Measurement of D ^sup ^ photoproduction at three different centre-of-mass energies at HERA

Abstract

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image)

Abstract

The photoproduction of D ^sup ±^ mesons has been measured with the ZEUS detector at HERA at three different ep centre-of-mass energies, ......, of 318, 251 and 225 GeV. For each data set, D ^sup ±^ mesons were required to have transverse momentum, p ^sub T^^sup D^, and pseudo-rapidity, [eta] ^sup D^, in the ranges 1.9 < p ^sub T^^sup D^ < 20 GeV and |[eta] ^sup D^| < 1.6. The events were required to have a virtuality of the incoming photon, Q ^sup 2^, of less than 1 GeV^sup 2^. The dependence on ...... was studied by normalising to the high-statistics measurement at ...... GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the ...... dependence of the data well.

Published for SISSA by Springer

Received: May 21, 2014 Revised: September 5, 2014 Accepted: September 11, 2014

Published: October 1, 2014

Measurement of D photoproduction at three di erent centre-of-mass energies at HERA

The ZEUS collaboration

JHEP10(2014)003

E-mail: mailto:[email protected]

Web End [email protected]

Abstract: The photoproduction of D mesons has been measured with the ZEUS detector at HERA at three dierent ep centre-of-mass energies, s, of 318, 251 and 225 GeV. For each data set, D mesons were required to have transverse momentum, pDT, and pseudo-rapidity, D, in the ranges 1.9 < pDT < 20 GeV and |D| < 1.6. The events were required

to have a virtuality of the incoming photon, Q2, of less than 1 GeV2. The dependence on s was studied by normalising to the high-statistics measurement at s = 318 GeV. This led to the cancellation of a number of systematic eects both in data and theory. Predictions from next-to-leading-order QCD describe the s dependence of the data well.

Keywords: Lepton-Nucleon Scattering, QCD, Heavy quark production, Charm physics

ArXiv ePrint: 1405.5068

Open Access, c

The Authors.

Article funded by SCOAP3. doi:http://dx.doi.org/10.1007/JHEP10(2014)003

Web End =10.1007/JHEP10(2014)003

Contents

1 Introduction 1

2 Experimental set-up 2

3 Event selection and signal extraction 23.1 Photoproduction event selection 23.2 Selection of D candidates and signal extraction 3

4 Monte Carlo samples 4

5 QCD calculations 5

6 Determination of normalised cross sections 7

7 Energy dependence of D + cross sections 10

8 Summary 10

The ZEUS collaboration 15

1 Introduction

The photoproduction of charm quarks at HERA is a rich testing ground for the predictions of perturbative quantum chromodynamics (pQCD). The predictions are expected to be reliable since the charm mass provides a hard scale in the perturbative expansion. The dominant production mechanism is boson-gluon fusion. Many measurements of charm photoproduction at high ep centre-of-mass energies, s = 318 GeV or s = 300 GeV, have been made at HERA [116] and compared with QCD predictions at next-to-leading order (NLO). The description of the data is generally reasonable, although the uncertainties on the theory are often large.

Previous results on charm photoproduction were obtained at a single ep centre-of-mass energy; the dependence on the ep centre-of-mass energy is presented here for the rst time. The variation of the cross section with centre-of-mass energy is sensitive to the gluon distribution in the proton, as dierent values of Bjorken x are probed. Measurements of D

production at three dierent centre-of-mass energies, s = 318, 251 and 225 GeV, are presented in this paper. The variation of s was achieved by varying the proton beam energy, Ep, while keeping the electron1 beam energy constant, Ee = 27.5 GeV. The data were collected in 2006 and 2007 with Ep = 920, 575 and 460 GeV, referred to, respectively,

1Hereafter electron refers to both electrons and positrons unless otherwise stated.

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as the high- (HER), medium- (MER) and low-energy-running (LER) samples. The corresponding luminosities of the HER, MER and LER samples are 144, 6.3 and 13.4 pb1,

respectively. A common analysis procedure is used for all samples and the cross sections at dierent s are presented normalised to that for the HER data, thereby leading to a cancellation of a number of systematic uncertainties both in data and theory.

2 Experimental set-up

A detailed description of the ZEUS detector can be found elsewhere [17]. A brief outline of the components that are most relevant for this analysis is given below.

In the kinematic range of the analysis, charged particles were tracked in the central tracking detector (CTD) [1820] and the microvertex detector (MVD) [21]. These components operated in a magnetic eld of 1.43 T provided by a thin superconducting solenoid. The CTD consisted of 72 cylindrical drift-chamber layers, organised in nine superlayers covering the polar-angle2 region 15 < < 164. The MVD silicon tracker consisted of a barrel (BMVD) and a forward (FMVD) section. The BMVD contained three layers and provided polar-angle coverage for tracks from 30 to 150. The four-layer FMVD extended the polar-angle coverage in the forward region to 7. For CTD-MVD tracks that pass through all nine CTD superlayers, the momentum resolution was (pT )/pT = 0.0029pT 0.00810.0012/pT ,

with pT in GeV.

The high-resolution uranium-scintillator calorimeter (CAL) [2225] consisted of three parts: the forward (FCAL), the barrel (BCAL) and the rear (RCAL) calorimeters. Each part was subdivided transversely into towers and longitudinally into one electromagnetic section (EMC) and either one (in RCAL) or two (in BCAL and FCAL) hadronic sections (HAC). The smallest subdivision of the calorimeter was called a cell. The CAL energy resolutions, as measured under test-beam conditions, were (E)/E = 0.18/E for electrons and (E)/E = 0.35/E for hadrons, with E in GeV.

The luminosity was measured using the Bethe-Heitler reaction ep ep by a lu

minosity detector which consisted of independent lead-scintillator calorimeter [2628] and magnetic spectrometer [29] systems. The fractional systematic uncertainty on the measured luminosity [30] was 1.8 %, composed of correlated and uncorrelated uncertainties of, respectively, 1.5% and 1%.

3 Event selection and signal extraction

3.1 Photoproduction event selection

A three-level trigger system [17, 31, 32] was used to select events online. The rst- and second-level trigger used CAL and CTD data to select ep collisions and to reject beam-gas

2The ZEUS coordinate system is a right-handed Cartesian system, with the Z axis pointing in the proton beam direction, referred to as the forward direction, and the X axis pointing towards the centre of HERA. The coordinate origin is at the centre of the CTD. The pseudorapidity is dened as = ln[notdef][notdef]tan

the polar angle, , is measured with respect to the Z axis.

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, where

events. At the third level, the full event information was available. In this analysis, triggers containing a D-meson candidate and/or two jets were used.

In order to remove non-ep background, the Z position of the primary vertex of an event, Zvtx, was required to be in the range |Zvtx| < 30 cm. Photoproduction events were

selected by requiring that no scattered electron with energy larger than 5 GeV was found in the CAL [33].

The fraction of the incoming electron momentum carried by the photon, y, was reconstructed via the Jacquet-Blondel [34] estimator, yJB, using energy-ow objects (EFOs) [35, 36]. Energy-ow objects combine track and calorimeter information to optimise the resolution of the variable. The value of yJB is given by yJB =

Pi Ei(1cos i)/2Ee where Ee is

the energy of the electron beam, Ei is the energy of the i-th EFO, i is its polar angle and the sum runs over all EFOs. The range 0.167 < yJB < 0.802 was used, where the lower cut was set by the trigger requirements and the upper cut suppressed remaining events from deep inelastic scattering with an unidentied low-energy scattered electron in the CAL. The range in yJB corresponds to reconstructed photon-proton centre-of-mass energy, WJB, ranges of 130 < WJB < 285 GeV, 103 < WJB < 225 GeV and 92 < WJB < 201 GeV for the HER, MER and LER samples, respectively.

3.2 Selection of D candidates and signal extraction

The D+ mesons3 were identied using the decay channel D+ D0+s with the subse

quent decay D0 K+, where +s refers to a low-momentum (slow) pion accompa

nying the D0. Tracks from the D+ decay products were required to have at least one hit in the MVD and in the inner superlayer of the CTD and to reach at least the third CTD superlayer. Tracks with opposite charge and with transverse momentum pK,T > 0.4 GeV were combined in pairs to form D0 candidates. The tracks were alternately assigned the kaon and pion mass and the invariant mass of the pair, M(K), was calculated. Each additional track with charge opposite to that of the kaon track and a transverse momentum psT > 0.12 GeV was assigned the pion mass and combined with the D0 candidate to form a D+ candidate. Since more combinatorial background exists in the forward direction as well as at low pDT [14], this was suppressed by requiring pDT/E >10T > 0.12, where pDT is the transverse momentum of the D+ meson and E >10T is the transverse energy measured using all CAL cells outside a cone of 10 around the forward direction. The mass dierence M M(Ks) M(K) was used to extract the D+ signal. The D+

candidates were required to have 1.83 < M(K) < 1.90 GeV, 0.143 < M < 0.148 GeV, 1.9 < pDT < 20 GeV and pseudorapidity, |D| < 1.6. To allow the background to be de

termined, D0 candidates with wrong-sign combinations, in which both tracks forming the D0 candidates have the same charge and the third track has the opposite charge, were also retained. The same kinematic restrictions were applied as for those D0 candidates with correct-charge combinations.

The distributions of M for D+ candidates in the HER, MER and LER periods, without the requirement on M, are shown in gures 13. Clear D+ peaks are seen.

3Hereafter the charge conjugated states are implied.

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Figure 1. Distribution of the mass dierence, M M(Ks)M(K), for the D candidates

for the HER (s = 318 GeV) data sample. The candidates are shown for correct-sign (lled circles) and wrong-sign combinations (empty circles). The background t is shown as a short-dashed (long-dashed) line for correct-sign (wrong-sign) combinations. The D signal region is marked as a shaded area.

The D+ signal was extracted by subtracting the correct-sign background estimate from the number of candidates in the signal window 0.143 < M < 0.148 GeV. The shape of the background was determined by performing a simultaneous t to the correct-sign and wrong-sign distributions, as outlined in a previous publication [37]. The t was performed in the region M < 0.168 GeV; the region with a possible signal contribution, 0.140 < M < 0.150 GeV, was removed from the t to the correct-sign distribution. The total signals are NDHER = 12256 191, NDMER = 417 37 and NDLER = 859 49 for the HER,

MER and LER samples, respectively.

4 Monte Carlo samples

The acceptance and eects of detector response were determined using samples of simulated events. The Monte Carlo (MC) programme Pythia 6.221 [38, 39], which implements leading-order matrix elements, followed by parton showers and hadronisation, was used. Dierent subprocesses were generated separately [15]. The CTEQ5L [40] and GRV-LO [41,

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Figure 2. Distribution of the mass dierence, M M(Ks)M(K), for the D candidates

for the MER (s = 251 GeV) data sample. Other details as in gure 1.

42] sets were used for the proton and photon parton density functions (PDFs), respectively. Samples of charm and beauty events were generated with quark masses, mc = 1.5 GeV and

mb = 4.75 GeV.

The generated MC events were passed through the ZEUS detector and trigger simulation programmes based on Geant 3.21 [43]. They were then reconstructed and analysed using the same programmes as used for the data.

5 QCD calculations

The data are compared with an NLO QCD prediction from Frixione et al. [44, 45] in the xed-avour-number scheme (FFNS), in which only light avours and gluons are present as partons in the proton and heavy quarks are produced in the hard interaction [46]. The following input parameters were set in the calculation: the renormalisation and factorisation scales were set to =

qm2c + p2T , where pT is the average transverse momentum of the charm quarks and the pole mass was mc = 1.5 GeV; the proton and photon PDFs were ZEUS-S 3-avour FFNS [47] and GRV-G HO [41, 42]; the value of the strong coupling constant was s(MZ) = 0.118 for ve avours; and the parameter, , in the Peterson fragmentation function [48] was = 0.079 [49]. The contribution to the D+ visible cross

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Figure 3. Distribution of the mass dierence, M M(Ks)M(K), for the D candidates

for the LER (s = 225 GeV) data sample. Other details as in gure 1.

section from beauty production is predicted by MC to be about 2.5%. This value was the same to within 0.1% for all three data sets. Therefore, the beauty contribution cancelled and the uncertainty was negligible when the cross sections were normalised. Hence, the beauty component was not included in the predictions.

Several sources of theoretical uncertainty were investigated and are listed in the following, with the respective eects on the (MER, LER) samples normalised to the HER data given in parentheses:

the renormalisation and factorisation scales were changed independently to 0.5 and 2

times their nominal value. The largest change in the positive and negative direction was taken as the systematic uncertainty (+3.51.6%, +5.22.3%);

the fragmentation parameter was varied in the range [49, 50] from 0.006 to 0.092

(+1.50.1%, +2.30.2%);

the proton PDF was changed to the ABM11 3-avour FFNS [51] parametrisations

(+0.9%, +1.3%);

the value of mc was changed to 1.35 and 1.65 GeV (+0.10.2%, +0.10.3%).

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Figure 4. Distributions of (a) pD T, (b) D and (c) WJB for D mesons in the HER (s = 318 GeV) data sample (points) compared with a mixture of charm and beauty events from the Pythia MC simulation (histogram).

6 Determination of normalised cross sections

Visible D+ photoproduction cross sections in the kinematic region 1.9 < pDT < 20 GeV,

|D| < 1.6, Q2 < 1 GeV2 and 0.167 < y < 0.802 were obtained using the formula

vis = NDdata

A BR L

,

where NDdata is the number of D+ mesons in the data, BR is the product of the branching fractions of the decay D+ D0+s with D0 K+ and L is the integrated luminosity

of the respective sample. The acceptance, A, is given by the ratio of the number of

reconstructed to generated D+ mesons in the MC simulation, using a mix of charm and beauty production. The sample of beauty MC events, both reconstructed and generated, was scaled by a factor of 1.6, consistent with previous ZEUS measurements [15, 16, 52]. In order to optimise the description of the data and hence determine the acceptances as accurately as possible, the MC was reweighted in WJB for the HER sample and in pDT for the HER, MER and LER data samples. The comparison of background-subtracted data and MC after these reweightings is shown in gures 4, 5 and 6, for the HER, MER and LER samples, respectively. The description of the data is reasonable, also for the D

distributions, for which no reweighting was performed.

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Figure 5. Distributions of (a) pD T, (b) D and (c) WJB for D mesons in the MER (s = 251 GeV) data sample (points) compared with a mixture of charm and beauty events from the Pythia MC simulation (histogram).

The measured cross sections were normalised to the HER data sample:

RHER,MER,LER = HER,MER,LERvis/HERvis.

This allowed the energy dependence of the cross section to be studied to higher precision as a number of systematic uncertainties in data and theory cancel.

The following sources of systematic uncertainty were considered [53], with the eect on RMER and RLER given in parentheses:

the lower and upper WJB cuts for data and reconstructed MC events were changed

by 5 GeV in order to assess the eects of the resolution of WJB and the impact of

any residual backgrounds (+0.70.8%, +2.12.1%);

the forms of the functions used for MC reweighting in WJB (HER only) and pDT were

varied within the uncertainties determined from the quality of the description of the data (+1.41.4%, +3.21.3%);

the lower and upper mass requirements for the D0 were varied to 1.80 GeV and

1.93 GeV, both in data and MC. This and the following two sources were performed to assess the uncertainty coming from estimation of the combinatorial background (6.7%, +0.74.1%);

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Figure 6. Distributions of (a) pD T, (b) D and (c) WJB for D mesons in the LER (s = 225 GeV) data sample (points) compared with a mixture of charm and beauty events from the Pythia MC simulation (histogram).

the upper edge of the t range in the M distribution was changed to 0.165 GeV,

both in data and MC (0.7%, 1.9%);

the minimum requirement on the ratio pDT/E >10T was varied between 0.05 and 0.20,

both in data and MC (+2.02.3%, +2.11.1%);

the uncorrelated uncertainty in the luminosity determination (1.4%, 1.4%).

The above systematic uncertainties were added in quadrature separately for positive and negative variations. Other sources of systematic uncertainty were found to be negligible and were ignored. These included the uncertainties on the track-nding eciency, additional reweighting of the MC samples in D as well as from the fraction of beauty events used in the acceptance correction. As a cross-check, the number of D+ mesons was also extracted by subtracting the wrong-sign from the correct-sign distribution; the result was consistent with the nominal procedure.

The statistical uncertainties for RMER and RLER include that from the HER sample, although the uncertainties from the MER and LER dominate. The systematic uncertainties also contain contributions from the HER result which are fully correlated between the LER and MER measurements.

9

7 Energy dependence of D + cross sections

Ratios of visible D+ photoproduction cross sections have been measured in the kinematic region 1.9 < pDT < 20 GeV, |D| < 1.6, Q2 < 1 GeV2 and 0.167 < y < 0.802. The range in

y corresponds to photon-proton centre-of-mass energy, W , ranges of 130 < W < 285 GeV, 103 < W < 225 GeV and 92 < W < 201 GeV in the HER, MER and LER samples, respectively. The ratios of the visible cross sections for the MER and LER samples to that of the HER sample are:

RMER = 0.780 0.074(stat.)+0.0220.058(syst.)

RLER = 0.786 0.049(stat.)+0.0370.043(syst.) .

These values, along with RHER (by constraint equal to unity), are shown in gure 7. The cross sections for the MER and LER samples are compatible within uncertainties, but signicantly smaller than the cross section for the HER data. This behaviour of increasing cross section with increasing ep centre-of-mass energy is predicted well by Pythia MC simulations and NLO QCD, although the predictions have a somewhat dierent slope. This shows that the proton PDFs constrained primarily from inclusive deep inelastic scattering data are able to describe this complementary process which probes in particular the gluon distribution. The physics possibilities of future colliders such as the Large Hadron Electron Collider (LHeC) [54, 55] are studied using current NLO QCD calculations. The results shown here enhance condence in the NLO QCD predictions of charm production rates, specically, and QCD processes, in general, for a future TeV-scale ep collider.

8 Summary

Photoproduction of D mesons has been measured at HERA at three dierent ep centreof-mass energies, s = 318, 251 and 225 GeV. For D mesons in the range 1.9 < pDT <20 GeV and |D| < 1.6, cross sections normalised to the result at s = 318 GeV were

measured. Photoproduction events were selected in the range Q2 < 1 GeV2 and 0.167 < y < 0.802 where the range in y corresponds to the photon-proton centre-of-mass energies of 130 < W < 285 GeV, 103 < W < 225 GeV and 92 < W < 201 GeV. The cross sections, normalised to that for the highest s, show an increase with increasing s. This is predicted well by perturbative QCD, demonstrating consistency of the gluon distribution probed here with that extracted in PDF ts to inclusive deep inelastic scattering data.

Acknowledgments

We appreciate the contributions to the construction, maintenance and operation of the ZEUS detector of many people who are not listed as authors. The HERA machine group and the DESY computing sta are especially acknowledged for their success in providing excellent operation of the collider and the data-analysis environment. We thank the DESY directorate for their strong support and encouragement.

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1.2 ZEUS

s

R

192 GeV

136 GeV 152 GeV

W

=

2 < 1 GeV

Q

2

ZEUS ep PYTHIA

NLO QCD

D* X

|

h

D* | < 1.6

1.9 < p

D* < 20 GeV

T

0.167 < y < 0.802

1

0.8

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0.6

0.4

0.2

0

240 260 280 300 320

(GeV)

s

Figure 7. Normalised D visible photoproduction cross sections as a function of the ep centreof-mass energy. The data (points) are shown with statistical uncertainties (inner error bars) and statistical and systematic uncertainties added in quadrature (outer error bars). The predictions from NLO QCD (solid line) are shown with the uncertainties given in section 5 added in quadrature separately for positive and negative variations (band). A prediction from the Pythia MC simulation is also shown (dashed line). The data and theory at s = 318 GeV are constrained by denition to be at unity, with no uncertainty. At each data point, the average photon-proton centre-of-mass energy, hW i, is also given.

Open Access. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

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The ZEUS collaboration

H. Abramowicz27,u, I. Abt21, L. Adamczyk8, M. Adamus34, R. Aggarwal4,a, S. Antonelli2,O. Arslan3, V. Aushev16,17,o, Y. Aushev17,o,p, O. Bachynska10, A.N. Barakbaev15, N. Bartosik10,O. Behnke10, J. Behr10, U. Behrens10, A. Bertolin23, S. Bhadra36, I. Bloch11, V. Bokhonov16,o, E.G. Boos15, K. Borras10, I. Brock3, R. Brugnera24, A. Bruni1, B. Brzozowska33, P.J. Bussey12,A. Caldwell21, M. Capua5, C.D. Catterall36, J. Chwastowski7,d, J. Ciborowski33,x,R. Ciesielski10,f, A.M. Cooper-Sarkar22, M. Corradi1, F. Corriveau18, G. DAgostini26,R.K. Dementiev20, R.C.E. Devenish22, G. Dolinska10, V. Drugakov11, S. Dusini23, J. Ferrando12,J. Figiel7, B. Foster13,l, G. Gach8, A. Garfagnini24, A. Geiser10, A. Gizhko10, L.K. Gladilin20,O. Gogota17, Yu.A. Golubkov20, J. Grebenyuk10, I. Gregor10, G. Grzelak33, O. Gueta27,M. Guzik8, W. Hain10, G. Hartner36, D. Hochman35, R. Hori14, Z.A. Ibrahim6, Y. Iga25,M. Ishitsuka28, A. Iudin17,p, F. Januschek10, I. Kadenko17, S. Kananov27, T. Kanno28,U. Karshon35, M. Kaur4, P. Kaur4,a, L.A. Khein20, D. Kisielewska8, R. Klanner13, U. Klein10,g,N. Kondrashova17,q, O. Kononenko17, Ie. Korol10, I.A. Korzhavina20, A. Kotaski9, U. Ktz10,N. Kovalchuk17,r, H. Kowalski10, O. Kuprash10, M. Kuze28, B.B. Levchenko20, A. Levy27,V. Libov10, S. Limentani24, M. Lisovyi10, E. Lobodzinska10, W. Lohmann11, B. Lhr10,E. Lohrmann13, A. Longhin23,t, D. Lontkovskyi10, O.Yu. Lukina20, J. Maeda28,v, I. Makarenko10,J. Malka10, J.F. Martin31, S. Mergelmeyer3, F. Mohamad Idris6,c, K. Mujkic10,h,V. Myronenko10,i, K. Nagano14, A. Nigro26, T. Nobe28, D. Notz10, R.J. Nowak33, K. Olkiewicz7, Yu. Onishchuk17, E. Paul3, W. Perlaski33,y, H. Perrey10, N.S. Pokrovskiy15,A.S. Proskuryakov20,aa, M. Przybycie8, A. Raval10, P. Rolo10,j, I. Rubinsky10, M. Ruspa30,V. Samojlov15, D.H. Saxon12, M. Schioppa5, W.B. Schmidke21,s, U. Schneekloth10,T. Schrner-Sadenius10, J. Schwartz18, L.M. Shcheglova20, R. Shevchenko17,p, O. Shkola17,r,I. Singh4,b, I.O. Skillicorn12, W. S lomiski9,e, V. Sola13, A. Solano29, A. Spiridonov10,k,L. Stanco23, N. Stefaniuk10, A. Stern27, T.P. Stewart31, P. Stopa7, J. Sztuk-Dambietz13,D. Szuba13, J. Szuba10, E. Tassi5, T. Temiraliev15, K. Tokushuku14,m, J. Tomaszewska33,z,A. Trofymov17,r, V. Trusov17, T. Tsurugai19, M. Turcato13, O. Turkot10,i, T. Tymieniecka34,A. Verbytskyi21, O. Viazlo17, R. Walczak22, W.A.T. Wan Abdullah6, K. Wichmann10,i,M. Wing32,w, G. Wolf10, S. Yamada14, Y. Yamazaki14,n, N. Zakharchuk17,r, A.F. Zarnecki33,L. Zawiejski7, O. Zenaiev10, B.O. Zhautykov15, N. Zhmak16,o, D.S. Zotkin20

1 INFN Bologna, Bologna, Italy A

2 University and INFN Bologna, Bologna, Italy A

3 Physikalisches Institut der Universitat Bonn, Bonn, Germany B

4 Panjab University, Department of Physics, Chandigarh, India

5 Calabria University, Physics Department and INFN, Cosenza, Italy A

6 National Centre for Particle Physics, Universiti Malaya, 50603 Kuala Lumpur, Malaysia C

7 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland D

8 AGH-University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow, Poland D

9 Department of Physics, Jagellonian University, Cracow, Poland

10 Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany

11 Deutsches Elektronen-Synchrotron DESY, Zeuthen, Germany

12 School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom E

13 Hamburg University, Institute of Experimental Physics, Hamburg, Germany F

14 Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japan G

15 Institute of Physics and Technology of Ministry of Education and Science of Kazakhstan, Almaty, Kazakhstan

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16 Institute for Nuclear Research, National Academy of Sciences, Kyiv, Ukraine

17 Department of Nuclear Physics, National Taras Shevchenko University of Kyiv, Kyiv, Ukraine

18 Department of Physics, McGill University, Montral, Qubec, Canada H3A 2T8 H

19 Meiji Gakuin University, Faculty of General Education, Yokohama, Japan G

20 Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics, Moscow, Russia I

21 Max-Planck-Institut fr Physik, Mnchen, Germany

22 Department of Physics, University of Oxford, Oxford, United Kingdom E

23 INFN Padova, Padova, Italy A

24 Dipartimento di Fisica dell Universit and INFN, Padova, Italy A

25 Polytechnic University, Tokyo, Japan G

26 Dipartimento di Fisica, Universit La Sapienza and INFN, Rome, Italy A

27 Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics, Tel Aviv University, Tel Aviv, Israel J

28 Department of Physics, Tokyo Institute of Technology, Tokyo, Japan G

29 Universit di Torino and INFN, Torino, Italy A

30 Universit del Piemonte Orientale, Novara, and INFN, Torino, Italy A

31 Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7 H

32 Physics and Astronomy Department, University College London, London, United Kingdom E

33 Faculty of Physics, University of Warsaw, Warsaw, Poland

34 National Centre for Nuclear Research, Warsaw, Poland

35 Department of Particle Physics and Astrophysics, Weizmann Institute, Rehovot, Israel

36 Department of Physics, York University, Ontario, Canada M3J 1P3 H

A supported by the Italian National Institute for Nuclear Physics (INFN)

B supported by the German Federal Ministry for Education and Research (BMBF), under contractNo. 05 H09PDF

C supported by HIR grant UM.C/625/1/HIR/149 and UMRG grants RU006-2013, RP012A-13AFR and RP012B-13AFR from Universiti Malaya, and ERGS grant ER004-2012A from the Ministry of Education, Malaysia

D supported by the National Science Centre under contract No. DEC-2012/06/M/ST2/00428

E supported by the Science and Technology Facilities Council, UK

F supported by the German Federal Ministry for Education and Research (BMBF), under contractNo. 05h09GUF, and the SFB 676 of the Deutsche Forschungsgemeinschaft (DFG)

G supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and its grants for Scientic Research

H supported by the Natural Sciences and Engineering Research Council of Canada (NSERC)

I supported by RF Presidential grant N 3042.2014.2 for the Leading Scientic Schools and by theRussian Ministry of Education and Science through its grant for Scientic Research on High Energy Physics

J supported by the Israel Science Foundation

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a also funded by Max Planck Institute for Physics, Munich, Germany

b also funded by Max Planck Institute for Physics, Munich, Germany, now at Sri Guru Granth SahibWorld University, Fatehgarh Sahib

c also at Agensi Nuklear Malaysia, 43000 Kajang, Bangi, Malaysia

d also at Cracow University of Technology, Faculty of Physics, Mathematics and Applied ComputerScience, Poland

e partially supported by the Polish National Science Centre projects DEC-2011/01/B/ST2/03643 andDEC-2011/03/B/ST2/00220

f now at Rockefeller University, New York, NY 10065, USA

g now at University of Liverpool, United Kingdom

h also aliated with University College London, UK

i supported by the Alexander von Humboldt Foundation

j now at CERN, Geneva, Switzerland

k also at Institute of Theoretical and Experimental Physics, Moscow, Russia

l Alexander von Humboldt Professor; also at DESY and University of Oxford

m also at University of Tokyo, Japan

n now at Kobe University, Japan

o supported by DESY, Germany

p member of National Technical University of Ukraine, Kyiv Polytechnic Institute, Kyiv, Ukraine

q now at DESY ATLAS group

r member of National University of Kyiv - Mohyla Academy, Kyiv, Ukraine

s now at BNL, USA

t now at LNF, Frascati, Italy

u also at Max Planck Institute for Physics, Munich, Germany, External Scientic Member

v now at Tokyo Metropolitan University, Japan

w also supported by DESY

x also at

Ld University, Poland

y member of

Ld University, Poland

z now at Polish Air Force Academy in Deblin

aa deceased

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