67 D. Gibin,158, 101 I. Gil-Botella,39
S. Gilligan,155 A. Gioiosa,103 S. Giovannella,95 C. Girerd,110 A. K. Giri,90 C. Giugliano,94 V. Giusti,103 D. Gnani,126
O. Gogota,124 S. Gollapinni,129 K. Gollwitzer,66 R. A. Gomes,63 L. V. Gomez Bermeo,182 L. S. Gomez Fajardo,182
F. Gonnella,16 D. Gonzalez-Diaz,85 M. Gonzalez-Lopez,133 M. C. Goodman,8S. Goswami,166 C. Gotti,98
J. Goudeau,130 E. Goudzovski,16 C. Grace,126 E. Gramellini,135 R. Gran,142 E. Granados,77 P. Granger,161
C. Grant,18 D. R. Gratieri,70, 30 G. Grauso,100 P. Green,156 S. Greenberg,126, 22 J. Greer,19 W. C. Griffith,191
F. T. Groetschla,35 K. Grzelak,208 L. Gu,125 W. Gu,20 V. Guarino,8M. Guarise,94, 67 R. Guenette,135 M. Guerzoni,92
D. Guffanti,98, 140 A. Guglielmi,101 B. Guo,185 F. Y. Guo,189 A. Gupta,184 V. Gupta,146, 3 G. Gurung,197
D. Gutierrez,170 P. Guzowski,135 M. M. Guzzo,30 S. Gwon,38 A. Habig,142 H. Hadavand,197 L. Haegel,110
R. Haenni,14 L. Hagaman,214 A. Hahn,66 J. Haiston,186 J. Hakenm¨uller,55 T. Hamernik,66 P. Hamilton,88
J. Hancock,16 F. Happacher,95 D. A. Harris,216, 66 A. Hart,172 J. Hartnell,191 T. Hartnett,178 J. Harton,44
T. Hasegawa,121 C. M. Hasnip,35 R. Hatcher,66 K. Hayrapetyan,172 J. Hays,172 E. Hazen,18 M. He,81 A. Heavey,66
K. M. Heeger,214 J. Heise,190 P. Hellmuth,131 S. Henry,175 J. Hern´andez-Gar´ıa,84 K. Herner,66 V. Hewes,40
A. Higuera,174 C. Hilgenberg,143 S. J. Hillier,16 A. Himmel,66 E. Hinkle,37 L.R. Hirsch,193 J. Ho,53 J. Hoff,66
A. Holin,178 T. Holvey,156 E. Hoppe,157 S. Horiuchi,207 G. A. Horton-Smith,119 T. Houdy,160 B. Howard,216
R. Howell,175 I. Hristova,178 M. S. Hronek,66 J. Huang,23 R.G. Huang,126 Z. Hulcher,184 M. Ibrahim,59 G. Iles,88
N. Ilic,199 A. M. Iliescu,95 R. Illingworth,66 G. Ingratta,92, 17 A. Ioannisian,215 B. Irwin,143 L. Isenhower,1
M. Ismerio Oliveira,65 R. Itay,184 C.M. Jackson,157 V. Jain,2E. James,66 W. Jang,197 B. Jargowsky,24 D. Jena,66
I. Jentz,213 X. Ji,20 C. Jiang,115 J. Jiang,189 L. Jiang,207 A. Jipa,21 J. H. Jo,20 F. R. Joaquim,127, 112 W. Johnson,186
C. Jollet,131 B. Jones,197 R. Jones,183 N. Jovancevic,152 M. Judah,168 C. K. Jung,189 T. Junk,66 Y. Jwa,184, 45
M. Kabirnezhad,88 A. C. Kaboth,176, 178 I. Kadenko,124 I. Kakorin , A. Kalitkina , D. Kalra,45 M. Kandemir,60
D. M. Kaplan,87 G. Karagiorgi,45 G. Karaman,108 A. Karcher,126 Y. Karyotakis,51 S. Kasai,123 S. P. Kasetti,130
L. Kashur,44 I. Katsioulas,16 A. Kauther,149 N. Kazaryan,215 L. Ke,20 E. Kearns,18 P.T. Keener,164 K.J. Kelly,195
E. Kemp,30 O. Kemularia,72 Y. Kermaidic,160 W. Ketchum,66 S. H. Kettell,20 M. Khabibullin , N. Khan,88
A. Khvedelidze,72 D. Kim,195 J. Kim,175 M. J. Kim,66 B. King,66 B. Kirby,45 M. Kirby,20 A. Kish,66 J. Klein,164
J. Kleykamp,144 A. Klustova,88 T. Kobilarcik,66 L. Koch,134 K. Koehler,213 L. W. Koerner,81 D. H. Koh,184
L. Kolupaeva , D. Korablev , M. Kordosky,212 T. Kosc,76 U. Kose,35 V. A. Kosteleck´y,91 K. Kothekar,19
I. Kotler,54 M. Kovalcuk,49 V. Kozhukalov , W. Krah,146 R. Kralik,191 M. Kramer,126 L. Kreczko,19
F. Krennrich,109 I. Kreslo,14 T. Kroupova,164 S. Kubota,135 M. Kubu,35 Y. Kudenko , V. A. Kudryavtsev,183
G. Kufatty,69 S. Kuhlmann,8S. Kulagin , J. Kumar,79 P. Kumar,183 S. Kumaran,24 J. Kunzmann,14 R. Kuravi,126
N. Kurita,184 C. Kuruppu,185 V. Kus,50 T. Kutter,130 M. Ku´zniak,217 J. Kvasnicka,49 T. Labree,149 T. Lackey,66
I. Lal˘au,21 A. Lambert,126 B. J. Land,164 C. E. Lane,54 N. Lane,135 K. Lang,198 T. Langford,214 M. Langstaff,135
F. Lanni,35 O. Lantwin,51 J. Larkin,20 P. Lasorak,88 D. Last,164 A. Laudrain,134 A. Laundrie,213 G. Laurenti,92
E. Lavaut,160 P. Laycock,20 I. Lazanu,21 R. LaZur,44 M. Lazzaroni,99, 141 T. Le,200 S. Leardini,85 J. Learned,79
T. LeCompte,184 V. Legin,124 G. Lehmann Miotto,35 R. Lehnert,91 M. A. Leigui de Oliveira,64 M. Leitner,126
D. Leon Silverio,186 L. M. Lepin,69 J.-Y Li,57 S. W. Li,24 Y. Li,20 H. Liao,119 C. S. Lin,126 D. Lindebaum,19
S. Linden,20 R. A. Lineros,32 A. Lister,213 B. R. Littlejohn,87 H. Liu,20 J. Liu,24 Y. Liu,37 S. Lockwitz,66
M. Lokajicek,49 I. Lomidze,72 K. Long,88 T. V. Lopes,62 J.Lopez,6I. L´opez de Rego,39 N. L´opez-March,84
T. Lord,209 J. M. LoSecco,151 W. C. Louis,129 A. Lozano Sanchez,54 X.-G. Lu,209 K.B. Luk,80, 126, 22 B. Lunday,164
X. Luo,27 E. Luppi,94, 67 D. MacFarlane,184 A. A. Machado,30 P. Machado,66 C. T. Macias,91 J. R. Macier,66
M. MacMahon,203 A. Maddalena,75 A. Madera,35 P. Madigan,22, 126 S. Magill,8C. Magueur,160 K. Mahn,139
A. Maio,127, 61 A. Major,55 K. Majumdar,128 S. Mameli,103 M. Man,199 R. C. Mandujano,24 J. Maneira,127, 61
S. Manly,175 A. Mann,200 K. Manolopoulos,178 M. Manrique Plata,91 S. Manthey Corchado,39 V. N. Manyam,20
M. Marchan,66 A. Marchionni,66 W. Marciano,20 D. Marfatia,79 C. Mariani,207 J. Maricic,79 F. Marinho,113
A. D. Marino,43 T. Markiewicz,184 F. Das Chagas Marques,30 C. Marquet,131 M. Marshak,143 C. M. Marshall,175
3
J. Marshall,209 L. Martina,97, 179 J. Mart´ın-Albo,84 N. Martinez,119 D.A. Martinez Caicedo,186 F. Mart´ınez
L´opez,172 P. Mart´ınez Mirav´e,84 S. Martynenko,20 V. Mascagna,98 C. Massari,98 A. Mastbaum,177 F. Matichard,126
S. Matsuno,79 G. Matteucci,100, 145 J. Matthews,130 C. Mauger,164 N. Mauri,92, 17 K. Mavrokoridis,128 I. Mawby,125
R. Mazza,98 T. McAskill,210 N. McConkey,172, 203 K. S. McFarland,175 C. McGrew,189 A. McNab,135 L. Meazza,98
V. C. N. Meddage,68 A. Mefodiev , B. Mehta,159 P. Mehta,116 P. Melas,11 O. Mena,84 H. Mendez,170 P. Mendez,35
D. P. M´endez,20 A. Menegolli,102, 163 G. Meng,101 A. C. E. A. Mercuri,193 A. Meregaglia,131 M. D. Messier,91
S. Metallo,143 W. Metcalf,130 M. Mewes,91 H. Meyer,211 T. Miao,66 J. Micallef,200,136 A. Miccoli,97 G. Michna,187
R. Milincic,79 F. Miller,213 G. Miller,135 W. Miller,143 O. Mineev , A. Minotti,98, 140 L. Miralles,35 O. G. Miranda,41
C. Mironov,161 S. Miryala,20 S. Miscetti,95 C. S. Mishra,66 P. Mishra,82 S. R. Mishra,185 A. Mislivec,143
M. Mitchell,130 D. Mladenov,35 I. Mocioiu,165 A. Mogan,66 N. Moggi,92, 17 R. Mohanta,82 T. A. Mohayai,91
N. Mokhov,66 J. Molina,10 L. Molina Bueno,84 E. Montagna,92, 17 A. Montanari,92 C. Montanari,102, 66, 163
D. Montanari,66 D. Montanino,97,179 L. M. Monta˜no Zetina,41 M. Mooney,44 A. F. Moor,183 Z. Moore,192
D. Moreno,7O. Moreno-Palacios,212 L. Morescalchi,103 D. Moretti,98 R. Moretti,98 C. Morris,81 C. Mossey,66
C. A. Moura,64 G. Mouster,125 W. Mu,66 L. Mualem,28 J. Mueller,44 M. Muether,211 F. Muheim,57 A. Muir,52
M. Mulhearn,23 D. Munford,81 L. J. Munteanu,35 H. Muramatsu,143 J. Muraz,76 M. Murphy,207 T. Murphy,192
J. Muse,143 A. Mytilinaki,178 J. Nachtman,108 Y. Nagai,59 S. Nagu,132 R. Nandakumar,178 D. Naples,168
S. Narita,114 A. Navrer-Agasson,88, 135 N. Nayak,20 M. Nebot-Guinot,57 A. Nehm,134 J. K. Nelson,212 O. Neogi,108
J. Nesbit,213 M. Nessi,66, 35 D. Newbold,178 M. Newcomer,164 R. Nichol,203 F. Nicolas-Arnaldos,73 A. Nikolica,164
J. Nikolov,152 E. Niner,66 K. Nishimura,79 A. Norman,66 A. Norrick,66 P. Novella,84 A. Nowak,125 J. A. Nowak,125
M. Oberling,8J. P. Ochoa-Ricoux,24 S. Oh,55 S.B. Oh,66 A. Olivier,151 A. Olshevskiy , T. Olson,81 Y. Onel,108
Y. Onishchuk,124 A. Oranday,91 G. D. Orebi Gann,22, 126 M. Osbiston,209 J. A. Osorio V´elez,6L. O’Sullivan,134
L. Otiniano Ormachea,46, 106 J. Ott,24 L. Pagani,23 G. Palacio,58 O. Palamara,66 S. Palestini,35 J. M. Paley,66
M. Pallavicini,96,71 C. Palomares,39 S. Pan,166 P. Panda,82 W. Panduro Vazquez,176 E. Pantic,23 V. Paolone,168
R. Papaleo,105 A. Papanestis,178 D. Papoulias,11 S. Paramesvaran,19 A. Paris,170 S. Parke,66 E. Parozzi,98, 140
S. Parsa,14 Z. Parsa,20 S. Parveen,116 M. Parvu,21 D. Pasciuto,103 S. Pascoli,92, 17 L. Pasqualini,92, 17 J. Pasternak,88
C. Patrick,57,203 L. Patrizii,92 R. B. Patterson,28 T. Patzak,161 A. Paudel,66 L. Paulucci,64 Z. Pavlovic,66
G. Pawloski,143 D. Payne,128 V. Pec,49 E. Pedreschi,103 S. J. M. Peeters,191 W. Pellico,66 A. Pena Perez,184
E. Pennacchio,110 A. Penzo,108 O. L. G. Peres,30 Y. F. Perez Gonzalez,56 L. P´erez-Molina,39 C. Pernas,212
J. Perry,57 D. Pershey,69 G. Pessina,98 G. Petrillo,184 C. Petta,93, 31 R. Petti,185 M. Pfaff,88 V. Pia,92, 17
L. Pickering,178,176 F. Pietropaolo,35, 101 V.L.Pimentel,47, 30 G. Pinaroli,20 S. Pincha,89 J. Pinchault,51 K. Pitts,207
K. Plows,156 C. Pollack,170 T. Pollman,146, 3 F. Pompa,84 X. Pons,35 N. Poonthottathil,86, 109 V. Popov,194
F. Poppi,92, 17 J. Porter,191 L. G. Porto Paix˜ao,30 M. Potekhin,20 R. Potenza,93,31 J. Pozimski,88 M. Pozzato,92, 17
T. Prakash,126 C. Pratt,23 M. Prest,98 F. Psihas,66 D. Pugnere,110 X. Qian,20 J. Queen,55 J. L. Raaf,66 V. Radeka,20
J. Rademacker,19 B. Radics,216 F. Raffaelli,103 A. Rafique,8E. Raguzin,20 M. Rai,209 S. Rajagopalan,20
M. Rajaoalisoa,40 I. Rakhno,66 L. Rakotondravohitra,5L. Ralte,90 M. A. Ramirez Delgado,164 B. Ramson,66
A. Rappoldi,102, 163 G. Raselli,102, 163 P. Ratoff,125 R. Ray,66 H. Razafinime,40 E. M. Rea,143 J. S. Real,76
B. Rebel,213, 66 R. Rechenmacher,66 J. Reichenbacher,186 S. D. Reitzner,66 H. Rejeb Sfar,35 E. Renner,129
A. Renshaw,81 S. Rescia,20 F. Resnati,35 Diego Restrepo,6C. Reynolds,172 M. Ribas,193 S. Riboldi,99 C. Riccio,189
G. Riccobene,105 J. S. Ricol,76 M. Rigan,191 E. V. Rinc´on,58 A. Ritchie-Yates,176 S. Ritter,134 D. Rivera,129
R. Rivera,66 A. Robert,76 J. L. Rocabado Rocha,84 L. Rochester,184 M. Roda,128 P. Rodrigues,156 M. J. Rodriguez
Alonso,35 J. Rodriguez Rondon,186 S. Rosauro-Alcaraz,160 P. Rosier,160 D. Ross,139 M. Rossella,102,163 M. Rossi,35
M. Ross-Lonergan,129 N. Roy,216 P. Roy,211 C. Rubbia,74 A. Ruggeri,92 G. Ruiz,135 B. Russell,136
D. Ruterbories,175 A. Rybnikov , S. Sacerdoti,161 S. Saha,168 S. K. Sahoo,90 N. Sahu,90 P. Sala,66 N. Samios,20
O. Samoylov , M. C. Sanchez,69 A. S´anchez Bravo,84 A. S´anchez-Castillo,73 P. Sanchez-Lucas,73 V. Sandberg,129
D. A. Sanders,144 S. Sanfilippo,105 D. Sankey,178 D. Santoro,99, 162 N. Saoulidou,11 P. Sapienza,105 C. Sarasty,40
I. Sarcevic,9I. Sarra,95 G. Savage,66 V. Savinov,168 G. Scanavini,214 A. Scaramelli,102 A. Scarff,183 T. Schefke,130
H. Schellman,155, 66 S. Schifano,94, 67 P. Schlabach,66 D. Schmitz,37 A. W. Schneider,136 K. Scholberg,55
A. Schukraft,66 B. Schuld,43 A. Segade,206 E. Segreto,30 A. Selyunin , D. Senadheera,168 S. H. Seo,66
C. R. Senise,201 J. Sensenig,164 M. H. Shaevitz,45 P. Shanahan,66 P. Sharma,159 R. Kumar,171 S. Sharma
Poudel,186 K. Shaw,191 T. Shaw,66 K. Shchablo,110 J. Shen,164 C. Shepherd-Themistocleous,178 A. Sheshukov ,
J. Shi,29 W. Shi,189 S. Shin,117 S. Shivakoti,211 I. Shoemaker,207 D. Shooltz,139 R. Shrock,189 B. Siddi,94
M. Siden,44 J. Silber,126 L. Simard,160 J. Sinclair,184 G. Sinev,186 J. Singh,23 L. Singh,48 P. Singh,172 V. Singh,48
S. Singh Chauhan,159 R. Sipos,35 C. Sironneau,161 G. Sirri,92 K. Siyeon,38 K. Skarpaas,184 J. Smedley,175
4
E. Smith,91 J. Smith,189 P. Smith,91 J. Smolik,50, 49 M. Smy,24 M. Snape,209 E.L. Snider,66 P. Snopok,87
D. Snowden-Ifft,153 M. Soares Nunes,66 H. Sobel,24 M. Soderberg,192 S. Sokolov , C. J. Solano Salinas,204, 106
S. S¨oldner-Rembold,88, 135 N. Solomey,211 V. Solovov,127 W. E. Sondheim,129 M. Sorel,84 A. Sotnikov ,
J. Soto-Oton,84 A. Sousa,40 K. Soustruznik,36 F. Spinella,103 J. Spitz,138 N. J. C. Spooner,183 K. Spurgeon,192
D. Stalder,10 M. Stancari,66 L. Stanco,158, 101 J. Steenis,23 R. Stein,19 H. M. Steiner,126 A. F. Steklain Lisbˆoa,193
A. Stepanova , J. Stewart,20 B. Stillwell,37 J. Stock,186 F. Stocker,35 T. Stokes,130 M. Strait,143 T. Strauss,66
L. Strigari,195 A. Stuart,42 J. G. Suarez,58 J. Subash,16 A. Surdo,97 L. Suter,66 C. M. Sutera,93, 31 K. Sutton,28
Y. Suvorov,100, 145 R. Svoboda,23 S. K. Swain,147 B. Szczerbinska,196 A. M. Szelc,57 A. Sztuc,203 A. Taffara,103
N. Talukdar,185 J. Tamara,7H. A. Tanaka,184 S. Tang,20 N. Taniuchi,29 A. M. Tapia Casanova,137 B. Tapia
Oregui,198 A. Tapper,88 S. Tariq,66 E. Tarpara,20 E. Tatar,83 R. Tayloe,91 D. Tedeschi,185 A. M. Teklu,189 J. Tena
Vidal,194 P. Tennessen,126, 4 M. Tenti,92 K. Terao,184 F. Terranova,98,140 G. Testera,96 T. Thakore,40 A. Thea,178
S. Thomas,192 A. Thompson,195 C. Thorn,20 S. C. Timm,66 E. Tiras,60, 108 V. Tishchenko,20 N. Todorovi´c,152
L. Tomassetti,94, 67 A. Tonazzo,161 D. Torbunov,20 M. Torti,98, 140 M. Tortola,84 F. Tortorici,93, 31 N. Tosi,92
D. Totani,27 M. Toups,66 C. Touramanis,128 D. Tran,81 R. Travaglini,92 J. Trevor,28 E. Triller,139 S. Trilov,19
J. Truchon,213 D. Truncali,181, 104 W. H. Trzaska,118 Y. Tsai,24 Y.-T. Tsai,184 Z. Tsamalaidze,72 K. V. Tsang,184
N. Tsverava,72 S. Z. Tu,115 S. Tufanli,35 C. Tunnell,174 S. Turnberg,87 J. Turner,56 M. Tuzi,84 J. Tyler,119
E. Tyley,183 M. Tzanov,130 M. A. Uchida,29 J. Ure˜na Gonz´alez,84 J. Urheim,91 T. Usher,184 H. Utaegbulam,175
S. Uzunyan,149 M. R. Vagins,120, 24 P. Vahle,212 S. Valder,191 G. A. Valdiviesso,62 E. Valencia,77 R. Valentim,201
Z. Vallari,28 E. Vallazza,98 J. W. F. Valle,84 R. Van Berg,164 R. G. Van de Water,129 D. V. Forero,137
A. Vannozzi,95 M. Van Nuland-Troost,146 F. Varanini,101 D. Vargas Oliva,199 S. Vasina , N. Vaughan,155
K. Vaziri,66 A. V´azquez-Ramos,73 J. Vega,46 S. Ventura,101 A. Verdugo,39 S. Vergani,203 M. Verzocchi,66
K. Vetter,66 M. Vicenzi,20 H. Vieira de Souza,161 C. Vignoli,75 C. Vilela,127 E. Villa,35 S. Viola,105 B. Viren,20
A. P. Vizcaya Hernandez,44 Q. Vuong,175 A. V. Waldron,172 M. Wallbank,40 J. Walsh,139 T. Walton,66 H. Wang,25
J. Wang,186 L. Wang,126 M.H.L.S. Wang,66 X. Wang,66 Y. Wang,25 K. Warburton,109 D. Warner,44 L. Warsame,88
M.O. Wascko,156, 178 D. Waters,203 A. Watson,16 K. Wawrowska,178, 191 A. Weber,134, 66 C. M. Weber,143
M. Weber,14 H. Wei,130 A. Weinstein,109 S. Westerdale,26 M. Wetstein,109 K. Whalen,178 A. White,197 A. White,214
L. H. Whitehead,29 D. Whittington,192 J. Wilhlemi,214 M. J. Wilking,143 A. Wilkinson,203 C. Wilkinson,126
F. Wilson,178 R. J. Wilson,44 P. Winter,8W. Wisniewski,184 J. Wolcott,200 J. Wolfs,175 T. Wongjirad,200
A. Wood,81 K. Wood,126 E. Worcester,20 M. Worcester,20 M. Wospakrik,66 K. Wresilo,29 C. Wret,175 S. Wu,143
W. Wu,66 W. Wu,24 M. Wurm,134 J. Wyenberg,53 Y. Xiao,24 I. Xiotidis,88 B. Yaeggy,40 N. Yahlali,84
E. Yandel,27 J. Yang,80 K. Yang,156 T. Yang,66 A. Yankelevich,24 N. Yershov , K. Yonehara,66 T. Young,148
B. Yu,20 H. Yu,20 J. Yu,197 Y. Yu,87 W. Yuan,57 R. Zaki,216 J. Zalesak,49 L. Zambelli,51 B. Zamorano,73
A. Zani,99 O. Zapata,6L. Zazueta,192 G. P. Zeller,66 J. Zennamo,66 K. Zeug,213 C. Zhang,20 S. Zhang,91
M. Zhao,20 E. Zhivun,20 E. D. Zimmerman,43 S. Zucchelli,92, 17 J. Zuklin,49 V. Zutshi,149 and R. Zwaska66
(The DUNE Collaboration)
1Abilene Christian University, Abilene, TX 79601, USA
2University at Albany, SUNY, Albany, NY 12222, USA
3University of Amsterdam, NL-1098 XG Amsterdam, The Netherlands
4Antalya Bilim University, 07190 D¨o¸semealtı/Antalya, Turkey
5University of Antananarivo, Antananarivo 101, Madagascar
6University of Antioquia, Medell´ın, Colombia
7Universidad Antonio Nari˜no, Bogot´a, Colombia
8Argonne National Laboratory, Argonne, IL 60439, USA
9University of Arizona, Tucson, AZ 85721, USA
10Universidad Nacional de Asunci´on, San Lorenzo, Paraguay
11University of Athens, Zografou GR 157 84, Greece
12Universidad del Atl´antico, Barranquilla, Atl´antico, Colombia
13Augustana University, Sioux Falls, SD 57197, USA
14University of Bern, CH-3012 Bern, Switzerland
15Beykent University, Istanbul, Turkey
16University of Birmingham, Birmingham B15 2TT, United Kingdom
17Universit`a di Bologna, 40127 Bologna, Italy
18Boston University, Boston, MA 02215, USA
19University of Bristol, Bristol BS8 1TL, United Kingdom
20Brookhaven National Laboratory, Upton, NY 11973, USA
21University of Bucharest, Bucharest, Romania
22University of California Berkeley, Berkeley, CA 94720, USA
5
23University of California Davis, Davis, CA 95616, USA
24University of California Irvine, Irvine, CA 92697, USA
25University of California Los Angeles, Los Angeles, CA 90095, USA
26University of California Riverside, Riverside CA 92521, USA
27University of California Santa Barbara, Santa Barbara, CA 93106, USA
28California Institute of Technology, Pasadena, CA 91125, USA
29University of Cambridge, Cambridge CB3 0HE, United Kingdom
30Universidade Estadual de Campinas, Campinas - SP, 13083-970, Brazil
31Universit`a di Catania, 2 - 95131 Catania, Italy
32Universidad Cat´olica del Norte, Antofagasta, Chile
33Centro Brasileiro de Pesquisas F´ısicas, Rio de Janeiro, RJ 22290-180, Brazil
34IRFU, CEA, Universit´e Paris-Saclay, F-91191 Gif-sur-Yvette, France
35CERN, The European Organization for Nuclear Research, 1211 Meyrin, Switzerland
36Institute of Particle and Nuclear Physics of the Faculty of Mathematics
and Physics of the Charles University, 180 00 Prague 8, Czech Republic
37University of Chicago, Chicago, IL 60637, USA
38Chung-Ang University, Seoul 06974, South Korea
39CIEMAT, Centro de Investigaciones Energ´eticas, Medioambientales y Tecnol´ogicas, E-28040 Madrid, Spain
40University of Cincinnati, Cincinnati, OH 45221, USA
41Centro de Investigaci´on y de Estudios Avanzados del Instituto Polit´ecnico Nacional (Cinvestav), Mexico City, Mexico
42Universidad de Colima, Colima, Mexico
43University of Colorado Boulder, Boulder, CO 80309, USA
44Colorado State University, Fort Collins, CO 80523, USA
45Columbia University, New York, NY 10027, USA
46Comisi´on Nacional de Investigaci´on y Desarrollo Aeroespacial, Lima, Peru
47Centro de Tecnologia da Informacao Renato Archer, Amarais - Campinas, SP - CEP 13069-901
48Central University of South Bihar, Gaya, 824236, India
49Institute of Physics, Czech Academy of Sciences, 182 00 Prague 8, Czech Republic
50Czech Technical University, 115 19 Prague 1, Czech Republic
51Laboratoire d’Annecy de Physique des Particules, Universit´e Savoie Mont Blanc, CNRS, LAPP-IN2P3, 74000 Annecy, France
52Daresbury Laboratory, Cheshire WA4 4AD, United Kingdom
53Dordt University, Sioux Center, IA 51250, USA
54Drexel University, Philadelphia, PA 19104, USA
55Duke University, Durham, NC 27708, USA
56Durham University, Durham DH1 3LE, United Kingdom
57University of Edinburgh, Edinburgh EH8 9YL, United Kingdom
58Universidad EIA, Envigado, Antioquia, Colombia
59E¨otv¨os Lor´and University, 1053 Budapest, Hungary
60Erciyes University, Kayseri, Turkey
61Faculdade de Ciˆencias da Universidade de Lisboa - FCUL, 1749-016 Lisboa, Portugal
62Universidade Federal de Alfenas, Po¸cos de Caldas - MG, 37715-400, Brazil
63Universidade Federal de Goias, Goiania, GO 74690-900, Brazil
64Universidade Federal do ABC, Santo Andr´e - SP, 09210-580, Brazil
65Universidade Federal do Rio de Janeiro, Rio de Janeiro - RJ, 21941-901, Brazil
66Fermi National Accelerator Laboratory, Batavia, IL 60510, USA
67University of Ferrara, Ferrara, Italy
68University of Florida, Gainesville, FL 32611-8440, USA
69Florida State University, Tallahassee, FL, 32306 USA
70Fluminense Federal University, 9 Icara´ı Niter´oi - RJ, 24220-900, Brazil
71Universit`a degli Studi di Genova, Genova, Italy
72Georgian Technical University, Tbilisi, Georgia
73University of Granada & CAFPE, 18002 Granada, Spain
74Gran Sasso Science Institute, L’Aquila, Italy
75Laboratori Nazionali del Gran Sasso, L’Aquila AQ, Italy
76University Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 38000 Grenoble, France
77Universidad de Guanajuato, Guanajuato, C.P. 37000, Mexico
78Harish-Chandra Research Institute, Jhunsi, Allahabad 211 019, India
79University of Hawaii, Honolulu, HI 96822, USA
80Hong Kong University of Science and Technology, Kowloon, Hong Kong, China
81University of Houston, Houston, TX 77204, USA
82University of Hyderabad, Gachibowli, Hyderabad - 500 046, India
83Idaho State University, Pocatello, ID 83209, USA
84Instituto de F´ısica Corpuscular, CSIC and Universitat de Val`encia, 46980 Paterna, Valencia, Spain
85Instituto Galego de F´ısica de Altas Enerx´ıas, University of Santiago de Compostela, Santiago de Compostela, 15782, Spain
6
86Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India
87Illinois Institute of Technology, Chicago, IL 60616, USA
88Imperial College of Science, Technology and Medicine, London SW7 2BZ, United Kingdom
89Indian Institute of Technology Guwahati, Guwahati, 781 039, India
90Indian Institute of Technology Hyderabad, Hyderabad, 502285, India
91Indiana University, Bloomington, IN 47405, USA
92Istituto Nazionale di Fisica Nucleare Sezione di Bologna, 40127 Bologna BO, Italy
93Istituto Nazionale di Fisica Nucleare Sezione di Catania, I-95123 Catania, Italy
94Istituto Nazionale di Fisica Nucleare Sezione di Ferrara, I-44122 Ferrara, Italy
95Istituto Nazionale di Fisica Nucleare Laboratori Nazionali di Frascati, Frascati, Roma, Italy
96Istituto Nazionale di Fisica Nucleare Sezione di Genova, 16146 Genova GE, Italy
97Istituto Nazionale di Fisica Nucleare Sezione di Lecce, 73100 - Lecce, Italy
98Istituto Nazionale di Fisica Nucleare Sezione di Milano Bicocca, 3 - I-20126 Milano, Italy
99Istituto Nazionale di Fisica Nucleare Sezione di Milano, 20133 Milano, Italy
100Istituto Nazionale di Fisica Nucleare Sezione di Napoli, I-80126 Napoli, Italy
101Istituto Nazionale di Fisica Nucleare Sezione di Padova, 35131 Padova, Italy
102Istituto Nazionale di Fisica Nucleare Sezione di Pavia, I-27100 Pavia, Italy
103Istituto Nazionale di Fisica Nucleare Laboratori Nazionali di Pisa, Pisa PI, Italy
104Istituto Nazionale di Fisica Nucleare Sezione di Roma, 00185 Roma RM, Italy
105Istituto Nazionale di Fisica Nucleare Laboratori Nazionali del Sud, 95123 Catania, Italy
106Universidad Nacional de Ingenier´ıa, Lima 25, Per´u
107University of Insubria, Via Ravasi, 2, 21100 Varese VA, Italy
108University of Iowa, Iowa City, IA 52242, USA
109Iowa State University, Ames, Iowa 50011, USA
110Institut de Physique des 2 Infinis de Lyon, 69622 Vil leurbanne, France
111Institute for Research in Fundamental Sciences, Tehran, Iran
112Instituto Superior T´ecnico - IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
113Instituto Tecnol´ogico de Aeron´autica, Sao Jose dos Campos, Brazil
114Iwate University, Morioka, Iwate 020-8551, Japan
115Jackson State University, Jackson, MS 39217, USA
116Jawaharlal Nehru University, New Delhi 110067, India
117Jeonbuk National University, Jeonrabuk-do 54896, South Korea
118Jyv¨askyl¨a University, FI-40014 Jyv¨askyl¨a, Finland
119Kansas State University, Manhattan, KS 66506, USA
120Kavli Institute for the Physics and Mathematics of the Universe, Kashiwa, Chiba 277-8583, Japan
121High Energy Accelerator Research Organization (KEK), Ibaraki, 305-0801, Japan
122Korea Institute of Science and Technology Information, Daejeon, 34141, South Korea
123National Institute of Technology, Kure College, Hiroshima, 737-8506, Japan
124Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine
125Lancaster University, Lancaster LA1 4YB, United Kingdom
126Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
127Laborat´orio de Instrumenta¸c˜ao e F´ısica Experimental de Part´ıculas, 1649-003 Lisboa and 3004-516 Coimbra, Portugal
128University of Liverpool, L69 7ZE, Liverpool, United Kingdom
129Los Alamos National Laboratory, Los Alamos, NM 87545, USA
130Louisiana State University, Baton Rouge, LA 70803, USA
131Laboratoire de Physique des Deux Infinis Bordeaux - IN2P3, F-33175 Gradignan, Bordeaux, France,
132University of Lucknow, Uttar Pradesh 226007, India
133Madrid Autonoma University and IFT UAM/CSIC, 28049 Madrid, Spain
134Johannes Gutenberg-Universit¨at Mainz, 55122 Mainz, Germany
135University of Manchester, Manchester M13 9PL, United Kingdom
136Massachusetts Institute of Technology, Cambridge, MA 02139, USA
137University of Medell´ın, Medell´ın, 050026 Colombia
138University of Michigan, Ann Arbor, MI 48109, USA
139Michigan State University, East Lansing, MI 48824, USA
140Universit`a di Milano Bicocca , 20126 Milano, Italy
141Universit`a degli Studi di Milano, I-20133 Milano, Italy
142University of Minnesota Duluth, Duluth, MN 55812, USA
143University of Minnesota Twin Cities, Minneapolis, MN 55455, USA
144University of Mississippi, University, MS 38677 USA
145Universit`a degli Studi di Napoli Federico II , 80138 Napoli NA, Italy
146Nikhef National Institute of Subatomic Physics, 1098 XG Amsterdam, Netherlands
147National Institute of Science Education and Research (NISER), Odisha 752050, India
148University of North Dakota, Grand Forks, ND 58202-8357, USA
149Northern Illinois University, DeKalb, IL 60115, USA
7
150Northwestern University, Evanston, Il 60208, USA
151University of Notre Dame, Notre Dame, IN 46556, USA
152University of Novi Sad, 21102 Novi Sad, Serbia
153Occidental College, Los Angeles, CA 90041
154Ohio State University, Columbus, OH 43210, USA
155Oregon State University, Corvallis, OR 97331, USA
156University of Oxford, Oxford, OX1 3RH, United Kingdom
157Pacific Northwest National Laboratory, Richland, WA 99352, USA
158Universt`a degli Studi di Padova, I-35131 Padova, Italy
159Panjab University, Chandigarh, 160014, India
160Universit´e Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France
161Universit´e Paris Cit´e, CNRS, Astroparticule et Cosmologie, Paris, France
162University of Parma, 43121 Parma PR, Italy
163Universit`a degli Studi di Pavia, 27100 Pavia PV, Italy
164University of Pennsylvania, Philadelphia, PA 19104, USA
165Pennsylvania State University, University Park, PA 16802, USA
166Physical Research Laboratory, Ahmedabad 380 009, India
167Universit`a di Pisa, I-56127 Pisa, Italy
168University of Pittsburgh, Pittsburgh, PA 15260, USA
169Pontificia Universidad Cat´olica del Per´u, Lima, Per´u
170University of Puerto Rico, Mayaguez 00681, Puerto Rico, USA
171Punjab Agricultural University, Ludhiana 141004, India
172Queen Mary University of London, London E1 4NS, United Kingdom
173Radboud University, NL-6525 AJ Nijmegen, Netherlands
174Rice University, Houston, TX 77005
175University of Rochester, Rochester, NY 14627, USA
176Royal Holloway College London, London, TW20 0EX, United Kingdom
177Rutgers University, Piscataway, NJ, 08854, USA
178STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom
179Universit`a del Salento, 73100 Lecce, Italy
180Universidad del Magdalena, Santa Marta - Colombia
181Sapienza University of Rome, 00185 Roma RM, Italy
182Universidad Sergio Arboleda, 11022 Bogot´a, Colombia
183University of Sheffield, Sheffield S3 7RH, United Kingdom
184SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
185University of South Carolina, Columbia, SC 29208, USA
186South Dakota School of Mines and Technology, Rapid City, SD 57701, USA
187South Dakota State University, Brookings, SD 57007, USA
188Southern Methodist University, Dallas, TX 75275, USA
189Stony Brook University, SUNY, Stony Brook, NY 11794, USA
190Sanford Underground Research Facility, Lead, SD, 57754, USA
191University of Sussex, Brighton, BN1 9RH, United Kingdom
192Syracuse University, Syracuse, NY 13244, USA
193Universidade Tecnol´ogica Federal do Paran´a, Curitiba, Brazil
194Tel Aviv University, Tel Aviv-Yafo, Israel
195Texas A&M University, College Station, Texas 77840
196Texas A&M University - Corpus Christi, Corpus Christi, TX 78412, USA
197University of Texas at Arlington, Arlington, TX 76019, USA
198University of Texas at Austin, Austin, TX 78712, USA
199University of Toronto, Toronto, Ontario M5S 1A1, Canada
200Tufts University, Medford, MA 02155, USA
201Universidade Federal de S˜ao Paulo, 09913-030, S˜ao Paulo, Brazil
202Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea
203University College London, London, WC1E 6BT, United Kingdom
204Universidad Nacional Mayor de San Marcos, Lima, Peru
205Valley City State University, Valley City, ND 58072, USA
206University of Vigo, E- 36310 Vigo Spain
207Virginia Tech, Blacksburg, VA 24060, USA
208University of Warsaw, 02-093 Warsaw, Poland
209University of Warwick, Coventry CV4 7AL, United Kingdom
210Wellesley College, Wellesley, MA 02481, USA
211Wichita State University, Wichita, KS 67260, USA
212William and Mary, Williamsburg, VA 23187, USA
213University of Wisconsin Madison, Madison, WI 53706, USA
8
214Yale University, New Haven, CT 06520, USA
215Yerevan Institute for Theoretical Physics and Modeling, Yerevan 0036, Armenia
216York University, Toronto M3J 1P3, Canada
217Astrocent, Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, Warsaw 00-614, Poland
DUNE Phase II
Abstract
The international collaboration designing and constructing the Deep Underground
Neutrino Experiment (DUNE) at the Long-Baseline Neutrino Facility (LBNF) has de-
veloped a two-phase strategy toward the implementation of this leading-edge, large-scale
science project. The 2023 report of the US Particle Physics Project Prioritization Panel
(P5) reaffirmed this vision and strongly endorsed DUNE Phase I and Phase II, as did the
European Strategy for Particle Physics. While the construction of the DUNE Phase I is
well underway, this White Paper focuses on DUNE Phase II planning. DUNE Phase-II
consists of a third and fourth far detector (FD) module, an upgraded near detector com-
plex, and an enhanced 2.1 MW beam. The fourth FD module is conceived as a “Module
of Opportunity”, aimed at expanding the physics opportunities, in addition to support-
ing the core DUNE science program, with more advanced technologies. This document
highlights the increased science opportunities offered by the DUNE Phase II near and far
detectors, including long-baseline neutrino oscillation physics, neutrino astrophysics, and
physics beyond the standard model. It describes the DUNE Phase II near and far detector
technologies and detector design concepts that are currently under consideration. A sum-
mary of key R&D goals and prototyping phases needed to realize the Phase II detector
technical designs is also provided. DUNE’s Phase II detectors, along with the increased
beam power, will complete the full scope of DUNE, enabling a multi-decadal program of
groundbreaking science with neutrinos.
10
DUNE Phase II
Contents
Executive summary 13
1 The elements of DUNE Phase II 15
2 DUNE Phase II physics 17
2.1 Long-baseline neutrino oscillation physics . . . . . . . . . . . . . . . . . . . . . . 18
2.1.1 Goals of the oscillation physics program of Phase II . . . . . . . . . . . . 18
2.1.2 The role of Phase II detectors . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2 Neutrino astrophysics and other low-energy physics opportunities . . . . . . . . 21
2.2.1 SNBneutrinos ................................ 22
2.2.2 Solarneutrinos ................................ 25
2.2.3 Other low-energy physics opportunities . . . . . . . . . . . . . . . . . . . 26
2.3 Physics beyond the Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.1 Rare event searches at the near detector . . . . . . . . . . . . . . . . . . 27
2.3.2 Rare event searches at the far detector . . . . . . . . . . . . . . . . . . . 29
2.3.3 Non-standard neutrino oscillation phenomena . . . . . . . . . . . . . . . 29
3 The DUNE phase II far detector 30
3.1 Introduction...................................... 30
3.2 The vertical drift detector design . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.2.1 Charge readout planes (anodes) . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.2 High-voltagesystem ............................. 33
3.2.3 Photon detection system . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3 Optimized charge and photon readouts for Phase II vertical drift FD modules . 35
3.3.1 Optimized photon readout with APEX . . . . . . . . . . . . . . . . . . . 36
3.3.2 Strip-based charge readout . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3.3 Pixel-based charge readout . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3.4 Optical-based charge readout . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3.5 Integrated charge and light readout on anode . . . . . . . . . . . . . . . 48
3.4 Liquid-argondoping ................................. 51
3.4.1 Liquidxenon ................................. 52
3.4.2 Photosensitive dopants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.5 Hybrid Cherenkov plus scintillation detection . . . . . . . . . . . . . . . . . . . 54
3.5.1 Hybrid detection concept . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.5.2 Theia physicsprogram ........................... 55
3.5.3 Technology readiness levels . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.6 Backgroundcontrol.................................. 57
3.6.1 External neutrons and photons . . . . . . . . . . . . . . . . . . . . . . . 58
3.6.2 Internal backgrounds from detector materials . . . . . . . . . . . . . . . 58
3.6.3 Intrinsic backgrounds from unstable isotopes in the target . . . . . . . . 59
3.6.4 Radonbackground .............................. 59
3.6.5 TheSLoMoconcept ............................. 59
11
DUNE Phase II
3.6.6 Research and development requirements . . . . . . . . . . . . . . . . . . 60
3.7 Toward detector concepts for Phase II FD modules . . . . . . . . . . . . . . . . 61
4 The DUNE Phase II near detector 65
4.1 Designmotivations .................................. 65
4.2 Phase II improved tracker concept . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.2.1 Charge readout of TPC . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2.2 Calorimeter concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.2.3 Magnetconcept................................ 73
4.2.4 Muonsystem ................................. 76
4.2.5 Light detection options . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.2.6 R&D and engineering road map . . . . . . . . . . . . . . . . . . . . . . . 77
4.3 Improvements to Phase I near detector components . . . . . . . . . . . . . . . . 78
4.3.1 Phase II ND-LAr detector . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.3.2 Phase II SAND detector . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.4 Near-detector options for non-argon far detector modules . . . . . . . . . . . . . 80
4.4.1 Oxygen and water targets in SAND . . . . . . . . . . . . . . . . . . . . . 80
4.4.2 Liquid scintillator targets in the ND-GAr calorimeter . . . . . . . . . . . 82
4.4.3 Water-based near detector . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Glossary 85
12
DUNE Phase II
Executive summary
The preponderance of matter over antimatter in the early universe, the dynamics of the super-
nova neutrino bursts (SNBs) that produced the heavy elements necessary for life, the nature of
dark matter, and whether protons eventually decay – these mysteries at the forefront of particle
physics and astrophysics are key to understanding the evolution of our universe.
The Deep Underground Neutrino Experiment (DUNE) will address these questions in a
multidecadal science program with its world-leading liquid argon (LAr) detector technology.
The international DUNE experiment, hosted by the Fermi National Accelerator Laboratory
(Fermilab), is designing, developing, and constructing a near detector (ND) complex at Fermilab
(the near site) and a suite of four large detector modules 1300 km downstream at the Sanford
Underground Research Facility (SURF) in South Dakota (the far site). These detectors will
record neutrinos over a wide energy range, originating from a new high-intensity neutrino
beamline at Fermilab. The modular far detector (FD) will also detect neutrinos produced by
cosmic rays in the atmosphere and from astrophysical sources. The ND and FD will also be
sensitive to a broad range of phenomena beyond the standard model (). The beamline as well as
the excavations, infrastructure, and facilities for housing and supporting the DUNE detectors
are provided by the Long-Baseline Neutrino Facility (LBNF).
The DUNE Collaboration was launched in 2015, following the recommendations of the 2013
update of the European Strategy for Particle Physics [1] and of the 2014 Report of the US
Particle Physics Project Prioritization Panel (P5) [2]. DUNE and LBNF will complete this
project in two phases, based on the availability of resources and the ability to reach science
milestones. The latest P5 report released in December 2023 reaffirmed this vision [3].
The construction of the first project phase (Phase I), funded through commitments by a
coalition of international funding agencies, is well underway. Its successful completion is cur-
rently the Collaboration’s main priority. Excavation at the far site is complete, and fabrication
of various beamline and detector components for Phase I is progressing well. The facilities
currently being constructed by LBNF at both the near and far sites are designed to host the
full scope (Phase I and Phase II) of the DUNE experiment.
The Phase II of DUNE that encompasses an enhanced 2.1 MW beam, a third and fourth far
detector (FD) module, and an upgraded ND complex, is the subject of this paper. The primary
objective of DUNE Phase II is a set of precise measurements of the parameters of the neutrino
mixing matrix, θ23,θ13, ∆m2
32, and δCP, to establish Charge Conjugation-Parity Symmetry
Violation (CPV) over a broad range of possible values of δCP, and to search for new physics
in neutrino oscillations. DUNE also seeks to detect neutrinos from low-energy astrophysical
sources. The additional mass brought by the Phase II FD modules would increase the statistics
of a supernova burst signal and extend DUNE’s reach beyond the Milky Way. The Phase II
FD module design concepts would also perform sensitive searches for new physics with solar
neutrinos by lowering the detection threshold in the relevant MeV-scale energy range and by
reducing the background rates in this energy regime. Finally, Phase II will expand DUNE’s
new physics discovery reach via more sensitive searches for rare processes at the ND and FD
sites, and for non-standard neutrino oscillation phenomena.
This world-class physics program requires an increase in the statistical power of the de-
13
DUNE Phase II
tectors, which will be achieved by increasing the FD target mass with the additional modules
and by exceeding 2 MW beam power, as recommended by the 2023 P5 committee in the US.
In addition, an upgraded ND will be required to control systematic uncertainties of neutrino
interactions on argon (or other selected FD target nuclei). The design of the Phase II FD
modules will incorporate lessons learned from the construction of the Phase I modules, with
the goal of optimizing physics performance, reliability, and cost.
The design of the third FD module will build on that of the second, the single-phase
technology used for far detector module 2 (FD2), optimizing for performance and cost. This
design implements -based horizontal anode planes at the top and bottom of the liquid-argon
time-projection chamber (LArTPC) drift volume with a cathode plane in the middle, and a
that hangs from the cryostat roof on which photon detectors will be mounted.
The fourth FD module is conceived as a “Module of Opportunity”, which would allow to
address new physics questions, in addition to the primary science program, with more advanced
technologies. R&D for the design of the fourth module focuses primarily on optimization of
readout techniques for both charge and scintillation light. It also considers the possibility of LAr
doping. A possible improvement of the LAr charge-readout technology is the replacement of
the PCB-readout by pixels or by an optical-based charge readout. A hybrid approach to detect
Cherenkov and scintillation light is also under investigation, motivated by a complementary
program of low-energy physics. All technologies proposed for the Module of Opportunity are
expected to provide additional and complementary CPV sensitivity. In addition, background
control is an essential ingredient of all FD module designs.
The Phase II ND will ensure that DUNE’s sensitivity to oscillation parameters is not lim-
ited by systematic uncertainties. It is optimized for highly performing particle ID (PID), low
tracking thresholds for protons and pions, and acceptance over a wide range of momenta. A
magnetized gaseous argon time-projection chamber (GArTPC) at the near site, which will
replace the Muon Spectrometer (TMS), will provide these constraints by measuring the inter-
action of neutrinos on argon with unprecedented precision due to its low thresholds. It offers
superior discrimination between neutrinos and antineutrinos, as well as momentum determina-
tion of particles exiting the detector.
These plans fully align with the recommendations of the 2023 P5 report [3], which proposes
a “second phase of DUNE (Phase II) with an early implementation of an enhanced 2.1 MW
beam, a third far detector (module), and an upgraded near detector complex as the definitive
long-baseline neutrino oscillation experiment of its kind,” as well as “research and development
(R&D) towards an advanced fourth detector.”
The Phase II R&D program is a global effort with contributions from all DUNE partners.
New collaborators are also invited to participate in the development and design of the new
detector technologies. Part of the R&D described in this document is carried out within the
framework of the European Committee for Future Accelerators (ECFA) detector R&D col-
laborations hosted by the European Laboratory for Particle Physics (CERN) and those being
formed under the umbrella of the Coordinating Panel for Advanced Detectors (CPAD) in the
US. DUNE has been designed to become the “best-in-class” global neutrino observatory. The
Phase II far and near detector components, and the increased beam power, will enable a new
era of precision and discovery in neutrino physics.
14
DUNE Phase II
1 The elements of DUNE Phase II
The DUNE experiment at the LBNF was conceived in 2015, following the recommendations of
the 2013 update of the European Strategy for Particle Physics [1] and of the 2014 Report of the
US Particle Physics Project Prioritization Panel (P5) [2]. The 2014 P5 Report recommended
developing, in collaboration with international partners, a coherent long-baseline neutrino pro-
gram hosted by Fermilab, with a mean sensitivity to leptonic CPV of better than three standard
deviations (σ) over more than 75% of the range of possible values of the CP-violating phase δCP.
The 2014 P5 Report also recommended a broad program of neutrino astrophysics and physics
Beyond the Standard Model (BSM) as part of DUNE, including demonstrated capability to
search for SNBs and for proton decay. Likewise, the 2013 Update of the European Strategy
for Particle Physics and its 2020 update [4] recommended that Europe and CERN (through its
Neutrino Platform) continue to collaborate towards the successful completion of the .
The DUNE Collaboration and the Project have made substantial progress toward the re-
alization of this enterprise, with the aim to start the scientific exploitation in 2029. Based
on recent estimates, including a flux prediction using a fully-engineered neutrino beamline, the
ultimate CPV measurement goal put forward by the 2014 P5 Report can be reached with an ex-
posure of about 1000 kt·MW·yr. This can be achieved in about 15 years of physics data-taking
(see Sec. 2.1), assuming that Phase II elements as described in this document are pursued.
DUNE’s neutrino astrophysics and BSM physics programs also benefit from multidecadal op-
erations, to realize DUNE’s full physics potential and achieve its scientific goals.
For the successful implementation of DUNE and LBNF, we need to consider the full extent
of the available resources and funding profiles, provide a realistic estimate of the project costs,
and achieve a clear understanding of the experimental configurations and exposures that are
necessary to reach various physics milestones. As a result of this exercise, the DUNE Collabo-
ration and the LBNF/DUNE-US Project have decided to pursue the experiment in two phases,
as summarized in Table 1.
Parameter Phase I Phase II Impact
FD mass 2 FD modules (20 kt fidu-
cial)
4 FD modules (40 kt fidu-
cial LAr equivalent)
FD statistics
Beam power 1.2 MW Up to 2.3 MW FD statistics
ND configuration ND-LAr+TMS, SAND ND-LAr, ND-GAr, SAND Systematics
Table 1: A high-level description of the two-phased approach to DUNE. The ND-LAr detector,
including its capability to move sideways (DUNE Precision Reaction-Independent Spectrum
Measurement (DUNE-PRISM)), and the System for on-Axis Neutrino Detection (SAND) are
present in both phases of the ND. Note that the non-argon options currently under consideration
for Phase II near and far detectors are not shown.
In developing this two-phase strategy, we are guided by the original recommendations for
the DUNE program, which remain valid and timely. The latest P5 report released in December
2023 reaffirmed this vision and strongly endorsed DUNE Phase I and II. In its report [3], the
15
DUNE Phase II
P5 panel reaffirmed that the highest priority in the coming decade, independent of budget
scenarios, is the completion of construction of existing projects which includes LBNF and
DUNE Phase I, and the Proton Improvement Plan II (PIP-II).
The panel also strongly recommended constructing a portfolio of major projects, of which
the second-highest priority was a “re-envisioned second phase of DUNE (Phase II) with an
early implementation of an enhanced 2.1 MW beam (aka ), a far detector module 3 (FD3),
and an upgraded ND complex as the definitive long-baseline neutrino oscillation experiment of
its kind.” The panel also endorsed DUNE’s fourth FD module (far detector module 4 (FD4))
concept as a “Module of Opportunity” and recommended exploring a range of alternative
targets, including low-radioactivity argon, xenon-doped argon, and novel organic or water-
based liquid scintillators, to maximize the science reach, particularly in the low-energy regime.
An accelerated and expanded R&D program in the next decade is recommended for FD4 and
if budget scenarios are favorable, initiation of construction is also recommended.
The overall project design for Phase I is complete, and this project phase is funded through
commitments by several international funding agencies and CERN. LBNF excavation at the
far site is complete, and fabrication of various beamline and detector components for Phase I
are well underway. An important component of the DUNE strategy is that the facilities con-
structed by LBNF at both the near and far sites are designed to support the full scope of the
DUNE experiment from the beginning. During Phase I, the facilities at the near site are thus
constructed to support a >2 MW primary beamline and neutrino beamline, as well as a hybrid
ND for all DUNE experimental phases. Likewise, the far site design includes underground halls
for four FD modules.
The Phase I beamline will produce a wide-band neutrino beam with up to 1.2 MW beam
power, designed to be upgradable to 2.4 MW. The Phase I ND includes a moveable LArTPC
with pixel readout called ND-LAr, integrated with a downstream muon spectrometer called
TMS [5], and an on-axis magnetized neutrino detector called SAND further downstream. The
ND-LAr+TMS detector can be moved sideways over a range of off-axis angles and neutrino
energies (DUNE-PRISM concept), for an optimal characterization of the neutrino-argon inter-
actions.
The Phase I FD includes two LArTPC modules, each containing 17kt of liquid argon
(LAr). The far detector module 1 (FD1) is a horizontal drift time projection chamber (TPC),
as developed and operated in at the CERN Neutrino Platform and similar in concept to the , ,
and detectors [6]. The FD2 is a vertical drift TPC. Its design capitalizes on the experience with
the demonstrator at CERN. For the cryogenic infrastructure in support of the two LArTPC
modules, Phase I will include two large cryostats (one per FD module), 35 kt of LAr, and three
nitrogen refrigeration units.
While several options are under consideration for the Phase II components of the far and
near site detectors, key elements have already been defined:
•A core component of Phase II is a More Capable Near Detector (). The main improvement
to the ND is the addition of a magnetized high-pressure gaseous argon TPC (HPgTPC),
surrounded by an electromagnetic calorimeter and by a muon detector called . ND-GAr
will serve both as a new muon spectrometer for ND-LAr, replacing the TMS in this
capacity, and as a new neutrino detector to study neutrino-argon interactions occurring
16
DUNE Phase II
in the HPgTPC. In addition, upgrades to the ND-LAr and SAND systems are considered,
as well as potential ND options in the case of a non-argon technology for FD4.
•Two additional FD modules, FD3 and FD4, will be added at the far site, for a total of
four. The DUNE FD2 vertical drift technology forms the basis for the envisioned designs
for FD3 and FD4. A non-argon option such as liquid scintillator (e.g., ) is also under
consideration as an alternative technology for FD4. The cryogenic infrastructure at the
far site will be upgraded for Phase II with a fourth nitrogen refrigeration unit to provide
capacity for up to an additional 35 kt of LAr.
•A beam upgrade to increase the intensity to >2 MW. This is achieved by ACE-MIRT,
which increases the frequency of beam spills by nearly a factor of two. While this is part
of Phase II, it is possible to implement the upgrades that comprise ACE-MIRT before
DUNE beam data taking begins.
The R&D underpinning the Phase II concepts is performed as part of a global program.
The Detector R&D () collaborations hosted by CERN, which have been established as part of
the European Committee for Future Accelerators (ECFA) roadmap, cover many of the detector
concepts under study for DUNE Phase II. The DRD1 collaboration focuses on gaseous detectors
and the DRD2 focuses on liquid detectors. Both collaborations have been formed recently. They
are expected to grow with collaborators from within and outside Europe. Both the DRD1 and
DRD2 collaborations were approved in December 2023 as official CERN experiments and held
their first collaboration meetings in February 2024 at CERN. The ECFA DRD collaborations are
strongly aligned with the Detector R&D collaborations (s) being formed under the Coordinating
Panel for Advanced Detectors (CPAD) umbrella in the US. There is an active effort underway
to coordinate activities across the CERN-hosted and US-based collaborations on synergistic
areas of R&D toward achieving common scientific and technological goals.
This document is organized as follows. Section 2 covers the science that DUNE will pursue
with Phase II, covering long-baseline neutrino oscillation physics, neutrino astrophysics, and
BSM physics. A progress report on DUNE’s Phase II far and near neutrino detectors is given
in Sections 3 and 4, respectively. These two sections cover our current understanding of the
detector requirements to carry out the Phase II physics goals, and a current snapshot of the
main detector design options that are under consideration. These sections also summarize the
critical R&D elements that remain to be addressed and the prototyping phases to be realized
before Phase II detector technical designs can be finalized.
2 DUNE Phase II physics
This section discusses selected DUNE science drivers in the areas of long-baseline physics, neu-
trino astrophysics, and BSM physics that uniquely benefit from an improved performance of
Phase II beam and detectors. The physics sensitivities are typically shown as functions of
high-level figures of merit, such as exposure time, detector mass, background levels or detec-
tor acceptance, mostly without entering into the detector technology details. Specific benefits
17
DUNE Phase II
brought by certain technologies are highlighted in Sections 3 and 4, together with the descrip-
tions of such technologies.
2.1 Long-baseline neutrino oscillation physics
The DUNE experiment is designed to measure the rate of appearance of electron (anti)neutrinos
(νeor ¯νe) and the rate of disappearance of muon (anti)neutrinos (νµor ¯νµ), as functions of
neutrino energy in a wide-band beam. DUNE is sensitive to all the parameters governing
ν1−ν3and ν2−ν3mixing in the three-flavor model: θ23 ,θ13, ∆m2
32 (including its sign, which
is given by the neutrino mass ordering), and the phase δCP.
During Phase I, DUNE can accumulate approximately 100kt·MW·yr of data in five years.
This corresponds to ≈400 νeand 150 ¯νecandidates in the FD, depending on the value of
the oscillation parameters and assuming equal fractions of neutrino and antineutrino running.
While these data sets will still be statistically limited once Phase I ND systematic constraints
are accounted for, they are sufficient to conclusively determine the neutrino mass ordering at
>5σsignificance, regardless of the true parameter values. If CPV is nearly maximal (δCP
≈ ±π/2), DUNE can establish CPV at 3σin Phase I. DUNE will also make measurements
of the disappearance parameters ∆m2
32 and sin22θ23 that improve upon current uncertainties.
However, the statistics of Phase I are too low to determine the octant of θ23 or to establish
CPV except in the most favorable scenarios.
2.1.1 Goals of the oscillation physics program of Phase II
The goals of the oscillation physics program of Phase II are high-precision measurements of all
four parameters: θ23,θ13 , ∆m2
32 and δCP, to establish CPV at high significance over a broad
range of possible values of δCP, and to test the three-flavor paradigm as a way to search for
new physics in neutrino oscillations. Achieving these goals requires 600 −1000 kt·MW·yr of
data statistics, depending on the measurement. This can be achieved by operating for 6 −10
additional calendar years with a greater than 2 MW beam and a FD of 40 kt LAr equivalent
fiducial mass. Without doubling the FD mass and the beam intensity, the additional time
required would be 24 −40 years.
In particular, the long-baseline sensitivities presented below make the following assumptions
concerning the time evolution of the protons on target (POT) delivery, the fiducial FD mass and
the ND systematic constraints. The beam power evolution is based on the assumptions of the
Fermilab Proton Intensity Upgrade Central Design Group [7]. The average beam power during
the first year of beam operations is 1.1 MW, increasing to 1.6MW during year 2, thanks to ACE-
MIRT upgrades [7]. Further beam optimizations are assumed in subsequent years, yielding a
beam power of 2.3 MW after approximately 15 years. The assumed POT delivery also includes
a 57% average uptime [8]. As regards the fiducial FD mass, the experiment is assumed to take
data with two FD modules (20 kt fiducial mass) during the first three years. The FD3 and FD4
modules are assumed to become fully operational in years 4 and 6, respectively, to provide a
nominal fiducial FD mass of 40 kt. Figure 1 shows how the accumulated exposure, expressed in
kt·MW·yr units, varies as a function of time with this assumed staging scenario. The 600 and
18
DUNE Phase II
Figure 1: DUNE integrated exposure, in kt·MW·yr units, as a function of time assumed for
the long-baseline (LBL) sensitivity results presented in this section. The integrated exposure
is built from the beam power and FD mass staging assumptions discussed in the text.
1000 kt·MW·yr integrated exposure milestones of DUNE Phase II appear within reach after
approximately 10 and 15 years of beam plus detector operations, respectively. Finally, it is
assumed that the Phase I ND systematic constraints will be in effect up to year 6, with the
improvements from Phase II ND starting in year 7. The new constraints, as they gradually
improve over the course of two years to their final values, will be applied to all past FD data.
The precision of the high-statistics measurements is ultimately limited by the systematic
uncertainties. To achieve DUNE’s science goals will therefore require unprecedented control of
systematic uncertainties. The significance for DUNE to establish CPV is shown as a function
of time in Figure 2. Phase II, with its full 1000 kt·MW·yr exposure, will enable DUNE to
establish CPV at >3σover 75% of possible δCP values, and measure it at a precision of
6◦−16◦, depending on the true value.
DUNE can also measure the angle θ23 with world-leading precision and determine the octant
if it is sufficiently non-maximal. The measurements of θ13 and ∆m2
32 will approach the precision
of the current measurement from Daya Bay [9] and the planned measurement from JUNO [10],
respectively, which are all performed with a different neutrino flavor, over a different baseline,
and at a different energy. Comparing the results obtained over this wide range of conditions
will provide a more complete and robust test of the three-flavor model. The resolutions to δCP ,
sin22θ13, and sin2θ23 are shown as a function of exposure in Figure 3.
DUNE is also sensitive to BSM physics that impacts neutrino oscillations, including non-
unitary mixing, non-standard interactions, violation of charge, parity, and time reversal sym-
19
DUNE Phase II
Figure 2: The significance for DUNE to establish CPV for 50% (left panel) and 75% (right)
of δCP values as a function of running time. See text for details about the assumed staging
scenario.
metry (CPT), and the possible existence of additional neutrino species (see Section 2.3).
2.1.2 The role of Phase II detectors
The two additional modules, FD3 and FD4, will provide the additional exposure and improved
statistical precision that is critical to achieve the full δCP sensitivity (Figure 2). They also offer
the opportunity to improve the neutrino energy reconstruction and the neutrino interaction
classification with enhanced detector technology, for example through optimized charge and
photon readout systems (Sec. 3.3). It is crucial that the data from these modules be combined
with data from FD1 and FD2, with the systematic constraints from the ND applied to all
FD modules. For this reason, the most straightforward approach is for FD3 and FD4 to be
LArTPCs, so that DUNE would immediately benefit from the ν-Ar measurement program of
the ND. The oscillation sensitivities presented in Figures 2 and 3 assume the performance of the
Horizontal Drift module using an end-to-end simulation and reconstruction. The alternative
LArTPC concepts being considered for FD3 and FD4 are expected to have similar, and perhaps
slightly improved performance for GeV-scale beam neutrinos, so the existing simulations serve
as a conservative estimate of the eventual sensitivity.
If FD4 is not a LArTPC, the impact on the long-baseline oscillation program is less straight-
forward. For the Theia concept discussed in Section 3.5, the performance is estimated using
a reconstruction based on the fiTQun package [11], and a boosted decision tree (BDT) [12].
The analysis is less sophisticated than the DUNE TDR sensitivities [8], using the GLOBeS
package to implement systematics as normalization shifts, but suggests that the sensitivity is
comparable to what can be achieved in a single LArTPC module. It does not yet make use of
the additional information potentially offered by the scintillation component, which can provide
tagging of neutrons and other sub-Cherenkov threshold particles, for improved event identifi-
cation and enhanced calorimetry. Combining a non-LArTPC module with LAr measurements
20
DUNE Phase II
Figure 3: The resolutions to δCP (left), sin22θ13 (center), and sin2θ23 (right), shown as a function
of exposure in kt-MW-yrs, assuming the full constraint from the ND, including MCND. The
ultimate precision of DUNE requires an exposure greater than 600 kt-MW-yrs, which requires
FD3 and FD4 to be built in a reasonable timescale.
could potentially provide a cross-check of extracted oscillation parameter values with different
detector systematics. A non-LAr FD4 would require a dedicated ND to constrain neutrino cross
section uncertainties and detector response on the FD4 nuclear target to a similar precision
as the LArTPC constraints. Near detector options for non-LAr FD modules are discussed in
Sec. 4.4.
The role of MCND (Section 4.2) is to ensure that DUNE can achieve the required level
of systematic uncertainties for Phase II and to ensure that the results are not systematically
limited. It would replace the TMS with a detector that has its own standalone physics capabil-
ities, including constraining neutrino-argon cross section uncertainties and expanding the BSM
reach of the ND, while also measuring muons exiting the ND-LAr detector. Further study of
the ultimate performance of the Phase I ND is important for scoping the Phase II ND.
2.2 Neutrino astrophysics and other low-energy physics opportuni-
ties
DUNE’s broad physics program includes the detection of neutrinos from astrophysical sources
in the MeV energy range [13], primarily neutrinos from the sun and a SNB. With argon as
active material, DUNE will be primarily sensitive to the astroparticle νeflux for energies below
100 MeV and above 5 MeV due to the relatively large νecharged current (CC) cross section for
the process: νe+40 Ar →e−+40 K∗. DUNE will be unique in this regard, making the experiment
highly complementary to existing and proposed experiments for the next decades aiming for
similar astrophysical neutrino measurements in the 10s of MeV regime: JUNO [14], Hyper-
Kamiokande [15], and dark matter detectors [16, 17]. This section highlights the improvements
a LArTPC FD module from Phase II would bring. It also includes a summary of the advantages
of a water-based liquid scintillator, that would be sensitive primarily to the ¯νeflux, within the
Phase II program.
21
DUNE Phase II
DUNE Phase I will be sensitive to solar and SNB neutrinos, achieving an energy resolution of
(10−20)%. The visible energy threshold will be >5 MeV for SNB neutrinos and higher for solar
neutrinos, which do not arrive in a short pulse. Large LArTPC detectors have demonstrated
much lower charge thresholds, ∼100 keV [18], but Phase I sensitivity will be limited to >5 MeV
due to light collection performance and radiological backgrounds. Thus, innovation on these
fronts can lower visible energy thresholds for astrophysical neutrinos by as much as two orders of
magnitude while also improving energy resolution. Lower thresholds would also fundamentally
expand the low-energy physics opportunities with DUNE Phase II. Figure 4 shows a selection
of potential signatures of astrophysical or other beam-unrelated origin with DUNE Phase II,
together with relevant backgrounds.
Figure 4: Detectable energy ranges in DUNE LArTPC FD modules for potential <20 MeV
signatures of astrophysical or other non-beam-related origin (blue), and for relevant, overlapping
backgrounds (orange). The DM signature refers to weakly-interacting massive particle (WIMP)
direct dark matter searches. Adapted from [19].
2.2.1 SNB neutrinos
DUNE will be part of a collaborative, multi-messenger network of neutrino and optical tele-
scopes studying the next galactic core-collapse supernova (CCSN). With different flavor sen-
sitivity from other large experiments, DUNE will provide complementary information about
the collapse. DUNE’s νesensitivity is most striking at the earliest times of the SNB, which is
dominated by νeemission from neutronization in the stellar core, as shown in the top panel of
Figure 5. During Phase I, DUNE will already be able to detect neutrinos from a CCSN with
energies >5 MeV [20], albeit with lower statistics. The larger mass of Phase II represents a
significant step in extending the detector’s sensitivity to a SNB signal, since the burst trig-
ger efficiency, reconstruction of the supernova direction (bottom right panel of Figure 5), and
precise measurement of the supernova spectral parameters (bottom left panel of Figure 5))are
dominated by the number of neutrino interactions in the detectors. While the expected event
rate varies significantly among supernova models, the 40 kt (fiducial) DUNE detector would be
22
DUNE Phase II
expected to observe ≈3000 neutrinos from an SNB at a distance of 10 kpc, just beyond the
center of the Milky Way [20].
6 8 10 12 14
Supernova Distance (kpc)
1
150
1
175
1
200
1
225
1
250
1
300
1
350
1
400
1
500
1
600
1
800
1
1200
1/ NeES
0.001
0.002
0.003
0.004
0.005
0.006
Sky Fraction
ceES eES = 1.00, c eCC eES = 0.00
ceES eES = 0.86, c eCC eES = 0.04
Figure 5: The total luminosity of neutrinos released during CCSN from [21] (top). Sensitiv-
ity regions in mean neutrino energy (related to the temperature of supernovae) and neutrino
luminosity space for three different supernova distances from [22] (bottom left). DUNE’s recon-
struction of the direction of a SNB in terms of the fraction of sky allowed at 68% confidence, as
a function of recorded number of neutrino-electron scattering events as well as the correspond-
ing supernova distance from [23] (bottom right).
The modular nature of DUNE’s FD makes the experiment ideal for SNB triggering and
contributing to SuperNova Early Warning System (SNEWS) [24]. Each FD module will inde-
pendently forward a CCSN alert to SNEWS which will be made available to optical astronomers.
Deployment of additional detectors in Phase II will effectively ensure that at least one FD mod-
ule is operational whenever a SNB arrives at the detector. With all modules taken together,
the increased mass from Phase II will allow DUNE to trigger on further supernovae, increasing
coverage in the neighborhood beyond the Milky Way (e.g., in the Large and Small Magellanic
Clouds).
As the neutrino signal escapes a core-collapse supernova hours before the first optical signal,
pin-pointing the source of the SNB is fundamentally important to facilitate optical observation
of the initial stages of the supernova. The electron tracks from neutrino-electron elastic scatter-
23
DUNE Phase II
ing, a sub-dominant interaction channel for SNB detection, are nearly parallel to the incoming
neutrino flux and can thus be used to reconstruct the neutrino direction. Supernova pointing
leverages the excellent tracking capabilities of a LArTPC to identify neutrino-electron scatter-
ing events yielding a pure sample of this low-rate channel. The increased mass from Phase II is
critical for realizing DUNE’s full potential. Using a typical flux model, the full 40 kt detector
would expect 326 neutrino-electron scattering events compared to 163 in Phase I [23]. This
reduces the field-of-view for optical follow-up searches following a SNB signal from 0.26% to
0.14% of the total sky at 1 σas shown in the bottom right panel of Figure 5. A Phase II module
with pixelated charge readout would also improve SNB pointing resolution by improving the
3D reconstruction of low-energy electron tracks.
The neutrino mass ordering has a strong impact on the expected signal at early times
(neutronization burst) when electron-type neutrinos dominate the neutrino flux at production
(see Figure 6 for expected event rates in DUNE). Neutrino flavor transformations can be in-
duced by neutrino-neutrino scattering and collective modes of oscillation [25]. These effects
will leave imprints on the neutrino signal and can be used to study these phenomena exper-
imentally. These effects will test fundamental neutrino properties by measuring the neutrino
self-interaction strength [26]. DUNE will also provide competitive constraints on the absolute
neutrino mass via measurements of the time of flight from the supernova to Earth [27].
With argon’s νeflavor sensitivity, DUNE will uniquely probe the neutrino component of
the diffuse supernova neutrino background (DSNB) [28] – Phase II will be critical for such a
low-rate search by increasing argon mass.
40 kton argon, 10 kpc
Time (seconds)
0.05 0.1 0.15 0.2 0.25
Events per bin
10
20
30
40
50
60
70
80 Infall Neutronization Accretion Cooling
No oscillations
Normal ordering
Inverted ordering
40 kton argon, 10 kpc
Figure 6: Expected event rates from [20] as a function of time for the electron-capture supernova
model in [29] and for 40 kt of argon during early stages of the burst. Shown are the event rate
for the unrealistic case of no flavor transitions (blue) and the event rates including the effect
of matter transitions for the normal (red) and inverted (green) mass orderings. Error bars are
the expected statistical uncertainty in each (varying) time bin.
With significant increase of the photodetector area, e.g., 10% coverage with silicon photo-
multipliers (SiPMs) [19], and use of 39Ar-depleted argon, a DUNE Phase II LArTPC module
24
DUNE Phase II
would be sensitive to faint light flashes from Coherent Elastic Neutrino-Nucleus Scattering
(CEνNS) interactions on argon during a SNB. The “CEvNS glow” from a supernova would be
observed as an increase of low-PE flashes observed through the duration of the burst. As a neu-
tral current (NC) process, this channel is sensitive to all neutrino flavors, thus giving orthogonal
information to the MeV-scale νeCC interactions. Importantly, CEvNS glow allows DUNE to
determine the supernova neutrino fluence independent of neutrino oscillation uncertainties.
A water-based liquid scintillator module (e.g., Theia) would sacrifice part of the SNB
νestatistics for a significant increase in ¯νeevents through inverse βdecay, with a threshold of
∼2 MeV. Such a module would detect approximately 5000 ¯νeinteractions from a SNB at 10 kpc
distance. The scintillation light would provide a tag for neutrons to allow separation between
inverse βdecay events and directionally-sensitive elastic scattering reactions. Using the high
light output from the scintillation, such a module would also be sensitive to pre-supernova
neutrinos [30], alerting neutrino experiments to an upcoming SNB.
2.2.2 Solar neutrinos
After more than a half century of study, there remain important open questions in particle and
astrophysics that solar neutrino measurements can potentially resolve. This is due in large part
to the precision tracking capabilities of the DUNE LArTPC detectors. In addition, because of
argon’s dominant νeCC interaction channel, the detected energy will correlate strongly with
the incoming neutrino energy. With these advantages, DUNE promises excellent potential for
improved measurements [31]. Initial studies suggest DUNE Phase I can select a sample of
8B solar neutrinos that would improve upon current solar measurements of ∆m2
21 [32] via the
precise measurement of the day-night flux asymmetry induced by Earth matter effects. DUNE
Phase I can also make the first observation at >5σof the “hep” flux produced via the 3He +
p→4He + e++νenuclear fusion.
The energy resolution of DUNE Phase I, (10 −20)%, could be improved down to ≈2%
through improvements to the Phase II photon detection system (PDS). This radically improves
determination of solar neutrino parameters. The measurement of the solar mass splitting ∆m2
21
requires precisely measuring the energy dependence of the neutrino oscillation pattern. A single
module with 2% resolution would make this measurement better than four modules with Phase I
energy reconstruction performance.
For beam-unrelated FD events, reconstructed photon flashes are used to select events within
the detector fiducial volume and to correct ionization charge loss along drift, greatly suppressing
backgrounds and improving energy reconstruction, respectively. In Phase I, DUNE’s solar
neutrino reach will be limited by non-perfect light flash reconstruction and by radiological
backgrounds, primarily neutron capture on argon, which can also confuse light-charge matching.
As described in Section 3, upgrades to the photon detection can increase DUNE light yield in
Phase II by a factor of five or more. This will make light flashes from solar neutrino signals
more apparent and improve vertex reconstruction from the flash to simplify the light-charge
matching algorithm. Neutron capture on 40Ar could be vetoed by rejecting optical flashes that
reconstruct near the 6.1 MeV Q-value and further mitigated by installation of passive shielding.
Together, these would reduce the solar neutrino detection threshold for a Phase II FD module.
25
DUNE Phase II
DUNE’s νeCC signal makes it ideal for measuring the energy dependence of the solar electron-
neutrino survival probability, Pee. With a visible energy threshold at or below 5 MeV for solar
neutrinos, possible with some technology choices outlined in Section 3, DUNE will probe the
upturn in Pee. This is the transition region between the low-energy regime where vacuum solar
oscillations dominate and the high-energy regime where the oscillation probability is determined
by Mikheyev-Smirnov-Wolfenstein effect (MSW) matter effects [33] inside the sun. The same
MSW matter effects, but in the earth, are central to DUNE’s measurements of neutrino mixing
parameters with long-baseline oscillation measurements. A significant increase in photodetector
coverage would allow measurements of carbon nitrogen oxygen (CNO) solar neutrinos that could
distinguish between solar metallicity models [19].
A FD module based on Theia would also be sensitive to solar neutrinos, through the
neutrino-electron scattering channel. The Theia technology is sensitive to both scintillation
and Cherenkov light from low-energy neutrinos – thus simultaneously providing low thresholds
and event directionality. Such a module could possibly probe the solar neutrino transition
region to even lower energies, near 2 MeV.
2.2.3 Other low-energy physics opportunities
Through heavy fiducialization and improved energy resolution from increased photodetector
coverage, DUNE’s low-energy physics can reach beyond astrophysical neutrinos in Phase II.
Planning is underway for future WIMP dark matter experiments. These liquid noble de-
tectors will scale up the current technologies active target masses with the goal to reach the
so-called “neutrino fog”, that is the cross-section below which the potential discovery of a dark
matter signal is slowed due to the uncertainty in the irreducible background from the coher-
ent elastic scattering of astrophysical neutrinos with nuclei [34]. Leading upcoming projects
include the xenon-based XLZD experiment [35], and the argon-based DarkSide-20k [36] and
ARGO experiments. A DUNE FD module could perform a competitive WIMP dark matter
search complementary to future argon dark matter experiments [37]. Particularly interesting
would be the sensitivity to the annual modulation of the WIMP signal, which due to DUNE’s
large target mass would allow a rapid confirmation of any observed signal in the current so-
called generation-2 experiments [19]. A 10% photodetector coverage with SiPMs could give the
necessary threshold of ∼100 keV. Such low thresholds would also require operating the detector
module with underground argon depleted in the 39Ar isotope, for background mitigation.
By introducing a large mass fraction of 136Xe or 130Te to a Phase II FD module based on
LArTPC or Theia technology, respectively, DUNE could also perform neutrinoless double-β
decay (0νββ) searches. The neutrinoless double βdecay community has laid out a strategic
plan [38] that calls for a diverse R&D program with sensitivity beyond next-generation ton-scale
experiments. DUNE Phase II can contribute toward this long-term 0νββ effort, in connection
with, and as a possible evolution of, the existing 0νββ program. A DUNE Theia module loaded
with 130Te could be a natural evolution of the loaded liquid scintillator technique currently
pursued by SNO+ [39] and KamLAND-Zen [40]. Similarly, a 136Xe-doped DUNE LArTPC
module with sufficiently good energy resolution (σ) of order 2% [41] could expand on liquid
xenon TPC strategies currently employed by nEXO [42]. Such a LArTPC 0νββ module would
26
DUNE Phase II
also require sourcing very large amounts of underground argon, in order to mitigate 42Ar-
induced backgrounds.
Finally, thanks to its ¯νesensitivity, a Theia module would also observe geo-neutrinos and
reactor neutrinos [12].
2.3 Physics beyond the Standard Model
DUNE has discovery sensitivity to a diverse range of physics Beyond the Standard Model
(BSM), which is complementary to those at collider experiments and other precision experi-
ments. BSM physics accessible at DUNE may be divided into three major areas of research:
rare processes in the beam observed at the ND (for example heavy neutrinos, light dark mat-
ter, or new physics that could enhance neutrino trident production), rare event BSM particle
searches at the FD (for example inelastic boosted dark matter, nucleon decays), and non-
standard neutrino oscillation phenomena (for example sterile neutrino mixing, non-standard
interactions). In the following, we give examples where DUNE Phase II will bring additional
unique sensitivity with respect to Phase I and to the performance of current experiments [43].
2.3.1 Rare event searches at the near detector
The high intensity and high energy of the LBNF proton beam enables DUNE to search for
a wide variety of long-lived, exotic particles that are produced in the target and decay in
the ND. Heavy neutral leptons (HNLs) and Axion-like particles (ALPs) are examples of well-
motivated searches that can be carried out in DUNE. Low density detectors are best suited
for such a search, because the signal scales with the detector volume while the background
(predominantly due to Standard Model neutrino interactions) scales with detector mass. In
Phase I, SAND can perform such searches with a density of ∼0.2 g/cm2. In Phase II, the ND-
GAr substantially improves the reach for these searches with even lower density and a larger
volume. Signal efficiencies and background rates after selection cuts are found to improve
significantly in Phase II, thanks to ND-GAr [46]. Background rates generally depend on the
decay final state. In some cases background-free searches appear possible, for example for
channels involving pairs of muons in the final state.
For HNLs, the decay rates are proportional to |UαN |2in the case of single dominant mixing,
where α=e, µ, τ and the matrix UαN specifies the mixing between the active SM neutrinos α
and the new heavy states N. Figure 7 shows the combined sensitivity for HNL decay channels
probing each individual mixing matrix element |UαN|2, as a function of the HNL mass and under
the assumption of no background (result adapted from [44]). As can be seen from the figure,
DUNE is world-leading at masses below mτ, complementary to the LHC heavier mass searches.
In addition, DUNE may have the potential to explore further the portion of parameter space
predicted by Type I seesaw models. Other phenomenological studies [47, 48, 49, 50] confirm
the potential of the DUNE Phase II ND for HNL searches.
ND-GAr is also sensitive to ALPs with masses between 20 MeV and 2 GeV [51, 46]. DUNE
is expected to improve over present constraints on ALP particles particularly for ALP masses
below the kaon mass. For a wide range of ALP lifetimes, the sensitivity improvement would
27
DUNE Phase II
Figure 7: Expected DUNE ND sensitivity at 90% CL to the mixing |UαN |2as a function of the
mass MN, for a total of 7.7·1021 POT, and combining all the possible HNL decay channels
leading to visible states in the detector. Backgrounds are assumed to be negligible. Results
are shown for a HNL coupled exclusively to: e(left panel), µ(middle panel), and τ(right
panel). The dotted gray lines enclose the region of parameter space where a Type I seesaw
model could generate light neutrino masses in agreement with oscillation experiments and upper
bounds coming from the latest KATRIN results on β-decay searches. A negligible background
level after cuts and a signal selection efficiency of 20% was assumed for this analysis. Figure
adapted from [44] to include the latest excluded areas from existing results; obtained with
the HNLimits [45] package. All sensitivity curves and currently excluded areas assume Dirac
neutrinos, and that the HNL only couples to one of the charged leptons as indicated by the
flavor index of the panel, while the other two mixings are set to zero.
span many orders of magnitude.
Another rare event search at the ND is neutrino trident production, that is, the production
of a pair of oppositely-charged leptons through the scattering of a neutrino on a heavy nucleus.
Neutrino trident production is a powerful probe of BSM physics in the leptonic sector [52, 53].
The Standard Model (SM) expectation is that the ND will collect approximately a dozen of
these rare events per ton of argon per year [54, 55]. To date, only the dimuon final-state has
been observed, although with considerable uncertainties. The main challenge in obtaining a
precise measurement of the dimuon trident cross-sections (νµ→νµµ+µ−and ¯νµ→¯νµµ+µ−)
at DUNE will be the copious backgrounds, mainly consisting of CC single-pion production
events (νµN→µπN′), as muon and pion tracks can be easily confused. ND-GAr will tackle
this search by improving muon-pion separation through dE/dx measurements in the HPgTPC
and the calorimeter system, and ND-GAr’s magnetic field will significantly improve signal-
background separation by tagging the opposite charges of the two muons in the final state.
28
DUNE Phase II
2.3.2 Rare event searches at the far detector
Phase II will also enhance BSM searches at the FD, and in particular searches that are expected
to be nearly background-free at the scale of the experiment’s full exposure. In such cases,
the decay or scattering rate sensitivity will be inversely proportional to the FD exposure (in
kt·yr), and added exposure in Phase II FD modules will be significant. Background-free (or
quasi-background-free) searches at the FD may include baryon-number-violating processes.
For example, current estimates [43] for the p→K+¯νsearch yield a mean background rate
expectation of 0.4 events for a 400 kt·yr exposure at the FD.
2.3.3 Non-standard neutrino oscillation phenomena
DUNE is sensitive to neutrino oscillation scenarios beyond the standard three-flavor picture,
including sterile neutrinos, non-standard interactions, and PMNS non-unitarity. These searches
rely on both the ND and FD, and require high precision and very large exposures, such that
both the Phase II ND and FD are important.
In addition to searching for BSM modifications to the muon and electron neutrino signals,
DUNE also has a unique capability to search for tau neutrino appearance because the broadband
LBNF beam has significant flux above the ∼3.5 GeV tau charged-current threshold. Searches
for tau appearance would enable DUNE to directly constrain the tau elements of the PMNS
matrix, and also to search for anomalous ντappearance, which may point to mixing with HNLs
or non-standard interactions [56, 57]. This would become particularly interesting if hints of
non-unitarity are observed in the muon and electron channels. The τlepton from beam ντ
CC interactions is not directly observable in the DUNE detectors due to its short 2.9×10−13 s
lifetime. However, the final states of τdecays (∼65% into hadrons, ∼18% into ντ+e−+ ¯νe,
and ∼17% into ντ+µ−+ ¯νµ) can be detected.
The LBNF beamline is designed such that the target and the horn focusing system can
be replaced. The LBNF/DUNE Construction Project will provide targets and horns designed
for 1.2 MW operation, in the standard low-energy beam tune configuration optimized for CPV
measurements. New ACE-MIRT upgrades designed for >1.2 MW operation will be needed, and
could provide the capability to run with a higher-energy beam tune optimized for detection
above the τproduction threshold. Studies indicate that the ντcharged-current interaction rate
will more than double at the FD in this case, compared to the standard LBNF beam optimized
for CPV [58]. Running with the high-energy tune is not currently planned, but could provide
further physics reach for DUNE in Phase II.
At the ND, the baseline is far too short for νµ→ντoscillations to occur within a three-
flavor scenario. However, ντoriginating in rapid oscillations driven by sterile neutrinos could be
detected. A challenge is that for the tau decay to muon channel, a large fraction of the signal
is at very high energy. In Phase I, the TMS cannot reconstruct momentum by curvature, and
is limited to measuring Tµ<∼6 GeV by range. It may be possible to search for anomalous tau
appearance in SAND, which is sensitive to higher energy muons by curvature but has much
smaller target mass. In Phase II, ND-GAr provides a magnetized spectrometer for ND-LAr
which can reconstruct very high-energy muons by curvature. With one year of data with the
Phase II ND, preliminary studies show that DUNE’s reach in this channel extends beyond the
29
DUNE Phase II
present strongest limits from NOMAD [59].
3 The DUNE phase II far detector
3.1 Introduction
The primary objective of the DUNE Phase II FD is to increase the fiducial mass of DUNE to at
least the originally planned 40 kt LAr-equivalent mass. For long-baseline neutrino oscillations,
it is critical that all four FD modules be compatible with the systematic constraints of the ND.
Non-LAr options for the Phase II FD would require corresponding additions or changes to the
ND complex in order to achieve a comparable level of systematic uncertainty. These options
are described in Section 4.4. For MeV-scale physics, the additional mass would double the
number of expected neutrino interactions in a SNB and extend the reach to supernovae beyond
the Milky Way. An exposure of hundreds of kt-yrs is required to improve upon oscillation
parameter measurements with solar neutrinos. Most BSM searches also require very long
exposures to be competitive.
Enhancements to the detector design have the potential to improve the DUNE program
by lowering the threshold for MeV-scale neutrinos or by reducing the background rates in this
energy regime. Phase II also presents opportunities to expand the DUNE science program
to new areas while preserving the essential core measurement capabilities. The design of the
Phase II FD modules will also incorporate lessons learned from the construction of Phase I, in
particular the vertical drift FD2, optimizing performance and cost.
3.2 The vertical drift detector design
The single-phase vertical drift technology as implemented in ProtoDUNE-VD and planned
for FD2 [60] (Figures 8 and 9) draws from the strengths of the DUNE prototypes [61] and
ProtoDUNE-SP [62] as well as the previous detectors ICARUS and MicroBooNE. Relative to
the well-established single-phase (SP) horizontal drift design that is based on large wire plane
assemblies, the vertical drift design simplifies detector construction and installation, reducing
overall detector costs. The vertical drift module uses most of the same structural elements as
the ProtoDUNE-DP design (e.g., charge-readout planes (CRPs) to form the anode planes, and
the field cage that hangs from the cryostat roof), and is constructed of modular elements that
are much easier to produce, transport, and install.
The cathode at the vertical mid-plane of the detector is suspended from the top CRP support
structure and subdivides the detector into two vertically stacked, 6.5 m high drift volumes, with
CRP readout for both the top and bottom drift volumes. The top CRPs are suspended from
ports on the cryostat roof whereas the bottom CRPs are supported by feet on the cryostat
floor.
The important features of the vertical drift design, particularly in comparison with the FD1
horizontal drift design, are:
30
DUNE Phase II
Figure 8: Schematic of the vertical drift FD2 concept with PCB-based charge readout. Corru-
gations on cryostat wall shown in yellow; PCB-based CRPs (brown, at top and bottom with
superstructure in gray for top CRPs); cathode (violet, at mid-height with openings for photon
detectors); field cage modules (white) hung vertically around the perimeter (the portions near
the anode planes are 70% optically transparent); photon detectors (light green at right), placed
in the openings on the cathode and on the cryostat walls, around the perimeter in the vertical
regions near the anode planes. Updated from [60].
Figure 9: Perspective view of the vertical drift FD2 detector. From [60].
31
DUNE Phase II
•maximizing the active volume1;
•high modularity of detector components;
•simplified anode structure based on standard industrial techniques;
•simplified cold testing of instrumented anode modules in modest size cryogenic vessels;
•field cage structure independent of the other detector components;
•extended drift distance;
•reduction of dead material in the active volume;
•allowance for improved light detection coverage;
•simplified and faster installation and quality assurance (QA)/quality control (QC) pro-
cedures; and
•cost-effectiveness.
3.2.1 Charge readout planes (anodes)
The baseline design FD2 anodes, illustrated in Figure 10, provide three-view charge readout via
two induction planes and one collection plane. The anodes are fabricated from two double-sided,
perforated, 3.2 mm thick printed circuit boards (PCBs), that are connected mechanically, with
their perforations aligned, to form charge-readout units (CRUs). A pair of CRUs is attached
to a composite frame to form a CRP; the frame provides mechanical support and planarity.
The holes allow the electrons to pass through to reach the collection strips. Each anode plane
consists of 80 CRPs in the same layout. The CRPs in the top drift volume, operating completely
immersed in the LAr, are suspended from the cryostat roof using a set of superstructures, and
the bottom CRPs are supported by posts positioned on the cryostat floor. The superstructures
hold either two or six CRPs, and allow adjustment, via an externally accessible suspension
system, to compensate for possible deformations in the cryostat roof geometry.
The FD2 top and bottom drift volumes implement different charge readout (CRO) elec-
tronics. The top anode is read out via the top drift electronics (), based on the design used in
ProtoDUNE-DP, that comprises both cold and warm components housed in signal feedthrough
chimneys (SFT chimneys). These chimneys penetrate the cryostat roof, allowing the compo-
nents to be fully accessible for repair or upgrade. The bottom detector electronics (), on the
other hand, implements the same cold electronics (CE) used in the horizontal drift FD1, which
features local amplification and digitization on the CRP in the LAr, thereby maximizing the
signal-to-noise.
1For reference, the FD2 detector model yields an active volume of 10,586 m3, a 5.6% increase over the
estimated FD1 active volume of 10,021 m3.
32
DUNE Phase II
Figure 10: A top superstructure (green structure on top) that holds a set of six CRPs, and
below it an exploded view of a CRP showing its components: the PCBs (brown), adapter
boards (green) and edge connectors that together form a CRU, and composite frame (black
and orange). From [60].
3.2.2 High-voltage system
The FD2 has a horizontal cathode plane placed at detector mid-height, held at a negative
voltage, and horizontal s (biased at near-ground potentials) at the top and bottom of the
detector, which together provide a nominal uniform Efield of 450 V/cm. The main high
voltage system (HVS) components are illustrated in Figure 11.
The HVS is divided into two systems: (1) supply and delivery, and (2) distribution. The
supply and delivery system consists of a negative high voltage power supply (), high voltage
(HV) cables with integrated resistors to form a low-pass filter network, a HV feedthrough (),
and a 6 m long extender inside the cryostat to deliver −294kV to the cathode. The distribution
system consists of the cathode plane, the field cage, and the field cage termination supplies.
The cathode plane is an array of 80 cathode modules, each with the same footprint as a CRP,
formed by highly resistive top and bottom panels mounted on fiber-reinforced plastic () frames.
The modular field cage consists of horizontal extruded aluminum electrode profiles stacked
vertically at a 6 cm pitch. A resistive chain for voltage division between the profiles provides
the voltage gradient between the cathode and the top-most and bottom-most field-shaping
profiles.
In addition to the primary function of providing uniform Efields in the two drift volumes,
both the cathode and the field cage designs are tailored to accommodate PDS modules (Sec-
tion 3.2.3) since it is not possible to place them behind the anode plane, as in the FD1-HD
design. Each cathode module is designed to hold four double-sided X-ARAPUCA PDS modules
that are exposed to the top and bottom drift volumes through highly transparent wire mesh
windows. Along the walls, the field cage is designed with narrow (15 mm width) profiles in
the region within 4 m of the anode plane to provide 70% optical transparency to single-sided
PDS modules mounted on the cryostat membrane walls behind them, and conventional (46 mm
width) profiles within 2.5 m of the cathode plane.
33
DUNE Phase II
Figure 11: A bird’s-eye view of the field cage, with one full-height field cage column (highlighted
in cyan) that extends the entire height, the HV feedthrough and extender (in the foreground),
and the cathode (with one cathode module highlighted in cyan and modules installed on
cathode). From [60].
34
DUNE Phase II
3.2.3 Photon detection system
The FD2 module will implement X-ARAPUCA [63, 64] PDS modules. Functionally, an X-
ARAPUCA module is a light trap that captures wavelength-shifted photons inside boxes
with highly reflective internal surfaces until they are eventually detected by SiPMs. An X-
ARAPUCA module has a light collecting area of approximately 600 ×600 mm2and a light
collection window on either one face (for wall-mount modules) or on two faces (for cathode-
mount modules). The wavelength-shifted photons are converted to electrical signals by 160
SiPMs distributed evenly around the perimeter of the photon detector (PD) module. Groups
of SiPMs are electrically connected to form just two output signals, each corresponding to the
sum of the response of 80 SiPMs.
Since their primary components are almost identical to those of FD1-HD, only modest R&D
was required for the FD2 PDS modules. The primary differences were to optimize the module
geometry and the proximity of the SiPMs to the wavelength-shifting (WLS) plates. Both of
these are more favorable in FD2, leading to more efficient light collection onto the SiPMs. As
discussed in Section 3.2.2, the design has the PDs mounted on the four cryostat membrane walls
and on the cathode structure, facing both top and bottom drift volumes. This configuration
produces approximately uniform light measurement across the entire TPC active volume.
Cathode-mount PDs are electrically referenced to the cathode voltage, avoiding any direct
path to ground. While membrane-mount PDs adopt the same copper-based sensor biasing
and readout techniques as in FD1-HD, cathode-mount PDs required new solutions to meet the
challenging constraint imposed by HVS operation. The cathode-mount PDS are powered using
non-conductive power-over-fiber (PoF) technology [65], and the output signals are transmitted
through non-conductive optical fibers, signal-over-fiber (SoF), thus providing voltage isolation
in both signal reception and transmission.
3.3 Optimized charge and photon readouts for Phase II vertical drift
FD modules
Several variations on the vertical drift design are under consideration to improve the perfor-
mance and/or reduce the cost. Potential improvements can be broadly grouped into two classes,
the charge readout and the photon readout systems.
Optimizations of the charge readout system include options to improve the production
processes and reduce the cost of the CRPs, possible optimizations of strip pitch and length,
and channel count (Section 3.3.2). Other options are to replace the strip-based CRP with
a pixel based CRP (Section 3.3.3) or with an optical readout based on electroluminescence
(Section 3.3.4).
The leading criteria for selecting an optimized technology for a Phase II photon readout
system are performance enhancement at low incremental costs, and the ability to leverage
minimum-risk development of solutions already demonstrated and adopted for Phase I. One of
the most attractive options is the proposed concept (Section 3.3.1), in which PDs are integrated
into the field cage. The APEX concept makes use of the PoF and SoF technologies developed for
FD2 and opens up the opportunity to greatly extend the optical coverage. Another optimization
35
DUNE Phase II
under consideration is the addition of photon detection to a pixel-based CRP (Section 3.3.5).
3.3.1 Optimized photon readout with APEX
The APEX concept (Aluminum profiles with embedded X-ARAPUCA) integrates a large-
area photon detection system into the detector module’s field cage. APEX is a simplified,
lightweight, and low(er)-cost photodetector solution for optimizing photon readout that in-
creases the active optical coverage of the LAr target volume. This solution is derived from the
well-established X-ARAPUCA technology with SiPM photosensors developed for FD2. Con-
crete examples of physics topics enabled by an improved light detection system are given in
Sec. 2.2, in the context of the neutrino astrophysics program of DUNE.
Figure 12: A bird’s-eye view of the field cage with integrated large-area photon detection
system, APEX. The field cage structure is constructed of modules vertically stacked in groups
of four hanging around the LAr drift volume perimeter from the top.
The field cage covers the four vertical sides of the VD LArTPC active volume between the
top anode and bottom anode planes, and thus offers the largest available surface for extended
optical coverage, i.e., APEX can provide up to ∼60% coverage of the surface enclosing the
LArTPC active volume if the field cage walls are fully instrumented, as shown in Fig. 12. In
the APEX concept, no PD modules are installed on the cathode. The PD readout electronics
would need to be referenced to the (high) voltage level of the field cage electrode profile on
which the PD module is installed, and therefore would require electrical isolation. Power and
signal transmission can be established via non-conductive optical fibers by using the PoF and
SoF technologies developed for the FD2 photon detectors that are integrated into that FD
module’s HV cathode plane. These technologies are described in Section 3.2.3. They have
been demonstrated to work reliably for electrical isolation with noise immunity and long-term
stability in LAr.
APEX keeps the same field cage structure as designed for FD2 (see Figure 11), which
includes 24 field cage supermodules, each made up of eight 3.0×3.2 m2field cage modules, for
36
DUNE Phase II
Figure 13: An APEX panel. Top left: one PD module installed on field cage profiles. Bottom
left: a PD module equipped with a SiPM strip at the center. Center: front view of an APEX
panel showing the 6 ×6 array of PD modules mounted on an field cage module. Right: a back
view of the field cage module showing its aluminum profile structure.
37
DUNE Phase II
a total of 192 modules. A field cage module consists of horizontal extruded aluminum C-shaped
electrode profiles (3 m long and 6 cm wide) stacked vertically at a 6 cm pitch and mounted on
vertical FR4 I-beams. An APEX panel, illustrated in Figure 13, is a standard vertical drift
field cage module instrumented with a 6 ×6 array of thin, large-area (∼50 ×50 cm2) X-
ARAPUCA-type PD modules installed onto the field cage structure and fully covering it, as
shown in Figure 13. Hydrodynamic simulations are under development to understand the
potential impact of APEX panels on the LAr recirculation.
Six PD modules constitute a horizontal row of the APEX panel. Each PD module vertically
spans about nine field cage profiles and is mechanically fastened and electrically referenced to
the profile at its mid-height (the fifth of nine). The cavity of this profile houses and provides
Faraday shielding for the cold electronics readout boards for all six of the PD modules in that
row of the array, providing signal conditioning and digitization in cold. Several PoF receivers
and an SoF transmitter (driver and laser diode) at the center of the ∼3 m long profile receive
power and transmit signal, respectively, for the PD modules in the row via optical fibers. The
signals from the six PD modules are multiplexed and transmitted over a single optical fiber
to the (warm) receivers and data acquisition (DAQ), as schematically represented in the block
diagram of Figure 14. The fibers are routed through the penetration at the top of the cryostat
using the central vertical I-beam of the field cage structure as conduit. Each row of six PD
modules in an APEX panel thus forms an electrically isolated system.
Figure 14: APEX cold readout concept: a row of six PD modules (three of the six are not shown
in order to display the readout elements) in an APEX panel forming an electrically isolated
single readout system.
The PD module, the basic unit of the APEX array, is a simplified version of the light trap
X-ARAPUCA concept used in the FD1 and FD2 PDS, designed to be a lightweight (∼1.8 kg),
compact object suitable for efficient mass production. Two WLS stages, #1 and #2 – with a
dichroic filter (DF) between them – convert, transmit, and trap incident LAr scintillation light
under the dichroic filter layer. These components are contained in solid PMMA (transparent
acrylic) slabs that are 6 mm thick, with a surface area of ∼50×50 cm2, illustrated in Figure 13,
bottom left. The DF layer is deposited directly on the front plane of the acrylic substrate, and
38
DUNE Phase II
the WLS #1 coating on top of the DF. Chromophore molecules embedded in the substrate
PMMA (WLS #2) matrix shift transmitted light to a wavelength above the DF cutoff. Light
trapping is optimized by ultra-high reflectivity non-metallic thin film lamination (e.g., Vikuiti
ESR) of the acrylic slab edges and backplane. An array of SiPMs mounted on a flex PCB are
optically bonded to the acrylic surface, as shown in Figure 13, bottom left. Photons trapped by
reflection in the slab are eventually absorbed by the photosensors, producing electronic signals.
We estimate that 80 large-area SiPMs per module, with high photon detection efficiency (),
ganged together into one readout channel, will be sufficient to reach an overall detector efficiency
of ϵD≃2%.
Assembly of APEX panels is expected to be simple. To assemble one, aluminum field cage
profiles are first assembled to form a field cage module, electronics boards are positioned in the
profiles, and PD modules are connected to the boards then fastened to the profiles to complete
the APEX panel. An APEX assembly can be built out of bulk materials (aluminum profiles and
acrylic plates) with low-radioactive content. For this reason, even an extended PDS coverage
compared to Phase I modules is not expected to be a dominant contributor to the internal
background budget discussed in Sec. 3.6.
Figure 15: Map showing the expected in the central (x, y) transverse plane at z= 0 for the
field cage-extended coverage APEX photon detection system. Dimmer regions are present near
the anode planes (with no PDs on them) and at mid-height (near the non-instrumented cathode
plane).
A simulation was performed for a Phase II FD module with APEX, assuming 55% optical
coverage of the LAr volume. The light yield LY (x, y, z) of the system was evaluated, i.e., the
number of photoelectrons (PEs) collected per unit of deposited energy anywhere in the LAr
volume, assuming 2% detection efficiency of the X-ARAPUCA module and standard LAr scin-
tillation light emission and propagation parameters. The simulation resulted in an average value
39
DUNE Phase II
⟨LY ⟩= 180 PE/MeV across the detector volume, with a minimum of LYmin = 109 PE/MeV
near the anode planes, thanks to the extended optical coverage of the APEX system. Such a
light yield would be about a factor of 5 higher than the FD2 one, where simulations indicate
an average light yield of 39 PE/MeV and a minimum light yield of 16 PE/MeV [60]. Figure 15
shows the light yield map in the transverse plane at the center of the FD module long axis.
APEX-specific studies on light-only and charge+light calorimetric performance, impact of non-
uniform light collection, and achievable PDS thresholds in the presence of background flashes,
are in progress.
A series of prototypes are planned to fully develop the APEX concept. A first round of
prototyping, carried out at CERN, has studied the impact on the drift field uniformity of
placing insulating material between field cage electrodes. The (expected) observation of a
slow buildup of static charge on the surface of the insulating material may, counter-intuitively,
allow reduction of the number of field cage electrodes, with a larger pitch. The current (2024)
focus is on a second (ton-scale) TPC prototype at CERN that will be instrumented with up
to eight full-size PD modules, primarily for mechanical and cryogenic tests. Additionally, a
PD module prototype with a full electronic chain, including PoF and SoF systems, will be
constructed and tested in parallel before being integrated into this prototype. A larger-sized
APEX demonstrator in a several cubic meter LAr cryostat, with O(100) SoF and PoF in/out
fibers, will be a third-stage prototyping goal in 2024-2025, likely at Fermilab. Finally, a full-
sized APEX PD-instrumented field cage will be deployed in the VD cryostat at CERN, along
with the proposed optical readout (Section 3.3.4).
3.3.2 Strip-based charge readout
The PCB-based vertical drift anodes, called CRPs, are made up of two stacked PCBs, providing
three projective views. The PCB face directly opposite the cathode has a copper guard plane to
absorb any unexpected discharges. The reverse side of this PCB is etched with strips that form
the first induction plane. The other PCB has strips on the side facing the inner PCB forming
the second induction plane, and has the collection plane strips on its reverse side [60]. The
PCBs are supported by composite frames and mechanically connected using spacers. CRPs
have been successfully demonstrated in the 50 L test stand and at full scale in the vertical drift
cold box. They have been installed in ProtoDUNE-VD in the NP02 cryostat at CERN and will
be deployed in the FD2 cryostat at SURF (see Figure 10).
This system has already been optimized for deployment in FD2, and as such forms a ref-
erence solution also for FD3. Additional optimizations should be explored for FD3 to reduce
cost or to improve performance further. There are various ways in which the strip-based charge
readout might be re-optimized that would impact the strip pitch, length, and orientation. A
more concrete optimization plan will be developed after assessing ProtoDUNE-VD performance
in 2025.
Additional considerations to be explored include the CRP fabrication techniques, including
faster production of the PCB itself and simpler quality control. Some of these ideas have been
tested in the 50 L test stand at CERN, particularly techniques to reduce PCB hole misalign-
ments.
40
DUNE Phase II
In addition to the CRP, the readout electronics need some re-optimization. Depending on
the timescale for construction of FD3, some of the existing electronics production lines may
no longer be available. This may require re-design of components associated with readout of
the top and/or bottom CRPs. For example, a potential optimization of the FD2 BDE includes
porting the , a custom pre-amplifier and shaping , from the 180 nm to the 65 nm production
process2to mitigate the risk of losing access to the 180 nm process. The two other BDE custom
ASICs, and , are already using the 65 nm process. Other potential optimizations for the FD2
BDE design include reducing the cable length for signal and power (it is 27 m for the current
FD2 design), simplifying detector installation.
3.3.3 Pixel-based charge readout
A pixel-based readout would replace the multi-layer strip-based readout with a single-layer
grid of charge-sensitive pixels at mm-scale granularity. Instrumenting each pixel with a ded-
icated electronics channel would achieve a LArTPC with true and unambiguous 3D readout,
where information on the third spatial dimension is provided by the LArTPC drift time. This
is advantageous compared to conventional wire-based two-dimensional readout, especially for
higher-multiplicity interactions of O(GeV) neutrinos. In interactions with several charged par-
ticles in the final state, it is possible for tracks to overlap in one 2D projection, making it more
difficult to reconstruct. Similarly, straight-line tracks in strip-based readout have pathological
angles where the track is recorded entirely along a single strip. Given channel densities of
O(105) pixels per m2of anode, pixel readout would require operation at O(100) µW power
consumption per channel, including amplification, digitization and multiplexing. This is nec-
essary in order to avoid excessive heating of the LArTPC detector, operating near LAr boiling
point. Significant progress has been made in recent years in the development of pixel readout
for LArTPCs, overcoming issues with excessive waste heat, as well as demonstrating cryo-
compatibility, O(104) digital multiplexing, and cost-effective, scalable production. Two options
for readout are discussed below, and .
LArPix Readout
LArPix [66] is a complete pixel readout system for LArTPCs, consisting of 6400-channel pixel
anode tiles, cryogenic-compatible data and power cabling, and a multi-tile digital controller
with an integrated operating system. It has been developed as the baseline technology of
Phase I ND-LAr. The system relies on the LArPix ASIC, a 64-channel detector system-on-a-
chip that includes analog amplification, self-triggering, digitization, digital multiplexing, and a
configuration controller.
The LArPix-v1 ASIC demonstrated that waste heat could be controlled through a custom
low-power amplifier and channel self-triggering, where the digitization and digital readout are
dormant until a signal is detected on the pixel. The LArPix-v2 ASIC incorporated a variety
of improvements to facilitate large-scale production of pixel anodes, including Hydra-IO, a
2The 180 nm and 65 nm processes are advanced lithographic techniques used in semiconductor fabrication;
the dimension refers to feature size.
41
DUNE Phase II
novel programmable chip-to-chip data routing technique to improve system reliability in the
inaccessible cryogenic detector environment.
The current 32×32 cm2LArPix pixel tile (Figure 16) has 6400 charge-sensitive pixels at
3.8 mm pitch and can be configured and read out via a single set of differential digital input
and output wires. The design leverages standard commercial techniques for PCB production to
realize a LArTPC anode, achieving 800 e−equivalent noise charge per channel on the sensitive
TPC-facing side of the tile, while powering and communicating with 100 LArPix ASICs on the
back side. The power consumption achieved by the current LArPix tile is 14 W/m2, ensuring
that the heat flux from the anode is lower than the one from the cryostat walls.
Data acquisition is controlled by the Pixel Array Controller and Network (PACMAN) card,
responsible for delivering power and communication to the tiles. A single compact controller
is currently capable of driving O(10) pixel tiles (e.g., O(105) pixels). It includes a CPU with
integrated operating system and programmable logic similar to a field programmable gate array
(FPGA). The controller is designed to mount on the room-temperature side of a LArTPC cryo-
stat feedthrough, and incorporates power filtering and ground isolation to ensure the integrity
of the low-noise environment within the detector.
Figure 16: Left: Prototype LArPix-v2 anode tile 32 cm in length by 32 cm in height, with
6400 gold-plated charge sensitive pixel pads at 3.8 mm pitch driven by (right) 100 LArPix-v2
ASICs.
Approximately 80 LArPix-v2 pixel tiles have been produced as part of the current proto-
typing program for the DUNE ND. Sets of 16 pixel tiles have been used to instrument each of
the four ton-scale LArTPC modules of the 2×2 Demonstrator (Figure 17), a prototype of the
modular LArTPC design planned for the ND. Each module has been operated at the University
of Bern, and has been used to image over 100 million cosmic ray events.
The LArPix-v2 development program has achieved its goal of a scalable design. All compo-
nents are produced via commercial vendors using traditional electronics production techniques,
and are ready for integrated testing; no additional assembly is required. LArPix-v2 system
production costs, including all cabling, controllers, and power supplies, are approximately $10k
42
DUNE Phase II
per square meter.
Operation of prototype LArPix anodes, in either vertical or horizontal orientations, show
that natural convection provides sufficient heat dissipation to mitigate argon phase transition
(bubble formation or boiling). In particular, the 2x2 Demonstrator [67], a prototype of the
DUNE ND, is constructed of multiple fiberglass boxes with a very low perforation, approxi-
mately 1% of the surface, and rather limited spaces for convective heat dissipation, yet it shows
no issues with thermal management and has achieved purity in excess of 2 ms. Future work
includes a demonstration of LArPix anode heat dissipation in a configuration similar to the
FD2 design.
Assuming completion of the development program of LArPix for the DUNE ND, LArPix
would already meet most of the requirements for deployment in a future FD module. The
development and integration of a high-speed, O(1) GHz, 16-to-1 digital multiplexer would sig-
nificantly reduce the number of cables and feedthroughs, making deployment in a FD much
more feasible. Tests of a large-scale LArPix prototype in the ProtoDUNE-VD system at the
CERN Neutrino Platform are important to validate the integration and interfaces with the
other aspects of the vertical drift design.
Q-Pix Readout
Q-Pix is a novel pixel-based technology for low-threshold, high-granularity readout that is
expected to improve reconstruction relative to projective-based readout, at a much reduced
data throughput. It is ideally suited to the low data rate readout environment of the DUNE
FD modules. The basic concepts of the Q-Pix circuit [68] are shown in Figure 18 (A). The
input pixel is envisioned to be a simple circular trace connected to the Q-Pix circuit via a PCB.
The circuit begins with the “Charge-Integrate/Reset” (CIR) circuit. This charge-sensitive
amplifier continuously integrates incoming signals on a feedback capacitor until a threshold on
a Schmitt trigger (regenerative comparator) is met. When this threshold is met, the Schmitt
trigger starts a rapid “reset” enabled by a Metal–oxide–semiconductor field-effect transistor
(MOSFET) switch, which drains the feedback capacitor and returns the circuit to a stable
baseline, at which point the cycle is free to begin again. To mitigate any potential charge
loss, an alternative design known as the “replenishment” scheme has also been evaluated. In
contrast to the reset architecture, the MOSFET now functions as a controlled current source
such that when the Schmitt trigger undergoes a transition, the MOSFET replenishes a charge
of ∆Q=I·∆t, where ∆tis the reset pulse width or discharge time.
Both the “reset” and “replenishment” schemes capture and store the present time of a local
clock within one ASIC. This changes the basic quantum of information for each pixel from the
traditional “charge per unit of time” to the difference between one clock capture and the next
sequential capture, the Reset Time Difference (RTD). This new unit of information measures
the time to integrate a pre-defined charge. Physics signals will produce a sequence of short,
O(µs), RTDs. On the other hand, in the absence of a signal, the quiescent input current
from 39Ar and other radiogenic or cosmogenic backgrounds would be small, producing long,
O(s), RTDs. Signal waveforms can be reconstructed from RTDs by exploiting the fact that the
average input current and the RTD are inversely correlated.
43
DUNE Phase II
Figure 17: Left: A photograph of one of the four ton-scale LArTPC modules for the 2x2
Demonstrator, a prototype of the DUNE ND. Right: an example cosmic ray imaged in true 3D
using a 102,400-channel LArPix-v2 system in this module (right).
Q-Pix has shown that this architecture can enhance the physics capabilities of a large-scale
LArTPC through its ability to provide full 3D information of the events, as opposed to the three
2D projections provided by FD1/FD2 readout. The first of these demonstrations shows the im-
proved reconstruction enabled by a pixel based detector when compared to a projective-based
readout for DUNE multi-GeV neutrino interactions [70]. This analysis showed enhanced effi-
ciency and purity across all neutrino interaction types analyzed and the ability to reconstruct
the topology and content of the hadronic system (including number of final state protons,
charged, and neutral pions). Moreover, through an analysis of supernova neutrino interactions
and a simulation of the Q-Pix architecture, it was shown that Q-Pix can significantly enhance
the low-energy neutrino capabilities for kiloton-scale LArTPCs. Specifically, Q-Pix: i) en-
hances the efficiency of reconstructing low-energy supernova neutrino events over the nominal
wire based readout, ii) allows for a high-purity and high-efficiency identification of supernova
neutrino candidates, and iii) affords these enhancements at data rates 106times less for the
same energy threshold [71].
44
DUNE Phase II
(A)
(B)
(C)
2. Q-Pix design and demonstration
The key principle of Q-Pix is the concept of ‘Least Ac-
tion’, which can be described as the pixel readout remain-
ing in a low-power quiescent state during periods when no
ionization charge is present. This state can be thought
of as the pixel being “OFF”. However, the pixel readout
needs to be ready and capable of collecting charge and
transitioning quickly to an “ON” state. The “ON” state
must still satisfy the low-power requirements placed on the
electronics present in a liquid argon environment to mini-
mize heating of the medium. To accomplish this, a simple
Charge-Integrate/Reset (CIR) circuit block with a time-
stamping mechanism based on free-running local clocks is
employed. Such a seemingly simple architecture is able to
achieve this principle of ‘least action’ in an unorthodox yet
surprisingly natural overall solution.
2.1. Q-Pix reset scheme
The initially proposed Q-Pix scheme[10] is shown in
Fig. 1(a). This scheme uses a charge-sensitive amplifier
(CSA) for charge integration. Once the voltage of the feed-
back capacitor Cfreaches the preset threshold, the Schmitt
trigger will turn on the MOSFET switch to quickly short
Cfand thus discharging and resetting the Q-Pix read-
out to a stable (arbitrary) baseline. This constitutes the
“Charge-Integrate Reset” (CIR) circuit. The time at which
the reset occurs is recorded using a local clock and repre-
sents the data output of the Q-Pix pixel. This structure
is referred to as the “reset scheme.”
(b)(a)
.
.
.
OutputInput
Charge sensitive
Amplifier
.
+
Schmitt
Trigger
MOSFET
.
.
.
.
OutputInput
Charge sensitive
Amplifier
.
+
Schmitt
Trigger
MOSFET
f
Cf
C
Figure 1: Q-Pix front-end schemes. Panel (a) depicts the reset
scheme. When the charge integrated by the charge-sensitive ampli-
fier reaches the Schmitt Trigger’s threshold, the MOSFET discharges
the charge on Cf, resetting the amplifier and generating a short, stan-
dardized reset signal. Panel (b) illustrates the replenishment scheme.
When the output of the CSA reaches the threshold of the Schmitt
Trigger, the MOSFET is activated, replenishing Cfwith a preset cur-
rent. This current flows opposite the input current direction from
the LArTPC detector.
2.2. Q-Pix replenishment scheme
An alternative architecture which can accomplish the
same goal, with potentially better performance is also con-
sidered for Q-Pix, known as the “replenishment scheme”
as depicted in Fig. 1 (b). In this scheme, the charge
integration process is the same as before, however, in-
stead the MOSFET switch is replaced by a MOSFET con-
trolled current source. Whenever the comparator triggers
a transition (representing that Cfhas reached the desired
threshold voltage), the MOSFET replenishes a charge of
Q=I·t,wheretis the pulse width. This constitutes
the “Charge-Integrate Replenishment” (CIR) circuit. The
Qthen forms a charge quantum of each measurement
and the time at which the replenishment is recorded using
a local clock.
2.3. Implementation of the CIR circuit
When deciding between the “reset” and “replenish-
ment” architecture a number of factors must be consid-
ered. In the “reset” scheme, the MOSFET switch ide-
ally operates in either open (disconnected) or closed (con-
ducting) state. When the amplifier is integrating charge,
the switch must be in a fully open state to prevent any
charge loss. This requires negligible leakage charge passing
through the switch compared to the input charge. During
the reset of Cf, the switch should be fully closed. This
means that the current through the MOSFET must be
sufficiently large to ensure that the Cfcan be reset to the
baseline level as quickly as possible. It should be noted,
that the reset circuit as outlined above will su↵er from
signal charge loss during the reset. In order to prevent
this charge loss, and the subsequently nonlinear errors that
would arise from this, an additional switch would be re-
quired to disconnect the input to the CSA during the re-
set. This may be fine for highly integrated ASICs with
minimal noise as the reset process can be controlled to be
brief enough to ensure that the leaked input charge during
the MOSFET’s ON time is negligible. However, discrete-
component designs with more uncertain parasitic parame-
ters and greater susceptibility to environmental noise may
face many difficulties.
These problems are largely absent for the “replenish-
ment” architecture as both the leakage current from the
MOSFET current source can be neglected (or calibrated
away) as well as an absence of charge loss during the CIR
process. Even if there is a significant input charge during
the discharging process, as long as the MOSFET current
and the discharge time are fixed, the quantization Qof
each measurement will remain constant. This allows the
Q-Pix to discharge the Cfthrough the MOSFET and inte-
grate with the input current simultaneously without loss of
charge. The replenishment scheme also brings additional
advantages. The voltage on the Source and Drain of the
MOSFET remain constant throughout the entire CIR pro-
cess, making it possible to precisely control the MOSFET
current and thus easily fine-tune the desired Q. Further-
more, it minimizes the potential influence of the MOSFET
parasitic parameters on the CSA feedback loop. For the
above reasons, the replenishment scheme was selected for
implementation in this work, as described below.
2.4. Q-Pix replenishment front-end with clocked reset
Fig. 2 represents a simplified schematic of the Q-Pix
front-end demonstration board which was developed for
2
“Reset scheme”
Figure 11: Current waveform reconstruction: simulated vs. measured. This figure showcases the application of CIC filters in reconstructing
Q-Pix output waveforms from SPICE simulations and actual measurements. In the SPICE simulations, the waveforms reconstructed with two
di↵erent CIC filter bandwidths closely match the input signals, affirming the viability of digital low-pass filters in waveform reconstruction.
The left side shows the waveform reconstructed from SPICE simulations based on the actual PCB design of the Q-Pix front-end board. On
the right side, the figure presents waveform reconstruction results from actual measurements, highlighting some shape di↵erences due to the
charge injection e↵ect, primarily originating from the package parasitic capacitance of the input path resistor. However, after introducing a
4 fF parasitic capacitance in the SPICE simulation, the resulting reconstructed waveform closely matches the actual measurement, further
vali da ti ng t he e↵ectiveness of Q-Pix in reconstructing waveforms despite external charge injection e↵ects.
previously mentioned, is already sufficient for our Q-Pix
demonstration.
However, the situation changes for the reset scheme,
as simulation results indicate that a large Cscan signifi-
cantly impact its performance. The reset scheme relies on
rapidly turning on the MOSFET to discharge Cfwhen its
voltage reaches the threshold, with Qbeing the amount
of charge discharged from Cffor each reset. Ideally, the
time constant Cf·Rds limits the minimum reset width,
where Rds represents the resistance between the source
and drain of the MOSFET when it is turned on. But
when Csis present and cannot be neglected, turning on
the MOSFET to discharge Cfalso causes the CSA out-
put to charge Csthrough the MOSFET. As Csis much
larger than Cf, the unknown charge in Csafter charging
significantly a↵ects Q. Consequently, the time constant
Cs·Rds, rather than Cf·Rds , limits the practically achiev-
able minimum reset width, which in our case would be 200
times the original value. According to the simulation, the
Rds of the chosen NMOS is approximately 40k⌦, and Cs
is 20 pF. Assuming a reset width of 2Cs·Rds = 1600 ns is
selected, the maximum equivalent sampling rate is limited
to 625 kHz. Moreover, an excessive reset widt h may lead
to a significant input charge loss in the reset scheme; for
an input current of 1 nA, a single reset pulse could result
in a 1.6 fC input charge loss.
Therefore, a large Cssuggests that, in principle, our
discrete component solution cannot implement the reset
scheme. While this is present in the discrete component
implementation of the Q-Pix frontend, this should not be
present in a fully silicon ASIC design in which there is
more critical control over these aspects.
CSA Output
-
+.
.
Waveform
generator 0.1pF
Cf
Rin
Cs
.
Cin
..
Figure 12: Key parasitic capacitances. This figure illustrates the
locations of two significant parasitic capacitances, Csand Cin that
substantially impact the Q-Pix’s input-output behavior. Stray ca-
pacitance Csprimarily influences the CSA’s response speed and sig-
nificantly a↵ects the reset scheme’s performance. Meanwhile, Cin is
associated with the packaging of the input resistor Rin,anditplays
a role in the input charge.
Cin primarily originates from the parasitic capacitance
associated with the package of the input resistor Rin. Al-
though e↵ectively in parallel with Rin, it is in series in the
10
Charge Input
Reconstructed (Method 1)
Reconstructed (Method 2)
“Replenishment scheme”
Figure 18: A) Schematic of the basic concepts of the Q-Pix circuits for the reset and replenish-
ment schemes. B) Left: Schematic of the 16-channel analog front-end and Right: schematic of
the 16-channel digital design. C) Current waveform reconstructed using a discrete-component
implementation of the Q-Pix replenishment scheme at a charge threshold of 0.46 fC (∼2875e−)
and reconstructed using different digital filtering based on analysis. Images A and C are adapted
from [69].
45
DUNE Phase II
A number of prototypes are currently under construction and evaluation to demonstrate the
Q-Pix readout architecture. These include designs in both 180 nm and 130 nm, evaluation of the
architecture using discrete commercial off-the-shelf (COTS) components, as well as extensive
digital prototyping using FPGAs. The 180 nm design is shown schematically in Figure 18
(B). It consists of a 16 channel analog chip implemented with the replenishment architecture,
and a 16 channel digital chip. On the other hand, Figure 18 (C) shows the implementation
of the replenishment architecture for the Q-Pix readout using COTS discrete components.
This prototype was able to demonstrate the fidelity of reconstructing input from an arbitrary
waveform generator with a replenishment threshold of 0.46 fC with replenishment pulse widths
∼300 −600 ns and linear responses to replenishment up to 2 MHz rates. This demonstration
provides confidence that the architecture proposed will be capable of meeting the performance
needs of future large scale LArTPCs. The consortium of universities and labs working on this
project expect both small and large scale demonstrator (O(1000 −100,000) pixel) LArTPCs
in the coming next few years.
3.3.4 Optical-based charge readout
The optical-based readout shares the same physics benefit as the pixel-based charge readout
solutions (Sec. 3.3.3) in providing a native 3D readout. This technology has also demonstrated
the best spatial resolution of any LArTPC readout option so far, with ≃1.1 mm per pixel [72].
The data-driven readout with native zero suppression yields a very efficient raw data storage,
of relevance for SNB physics. The overall optical gain and the low-noise readout environment
enable low-threshold (≃500 e−per pixel) operation, supporting DUNE’s MeV-scale neutrino
astrophysics program. From the technical point of view, the (off-cryostat) optical readout also
benefits from simplicity of access, greatly simplifying maintenance and upgrade operations.
Finally, depending on the granularity versus cost trade-off chosen, significant cost savings com-
pared to other readout technologies may also be present.
The optical charge readout with fast cameras was developed within the ARIADNE program
and represents a cost-effective and powerful alternative approach to the existing charge read-
out methodology. As first demonstrated in the one-ton dual-phase ARIADNE detector, the
secondary scintillation (S2) light produced in Thick GEM (THGEM) holes can be captured by
fast Timepix3 (TPX3) cameras to reconstruct the primary ionization track in 3D.
The operation principle of a dual-phase optical TPC readout with a TPX3 system is shown
in Figure 19a. When a charged particle enters the LAr volume, it causes prompt scintillation
light (S1) and ionization. The free ionization electrons are drifted in a uniform electric field to
the surface of the liquid. A higher field induced between an extraction grid and the bottom
electrode of the THGEM extracts the electrons to the gas phase. Once in gas, the electrons are
accelerated within the 500 µm holes of the THGEM at a field set between 22 and 31 kV/cm. As
well as charge amplification, secondary scintillation (S2) light is produced. The light is shifted
with a tetra-phenyl butadiene (TPB) coated sheet to 430 nm and then detected by cameras
mounted on optical viewports above the THGEM plane.
Originally, the optical readout was tested with EMCCD cameras within the one-ton ARI-
ADNE detector at the T9 charged-particle beamline at CERN [72], and later was upgraded
46
DUNE Phase II
Figure 19: (a) Detection principle of dual-phase optical TPC readout with TPX3 camera, first
demonstrated in the one-ton ARIADNE detector. (b) LAr interactions from cosmic-ray muons.
Figures taken from [73].
with fast TPX3. The TPX3 camera assembly boosts the S2 light signal and simultaneously
measures Time over Threshold (ToT) and Time of Arrival (ToA) information with 10-bit reso-
lution. ToT allows accurate calorimetry and ToA gives accurate timing (1.6ns resolution). The
TPX3 chip then sends a packet containing information that allows for full 3D reconstruction
using a single device. The high readout rate (up to 80 Mhits/s), natively 3D raw data, and low
storage due to zero suppression make TPX3 ideal for optical TPC readout.
The TPX3 camera system was first tested in low-pressure CF4 gas within the ARIADNE 40l
TPC prototype [74]; following this demonstration, a TPX3 camera was mounted on ARIADNE
and particle tracks from cosmic-ray showers were successfully imaged in 3D for the first time
(Figure 19b) [73]. The cameras are shown to be sensitive even to pure electroluminescence
light generated at the lower end of the THGEM field; this mitigates difficulties often faced
when trying to operate THGEMs at a higher field, where there can be issues with stability.
Use of cameras has additional benefits, such as ease of upgrade as they are externally mounted.
Thus, they are decoupled from TPC and acoustic noise, and large areas can be covered with
one camera, bringing both cost and operational benefits.
To demonstrate this technology further and at a scale relevant to the 10 kt (fiducial) FD
modules, a larger-scale test (ARIADNE+) was recently performed [75] at CERN. Four cameras,
each imaging a 1×1 m2field of view, were employed. One camera utilized a novel VUV image
intensifier, eliminating the need for a wavelength shifter. The test also showcased a light
readout plane (LRP) comprising sixteen, 50×50 cm2surface area, glass THGEMs. The novel
47
DUNE Phase II
Figure 20: (a) The light readout plane under the cryostat lid; (b) the ARIADNE+team on top
of the cryostat; (c) a recorded image of an interaction in LAr.
manufacturing process for the glass THGEMs allows for mass production at large scale [76].
Stable operation was achieved, and cosmic-ray muon data from both the visible and VUV
intensifiers were collected. An image of the detector setup is shown in Figure 20 and results
are published in [77].
The TPX3Cam camera and image intensifiers are commercially available, and a proposal to
instrument the ProtoDUNE cryostat with optical readout is underway, with testing anticipated
to take place in 2025/2026. Further R&D into custom optics and characterization of the next
generation Timepix4 (TPX4) cameras, which are anticipated to become commercially available
by the end of 2025, can offer further benefits. Another promising ongoing R&D effort is a TPX4
camera with an integrated image intensifier [78]. One of these devices will be tested in the near
future within the ARIADNE one-ton detector. Given the current progress of the TPX4 camera
system, partial TPX4 instrumentation in NP02 is anticipated.
3.3.5 Integrated charge and light readout on anode
DUNE is also pursuing the integration of both light and charge detection modes on the anode
into a single detector element. If such a device could be made sensitive both to VUV photons at
reasonable quantum efficiency and to ionization electrons, this would transform the way noble
element detectors collect and process both the charge and light signals. A detection element of
this kind would offer: i) intrinsic fine-grained information for both charge and light, providing
accurate matching between charge and light information; ii) a significant enhancement in the
amount of light collected near the anode and much improved uniformity of response, through
increased surface area coverage; and iii) simplification in the design and operation of noble
element detectors. The technologies under investigation are described in this section, Solar
neutrinos in Liquid Argon (SoLAr), , and Q-Pix Light Imaging in Liquid Argon (Q-Pix-LILAr).
48
DUNE Phase II
SoLAr The SoLAr technology [79] is based on the concept of a monolithic, light-charge,
pixel-based readout to achieve a low energy threshold with excellent energy resolution (≈7% at
few-MeV neutrino energies [31]) and background rejection through pulse-shape discrimination.
The SoLAr readout unit (SRU) under development is a pixel tile based on PCB technology
that embeds charge readout pads located at the focal point of the LArTPC field-shaping system
to collect drifting charges, and highly efficient VUV SiPMs to collect photons in thousands
of microcells operated in Geiger mode. In order to maintain a uniform electric field, novel
monolithic VUV SiPM sensors need to be developed with these features that have charge
readout pads and highly efficient UV-light sensitive microcells.
In 2020, a joint research program between LAr detector scientists and an industrial partner
(Hamamatsu Photonics) delivered a SiPM that reached a record efficiency (15% PDE) for
128 nm light at the argon boiling point (87 K). Nearly at the same time, the first integrated
system for multiplexing the SiPM signal was commissioned and operated inside strong electric
fields. In 2021 a further development with Hamamatsu Photonics produced a new SiPM with
through-silicon vias that will enable the combination of light detection with the charge readout
required for SoLAr.
First SoLAr Prototype
Anode plane design
11/4/22 DUNE Module of Opportunity Workshop, Valencia 2-4 Nov 2022, S.Parsa 10
•Charge pixel pads: 3mm
•Pixel pitch:3.5mm
•SiPM sensitive area 6mmx6mm
•SiPM pitch: 17.5mm
•Readout area: 70mmx70mm
Figure 21: The small-scale SoLAr prototype PCB tested at the University of Bern, front and
back sides. The anode consists of a 7×7 cm2readout area with 16 VUV SiPMs (the LAr-facing
side, at right) and four LArPix-v2a chips on the backplane, at left. The charge pixel pads are
3 mm in size and are placed at a 3.5 mm pitch. The SiPMs have a 6×6 mm2sensitive area and
are placed at a 17.5 mm pitch.
In the SoLAr preparatory phase (2021-2022), combined light-charge collection was demon-
strated using small-size prototypes [80]. The prototypes were operated successfully and have
demonstrated that the principle of combining charge and light readout is possible (Figure 21).
Simulations accounting for light propagation effects have shown that a 7% energy resolution
can be achieved at typical solar neutrino energies (5–20 MeV) and using the scintillation sig-
nal only by replacing anode planes with a pixelated readout integrating a light-sensitive area
covering ∼10% of the surface. This system would enhance the amount of collected light by a
factor of five compared with FD1, reducing the frequency at which low-energy background gets
incorrectly reconstructed to the (higher) energy region of interest of the signal. The authors
49
DUNE Phase II
of [31] have studied this remarkable impact of energy resolution in the background budget of a
LArTPC using conventional readout in a membrane cryostat.
The combination of shielding and a 7% energy resolution gives access to the 5–10 MeV
region, where most of the 8B neutrinos (8B→8Be∗+ e++νe) reside, by greatly reducing the
dominant background from neutrons and 42K above 5MeV visible energies. The energy resolu-
tion is instrumental for sharpening the 17 MeV cutoff of the 8B neutrino spectrum, which lies
just below the “hep” cutoff of 18.8 MeV, and opens a 1.8 MeV window that allows observation
of a pure sample of hep neutrinos (3He + p →4He + e++νe) [81]. Light collection outside
the anode is ensured by X-ARAPUCA tiles, for a total coverage of (8 −10)%.
The latter provide the appropriate light yield without resorting to xenon doping, thus
preserving the pulse-shape discrimination power of liquid argon. Pulse-shape discrimination
is further enhanced with respect to any existing LArTPC by the unique performance of the
SRU and the increase of collected light.
Finally, SoLAr will implement neutron shielding embedded directly in the cryostat walls,
delivering a novel membrane-based cryogenic system that also suppresses environmental back-
ground to the limit where the only residual background is generated inside the LArTPC. This
will provide a radiopure environment and reduce external neutron background in the 1-4 MeV
region by three orders of magnitude.
LightPix A variant of the LArPix ASIC has been designed for scalable readout of very large
arrays of SiPMs. Called LightPix, this ASIC reuses much of the LArPix system design to
provide a system that can read out >105individual SiPMs in a cryogenic environment at costs
far below $1 per channel. LightPix may be useful for instrumenting a future far detector PDS
with higher quantities of SiPMs than the FD1/FD2 PDS design. This could be used as a
readout unit in conjunction with an anode-based light pixel solution, e.g., SoLAr.
LightPix prototypying in combination with VUV-sensitive SiPMs is underway. The first-
generation 64-channel LightPix-v1 ASIC includes a custom low-power time-to-digital converter
(TDC) with sub-ns resolution to enable precise measurement of photon arrival times. It also
implements programmable digital coincidence logic for the suppression of dark counts, par-
ticularly useful for room-temperature detector applications. The LightPix-v1 ASIC was used
to demonstrate particle detection in two small-scale prototype VUV-scintillation detectors: a
16-channel system integrated into a LArPix pixel tile LArTPC detector at LBNL, and a 300-
channel system for readout of a high-pressure gaseous helium detector at UC-Berkeley/LBNL.
A second-generation ASIC, LightPix-v2, is in fabrication. Changes include a new front-end am-
plifier optimized for use with larger (higher-capacitance) SiPMs, as well as a charge-integrator
for use in higher-occupancy environments.
Q-Pix-LILAr The Q-Pix consortium is pursuing a different integrated charge and light read-
out system on the anode, by coating a charge readout pixel with a type of photo-conductive
material that, when struck by a VUV photon, would generate a signal (charge) that could be
detected by the same charge readout scheme considered for the ionization charge. The Q-Pix-
LILAr concept is shown schematically in Figure 22 (A). Moreover, with the proper choice of
50
DUNE Phase II
photoconductor, such a device could have a broad photon wavelength response, thus offering
detection of the full spectrum of light produced in noble element TPCs.
Figure 22: A) Schematic design for the Q-Pix-LILAr integrated charge and light readout,
from [82]. B) Example design for a multimodal (charge and light) pixel where interdigitated
electrodes (IDE, not shown) are deposited around the central ionization collection pixel. Once
the photoconductor creates single electrons from photon conversion, IDEs define a region of
high electric field where avalanche multiplication of those single electrons occurs, producing
detectable signals.
Three such photo-conductive materials have been explored in recent R&D: Amorphous
selenium (aSe), zinc oxide (ZnO), and organic photodiodes (OPDs). Their application in a
liquid argon environment is currently under investigation. Initial studies of constructing a
multimodal pixel detector have recently focused on utilizing aSe, as the ability to prototype
and test it was the simplest. The first study on aSe in cold used commercially manufactured
PCBs to demonstrate that these aSe-based interdigitated electrodes (IDE) are sensitive to VUV
light at cryogenic temperatures, are cryo-resistant, and are able to maintain argon purity [82].
Designs for a multimodal pixel are shown in Figure 22 (B) where an IDE is deposited around
the central ionization collection pixel. This design provides a straightforward way to apply a
local electric field to the aSe, to enable charge gain, and to instrument the area between the
charge collection pixels.
More recent studies have pushed this capability further to characterize the performance of
such a design to a low photon flux (O(100) photons), at high electric fields (>70 V/µm) and at
cryogenic temperatures. These results continue to show promise. Further R&D into aSe-based
devices, as well as other photoconductors, is anticipated to be an area of active research in the
near future.
3.4 Liquid-argon doping
A promising direction for expanding DUNE capabilities in a Phase II FD module is to in-
troduce dopants to the LAr, creating a detector medium other than pure argon. Generically,
51
DUNE Phase II
these LAr “doping” techniques may be used to modify the detector response in a desirable
way or to introduce new target materials of interest into the bulk detector volume. These
approaches are analogous to widely-used strategies in e.g., scintillator or solid state detectors,
where secondary fluors are sometimes added to scintillators to shift photon wavelengths, or
elements like gadolinium or lithium are added to increase neutron or neutrino cross sections,
respectively. A key constraint for LAr dopants is that they must not interfere with the op-
eration of the LArTPC by introducing electronegative impurities that non-negligibly degrade
the LAr transparency to electrons. Furthermore, as for any large-scale detector with complex
physics of signal generation, the relevant microphysics (including radiative and non-radiative
molecular energy transfer, electron-ion recombination, and scintillation-light production) must
be well understood through a robust R&D program to adequately assess the scalability to the
DUNE FD scale. Several such avenues are being explored that would enhance the charge or
light detection capabilities, or introduce new signals of interest. This section discusses two
promising potential additives that have been previously demonstrated in large-scale LArTPCs.
The first category is liquid xenon, which is of interest at low concentrations for impact on the
scintillation light signal, and at higher concentrations as a signal source. The second includes
photosensitive dopants that convert scintillation light to ionization charge.
These LAr dopants can be particularly impactful for DUNE Phase II prospects to broaden
the low-energy physics program, targeting signals in the MeV to keV energy range. Detection of
signals in this regime can enhance the GeV-scale neutrino oscillation physics program through
enhanced neutrino energy reconstruction [83]. In combination with techniques that lower ra-
dioactive and external backgrounds, the detection of keV–MeV signals also provide sensitivity
to a broad array of previously inaccessible signals spanning BSM physics and low-energy neu-
trino astrophysics. Examples include low-energy solar and SNB neutrinos, searches for rare
decays such as 0νββ, exotic physics such as fractionally-charged particles, and dark matter
scattering. A more complete list can be found in [84]. An expanded program in these areas
would complement DUNE’s program while leveraging the large mass and deep-underground
location.
3.4.1 Liquid xenon
Liquid xenon is a potential additive to the LAr in DUNE Phase II, either at a low (parts per
million (ppm)) or high (up to the percent level) concentration. The loading techniques [85] and
stability conditions [86] of LAr+LXe mixtures have been explored across this broad range of
concentrations.
At low concentrations, the presence of xenon impacts the production of scintillation light in
LAr, acting as a highly efficient wavelength shifter that converts the 128 nm primary scintillation
wavelength in argon to a longer 178 nm wavelength. This has several advantages, including
reduced Rayleigh scattering, improved light detection uniformity, a narrowing of the scintillation
timing distribution, and a reduction in energy losses to impurities such as nitrogen. Such losses
would result from non-radiative energy transfers involving the long-lived triplet state of Ar,
transfers that are suppressed with the introduction of xenon. This leads to a much improved
robustness of the scintillation light yield against LAr impurities, without appreciable impact on
52
DUNE Phase II
the charge signal. In ProtoDUNE-SP xenon doping up to ∼20 ppm verified the enhancements
to optical response and the recovery of light yield in the presence of impurities [85]. Xenon
doping at a 10 ppm level is already assumed in the FD2 Phase I module [60].
At higher concentrations, up to the percent level, xenon may also be of interest as a signal
source. 136Xe is a candidate isotope for 0νββ which, if observed, would establish the Majorana
nature of the neutrino and demonstrate a violation of lepton number conservation [87]. The
introduction of xenon, either in its natural form (8.9% 136Xe) or enriched to 136Xe, into a large-
scale, deep-underground LArTPC detector could provide an opportunity to search for this
important decay mode [41]. Mitigation of important backgrounds (39Ar, 42Ar, neutrons) near
the 2.458 MeV Q-value for this decay are consistent with the requirements of other potential
low-energy physics goals considered for DUNE Phase II, as described in Section 3.6. A key
challenge for a competitive search is the massive procurement of xenon, at a level exceeding
the world’s current production by more than one order of magnitude, and possibly xenon
enrichment at the same scale [88]. Another crucial challenge is achieving an energy resolution
at the percent level for MeV-scale electrons; photosensitive dopants, discussed in the following,
provide one avenue toward achieving this.
3.4.2 Photosensitive dopants
In a typical pure-LAr TPC, the energy deposited by charged particles is ultimately divided
between ionization electrons, drifted in the electric field and detected at the anode plane, and
scintillation light, detected by a photon detection system. The photon signal, which is produced
promptly with ns-scale timing, is used for 3D event position reconstruction as well as triggering
and absolute timing of neutrino interactions. In a LArTPC doped with a photosensitive dopant,
the scintillation signal would be converted to ionization charge, effectively transferring the full
deposited energy into that channel. Potential photosensitive dopants under consideration are
a class of hydrocarbons with work functions on the order of the LAr (or Xe-doped LAr) VUV
primary scintillation photon energy (7–9 eV). A dopant of this kind would convert scintillation
light into ionization electrons very efficiently with minimal loss of spatial resolution.
The use of such dopants in LArTPCs can offer benefits to both the GeV- and MeV-scale
physics programs of DUNE Phase II. In general, the transfer of deposited energy into the
ionization channel leads to an enhancement of the ionization charge, which is measured with
excellent efficiency in a LArTPC. This enhancement is particularly pronounced in regions of
high energy deposition, improving prospects for particle identification using charge calorimetry.
Furthermore, LAr with photosensitive dopants exhibits a significantly more linear relationship
between deposited and visible charge, reducing the scale and uncertainties of corrections related
to electron-ion recombination effects.
The general impact of such dopants in large-scale LArTPCs in practice was studied by the
ICARUS Collaboration. ICARUS performed a long-term test of the Tetra-methyl-germanium
(TMG) dopant in a three-ton LArTPC exposed to cosmic rays and γsources, observing a
clear enhancement in the ionization charge signal, and a significantly more linear response in
reconstructed to deposited charge [89]. Importantly, this test also demonstrated long-term
stability in realistic LArTPC operating conditions. A complete and detailed model of the
53
DUNE Phase II
microphysics of energy transfer between LAr and candidate photosensitive dopants will require
a comprehensive assessment of potential dopants and their ionization response across a broad
range of signal energies for the Phase II program.
The enhancements provided by photosensitive dopants are particularly notable for improv-
ing energy resolution at low energies, e.g., to capture point-like signals at or below the MeV
scale. A significant challenge with measuring such signals is the efficient collection of small
amounts of scintillation light. In the Phase I design, a limited photon detection efficiency of
order O(0.1%) may limit the capabilities of DUNE to extract spectral information regarding
MeV-scale signals, and thus to perform energy-based background mitigations. Ideally, a de-
tector would measure both the ionization and scintillation anti-correlated signals to measure a
precise total energy, as in the case of the EXO-200 experiment [90] and as also investigated in
[91].
In principle, a large LArTPC can achieve percent-level energy resolution for MeV-scale sig-
nals of interest, but this would require detection of tens of percent of the scintillation photons,
a level of efficiency impractical with current and near-future designs. Meanwhile, by convert-
ing the isotropic scintillation light into directional ionization charge, photosensitive dopants
at the ppm level could allow the full energy to be measured with high efficiency by the TPC
charge detection system. In this sense, charge alone would provide a precise energy measure-
ment, analogous to a correlated charge/light measurement. Previous work in the context of
LAr calorimeters has also considered the impact of several candidate dopants on MeV-scale α
particles, demonstrating substantial charge enhancements for low-energy events with relatively
large scintillation signals [92]. Straightforward future R&D using βor γsources to study the
low-energy electromagnetic response can further clarify the impact and achievable energy res-
olution for MeV-scale signals of interest for beam neutrino energy measurements, low-energy
neutrino astrophysics, and keV- to MeV-scale BSM signatures. To fully realize the potential
of photosensitive dopants in LArTPCs, studies to explore the microphysics involved, and R&D
to determine the optimal dopant types and concentrations, will also be needed.
3.5 Hybrid Cherenkov plus scintillation detection
The Theia hybrid Cherenkov+scintillation detection concept is motivated by a science pro-
gram of low-energy astroparticle, rare event, and precision physics (Section 3.5.2). It also
contributes to the overall CPV sensitivity (Sec. 2.1). The envisioned 25 kt Theia detector of-
fers good particle and event identification at both low and high energies, coupled with a target
of high radio-purity, no inherent radio isotopes, and excellent neutron shielding. This allows
the detector to probe physics that requires low threshold and low background.
3.5.1 Hybrid detection concept
A detector of the envisioned hybrid design would separate Cherenkov and scintillation light by
the use of a novel liquid scintillator [93], fast timing, and spectral sorting. Cherenkov light
offers electron/muon discrimination at high energy via ring imaging and sensitivity to particle
direction at low energy. The scintillation signature offers improved energy and vertex resolution,
54
DUNE Phase II
PID capability via species-dependent quenching effects on the time profile, and low-threshold
(sub-Cherenkov-threshold) particle detection. The combination boasts an additional handle on
PID from the relative intensity of the two signals.
This detector design, being developed as Theia, would offer excellent energy resolution for
high-energy neutrino interactions (better than 10% neutrino energy resolution has been achieved
with preliminary algorithms), along with access to a rich program of low-energy, rare-event,
and precision physics.
This is likely a cost-effective option, particularly among those designed to broaden the
physics program, thanks to the relatively simple and well-understood detector design that
omits both cryostat and field cage. The Theia detector concept is shown in Figure 23.
Figure 23: Illustration of sited in a DUNE FD cavern, with an interior view of the Theia-25
concept modeled using the Chroma optical simulation package [94]. Taken from [12].
3.5.2 Theia physics program
Theia will seek to make leading measurements over as broad a range of neutrino physics and
astrophysics as possible. The scientific program includes:
•observations of solar neutrinos – both a precision measurement of the CNO flux, and a
probe of the MSW transition region;
•determination of neutrino mass ordering and measurement of the neutrino charge conju-
gation and parity (CP)-violating phase δCP;
55
DUNE Phase II
•observations of diffuse supernova neutrinos, and sensitivity to neutrinos from an SNB
with directional sensitivity;
•sensitive searches for nucleon decay in modes complementary to LAr; and, ultimately,
•a search for 0νββ, with sensitivity reaching the normal ordering regime of neutrino mass
phase space (mββ ≃6 meV).
Table 2 summarizes the physics reach of Theia-25. The full description of the analysis in
each case can be found in [12].
Table 2: Projected Theia physics reach, from Ref. [12]. Exposure is listed in terms of the
fiducial volume assumed for each analysis. The total detector volume assumed is 70×20×18 m3.
For 0νββ, the target mass assumed is the mass of the candidate isotope within the fiducial
volume (assumed to be housed within an inner containment vessel). Limits are given at the
90% CL.
Physics Goal Reach Exposure (Assumptions)
Long-baseline oscillations Equivalent to 10-kt 127 kt-MW-yr
LAr module
Supernova burst <2◦pointing accuracy 25-kt detector, 10 kpc distance
5,000 events
DSNB 5σdiscovery 125 kt-yr (5 yr)
CNO neutrino flux <10% 62.5 kt-yr (5 yr, 50% fid. vol.)
Reactor neutrino detection 2000 events 100 kt-yr (5 yr, 80% fid. vol.)
Geo neutrino detection 2650 events 100 kt-yr (5 yrs, 80% fid. vol.)
0νββ T1/2>1.1×1028 yr 211 ton-yr 130Te
Nucleon decay p→νK+τ /B > 1.11 ×1034 yr 170 kt-yr (10 yr, 17-kt fid. vol.)
Nucleon decay p→3ν τ/B > 1.21 ×1032 yr 170 kt-yr (10 yr, 17-kt fid. vol.)
3.5.3 Technology readiness levels
The Theia reference design makes use of a number of novel technologies to achieve successful
hybrid event detection. This design would be used to enhance the Cherenkov signal by reducing
and potentially delaying the scintillation component. The use of angular, timing, and spec-
tral information offers discrimination between Cherenkov and scintillation light for both low-
and high-energy events. Fast photon detectors – such as the 8” PMTs now manufactured by
Hamamatsu, which have better than 500 ps transit time spread – will be coupled with spectral
sorting achieved via use of dichroic filters [95].
Successful separation of Cherenkov and scintillation light has been demonstrated even in a
standard scintillator like LAB-PPO [96] with the use of sufficiently fast photon detectors, and
will be even more powerful when coupled with the spectral sorting capabilities envisioned for
Theia.
56
DUNE Phase II
Radiopurity levels exceeding the requirements for the Theia low-energy program have been
successfully demonstrated by water Cherenkov experiments (SNO) and scintillator experiments
(Borexino).
Further optimization of the design could be achieved by considering deployment of Large
Area Picosecond Photo-Detectors (LAPPDs) [97, 98], for improved vertex resolution, or slow
scintillators [99, 100] to provide further separation of the prompt Cherenkov component from
the slower scintillation. A more complete discussion of the relevant technology is provided
in [101].
The R&D for Theia will be completed with the successful operation of a number of tech-
nology demonstrators currently under construction: (i) a one-ton test tank and a 30-ton Water-
based Liquid Scintillator (WbLS) deployment demonstrator at Brookhaven National Labora-
tory (BNL) will demonstrate the required properties and handling of the scintillator; (ii) a low-
energy performance demonstrator, , at Lawrence Berkeley National Laboratory (LBNL) [102]
will demonstrate the performance capabilities of the scintillator, fast photon detectors, and
spectral sorting; and (iii) a high-energy demonstration at ANNIE, at Fermilab, will validate
GeV-scale neutrino detection using hybrid technology [103]. These detectors are all currently
operational or under commissioning.
3.6 Background control
The potential to enhance the physics scope of DUNE Phase II with lower energy thresholds
has been attracting significant attention within the wider community [84]. The proposed ideas
tend to rely on two enhancements over the Phase I program: greater control of radioactive
backgrounds and improved energy resolution at lower energies. DUNE is well placed to improve
the lower-energy physics scope, first because of the depth of the FD, which is well shielded
from cosmic-induced backgrounds. Secondly, the sheer size of the detector volumes allows for
significant fiducialization to reduce external backgrounds originating within the SURF cavern
rock and shotcrete. Phase II designs that minimize material in the active regions, such as the
FD2 or dual-phase (DP) designs, are most favorable for low-background physics due to reduced
risk of radioactive backgrounds.
We can define two natural physics target energy regions. While these targets are motivated
by the intrinsic backgrounds in argon-based detector modules (Sections 3.2 through 3.4), most
of this background control discussion also applies to water-based detectors (Section 3.5), as
detailed in the following.
The first background target extends the energy threshold down to about 5 MeV. With careful
control of neutron, γ, and radon related backgrounds, combined with improvements in the low-
energy readout, an extended SNB neutrino program can be envisaged, with improved reach
in terms of supernova distance sensitivity (to the Magellanic Clouds), for elastic scatters with
improved directionality, and to the (softer energy) early or late parts of the supernova neutrino
flux. A low-energy threshold could also allow a precision solar neutrino program to explore
solar-reactor oscillation tensions and non-standard interactions. In an argon-based detector,
this 5 MeV threshold is set by the intrinsic 42Ar-42K decay chain, as shown in Figure 4.
The second background target would extend the energy threshold to even lower values of
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DUNE Phase II
∼1 MeV or less. With such a low threshold, ambitious but high-reward physics measurements
would include: solar CNO measurements; searches for 0νββ with xenon loading; and even high-
mass weakly interacting massive particle dark matter detection could be possible [37]. In an
argon-based detector, this could be accomplished only by using underground sources of argon,
thus largely suppressing the intrinsic 42Ar activity.
This section outlines some of the most significant radioactive backgrounds and identifies
paths to reduce them in Phase II detector modules.
3.6.1 External neutrons and photons
In DUNE Phase I, the dominant background to low-energy SNB neutrinos will be from exter-
nal neutrons, that is neutrons originating from outside the detector (SURF cavern rock and
shotcrete). These neutrons are primarily of radiogenic origin. When captured in the LAr, they
can produce 6.1 MeV or 8.8 MeV γcascades which Compton scatter or pair produce electrons
that directly mimic the CC neutrino signals. On the other hand, in a water-based detector,
neutron captures on free hydrogen would result in lower-energy gammas of 2.2 MeV.
To remove external neutrons in argon-based detectors, passive shielding can be deployed,
as first suggested in [31]. A layer of 40 cm of water, or 30 cm of polyethylene or borated
polyethylene, is sufficient to attenuate the neutron flux from spontaneous fission or (α, n)
reactions in the rock by 3 orders of magnitude, making it subdominant. A shield of this size
fits within the warm support structure of the cryostat. Alternative approaches would involve
modifications to the cryostat design, for example, layering the insulating foam with neutron-
capturing materials such as gadolinium-doped acrylic. These same measures will ameliorate
the cavern γbackground originating from 238U and 232Th natural decay chains.
In a water-based detector, no passive neutron shield around the detector would be necessary.
Excellent neutron shielding via detector fiducialization would be reached in this case thanks to
the plentiful free hydrogen available as part of the detector target.
Spallation-induced neutron and cosmogenic background events are also possible, though
they are primarily short-lived and expected to be orders of magnitude less than the radiogenic
backgrounds. A full study of these backgrounds in [104] show that these can be further reduced
by tagged-muon-proximity event selections.
3.6.2 Internal backgrounds from detector materials
After the external cavern neutrons, the most significant source of neutron background comes
from contaminants in materials within the detector, from (α, n)-induced reactions within the
cryostat and other components. Photons produced in these events can also distort reconstructed
quantities due to light flash or charge blip backgrounds, particularly when close to the readout,
such as the cryostat-mounted light sensors. Dark matter experiments have successfully managed
such backgrounds with careful material selection programs, using radioactive assay techniques
to select favorable materials for detector construction, and to ensure quality assurance during
production and installation processes. The world-leading argon-based dark matter detectors
have lowered backgrounds by five orders of magnitude below the DUNE Phase I target. To
maintain the sub-dominance of these internal backgrounds relative to externals removed by
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DUNE Phase II
shielding, a DUNE Phase II argon-based detector module will require a less stringent reduction
target of three orders of magnitude on detector components such as cryostat stainless steel [19].
For a Theia-type module, internal backgrounds within the fiducial volume are driven by
the cleanliness of the target itself. The chemical purity of the water-based liquid scintillator
target is 10−17 g/g in both uranium and thorium contaminants, which is considered achievable
by improving target material purification techniques [12].
3.6.3 Intrinsic backgrounds from unstable isotopes in the target
Argon extracted from the atmosphere contains two background isotopes that can limit sensi-
tivity at the lowest energy for any argon-based detector: 39 Ar, with a decay Q-value of 565keV;
and 42Ar, with a decay Q-value of 599 keV and its daughter isotope 42K, which decays with
a Q-value of 3525keV. The 42Ar-42 K chain sets a lower limit of about 5 MeV, dependent on
the ultimate low-energy resolution, for low-threshold physics with atmospheric argon. Dark
matter experiments have successfully extracted argon from underground sources, which are
depleted in both 42Ar and 39Ar [105]. These experiments show reduction factors of order 1400
for 39Ar and have seen no 42Ar. The currently only known source of underground argon is
too small to fill a detector the scale of DUNE, but work is ongoing to identify new, larger
sources which can be used cost-effectively. Recent estimates of the potential reduction of 42Ar
in underground-sourced argon is expected to be eight orders of magnitude [106].
Intrinsic argon background contributions would be absent in a Theia-type module. The
most abundant radioactive isotope in this target material would be 14C. With a decay Q-
value of 156keV, 14C would not be a relevant background for any of the low-energy physics
measurements and searches discussed in Section 2.2 in connection with a Theia module.
3.6.4 Radon background
Radon gas has high mobility, emanates from all detector materials, and can diffuse easily
throughout the entire detector volume. This background can mimic directly low-energy neu-
trinos, through (α,γ) reactions and misidentified αevents in the detector. It also produces
daughter products which can plateout on internal components such as the photon detector
system, distorting the low-energy reconstruction. Several approaches should be adopted to
control this background, including: direct removal of radon in the purification system using an
inline radon trap; selection of detector materials for low radon emanation; surface treatments
to contain or remove radon sources; removal of a significant emanation source from dust by
controlling and cleaning to higher cleanliness standards than in Phase I; removal of radon from
air during installation to lower the risk of plateout backgrounds when the detector is open; and
analysis techniques such as αtagging by pulse shape discrimination.
3.6.5 The SLoMo concept
One proposed design for a low-background, argon-based, Phase II far detector is the Sanford
Underground Low background Module (SLoMo). This design, shown in Figure 24 provides a
path to lower background levels using the techniques outlined above, reducing most background
59
DUNE Phase II
sources by three orders of magnitude below the expected Phase I levels. This is combined
with a significant increase in light coverage within the detector using high quantum efficiency,
DarkSide-style, SiPM tiles [107] to increase the energy resolution and pulse shape discrimination
power at lower energies.
Figure 24: Design for SLoMo, highlighting background control methods required to achieve
goals.
To get this light coverage, SLoMo aims to densely instrument an interior 1–2 kt of highly
fiducialized underground argon (UAr) in the center of a vertical drift-like detector. The struc-
ture on which to mount the DarkSide SiPM modules is not fixed in this design, though we
propose light-tight acrylic walls covered in wavelength-shifting foils. Reference [19] shows that
a 20% SiPM coverage, combined with charge detection by existing VD CRPs and viewing an
inner volume, should easily lead to a sub-2% energy resolution (sigma) at 2 MeV. This feature,
along with the negligibly low amount of 42Ar in UAr, makes possible 0νββ studies with xenon
loading, should this be a program DUNE wishes to pursue. Reducing 42 Ar to very low levels
also allows detectable energy spectra from a supernova to reach well into the region where νe−e
elastic scattering dominates and thus pointing, in principle, is improved. A 20% SiPM module
coverage would come at an affordable cost and would detect enough photons to allow pulse
shape discrimination. The combination of high SiPM coverage, low neutron background, fidu-
cialization and radon control would allow competitive WIMP dark matter searches in SLoMo.
Solar CNO investigations would also become possible, as would observation of further phenom-
ena, such as the “supernova glow” [108]. This design is outlined in [19], where the significant
physics gains are further explained.
3.6.6 Research and development requirements
All the Phase II options to lower the energy threshold require a radioactive background budget
to be specified and low-background techniques to be deployed to ensure it is achieved. The
60
DUNE Phase II
R&D required to achieve these goals includes:
•Large-scale materials and assay campaigns, scaling up material selection techniques used
by low-background fundamental physics experiments to the kt scale.
•Cleanliness requirements and approaches for the kt scale.
•Radon control in detector liquids, including emanation assay and control at the FD scale.
•Low-background photon detection systems, developing new designs that can increase the
light detection efficiency without overwhelming a background budget.
•Background model and simulation campaign for physics sensitivity analyses.
•Novel analysis techniques, such as pulse shape discrimination, to remove background
events.
•Compact shield designs for argon-based modules, that can fit in the limited DUNE cavern
space or within the cryostat structure.
•New sources of underground argon, capable of filling an argon-based DUNE FD module
cost-effectively.
3.7 Toward detector concepts for Phase II FD modules
The DUNE FD2 vertical drift technology forms the basis for the reference design for FD3 and
FD4. As such, the R&D for FD3 and FD4 is primarily focused on upgraded photon detector
and charge readout systems for the vertical drift layout. Most of these candidate systems are
either further developments of the current systems or replacements based on technologies that
are already under active R&D or in early prototyping phases. A non-LAr option such as Theia
is also under consideration as an alternative technology for FD4. A summary of technologies
under consideration, both LAr and non-LAr options, for these FD modules, along with R&D
status and plans, is provided in Table 3.
The detector technologies described in the previous sections (Section 3.2 through 3.6) will
form the building blocks to define full detector designs for both FD3 and FD4. These technolo-
gies are not standalone, and most of them can be combined or integrated together, as shown in
Table 4. It is important to note that the check marks in the table for FD3 are not solely driven
by Technology Readiness Level (TRL) since several other technologies listed (e.g., ARIADNE,
LArPix) are also technically mature.
The choices for FD3 are primarily motivated by how straightforward the proposed upgrades
are to implement without requiring major modifications to the baseline FD2 design on which
FD3 will be based. This is an important consideration since in the case of FD3, the DUNE
collaboration is aiming to meet the technically limited schedule, which calls for FD3 installation
to start no later than 2029. However, as the other technologies listed in Table 3 evolve, they
may demonstrate that they meet our FD3 requirements. If so, and if timelines can be met,
61
DUNE Phase II
Technology Prototyping Plans Key R&D Goals
CRP
(Sec. 3.3.2)
2024: Cold Box tests at CERN.
2025-2026: ProtoDUNE-VD at CERN.
Port LArASIC to 65 nm
process
APEX
(Sec. 3.3.1)
2024: 50 L & 1-ton prototypes at CERN.
2024-2025: O(100)-channel
demonstrator at Fermilab.
2025-2028: ProtoDUNE-VD at CERN.
Mechanical integration of
APEX PD in field cage
Signal conditioning, digiti-
zation and multiplexing in
cold
LArPix,
LightPix
(Secs. 3.3.3
and 3.3.5)
2024: 2x2 ND demonstrator at Fermilab.
2024-2025: Cold Box tests at CERN.
2026-2028: ProtoDUNE at CERN.
Micropower, cryo-
compatible, detector-
on-a-chip ASIC
Scalable integrated 3D pixel
anode tile
Digital aggregator ASIC
and PCB
Q-Pix,Q-
Pix-LILAr
(Secs. 3.3.3
and 3.3.5)
2024: Prototype chips in small-scale
demonstrator.
2025-2026: 16 channels/chip prototypes
in ton-scale demonstrator at ORNL.
2026-2027: Full 32-64 channel “physics
chip”.
Charge replenishment and
measurement of reset time
Power consumption
R&D on aSe-based devices
and other photoconductors
ARIADNE
(Sec. 3.3.4)
2024: Glass THGEM production at
Liverpool.
2025-2026: ProtoDUNE-VD at CERN.
Custom optics for TPX3
camera
Light Readout Plane design
with glass-THGEMs
Characterization of next-
generation TPX4 camera
SoLAr
(Sec. 3.3.5)
2024: Small-size prototypes at Bern.
2025-2028: Mid-scale demonstrator at
Boulby.
Development of VUV-
sensitive SiPMs
ASIC-based readout elec-
tronics
Hybrid
Cherenkov+
scintilla-
tion (Sec-
tion 3.5.1)
2024-2025: Prototypes at BNL (1- &
30-ton), LBNL (Eos), Fermilab
(ANNIE).
2025-26: BUTTON at Boulby.
Theia organic component
manufacturing
Theia in situ purification
Spectral photon sorting (di-
choicons)
Table 3: Prototyping plans and key R&D goals for the main Phase II FD technologies under
consideration.
62
DUNE Phase II
they will remain under consideration for FD3 (with the exception of Theia). Therefore, their
continued R&D in view of FD3 is encouraged.
While full detector solutions will be defined in the forthcoming years through dedicated
design reports, the following outlines the high-level detector concepts currently under consid-
eration by the DUNE collaboration.
Technology Option for Can integrate with
FD3 FD4
CRP (strip-based charge readout) ✓ ✓ APEX
APEX (X-ARAPUCA light read-
out on field cage with SiPMs)
✓ ✓ CRP, LArPix, Q-Pix, ARI-
ADNE, SoLAr
LArPix,LightPix (pixel charge
and light readout)
✓APEX, SoLAr
Q-Pix,Q-Pix-LILAr (pixel charge
and light readout)
✓APEX, SoLAr
ARIADNE (dual-phase with opti-
cal readout of ionization signal)
✓APEX
SoLAr (integrated charge and light
pixel readout)
✓APEX, LArPix, Q-Pix
Hybrid Cherenkov + scintilla-
tion
✓N.A.
Table 4: LArTPC integration of the detector technologies currently being considered for the
Phase II FD modules. Here, “FD3” refers to the FD3 reference design requiring only minimal
modification to the FD2 vertical drift design. The “FD4” options could also become options
for FD3 over time.
For FD3, we envisage a vertical drift LArTPC that is similar in concept to FD2 (Section 3.2).
We do not anticipate any changes to the FD2 high voltage system, with two drift volumes of
6.5 m drift length each. The CRPs at both anodes would feature three 2D projective views
of the events, obtained from two double-sided perforated PCBs stacked together, similar to
FD2. Continued R&D beyond the current CRP design for FD2 will focus on optimizations
of strip pitch, length and orientation, as well as on streamlining CRP construction techniques
(Section 3.3.2). Upgrades to FD2 charge readout electronics are possible, such as the adoption
of the 65 nm process for the fabrication of all FD3 ASICs.
The FD3 PDS would be composed of X-ARAPUCA-based PD modules read by SiPMs
using PoF and SoF, similar to FD1 and FD2. The installation location (field cage, cathode
and/or membrane wall), optical coverage, and PD module design of the FD3 PDS will be
determined through APEX technology R&D (Section 3.3.1). This R&D will also determine the
reference solution for PDS readout electronics, particularly whether analog optical signals will
be transmitted outside the cryostat as in FD2, or a digital optical transmission solution will be
adopted. Background control could include incremental improvements over FD2 protocols, but
no dedicated passive shields (beyond the cryostat itself) nor underground argon (Section 3.6)
63
DUNE Phase II
would be deployed. We envisage LAr doping as for FD2, via the addition of trace (ppm-level)
amounts of liquid xenon (Section 3.4).
The concepts for FD4 introduce further improvements. The concept for the reference design
is a vertical drift LArTPC with a central cathode and two anodes with pixel-based readouts.
The projective readout of CRPs would be replaced by a native 3D charge readout system, either
employing charge pixels (see LArPix and Q-Pix technologies in Section 3.3.3) or through an
optical-based charge readout (see ARIADNE technology in Section 3.3.4). The anode pixels
may also serve as scintillation light detection units (see the SoLAr, LightPix and Q-Pix-LILAr
options in Section 3.3.5). The symmetric TPC configuration may in principle allow for imple-
mentation of different pixel-based solutions at the top and bottom anodes, depending on the
R&D outcome and available resources, as is the case for the different top and bottom electronics
adopted in FD2.
A single-drift LArTPC solution for FD4 with a unique ARIADNE-based anode plane on
top and the cathode placed at the bottom of the detector is also possible. This solution
would require upgrades to the HV system to accommodate a longer (13 m) drift. Commercial
600 kV power supplies with fluctuations in the output voltage that are sufficiently small for
this application already exist. On the other hand, R&D would be needed to scale up the
high-voltage feedthrough design currently being used in the ProtoDUNE-VD demonstrator,
in order to adapt to the larger diameter high-voltage cable and to the higher voltage values.
Scintillation light detection away from the anodes would be performed with X-ARAPUCA
modules further improved from FD3 (see Section 3.3.1). Compact shield designs and greater
control of radioactive backgrounds would be explored for FD4, given that an important goal
for this module would be to extend the physics scope to lower energy thresholds.
A hybrid detector module capable of separately measuring scintillation and Cherenkov light
(see Theia technology in Section 3.5) would provide a fully complementary detection technol-
ogy for FD4 compared to FD1-3, and currently forms the basis of the alternative FD4 concept
being explored by the DUNE Collaboration. This module would be designed for both high-
precision Cherenkov ring imaging and long-baseline neutrino oscillation sensitivity, and a rich
program across a broad spectrum of physics topics in the MeV-scale energy regime, see Table 2.
This can be achieved via either a phased approach, with both the light yield of a water-based
liquid scintillator target and the coverage of fast-timing photosensors increasing over time in
order to broaden the physics program, or with a high light-yield liquid scintillator and sufficient
Cherenkov separation to preserve the Cherenkov purity from the start. Near detector options
for non-LAr FD modules are discussed in Section 4.4.
The DAQ system for FD3 and FD4 will be based on the same architecture designed for
the first two FD modules. The DUNE timing system will be extended to these modules,
facilitating inter-module synchronization and triggering. Most likely, the DAQ will pursue the
use of Ethernet and standard protocols for the readout interface to the detector electronics. Raw
data will be stored using the same file format, easing the integration with offline computing.
The configuration, control, and monitoring system will be re-used, with customizations as
needed. Use of the existing DAQ software will allow us to focus efforts on the aspects that may
be implemented differently, and to take advantage of advances in computing technologies. For
example, the trigger and data filter may evolve to rely on more sophisticated data processing
64
DUNE Phase II
techniques and technologies, such as Artificial Intelligence (AI), particularly at low energies.
Decisions on the technology choices for FD3 and FD4 are expected to come no later than
2027 and 2028, respectively. As noted earlier in this section, the reference designs for FD3 and
FD4 are upgraded versions of the vertical drift LArTPC technology, with Theia serving as an
alternative technology choice only in the case of FD4.
The final design milestones for Phase II FD modules are driven by the number and extent of
the upgrades planned. For example, in the case of an FD2-like module where the only upgrades
are optimization of CRPs and the APEX light system, one can envision being ready for by
2028 in a technically limited schedule. In this scenario, the earliest start for installation of FD3
can be anticipated in 2029 with completion of installation and filling in 2034. Alternatively,
if one were to implement pixel-based upgrades such as LArPix, Q-Pix, SoLAr, or ARIADNE
(top anode plane only), the FDR milestone would likely be delayed until at least 2030.
An asymmetric DP vertical drift LArTPC for FD4, with a single drift volume instrumented
via a single ARIADNE readout plane, would require significant changes to the HV system. It
is possible to reach the FDR milestone for this option by 2031-32. In the case of the Theia
option, a FDR milestone no earlier than 2033 is anticipated. The ProtoDUNEs at CERN will
continue to serve as important platforms to demonstrate several of these technologies and their
potential for integration.
4 The DUNE Phase II near detector
In Phase II, DUNE will have accumulated FD statistics of several thousand oscillated electron
neutrinos, resulting in statistical uncertainties at the few-percent level on the number of electron
appearance events. To reach the physics goals of DUNE, a similar level of systematic uncertainty
must be achieved, which requires precise constraints from the ND. To understand the needs of
the Phase II ND, we must first understand the expected performance of the Phase I ND, which
consists of two measurement systems, ND-LAr+TMS, and SAND. In Section 4.1, we describe
why the Phase I ND is critical for DUNE physics, discuss limitations inherent to its design,
and outline the Phase II requirements that are needed to provide improved constraints on the
argon-based FD data sample. This is a difficult challenge as the ultimate performance of the
Phase I ND is not yet understood, and will depend on analysis techniques developed over the
coming decade. Section 4.2 describes a detector concept that meets the design motivations of
Section 4.1. Further improvements may come from upgrades to the Phase I ND components,
see Section 4.3. Near-detector options to constrain possible non-argon FD data samples are
discussed in Section 4.4.
4.1 Design motivations
The Phase I ND-LAr+TMS detector is designed to measure neutrino interactions on the same
nuclear target as the FD, and with a detector response similar to the FD. Neutrino energy in
the FD is estimated by summing the lepton energy with the hadronic energy. The FD measures
the muon energy by range, and the energies of all other particles calorimetrically, in both cases
65
DUNE Phase II
exploiting energy deposits occurring in LAr. The ND-LAr+TMS detector also measures muons
by range, and other particles calorimetrically. It is able to reconstruct the same observables
as the FD, and measures them with essentially the same resolutions, in an unoscillated beam.
This capability is the core requirement of the DUNE ND, and will be a critically important
constraint for all DUNE long-baseline measurements. The ND-LAr+TMS system moves off-
axis (via DUNE-PRISM) to collect data at different fluxes, and directly constrains the energy
dependence of neutrino cross sections. SAND is permanently on-axis, and measures neutrino
cross sections on various nuclear targets while also monitoring the beam. SAND has a LAr
target, so that it can also measure cross section ratios, including on argon.
The dimensions of Phase I ND-LAr are driven by containment of electrons and hadrons,
rather than by event rate, so that they can be measured calorimetrically in the same way as
in the FD. To minimize cost, the dimensions have been chosen to be as small as possible while
maintaining full coverage of the neutrino-argon phase space. However, this means that the
acceptance is non-uniform and depends on the event kinematics, complicating the calorimet-
ric energy measurement. Beam-induced muons will be reconstructed by the ND-LAr+TMS
combined system. TMS is able to provide sign selection of muons, which is especially impor-
tant to reject wrong-sign backgrounds in antineutrino mode. However, ND-LAr itself is not
magnetized, so the sign selection is only possible for the muons that enter TMS (≳800 MeV
kinetic energy), and there is no sign selection for other particles. While TMS will provide muon
momentum and sign reconstruction for the energy region relevant for long-baseline oscillation
physics, the design is such that muons above 6 GeV kinetic energy will not be ranged out nor
sign-selected.
The main purpose of the SAND detector will be to monitor the neutrino beam, but it will
also be capable of making independent measurements of the neutrino flux and flavor content.
This additional capability adds robustness to the ND complex, enabling better control over
systematics and background. Phase I SAND will be able to measure the sign of all charged
particles in its low-density CH2tracker, but not generally for hadrons produced in the argon
target. The SAND tracker will also measure neutrino cross sections on carbon and hydrogen
targets.
To constrain neutrino-argon interaction modeling, it is useful to identify specific exclusive
processes. Of those, about two thirds of neutrino interactions in DUNE will have pions in
the final state. ND-LAr is an excellent detector for identifying pions and protons when they
are above threshold, and do not undergo strong interactions inside the detector. However,
many events in the DUNE energy range have pions with hundreds of MeV kinetic energy,
which travel several interaction lengths and frequently scatter, transferring some energy to
the atomic nuclei that is then not seen in a calorimetric energy reconstruction. On the other
hand, below threshold pions decay to final state particles, including neutrinos, leading to large
fractions of their rest mass not being visible calorimetrically. Also, protons below 300 MeV/c
are impossible to detect in ND-LAr because they deposit all of their energy over a range of only
a few mm, producing highly saturated ionization charges recorded on a single pixel. Predictions
on the multiplicity of such low-momentum protons from neutrino-argon interaction models are
particularly uncertain.
These Phase I limitations motivate the design of the Phase II ND. Specifically, the Phase II
66
DUNE Phase II
ND should have, when compared to the Phase I ND:
•argon as the primary target nucleus,
•improved PID across a broad range of energies and angles,
•lower tracking thresholds for protons and pions,
•minimal secondary interactions in the tracker volume,
•4πacceptance over a wide range of momenta, and
•magnetization to achieve sign selection over a broader muon momentum range.
Employing an argon target will ensure that constraints from the Phase II ND can be applied
directly to the argon-based FD without any extrapolation in atomic number.
A broad acceptance and high PID efficiency will enable exclusive final states to be identified,
which will improve the constraints on neutrino interaction modeling. Low thresholds will make
the Phase II ND highly sensitive to nuclear effects. Magnetization will ensure sign selection at
all energies and angles, for both charged leptons and charged pions.
In the event that one of the Phase II FD modules consists of a neutrino target material
that is not argon-based and of a detector technology other than LArTPC, such as the Theia
detector concept described in Section 3.5, the requirements for the Phase II ND complex will
need to be expanded to account for the additional target material(s) and the different neutrino
detection method.
4.2 Phase II improved tracker concept
For Phase II, an improved tracker concept based on a GArTPC would replace TMS downstream
of ND-LAr. Drawings for the envisaged layouts of the Phase I and Phase II detector suites are
shown in Figure 25. A GArTPC can reconstruct pions, protons and nuclear fragments with
lower detection thresholds than a LArTPC can. Figure 26, which compares the same simulated
event in each, shows this. The protons travel a much longer distance and can be more clearly
separated in gaseous argon. The GArTPC is also less susceptible to confusion of primary
and secondary interactions, since secondary interactions occur infrequently in the lower-density
gas detector. If the TPC is inside a magnetic field, it can better distinguish neutrinos and
antineutrinos and can determine the momenta of particles whose trajectories are not contained
in the detector. It can also measure neutrino interactions over all directions, unlike the ND-
LAr, which loses acceptance at high angles with respect to the beam direction. Therefore, a
GArTPC detector system at the near site, called ND-GAr in the following, provides a valuable
and complementary data sample to better understand neutrino-argon interactions.
However, a drawback of a GArTPC is the lower neutrino event rate in a given volume
due to the lower density. One way to improve this is to use high-pressure argon gas. A
cylindrical volume with a diameter and length both of roughly 5 m, and gas at 10 bar, would
have a fiducial mass of nearly one ton of argon, yielding approximately one million neutrino
67
DUNE Phase II
Figure 25: Layout of the envisaged Phase I (left) and Phase II (right) ND suite. The neutrino
beam enters from the bottom-right corner, and exits at the top-left corner, of the drawings. The
SAND detector is shown at its permanent on-axis location, while all other detectors upstream
are shown at their maximum off-axis location.
interactions per year. The trade-off between sufficient target mass and low detector density
has not been optimized, but would nonetheless be adjustable during operations by setting the
detector pressure.
As illustrated in Figure 27, the reference design concept for the ND-GAr detector comprises:
1. a pressurized GArTPC,
2. a surrounding calorimeter,
3. a magnet, and
4. a muon-tagging system.
A PDS may also prove necessary to reduce pileup and to provide the event t0for the drift
time determination in events that do not reach the calorimeter. It would also help improve
the track matching between the TPC and the external calorimeter and muon systems [110].
All these subsystems are described in the following. The entire ND-GAr system will move
perpendicularly to the beam direction together with ND-LAr, as part of the DUNE-PRISM
concept.
This detector concept is motivated by the considerations in Section 4.1. It also affords
significant opportunities to study BSM physics, as discussed in Section 2.3.
4.2.1 Charge readout of TPC
A variety of techniques can be used to amplify and collect the ionization electrons after their
drift to the TPC anode, and the options currently under consideration for ND-GAr are briefly
68
DUNE Phase II
LArSoft
Run: 1/0
Event: 1
UTC Tue Mar 2, 1982
08:09:8.102468080
0 500 1000 1500 2000 2500 3000 3500 4000 t [ticks]
60−
40−
20−
0
20
40
q [ADC]
680 690 700 710 720 730
900
1000
1100
1200
1300
1400
1500
930 940 950 960 970 980
1000
1100
1200
1300
1400
75 80 85 90 95 100 105
1000
1100
1200
1300
1400
1500
Figure 26: The same CC νµevent with seven low energy protons (kinetic energies ranging
from 7 to 51 MeV) simulated in a LArTPC (left) and a GArTPC (right). The LArTPC event
display shows time ticks versus channel number for the three projective views of the event. The
GArTPC reconstruction algorithm finds all eight tracks in the event (seven proton tracks and
one muon track), although only six are visible by eye in this view. All proton tracks travel
2.4 cm or less in LArTPC. From [109].
presented here. In all cases, a high-pressure gas mixture with high argon content (>90% mo-
lar fraction) is envisaged. A 96:4 Ar:CH4mixture was tested successfully during ND-GAr
R&D [111, 112]. Therefore, non-Ar components in the ND-GAr target will contribute at the
few percent level at most to the overall event rate in the TPC. In order to extract pure ν-Ar
interactions, such percent-level corrections can be made with high accuracy using Transverse
Kinematic Imbalance techniques [113], joint ND-GAr-SAND fits, and Monte Carlo-based es-
timates. High-pressure argon gas mixtures have been used in the past, such as in the PEP-4
detector at SLAC [114], which used a (flammable) gas mixture of 80:20 Ar:CH4, operated at
8.5 atm. A known challenge for high-pressure gas detectors is that the gas amplification gain
decreases as the gas pressure increases. For the DUNE ND-GAr, R&D to ensure adequate
stability and gain in a non-flammable gas is underway.
Multi-Wire Proportional Chambers To collect sufficient event statistics, the HPgTPC,
at the core of ND-GAr, must be both large and capable of functioning under high pressures.
A TPC of the size used in the ALICE experiment at CERN [115] may be adequate in terms of
size, but only if the gas inside is pressurized to approximately 10 atm. As a result of the recent
upgrade of ALICE’s readout system to gaseous electron multipliers (s), the previously operated
ALICE multi-wire proportional chambers have become available. They were previously oper-
ated in ALICE at 1 atm, hence their operation needed to be assessed within a high-pressure
argon gas environment.
Two test stands, one each in the UK and the US, called the Gas-argon Operation of ALICE
TPC (GOAT) and the Test stand of an Overpressure Argon Detector (TOAD), respectively, are
69
DUNE Phase II
Figure 27: Cutaway view of the full ND-GAr detector system, showing the HPgTPC, the
calorimeter, the magnet, and the iron yoke. The detectors for the muon-tagging system are not
shown.
being used to test the ALICE chambers under high pressure. GOAT used a pressure vessel rated
to 10 atm. It tested an ALICE inner chamber for its achievable gas gain at various pressure set
points, amplification voltages, and gas mixtures [111]. TOAD had previously tested an ALICE
outer chamber for its achievable gas gain up to 5 atm. Currently, it is being commissioned in
the Fermilab for data-taking in a test beam and for performing a full detector slice test of the
electronics and DAQ. In both test stands, wire-based readout chambers have been tested in
high-pressure environments, demonstrating that they can provide reasonable gas gains when
they operate at or above the high voltage values they were subject to in ALICE. Despite this,
the long-term operation and stability of these chambers at such high voltages remain to be
investigated. There are also plans to test charge readout systems based on micro-pattern gas
detectors, such as GEMs, as described below.
TPC Readout with GEMs In a TPC using GEMs or “thick GEMs” (THGEMs), the
ionization drift electrons enter the THGEM holes and are accelerated in a high electric field.
At sufficiently high fields, this acceleration causes the electrons to further ionize the gas medium,
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DUNE Phase II
resulting in a Townsend avalanche. This exponentially increases the number of electrons and
therefore the signal size.
Typically, GEMs and THGEMs are produced starting from double copper-clad substrates,
either by photolithography of kapton in the case of the former, or Computer Numerical Con-
trol (CNC) drilling of epoxy laminates/FR-4 in the latter. We propose to use a new type of
THGEM made out of glass, as also proposed in the context of the optical-based charge readout
option for the Phase II FD (Section 3.3.4). These glass THGEMs developed at Liverpool (UK)
are fabricated using a new masked abrasive machining process. The innovation allows for cus-
tomization of glass THGEMs, where both substrate and electrode materials can be tailored to
our requirements, which include high stiffness, low outgassing, and resilience to damage from
discharges.
The amplified electrons from the THGEMs would be read out on a segmented anode to
allow for tracking reconstruction. Borosilicate glass and fused silica are isotropic and homoge-
neous substrate materials that can be machined to typical THGEM thicknesses while remain-
ing sturdy and potentially providing better surface finishes than FR-4-based THGEMs. Their
transparency, made possible by indium tin oxide (ITO) electrodes, makes them suitable for
optical imaging of primary ionization, as demonstrated up to 1.5 bar with cosmic ray imaging
at estimated optical gains up to 106[116].
Future optimization of glass GEMs may include enhancements in light collection with
wavelength-shifting substrates [117], wavelength-shifting coatings [118], or diamond-like car-
bon (DLC) coatings for stability [119, 120]. R&D toward a THGEM-based readout is ongoing
in Spain, where a 10-bar full 3D Optical TPC (Gaseous Argon T0 (GAT0)) is under commis-
sioning. In addition, R&D toward a GEM-based readout for ND-GAr is currently underway in
the US with the GEM Over-pressurized with Reference Gases (GORG) test stand, currently
testing a triple-GEM stack.
TPC Readout electronics Due to the high-pressure nature of this detector, readout elec-
tronics must be developed that can operate inside the pressure vessel to minimize the analog
signal path. The electronics must also be zero-suppressed and compatible with the existing
DUNE DAQ infrastructure for the Phase I ND. Readout electronics has traditionally been one
of the cost drivers of TPCs. While the pixel size to be used in the final detector module has
not been determined, detectors like ALICE had 700k channels. With this number of channels,
work is needed to ensure that the electronics system is cost-effective.
R&D work is underway in the UK and US to deliver such electronics. A prototype system
using the SAMPA ASIC, developed for the ALICE TPC upgrade and the sPHENIX detector,
plus FPGA-based control and aggregation, is already in hand. This solution, scaled up to the
full ND-GAr detector, is expected to be much cheaper than the ones adopted for ALICE and
sPHENIX, thanks to the much lower data rates. If full 3D optical tracking is ultimately adopted,
the readout electronics would align with the technical proposal described in Section 3.3.4 for
FD3 and FD4.
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DUNE Phase II
Figure 28: Possible structure of a combined tile and strip layer sampling calorimeter. The
(yellow) tile/absorber layers are oriented towards the TPC; they are followed by (green)
strip/absorber layers. Dimensions are in mm.
4.2.2 Calorimeter concept
The GArTPC will excel in measuring charged particle tracks, but to first order is blind to
neutral particles. As such, it is important to have a system that can detect them. At neutrino
energies of a few GeV, these are mostly photons (for example from π0-decays) and neutrons
(from nuclear break-up) in the kinetic energy range from ≲100 MeV to ∼GeV. The photon
energy will be determined calorimetrically, while the neutron energy can be determined by
measuring the time of flight between the production vertex and a nuclear re-scatter in the
calorimeter [121]. Both photons and neutrons will be key to measuring nuclear effects that will
influence the relationship between true and reconstructed neutrino energy, and the dynamics
of the neutrino interactions.
It is also the case that the HPgTPC should occupy the largest possible volume, and the
calorimeter has to surround the TPC. As such, it has a rather large surface area even for
modern particle physics detectors. Optimizing this detector to achieve the physics goals while
still being affordable is a key task of the gaseous argon detector group.
A possible affordable technology with the required performance is based on a plastic scin-
tillator sampling calorimeter that is constructed from active tile layers using a combination of
the technology developed by the CALICE R&D Collaboration [122] and the more traditional
scintillator strip, WLS fiber, and SiPM readout combination, used in neutrino experiments such
as the near detector. A preliminary structure of the calorimeter is illustrated in Figure 27.
Further details of the potential layout of the barrel detector are shown in Figure 28.
A potential barrel geometry consists of 60 layers with the following layout:
•eight inner layers of 2 mm copper + 5 mm of 2.5 ×2.5 cm2tiles + 1 mm FR-4, and
•52 layers of 2mm copper + 5 mm of cross-strips 4 cm wide
A possible barrel calorimeter depth is about 44 cm. The initial performance evaluation for
photons, based on a preliminary design that was investigated, is summarized in Figure 29.
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DUNE Phase II
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Photon Energy [GeV]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
mean
/ E
E
σ
Baseline Cu
2 mm Pb
1 mm Pb
0.7 mm Pb
/ndf 51.9/11
2
χ
A 5.7%
B 1.6%
C 4.8%
/ndf 9.643/11
2
χ
A 8.1%
B 2.1%
C 0.5%
/ndf 36.98/11
2
χ
A 5.4%
B 1.4%
C 1.5%
/ndf 113.7/11
2
χ
A 5.0%
B 0.7%
C 3.1%
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Photon Energy [GeV]
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
Ratio Energy Resolution
Baseline Cu
2 mm Pb
1 mm Pb
0.7 mm Pb
Figure 29: Left: energy resolution as a function of photon energy for different absorber config-
urations. The function σE
E=A
√E⊕B
E⊕Chas been fitted to the simulated data, where the ⊕
symbols refer to a quadrature sum of the three terms. Right: Ratio of the energy resolution for
the different absorber configurations. The best resolution is achieved using thin lead absorber.
The overall depth of the electromagnetic calorimeter (ECAL) has been kept constant. More
details can be found in [5].
For the present study, copper has been chosen as the absorber material, as initial studies
have shown that this material provides a good compromise between calorimeter compactness,
energy, and angular resolution. It also allows for the removal of heat generated by the electronics
in the tile layer. There are several possible readout ASICs on the market to determine the time
and charge of the SiPM signals, one possibility being the KLauS ASIC [123].
4.2.3 Magnet concept
To achieve the physics goals, the TPC volume of the ND must be magnetized in order to
measure the momenta of muons and other particles, and to determine the sign of their charge.
The magnetized system will analyze both the tracks originating from ND-LAr and penetrating
from upstream, and the tracks produced within the magnetic volume by neutrino interactions.
The need to make the magnet as compact as possible, thus minimizing the material at the
downstream end of the TPC and in front of the calorimeter, suggests an integrated design
in which the magnet structure serves also as a pressure vessel for the TPC gas volume. The
magnetic design described in [124], and summarized here, fulfills these requirements and is
cost-effective.
The magnet system consists of a superconducting solenoid surrounded by an iron return
yoke. The superconducting solenoid cryostat serves not only as a pressure vessel body for
the HPgTPC, but also as support for it and the calorimeter elements located in its bore.
Additionally, the design of the iron magnet yoke uses the mechanical strength of the yoke’s
pole faces to eliminate the large domed heads that would normally be required for a large-
diameter pressure vessel.
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DUNE Phase II
Another important design requirement for ND-GAr is the ability to accurately measure the
momentum of muons that originate in ND-LAr. This requirement limits the amount of material
allowed on the upstream side of ND-GAr and motivates an unconventional and asymmetrical
iron yoke design. An iron yoke that eliminates a portion of the iron along the upstream face has
been developed and designed, and is called Solenoid with Partial return Yoke (SPY). Figure 30
illustrates the SPY magnet system.
Figure 30: The SPY magnet system. The hole in the yokes is on the upstream side, to minimize
material traversed by tracks originating from neutrino interactions in ND-LAr.
The following lists the main requirements and technological features of this design in more
detail:
•The momentum analyzing power of the ND-GAr assembly (magnet + TPC) must provide
at least 3% momentum resolution for the muons originating within ND-LAr. Additionally,
for particles produced as a result of neutrino interactions in the HPgTPC, the resolution
in neutrino energy reconstruction must be at least as good as that of the DUNE FD.
•The magnetic field uniformity, thanks to recent and relevant improvements in the capa-
bility of event reconstruction, is not required to be very high. A ±10% tolerance within
the magnetic volume is expected to be sufficient, provided that a very accurate map for
the magnet “as built” is measured. However, it is worth emphasizing that the magnet
design fully described in [124] greatly exceeds the ±10% requirement, and should offer
a±2% variation over the whole volume. Careful studies were also done to evaluate and
minimize the magnetic forces between ND-GAr and SAND.
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DUNE Phase II
•The superconductor will be co-extruded in high-purity aluminum to provide quench pro-
tection. The current reference solution for cable material is one based on niobium tita-
nium. Higher temperature superconductors such as MgB2will also be considered as part
of an R&D program currently in progress.
•The ND-GAr assembly must provide good acceptance for muons exiting ND-LAr and must
fit within the space constraints imposed by the ND hall design and by DUNE-PRISM.
•The ND-GAr’s magnet system must present as little material as possible in the path of
the muons exiting from ND-LAr. A similar requirement holds in the downstream face of
the yoke, to assist in the discrimination of muons from pions.
•The vacuum cryostat must be capable of providing mechanical support and a cryogenic
environment for the superconducting coils. The inner wall of the vacuum cryostat must
be sufficiently strong to serve as the outer wall of the pressure vessel for the HPgTPC,
and to support the weight of the calorimeter.
•The carbon steel of the return yoke must provide a uniform 0.5 T magnetic field over the
full length of the solenoid, and limit fringe fields to the ≤0.01 T levels required by the
experiment and by the co-existence with SAND. It must also provide flat carbon steel
pole tips for the magnet return yoke that match the magnetic field boundary conditions
at the ends of the solenoid, and provide the mechanical support for the pressure vessel
end flanges.
The main parameters achieved in the current design [124] are summarized in Table 5.
Parameter Requirement Notes
Central field 0.5 T
Field uniformity ±10% Current design achieves ±2%
Ramp time to full field 30 min
Stray field ≤0.01 T Stray field in SAND negligible, in LAr fiducial vol-
ume (FV) ≃10 G
Bore diameter 6.73 m Reduction possible with TPC and ECAL opti-
mizations
Coils diameter 7.85 m Cryostat diameter at stiffening rings
Solenoid length ≃7.8 m
Solenoid weight ≃150 t
Yoke total weight ≃757 t
Table 5: List of SPY parameters according to the current reference design.
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DUNE Phase II
4.2.4 Muon system
A GArTPC ND system will need to be outside the calorimeter to improve pion/muon separa-
tion. The muon tagger would likely implement a well established technology, such as a coarsely
instrumented scintillator detector. It is not likely to require substantial R&D, but will need
engineering effort.
4.2.5 Light detection options
Enabling time-tagging by the TPC would provide an absolute determination of the vertex po-
sition and interaction time, thus simplifying the matching with external detectors and enabling
reconstruction of interactions whose by-products range out before reaching them. The only
demonstrated technique to accomplish this in TPCs relates to primary scintillation, which due
to the complexity of the system would require significant R&D, primarily to study the level
of localization needed in order to associate time information with a given interaction. The
choice of gas mixture for the detector will also be key, as different mixtures have very different
scintillation properties [125, 126].
Although pure argon gas emits scintillation light copiously at a level of 20000 photons/MeV,
gases employed historically in TPCs for accurate tracking in magnetic fields do not [127]. The
recent demonstration of strong (and fast) wavelength shifting in the Ar/CF4system, with yields
in the range 700–1400 photons/MeV [128, 129], opens up the possibility of ns-level time tagging
for energy deposits down to at least 5 MeV [110]. A mere 1% CF4addition (per volume) seems
sufficient to achieve this performance while keeping the electron diffusion at 3.6 mm for a 5 m
drift (compared to 20 mm for pure argon) for a 200 kV cathode bias. These values are even
below those expected for a conventional Ar/CH4(90/10) mixture.
In view of the requirements for single-photon detection and magnetic field compatibility,
and given the spectral range of the scintillation, two technologies are of particular interest, as
described below. A third, light readout of secondary scintillation at the amplification stage, is
also an option that could be explored, based on an Ar/CH4(99/1) mixture (Section 4.2.1).
SiPMs SiPMs are well suited for detection in the visible range, and several ganging schemes
are currently available for large area coverage (e.g., [130]). Silicon suffers from high dark rate
at room temperature and, in fact, simulations point to the need for cryogenic operation (-25 C)
to reach MeV-thresholds in ND-GAr. Methods to do this are under study. A comprehensive
R&D program has been laid out and is led by Spain. A conceptual description of the ganging
scheme and active-cryostat concept proposed, along with proof-of-principle demonstrations for
both, can be found in [110].
LAPPDs Large-Area Picosecond Photo-Detectors (LAPPDs) are novel photosensors based
on microchannel plate technology. With sensitive regions of order 20×20cm and sub-cm po-
sition resolution, this type of detector is a good candidate for covering large areas. LAPPDs
are tolerant of magnetic fields and handle sub-ns timing with an excellent signal-to-noise ratio,
and without any cooling requirements. They were recently demonstrated to work for neu-
trino detection by the ANNIE experiment. Ideal coverage could be achieved with about 100
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DUNE Phase II
LAPPDs, which could be delivered within a few years at current production rates. Depending
on the choice of quencher/wavelength shifter, modifying the photocathode composition or a
wavelength shifter coating might be required.
Studies to optimize this system are required, and include determining optimal coverage, the
best photocathode design, and enclosures to allow the LAPPDs to operate at high pressure.
4.2.6 R&D and engineering road map
R&D will be necessary for this Phase II improved tracker concept, starting in 2024 and lasting
for several years. It will be important to fully define the detector requirements, then aim for a
technical design report in the late 2020s, and be ready to begin construction in the early 2030s.
The essential R&D and design work needed for ND-GAr includes, but is not limited to, the
following items:
ND-GAr magnet INFN Genova is pursuing R&D on using magnesium diboride (MgB2)
superconducting cables, which have a higher critical temperature and do not face some of the
challenges of co-extruding NbTi superconducting cables with high-purity aluminum.
ND-GAr TPC charge readout and electronics test stands Several R&D efforts are
already underway, as described in Section 4.2.1. Examples include the GOAT, TOAD, GORG,
and GAT0 test stands. Charge readout TPCs are a mature technology, with gas mixtures
identified that give sufficient gain. The current R&D priority is to test the full readout chain,
from amplification technology to readout electronics, in a high-pressure test stand, using a
non-flammable gas with a high argon fraction, to ensure adequate stability and gain. Electron
diffusion measurements will also be performed for the same gas mixtures.
Concerning the amplification stage, current testing has been done with wire chambers.
However, modern TPCs such as those for ALICE and sPHENIX use GEMs to achieve better
stability of operation and higher gains. For this reason, R&D for a GEM/THGEM-based
amplification stage has started in the context of the DUNE Phase II ND, as well. The stability
of proposed wavelength-shifting gases such as Ar/CF4(99/1) must be studied, as they are low-
quenched. Conventional GEM, THGEM, glass-GEMs, glass-Micromegas and wire chamber
amplification stages are all currently under evaluation in Spain, the UK, and the US.
Once detailed requirements on tracking performance are established, further R&D on read-
out electronics and on the segmentation of the charge readout pads/strips will be pursued
accordingly. The TPC charge readout R&D work is currently ongoing in the UK (GEM work
and readout electronics), Spain (glass-GEM, SiPMs + TPX3 cameras), and the US (readout
electronics and test stands) using sources and test beams.
Light detection in ND-GAr TPC The realization of light readout at the scale of the ND-
GAr TPC poses important engineering challenges in relation to photosensor technology, HV
integration, and good light collection. Dedicated physics studies are needed to establish the best
design path towards the optimization of the detection thresholds, time-tagging performance,
and photosensor coverage. Both light readout options discussed above have R&D needs, for
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DUNE Phase II
example cooling control for SiPMs and operation at high pressure for LAPPDs. Groups in
Spain are performing R&D on the optimization of the SiPM-based optical readout concept:
required coverage, use of reflectors and light collectors, SiPM channel ganging and cooling
schemes. R&D on LAPPDs is also underway in the US.
Also, the outstanding tracking performance of ND-GAr needs to be guaranteed while en-
suring that the photosensor plane not be blinded during the avalanche multiplication process
in the anode region. This will require an additional R&D step targeting the minimization of
photon-feedback, as it is customary for instance in ring-imaging Cherenkov detector applica-
tions [131].
ND-GAr calorimeter R&D was underway in Germany on coupling fibers to SiPMs to
maximize light collection and uniformly illuminate the SiPM face. Studies must also be done
to optimize the calorimeter design, including the number of strip and tile layers, and their
granularity. A cost-effective readout electronics system must also be developed.
ND-GAr calibration systems, field cage, and gas systems Engineering work is also
required to design the infrastructure and support services for the ND-GAr detector. The
ALICE detector featured a high-performance TPC of similar size [115], therefore that design
can potentially be used as a starting point. For example, a laser calibration system that can
uniformly illuminate the drift volume could provide the required accurate monitoring of drift
velocity variations and inhomogeneities within the volume. Such a system must be designed
in close connection with the HV field cage. The movable ND-GAr will require design of a
mechanically robust field cage with mechanical end-cap structures. A buffer region in between
the field cage and pressure vessel will be needed to degrade the high voltage, and this may
require the use of an additional insulating gas.
The detector performance depends crucially on the stability and quality of the gas in the
drift region, therefore it will be necessary to develop a system to control and monitor the gas
mixture in the drift volume. Control operations include pressurization, recirculation, purifica-
tion, and evacuation of the gas. The current design of the magnet system does not incorporate
a method for evacuation [132]. However, modifying it to function under both pressure and vac-
uum conditions is well understood. Generally, achieving vacuum is desirable to facilitate the
reduction and monitoring of O2and H2O impurities (as well as other unforeseen contaminants).
It is also worth considering purifying argon gas in the gas handling system – which might yield
similar results – although evacuation could potentially be faster.
4.3 Improvements to Phase I near detector components
As part of the Phase II program, possible enhancements and improvements to the exisiting
Phase I components of the ND are being considered. This section discusses such possible
improvements to the Phase I detector components ND-LAr and SAND.
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DUNE Phase II
4.3.1 Phase II ND-LAr detector
ND-LAr is the LAr component of the DUNE ND complex. With the intense neutrino flux and
high event rate at the ND, traditional, monolithic, projective wire readout LArTPCs would be
stretched beyond their performance limits. To overcome this hurdle, ND-LAr will be fabricated
out of a matrix of smaller, optically isolated TPCs, read out individually via a pixelated readout.
The subdivision of the volume into many smaller TPCs allows for shorter drift distances and
times. This and the optical isolation lead to fewer problems with overlapping interactions.
The ND-LAr design consists of 35 optically separated LArTPC modules, which allows for
independent identification of ν-Ar interactions in an intense beam environment using optical
timing. Each TPC consists of a HV cathode, a low-profile field cage that minimizes the amount
of inactive material between modules, a light collection system, and a pixel-based charge read-
out.
One key aspect of ND-LAr operation is the ability to cope with many neutrino interactions
in each spill. The LBNF neutrino beam consists of a 10 µs wide spill, which leads to O(50) ν
interactions per spill in Phase I and O(100) in Phase II. Given the relatively low expected cosmic
ray rate while the beam is on (estimated to be ∼0.3/spill at 60 m depth), this beam-related
pile-up is the primary challenge confronting the reconstruction of the ND-LAr events. The 3D
pixel charge signal will be read out continuously. The slow drifting electrons (with charge from
the cathode taking ∼300 µs to travel the 50 cm drift distance) will be read out with an arrival
time accuracy of 200 ns and a corresponding charge amplitude within a ∼2µs-wide bin. This
coupled with the beam spill width gives a position accuracy of 16 mm. While this is already
good spatial positioning, the ND-LAr light system will provide an even more accurate time
tag of the charge as well as the ability to tag subclusters and spatially disassociated charge
depositions resulting from neutral particles, such as neutrons, that come from the neutrino
interaction. Thus, the ND-LAr light system has a different role from that in the FD, as it must
time-tag charge signal subclusters to enable accurate association of all charge to the proper
neutrino event, and to reject pile-up of charge from other neutrino signals.
The current ND-LAr design being implemented for Phase I satisfies the general requirements
of DUNE for Phase II in terms of increased beam power and lifetime of detector components.
Nonetheless, additional potential modifications to ND-LAr that might enhance its capabilities
are under consideration. Given that the ND-LAr uptime during DUNE operations is an impor-
tant factor to take into consideration, those modifications can be divided into two categories:
ND-LAr upgrades that imply modifications to the inner detector hardware and thus require
emptying the LAr, and those that do not. In the former, more disruptive, category, current
ideas under exploration include: improvements to neutron detection methods by upgrading op-
tical detectors with 6Li-glass scintillator, replacement of charge tiles of a module with smaller
pixels and lower threshold, use of photosensitive dopants, and use of radiopure underground
argon. In the latter (less disruptive) category, possible upgrade options span the following:
doping of argon with xenon, upgrade of the off-detector electronics, addition of a rock muon
tracker in front of ND-LAr, and use of an additional calibration system based on 222Rn injec-
tion. A decision on these possible ND-LAr upgrade paths will come after the Phase I ND-LAr
detector is commissioned.
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DUNE Phase II
4.3.2 Phase II SAND detector
SAND is a multipurpose detector composed of a superconducting solenoid, a high-performance
ECAL, a light tracker, and an active LAr target called . The magnet and the ECAL were part
of the detector at INFN Frascati and will be refurbished for Phase I, without the need for
upgrades during Phase II. The tracker, based on straw tubes, will be a completely new detector
capable of reconstructing charged particle tracks in the magnetic field. Major upgrades for the
tracker are not foreseen for Phase II.
GRAIN is an innovative LAr detector that will employ a completely new readout technique,
using only scintillation light for track reconstruction. This task is accomplished by cameras with
light sensors made of a matrix of SiPMs and optical elements, such as special lenses or Coded
Aperture Masks. The GRAIN project is very challenging because, due to the low efficiency
of light sensors to VUV scintillation light, the number of photons detected and used by the
reconstruction algorithms is low.
For Phase II GRAIN, the goal is to enhance light collection by improving the SiPM PDE in
the VUV range. For this purpose, we are developing with “Fondazione Bruno Kessler” (FBK-
Trento) Backside Illuminated SiPMs (BSI SiPMs). In this architecture, the light entrance
window is on the back of the silicon, while all the metallic contacts are on the front side. This
will allow us to improve the fill factor and optimize the anti-reflective coating on the entrance
window. It is planned to substitute all the GRAIN matrices of traditional Front Side SiPMs
with the BSI ones for Phase II, if they will be available and mature in time.
4.4 Near-detector options for non-argon far detector modules
In the event that one of the Phase II FD modules consists of a neutrino target material that is
not argon-based, such as the Theia detector concept described in Section 3.5, the Phase II ND
complex will need to provide measurements of neutrino interactions on those same target nuclei.
Several options are under consideration for modifying the Phase I suite of ND sub-detectors
to make such measurements, including modifying the Phase I SAND to incorporate oxygen
and water targets, embedding liquid scintillator targets within the ECAL of the GArTPC, and
constructing a new, dedicated, water-based near detector. While they introduce identical or
similar nuclear targets, these particular options do not establish a functionally similar detector
at the near site that would also mitigate detector-related uncertainties at the far detector,
analogous to ND-LAr for the argon-based FD modules.
4.4.1 Oxygen and water targets in SAND
The SAND detector is equipped with a modular Straw Tube Tracker (STT) with target layers
that are designed to be individually replaceable with different materials. A total of 78 thin
planes, each about 1.6% of a radiation length X0, of various passive materials are alternated
and dispersed throughout active layers, which are made of four straw planes, to guarantee the
same acceptance to final state particles produced in (anti)neutrino interactions. The STT allows
minimizing the thickness of individual active layers and to approximate the ideal case of a pure
target detector – the targets constitute about 97% of the mass – while keeping the total thickness
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DUNE Phase II
of the stack comparable to one radiation length and an average density of about 0.17 g/cm3.
The lightness of the tracking straws and the chemical purity of the targets, together with the
physical spacing among the individual target planes, make the vertex resolution (≪1 mm) less
critical in associating the interactions to the correct target material. The average momentum
resolution expected for muons is δp/p ∼3.5% and the average angular resolution better than
2 mrad. The momentum scale can be calibrated to about 0.2% using reconstructed K0→π+π−
decays.
The STT is optimized for the “solid” hydrogen technique, in which ν(¯ν) interactions on free
protons are obtained by subtracting measurements on dedicated graphite (C) targets from those
on polypropylene (CH2) targets [133, 134, 135]. The default target configuration in Phase I
includes 70 CH2targets and eight C targets. The use of a distributed target mass within a
low-density tracker results in an approximately uniform acceptance over the full 4πangle, as
shown in Figure 31. The acceptance disparity between different targets can be kept within
10−3for all particles (Figure 31) due to their thinness and their alternation throughout the
detector volume. The subtraction procedure between different materials can then be considered
model-independent within these uncertainties. Furthermore, the detector acceptance effectively
cancels in comparisons between the selected interactions on different target nuclei.
Figure 31: Left: Muon acceptance for νµCC interactions in a forward horn current () beam in
SAND. Right: Discrepancy in acceptance between the CH2and C targets in SAND.
The ND can operate with both oxygen and water targets concurrently by replacing some of
the initial CH2targets with polyoxymethylene (CH2O, acetal) planes with equivalent thickness,
i.e., in terms of radiation length and nuclear interaction length λI. Interactions on oxygen are
obtained from a subtraction between CH2O and CH2targets, while interactions on water are
obtained from a subtraction between CH2O and C targets [136].
To this end, 4.5 mm thick acetal slabs can be used, corresponding to about 0.016 X0and
0.008 λI. The oxygen content by mass within acetal dominates at 53.3%. By replacing only
20 polypropylene targets (out of 70) with the equivalent CH2O targets, we obtain an oxygen
target mass of about 760 kg and a water target mass of about 850 kg. Assuming an exposure of
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DUNE Phase II
3×1021 POT, corresponding to about two years with the Phase I beam intensity and to about
one year with the Phase II beam, we expect to collect 3 ×106νµCC events with the FHC beam
and 1 ×106¯νµCC events with the beam on oxygen. The subtraction procedure introduces an
increase of about 40% in the statistical uncertainties with respect to the use of ideal targets. For
3×1021 POT, the resulting statistical bin-to-bin uncertainties in the ν-nucleus cross-sections as a
function of neutrino energy are comparable to the expected systematic uncertainties introduced
by the STT momentum scale uncertainty of 0.2% [136].
4.4.2 Liquid scintillator targets in the ND-GAr calorimeter
The GArTPC described in Section 4.2 is capable of supporting active Theia-type targets
within the downstream portion of the upstream ECAL, as shown in Figure 32. The Theia
layers consist of X and Y bars (similar to the NOvA configuration discussed in the next section),
and interactions in these layers produce particles that enter the high-pressure gas TPC where
they are precisely tracked. Neutral particles are measured by the surrounding ECAL, and the
active Theia layers provide an additional measure of low-energy particles near the interaction
vertex (“vertex activity”). For neutrino interactions within the GArTPC, the Theia layers
will form an initial low-density section of the ECAL that can provide fast timing for particles
exiting the TPC.
WbLS Layers
HPgTPC
Figure 32: An upstream segment of the GArTPC ECAL, with the beam is pointing downward.
The Theia layers constitute the most downstream portion of the ECAL, and particles produced
in these layers via neutrino interactions are tracked in the downstream HPgTPC.
There is sufficient space within the ECAL to include Theia layers with a thickness of
at least 10 cm, which would provide more than a ton of target mass. This would produce
O(1M) charged current νµinteractions in a 14 week run on-axis, and O(10k) charged current
νµinteractions in a two week run at the furthest off-axis position, both of which would be
expected to occur within a nominal DUNE yearly run.
82
DUNE Phase II
4.4.3 Water-based near detector
It is possible to install a detector specifically designed to make measurements for a water-
based FD module in the DUNE ND hall. If a new GArTPC is built, it will serve as the
downstream spectrometer for ND-LAr, allowing TMS to be used as a downstream spectrometer
for a dedicated Water-based Near Detector (WbND). Any configuration of the ND suite will
be subject to the space limitations imposed by the near site infrastructure, as completed before
the beginning of beam operations. Two possible options for a WbND are a NOvA-style ND,
or a LiquidO ND, both discussed below.
NOvA-style near detector The NOvA ND consists of individual cells, as shown in Fig-
ure 33, arranged in horizontal and vertical layers. The cells consist of PVC extrusions filled
with liquid scintillator, and a wavelength-shifting fiber collects the light and guides it to the
avalanche photodiode (APD) for readout [137].
2
twice as long as the extrusion and looped at the “far end” of the cell (Fig. 1). Generally, the
scintillation light is captured by the WLS fiber after several reflections off the cell walls.
Simulations show that scintillation light reflects about 8 times on average before entering the
fiber. This is the key reason to use highly-reflective PVC surfaces. The Far Detector has a total
of 344,064 PVC cells, individually equipped with optical fibers to transport scintillation light to a
32-channel avalanche photodiode (APD) that sits just over an optical connector attached to each
32 cell module.
Figure 1: Ionizing particles passing through the scintillating liquid contained within an extrusion cell produce light, which
reflects off the PVC walls multiple times until being captured by a wavelength shifting fiber optic loop. Light within the fiber
optic travels the length of the extrusion and is detected by an avalanche photodiode (APD). Dimensions refer to liquid volume.
Detector Structure
The extrusions form the mechanical backbone of the NOvA detectors, providing the strength
necessary to maintain a very large structure filled with liquid scintillator. In order to capture the
scintillation light for readout, the extrusion cell walls must have a high reflectance; significantly
higher than found in commercial PVC products. We have developed a PVC-based formulation
to achieve high reflectance while maintaining the necessary mechanical strength. This paper
describes the techniques developed to produce more than 11 million pounds of NOvA extrusions
that meet strict reflectance, strength and dimensional requirements. An extrusion profile
schematic is shown in Fig. 2, and a photograph in Fig. 3a.
Figure 2: NOvA extrusion cross section with cells numbered 1 through 16 (dimensions are in millimeters).
The Near and Far Detectors consist of free-standing blocks of PVC extrusions, filled with liquid
scintillator. The NOvA Far Detector is at this time potentially the largest self-supporting plastic
structure ever built. Although the primary purpose of this paper is to describe PVC extrusion
development, a brief description of the detector assembly process is helpful to provide context
for the physical and optical requirements of PVC extrusions as detector elements.
Typical charged particle path
To one
APD pixel
L = 15.5 m
3.5 cm
5.6 cm
Scintillation Light
Wavelength-shifting
Fiber Loop
Figure 33: The fundamental unit cell of the detector of the NOvA near detector; the cells are
arranged in horizontal and vertical layers.
The NOvA near detector design could be used to construct a WbND by replacing the NOvA
scintillator with Theia WbLS. Its cell size and scintillator fraction would have to be tuned to
ensure a high muon reconstruction efficiency. This type of detector would also be capable of a
calorimetric measurement of the hadronic energy in the neutrino final state, including better
sensitivity to neutrons than a LAr detector, due to the presence of free hydrogen in the target
material. This detector technology is well established and would require minimal additional
R&D.
LiquidO near detector A promising new detector concept for the DUNE ND is based on
using opaque scintillators with millimeter-scale scattering length to produce high-resolution
images of neutrino interactions [138, 139]. The scintillation photons are stochastically confined
close to the point of production via scattering, and a lattice of wavelength-shifting fibers at
≃1 cm pitch is used to extract the light. This technology, called LiquidO, removes the need for
manual segmentation: the lattice of fibers is constructed first, and then the opaque scintillator
poured in around the fibers. Substantially better spatial resolution per readout channel is
achieved by using the profile of the light detected across multiple fibers. Figure 34 shows a CC
83
DUNE Phase II
muon neutrino event as imaged with a LiquidO technology ND. Furthermore, and importantly
for a potential Theia DUNE Phase II FD module, the scintillator isotopic composition can
be varied by exchanging the scintillator material, e.g., oil-based scintillators can be swapped
with water-based ones. A design analogous to the T2K Super-FGD detector is envisaged
for DUNE with the fibers running in all three perpendicular directions, allowing fine-grained
precision tracking and excellent calorimetry. The hydrogen-rich nature of organic or water-
based scintillators, together with their fast timing, is advantageous for neutron time-of-flight
measurements and for particle detection in high-rate environments.
Figure 34: Illustration of a simulated 2 GeV electron neutrino interaction in a LiquidO-style
ND with a 1 cm fiber pitch. The image shows sub-cm spatial resolution and excellent particle
ID can be achieved.
Acknowledgements
This document was prepared by the DUNE collaboration using the resources of the Fermi
National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science,
HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under
Contract No. DE-AC02-07CH11359. This work was supported by CNPq, FAPERJ, FAPEG
and FAPESP, Brazil; CFI, IPP and NSERC, Canada; CERN; Mˇ
SMT, Czech Republic; ERDF,
H2020-EU and MSCA, European Union; CNRS/IN2P3 and CEA, France; INFN, Italy; FCT,
Portugal; NRF, South Korea; CAM, Fundaci´on “La Caixa”, Junta de Andaluc´ıa-FEDER,
MICINN, and Xunta de Galicia, Spain; SERI and SNSF, Switzerland; T ¨
UB˙
ITAK, Turkey; The
Royal Society and UKRI/STFC, United Kingdom; DOE and NSF, United States of America.
Fermilab Report Number: FERMILAB-TM-2833-LBNF
84
DUNE Phase II
Glossary
Eos The XRootD-based distributed file system developed by CERN. 56, 61
Theia-25 A 25 kt version of the Theia detector concept that could serve as DUNE’s fourth
far detector module.. 54, 55
Theia Proposed hybrid detector with both Cherenkov and scintillation detection capabilities.
16, 19, 24–26, 53–58, 60, 61, 63, 64, 66, 79, 81, 82
neutrinoless double-βdecay (0νββ)A hypothetical nuclear transition in which a nucleus
with with Z protons decays into a nucleus with Z+2 protons and the same mass number,
together with the emission of two electrons and no neutrinos.. 25, 51, 52, 55, 56, 59
ACE-MIRT The Accelerator Complex Evolution with Main Injector Ramp and Target up-
grade is a proposed set of major upgrades to the Fermilab accelerator complex aimed at
an early implementation of an enhanced 2.1 MW beam for DUNE.. 15, 17, 28
Artificial Intelligence (AI) A field of study in computer science which develops and studies
intelligent machines.. 63
Axion-like particle (ALP) A hypothetical pseudoscalar particle that appears in the spon-
taneous breaking of a global symmetry.. 26
anode plane a planar array of charge readout devices covering an entire face of a detector
module. 32
APEX Aluminum Profiles with Embedded X-arapuca. 34–39, 61, 62, 64
ARIADNE Charge readout technology for LArTPC dual-phase detectors based on gaseous
electron multipliers and fast optical cameras.. 39, 45–47, 60–64
Amorphous selenium (aSe) A type of photoconductive material.. 50, 61
ASIC application-specific integrated circuit. 40–42, 49, 61, 62, 70, 71
BDE bottom detector electronics. 31, 40
boosted decision tree (BDT) A method of multivariate analysis. 19
Brookhaven National Laboratory (BNL) US national laboratory in Upton, NY. 56
BSM beyond the Standard Model. 12, 14, 16, 18, 20, 26–29, 51, 53, 68
charged current (CC) Refers to an interaction between elementary particles where a charged
weak force carrier (W+or W−) is exchanged. 20, 24, 27, 28, 57, 67, 80, 82
85
DUNE Phase II
core-collapse supernova (CCSN) The collapse of stars more than 8×as massive as the sun
which produces an intense burst of neutrinos at the end of its fusion cycle in a matter
of seconds which ejects the outermost stellar gas leaving behind a neutron star remnant..
21, 22
cold electronics (CE) Analog and digital readout electronics that operate at cryogenic tem-
peratures. 31
Coherent Elastic Neutrino-Nucleus Scattering (CEνNS) A type of neutrino interac-
tion with matter.. 24
European Laboratory for Particle Physics (CERN) The leading particle physics labo-
ratory in Europe and home to the ProtoDUNEs and other prototypes and demonstrators,
including the s. 13–15, 39, 42, 61
CMOS Complementary metal-oxide-semiconductor. 43
Computer Numerical Control (CNC) A precise drilling method that utilizes a rotating
cutting tool to produce round holes in a stationary work piece. 69
carbon nitrogen oxygen (CNO) The CNO cycle (for carbon-nitrogen-oxygen) is one of the
two known sets of fusion reactions by which stars convert hydrogen to helium, the other
being the proton-proton chain reaction (pp-chain reaction). In the CNO cycle, four
protons fuse, using carbon, nitrogen, and oxygen isotopes as catalysts, to produce one
alpha particle, two positrons and two electron neutrinos. 25, 54, 56, 59
ColdADC A newly developed 16-channels ASIC providing analog to digital conversion. 40
COLDATA A 64-channel control and communications ASIC. 40
commercial off-the-shelf (COTS) Items, typically hardware such as computers, that may
be purchased whole, without any custom design or fabrication and thus at normal con-
sumer prices and availability. 45
charge conjugation and parity (CP) Product of charge conjugation and parity transfor-
mations. 54
Coordinating Panel for Advanced Detectors (CPAD) US panel that seeks to promote,
coordinate and assist in the research and development of instrumentation and detectors
for high-energy physics experiments.. 13, 16
charge, parity, and time reversal symmetry (CPT) product of charge, parity and time-
reversal transformations. 18
Charge Conjugation-Parity Symmetry Violation (CPV) Lack of symmetry in a system
before and after charge conjugation and parity transformations are applied. For CP
symmetry to hold, a particle turns into its corresponding antiparticle under a charge
86
DUNE Phase II
transformation, and a parity transformation inverts its space coordinates, i.e. produces
the mirror image. 12–14, 17, 18, 28, 53
charge readout (CRO) The system for detecting ionization charge distributions in a detector
module. 31
charge-readout plane (CRP) An anode technology using a stack of perforated PCBs with
etched electrode strips to provide CRO in 3D; it has two induction layers and one collection
layer; it is used in the SP vertical drift FD and DP designs. 29, 31, 32, 34, 35, 39, 40, 59,
61, 62, 64
charge-readout unit (CRU) In the SP vertical drift design an assembly of the s plus adapter
boards; two to a CRP. 31
data acquisition (DAQ) The data acquisition system accepts data from the detector front-
end (FE) electronics, buffers the data, performs a , builds events from the selected data
and delivers the result to the offline . 37, 63, 69, 70
dichroic filter (DF) Optical filter that reflects some wavelengths of light and transmits oth-
ers, with almost no absorption for all wavelengths of interest. 37, 38
dual-phase (DP) Distinguishes a LArTPC technology by the fact that it operates using argon
in both gas and liquid phases; sometimes called double-phase. 56, 64
DRD ECFA Detector R&D. 16
diffuse supernova neutrino background (DSNB) The term describing the pervasive, con-
stant flux of neutrinos due to all past supernova neutrino bursts. 23
Deep Underground Neutrino Experiment (DUNE) A leading-edge, international exper-
iment for neutrino science and proton decay studies; refers to the entire international
experiment and collaboration. 12, 14
DUNE Precision Reaction-Independent Spectrum Measurement (DUNE-PRISM)
a mobile near detector that can perform measurements over a range of angles off-axis from
the neutrino beam direction in order to sample many different neutrino energy distribu-
tions. 14, 15, 64, 68, 73
electromagnetic calorimeter (ECAL) A detector component that measures energy depo-
sition of traversing particles (in the DUNE near detector design). 72, 74, 78, 79, 81
European Committee for Future Accelerators (ECFA) Committee charged with the long-
range planning of European high-energy facilities: accelerators, large-scale facilities and
equipment.. 13, 16
87
DUNE Phase II
far detector (FD) The 70 kt total (40 kt fiducial) mass LArTPC DUNE detector, composed
of four 17.5 kt total (10 kt fiducial) mass modules, to be installed at the far site at SURF
in Lead, SD, USA. 12, 13, 15–22, 24–26, 28, 29, 42, 46, 50, 51, 56, 62–64, 66, 69, 73, 78,
79, 81, 82
far detector module 1 (FD1) The first DUNE far detector module to be built at SURF.
15, 19, 29, 31, 37, 43, 48, 49, 62
far detector module 2 (FD2) The second DUNE far detector module to be built at SURF.
13, 15, 16, 19, 29–32, 34, 35, 37, 39, 42, 43, 49, 52, 56, 60, 62–64
far detector module 3 (FD3) The third DUNE far detector module to be built at SURF.
15–17, 19, 20, 39, 60, 62, 63, 70
far detector module 4 (FD4) The fourth DUNE far detector module to be built at SURF.
15–17, 19, 20, 60, 62, 63, 70
FDR Depending on context, either “final design report,” a formal project document that
describes the experiment at a final level, or “final design review,” a formal review of the
final design of the experiment or of a component. 64
Fermi National Accelerator Laboratory (Fermilab) U.S. national laboratory in Batavia,
IL. It is the laboratory that hosts LBNF and DUNE, and serves as the experiment’s near
site. 12, 14, 56, 61, 69
FHC forward horn current (νµmode). 80
field cage The component of a LArTPC that contains and shapes the applied Efield. 13,
29–32, 34, 35, 37–39, 54, 61, 62, 77
field programmable gate array (FPGA) An integrated circuit technology that allows the
hardware to be reconfigured to execute different algorithms after its manufacture and
deployment. 41, 45, 70
FRP fiber-reinforced plastic. 32
FTBF Fermilab Test Beam Facility. 69
fiducial volume (FV) The detector volume within the TPC that is selected for physics anal-
ysis through cuts on reconstructed event position. 74
gaseous argon time-projection chamber (GArTPC) A TPC filled with gaseous argon.
13, 66, 67, 70, 74, 79, 81
Gaseous Argon T0 (GAT0) An Optical TPC demonstrator in Spain. A test stand for ND-
GAr R&D. 70, 76
88
DUNE Phase II
Geant4 A software toolkit for the simulation of the passage of particles through matter using
Monte Carlo (MC) methods. 38
GEM Gaseous electron multiplier. 69, 70, 76
Gas-argon Operation of ALICE TPC (GOAT) A test stand for ND-GAr R&D.. 69, 76
GEM Over-pressurized with Reference Gases (GORG) A test stand for ND-GAr R&D.
70, 76
GRAIN In the SAND detector, a small cryostat containing LAr installed upstream of the
straw-tube tracker inside the ECAL. 78, 79
HNL heavy neutral lepton. 26–28
horizontal drift single-phase, horizontal drift LArTPC technology. 29, 31
high-pressure gaseous argon TPC (HPgTPC) A TPC filled with gaseous argon; a pos-
sible component of the DUNE ND. 15, 16, 27, 68, 69, 71–74, 81
high voltage (HV) Generally describes a voltage applied to drive the motion of free electrons
through some media, e.g., LAr. 32, 35, 63, 64, 76, 77
HVFT HV feedthrough. 32
HVPS HV power supply. 32
high voltage system (HVS) The detector subsystem that provides the TPC drift field. 32,
34
ICARUS A neutrino experiment that was located at the Laboratori Nazionali del Gran Sasso
(LNGS) in Italy, then refurbished at CERN for re-use in the same neutrino beam from
Fermilab used by the , MicroBooNE and SBND experiments at Fermilab. 15, 29, 52
KLOE KLOE is a e+e−collider detector spectrometer operated at DAFNE, the ϕ-meson
factory at Frascati, Rome. In DUNE it will consist of a 26 cm Pb+scintillating fiber
ECAL surrounding a cylindrical open detector region that is 4.00 m in diameter and
4.30 m long. The ECAL and detector region are embedded in a 0.6 T magnetic field
created by a 4.86 m diameter superconducting coil and a 475 tonne iron yoke. 78
Large Area Picosecond Photo-Detector (LAPPD) A kind of imaging photodetector de-
signed to provide exquisite time resolution.. 56, 75, 76
liquid argon (LAr) Argon in its liquid phase; it is a cryogenic liquid with a boiling point
of 87 K and density of 1.4 g/ml. 12–17, 19, 20, 29, 35, 37–40, 45–48, 50–53, 55, 57, 60,
62–65, 74, 77, 78, 82
89
DUNE Phase II
LArASIC A 16-channel FE ASIC that provides signal amplification and pulse shaping. 40
LArIAT The repurposed ArgoNeuT LArTPC, modified for use in a charged particle beam,
dedicated to the calibration and precise characterization of the output response of these
detectors. 53
LArPix ASIC pixelated charge readout for a TPC. 40–43, 49, 60–62, 64
liquid-argon time-projection chamber (LArTPC) A TPC filled with liquid argon; the
basis for the DUNE FD modules. 13, 15, 19–21, 23–25, 35, 40–43, 45, 48, 49, 51–53,
62–64, 66, 67, 77
long-baseline (LBL) Refers to the distance between the neutrino source and the FD. It can
also refer to the distance between the near and far detectors. The “long” designation is
an approximate and relative distinction. For DUNE, this distance (between Fermilab and
SURF) is approximately 1300 km. 18
Long-Baseline Neutrino Facility (LBNF) Long-Baseline Neutrino Facility; refers to the
facilities that support the experiment including in-kind contributions under the line-item
project. The portion of LBNF/DUNE-US responsible for developing the neutrino beam,
the far site cryostats, and far and near site cryogenics systems, and the conventional
facilities, including the excavations. 12, 14, 15, 26, 28, 78
LBNF/DUNE Construction Project The international project to design and build the fa-
cilities and detectors for the LBNF and DUNE enterprise (LBNF/DUNE); it includes the
LBNF/DUNE-US and projects at multiple international partners to manage the contri-
butions from non-US institutions and funding agencies to design, build, and install the
detector components. 14, 28
LBNF/DUNE-US Long-Baseline Neutrino Facility/Deep Underground Neutrino Experiment
- United States; project to design and build the conventional and beamline facilities and
the contributions to the detectors. It is organized as a DOE/Fermilab project and in-
corporates contributions to the facilities from international partners. It also acts as host
for the installation and integration of the DUNE detectors. 14
Lawrence Berkeley National Laboratory (LBNL) US national laboratory in Berkeley,
CA. 56
light yield detected photons per unit deposited energy. 38, 39
LightPix Low-power, cryogenic-compatible and scalable SiPM readout electronics based on
the LArPix ASIC. 47, 49, 61–63
MCND More Capable Near Detector. 15, 20
MicroBooNE A LArTPC neutrino oscillation experiment at Fermilab. 15, 29
90
DUNE Phase II
Metal–oxide–semiconductor field-effect transistor (MOSFET) A type of field-effect tran-
sistor. 42
Mikheyev-Smirnov-Wolfenstein effect (MSW) Explains the oscillatory behavior of neu-
trinos produced inside the sun as they traverse the solar matter. 25, 54
neutral current (NC) Refers to an interaction between elementary particles where a neu-
trally charged weak force carrier (Z0) is exchanged. 24
near detector (ND) Refers to the collection of DUNE detector components installed close
to the neutrino source at Fermilab; also a subproject of LBNF/DUNE-US that includes
installation, infrastructure, and the cryogenics systems for this detector. 12, 13, 15, 17–20,
26, 27, 29, 41–43, 64–66, 70, 72–74, 76, 77, 79, 81–83
ND-GAr component of the near detector with a core gaseous argon TPC surrounded by an
ECAL and a magnet. 15, 26–28, 67–70, 72–77
ND-LAr LArTPC component of the near detector based on technology. 13–16, 20, 28, 40,
64–68, 72–74, 77–79, 81
NP02 The CERN North Area in Experiment Hall North One (EHN1) intersected by the
hadron beamline, the location of the 800 t cryostat used for ProtoDUNE-DP and for SP
vertical drift tests and prototypes; also used to refer to the 800 t cryostat in this area. 47
PCB printed circuit board. 13, 30–32, 38, 39, 41, 42, 48, 50, 61, 62
photon detector (PD) The detector elements involved in measurement of the number and
arrival times of optical photons produced in a detector module. 34–39, 61, 62
PDE photon detection efficiency. 38, 48, 79
photon detection system (PDS) The detector subsystem sensitive to light produced in the
LAr. 24, 32, 34, 37–39, 49, 62, 68
photoelectron (PE) An electron ejected from the surface of a material by the photoelectric
effect. 38
PEEK Polyether ether ketone, a colorless organic thermoplastic polymer. 39
particle ID (PID) Particle identification. 13, 53, 54, 65, 66
Proton Improvement Plan II (PIP-II) A Fermilab project for improving the protons on
target delivered delivered by the LBNF neutrino production beam. This is version two of
this plan and it is planned to be followed by a PIP-III. 15
91
DUNE Phase II
power-over-fiber (PoF) a technology in which a fiber optic cable carries optical power, which
is used as an energy source rather than, or as well as, carrying data; this allows a device
to be remotely powered, while providing electrical isolation between the device and the
power supply. 34, 35, 37, 39, 62
protons on target (POT) Typically used as a unit of normalization for the number of pro-
tons striking the neutrino production target. 17, 27, 80
parts per million (ppm) A concentration equal to one part in 106. 51–53, 62
ProtoDUNE Either of the two initial DUNE prototype detectors constructed at CERN. One
prototype implemented SP technology and the other DP. 39
ProtoDUNE-DP The DP ProtoDUNE detector constructed at CERN in NP02. 29
ProtoDUNE-SP The horizontal drift detector module (FD1-HD) ProtoDUNE detector con-
structed at CERN in . 15, 29, 51
ProtoDUNE-VD ProtoDUNE with vertical drift technology. This refers to the CRP-based
prototype to run in NP02 (in the phase). 15, 29, 39, 61, 63
Q-Pix A pixel-based, 3D, readout technology based on a continuously integrating low-power
charge-sensitive amplifier viewed by a Schmitt trigger. 40, 42–45, 49, 61, 62, 64
Q-Pix Light Imaging in Liquid Argon (Q-Pix-LILAr) A Q-Pix pixel coated with a type
of photoconductive material, to perform integrated charge/light readout on the anode..
47, 49, 50, 61–63
quality assurance (QA) The process of ensuring that the quality of each element meets
requirements during design and development, and to detect and correct poor results prior
to production. 31
quality control (QC) The process (e.g., inspection, testing, measurements) of ensuring that
each manufactured element meets its quality requirements prior to assembly or installa-
tion. 31
RDC Detector R&D collaborations. 16
RHC reverse horn current ( νµ→νµmode). 80
System for on-Axis Neutrino Detection (SAND) The beam monitor component of the
near detector that remains on-axis at all times and serves as a dedicated neutrino spectrum
monitor. 14–16, 64–66, 69, 73, 74, 77–80
SBND The Short-Baseline Near Detector experiment at Fermilab. 15
92
DUNE Phase II
signal feedthrough chimney (SFT chimney) A volume above the cryostat penetration
used for a signal feedthrough. 31
silicon photomultiplier (SiPM) A solid-state avalanche photodiode sensitive to single pho-
toelectron signals. 23, 25, 34–36, 38, 48, 49, 58, 59, 61, 62, 71, 75–77, 79
Sanford Underground Low background Module (SLoMo) A dedicated low background
far detector module that would enhance the physics program of DUNE.. 58, 59
Standard Model (SM) Refers to a theory describing the interaction of elementary particles.
27
supernova neutrino burst (SNB) A prompt increase in the flux of low-energy neutrinos
emitted in the first few seconds of a CCSN. It can also refer to a trigger command type
that may be due to this phenomenon, or detector conditions that mimic its interaction
signature. 12, 14, 20–24, 29, 45, 51, 54, 56, 57
SuperNova Early Warning System (SNEWS) A global supernova neutrino burst trigger
formed by a coincidence of SNB triggers collected from participating experiments. 22
signal-over-fiber (SoF) a technology in which a fiber optic cable carries detector output that
has been converted from an electrical to an optical pulse. 34, 35, 37, 39, 62
Solar neutrinos in Liquid Argon (SoLAr) A new concept for a liquid-argon neutrino de-
tector technology to extend the sensitivities of these devices to the MeV energy range.
47–49, 61–64
single-phase (SP) Distinguishes a LArTPC technology by the fact that it operates using
argon in its liquid phase only; a legacy DUNE term now replaced by horizontal drift and
vertical drift. 29
Solenoid with Partial return Yoke (SPY) Magnet concept currently envisaged to mag-
netize ND-GAr.. 72–74
Straw Tube Tracker (STT) Target/tracker system that is part of the SAND near detector..
79, 80
Sanford Underground Research Facility (SURF) SURF is an underground laboratory
in Lead, South Dakota, where the DUNE FD will be installed and operated. It is the
deepest underground laboratory in the United States.. 12, 39, 57
T2K T2K (Tokai to Kamioka) is a long-baseline neutrino experiment in Japan studying neu-
trino oscillations. 71, 82
TDE top detector electronics. 31
Thick GEM (THGEM) High-gain gaseous electron multiplier. 45, 46, 61, 69, 70, 76
93
DUNE Phase II
Tetra-methyl-germanium (TMG) A photosensitive hydrocarbon capable of converting VUV
scintillation light into ionization charge in a LAr detector.. 52
Muon Spectrometer (TMS) A muon spectrometer for the Near Detector that will be in-
stalled for the initial running period of DUNE, before the multi-purpose detector (MPD)
detector component is ready. 13, 15, 16, 20, 28, 64–66, 81
Test stand of an Overpressure Argon Detector (TOAD) A test of a high-pressure gaseous
argon TPC in the Fermilab Test Beam Facility FTBF. 69, 76
tetra-phenyl butadiene (TPB) A WLS material. 45
time projection chamber (TPC) Depending on context: (1) A type of particle detector
that uses an Efield together with a sensitive volume of gas or liquid, e.g., LAr, to perform
a 3D reconstruction of a particle trajectory or interaction. The activity is recorded by
digitizing the waveforms of current induced on the anode as the distribution of ionization
charge passes by or is collected on the electrode. (2) TPC is also used in LBNF/DUNE-US
for “total project cost”. 15, 49, 52, 63
Technology Readiness Level (TRL) A method for estimating the maturity of technolo-
gies.. 60
vertical drift single-phase, vertical drift LArTPC technology. 13, 16, 29, 30, 37, 39, 42, 59,
62, 64
VUV vacuum ultra-violet. 45–49, 52, 61, 79
Water-based Liquid Scintillator (WbLS) A scintillating material consisting of water loaded
with liquid scintillator.. 56, 82
Water-based Near Detector (WbND) A possible DUNE Phase II near detector sub-system
employing water as neutrino target.. 81, 82
weakly-interacting massive particle (WIMP) A hypothesized particle that may be a com-
ponent of dark matter. 21, 25, 59
wavelength-shifting (WLS) A material or process by which incident photons are absorbed
by a material and photons are emitted at a different, typically longer, wavelength. 34,
37, 38, 71
X-ARAPUCA Extended design with WLS coating on only the external face of the dichroic
filter window(s) but with a WLS doped plate inside the cell. 32–35, 37, 38, 49, 62, 63
94
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