Measurement of the inclusive phi cross-section in pp collisions at sqrt(s) = 7 TeV

Abstract

The cross-section for inclusive phi meson production in pp collisions at a
centre-of-mass energy of sqrt(s) = 7 TeV has been measured with the LHCb
detector at the Large Hadron Collider. The differential cross-section is
measured as a function of the phi transverse momentum p_T and rapidity y in the
region 0.6 < p_T < 5.0 GeV/c and 2.44 < y < 4.06. The cross-section for
inclusive phi production in this kinematic range is sigma(pp -> phi X) = 1758
pm 19(stat) ^{+43}_{-14}(syst) pm 182(scale) microbarn, where the first
systematic uncertainty depends on the p_T and y region and the second is
related to the overall scale. Predictions based on the Pythia 6.4 generator
underestimate the cross-section.

Full text

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arXiv:1107.3935v1 [hep-ex] 20 Jul 2011
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
LHCb-PAPER-2011-007, CERN-PH-EP-2011-106
(submitted to PLB)
July 21, 2011
Measurement of the inclusive φ
cross-section in pp collisions at
√s = 7TeV
The LHCb Collaboration1
Abstract
The cross-section for inclusive φ meson production in pp collisions at a centre-
of-mass energy of√s = 7TeV has been measured with the LHCb detector at
the Large Hadron Collider. The differential cross-section is measured as a func-
tion of the φ transverse momentum pT and rapidity y in the region 0.6 < pT <
5.0GeV/c and 2.44 < y < 4.06. The cross-section for inclusive φ production in
this kinematic range is σ(pp → φX) = 1758 ± 19(stat)+43
where the first systematic uncertainty depends on the pT and y region and the sec-
ond is related to the overall scale. Predictions based on the Pythia 6.4 generator
underestimate the cross-section.
−14(syst) ± 182(scale) µb,
1Authors are listed on the following pages.

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ii

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LHCb Collaboration
R. Aaij23, B. Adeva36, M. Adinolfi42, C. Adrover6, A. Affolder48, Z. Ajaltouni5,
J. Albrecht37, F. Alessio6,37, M. Alexander47, G. Alkhazov29, P. Alvarez Cartelle36,
A.A. Alves Jr22, S. Amato2, Y. Amhis38, J. Anderson39, R.B. Appleby50,
O. Aquines Gutierrez10, L. Arrabito53, A. Artamonov34, M. Artuso52,37, E. Aslanides6,
G. Auriemma22,m, S. Bachmann11, J.J. Back44, D.S. Bailey50, V. Balagura30,37,
W. Baldini16, R.J. Barlow50, C. Barschel37, S. Barsuk7, W. Barter43, A. Bates47,
C. Bauer10, Th. Bauer23, A. Bay38, I. Bediaga1, K. Belous34, I. Belyaev30,37,
E. Ben-Haim8, M. Benayoun8, G. Bencivenni18, S. Benson46, J. Benton42, R. Bernet39,
M.-O. Bettler17,37, M. van Beuzekom23, A. Bien11, S. Bifani12, A. Bizzeti17,h,
P.M. Bjørnstad50, T. Blake49, F. Blanc38, C. Blanks49, J. Blouw11, S. Blusk52,
A. Bobrov33, V. Bocci22, A. Bondar33, N. Bondar29, W. Bonivento15, S. Borghi47,
A. Borgia52, T.J.V. Bowcock48, C. Bozzi16, T. Brambach9, J. van den Brand24,
J. Bressieux38, D. Brett50, S. Brisbane51, M. Britsch10, T. Britton52, N.H. Brook42,
A. B¨ uchler-Germann39, A. Bursche39, J. Buytaert37, S. Cadeddu15,
J.M. Caicedo Carvajal37, O. Callot7, M. Calvi20,j, M. Calvo Gomez35,n, A. Camboni35,
P. Campana18,37, A. Carbone14, G. Carboni21,k, R. Cardinale19,i, A. Cardini15,
L. Carson36, K. Carvalho Akiba23, G. Casse48, M. Cattaneo37, M. Charles51,
Ph. Charpentier37, N. Chiapolini39, X. Cid Vidal36, P.E.L. Clarke46, M. Clemencic37,
H.V. Cliff43, J. Closier37, C. Coca28, V. Coco23, J. Cogan6, P. Collins37, F. Constantin28,
G. Conti38, A. Contu51, A. Cook42, M. Coombes42, G. Corti37, G.A. Cowan38,
R. Currie46, B. D’Almagne7, C. D’Ambrosio37, P. David8, I. De Bonis4, S. De Capua21,k,
M. De Cian39, F. De Lorenzi12, J.M. De Miranda1, L. De Paula2, P. De Simone18,
D. Decamp4, M. Deckenhoff9, H. Degaudenzi38,37, M. Deissenroth11, L. Del Buono8,
C. Deplano15, O. Deschamps5, F. Dettori15,d, J. Dickens43, H. Dijkstra37,
P. Diniz Batista1, D. Dossett44, A. Dovbnya40, F. Dupertuis38, R. Dzhelyadin34,
C. Eames49, S. Easo45, U. Egede49, V. Egorychev30, S. Eidelman33, D. van Eijk23,
F. Eisele11, S. Eisenhardt46, R. Ekelhof9, L. Eklund47, Ch. Elsasser39,
D.G. d’Enterria35,o, D. Esperante Pereira36, L. Est` eve43, A. Falabella16,e, E. Fanchini20,j,
C. F¨ arber11, G. Fardell46, C. Farinelli23, S. Farry12, V. Fave38, V. Fernandez Albor36,
M. Ferro-Luzzi37, S. Filippov32, C. Fitzpatrick46, M. Fontana10, F. Fontanelli19,i,
R. Forty37, M. Frank37, C. Frei37, M. Frosini17,f,37, S. Furcas20, A. Gallas Torreira36,
D. Galli14,c, M. Gandelman2, P. Gandini51, Y. Gao3, J-C. Garnier37, J. Garofoli52,
J. Garra Tico43, L. Garrido35, C. Gaspar37, N. Gauvin38, M. Gersabeck37, T. Gershon44,
Ph. Ghez4, V. Gibson43, V.V. Gligorov37, C. G¨ obel54, D. Golubkov30, A. Golutvin49,30,37,
A. Gomes2, H. Gordon51, M. Grabalosa G´ andara35, R. Graciani Diaz35,
L.A. Granado Cardoso37, E. Graug´ es35, G. Graziani17, A. Grecu28, S. Gregson43,
B. Gui52, E. Gushchin32, Yu. Guz34, T. Gys37, G. Haefeli38, C. Haen37, S.C. Haines43,
T. Hampson42, S. Hansmann-Menzemer11, R. Harji49, N. Harnew51, J. Harrison50,
P.F. Harrison44, J. He7, V. Heijne23, K. Hennessy48, P. Henrard5,
J.A. Hernando Morata36, E. van Herwijnen37, W. Hofmann10, K. Holubyev11,
P. Hopchev4, W. Hulsbergen23, P. Hunt51, T. Huse48, R.S. Huston12, D. Hutchcroft48,
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D. Hynds47, V. Iakovenko41, P. Ilten12, J. Imong42, R. Jacobsson37, A. Jaeger11,
M. Jahjah Hussein5, E. Jans23, F. Jansen23, P. Jaton38, B. Jean-Marie7, F. Jing3,
M. John51, D. Johnson51, C.R. Jones43, B. Jost37, S. Kandybei40, M. Karacson37,
T.M. Karbach9, J. Keaveney12, U. Kerzel37, T. Ketel24, A. Keune38, B. Khanji6,
Y.M. Kim46, M. Knecht38, S. Koblitz37, P. Koppenburg23, A. Kozlinskiy23,
L. Kravchuk32, K. Kreplin11, G. Krocker11, P. Krokovny11, F. Kruse9, K. Kruzelecki37,
M. Kucharczyk20,25, S. Kukulak25, R. Kumar14,37, T. Kvaratskheliya30,37, V.N. La Thi38,
D. Lacarrere37, G. Lafferty50, A. Lai15, D. Lambert46, R.W. Lambert37, E. Lanciotti37,
G. Lanfranchi18, C. Langenbruch11, T. Latham44, R. Le Gac6, J. van Leerdam23,
J.-P. Lees4, R. Lef` evre5, A. Leflat31,37, J. Lefranccois7, O. Leroy6, T. Lesiak25, L. Li3,
Y.Y. Li43, L. Li Gioi5, M. Lieng9, R. Lindner37, C. Linn11, B. Liu3, G. Liu37,
J.H. Lopes2, E. Lopez Asamar35, N. Lopez-March38, J. Luisier38, F. Machefert7,
I.V. Machikhiliyan4,30, F. Maciuc10, O. Maev29,37, J. Magnin1, S. Malde51,
R.M.D. Mamunur37, G. Manca15,d, G. Mancinelli6, N. Mangiafave43, U. Marconi14,
R. M¨ arki38, J. Marks11, G. Martellotti22, A. Martens7, L. Martin51, A. Mart´ ın S´ anchez7,
D. Martinez Santos37, A. Massafferri1, Z. Mathe12, C. Matteuzzi20, M. Matveev29,
E. Maurice6, B. Maynard52, A. Mazurov32,16,37, G. McGregor50, R. McNulty12,
C. Mclean14, M. Meissner11, M. Merk23, J. Merkel9, R. Messi21,k, S. Miglioranzi37,
D.A. Milanes13,37, M.-N. Minard4, S. Monteil5, D. Moran12, P. Morawski25,
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I. Nasteva1, M. Nedos9, M. Needham46, N. Neufeld37, C. Nguyen-Mau38,p, M. Nicol7,
S. Nies9, V. Niess5, N. Nikitin31, A. Oblakowska-Mucha26, V. Obraztsov34, S. Oggero23,
S. Ogilvy47, O. Okhrimenko41, R. Oldeman15,d, M. Orlandea28, J.M. Otalora Goicochea2,
B. Pal52, J. Palacios39, M. Palutan18, J. Panman37, A. Papanestis45, M. Pappagallo13,b,
C. Parkes47,37, C.J. Parkinson49, G. Passaleva17, G.D. Patel48, M. Patel49,
S.K. Paterson49, G.N. Patrick45, C. Patrignani19,i, C. Pavel-Nicorescu28,
A. Pazos Alvarez36, A. Pellegrino23, G. Penso22,l, M. Pepe Altarelli37, S. Perazzini14,c,
D.L. Perego20,j, E. Perez Trigo36, A. P´ erez-Calero Yzquierdo35, P. Perret5,
M. Perrin-Terrin6, G. Pessina20, A. Petrella16,37, A. Petrolini19,i, B. Pie Valls35,
B. Pietrzyk4, T. Pilar44, D. Pinci22, R. Plackett47, S. Playfer46, M. Plo Casasus36,
G. Polok25, A. Poluektov44,33, E. Polycarpo2, D. Popov10, B. Popovici28, C. Potterat35,
A. Powell51, T. du Pree23, J. Prisciandaro38, V. Pugatch41, A. Puig Navarro35,
W. Qian52, J.H. Rademacker42, B. Rakotomiaramanana38, I. Raniuk40, G. Raven24,
S. Redford51, M.M. Reid44, A.C. dos Reis1, S. Ricciardi45, K. Rinnert48,
D.A. Roa Romero5, P. Robbe7, E. Rodrigues47, F. Rodrigues2, P. Rodriguez Perez36,
G.J. Rogers43, V. Romanovsky34, J. Rouvinet38, T. Ruf37, H. Ruiz35, G. Sabatino21,k,
J.J. Saborido Silva36, N. Sagidova29, P. Sail47, B. Saitta15,d, C. Salzmann39,
M. Sannino19,i, R. Santacesaria22, R. Santinelli37, E. Santovetti21,k, M. Sapunov6,
A. Sarti18,l, C. Satriano22,m, A. Satta21, M. Savrie16,e, D. Savrina30, P. Schaack49,
M. Schiller11, S. Schleich9, M. Schmelling10, B. Schmidt37, O. Schneider38, A. Schopper37,
M.-H. Schune7, R. Schwemmer37, A. Sciubba18,l, M. Seco36, A. Semennikov30,
K. Senderowska26, N. Serra39, J. Serrano6, P. Seyfert11, B. Shao3, M. Shapkin34,
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I. Shapoval40,37, P. Shatalov30, Y. Shcheglov29, T. Shears48, L. Shekhtman33,
O. Shevchenko40, V. Shevchenko30, A. Shires49, R. Silva Coutinho54, H.P. Skottowe43,
T. Skwarnicki52, A.C. Smith37, N.A. Smith48, K. Sobczak5, F.J.P. Soler47, A. Solomin42,
F. Soomro49, B. Souza De Paula2, B. Spaan9, A. Sparkes46, P. Spradlin47, F. Stagni37,
S. Stahl11, O. Steinkamp39, S. Stoica28, S. Stone52,37, B. Storaci23, U. Straumann39,
N. Styles46, S. Swientek9, M. Szczekowski27, P. Szczypka38, T. Szumlak26,
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J. van Tilburg11, V. Tisserand4, M. Tobin39, S. Topp-Joergensen51, M.T. Tran38,
A. Tsaregorodtsev6, N. Tuning23, A. Ukleja27, P. Urquijo52, U. Uwer11, V. Vagnoni14,
G. Valenti14, R. Vazquez Gomez35, P. Vazquez Regueiro36, S. Vecchi16, J.J. Velthuis42,
M. Veltri17,g, K. Vervink37, B. Viaud7, I. Videau7, X. Vilasis-Cardona35,n, J. Visniakov36,
A. Vollhardt39, D. Voong42, A. Vorobyev29, H. Voss10, K. Wacker9, S. Wandernoth11,
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F. Xing51, Z. Yang3, R. Young46, O. Yushchenko34, M. Zavertyaev10,a, L. Zhang52,
W.C. Zhang12, Y. Zhang3, A. Zhelezov11, L. Zhong3, E. Zverev31, A. Zvyagin37.
1Centro Brasileiro de Pesquisas F´ ısicas (CBPF), Rio de Janeiro, Brazil
2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3Center for High Energy Physics, Tsinghua University, Beijing, China
4LAPP, Universit´ e de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France
5Clermont Universit´ e, Universit´ e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France
6CPPM, Aix-Marseille Universit´ e, CNRS/IN2P3, Marseille, France
7LAL, Universit´ e Paris-Sud, CNRS/IN2P3, Orsay, France
8LPNHE, Universit´ e Pierre et Marie Curie, Universit´ e Paris Diderot, CNRS/IN2P3, Paris, France
9Fakult¨ at Physik, Technische Universit¨ at Dortmund, Dortmund, Germany
10Max-Planck-Institut f¨ ur Kernphysik (MPIK), Heidelberg, Germany
11Physikalisches Institut, Ruprecht-Karls-Universit¨ at Heidelberg, Heidelberg, Germany
12School of Physics, University College Dublin, Dublin, Ireland
13Sezione INFN di Bari, Bari, Italy
14Sezione INFN di Bologna, Bologna, Italy
15Sezione INFN di Cagliari, Cagliari, Italy
16Sezione INFN di Ferrara, Ferrara, Italy
17Sezione INFN di Firenze, Firenze, Italy
18Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy
19Sezione INFN di Genova, Genova, Italy
20Sezione INFN di Milano Bicocca, Milano, Italy
21Sezione INFN di Roma Tor Vergata, Roma, Italy
22Sezione INFN di Roma La Sapienza, Roma, Italy
23Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands
24Nikhef National Institute for Subatomic Physics and Vrije Universiteit, Amsterdam, Netherlands
25Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Cracow, Poland
26Faculty of Physics & Applied Computer Science, Cracow, Poland
27Soltan Institute for Nuclear Studies, Warsaw, Poland
28Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania
29Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
30Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
31Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia
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32Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia
33Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia
34Institute for High Energy Physics (IHEP), Protvino, Russia
35Universitat de Barcelona, Barcelona, Spain
36Universidad de Santiago de Compostela, Santiago de Compostela, Spain
37European Organization for Nuclear Research (CERN), Geneva, Switzerland
38Ecole Polytechnique F´ ed´ erale de Lausanne (EPFL), Lausanne, Switzerland
39Physik-Institut, Universit¨ at Z¨ urich, Z¨ urich, Switzerland
40NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
41Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine
42H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom
43Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
44Department of Physics, University of Warwick, Coventry, United Kingdom
45STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
46School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
47School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom
48Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
49Imperial College London, London, United Kingdom
50School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom
51Department of Physics, University of Oxford, Oxford, United Kingdom
52Syracuse University, Syracuse, NY, United States
53CC-IN2P3, CNRS/IN2P3, Lyon-Villeurbanne, France, associated member
54Pontif´ ıcia Universidade Cat´ olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to2
aP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia
bUniversit` a di Bari, Bari, Italy
cUniversit` a di Bologna, Bologna, Italy
dUniversit` a di Cagliari, Cagliari, Italy
eUniversit` a di Ferrara, Ferrara, Italy
fUniversit` a di Firenze, Firenze, Italy
gUniversit` a di Urbino, Urbino, Italy
hUniversit` a di Modena e Reggio Emilia, Modena, Italy
iUniversit` a di Genova, Genova, Italy
jUniversit` a di Milano Bicocca, Milano, Italy
kUniversit` a di Roma Tor Vergata, Roma, Italy
lUniversit` a di Roma La Sapienza, Roma, Italy
mUniversit` a della Basilicata, Potenza, Italy
nLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
oInstituci´ o Catalana de Recerca i Estudis Avanccats (ICREA), Barcelona, Spain
pHanoi University of Science, Hanoi, Viet Nam
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1 Introduction
Two specific regimes can be distinguished in hadron production in pp collisions: the so
called hard regime at high transverse momenta, which can be described by perturba-
tive QCD; and the soft regime, which is described by phenomenological models. The
underlying event in pp processes falls into the second category. Therefore soft QCD inter-
actions need careful study to enable tuning of the models at a new centre-of-mass energy.
Strangeness production is an important ingredient of this effort. Measurements of φ pro-
duction have been reported by various experiments [1–7] in different collision types, for
different centre-of-mass energies and different kinematic coverage. LHCb is fully instru-
mented in the forward region and thus yields unique results complementary to previous
experiments and to the other LHC experiments.
A measurement of the inclusive differential φ cross-section in pp collisions at
√s = 7TeV is presented in this paper. The analysis uses as kinematic variables the φ
meson transverse momentum pT and the rapidity y =1
in the pp centre-of-mass system2. φ mesons are reconstructed using the K+K−decay
mode and thus the selection relies strongly on LHCb’s RICH (Ring Imaging Cherenkov)
detectors for particle identification (PID) purposes. Their performance is determined
from data with a tag-and-probe approach. The measured cross-section is compared to
two different Monte Carlo (MC) predictions based on Pythia 6.4 [8].
2ln[(E + pz)/(E − pz)] measured
2LHCb detector and data set
Designed for precise measurements of B meson decays, the LHCb detector is a forward
spectrometer with a polar angle coverage with respect to the beam line of approximately
15 to 300 mrad in the horizontal bending plane, and 15 to 250 mrad in the vertical non-
bending plane. The tracking system consists of the Vertex Locator (VELO) surrounding
the pp interaction region, a tracking station upstream of the dipole magnet, and three
tracking stations downstream of the magnet.
Particles travelling from the interaction region to the downstream tracking stations
are deflected by a dipole field of around 4Tm, whose polarity can be switched. For this
study, roughly the same amount of data was taken with both magnet polarities.
The detector has a dedicated PID system that includes two Ring Imaging Cherenkov
detectors. RICH1 is installed in front of the magnet and uses two radiators (Aerogel and
C4F10), and RICH2 is installed beyond the magnet, with a CF4radiator. Combining all
radiators, the RICH system provides pion-kaon separation in a momentum range up to
100GeV/c. Downstream of the tracking stations the detector has a calorimeter system,
consisting of the Scintillating Pad Detector (SPD), a preshower, the electromagnetic and
the hadronic calorimeter, and five muon stations. Details of the LHCb detector can be
found in Ref. [9].
2The detector reference frame is a right handed coordinate system with +z pointing downstream from
the interaction point in the direction of the spectrometer and the +y axis pointing upwards.
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The study described in this note is based on an integrated luminosity of 14.7nb−1of
pp collisions collected in May 2010, where the instantaneous luminosity was low.
The trigger system consists of a hardware based first level trigger and a high level
trigger (HLT) implemented in software. The first level trigger was in pass-through mode,
whereas at least one track, reconstructed with VELO information, was required to be
found by the HLT. On Monte Carlo simulated events, this trigger configuration is found
to be 100% efficient for reconstructed φ candidates. However, to limit the acquisition
rate, a prescaling was applied.
The luminosity was measured by two van der Meer scans [10] and a novel method mea-
suring the beam geometry with the VELO, as described in Ref. [11]. Both methods rely
on the measurement of the beam currents as well as the beam profile determination. Us-
ing these results, the absolute luminosity scale is determined, using the method described
in Ref. [12], with a 3.5% uncertainty, dominated by the knowledge of the beam currents.
The instantaneous luminosity determination is then based on a continuous recording of
the hit rate in the SPD, which has been normalized to the absolute luminosity scale. The
probability for multiple pp collisions per bunch-crossing was negligibly low in the data
taking period considered here.
As the RICH detectors are calibrated separately for the two magnet polarities, the
measurement is carried out separately for each sample before combining them for the
final result.
Trigger and reconstruction efficiencies are determined using a sample of 1.25 · 108
simulated minimum bias events. These have been produced in the LHCb MC setting,
which is based on a custom Pythia tune for the description of pp collisions, while particle
decays are generally handled by EvtGen [13]. The total minimum bias cross-section
in LHCb MC simulation is 91.05mb, composed of the following Pythia process types:
48.80mb inelastic-non-diffractive, 2×6.84mb single diffractive, 9.19mb double diffractive
and 19.28mb elastic. Details on the LHCb MC setting can be found in Ref. [14].
3 Data selection and efficiencies
Two oppositely charged tracks, each of which are required to have hits in both the VELO
and the main tracking system, are combined to form φ → K+K−candidates. The RICH
system provides kaon-pion separation for reconstructed tracks, which is crucial for the
inclusive φ production analysis. As a first step, at least one kaon is required to pass a
tight cut based on the RICH response during the selection. In a second step, both kaons
have to pass this criterion. The samples of φ candidates passing the cuts of the first and
second steps are referred to as “tag” and “probe” samples, respectively. They are used to
measure the PID efficiency in the selection as explained below. The reconstructed K+K−
mass is required to be between 995MeV/c2and 1045MeV/c2in both samples.
No cut designed to discriminate prompt and non-prompt φ mesons is applied in the
selection, so the measurement includes both. However, due to the high minimum bias
cross-section compared to charm or beauty production, the non-prompt contribution is
2

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small; in MC simulation it is found to be 1.6%.
The region of interest 0.6 < pT< 5.0GeV/c and 2.44 < y < 4.06 is divided into 9 bins
in y and 12 bins in pT. The differential cross-section per bin in pT and y is determined
by the equation:
d2σ
dy dpT
=
1
∆y ∆pT
·
Ntag
L · εreco· εpid· B(φ → K+K−), (1)
where Ntag is the number of reconstructed φ candidates in the tag sample, L the inte-
grated luminosity and B(φ → K+K−) = (49.2±0.6)% the branching fraction taken from
Ref. [15]. The selection efficiency is split up into two parts in Eq. 1: reconstruction εreco,
including the geometrical acceptance, and the PID efficiency εpid. Both efficiencies are a
function of the pT and y values of the φ meson and thus determined separately for each
bin.
In the centre of the kinematic region, the reconstruction efficiency is of the order of
65-70%. It drops to 30-40% with low transverse momenta and high or low rapidity values.
The PID efficiency is above 95% in the centre of the kinematic region and drops to 60-70%
at the edges of the considered kinematic region.
The reconstruction efficiency is determined from simulation. To limit the MC depen-
dence, the PID efficiency is determined from data using the tag-and-probe method: in
the φ selection, at least one of the two kaons is required to pass the PID criterion. The
number of φ candidates passing this requirement is given by Ntag. In a subsequent step,
both kaons must pass the PID criterion. The number of φ candidates passing this step is
given by Nprobe. The efficiency εpidthat at least one of the two kaons from a φ candidate
fulfils the kaon PID requirement for each bin is thus given by:
εpid= 1 −
?Ntag− Nprobe
Ntag+ Nprobe
?2
. (2)
This formula is valid only if the efficiencies that the two kaons satisfy the requirements
are independent. However, owing to the variation of the RICH efficiency with track
multiplicity, correlations between the values of the discriminant variable of the RICH are
observed and are accounted for in the systematic uncertainty.
4 Signal extraction
Simultaneous maximum likelihood fits to the φ candidate mass distributions on the tag
and the probe samples are performed in each bin of pTand y to extract the signal yields.
The number of reconstructed candidates without PID requirements Nreco = Ntag/εpid
is a free parameter in the fit. A Breit-Wigner distribution convolved with a Gaussian
resolution function is used to describe the signal shape
fsig=
1
(m − m0)2+1
4Γ2/c4⊗ exp
?
−1
2
m′2
σ2
?
(3)
3

Page 10

))
22
) (MeV/c) (MeV/c
--
KK
++
m(Km(K
1000 1000 10101010 1020 1020103010301040 1040
)
2
candidates / ( 1 MeV/c
00
500 500
10001000
1500 1500
20002000
2500 2500
3000 3000
35003500
40004000
45004500
)
2
candidates / ( 1 MeV/c
= 7 TeV s
= 7 TeV s
LHCbLHCb
))
22
) (MeV/c ) (MeV/c
--
KK
++
m(K m(K
10001000 10101010 10201020 103010301040 1040
)
2
candidates / ( 1 MeV/c
00
20 20
4040
6060
80 80
100100
120120
140140
160 160
180 180
200 200
220220
240 240
)
2
candidates / ( 1 MeV/c
= 7 TeV s
= 7 TeV s
LHCbLHCb
Figure 1: Fit to the tag (left) and the probe (right) sample in the bin 0.6 < pT< 0.8GeV/c,
3.34 < y < 3.52 for one of the two magnet polarities. Shown are the data points, the fit
result (thick solid line) as well as the signal (thin solid line) and the background component
(dash-dotted line).
while the background shape is described by
fbkg= 1 − exp(c1· (m − c2)) (4)
containing two free parameters.
The fitted φ mass and the Gaussian width σ are common parameters for both tag
and probe sample, while the Breit-Wigner width Γ is fixed to the value 4.26 MeV taken
from Ref. [15]. In Fig. 1, fit results to the two samples in a given pT/y bin are shown for
illustration purposes.
5 Systematic uncertainties
The uncertainties in this analysis are dominated by systematic contributions, divided into
the ones which are common to all bins and the ones which vary from bin to bin. The former
are summarized in Table 1, whereas the latter are plotted with the data in Figure 2 and
listed in Table 2. The bin-dependent uncertainties consist of the reconstruction efficiency
uncertainty due to the limited simulation sample size and to the modelling of a diffractive
contribution, as well as the uncertainty of the tag-and-probe PID determination due to
correlations. The combined uncertainties contribute 3–7% for the statistically dominant
bins.
The largest shared systematics are the uncertainty on the tracking efficiencies, which
have been discussed in Ref. [16], and the luminosity normalization. The track multiplicity
in data is higher than in the simulation. Studies of the track multiplicity dependence of the
reconstruction efficiency result in an uncertainty of 3% due to this multiplicity difference.
4

Page 11

Table 1: Summary of relative systematic uncertainties that are common to all bins.
Source
Tracking efficiency
Luminosity (normalization)
Track multiplicity
Fit systematics
MC association
Doubly identified candidates
Branching fraction
Bin migration
Material interactions
Total
(%)
8
4
3
3
2
2
1
1
1
10
Two major effects contribute to the uncertainty due to the fit procedure. Fixing
the Gaussian width to the same value on tag-and-probe sample introduces only a 1%
systematic uncertainty, since the distribution is dominated by the Breit-Wigner width. A
larger systematic effect (2-3%) is observed when varying the mass range of the fit, which
results in a total uncertainty of 3%.
In the simulation, the reconstructed track is required to match the true generated
track to determine the reconstruction efficiency. A 2% uncertainty is assigned due to this
procedure. A small fraction of doubly identified candidates is found: it is possible that
the detector hits from one particle are reconstructed as more than one track. The rate
difference of these doubly identified candidates between data and simulation is found to
be 2%, which is the systematic uncertainty assigned due to this effect. The φ → K+K−
branching fraction contributes a 1% systematic uncertainty.
between different bins due to resolution effects is found to be small, and is accounted for
by assigning a 1% uncertainty. Uncertainties from the modelling of the material budget
and the material interaction cross-section are estimated to be 1%.
Migration of candidates
6 Results
The cross-sections determined with the two magnet polarities agree within their statistical
uncertainties. All results given here are unweighted averages of the two samples. Com-
parisons to simulation samples generated with two different Pythia tunings are made,
namely Perugia 0 [17] and the LHCb default Monte Carlo tuning.
The integrated cross-section in the region 0.6 < pT < 5.0GeV/c and 2.44 < y < 4.06
is
σ(pp → φX) = 1758 ± 19(stat)+43
where the first systematic uncertainty arises from the bin-dependent contribution, while
the second one is the common systematic uncertainty, as described in Section 5. The
−14(syst) ± 182(scale)µb,
5

Page 12

differential cross-section values are given in Table 2 and projections on the y and pTaxes
within the same kinematic region are shown in Figure 2.
The simulations underestimate the measured φ production in the considered kinematic
region by a factor 1.43±0.15 (LHCb MC) and 2.06±0.22 (Perugia 0). Additionally, the
shape of the pTspectrum and the slope in the y spectrum differ between the data and the
simulation (see Fig. 2). Fitting a straight linedσ
is a = −44 ± 27µb on data, but a = −181 ± 2µb for the default LHCb MC tuning and
a = −149 ± 3µb for the Perugia 0 tuning. Uncertainties given on a are statistical only.
The mean pTin the range 0.6 < pT< 5.0GeV/c is 1.24±0.01GeV/c (data, stat. error
only), 1.077GeV/c (LHCb MC) and 1.238GeV/c (Perugia 0 MC).
dy= a · y + b to the y spectrum, the slope
7 Conclusions
A study of inclusive φ production in pp collisions at a centre-of-mass energy of 7TeV
at the Large Hadron Collider is reported. The differential cross-section as a function
of pT and y measured in the range 0.6 < pT < 5.0GeV/c and 2.44 < y < 4.06 is
σ(pp → φX) = 1758 ± 19(stat)+43
certainty depends on the pT and y scale and the second is related to the overall scale.
Predictions based on the Pythia 6.4 generator underestimate the cross-section.
−14(syst) ± 182(scale)µb, where the first systematic un-
Acknowledgements
We express our gratitude to our colleagues in the CERN accelerator departments for
the excellent performance of the LHC. We thank the technical and administrative staff at
CERN and at the LHCb institutes, and acknowledge support from the National Agencies:
CAPES, CNPq, FAPERJ and FINEP (Brazil); CERN; NSFC (China); CNRS/IN2P3
(France); BMBF, DFG, HGF and MPG (Germany); SFI (Ireland); INFN (Italy); FOM
and NWO (Netherlands); SCSR (Poland); ANCS (Romania); MinES of Russia and
Rosatom (Russia); MICINN, XUNGAL and GENCAT (Spain); SNSF and SER (Switzer-
land); NAS Ukraine (Ukraine); STFC (United Kingdom); NSF (USA). We also acknowl-
edge the support received from the ERC under FP7 and the R´ egion Auvergne.
6

Page 13

Table 2: Binned differential cross-section, in µb/MeV/c, as function of pT (GeV/c) and
y. The statistical and the bin-dependent systematic uncertainties are quoted. There is
an additional bin-independent uncertainty of 10% related to the normalization (Table 1).
pT/ y
0.6-0.8
0.8-1.0
1.0-1.2
1.2-1.4
1.4-1.6
1.6-1.8
1.8-2.0
2.0-2.4
2.4-2.8
2.8-3.2
3.2-4.0
4.0-5.0
2.44-2.622.62-2.802.80-2.98
1.001 ± 0.140+0.076
0.959 ± 0.112+0.129
0.758 ± 0.043+0.089
0.648 ± 0.033+0.067
0.469 ± 0.023+0.037
0.422 ± 0.020+0.039
0.334 ± 0.016+0.027
0.209 ± 0.008+0.010
0.127 ± 0.005+0.003
0.078 ± 0.004+0.002
0.040 ± 0.002+0.001
0.014 ± 0.001+0.001
2.98-3.16
1.171 ± 0.100+0.058
1.032 ± 0.080+0.049
0.818 ± 0.034+0.031
0.648 ± 0.026+0.016
0.484 ± 0.019+0.013
0.408 ± 0.016+0.008
0.320 ± 0.014+0.006
0.206 ± 0.006+0.004
0.109 ± 0.004+0.003
0.065 ± 0.003+0.002
0.031 ± 0.001+0.001
0.010 ± 0.001+0.001
3.52-3.70
1.341 ± 0.158+0.034
0.816 ± 0.075+0.013
0.785 ± 0.032+0.010
0.609 ± 0.023+0.012
0.484 ± 0.018+0.016
0.336 ± 0.013+0.008
0.231 ± 0.010+0.006
0.164 ± 0.005+0.007
0.082 ± 0.002+0.004
0.059 ± 0.003+0.004
0.022 ± 0.001+0.001
0.008 ± 0.001+0.001
−0.026
0.853 ± 0.114+0.081
0.797 ± 0.084+0.074
0.776 ± 0.038+0.063
0.627 ± 0.028+0.049
0.511 ± 0.022+0.033
0.381 ± 0.017+0.021
0.323 ± 0.015+0.014
0.192 ± 0.007+0.006
0.112 ± 0.005+0.002
0.069 ± 0.003+0.002
0.038 ± 0.002+0.001
0.014 ± 0.001+0.001
3.16-3.34
1.060 ± 0.092+0.027
0.862 ± 0.080+0.014
0.851 ± 0.033+0.010
0.693 ± 0.026+0.009
0.499 ± 0.018+0.009
0.382 ± 0.015+0.008
0.308 ± 0.008+0.009
0.194 ± 0.006+0.006
0.106 ± 0.004+0.003
0.057 ± 0.003+0.002
0.029 ± 0.001+0.001
0.010 ± 0.001+0.000
3.70-3.88
1.164 ± 0.157+0.030
1.065 ± 0.075+0.018
0.690 ± 0.031+0.010
0.561 ± 0.022+0.010
0.433 ± 0.017+0.011
0.315 ± 0.014+0.011
0.228 ± 0.011+0.009
0.140 ± 0.005+0.006
0.078 ± 0.004+0.003
0.049 ± 0.003+0.002
0.019 ± 0.001+0.002
0.007 ± 0.001+0.001
−0.022
1.069 ± 0.108+0.093
0.819 ± 0.079+0.053
0.795 ± 0.026+0.042
0.604 ± 0.026+0.024
0.521 ± 0.022+0.023
0.409 ± 0.018+0.015
0.276 ± 0.012+0.009
0.201 ± 0.007+0.003
0.111 ± 0.004+0.002
0.063 ± 0.003+0.002
0.034 ± 0.001+0.001
0.011 ± 0.001+0.000
3.34-3.52
1.131 ± 0.146+0.029
1.170 ± 0.082+0.018
0.781 ± 0.031+0.009
0.661 ± 0.023+0.011
0.470 ± 0.017+0.013
0.348 ± 0.013+0.009
0.255 ± 0.010+0.009
0.169 ± 0.005+0.005
0.106 ± 0.004+0.005
0.053 ± 0.003+0.003
0.025 ± 0.002+0.001
0.009 ± 0.001+0.000
3.88-4.06
1.341 ± 0.193+0.120
0.975 ± 0.115+0.018
0.760 ± 0.039+0.013
0.531 ± 0.027+0.012
0.409 ± 0.021+0.016
0.279 ± 0.014+0.011
0.213 ± 0.011+0.007
0.131 ± 0.006+0.003
0.070 ± 0.004+0.004
0.039 ± 0.003+0.006
0.022 ± 0.002+0.003
0.007 ± 0.002+0.000
−0.027
−0.015
−0.012
−0.012
−0.009
−0.009
−0.009
−0.009
−0.008
−0.008
−0.008
−0.008
−0.008
−0.008
−0.007
−0.007
−0.007
−0.007
−0.005
−0.004
−0.003
−0.003
−0.003
−0.003
−0.002
−0.002
−0.002
−0.002
−0.001
−0.001
−0.001
−0.001
−0.000
−0.000
pT/ y
0.6-0.8
0.8-1.0
1.0-1.2
1.2-1.4
1.4-1.6
1.6-1.8
1.8-2.0
2.0-2.4
2.4-2.8
2.8-3.2
3.2-4.0
4.0-5.0
−0.029
−0.043
−0.176
−0.015
−0.013
−0.058
−0.009
−0.010
−0.009
−0.008
−0.008
−0.008
−0.006
−0.007
−0.006
−0.007
−0.006
−0.005
−0.007
−0.006
−0.004
−0.004
−0.003
−0.003
−0.002
−0.002
−0.002
−0.002
−0.001
−0.001
−0.001
−0.001
−0.001
−0.000
−0.000
−0.000
pT/ y
0.6-0.8
0.8-1.0
1.0-1.2
1.2-1.4
1.4-1.6
1.6-1.8
1.8-2.0
2.0-2.4
2.4-2.8
2.8-3.2
3.2-4.0
4.0-5.0
−0.207
−0.065
−0.036
−0.035
−0.059
−0.070
−0.012
−0.011
−0.039
−0.008
−0.008
−0.010
−0.007
−0.007
−0.008
−0.006
−0.006
−0.006
−0.004
−0.005
−0.005
−0.003
−0.002
−0.003
−0.002
−0.002
−0.002
−0.002
−0.001
−0.001
−0.001
−0.000
−0.001
−0.000
−0.000
−0.002
7

Page 14

01000 20003000 40005000
b/(MeV/c))
µ
(
/dp
σ
d
T
-2
10
-1
10
1
LHCb Data
LHCb MC
Perugia 0 MC
) (MeV/c)
φ (
T
p
0 10002000 300040005000
Ratio
1
2
3
2.44 < y < 4.06
= 7 TeV s
LHCb
2 2.53 3.54 4.5
b)
µ
/dy (
σ
d
0
3
200
400
600
800
1000
1200
1400
LHCb Data
LHCb MC
Perugia 0 MC
) φ
y(
2 2.53 3.54 4.5
Ratio
1
2
< 5.0 GeV/c
T
0.6 < p
= 7 TeV s
LHCb
Figure 2: Inclusive differential φ production cross-section as a function of pT(top) and y
(bottom), measured with data (points), and compared to the LHCb default MC tuning
(solid line) and Perugia 0 tuning (dashed line). The error bars represent the statistical
uncertainty, the braces show the bin dependent systematic errors, the overall scale un-
certainty from Table 1 is not plotted. The lower parts of the plots show the ratio data
cross-section over Monte Carlo cross-section. Error bars in the ratio plots show statistical
uncertainties only.
8

Page 15

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9