Jet modification via $\pi^0$-hadron correlations in Au+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

Abstract

High-momentum two-particle correlations are a useful tool for studying jet-quenching effects in the quark-gluon plasma. Angular correlations between neutral-pion triggers and charged hadrons with transverse momenta in the range 4--12~GeV/c and 0.5--7~GeV/c, respectively, have been measured by the PHENIX experiment in 2014 for Au+Au collisions at sNN=200\sqrt{s_{_{NN}}}=200~GeV. Suppression is observed in the yield of high-momentum jet fragments opposite the trigger particle, which indicates jet suppression stemming from in-medium partonic energy loss, while enhancement is observed for low-momentum particles. The ratio and differences between the yield in Au+Au collisions and p+p collisions, IAAI_{AA} and ΔAA\Delta_{AA}, as a function of the trigger-hadron azimuthal separation, Δϕ\Delta\phi, are measured for the first time at the Relativistic Heavy Ion Collider. These results better quantify how the yield of low-pTp_T associated hadrons is enhanced at wide angle, which is crucial for studying energy loss as well as medium-response effects.

Full text

Jet modification via π0-hadron correlations in Au+Au collisions at √sN N = 200 GeV
N.J. Abdulameer,17 U. Acharya,22 A. Adare,13 S. Afanasiev,32 C. Aidala,46, 48 N.N. Ajitanand,70, ∗Y. Akiba,64, 65 , †
H. Al-Bataineh,57 J. Alexander,70 M. Alfred,24 K. Aoki,34, 37, 64 N. Apadula,29, 71 L. Aphecetche,72 J. Asai,64
H. Asano,37, 64 E.T. Atomssa,38 R. Averbeck,71 T.C. Awes,60 B. Azmoun,8V. Babintsev,25 M. Bai,7G. Baksay,20
L. Baksay,20 A. Baldisseri,16 N.S. Bandara,46 B. Bannier,71 K.N. Barish,9P.D. Barnes,41, ∗B. Bassalleck,56
A.T. Basye,1S. Bathe,6, 9, 65 S. Batsouli,60 V. Baublis,63 C. Baumann,8, 50 A. Bazilevsky,8M. Beaumier,9
S. Beckman,13 S. Belikov,8, ∗R. Belmont,13, 58 R. Bennett,71 A. Berdnikov,67 Y. Berdnikov,67 L. Bichon,77
A.A. Bickley,13 B. Blankenship,77 D.S. Blau,36, 55 J.G. Boissevain,41 J.S. Bok,57 H. Borel,16 V. Borisov,67
K. Boyle,65, 71 M.L. Brooks,41 J. Bryslawskyj,6, 9 H. Buesching,8V. Bumazhnov,25 G. Bunce,8, 65 S. Butsyk,41
C.M. Camacho,41 S. Campbell,14, 29, 71 B.S. Chang,81 W.C. Chang,2J.L. Charvet,16 C.-H. Chen,65, 71 D. Chen,71
S. Chernichenko,25 M. Chiu,8, 26 C.Y. Chi,14 I.J. Choi,26, 81 J.B. Choi,31 , ∗R.K. Choudhury,5T. Chujo,76
P. Chung,70 A. Churyn,25 V. Cianciolo,60 Z. Citron,71,79 B.A. Cole,14 M. Connors,22, 65 P. Constantin,41 R. Corliss,71
M. Csan´ad,18 T. Cs¨org˝o,80 D. d’Enterria,38 T. Dahms,71 S. Dairaku,37, 64 T.W. Danley,59 K. Das,21 A. Datta,56
M.S. Daugherity,1G. David,8, 71 K. DeBlasio,56 K. Dehmelt,20, 71 A. Denisov,25 A. Deshpande,65, 71 E.J. Desmond,8
O. Dietzsch,68 A. Dion,71 P.B. Diss,45 M. Donadelli,68 V. Doomra,71 J.H. Do,81 O. Drapier,38 A. Drees,71
K.A. Drees,7A.K. Dubey,79 J.M. Durham,41, 71 A. Durum,25 D. Dutta,5V. Dzhordzhadze,9Y.V. Efremenko,60
F. Ellinghaus,13 H. En’yo,64, 65 T. Engelmore,14 A. Enokizono,40, 64, 66 R. Esha,71 K.O. Eyser,8, 9 B. Fadem,51
N. Feege,71 D.E. Fields,56, 65 M. Finger, Jr.,10 M. Finger,10 D. Firak,17, 71 D. Fitzgerald,48 F. Fleuret,38 S.L. Fokin,36
Z. Fraenkel,79, ∗J.E. Frantz,59, 71 A. Franz,8A.D. Frawley,21 K. Fujiwara,64 Y. Fukao,37, 64 T. Fusayasu,53
P. Gallus,15 C. Gal,71 P. Garg,4, 71 I. Garishvili,40, 73 H. Ge,71 F. Giordano,26 A. Glenn,13, 40 H. Gong,71 M. Gonin,38
J. Gosset,16 Y. Goto,64, 65 R. Granier de Cassagnac,38 N. Grau,3, 14 S.V. Greene,77 M. Grosse Perdekamp,26, 65
T. Gunji,12 T. Guo,71 H.-˚
A. Gustafsson,43, ∗T. Hachiya,23, 64, 65 A. Hadj Henni,72 J.S. Haggerty,8K.I. Hahn,19
H. Hamagaki,12 H.F. Hamilton,1J. Hanks,14, 71 R. Han,62 S.Y. Han,19, 35 E.P. Hartouni,40 K. Haruna,23
S. Hasegawa,30 T.O.S. Haseler,22 K. Hashimoto,64, 66 E. Haslum,43 R. Hayano,12 M. Heffner,40 T.K. Hemmick,71
T. Hester,9X. He,22 J.C. Hill,29 A. Hodges,22, 26 M. Hohlmann,20 R.S. Hollis,9W. Holzmann,70 K. Homma,23
B. Hong,35 T. Horaguchi,12, 64, 75 D. Hornback,73 T. Hoshino,23 N. Hotvedt,29 J. Huang,8T. Ichihara,64, 65
R. Ichimiya,64 H. Iinuma,37, 64 Y. Ikeda,76 K. Imai,30, 37, 64 J. Imrek,17 M. Inaba,76 A. Iordanova,9D. Isenhower,1
M. Ishihara,64 T. Isobe,12, 64 M. Issah,70 A. Isupov,32 D. Ivanishchev,63 B.V. Jacak,71 M. Jezghani,22 X. Jiang,41
J. Jin,14 Z. Ji,71 B.M. Johnson,8, 22 K.S. Joo,52 D. Jouan,61 D.S. Jumper,1, 26 F. Kajihara,12 S. Kametani,64
N. Kamihara,65 J. Kamin,71 S. Kanda,12 J.H. Kang,81 J. Kapustinsky,41 D. Kawall,46,65 A.V. Kazantsev,36
T. Kempel,29 J.A. Key,56 V. Khachatryan,71 A. Khanzadeev,63 K.M. Kijima,23 J. Kikuchi,78 B. Kimelman,51
B.I. Kim,35 C. Kim,35 D.H. Kim,52 D.J. Kim,33, 81 E. Kim,69 E.-J. Kim,31 G.W. Kim,19 M. Kim,69 S.H. Kim,81
E. Kinney,13 K. Kiriluk,13 ´
A. Kiss,18 E. Kistenev,8R. Kitamura,12 J. Klatsky,21 J. Klay,40 C. Klein-Boesing,50
D. Kleinjan,9P. Kline,71 T. Koblesky,13 L. Kochenda,63 B. Komkov,63 M. Konno,76 J. Koster,26 D. Kotov,63, 67
L. Kovacs,18 A. Kozlov,79 A. Kravitz,14 A. Kr´al,15 G.J. Kunde,41 B. Kurgyis,18,71 K. Kurita,64, 66 M. Kurosawa,64,65
M.J. Kweon,35 Y. Kwon,73, 81 G.S. Kyle,57 Y.S. Lai,14 J.G. Lajoie,29 D. Layton,26 A. Lebedev,29 D.M. Lee,41
K.B. Lee,35 S. Lee,81 S.H. Lee,29, 71 T. Lee,69 M.J. Leitch,41 M.A.L. Leite,68 B. Lenzi,68 P. Liebing,65 S.H. Lim,81
A. Litvinenko,32 H. Liu,57 M.X. Liu,41 T. Liˇska,15 X. Li,11 S. Lokos,18 D.A. Loomis,48 B. Love,77 D. Lynch,8
C.F. Maguire,77 Y.I. Makdisi,7M. Makek,82 A. Malakhov,32 M.D. Malik,56 A. Manion,71 V.I. Manko,36
E. Mannel,8, 14 Y. Mao,62, 64 H. Masui,76 F. Matathias,14 L. Maˇsek,10, 28 M. McCumber,41, 71 P.L. McGaughey,41
D. McGlinchey,13, 41 C. McKinney,26 N. Means,71 A. Meles,57 M. Mendoza,9B. Meredith,26 Y. Miake,76
A.C. Mignerey,45 P. Mikeˇs,28 K. Miki,76 A. Milov,8, 79 D.K. Mishra,5M. Mishra,4J.T. Mitchell,8M. Mitrankova,67
Iu. Mitrankov,67 S. Miyasaka,64,75 S. Mizuno,64, 76 A.K. Mohanty,5P. Montuenga,26 T. Moon,35, 81
Y. Morino,12 A. Morreale,9D.P. Morrison,8T.V. Moukhanova,36 D. Mukhopadhyay,77 B. Mulilo,35, 64, 83
T. Murakami,37, 64 J. Murata,64, 66 A. Mwai,70 S. Nagamiya,34, 64 K. Nagashima,23 J.L. Nagle,13 M. Naglis,79
M.I. Nagy,18 I. Nakagawa,64, 65 H. Nakagomi,64,76 Y. Nakamiya,23 T. Nakamura,23 K. Nakano,64,75 C. Nattrass,73
P.K. Netrakanti,5J. Newby,40 M. Nguyen,71 T. Niida,76 S. Nishimura,12 R. Nouicer,8, 65 N. Novitzky,33, 71
T. Nov´ak,47, 80 G. Nukazuka,64, 65 A.S. Nyanin,36 E. O’Brien,8S.X. Oda,12 C.A. Ogilvie,29 K. Okada,65 M. Oka,76
Y. Onuki,64 J.D. Orjuela Koop,13 M. Orosz,17 J.D. Osborn,48, 60 A. Oskarsson,43 M. Ouchida,23 K. Ozawa,12, 34, 76
R. Pak,8A.P.T. Palounek,41 V. Pantuev,27, 71 V. Papavassiliou,57 J. Park,69 J.S. Park,69 S. Park,49, 64, 69, 71
W.J. Park,35 M. Patel,29 S.F. Pate,57 H. Pei,29 J.-C. Peng,26 H. Pereira,16 D.V. Perepelitsa,8, 13 G.D.N. Perera,57
V. Peresedov,32 D.Yu. Peressounko,36 J. Perry,29 R. Petti,8, 71 C. Pinkenburg,8R. Pinson,1R.P. Pisani,8
arXiv:2406.08301v1 [nucl-ex] 12 Jun 2024

2
M. Potekhin,8M.L. Purschke,8A.K. Purwar,41 H. Qu,22 A. Rakotozafindrabe,38 J. Rak,33, 56 B.J. Ramson,48
I. Ravinovich,79 K.F. Read,60, 73 S. Rembeczki,20 K. Reygers,50 D. Reynolds,70 V. Riabov,55, 63 Y. Riabov,63, 67
D. Richford,6T. Rinn,29 D. Roach,77 G. Roche,42, ∗S.D. Rolnick,9M. Rosati,29 S.S.E. Rosendahl,43 P. Rosnet,42
Z. Rowan,6J.G. Rubin,48 P. Rukoyatkin,32 P. Ruˇziˇcka,28 V.L. Rykov,64 B. Sahlmueller,50, 71 N. Saito,34, 37, 64, 65
T. Sakaguchi,8S. Sakai,76 K. Sakashita,64, 75 H. Sako,30 V. Samsonov,55,63 M. Sarsour,22 S. Sato,30, 34 T. Sato,76
S. Sawada,34 B. Schaefer,77 B.K. Schmoll,73 K. Sedgwick,9J. Seele,13 R. Seidl,26, 64, 65 A.Yu. Semenov,29
V. Semenov,25, 27 A. Sen,29, 73 R. Seto,9P. Sett,5A. Sexton,45 D. Sharma,71, 79 I. Shein,25 T.-A. Shibata,64, 75
K. Shigaki,23 M. Shimomura,29, 54, 76 K. Shoji,37, 64 P. Shukla,5A. Sickles,8, 26 C.L. Silva,41, 68 D. Silvermyr,43, 60
C. Silvestre,16 K.S. Sim,35 B.K. Singh,4C.P. Singh,4C.P. Singh,4, ∗V. Singh,4M. Sluneˇcka,10 K.L. Smith,21, 41
M. Snowball,41 A. Soldatov,25 R.A. Soltz,40 W.E. Sondheim,41 S.P. Sorensen,73 I.V. Sourikova,8F. Staley,16
P.W. Stankus,60 E. Stenlund,43 M. Stepanov,46, 57 , ∗A. Ster,80 S.P. Stoll,8T. Sugitate,23 C. Suire,61 A. Sukhanov,8
T. Sumita,64 J. Sun,71 Z. Sun,17, 71 J. Sziklai,80 E.M. Takagui,68 A. Taketani,64, 65 R. Tanabe,76 Y. Tanaka,53
K. Tanida,30, 64, 65, 69 M.J. Tannenbaum,8S. Tarafdar,77, 79 A. Taranenko,55, 70 P. Tarj´an,17 H. Themann,71
T.L. Thomas,56 R. Tieulent,22, 44 A. Timilsina,29 T. Todoroki,64, 65, 76 M. Togawa,37, 64 A. Toia,71 Y. Tomita,76
L. Tom´aˇsek,28 M. Tom´aˇsek,15, 28 H. Torii,23,64 C.L. Towell,1R. Towell,1R.S. Towell,1V-N. Tram,38 I. Tserruya,79
Y. Tsuchimoto,23 B. Ujvari,17 C. Vale,29 H. Valle,77 H.W. van Hecke,41 A. Veicht,14, 26 J. Velkovska,77
A.A. Vinogradov,36 M. Virius,15 V. Vrba,15, 28 E. Vznuzdaev,63 R. V´ertesi,17, 80 X.R. Wang,57, 65 Y. Watanabe,64, 65
Y.S. Watanabe,12, 34 F. Wei,29, 57 J. Wessels,50 A.S. White,48 S.N. White,8D. Winter,14 C.L. Woody,8
M. Wysocki,13, 60 B. Xia,59 W. Xie,65 L. Xue,22 S. Yalcin,71 Y.L. Yamaguchi,12, 71, 78 K. Yamaura,23 R. Yang,26
A. Yanovich,25 J. Ying,22 S. Yokkaichi,64, 65 I. Yoon,69 J.H. Yoo,35 G.R. Young,60 I. Younus,39, 56 I.E. Yushmanov,36
H. Yu,57, 62 W.A. Zajc,14 O. Zaudtke,50 A. Zelenski,7C. Zhang,60 S. Zhou,11 L. Zolin,32 and L. Zou9
(PHENIX Collaboration)
1Abilene Christian University, Abilene, Texas 79699, USA
2Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
3Department of Physics, Augustana University, Sioux Falls, South Dakota 57197, USA
4Department of Physics, Banaras Hindu University, Varanasi 221005, India
5Bhabha Atomic Research Centre, Bombay 400 085, India
6Baruch College, City University of New York, New York, New York, 10010 USA
7Collider-Accelerator Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
8Physics Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
9University of California-Riverside, Riverside, California 92521, USA
10Charles University, Faculty of Mathematics and Physics, 180 00 Troja, Prague, Czech Republic
11Science and Technology on Nuclear Data Laboratory, China Institute
of Atomic Energy, Beijing 102413, People’s Republic of China
12Center for Nuclear Study, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
13University of Colorado, Boulder, Colorado 80309, USA
14Columbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533, USA
15Czech Technical University, Zikova 4, 166 36 Prague 6, Czech Republic
16Dapnia, CEA Saclay, F-91191, Gif-sur-Yvette, France
17Debrecen University, H-4010 Debrecen, Egyetem t´er 1, Hungary
18ELTE, E¨otv¨os Lor´and University, H-1117 Budapest, P´azm´any P. s. 1/A, Hungary
19Ewha Womans University, Seoul 120-750, Korea
20Florida Institute of Technology, Melbourne, Florida 32901, USA
21Florida State University, Tallahassee, Florida 32306, USA
22Georgia State University, Atlanta, Georgia 30303, USA
23Physics Program and International Institute for Sustainability with Knotted Chiral Meta
Matter (SKCM2), Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
24Department of Physics and Astronomy, Howard University, Washington, DC 20059, USA
25IHEP Protvino, State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, 142281, Russia
26University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
27Institute for Nuclear Research of the Russian Academy of Sciences, prospekt 60-letiya Oktyabrya 7a, Moscow 117312, Russia
28Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
29Iowa State University, Ames, Iowa 50011, USA
30Advanced Science Research Center, Japan Atomic Energy Agency, 2-4
Shirakata Shirane, Tokai-mura, Naka-gun, Ibaraki-ken 319-1195, Japan
31Jeonbuk National University, Jeonju, 54896, Korea
32Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia
33Helsinki Institute of Physics and University of Jyv¨askyl¨a, P.O.Box 35, FI-40014 Jyv¨askyl¨a, Finland
34KEK, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan

3
35Korea University, Seoul 02841, Korea
36National Research Center “Kurchatov Institute”, Moscow, 123098 Russia
37Kyoto University, Kyoto 606-8502, Japan
38Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS-IN2P3, Route de Saclay, F-91128, Palaiseau, France
39Physics Department, Lahore University of Management Sciences, Lahore 54792, Pakistan
40Lawrence Livermore National Laboratory, Livermore, California 94550, USA
41Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
42LPC, Universit´e Blaise Pascal, CNRS-IN2P3, Clermont-Fd, 63177 Aubiere Cedex, France
43Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden
44IPNL, CNRS/IN2P3, Univ Lyon, Universit´e Lyon 1, F-69622, Villeurbanne, France
45University of Maryland, Col lege Park, Maryland 20742, USA
46Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003-9337, USA
47MATE, Laboratory of Femtoscopy, K´aroly R´obert Campus, H-3200 Gy¨ongy¨os, M´atrai´ut 36, Hungary
48Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA
49Mississippi State University, Mississippi State, Mississippi 39762, USA
50Institut f¨ur Kernphysik, University of M¨unster, D-48149 M¨unster, Germany
51Muhlenberg College, Allentown, Pennsylvania 18104-5586, USA
52Myongji University, Yongin, Kyonggido 449-728, Korea
53Nagasaki Institute of Applied Science, Nagasaki-shi, Nagasaki 851-0193, Japan
54Nara Women’s University, Kita-uoya Nishi-machi Nara 630-8506, Japan
55National Research Nuclear University, MEPhI, Moscow Engineering Physics Institute, Moscow, 115409, Russia
56University of New Mexico, Albuquerque, New Mexico 87131, USA
57New Mexico State University, Las Cruces, New Mexico 88003, USA
58Physics and Astronomy Department, University of North Carolina at Greensboro, Greensboro, North Carolina 27412, USA
59Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA
60Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
61IPN-Orsay, Univ. Paris-Sud, CNRS/IN2P3, Universit´e Paris-Saclay, BP1, F-91406, Orsay, France
62Peking University, Beijing 100871, People’s Republic of China
63PNPI, Petersburg Nuclear Physics Institute, Gatchina, Leningrad region, 188300, Russia
64RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198, Japan
65RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
66Physics Department, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima, Tokyo 171-8501, Japan
67Saint Petersburg State Polytechnic University, St. Petersburg, 195251 Russia
68Universidade de S˜ao Paulo, Instituto de F´ısica, Caixa Postal 66318, S˜ao Paulo CEP05315-970, Brazil
69Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea
70Chemistry Department, Stony Brook University, SUNY, Stony Brook, New York 11794-3400, USA
71Department of Physics and Astronomy, Stony Brook University, SUNY, Stony Brook, New York 11794-3800, USA
72SUBATECH (Ecole des Mines de Nantes, CNRS-IN2P3, Universit´e de Nantes) BP 20722-44307, Nantes, France
73University of Tennessee, Knoxville, Tennessee 37996, USA
74Texas Southern University, Houston, TX 77004, USA
75Department of Physics, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152-8551, Japan
76Tomonaga Center for the History of the Universe, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
77Vanderbilt University, Nashville, Tennessee 37235, USA
78Waseda University, Advanced Research Institute for Science and
Engineering, 17 Kikui-cho, Shinjuku-ku, Tokyo 162-0044, Japan
79Weizmann Institute, Rehovot 76100, Israel
80Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Hungarian
Academy of Sciences (Wigner RCP, RMKI) H-1525 Budapest 114, POBox 49, Budapest, Hungary
81Yonsei University, IPAP, Seoul 120-749, Korea
82Department of Physics, Faculty of Science, University of Zagreb, Bijeniˇcka c. 32 HR-10002 Zagreb, Croatia
83Department of Physics, School of Natural Sciences, University
of Zambia, Great East Road Campus, Box 32379, Lusaka, Zambia
High-momentum two-particle correlations are a useful tool for studying jet-quenching effects in the
quark-gluon plasma. Angular correlations between neutral-pion triggers and charged hadrons with
transverse momenta in the range 4–12 GeV/cand 0.5–7 GeV/c, respectively, have been measured
by the PHENIX experiment in 2014 for Au+Au collisions at √sNN = 200 GeV. Suppression is
observed in the yield of high-momentum jet fragments opposite the trigger particle, which indicates
jet suppression stemming from in-medium partonic energy loss, while enhancement is observed for
low-momentum particles. The ratio and differences between the yield in Au+Au collisions and p+p
collisions, IAA and ∆AA, as a function of the trigger-hadron azimuthal separation, ∆ϕ, are measured
for the first time at the Relativistic Heavy Ion Collider. These results better quantify how the yield
of low-pTassociated hadrons is enhanced at wide angle, which is crucial for studying energy loss as
well as medium-response effects.

4
I. INTRODUCTION
Jets, collimated sprays of energetic particles originat-
ing from the fragmentation of hard-scattered partons, are
an important probe of the quark-gluon plasma (QGP)
created in ultra-relativistic collisions of heavy ions, such
as those at the Relativistic Heavy Ion Collider (RHIC)
and the Large Hadron Collider (LHC) [1]. In particular,
these hard-scattered partons interact with the QGP and
lose energy when traveling through the medium before
fragmenting into final-state jet particles. This partonic
energy loss gives rise to jets that have been modified rel-
ative to jets that are measured in p+pcollisions, where
no QGP medium is formed. The momentum distribution
as well as the spatial distribution of particles within the
resulting jets in particular are seen to be modified [2–
6]. Measurements of jet modification allow for direct
quantification of the energy transport properties of the
medium [7]. Once the parton shower interacts with the
QGP, the jets and medium particles are intrinsically cou-
pled to one another. Therefore, the observed modifica-
tions can also embody a response from the QGP, which
is often referred to as a medium response [8, 9].
High-transverse-momentum neutral pions, π0, can be
reconstructed via their two-photon decay channel and
used as jet proxies as they carry a large fraction of the
jet momentum. Measuring the angular correlations be-
tween the π0and charged hadrons in the event, reveals
how charged hadrons are distributed in the jet triggered
by the π0as well as the opposing jet that appears 180 de-
grees away from the π0. The abundance of neutral pions,
which can be reconstructed using the high-granularity
PHENIX electromagnetic calorimeter (EMCal) out to
high pT, are great candidates for trigger particles. Two-
particle correlations, such as π0-hadron correlations, are
preferred over full-jet reconstruction for dijet measure-
ments in PHENIX to overcome the limited PHENIX ac-
ceptance.
The previous π0-hadron correlations results from
PHENIX [10] used an earlier and smaller data set from
2007. In subtraction of the underlying event, the third-
and fourth-order harmonics, v3and v4, were not con-
sidered. Therefore, the correlations related to jets were
not fully decoupled from correlations with the under-
lying event. The 2014 results presented here use the
largest Au+Au data set ever collected by PHENIX and
include underlying event subtraction using updated mea-
surements of the higher-order harmonic terms. The im-
proved statistical precision and purity of the measure-
ment enables comparisons of the away-side correlation
yield in Au+Au to that in p+pas a function of the
azimuthal separation, ∆ϕ, which provides insight into
how the distribution of particles correlated with the jet
is modified.
∗Deceased
†PHENIX Spokesperson: akiba@rcf.rhic.bnl.gov
II. EXPERIMENT
Figure 1 shows the 2014 detector configuration. In
this study, the PHENIX collaboration processed 5 billion
minimum-bias events triggered by the PHENIX beam-
beam counters [11] and collected by the central-arm de-
tectors [12] for Au+Au collisions at √sNN = 200 GeV.
The p+p-collision data at √sNN = 200 GeV were col-
lected by PHENIX in 2006 and used 3.2 million high-pT
photon-triggered events for baseline measurements [10].
2014
FIG. 1. Configuration of PHENIX central arm detector in
2014.
III. DATA ANALYSIS
The π0’s, which are used as a jet proxy in this analy-
sis, are reconstructed from their decay photons by pair-
ing together EMCal clusters with an energy of 1 GeV
or greater. To remove contamination from charged par-
ticles, EMCal clusters are required to be greater than
8 cm away from the closest track projection from the drift
chambers to the EMCal. Additionally, a cut is made on
the cluster shape to remove further potential contami-
nation from hadrons. The photon pairs must have an
energy asymmetry (α=|Eγ1−Eγ2|
Eγ1+Eγ2
, where Eγ1and Eγ2
are the energies of the first and second photon, respec-
tively) of less than 80% of the sum of the photon en-
ergy. Finally, each reconstructed π0is required to have
an invariant mass between 0.12 and 0.16 GeV/c2. Re-
constructed π0’s used as jet proxies in this analysis have
transverse momenta, pT,π0, of 4–12 GeV/c.
Reconstructed π0’s are then paired with reconstructed
charged tracks. Reconstructed tracks are required to
have 0.5≤pT,h ≤7 GeV/c, where the upper limit of
7 GeV/cis chosen to limit contamination from secon-
daries produced by high-pThadrons within the detector
that are misreconstructed as high-pTtracks.

5
The ∆ϕcorrelation functions between π0’s and asso-
ciated charged hadrons are normalized by the number of
π0’s, Nπ0and then corrected for the single-hadron recon-
struction efficiency (ϵ) and the detector acceptance via
simulation and event mixing. To obtain the correlation
functions purely from jets, correlations due to the under-
lying event and flow are subtracted from the correlation
functions. Then, the jet function, which is the differen-
tial yield of jet-associated π0-hadron pairs per number of
π0’s in a given π0pTbin, Nπ0−h, with respect to ∆ϕ,
can be written as
1
Nπ0
dNπ0−h
d∆ϕ=1
Nπ0
Nπ0−h
ϵRd∆ϕ(dNsame
π0−h/d∆ϕ
dNmix
π0−h/d∆ϕ(1)
−b0"1+2
4
X
n=2⟨vπ0
nvh
n⟩cos(n·∆ϕ)#)
where Nsame
π0−hand Nmix
π0−hare the number of same-event
and mixed-event π0-hadron pairs, respectively.
The contribution to the correlation due to flow ap-
pears in the second term of Ea. (1) as a Fourier series
in terms of the azimuthal correlation angle. The coef-
ficient b0of the Fourier series is the magnitude of the
underlying event estimated using zero-yield-at-minimum
method (ZYAM) and absolute background normalization
method (ABS) [13] in low pT,h <1 GeV/cand high pT ,h
≥1 GeV/c, respectively. To improve the purity of the
extracted jet-hadron correlation signal, the second to the
fourth-order harmonics are subtracted (v2−v4). The
first-order harmonic (v1) is not accounted for because
its contribution is expected to be negligible at midrapid-
ity [14, 15]. The nth -order flow-harmonic coefficients are
factorized to vπ0
nand vh
nfor π0’s and charged hadrons,
respectively.
The π0vπ0
2and charged hadron vh
nin Au+Au colli-
sions at 200 GeV come from previous PHENIX mea-
surements [16, 17]. However, the higher-order π0flow-
harmonic coefficients n= 3,4 in these momentum ranges
have not been measured at RHIC energies. Thus, to
estimate vπ0
3and vπ0
4, acoustic scaling [18] is applied.
Acoustic scaling is the observation that there is a pT-
independent relation between different powers of the var-
ious flow harmonics given by the scaling factors, gn, de-
fined as:
gn=vn
(v2)n/2.(2)
Assuming the scaling factors of π0’s and charged
hadron are approximately equal due to isospin symmetry
(i.e. gh
n=gπ0
n), vπ0
3and vπ0
4can then be approximated
by rearranging Eq. (2) to become:
vπ0
n=gh
n·(vπ0
2)n/2.(3)
Modification to the per-jet, integrated yield of hadrons
is quantified by the yield-modification factor IAA, de-
fined as:
IAA(pT ,h) = R3π/2
π/2[dN AuAu
π0−h/d∆ϕ]·d∆ϕ
R3π/2
π/2[dN pp
π0−h/d∆ϕ]·d∆ϕ.(4)
The IAA, shown in Fig. 2, is defined as the ratio of
the integrated per-trigger yield of the away-side jet func-
tion within π
2≤∆ϕ≤3π
2in Au+Au to that measured in
p+pcollisions. Additionally, for the first time at RHIC,
the IAA as a function of ∆ϕ, has been measured and is
defined as the point-by-point ratio of per-trigger yield of
the away-side jet function in Au+Au and p+p, that is,
IAA(∆ϕ) = dNAuAu
π0−h/d∆ϕ
dNpp
π0−h/d∆ϕ.(5)
The IAA as a function of ∆ϕresults are shown in Fig. 3.
Downward fluctuations can cause negative yield at a par-
ticular ∆ϕbin. In such cases, the IAA point is not shown.
Additionally, for clarity, data points with a relative sta-
tistical or systematic uncertainty equal to or greater than
100% are also not shown.
Because IAA(∆ϕ) in regions with small yield in Au+Au
can be inflated through dividing by yields in p+pclose
to zero, a complimentary observable that can also be ex-
tracted is the difference between the yields in Au+Au
and p+p, that is,
∆AA(∆ϕ) = dNAuAu
π0−h
d∆ϕ−dNpp
π0−h
d∆ϕ.(6)
IV. SYSTEMATIC UNCERTAINTY
Seven sources of systematic uncertainty are considered
in this analysis. The first three arise from the second-
to fourth-order flow-harmonic coefficients. The fourth
is the estimation of the underlying event magnitude, b0,
using either ZYAM or ABS. The fifth arises from π0re-
construction. The sixth source is the single particle effi-
ciency, which is represented by a global scale uncertainty
of 6.9%. The seventh and final source of systematic un-
certainty comes from the p+pmeasurement used in this
analysis, which is discussed in detail in Ref. [10].
The uncertainties from flow-harmonic coefficients are
estimated by setting the coefficients to their upper and
lower limits individually (including the uncertainty of the
corresponding scaling factor), re-extracting the jet func-
tions, and then re-calculating the observable of interest.
The relative uncertainties from the flow-harmonic coef-
ficients are within a few percent at pT,h >1 GeV/c.
Note that, the even-order-flow-harmonic coefficients do
not contribute to the integrated-yield-modification mea-
surements because the integral of the even cosine terms
equals zero. However, in the lowest pT,h bin where ZYAM
is used in the flow subtraction, b0is allowed to vary in the
uncertainties analyses due to flow-harmonic coefficients
causing larger uncertainty ranges between 10%–30% in

6
1 2 3 4 5 6 7
(GeV/c)
T,h
p
0
1
2
3
AA
I
ZYAM
ABS
< 5 GeV/c
0
πT,
4 < p
0%-20% 20%-40%
(a)
1 2 3 4 5 6 7
(GeV/c)
T,h
p
0
1
2
3
AA
I
< 7 GeV/c
0
πT,
5 < p
hadron−
0
π
Au+Au 200 GeV
2
π
+ π < φ∆ <
2
π
− π
(b)
1 2 3 4 5 6 7
(GeV/c)
T,h
p
0
1
2
3
AA
I
< 9 GeV/c
0
πT,
7 < p
PHENIX
(c)
1 2 3 4 5 6 7
(GeV/c)
T,h
p
0
1
2
3
AA
I
< 12 GeV/c
0
πT,
9 < p
(d)
FIG. 2. Integrated away-side IAA as a function of pT,h. The π0trigger pT,π 0range is shown at the top of each panel. Statistical
and systematic uncertainties are drawn as vertical lines and boxes, respectively. A global scaling uncertainty of 6.9% is drawn
as a blue box on the right of each panel at IAA = 1.
2 2.5 3
(rad)φ∆
0
2
4
6
AA
I
< 1.0 GeV/c
T,h
0.5 < p
< 2.0 GeV/c
T,h
1.0 < p
< 5.0 GeV/c
T,h
3.0 < p
< 5.0 GeV/c
0
πT,
4.0 < p
(a)
2 2.5 3
(rad)φ∆
0
2
4
6
< 7.0 GeV/c
0
πT,
5.0 < p
PHENIX
hadron−
0
π
Au+Au 200 GeV
20%−0%
(b)
2 2.5 3
(rad)φ∆
0
2
4
6
< 9.0 GeV/c
0
πT,
7.0 < p
(c)
2 2.5 3
(rad)φ∆
0
2
4
6
< 12.0 GeV/c
0
πT,
9.0 < p
(d)
2 2.5 3
(rad)φ∆
0
2
4
6
AA
I
< 1.0 GeV/c
T,h
0.5 < p
< 2.0 GeV/c
T,h
1.0 < p
< 5.0 GeV/c
T,h
3.0 < p
< 5.0 GeV/c
0
πT,
4.0 < p
(e)
2 2.5 3
(rad)φ∆
0
2
4
6
< 7.0 GeV/c
0
πT,
5.0 < p
PHENIX
hadron−
0
π
Au+Au 200 GeV
40%−20%
(f)
2 2.5 3
(rad)φ∆
0
2
4
6
< 9.0 GeV/c
0
πT,
7.0 < p
(g)
2 2.5 3
(rad)φ∆
0
2
4
6
< 12.0 GeV/c
0
πT,
9.0 < p
(h)
FIG. 3. Differential away-side IAA as a function of ∆ϕin (a) to (d) 0%–20% and (e) to (h) 20%–40% centrality classes. The
π0trigger pT,π 0range is shown at the top of each panel. Statistical and systematic uncertainties are drawn as vertical lines
and boxes, respectively. A global uncertainty of 6.9% is not shown.
both differential and integrated yield-modification mea-
surements.
The uncertainties arising from b0itself are estimated
by varying the b0obtained from ZYAM and ABS to its
upper and lower limits. These relative uncertainties are
dominant at pT,h <3 GeV/c. The relative uncertain-
ties from ABS ranges within 10% at pT,h >1 GeV/c,
while the relative uncertainty from ZYAM ranges be-
tween 10%–50% at the lowest pT ,h bin.
The uncertainty from π0reconstruction is estimated
for each pT,π0⊗pT ,h bin via side-band analysis which in-
volves remeasuring the jet functions using photon pairs
with an invariant mass within 0.65–0.11 GeV/c2or
0.165–0.2 GeV/c2, instead of the nominal π0mass win-
dow, 0.12–0.16 GeV/c2. The π0reconstruction contribu-
tion becomes one of the dominant sources of uncertainty
as pT,h increases. The relative uncertainty from π0re-
construction rises from a few percent to 20%.
Another dominant source of uncertainty at high pT ,h
comes from the p+pcollision data. The relative uncer-
tainty from that increases from a few percent at 2 <
pT,h <3 GeV/cto 20% at 5 < pT,h <7 GeV/c.

7
Except the global scaled uncertainty from single par-
ticle efficiency, uncertainties from other sources are cor-
related data-point-to-data-point. Note that, because the
uncertainty from π0reconstruction is estimated as a func-
tion of pT, it is a correlated uncertainty for IAA(pT), but
a global scaled uncertainty for IAA(∆ϕ) and ∆AA(∆ϕ).
V. RESULTS
1−0 1 2 3 4
(rad)φ∆
0
0.1
0.2
0.3
φ∆)dN/
0
π
(1/N
(a)
AuAu 200 GeV PHENIX
1 GeV/c− 0.5⊗7 −20%, 5−0%
1−0 1 2 3 4
(rad)φ∆
0
0.05
0.1
0.15 (b) 3 GeV/c− 2⊗7 −20%, 5−0%
1−0 1 2 3 4
(rad)φ∆
0
0.1
0.2
0.3 (c)
1 GeV/c− 0.5⊗7 −40%, 5−20%
1−0 1 2 3 4
(rad)φ∆
0
0.05
0.1
0.15 (d)
3 GeV/c− 2⊗7 −40%, 5−20%
FIG. 4. Per-trigger jet-pair yield as a function of ∆ϕfor se-
lected π0trigger and charged-hadron-associated pTcombina-
tions (pT,π 0⊗pT,h ) in Au+Au collisions. Statistical and sys-
tematic uncertainties are drawn as vertical lines and boxes, re-
spectively. A global scaling uncertainty of 6.9% is not shown.
Figure 4 shows the jet function in 5 ≤pT,π0<7 GeV/c
after subtracting the underlying event from the correla-
tion functions. The away-side jet peaks shown in Fig. 4
appear closer to a Gaussian function compared to previ-
ous PHENIX results [10], where there were pronounced
peaks appearing to the left and right of the away-side
jet peak, a phenomenon often attributed to a “mach-
cone” effect created by super-sonic traversal of the QGP
by hard-scattered partons. However, such an effect is no
longer seen once contamination from the third and fourth
harmonics is removed. These changes are more pro-
nounced at low pT,h where the underlying event is large.
The away-side (∆ϕ > π/2) IAA as a function of the
associated-hadron momentum, IAA (pT,h ), is shown in
Fig. 2 for four π0momentum ranges. In each π0momen-
tum range, the IAA(pT ,h) is above unity at low pT ,h, but
falls as pT,h increases, eventually reaching below unity
at high pT,h . The behavior of the IAA at low-associated
hadron momentum indicates that there is an enhance-
ment in the yield of soft particles in central Au+Au colli-
sions, whereas the sub-unity of the IAA at high pTis con-
sistent with a suppression in the yield high-momentum
associated hadrons. The current understanding of jet-
medium interactions indicates that in-medium energy
loss by high-energy partons is the cause of the suppres-
sion in the yield of high-momentum hadrons. However,
as shown in [2], models can reproduce the enhancement
measured at low momentum by including a mechanism
by which energy embedded into the medium by hard par-
tons is redistributed into the production of soft particles
as a medium response. Unlike in Ref. [2], in which the
IAA(pT ,h) is measured as a function of ξ=−ln(zT), the
transition from enhancement to suppression is shown in
Fig. 2 to occur at a consistent pT,h of 1–2 GeV/cin each
π0momentum range. This indicates a constant medium
response that is independent of the jet energy.
Lastly, this measurement is made in the 0%–20% and
20%–40% centrality bins, which are shown in Fig. 2
as circle [black] and diamond [red] points, respectively.
There is no definitive centrality dependence observed in
IAA(pT ,h). However, above 1 GeV/c, the IAA(pT ,h) in
the 20%–40% bin is systematically closer to unity than
that in the 0%–20% bin. For the enhancement regime,
where partons might traverse a greater path-length on av-
erage, this could be indicative of a higher probability of
complete thermalization of soft radiation. Likewise, this
shorter path-length might lead to a lower mean energy
loss for high-energy partons, leading to the less-severe
suppression seen above the transition point. This result
is qualitatively in agreement with results from both the
STAR [3] and ALICE [19] collaborations. The differ-
ence in the magnitude of the enhancement measured by
the ALICE experiment (a factor of ≈5) vs here (a fac-
tor of ≈2) could arise due to differences in the plasmas
created at the LHC and RHIC, such as the mean path-
length traversed by hard partons being larger, leading to
an increased production of low-pThadrons. Similarly, the
large enchancement measured in this result versus that
seen by the STAR experiment Ref. [3] is due to the fact
that this measurement extends down to a hadron momen-
tum of 0.5 GeV/c, where the enhancement is very strong;
whereas the threshold is at 1.2 GeV/cin the STAR re-
sult, where the IAA is closer to unity.
Figure 3 shows the IAA as a function of ∆ϕ,IAA(∆ϕ),
which allows for quantification of the modification to
the jet yield at different distances from the away-side
jet axis (∆ϕ≈π). The IAA(∆ϕ) shows an enhancement
in the yield of low-momentum hadrons across the away-
side jet peak, although this enhancement is strongest at
wide angles relative to the peak. The away-side peak
is also the first region where the IAA(∆ϕ) begins to fall
beneath unity as shown by the 1.0≤pT,h <2.0 GeV/c
(red diamonds) in both the 0%–20% and 20%–40% cen-
trality bins. In the highest momentum bin reported,
3.0≤pT,h <5.0 GeV/c, the yield of charged hadrons
is suppressed across all angles shown, a result of the par-
tonic energy loss induced by parton-medium interactions.
In contrast, the enhancement is most severe at wide an-
gles relative to the away-side jet peak similar to what is

8
1.5 2 2.5 3
(rad)φ∆
0
0.05
0.1
0.15
AA
∆
20%−0% 40%−20%
< 1.0 GeV/c
T,h
0.5 < p
Au+Au 200 GeV
< 5 GeV
0
πT,
hadron, 4 < p−
0
π
(a)
1.5 2 2.5 3
(rad)φ∆
0
0.05
< 2.0 GeV/c
T,h
1.0 < p
PHENIX
(b)
1.5 2 2.5 3
(rad)φ∆
0.015−
0.01−
0.005−
0
0.005 < 5.0 GeV/c
T,h
3.0 < p(c)
1.5 2 2.5 3
(rad)φ∆
0.2−
0
0.2
0.4
AA
∆
Hybrid
No wake
Wake
< 1.0 GeV/c
T,h
0.5 < p
20%−0%Au+Au 200 GeV, < 5 GeV
0
πT,
hadron, 4 < p−
0
π
(d)
1.5 2 2.5 3
(rad)φ∆
0.1−
0
0.1
< 2.0 GeV/c
T,h
1.0 < p
PHENIX
(e)
1.5 2 2.5 3
(rad)φ∆
0.04−
0.02−
0
0.02 < 5.0 GeV/c
T,h
3.0 < p(f)
FIG. 5. (a)–(c): Differential away-side ∆AA in 0%–20% (circles [black]) and 20%–40% (diamonds [red]) centrality classes
from ∆ϕ≈π/2–π. (d)–(f): Differential away-side ∆AA in 0%–20% centrality class for the same ∆ϕrange compared to hybrid
models with “Wake” (backward [red] slashes) and “No wake” (forward [blue] slashes). A global uncertainty of 6.9% is not
shown.
seen in Ref. [2].
Figure 5 shows the difference between Au+Au and p+p
in the per-trigger yield, ∆AA , as a function of ∆ϕfor
hadrons with 0.5< pT<1 GeV/c. The enhancement
(where the difference between the Au+Au and p+pyields
is positive) is again observed over a wide range of angles.
The enhancement increases when moving away from the
away-side jet axis, that is ∆ϕ=π. The enhancement
seen at wider angles is also consistent with the phenom-
ena of jet broadening. It is notable that the enhancement
is observed near the ∆ϕ=π/2 region because, as shown
in Fig. 4, that is the minimum of the per-trigger jet-
pair yield. One key advantage of taking the difference
in Au+Au and p+pover computing the IAA is that it is
less sensitive than the IAA to the p+pyields fluctuating
close to zero, particularly near ∆ϕ=π/2. This approach
provides stronger constraints on theoretical models than
the IAA in these regions. The modification seen in Fig. 5
is further explored by observing how the measurement
changes as a function of hadron pT.
Figure 5 shows the difference in the per-trigger yields
between Au+Au and p+pas a function of ∆ϕfor dif-
ferent pT,h bins associated with 4–5 GeV/c π0, which
clearly demonstrates the transition from enhancement at
low pT,h to suppression at high pT ,h. In particular, the
suppression in the per-trigger yield is most severe near
the jet axis (∆ϕ≈π). This suppression pattern differs
slightly from that seen in measurements at the LHC, such
as in [20], where the yield of hadrons within a jet is found
to be almost unmodified at the jet axis, regardless of the
momentum range. However, for these RHIC results the
IAA and ∆AA vs ∆ϕare measured from the recoil jet
opposite the jet containing the trigger π0, which imposes
almost no bias on the recoil jet. Note that anti-kTjets
like those measured in Ref. [20] have more stringent re-
quirements and could bias the sample of reconstructed
jets in Au+Au to be more similar to those in p+pcolli-
sions.
Figure 5 plots (d) to (f) show the Au+Au and p+p
yield differences versus ∆ϕfor selected pT,π0⊗pT ,h bins
overlaid with calculations from the HYBRID model [9]
(all available pT ,π0⊗pT ,h bins are shown in Figs. 6 and
7). This model uses a combination of perturbative quan-
tum chromodynamics and anti-de Sitter/conformal field
theory to handle hard and soft interactions within the
medium, respectively. One can see that at high pT ,h,
the HYBRID model reproduces the data well within the
uncertainty of the model. Two versions of the model are
presented, differentiated by how they handle the medium
response to the embedded partonic energy by the hard-
scattered parton. The curve labeled “Wake” models a
medium response to the lost energy as a hydrodynamic
wake of soft particles, which well reproduces the wide-
angle enhancement seen in the data at low pT,h. The
curve labeled “No wake” does not include this effect, and,
thus, fails to reproduce the data at low pT,h . The suc-

9
1.5 2 2.5 3
(rad)φ∆
0.2−
0
0.2
AA
∆
Hybrid
No wake
Wake
1 GeV/c− 0.5⊗5 −4
(a)
PHENIX
1.5 2 2.5 3
(rad)φ∆
0.1−
0
0.1
0.2 2 GeV/c− 1⊗5 −4
(b)
Au+Au 200 GeV
20%−0%hadron−
0
π
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
3 GeV/c− 2⊗5 −4
(c)
1.5 2 2.5 3
(rad)φ∆
0.04−
0.02−
0
0.02
0.04 5 GeV/c− 3⊗5 −4
(d)
1.5 2 2.5 3
(rad)φ∆
0.01−
0
0.01
7 GeV/c− 5⊗5 −4
(e)
1.5 2 2.5 3
(rad)φ∆
0.2−
0
0.2
AA
∆
1 GeV/c− 0.5⊗7 −5
(f)
1.5 2 2.5 3
(rad)φ∆
0.2−
0.1−
0
0.1
0.2 2 GeV/c− 1⊗7 −5
(g)
1.5 2 2.5 3
(rad)φ∆
0.1−
0.05−
0
0.05
0.1 3 GeV/c− 2⊗7 −5
(h)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
5 GeV/c− 3⊗7 −5
(i)
1.5 2 2.5 3
(rad)φ∆
0.02−
0.01−
0
0.01
0.02 7 GeV/c− 5⊗7 −5
(j)
1.5 2 2.5 3
(rad)φ∆
0.2−
0
0.2
0.4
AA
∆
1 GeV/c− 0.5⊗9 −7
(k)
1.5 2 2.5 3
(rad)φ∆
0.2−
0
0.2
0.4 2 GeV/c− 1⊗9 −7
(l)
1.5 2 2.5 3
(rad)φ∆
0.1−
0
0.1
3 GeV/c− 2⊗9 −7
(m)
1.5 2 2.5 3
(rad)φ∆
0.1−
0.05−
0
0.05
0.1 5 GeV/c− 3⊗9 −7
(n)
1.5 2 2.5 3
(rad)φ∆
0.04−
0.02−
0
0.02
0.04 7 GeV/c− 5⊗9 −7
(o)
1.5 2 2.5 3
(rad)φ∆
0.5−
0
0.5
AA
∆
1 GeV/c− 0.5⊗12 −9
(p)
1.5 2 2.5 3
(rad)φ∆
0.4−
0.2−
0
0.2
0.4 2 GeV/c− 1⊗12 −9
(q)
1.5 2 2.5 3
(rad)φ∆
0.2−
0.1−
0
0.1
0.2
3 GeV/c− 2⊗12 −9
(r)
1.5 2 2.5 3
(rad)φ∆
0.1−
0
0.1
0.2 5 GeV/c− 3⊗12 −9
(s)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
7 GeV/c− 5⊗12 −9
(t)
FIG. 6. Differential away-side ∆AA in 0%–20% centrality from ∆ϕ≈π/2–πfor various π0trigger and charged-hadron-associated
pTcombinations (pT,π0⊗pT ,h). As in Fig. 5(d)–(f), the “Wake” and “No wake” hybrid models are overlaid as backward [red]
slashes and forward [blue] slashes.

10
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
AA
∆
1 GeV/c− 0.5⊗5 −4(a)
Au+Au 200 GeV
40%−20%
hadron−
0
π
PHENIX
1.5 2 2.5 3
(rad)φ∆
0.04−
0.02−
0
0.02
0.04 2 GeV/c− 1⊗5 −4(b)
1.5 2 2.5 3
(rad)φ∆
0.01−
0
0.01
3 GeV/c− 2⊗5 −4(c)
1.5 2 2.5 3
(rad)φ∆
0.01−
0
0.01
5 GeV/c− 3⊗5 −4(d)
1.5 2 2.5 3
(rad)φ∆
0.002−
0.001−
0
0.001
0.002
7 GeV/c− 5⊗5 −4(e)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
AA
∆
1 GeV/c− 0.5⊗7 −5
(f)
1.5 2 2.5 3
(rad)φ∆
0
0.05 2 GeV/c− 1⊗7 −5(g)
1.5 2 2.5 3
(rad)φ∆
0.02−
0
0.02
3 GeV/c− 2⊗7 −5(h)
1.5 2 2.5 3
(rad)φ∆
0.02−
0.01−
0
0.01
0.02 5 GeV/c− 3⊗7 −5(i)
1.5 2 2.5 3
(rad)φ∆
0.002−
0
0.002
0.004 7 GeV/c− 5⊗7 −5(j)
1.5 2 2.5 3
(rad)φ∆
0.1−
0.05−
0
0.05
0.1
AA
∆
1 GeV/c− 0.5⊗9 −7(k)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
2 GeV/c− 1⊗9 −7(l)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
3 GeV/c− 2⊗9 −7(m)
1.5 2 2.5 3
(rad)φ∆
0.02−
0
0.02
0.04 5 GeV/c− 3⊗9 −7(n)
1.5 2 2.5 3
(rad)φ∆
0.01−
0
0.01
0.02 7 GeV/c− 5⊗9 −7(o)
1.5 2 2.5 3
(rad)φ∆
0.5−
0
0.5
AA
∆
1 GeV/c− 0.5⊗12 −9(p)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
0.1 2 GeV/c− 1⊗12 −9(q)
1.5 2 2.5 3
(rad)φ∆
0.02−
0
0.02
0.04 3 GeV/c− 2⊗12 −9(r)
1.5 2 2.5 3
(rad)φ∆
0.05−
0
0.05
5 GeV/c− 3⊗12 −9(s)
1.5 2 2.5 3
(rad)φ∆
0
0.05 7 GeV/c− 5⊗12 −9(t)
FIG. 7. Differential away-side ∆AA as a function of ∆ϕin 20%–40% centrality for various π0trigger and charged-hadron-
associated pTcombinations (pT,π 0⊗pT,h ).

11
cess of this model at low pT,h relies on a qualitatively
similar mechanism as the CoLBT-Hydro model shown in
Ref. [2]. Both models include hydrodynamic responses
from the medium that contribute to the creation of an
excess of soft particles in the final-state particle distribu-
tion.
VI. SUMMARY
The PHENIX collaboration presented a new π0-hadron
correlation measurement in Au+Au collision at 200 GeV
with data taken in 2014 at RHIC. With the enhanced
statistics of the 2014 data set and improved background
subtraction that accounts for contributions from flow
up to the fourth-order flow coefficient, the results pre-
sented here are an improvement over previous PHENIX
measurements. These jet functions and their integrated
yields are then used to calculate both the quotient, IAA,
and the difference, ∆AA, between Au+Au and p+pyields
vs ∆ϕ(as well as the IAA) as a function of the associated-
hadron pT.
The integrated per-trigger-yield modification, IAA as
a function of pT,h , is indicative of partonic energy loss
by hard partons via parton-medium interactions, leading
to the suppression of hard jet particles and enhancement
of soft jet particles. The new observables, differential
per-trigger-yield modifications as a function of ∆ϕ, show
uneven modifications inside the away-side jets. The an-
gular dependence of IAA and ∆AA, also changes with
jet-particle transverse momentum. The transition from
enhancement of low-momentum particles to suppression
at higher momentum is consistent with models such as
the Hybrid model that include medium response. The
differential IAA is sensitive to the small modification at
the edge of the jets, while the differential ∆AA is less
sensitive to statistical fluctuations. Using a variety of jet
related observables will further constrain the models in
the study of jet modifications, allowing for more precise
determination of QGP properties.
ACKNOWLEDGMENTS
We thank the staff of the Collider-Accelerator and
Physics Departments at Brookhaven National Labora-
tory and the staff of the other PHENIX participating in-
stitutions for their vital contributions. We acknowledge
support from the Office of Nuclear Physics in the Of-
fice of Science of the Department of Energy, the National
Science Foundation, a sponsored research grant from Re-
naissance Technologies LLC, Abilene Christian Univer-
sity Research Council, Research Foundation of SUNY,
and Dean of the College of Arts and Sciences, Van-
derbilt University (U.S.A), Ministry of Education, Cul-
ture, Sports, Science, and Technology and the Japan So-
ciety for the Promotion of Science (Japan), Conselho
Nacional de Desenvolvimento Cient´ıfico e Tecnol´ogico
and Funda¸c˜ao de Amparo `a Pesquisa do Estado de S˜ao
Paulo (Brazil), Natural Science Foundation of China
(People’s Republic of China), Croatian Science Founda-
tion and Ministry of Science and Education (Croatia),
Ministry of Education, Youth and Sports (Czech Repub-
lic), Centre National de la Recherche Scientifique, Com-
missariat `a l’´
Energie Atomique, and Institut National
de Physique Nucl´eaire et de Physique des Particules
(France), Bundesministerium f¨ur Bildung und Forschung,
Deutscher Akademischer Austausch Dienst, and Alexan-
der von Humboldt Stiftung (Germany), J. Bolyai Re-
search Scholarship, EFOP, HUN-REN ATOMKI, NK-
FIH, and OTKA (Hungary), Department of Atomic En-
ergy and Department of Science and Technology (In-
dia), Israel Science Foundation (Israel), Basic Science
Research and SRC(CENuM) Programs through NRF
funded by the Ministry of Education and the Ministry of
Science and ICT (Korea). Physics Department, Lahore
University of Management Sciences (Pakistan), Ministry
of Education and Science, Russian Academy of Sciences,
Federal Agency of Atomic Energy (Russia), VR and Wal-
lenberg Foundation (Sweden), University of Zambia, the
Government of the Republic of Zambia (Zambia), the
U.S. Civilian Research and Development Foundation for
the Independent States of the Former Soviet Union, the
Hungarian American Enterprise Scholarship Fund, the
US-Hungarian Fulbright Foundation, and the US-Israel
Binational Science Foundation.
[1] M. Connors, R. Nattrass, C. Reed, and S. Salur, Jet mea-
surements in heavy ion physics, Rev. Mod. Phys. 90,
025005 (2018).
[2] U. Acharya et al. (PHENIX Collaboration), Measure-
ment of jet-medium interactions via direct photon-
hadron correlations in Au+Au and d+Au collisions at
√sNN = 200 GeV, Phys. Rev. C 102, 054910 (2020).
[3] L. Adamczyk et al. (STAR Collaboration), Jet-like cor-
relations with direct-photon and neutral-pion triggers at
√sNN = 200 GeV, Phys. Lett. B 760, 689 (2016).
[4] J. Adam et al. (ALICE Collaboration), Measure-
ment of jet suppression in central Pb-Pb collisions at
√sNN=2.76 TeV, Phys. Lett. B 746, 1 (2015).
[5] G. Aad et al. (ATLAS Collaboration), Observation of
a Centrality-Dependent Dijet Asymmetry in Lead-Lead
Collisions at √sNN = 2.77 TeV with the ATLAS Detec-
tor at the LHC, Phys. Rev. Lett. 105, 252303 (2010).
[6] S. Chatrchyan et al. (CMS Collaboration), Observa-
tion and studies of jet quenching in PbPb collisions at
nucleon-nucleon center-of-mass energy = 2.76 TeV, Phys.
Rev. C 84, 024906 (2011).
[7] K. M. Burke, A. Buzzatti, N. Chang, C. Gale, M. Gyu-

12
lassy, U. Heinz, S. Jeon, A. Majumder, B. M¨uller, G.-Y.
Qin, B. Schenke, C. Shen, X.-N. Wang, J. Xu, C. Young,
and H. Zhang (JET Collaboration), Extracting the jet
transport coefficient from jet quenching in high-energy
heavy-ion collisions, Phys. Rev. C 90, 014909 (2014).
[8] Z. Yang, W. Chen, Y. He, W. Ke, L. Pang, and X.-
N. Wang, Search for the Elusive Jet-Induced Diffu-
sion Wake in Z/γ-Jets with 2D Jet Tomography in
High-Energy Heavy-Ion Collisions, Phys. Rev. Lett. 127,
082301 (2021).
[9] J. Casalderrey-Solana, D. C. Gulhan, J. G. Milhano,
D. Pablos, and K. Rajagopal, A Hybrid Strong/Weak
Coupling Approach to Jet Quenching, J, High Energy
Phys. 10, 019 (2014), [Erratum: J, High Energy Phys.
09 (2015), 175].
[10] A. Adare et al. (PHENIX Collaboration), Transition in
Yield and Azimuthal Shape Modification in Dihadron
Correlations in Relativistic Heavy Ion Collisions, Phys.
Rev. Lett. 104, 252301 (2010).
[11] M. Allen et al. (PHENIX Collaboration), PHENIX inner
detectors, Nucl. Instrum. Methods Phys. Res., Sec. A
499, 549 (2003).
[12] K. Adcox et al. (PHENIX Collaboration), PHENIX cen-
tral arm tracking detectors, Nucl. Instrum. Methods
Phys. Res., Sec. A 499, 489 (2003).
[13] A. Sickles, M. P. McCumber, and A. Adare, Extraction
of correlated jet pair signals in relativistic heavy ion col-
lisions, Phys. Rev. C 81, 014908 (2010).
[14] B. I. Abelev et al. (STAR Collaboration), System-Size
Independence of Directed Flow Measured at the BNL
Relativistic Heavy-Ion Collider, Phys. Rev. Lett. 101,
252301 (2008).
[15] L. Adamczyk et al. (STAR Collaboration), Beam-Energy
Dependence of the Directed Flow of Protons, Antipro-
tons, and Pions in Au+Au Collisions, Phys. Rev. Lett.
112, 162301 (2014).
[16] A. Adare et al. (PHENIX Collaboration), Measurement
of two–particle correlations with respect to second– and
third–order event planes in Au+Au collisions at √sNN =
200 GeV, Phys. Rev. C 99, 054903 (2019).
[17] A. Adare et al. (PHENIX Collaboration), Azimuthal
Anisotropy of π0Production in Au+Au Collisions at
√sNN = 200 GeV: Path-Length Dependence of Jet
Quenching and the Role of Initial Geometry, Phys. Rev.
Lett. 105, 142301 (2010).
[18] R. A. Lacey, A. Taranenko, N. N. Ajitanand, and J. M.
Alexander, Scaling of the higher-order flow harmonics:
implications for initial-eccentricity models and the ’vis-
cous horizon’ (2011), arXiv:1105.3782.
[19] J. Adam et al. (ALICE Collaboration), Jet-like correla-
tions with neutral pion triggers in pp and central Pb-Pb
collisions at 2.76 TeV, Phys. Lett. B 763, 238 (2016).
[20] G. Aad et al. (ATLAS Collaboration), Measurement of
angular and momentum distributions of charged particles
within and around jets in Pb+Pb and pp collisions at
√sNN = 5.02 TeV with the ATLAS detector, Phys. Rev.
C100, 064901 (2019).