Pseudorapidity distributions of charged hadrons in xenon-xenon collisions at sqrt(sNN)=5.44 TeV

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Physics

Letters

B

www.elsevier.com/locate/physletb

Pseudorapidity

distributions

of

charged

hadrons

in

xenon-xenon

collisions

at

√

s

=

5

.

44 TeV

Receivedinrevisedform24September 2019

Accepted18October2019 Availableonline23October2019 Editor:M.Doser Keywords: CMS Physics Xenon-xenon Hadrons Multiplicity Spectra

Measurementsofthepseudorapiditydistributionsofchargedhadronsproducedinxenon-xenoncollisions atanucleon-nucleoncentre-of-massenergyof√sNN=5.44 TeV arepresented.Themeasurementsare

based on data collectedby the CMS experiment atthe LHC. The yield of primary charged hadrons produced in xenon-xenon collisions in the pseudorapidity range _|η|<3.2 is determined using the silicon pixel detector in the CMS tracking system. For the 5% most central collisions, the charged-hadron pseudorapidity density in the midrapidity region |η|<0.5 is found to be 1187±36 (syst), withanegligiblestatistical uncertainty.The rapiditydistributionofcharged hadronsisalsopresented intherange|y|<3.2 andisfoundto beindependentofrapidityaround y =0.ExistingMonte-Carlo event generators are unableto simultaneously describeboth results. Comparisons of charged-hadron multiplicities between xenon-xenon and lead-lead collisions at similar collision energies show that particleproductionatmidrapidityis strongly dependent onthecollisiongeometry inaddition tothe systemsizeandcollisionenergy.

©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Collisions between ultra-relativistic heavy ions are the only known way of experimentally studying quantum chromodynam-ics(QCD) matter athigh temperaturesand energydensities. The currentunderstandingisthat insuch collisions,a state ofmatter known as the quark-gluon plasma (QGP) is formed shortly after theinitialimpactbetweenthenuclei [1].

The multiplicity and pseudorapidity distributions of the pro-ducedchargedparticles arekey observablesthat characterise the initial condition and subsequent hydrodynamic evolution of the QGP [2]. The dependenceof the charged-particle multiplicity on thecollidingsystem, centre-of-mass energy,andcollision geome-try can provide information about nuclear shadowing and gluon saturationeffects [3],aswellastherelative contributionsto par-ticleproductionfromhardscatteringandsoftprocesses [4].These observablesalsoprovideinput formodels oftheparticle produc-tionprocess [5],fromwhichinformationabouttheformationand propertiesoftheQGPcanbeextracted.

InOctober2017,theCERNLHCcollidedxenon(Xe129)ionsata nucleon-nucleoncentre-of-massenergyof√sNN=5.44 TeV, mark-ing the first time ions other than protons and lead (Pb208) have

 _{E-mailaddress:cms-publication-committee-chair@cern.ch.}

been circulated in the LHC. This new collision system provides a unique opportunity to study the dependence of the charged-particlemultiplicityonthesizeofthematterproducedatLHC en-ergies.Previousmeasurementsofcharged-particlemultiplicitiesin copper-copper(CuCu)andgold-gold(AuAu)collisionsatRHIChave been observed to be sensitive to the collision geometry [6]. The XeXecollisiondataarethusimportantfordeterminingifthis fea-tureisalsopresentathigherenergies.Comparisonsofthedatato predictionsofmodels tunedto describePbPb collisiondata [7–9] canalsobeusedtotesttheextenttowhichthesemodelsareable todescribeothercollisionsystems.

In this Letter, measurements of the pseudorapidity density of primary chargedhadrons,dNch/dη,intherange|η|<3.2 are re-portedforXeXecollisions delivered bytheLHC. Followingearlier analysesinproton-protoncollisionsat0.9–13 TeV [10–14], proton-lead collisions at 5.02 and 8.16 TeV [15], and PbPb collisions at 2.76 TeV [16], “primary”charged hadronsare definedasprompt charged hadronsand decayproducts of all particles withproper decaylengthcτ <1 cm,where c isthespeedoflight invacuum and τ is the proper lifetime of the particle. Contributions from promptleptons, decayproducts oflonger-livedparticles,and sec-ondaryinteractionsareexcluded.

Theresultsarecompared toameasurementbytheALICE Col-laboration [17] andtopredictionsfromthe EposLHCv3400 [8,18], Hydjet _{1.9 [9], and Ampt 1.26t5 [19] eventgenerators. The Epos}

https://doi.org/10.1016/j.physletb.2019.135049

0370-2693/©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

generator is based on Gribov–Regge theory [20,21] and includes theeffectofcollectivehadronisation inhadron-hadron scattering. The Hydjet generatortreatsaheavyioncollisionasasuperposition of a hydrodynamically parametrised soft component and a hard componentresulting from multi-parton fragmentation. The Ampt generatorcombines the Hijing eventgenerator [22] withZhang’s partoncascadeprocedure [23] andtheARTmodel [24] forthelast stageofpartonhadronisation.

2. TheCMSdetector

The central feature of the CMS apparatus is a superconduct-ing solenoidof6 m internaldiameter, providinga magneticfield of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker covering the range |η|<2.5, a lead tungstate crys-talelectromagneticcalorimeter,andabrassandscintillatorhadron calorimeter,each composed ofa barrelandtwo endcap sections. Forward calorimeters (HF), made of steel and quartz-fibres and locatedoneithersideoftheinteractionpoint,extendthe pseudo-rapidity coverage providedby thebarrel andendcapdetectorsto |η|<5.2.Muonsaredetected ingas-ionisationchambers embed-dedinthe steelflux-return yokeoutsidethe solenoid. The beam pickup timing forexperiments(BPTX) devicesare locatedaround thebeampipe atadistance of175 mfromthe interactionpoint oneithersideandprovidepreciseinformationonthetimingofthe incomingbeams.AmoredetaileddescriptionoftheCMSdetector, together withadefinitionof thecoordinatesystemusedandthe relevantkinematicvariables,canbefoundinRef. [25].

Charged hadronsare reconstructed using the siliconpixel de-tectorsinstalledduringthePhase1upgrade [26],whichconsistof fourconcentriccylindricalshells(layers)inthebarrelregion(BPIX) andthreedisks onboth sidesoftheinteraction point inthe for-ward region(FPIX). The BPIXandFPIX consistof a totalof 1184 and672modules,respectively,andprovideexcellentposition res-olutionwiththeir 100×150 μm pixels.In thisLetter, the layers oftheBPIXaredenotedinincreasingorderoftheirradialdistance fromthe beamaxis,i.e. the layerclosest to thebeam axisis re-ferredtoaslayer1,thenextclosestlayerisreferredtoaslayer2, andsoon,whilethedisksoftheFPIXarereferredtoinincreasing orderof their longitudinal distance fromthe nominalinteraction point.

3. Eventselection

This analysis is based on approximately 1.36 million events. The average interaction probability per bunch crossing was 1.8%. Eventsareselected intwo stages:(i)online, acoincidenceof sig-nalsfrombothBPTXdevicesandatleastoneenergydepositabove 3 GeVoneithersideoftheHFarerequired;(ii)offline,three en-ergy deposits above 3 GeV on each side of the HF and at least onereconstructedvertex,accordingtothetracklet-basedvertex re-construction methoddescribed inRef. [16], arerequired. Astudy of noncolliding ion bunches shows that the above requirements are sufficient to reject all backgrounds not originating from in-teractionsbetweenxenon ions. Consequently,the contribution of backgroundeventsfrombeam,beam-halo,andcosmicraysources totheobservedyieldsisnegligible.

Contamination from electromagnetic (EM) interactions be-tweenxenonions isstudiedusingsimulatedeventsgeneratedby STARlight 2.2 [27] interfaced with Dpmjet-III 3.0-5 [28], and is estimatedto bearound 1%. Theevent selectionefficiencyis esti-matedby fittingthedistributionofthetotaltransverse energyin theHFcalorimeterusingatemplateextractedfromsimulated Epos LHC_{events [16].Variationsinthefitparameters,aswellasother} observablescorrelated witheventactivity, are used todetermine

the uncertaintyinthismethod.In combinationwiththe contam-ination rate, an overall value of 95±3% is quoted forthe event selectionefficiency.

Nucleiareextensiveobjects,andtheircollisionscanbe charac-terisedbythecentrality,whichisrelatedtotheimpactparameter of thecollision.The centralitycan beestimatedfromthe sumof thetransverse energyintheHFcalorimeter [16,29]. The distribu-tion of thetotal transverse energy, aftercorrecting for theevent selection efficiency, is divided into equal partitions and used to classify events into centralities. The centrality represents a per-centileofthetotalnuclearinteractioncrosssection [16];themost central collisions, i.e. the collisions with the smallestimpact pa-rameter,aredenotedbylowerpercentiles.Tominimisetheamount ofEM contamination,which isconcentratedin the20%most pe-ripheralevents,theanalysisisrestrictedtoeventswithcentrality inthe0–80%range,wheretheeventselectionisfullyefficient.

The eventcentrality is also related to the number of partici-patingnucleons Npart,whichisdeterminedfromaGlaubermodel calculation [30,31]. For this calculation, the nucleon-nucleon in-elastic crosssection istaken tobe 68.4±0.5 mb [31],while the nuclear radius, skin depth,and deformation parameter β2 of the xenon nucleusareset to 5.36±0.1 fm, 0.59±0.07 fm [32],and 0.18±0.02 [17],respectively.Simulated EposLHCeventsareused to account for the energy resolution of the HF calorimeters and fluctuationsineventactivity,whichsmearthecentrality distribu-tions. The resulting values and associated uncertainties for Npart are listed inthe supplemental material [URL will be inserted by publisher].

4. Analysis

The measurement of dNch/dη is performed using tracklets, which arepairs ofpixelclustersfromtwodifferentlayers (disks) of the silicon pixel detector. Pairs of pixel clusters that are pro-duced by the same charged particle have small differences in η

andazimuthal angleφ withrespect tothe primaryvertex. These correlations are exploited in the analysis to reconstruct tracklets that reflectthe original distribution ofprimary chargedhadrons. Thevertexandtrackletreconstruction algorithmsaredescribedin Ref. [16].

Sixpossibletypesoftrackletscanbeformedfromdistinct com-binations ofthe four layers of the BPIX. In addition, three types oftrackletscanbeformedfromunique combinationsofthethree disksoftheFPIX.Theindividualmeasurementsfromallnine com-binationsareaveragedandsymmetrisedabout η=0 toobtainthe final results. Thedifferent combinationsare alsousefulfor layer-by-layer systematic checks,as they have differentsensitivities to theparticlemomentumspectrum.ParticleswithpT above40 MeV canbereconstructedusingthetwoBPIXlayersclosesttothebeam pipe.

Theangulardistancebetweenthetwoclustersthatmakeup a trackletisdefinedas r=ηi−ηj 2 +φi− φj 2 , (1)

where ηi(j) is the pseudorapidity ofthe pixel cluster position in

thei(j)thlayerordisk,calculatedwithrespecttotheprimary ver-texposition,andφi(j)isdefinedsimilarlyfortheazimuthalangle.

Ther distributionfortrackletsreconstructedfromlayers1and2

oftheBPIXisshowninFig.1.Thespectrumiscomparedtofully simulatedeventsgeneratedby EposLHC, Hydjet,and Ampt.

Tracklets with r<0.5 are selected for analysis. This selec-tion criterion suppresses the combinatorialbackground from un-correlatedbackgroundclustersandlowtransversemomentum(pT) particles that loop around in the high magnetic field and leave

Fig. 1. The r distributionsfortrackletsreconstructedfromthetwolayersofthe BPIXclosesttothebeampipe.Thedistributionsarenormalisedbythenumberof tracklets.Thespectrumincollisiondata(blacksquares)iscomparedtothespectra obtainedfromfullysimulatedeventsgeneratedwith EposLHCv3400 [8,18], Hydjet 1.9 [9],and Ampt 1.26t5 [19].Theratioofthedistributionsinsimulationtodatais showninthebottompanel.Thestatisticaluncertaintiesaresmallerthanthemarker sizesforalldistributionsshown.

multiplechargedepositsperlayerofthepixeldetector.The recon-structed tracklet spectrum is then corrected to the hadron-level event definition by applying a number of correction factors ac-counting for the geometric acceptance, reconstruction efficiency, andeventselectionefficiency.Thesecorrectionfactorsarederived from MC simulations generated with the aforementioned event generators. The detectorresponse is simulated with Geant4 [33] andprocessedthroughthesameeventreconstructionchainasthe collisiondata.Allsimulations are producedwiththesamevertex distributionalongtheinteractionregionasisobservedindata.

Simulationsgenerated with EposLHC are usedasthe primary referenceforthederivationofthesecorrectionfactorsbecausethe

r spectrum obtainedfrom thesesimulated events mostclosely

resemblesthecorresponding spectrumindataatlarge r,where thecombinatorial background isdominant. The other event gen-eratorsareusedinthestudyofsystematicuncertainties.The cor-rection factors are calculated as functionsof the primary vertex position,pseudorapidity,andtrackletmultiplicity.Typicalvaluesof thesecorrection factors at|η|=0 (1.6)range from1.12(0.95) at lowmultiplicitiesto1.01(0.85)athighmultiplicities.

The Jacobian transformation from η to rapidity, y, can also be derived from simulations by relating the rapidity density of charged hadrons to the corresponding pseudorapidity density in each η interval [34,35]. The particle composition in data is as-sumedtofall withintherangeofparticle compositionspredicted by the various event generators. The final transformation factors appliedarethemeanvaluesofthefactorsderivedfromeachevent generator.

The sumof transverse energy in the HF, on which the event selection is based, is correlated with the charged-hadron multi-plicity in the region around η=0 where the measurement is made. Hence, the eventselection criteriaare susceptibleto mul-tiplicityfluctuationsand maylead to a nonnegligible biasin the results [36].ThemagnitudeofthisbiasisstudiedusingvariousMC eventgenerators bycomparingtheaveragedNch/dηat midrapid-ity,definedas|η|<0.5,fortwosetsofgeneratedevents:(i)events selected based on the transverse energy sumin the HF, and (ii) eventsselectedbasedon Npart,weighted tohavethesame distri-butionofNpart astheformerselection.Thisprovidesacomparison ofresultswithandwithouttheselectionbiaswhilealso account-ingfordetectoreffectsthatsmeartheNpartdistributionofselected events.Thebiascausedby theeventselectioncriteriaisfoundto benegligibleinthecentralityintervalusedinthisanalysis.

5. Systematicuncertainties

The uncertainties resulting fromvarious systematic effects af-fectingthemeasurement areevaluated. Thesources ofthese sys-tematicuncertainties includedifferencesbetweendata and simu-lationforeffects such asthe probability ofpixelcluster splitting, pixelclusterreconstructionefficiency,andthefractionof uncorre-latedpixel clusters,aswell asthe uncertainties inthealignment ofpixel detectormodules, trackletselection criteria, parametrisa-tion of correction factors, consistency between different tracklet combinations, and model dependence of the correction factors. Additionally, the uncertainty in the eventselection is taken into account asan independent,fullycorrelateduncertainty. The indi-vidual contributions are then summed in quadrature to give the totalsystematicuncertainty.

Pixel cluster splittingrefers to when the charge deposit from a single chargedparticleisreconstructed astwopixel clustersin closeproximity.Thedifferenceintherelativefractionofsplit clus-tersbetweendata andsimulation canbe estimatedby artificially splittingthepixelclustersinsimulationandcomparingthe result-ingmodified r distributionofclusterpairsinsimulationtothat indata.Thisdifferenceisfoundtobenomorethan2%,which re-sults ina variation of1.8–2.0% inthe dNch/dηresults. The pixel clusterreconstruction efficiencycanbe estimatedby studyingthe fractionoftrackletsreconstructedfrompixelclustersfromthefirst andthirdlayers that haveamatching pixelclusterin thesecond layer. The ratioof thisefficiencyin dataandsimulation showsa relativedifferenceof0.5%,whichhasaneffectof0.5%when prop-agatedtothefinalresults.Thepixelclusterpositionsaresmeared bytheuncertaintyinthealignmentofthepixeldetectormodules, andtheeffect onthefinal resultsis foundto be <0.1%.The dif-ference in the numberof uncorrelatedpixel clustersindata and simulationisestimatedbycomparingthetrackletr distributions intheregionr>0.3,wheretrackletsreconstructedfromtwo un-correlatedclustersaredominant. Additionalpixelclusters(on the orderof1–4%)wererandomlyaddedtothesimulatedeventssuch thatthetrackletr distributionsatlarger matchthoseindata. Adifferenceof0.5%inthefinalresultsisobservedat η=0,which increasesmonotonicallywith|η|to2.4%at|η|=3.2.

The tracklet selection criteria affect the minimum pT and signal-to-backgroundratioofreconstructedtracklets.The sensitiv-ityofthecorrection factorstotheseeffectsischeckedbyvarying thenominalselectioncriteriononr by±0.1.Theeffectofsuch variationsonthefinalresultsisfoundtobeabout0.2%.The mul-tiplicity variable used in the parametrisation of the correction factorscanbechangedtobethenumberofpixelclusters,whichis independentofthetrackletreconstructionefficiency.Theeffectsof suchachangearenegligible.Inanygiven ηrange,measurements canbe madeusingmultipletrackletcombinations.The maximum deviationofthemeasurementsobtainedusingeachtracklet com-bination from the final averaged and symmetrised result, which ranges from1.0to 2.1% within|η|<1.4 and up to5.0%atlarger valuesof|η|,isquotedasasystematicuncertainty.Themodel de-pendenceofthecorrectionfactorsisstudiedbyusingdifferentsets of correction factors derived from Hydjet and Ampt, which have differentdescriptions ofthe particleproductionmechanisms.The predictedparticlespectraandcomposition candiffersignificantly amongtheeventgenerators,whichaffectthecorrectionforleptons andtheextrapolationofthe measuredtrackletspectra to pT=0. The maximum deviation from the nominal results is quoted as an uncertainty, and ranges from 2.0–2.2% within |η|<1.0 to a maximumof5.0%around|η|=2.0.Themodeldependenceofthe Jacobian transformation from η to rapidity isalso evaluated ina similar manner, andthe maximum deviation, which ranges from

Table 1

Sourcesofsystematicuncertaintyaffecting the measurementofchargedhadron multiplicitiesandNpartinXeXecollisionsat√sNN=5.44 TeV.

Source [%]

Pixel cluster splitting 1.8–2.0

Pixel cluster reconstruction efficiency 0.5

Alignment uncertainty <0.1

Uncorrelated pixel clusters 0.5–2.4

Tracklet selection 0.2

Tracklet reconstruction efficiency <0.05

Consistency between tracklet combinations 1.0–5.0

Model dependence 2.0–5.0

Model dependence (Jacobian transformation) 0.5–2.5

Event selection efficiency (0–5% to 75–80%) 0.4–25.7

Glauber model calculation 0.7–8.9

0.5%around|η|=1.4 to2.1%(2.5%)around|η|=0 (3.2),isquoted asanadditionaluncertaintyforthedNch/d y results.

Thedeterminationofeventcentralitydependsonthehadronic eventselectionefficiency,aswellastheamountofcontamination fromEMprocesses.Sincetheinefficiencyislimitedtothemost pe-ripheralcollisions,theeffectoftheuncertaintyintheevent selec-tionefficiencyistoshifttheeventsintoothercentralityintervals. Hence,toevaluatetheuncertaintyinthefinalresults,differentsets ofcentralitycalibrations,derived aftervarying theeventselection efficiencyby itsuncertainty, areused tocategorisethedata. This leads to a difference of 0.4–25.7% in the final results, largest in the75–80% centralityinterval anddecreasing towards more cen-tralcollisions, which isfully correlatedacross different centrality intervals and η values.The uncertainties in the Npart values are determinedbypropagating theuncertaintiesintheparameters of theGlaubermodel,whicharelistedinSection3,andwhichrange from0.7to8.9%.

AsummaryofthesystematicuncertaintiesisgiveninTable1. Withtheexceptionoftheuncertaintiesintheeventselection effi-ciencyandtheNpartvalues,thesystematicuncertaintiesarelargely independent of centralityand highly correlated point-to-point in theregion|η|<1.4,whereonlycombinationsofBPIXlayers con-tributetotheresult.

6. Results

The pseudorapidity distributions of chargedhadrons for|η|<

3.2 are showninFig.2(upper)foreventsinthe0–80%centrality interval,andinFig.2(lower) foreventsinthe0–5% and50–55% centralityintervals. Thebottom panelin Fig.2(lower) showsthe ratiosofthedNch/dηdistributionsforeventsinthe0–5% central-ityintervalto thoseinthe50–55% centralityinterval,normalised tounityatmidrapidity.Thereisahintofacentralitydependence intheshape ofthe dNch/dη distribution,inthat thedistribution inperipheralcollisionsisflatterthanthatincentralcollisions.

None of the event generators are able to fully describe the dNch/dη distributions in the three centrality intervals shown, in particularthedNch/dηatmidrapidity.However,theshapesofthe distributions,wheretheoverallnormalisationsarefactoredout,are consistent withthose predictedby the EposLHC eventgenerator within the total systematic uncertainties. The centrality depen-denceoftheshapeofthedNch/dηdistributions isdescribed well by EposLHC butnot by the other eventgenerators, asshownin thebottompanelofFig.2(lower).

Therapidity distributionofchargedhadronsinXeXecollisions with0–80%centralityisshowninFig.3.ThedNch/d y distribution indataisobservedtobeconsistentwitharapidityplateauinthe region|y|<1.The dNch/d y distributionsobtainedfromthe Epos LHC, Hydjet,and Ampt eventgenerators arealsoshownfor

com-Fig. 2. Averaged and symmetrised dNch/dη distributions in XeXe collisions at

√

sNN=5.44 TeV (greysquares),for eventsinthe0–80%centralityinterval

(up-per), aswell asthe 0–5%(red squares)and 50–55%(bluecircles) centrality in-tervals (lower).Predictions fromthe EposLHCv3400 [8,18], Hydjet 1.9 [9],and Ampt1.26t5 [19] eventgeneratorsarealso shownforcomparison.Theratiosof thedNch/dηdistributionsforeventsinthe0–5%tothoseinthe50–55%

central-ityinterval,normalisedtounityatmidrapidity,areshowninthebottompanel.The bandsaroundthedatapointsdenotethetotalsystematicuncertainties,whilethe statisticaluncertaintiesarenegligible.

Fig. 3. Averagedand symmetrised charged-hadrondNch/d y distribution inXeXe

collisionsat√sNN=5.44 TeV foreventswith0–80%centrality(greysquares).The

bandaroundthedatapointsdenotesthetotalsystematicuncertainties,whilethe statisticaluncertaintiesarenegligible.Predictionsfromthe EposLHCv3400 [8,18], Hydjet1.9 [9],and Ampt 1.26t5 [19] eventgeneratorsarealsoshownincomparison.

parison.Noneoftheeventgeneratorsdescribetheplateauaround y=0.

Fig.4(upper)showsthecharged-hadrondNch/dηat midrapid-ity as a function of centrality. For events in the 0–5% centrality

Fig. 4. Charged-hadrondNch/dηinXeXecollisionsat √sNN=5.44 TeV at

midra-pidityasafunctionofeventcentrality,shownasis(upper)andnormalisedby2 A (lower),whereA istheatomicnumberofthenuclei.Theresultsarecomparedto measurementsinPbPbandXeXecollisionsbytheCMS [16] andALICE [17,37,38] Collaborations,andtomeasurementsinCuCuandAuAucollisionsbythePHOBOS Collaboration [39].Thebandsaroundthedatapointsdenotethetotalsystematic uncertainties,whilethestatisticaluncertaintiesarenegligible.

interval, dNch/dη is found to be 1187±36(syst) at midrapidity. ThisisnearlyafactoroftwogreaterthantheinterpolateddNch/dη inproton-protoncollisionsatthesameenergy [11] afterscalingby A,theatomic numberofthenuclei. The resultsarecompared to a measurement at the same energy for chargedparticles by the ALICECollaboration [17], which includes leptons in the analysis. Withinthetotaluncertainties,themeasurementsareconsistentin the0–60%centralityinterval,althoughtheALICECollaboration re-portsaslightlyhigherdNch/dηformoreperipheralcollisions.

The results are also compared to previous measurements in PbPbcollisionsat√sNN=2.76 and5.02 TeV bytheCMS [16] and ALICE [37,38] Collaborations. As one wouldexpect, forthe same centrality, dNch/dη increases with energy and system size. It is interesting to note that fordifferent collidingnucleiat thesame energy,dNch/dηisproportionalto2 A.ThisisevidentfromFig.4 (lower),where (dNch/dη)/2 A isshownas functionsofcentrality fora variety ofcollidingnuclei andenergies. Theseresults show thatthefeature observedatlowerenergies, thatthe geometryof thecolliding systemsplays an important role indetermining the productionofparticles [6],isalsopresentatthemuchhigherLHC energies.

Tostudytherelevanceforparticleproductionofthenumberof participatingnucleons,(dNch/dη)/Npartisshownasafunctionof

Npartin Fig.5(upper). The resultsare comparedto a measure-mentatthesameenergybytheALICECollaborationandto previ-ousmeasurementsinPbPbcollisionsat√sNN=2.76 and5.02 TeV. Ascanbeseen,theper-participantmultiplicityforXeXeandPbPb collisionswithsimilarNpart,butcorrespondingtodifferent cen-tralityclassesinthetwocollisionsystems,areinconsistent.Thisis mostapparentwhennearlycompletelyoverlappingXeXecollisions (0–5%centralityorNpart≈236)arecomparedtoPbPb collisions withsimilar Npart,forwhichthecorrespondingcentralityis ap-proximately 15–20%.However, as showninFig. 5 (lower),where Npart/2 A is used as a proxy forcentrality (the correspondence betweencentralityandNpart/2 A istabulatedinthesupplemental material [URL willbe inserted by publisher]),the per-participant

Fig. 5. AveragedNch/dηatmidrapiditynormalisedbyNpart,shownasafunction

ofNpart(upper)andNpart/2 A (lower),where A istheatomicnumberofthe

nuclei.TheresultsarecomparedtomeasurementsinPbPbandXeXecollisionsby theCMS [16] andALICE [17,37,38] Collaborations.Thebandsaroundthedatapoints denotethesystematicuncertainties,whilethestatisticaluncertaintiesarenegligible.

Fig. 6. AveragedNch/dηatmidrapiditynormalisedby2 A,shownasafunctionof

Npart/2 A,whereA istheatomicnumberofthenuclei.Theresultsarecompared

tomeasurementsinPbPbandXeXecollisionsbytheCMS [16] andALICE [17,37,38] Collaborations,andtomeasurementsinCuCuandAuAucollisionsbythePHOBOS Collaboration [39].Thebandsaroundthedatapointsdenotethesystematic uncer-tainties,whilethestatisticaluncertaintiesarenegligible.

charged-hadronmultiplicityfordifferentcollidingnucleiareequal withinuncertaintieswhenthegeometry(centrality)andenergyof thecomparedsystemsarethesame.

AnequivalentrepresentationofFig.5(lower)isshowninFig.6, where (dNch/dη)/2 A is shown as a function of Npart/2 A. In this form, it is clear that multiparticle production scales as 2 A times a function ofNpart/2 A, indicating a dependenceon both the systemsize (given by 2 A)and thegeometry ofthe colliding

system(representedbyNpart/2 A).Consideringthatmultiparticle productionprocessesinheavy ioncollisionsare highly complex— starting with the initial impact of the two nuclei, through the creation and evolution of a relativistic fluid, and followed by a hadronisation and scattering phase—it is not surprising that the resultdependsonboththecollidingsystemandenergy,ina non-trivialway.

7. Summary

Thepseudorapiditydistributions ofchargedhadronsin xenon-xenon collisions at a centre-of-mass energy of 5.44 TeV per nu-cleon pair are reported. Using data taken with the upgraded 4-layer silicon pixel detectors, the charged-hadron pseudorapid-ity densities, dNch/dη, are measured to an extended η range of

|η|<3.2.Foreventsin the0–5% centralityinterval,the dNch/dη atmidrapidity is measured to be 1187±36 (syst), witha negli-giblestatisticaluncertainty.Theresultsarefoundtobeconsistent withtheALICECollaboration’smeasurement. Thecharged-hadron rapidity density is also presented, and is found to be consistent witharapidityplateauintheregion|y|<1.Theresultsare com-pared to predictions from the EposLHC _{v3400, Hydjet 1.9, and} Ampt 1.26t5 event generators. None of the eventgenerators are able to fully describe the measurements in terms of the magni-tude,pseudorapiditydependence,andcentralitydependenceofthe dNch/dηdistributions,although EposLHCdescribestheshapewell. The per-participant dNch/dη atmidrapidity in XeXe collisions is observed to rise faster with Npart than in PbPb collisions. How-ever, whencomparing events withsimilar fractional overlap,the per-participant dNch/dη is consistent between the two collision systems. The results also show that the dNch/dη at midrapidity is a function of the collision geometry after normalising by 2 A, where A,istheatomicnumberofthenuclei.Thisisobservedfor avariety ofcollision systemsandenergies, bothat RHICandthe LHC, demonstrating that final-state charged-hadron multiplicities are strongly dependent on the collision geometry. These results provide important constraints on models and generators which describe multiparticle production in heavy ion collisions at high energies.Theymayalsohelp inthecharacterisation oftheinitial conditionsofthequarkgluonplasma,whichisneededforthe un-derstandingofits subsequenthydrodynamic evolution,aswell as thepropertiesofthisfluid.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructureessential to ouranalyses. Finally, we acknowledge the enduring support for the construc-tionandoperation oftheLHCandthe CMSdetectorprovidedby thefollowingfunding agencies:BMBWFandFWF(Austria); FNRS andFWO (Belgium); CNPq,CAPES, FAPERJ, FAPERGS, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIENCIAS (Colombia); MSESand CSF (Croatia); RPF (Cyprus); SENESCYT(Ecuador);MoER,ERCIUT,andERDF(Estonia);Academy ofFinland,MEC,andHIP(Finland);CEAandCNRS/IN2P3(France); BMBF, DFG, and HGF (Germany); GSRT (Greece); NKFIA (Hun-gary);DAEandDST(India);IPM(Iran);SFI(Ireland);INFN(Italy); MSIPandNRF (RepublicofKorea);MES (Latvia);LAS (Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, andUASLP-FAI(Mexico);MOS(Montenegro);MBIE(NewZealand);

PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna);MON,ROSATOM,RAS,RFBR,andNRCKI(Russia);MESTD (Serbia);SEIDI,CPAN,PCTI,andFEDER(Spain);MoSTR (SriLanka); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU andSFFR (Ukraine); STFC (United Kingdom);DOEand NSF (USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandHorizon2020Grant, contract Nos. 675440 and 765710 (European Union); the Lev-entis Foundation; the A.P. Sloan Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Of-fice; the Fonds pour la Formation à la Recherche dans l’Indus-trie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excellence of Sci-ence – EOS” – be.h project n. 30820817; the Beijing Municipal Science & Technology Commission, No. Z181100004218003; the Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Lendület (“Momentum”) Program and the János Bolyai Research Scholarship of the Hungarian Academy of Sci-ences, the New National Excellence Program ÚNKP, the NKFIA researchgrants123842,123959,124845,124850,125105,128713, 128786, and 129058 (Hungary); the Council of Science and In-dustrial Research,India;theHOMING PLUSprogramofthe Foun-dation for Polish Science, cofinanced from European Union, Re-gional Development Fund, the Mobility Plus program of the Ministry of Science and Higher Education, the National Science Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2014/13/B/ST2/02543, 2014/15/B/ST2/03998, and 2015/19/B/ST2/ 02861,Sonata-bis2012/07/E/ST2/01406;theNationalPriorities Re-search Program by Qatar National Research Fund; the Programa EstataldeFomentodelaInvestigaciónCientíficayTécnicade Exce-lenciaMaríade Maeztu,grantMDM-2015-0509andthePrograma Severo Ochoa del Principado de Asturias; the Thalisand Aristeia programscofinancedbyEU-ESFandtheGreekNSRF;the Rachada-pisek Sompot Fund for Postdoctoral Fellowship, Chulalongkorn University andthe ChulalongkornAcademic intoIts 2nd Century Project Advancement Project (Thailand); The Welch Foundation, contractC-1845;andtheWestonHavensFoundation(USA). Appendix A. Supplementarymaterial

Supplementarymaterialrelatedtothisarticlecanbefound on-lineathttps://doi.org/10.1016/j.physletb.2019.135049.

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TheCMSCollaboration

A.M. Sirunyan,A. Tumasyan YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, F. Ambrogi, E. Asilar,T. Bergauer, J. Brandstetter, M. Dragicevic, J. Erö,A. Escalante Del Valle, M. Flechl,R. Frühwirth1,V.M. Ghete, J. Hrubec, M. Jeitler1,N. Krammer, I. Krätschmer,D. Liko,

T. Madlener,I. Mikulec, N. Rad, H. Rohringer, J. Schieck1, R. Schöfbeck, M. Spanring, D. Spitzbart, A. Taurok,W. Waltenberger, J. Wittmann, C.-E. Wulz1, M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Chekhovsky, V. Mossolov,J. Suarez Gonzalez InstituteforNuclearProblems,Minsk,Belarus

E.A. De Wolf,D. Di Croce, X. Janssen, J. Lauwers,M. Pieters,H. Van Haevermaet, P. Van Mechelen, N. Van Remortel

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,F. Blekman, J. D’Hondt, I. De Bruyn, J. De Clercq, K. Deroover, G. Flouris, D. Lontkovskyi, S. Lowette,I. Marchesini, S. Moortgat, L. Moreels,Q. Python, K. Skovpen, S. Tavernier, W. Van Doninck, P. Van Mulders, I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

D. Beghin,B. Bilin, H. Brun, B. Clerbaux, G. De Lentdecker, H. Delannoy, B. Dorney,G. Fasanella, L. Favart, R. Goldouzian, A. Grebenyuk,A.K. Kalsi, T. Lenzi,J. Luetic, N. Postiau,E. Starling, L. Thomas,

C. Vander Velde, P. Vanlaer, D. Vannerom,Q. Wang UniversitéLibredeBruxelles,Bruxelles,Belgium

T. Cornelis,D. Dobur, A. Fagot,M. Gul, I. Khvastunov2, D. Poyraz, C. Roskas, D. Trocino,M. Tytgat, W. Verbeke,B. Vermassen, M. Vit, N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,O. Bondu, S. Brochet,G. Bruno, C. Caputo, P. David,C. Delaere, M. Delcourt, B. Francois, A. Giammanco,G. Krintiras, V. Lemaitre,A. Magitteri, A. Mertens, M. Musich, K. Piotrzkowski,A. Saggio, M. Vidal Marono, S. Wertz, J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

F.L. Alves,G.A. Alves, M. Correa Martins Junior,G. Correia Silva,C. Hensel, A. Moraes,M.E. Pol, P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas, W. Carvalho,J. Chinellato3,E. Coelho, E.M. Da Costa, G.G. Da Silveira4, D. De Jesus Damiao,C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson,D. Matos Figueiredo, M. Melo De Almeida,C. Mora Herrera, L. Mundim,H. Nogima, W.L. Prado Da Silva, L.J. Sanchez Rosas, A. Santoro, A. Sznajder,M. Thiel, E.J. Tonelli Manganote3,F. Torres Da Silva De Araujo, A. Vilela Pereira UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahujaa, C.A. Bernardesa, L. Calligarisa, T.R. Fernandez Perez Tomeia,E.M. Gregoresb, P.G. Mercadanteb,S.F. Novaesa,Sandra S. Padulaa

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,SãoPaulo,Brazil}

A. Aleksandrov, R. Hadjiiska, P. Iaydjiev,A. Marinov, M. Misheva, M. Rodozov, M. Shopova,G. Sultanov InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

A. Dimitrov, L. Litov,B. Pavlov, P. Petkov UniversityofSofia,Sofia,Bulgaria

W. Fang5, X. Gao5,L. Yuan BeihangUniversity,Beijing,China

M. Ahmad, J.G. Bian, G.M. Chen, H.S. Chen,M. Chen, Y. Chen, C.H. Jiang, D. Leggat, H. Liao,Z. Liu, F. Romeo,S.M. Shaheen6, A. Spiezia,J. Tao, Z. Wang, E. Yazgan, H. Zhang, S. Zhang6, J. Zhao InstituteofHighEnergyPhysics,Beijing,China

Y. Ban, G. Chen, A. Levin,J. Li, L. Li,Q. Li, Y. Mao, S.J. Qian, D. Wang,Z. Xu StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

Y. Wang

TsinghuaUniversity,Beijing,China

C. Avila,A. Cabrera, C.A. Carrillo Montoya, L.F. Chaparro Sierra, C. Florez,C.F. González Hernández, M.A. Segura Delgado

UniversidaddeLosAndes,Bogota,Colombia

B. Courbon,N. Godinovic, D. Lelas,I. Puljak, T. Sculac

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia Z. Antunovic,M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,D. Ferencek, K. Kadija,B. Mesic, A. Starodumov7, T. Susa InstituteRudjerBoskovic,Zagreb,Croatia

M.W. Ather,A. Attikis, M. Kolosova, G. Mavromanolakis,J. Mousa, C. Nicolaou, F. Ptochos,P.A. Razis, H. Rykaczewski

UniversityofCyprus,Nicosia,Cyprus M. Finger8,M. Finger Jr.8 CharlesUniversity,Prague,CzechRepublic E. Ayala

EscuelaPolitecnicaNacional,Quito,Ecuador E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

A. Ellithi Kamel9,M.A. Mahmoud10,11, Y. Mohammed10

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

S. Bhowmik, A. Carvalho Antunes De Oliveira,R.K. Dewanjee, K. Ehataht,M. Kadastik, M. Raidal, C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,H. Kirschenmann, J. Pekkanen,M. Voutilainen DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Havukainen, J.K. Heikkilä, T. Järvinen,V. Karimäki, R. Kinnunen, T. Lampén, K. Lassila-Perini,S. Laurila, S. Lehti,T. Lindén, P. Luukka, T. Mäenpää,H. Siikonen, E. Tuominen, J. Tuominiemi

HelsinkiInstituteofPhysics,Helsinki,Finland T. Tuuva

M. Besancon, F. Couderc,M. Dejardin, D. Denegri, J.L. Faure, F. Ferri, S. Ganjour, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry,C. Leloup,E. Locci, J. Malcles,G. Negro, J. Rander, A. Rosowsky, M.Ö. Sahin,M. Titov

IRFU,CEA,UniversitéParis-Saclay,Gif-sur-Yvette,France

A. Abdulsalam12,C. Amendola, I. Antropov, F. Beaudette, P. Busson, C. Charlot, R. Granier de Cassagnac, I. Kucher, A. Lobanov, J. Martin Blanco, C. Martin Perez, M. Nguyen,C. Ochando, G. Ortona, P. Paganini, P. Pigard,J. Rembser, R. Salerno,J.B. Sauvan, Y. Sirois, A.G. Stahl Leiton, A. Zabi, A. Zghiche

LaboratoireLeprince-Ringuet,Ecolepolytechnique,CNRS/IN2P3,UniversitéParis-Saclay,Palaiseau,France

J.-L. Agram13, J. Andrea, D. Bloch,J.-M. Brom, E.C. Chabert, V. Cherepanov, C. Collard,E. Conte13, J.-C. Fontaine13,D. Gelé, U. Goerlach, M. Jansová, A.-C. Le Bihan, N. Tonon,P. Van Hove

UniversitédeStrasbourg,CNRS,IPHCUMR7178,Strasbourg,France S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,C. Bernet, G. Boudoul, N. Chanon, R. Chierici,D. Contardo, P. Depasse, H. El Mamouni, J. Fay, L. Finco, S. Gascon,M. Gouzevitch, G. Grenier, B. Ille, F. Lagarde, I.B. Laktineh, H. Lattaud, M. Lethuillier, L. Mirabito,S. Perries, A. Popov14,V. Sordini, G. Touquet, M. Vander Donckt, S. Viret UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France

A. Khvedelidze8

GeorgianTechnicalUniversity,Tbilisi,Georgia D. Lomidze

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, L. Feld, M.K. Kiesel, K. Klein, M. Lipinski, M. Preuten,M.P. Rauch, C. Schomakers,J. Schulz, M. Teroerde,B. Wittmer, V. Zhukov14

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

A. Albert, D. Duchardt, M. Erdmann,S. Erdweg, T. Esch,R. Fischer, S. Ghosh,A. Güth, T. Hebbeker, C. Heidemann,K. Hoepfner, H. Keller, L. Mastrolorenzo, M. Merschmeyer,A. Meyer, P. Millet, S. Mukherjee,T. Pook, M. Radziej, H. Reithler,M. Rieger, A. Schmidt, D. Teyssier,S. Thüer RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

G. Flügge, O. Hlushchenko,T. Kress, A. Künsken, T. Müller, A. Nehrkorn, A. Nowack,C. Pistone, O. Pooth, D. Roy, H. Sert, A. Stahl15

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin,T. Arndt, C. Asawatangtrakuldee, I. Babounikau, K. Beernaert,O. Behnke, U. Behrens, A. Bermúdez Martínez, D. Bertsche, A.A. Bin Anuar, K. Borras16,V. Botta, A. Campbell, P. Connor, C. Contreras-Campana, V. Danilov,A. De Wit, M.M. Defranchis, C. Diez Pardos,D. Domínguez Damiani, G. Eckerlin, T. Eichhorn, A. Elwood, E. Eren, E. Gallo17,A. Geiser, A. Grohsjean, M. Guthoff,M. Haranko, A. Harb,J. Hauk, H. Jung, M. Kasemann,J. Keaveney, C. Kleinwort, J. Knolle,D. Krücker, W. Lange, A. Lelek, T. Lenz,J. Leonard, K. Lipka,W. Lohmann18, R. Mankel, I.-A. Melzer-Pellmann, A.B. Meyer, M. Meyer, M. Missiroli, G. Mittag, J. Mnich, V. Myronenko,S.K. Pflitsch, D. Pitzl,A. Raspereza,

M. Savitskyi,P. Saxena, P. Schütze,C. Schwanenberger, R. Shevchenko, A. Singh, H. Tholen,O. Turkot, A. Vagnerini,G.P. Van Onsem, R. Walsh, Y. Wen,K. Wichmann, C. Wissing,O. Zenaiev

R. Aggleton,S. Bein, L. Benato, A. Benecke, V. Blobel, T. Dreyer, E. Garutti,D. Gonzalez, P. Gunnellini, J. Haller, A. Hinzmann, A. Karavdina,G. Kasieczka, R. Klanner, R. Kogler,N. Kovalchuk, S. Kurz,

V. Kutzner, J. Lange,D. Marconi,J. Multhaup, M. Niedziela, C.E.N. Niemeyer,D. Nowatschin, A. Perieanu, A. Reimers,O. Rieger, C. Scharf, P. Schleper, S. Schumann, J. Schwandt, J. Sonneveld,H. Stadie,

G. Steinbrück, F.M. Stober,M. Stöver, A. Vanhoefer, B. Vormwald, I. Zoi UniversityofHamburg,Hamburg,Germany

M. Akbiyik, C. Barth,M. Baselga,S. Baur, E. Butz, R. Caspart, T. Chwalek, F. Colombo, W. De Boer, A. Dierlamm,K. El Morabit, N. Faltermann, B. Freund,M. Giffels,M.A. Harrendorf, F. Hartmann15, S.M. Heindl,U. Husemann, F. Kassel15, I. Katkov14, S. Kudella, H. Mildner, S. Mitra, M.U. Mozer, Th. Müller, M. Plagge, G. Quast, K. Rabbertz,M. Schröder, I. Shvetsov, G. Sieber,H.J. Simonis, R. Ulrich, S. Wayand,M. Weber, T. Weiler, S. Williamson, C. Wöhrmann, R. Wolf

KarlsruherInstitutfuerTechnologie,Karlsruhe,Germany

G. Anagnostou,G. Daskalakis, T. Geralis,A. Kyriakis, D. Loukas,G. Paspalaki, I. Topsis-Giotis InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

G. Karathanasis,S. Kesisoglou, P. Kontaxakis, A. Panagiotou,I. Papavergou, N. Saoulidou, E. Tziaferi, K. Vellidis

NationalandKapodistrianUniversityofAthens,Athens,Greece

K. Kousouris,I. Papakrivopoulos,G. Tsipolitis NationalTechnicalUniversityofAthens,Athens,Greece

I. Evangelou,C. Foudas, P. Gianneios, P. Katsoulis, P. Kokkas, S. Mallios,N. Manthos, I. Papadopoulos, E. Paradas, J. Strologas,F.A. Triantis, D. Tsitsonis

UniversityofIoánnina,Ioánnina,Greece

M. Bartók19,M. Csanad, N. Filipovic, P. Major, M.I. Nagy, G. Pasztor, O. Surányi, G.I. Veres MTA-ELTELendületCMSParticleandNuclearPhysicsGroup,EötvösLorándUniversity,Budapest,Hungary

G. Bencze,C. Hajdu, D. Horvath20, Á. Hunyadi, F. Sikler,T.Á. Vámi, V. Veszpremi, G. Vesztergombi† WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni,S. Czellar, J. Karancsi21,A. Makovec,J. Molnar, Z. Szillasi InstituteofNuclearResearchATOMKI,Debrecen,Hungary

P. Raics,Z.L. Trocsanyi, B. Ujvari InstituteofPhysics,UniversityofDebrecen,Debrecen,Hungary S. Choudhury,J.R. Komaragiri, P.C. Tiwari IndianInstituteofScience(IISc),Bangalore,India

S. Bahinipati22,C. Kar, P. Mal, K. Mandal, A. Nayak23,D.K. Sahoo22,S.K. Swain NationalInstituteofScienceEducationandResearch,HBNI,Bhubaneswar,India

S. Bansal,S.B. Beri, V. Bhatnagar, S. Chauhan,R. Chawla, N. Dhingra, R. Gupta, A. Kaur, M. Kaur, S. Kaur, R. Kumar,P. Kumari, M. Lohan, A. Mehta,K. Sandeep, S. Sharma, J.B. Singh, A.K. Virdi, G. Walia

A. Bhardwaj,B.C. Choudhary, R.B. Garg, M. Gola,S. Keshri, Ashok Kumar, S. Malhotra,M. Naimuddin, P. Priyanka, K. Ranjan,Aashaq Shah, R. Sharma

UniversityofDelhi,Delhi,India

R. Bhardwaj24,M. Bharti24,R. Bhattacharya,S. Bhattacharya, U. Bhawandeep24,D. Bhowmik, S. Dey, S. Dutt24,S. Dutta, S. Ghosh,K. Mondal, S. Nandan, A. Purohit, P.K. Rout, A. Roy,S. Roy Chowdhury, G. Saha,S. Sarkar, M. Sharan, B. Singh24, S. Thakur24

SahaInstituteofNuclearPhysics,HBNI,Kolkata,India P.K. Behera

IndianInstituteofTechnologyMadras,Madras,India

R. Chudasama, D. Dutta, V. Jha, V. Kumar, P.K. Netrakanti,L.M. Pant, P. Shukla BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz, M.A. Bhat,S. Dugad,G.B. Mohanty, N. Sur,B. Sutar, Ravindra Kumar Verma TataInstituteofFundamentalResearch-A,Mumbai,India

S. Banerjee, S. Bhattacharya, S. Chatterjee,P. Das, M. Guchait, Sa. Jain, S. Karmakar,S. Kumar, M. Maity25, G. Majumder,K. Mazumdar, N. Sahoo, T. Sarkar25

TataInstituteofFundamentalResearch-B,Mumbai,India

S. Chauhan,S. Dube, V. Hegde, A. Kapoor, K. Kothekar, S. Pandey, A. Rane, S. Sharma IndianInstituteofScienceEducationandResearch(IISER),Pune,India

S. Chenarani26, E. Eskandari Tadavani,S.M. Etesami26,M. Khakzad, M. Mohammadi Najafabadi, M. Naseri, F. Rezaei Hosseinabadi, B. Safarzadeh27,M. Zeinali

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran M. Felcini,M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b, C. Calabriaa,b,A. Colaleoa,D. Creanzaa,c, L. Cristellaa,b,N. De Filippisa,c,

M. De Palmaa,b, A. Di Florioa,b, F. Erricoa,b,L. Fiorea, A. Gelmia,b,G. Iasellia,c,M. Incea,b, S. Lezkia,b, G. Maggia,c,M. Maggia, G. Minielloa,b, S. Mya,b, S. Nuzzoa,b, A. Pompilia,b,G. Pugliesea,c, R. Radognaa, A. Ranieria, G. Selvaggia,b,A. Sharmaa, L. Silvestrisa, R. Vendittia, P. Verwilligena,G. Zitoa

a_{INFNSezionediBari,Bari,Italy} b_{UniversitàdiBari,Bari,Italy} c_{PolitecnicodiBari,Bari,Italy}

G. Abbiendia,C. Battilanaa,b,D. Bonacorsia,b,L. Borgonovia,b,S. Braibant-Giacomellia,b,

R. Campaninia,b, P. Capiluppia,b,A. Castroa,b,F.R. Cavalloa, S.S. Chhibraa,b, C. Cioccaa, G. Codispotia,b, M. Cuffiania,b,G.M. Dallavallea,F. Fabbria,A. Fanfania,b,E. Fontanesi, P. Giacomellia, C. Grandia, L. Guiduccia,b,S. Lo Meoa,S. Marcellinia,G. Masettia,A. Montanaria,F.L. Navarriaa,b, A. Perrottaa, F. Primaveraa,b,15,A.M. Rossia,b,T. Rovellia,b,G.P. Sirolia,b, N. Tosia

a_{INFNSezionediBologna,Bologna,Italy} b_{UniversitàdiBologna,Bologna,Italy}

S. Albergoa,b,A. Di Mattiaa,R. Potenzaa,b, A. Tricomia,b,C. Tuvea,b

a_{INFNSezionediCatania,Catania,Italy} b_{UniversitàdiCatania,Catania,Italy}

G. Barbaglia,K. Chatterjeea,b,V. Ciullia,b,C. Civininia,R. D’Alessandroa,b, E. Focardia,b, G. Latino, P. Lenzia,b, M. Meschinia, S. Paolettia,L. Russoa,28, G. Sguazzonia,D. Stroma, L. Viliania

a_{INFNSezionediFirenze,Firenze,Italy} b_{UniversitàdiFirenze,Firenze,Italy}

L. Benussi,S. Bianco, F. Fabbri, D. Piccolo INFNLaboratoriNazionalidiFrascati,Frascati,Italy

F. Ferroa, F. Raveraa,b, E. Robuttia,S. Tosia,b

a_{INFNSezionediGenova,Genova,Italy} b_{UniversitàdiGenova,Genova,Italy}

A. Benagliaa,A. Beschib,L. Brianzaa,b,F. Brivioa,b,V. Cirioloa,b,15, S. Di Guidaa,b,15, M.E. Dinardoa,b, S. Fiorendia,b,S. Gennaia,A. Ghezzia,b, P. Govonia,b,M. Malbertia,b, S. Malvezzia, A. Massironia,b, D. Menascea, F. Monti, L. Moronia, M. Paganonia,b, D. Pedrinia,S. Ragazzia,b, T. Tabarelli de Fatisa,b, D. Zuoloa,b

a_{INFNSezionediMilano-Bicocca,Milano,Italy} b_{UniversitàdiMilano-Bicocca,Milano,Italy}

S. Buontempoa, N. Cavalloa,c,A. De Iorioa,b,A. Di Crescenzoa,b, F. Fabozzia,c,F. Fiengaa,G. Galatia, A.O.M. Iorioa,b,W.A. Khana, L. Listaa,S. Meolaa,d,15,P. Paoluccia,15,C. Sciaccaa,b,E. Voevodinaa,b

a_{INFNSezionediNapoli,Napoli,Italy} b_{UniversitàdiNapoli‘FedericoII’,Napoli,Italy} c_{UniversitàdellaBasilicata,Potenza,Italy} d_{UniversitàG.Marconi,Roma,Italy}

P. Azzia, N. Bacchettaa, D. Biselloa,b, A. Bolettia,b, A. Bragagnolo,R. Carlina,b,P. Checchiaa, M. Dall’Ossoa,b, P. De Castro Manzanoa,T. Dorigoa,U. Dossellia, F. Gasparinia,b, U. Gasparinia,b, A. Gozzelinoa, S.Y. Hoh, S. Lacapraraa,P. Lujan, M. Margonia,b, A.T. Meneguzzoa,b,J. Pazzinia,b,

P. Ronchesea,b, R. Rossina,b,F. Simonettoa,b,A. Tiko,E. Torassaa,M. Zanettia,b, P. Zottoa,b,G. Zumerlea,b

a_{INFNSezionediPadova,Padova,Italy} b_{UniversitàdiPadova,Padova,Italy} c_{UniversitàdiTrento,Trento,Italy}

A. Braghieria, A. Magnania,P. Montagnaa,b, S.P. Rattia,b,V. Rea,M. Ressegottia,b,C. Riccardia,b, P. Salvinia, I. Vaia,b,P. Vituloa,b

a_{INFNSezionediPavia,Pavia,Italy} b_{UniversitàdiPavia,Pavia,Italy}

M. Biasinia,b,G.M. Bileia,C. Cecchia,b,D. Ciangottinia,b, L. Fanòa,b,P. Laricciaa,b,R. Leonardia,b, E. Manonia,G. Mantovania,b,V. Mariania,b,M. Menichellia, A. Rossia,b,A. Santocchiaa,b, D. Spigaa

a_{INFNSezionediPerugia,Perugia,Italy} b_{UniversitàdiPerugia,Perugia,Italy}

K. Androsova, P. Azzurria, G. Bagliesia, L. Bianchinia, T. Boccalia, L. Borrello, R. Castaldia,M.A. Cioccia,b, R. Dell’Orsoa,G. Fedia, F. Fioria,c, L. Gianninia,c, A. Giassia, M.T. Grippoa,F. Ligabuea,c, E. Mancaa,c, G. Mandorlia,c, A. Messineoa,b, F. Pallaa,A. Rizzia,b,P. Spagnoloa,R. Tenchinia,G. Tonellia,b,

A. Venturia,P.G. Verdinia

a_{INFNSezionediPisa,Pisa,Italy} b_{UniversitàdiPisa,Pisa,Italy}

L. Baronea,b,F. Cavallaria, M. Cipriania,b,D. Del Rea,b, E. Di Marcoa,b, M. Diemoza,S. Gellia,b,

E. Longoa,b, B. Marzocchia,b,P. Meridiania, G. Organtinia,b,F. Pandolfia, R. Paramattia,b, F. Preiatoa,b, S. Rahatloua,b,C. Rovellia,F. Santanastasioa,b

a_{INFNSezionediRoma,Rome,Italy} b_{SapienzaUniversitàdiRoma,Rome,Italy}

N. Amapanea,b, R. Arcidiaconoa,c,S. Argiroa,b,M. Arneodoa,c,N. Bartosika,R. Bellana,b, C. Biinoa, N. Cartigliaa, F. Cennaa,b,S. Comettia,M. Costaa,b, R. Covarellia,b,N. Demariaa,B. Kiania,b,C. Mariottia, S. Masellia, E. Migliorea,b,V. Monacoa,b,E. Monteila,b,M. Montenoa, M.M. Obertinoa,b,L. Pachera,b, N. Pastronea,M. Pelliccionia, G.L. Pinna Angionia,b,A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b,

K. Shchelinaa,b, V. Solaa, A. Solanoa,b,D. Soldia,b,A. Staianoa

a_{INFNSezionediTorino,Torino,Italy} b_{UniversitàdiTorino,Torino,Italy}

c_{UniversitàdelPiemonteOrientale,Novara,Italy}

S. Belfortea,V. Candelisea,b,M. Casarsaa, F. Cossuttia,A. Da Rolda,b,G. Della Riccaa,b, F. Vazzolera,b, A. Zanettia

a_{INFNSezionediTrieste,Trieste,Italy} b_{UniversitàdiTrieste,Trieste,Italy}

D.H. Kim,G.N. Kim, M.S. Kim,J. Lee, S. Lee,S.W. Lee, C.S. Moon, Y.D. Oh, S.I. Pak, S. Sekmen,D.C. Son, Y.C. Yang

KyungpookNationalUniversity,Daegu,RepublicofKorea H. Kim,D.H. Moon, G. Oh

ChonnamNationalUniversity,InstituteforUniverseandElementaryParticles,Kwangju,RepublicofKorea J. Goh29,T.J. Kim

HanyangUniversity,Seoul,RepublicofKorea

S. Cho,S. Choi, Y. Go, D. Gyun,S. Ha, B. Hong,Y. Jo, K. Lee,K.S. Lee, S. Lee, J. Lim, S.K. Park, Y. Roh KoreaUniversity,Seoul,RepublicofKorea

H.S. Kim

SejongUniversity,Seoul,RepublicofKorea

J. Almond, J. Kim,J.S. Kim, H. Lee,K. Lee, K. Nam,S.B. Oh, B.C. Radburn-Smith, S.h. Seo, U.K. Yang, H.D. Yoo,G.B. Yu

SeoulNationalUniversity,Seoul,RepublicofKorea

D. Jeon, H. Kim,J.H. Kim, J.S.H. Lee, I.C. Park UniversityofSeoul,Seoul,RepublicofKorea

Y. Choi,C. Hwang, J. Lee, I. Yu SungkyunkwanUniversity,Suwon,RepublicofKorea

V. Dudenas, A. Juodagalvis,J. Vaitkus VilniusUniversity,Vilnius,Lithuania

I. Ahmed,Z.A. Ibrahim, M.A.B. Md Ali30,F. Mohamad Idris31,W.A.T. Wan Abdullah, M.N. Yusli, Z. Zolkapli

J.F. Benitez, A. Castaneda Hernandez,J.A. Murillo Quijada UniversidaddeSonora(UNISON),Hermosillo,Mexico

H. Castilla-Valdez,E. De La Cruz-Burelo, M.C. Duran-Osuna, I. Heredia-De La Cruz32,R. Lopez-Fernandez, J. Mejia Guisao,R.I. Rabadan-Trejo,M. Ramirez-Garcia, G. Ramirez-Sanchez, R. Reyes-Almanza,

A. Sanchez-Hernandez

CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico

S. Carrillo Moreno, C. Oropeza Barrera, F. Vazquez Valencia UniversidadIberoamericana,MexicoCity,Mexico

J. Eysermans,I. Pedraza, H.A. Salazar Ibarguen, C. Uribe Estrada BenemeritaUniversidadAutonomadePuebla,Puebla,Mexico

A. Morelos Pineda

UniversidadAutónomadeSanLuisPotosí,SanLuisPotosí,Mexico D. Krofcheck

UniversityofAuckland,Auckland,NewZealand S. Bheesette,P.H. Butler UniversityofCanterbury,Christchurch,NewZealand

A. Ahmad,M. Ahmad, M.I. Asghar, Q. Hassan, H.R. Hoorani,A. Saddique, M.A. Shah, M. Shoaib,M. Waqas NationalCentreforPhysics,Quaid-I-AzamUniversity,Islamabad,Pakistan

H. Bialkowska,M. Bluj, B. Boimska,T. Frueboes, M. Górski, M. Kazana, M. Szleper,P. Traczyk, P. Zalewski NationalCentreforNuclearResearch,Swierk,Poland

K. Bunkowski, A. Byszuk33,K. Doroba, A. Kalinowski, M. Konecki,J. Krolikowski, M. Misiura, M. Olszewski,A. Pyskir, M. Walczak

InstituteofExperimentalPhysics,FacultyofPhysics,UniversityofWarsaw,Warsaw,Poland

M. Araujo,P. Bargassa, C. Beirão Da Cruz E Silva, A. Di Francesco, P. Faccioli,B. Galinhas, M. Gallinaro, J. Hollar,N. Leonardo, M.V. Nemallapudi,J. Seixas, G. Strong,O. Toldaiev, D. Vadruccio,J. Varela LaboratóriodeInstrumentaçãoeFísicaExperimentaldePartículas,Lisboa,Portugal

S. Afanasiev,P. Bunin, M. Gavrilenko,I. Golutvin, I. Gorbunov, A. Kamenev,V. Karjavine,A. Lanev, A. Malakhov,V. Matveev34,35, P. Moisenz, V. Palichik,V. Perelygin, S. Shmatov, S. Shulha,N. Skatchkov, V. Smirnov,N. Voytishin, A. Zarubin

JointInstituteforNuclearResearch,Dubna,Russia

V. Golovtsov,Y. Ivanov, V. Kim36,E. Kuznetsova37, P. Levchenko,V. Murzin,V. Oreshkin, I. Smirnov, D. Sosnov,V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev

PetersburgNuclearPhysicsInstitute,Gatchina(St.Petersburg),Russia

Yu. Andreev,A. Dermenev,S. Gninenko, N. Golubev, A. Karneyeu, M. Kirsanov,N. Krasnikov, A. Pashenkov,D. Tlisov, A. Toropin

V. Epshteyn, V. Gavrilov, N. Lychkovskaya,V. Popov, I. Pozdnyakov, G. Safronov, A. Spiridonov, A. Stepennov, V. Stolin, M. Toms,E. Vlasov, A. Zhokin

InstituteforTheoreticalandExperimentalPhysics,Moscow,Russia T. Aushev

MoscowInstituteofPhysicsandTechnology,Moscow,Russia

M. Chadeeva38,P. Parygin,D. Philippov, S. Polikarpov38,E. Popova,V. Rusinov NationalResearchNuclearUniversity‘MoscowEngineeringPhysicsInstitute’(MEPhI),Moscow,Russia

V. Andreev,M. Azarkin, I. Dremin35,M. Kirakosyan, S.V. Rusakov, A. Terkulov P.N.LebedevPhysicalInstitute,Moscow,Russia

A. Baskakov,A. Belyaev, E. Boos,A. Ershov, A. Gribushin, A. Kaminskiy39,O. Kodolova, V. Korotkikh, I. Lokhtin,I. Miagkov, S. Obraztsov, S. Petrushanko,V. Savrin, A. Snigirev, I. Vardanyan

SkobeltsynInstituteofNuclearPhysics,LomonosovMoscowStateUniversity,Moscow,Russia

A. Barnyakov40,V. Blinov40,T. Dimova40,L. Kardapoltsev40,Y. Skovpen40 NovosibirskStateUniversity(NSU),Novosibirsk,Russia

I. Azhgirey,I. Bayshev,S. Bitioukov, D. Elumakhov, A. Godizov, V. Kachanov, A. Kalinin, D. Konstantinov, P. Mandrik,V. Petrov, R. Ryutin, S. Slabospitskii, A. Sobol, S. Troshin, N. Tyurin, A. Uzunian, A. Volkov InstituteforHighEnergyPhysicsofNationalResearchCentre‘KurchatovInstitute’,Protvino,Russia

A. Babaev, S. Baidali,V. Okhotnikov NationalResearchTomskPolytechnicUniversity,Tomsk,Russia

P. Adzic41, P. Cirkovic, D. Devetak,M. Dordevic, J. Milosevic UniversityofBelgrade,FacultyofPhysicsandVincaInstituteofNuclearSciences,Belgrade,Serbia

J. Alcaraz Maestre, A. Álvarez Fernández, I. Bachiller, M. Barrio Luna,J.A. Brochero Cifuentes, M. Cerrada, N. Colino, B. De La Cruz,A. Delgado Peris, C. Fernandez Bedoya,J.P. Fernández Ramos, J. Flix, M.C. Fouz, O. Gonzalez Lopez,S. Goy Lopez, J.M. Hernandez, M.I. Josa,D. Moran, A. Pérez-Calero Yzquierdo,

J. Puerta Pelayo, I. Redondo,L. Romero, M.S. Soares, A. Triossi CentrodeInvestigacionesEnergéticasMedioambientalesyTecnológicas(CIEMAT),Madrid,Spain

C. Albajar, J.F. de Trocóniz UniversidadAutónomadeMadrid,Madrid,Spain

J. Cuevas, C. Erice,J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero,J.R. González Fernández, E. Palencia Cortezon,V. Rodríguez Bouza, S. Sanchez Cruz, P. Vischia, J.M. Vizan Garcia

UniversidaddeOviedo,Oviedo,Spain

I.J. Cabrillo, A. Calderon, B. Chazin Quero,J. Duarte Campderros, M. Fernandez,P.J. Fernández Manteca, A. García Alonso,J. Garcia-Ferrero, G. Gomez, A. Lopez Virto,J. Marco, C. Martinez Rivero,

P. Martinez Ruiz del Arbol, F. Matorras,J. Piedra Gomez, C. Prieels, T. Rodrigo, A. Ruiz-Jimeno, L. Scodellaro,N. Trevisani, I. Vila, R. Vilar Cortabitarte

InstitutodeFísicadeCantabria(IFCA),CSIC-UniversidaddeCantabria,Santander,Spain N. Wickramage

D. Abbaneo, B. Akgun,E. Auffray, G. Auzinger, P. Baillon, A.H. Ball, D. Barney, J. Bendavid,M. Bianco, A. Bocci, C. Botta,E. Brondolin, T. Camporesi, M. Cepeda, G. Cerminara, E. Chapon, Y. Chen, G. Cucciati, D. d’Enterria, A. Dabrowski,N. Daci, V. Daponte, A. David,A. De Roeck, N. Deelen, M. Dobson,

M. Dünser,N. Dupont,A. Elliott-Peisert, P. Everaerts,F. Fallavollita42,D. Fasanella, G. Franzoni, J. Fulcher, W. Funk, D. Gigi,A. Gilbert, K. Gill,F. Glege, M. Guilbaud, D. Gulhan, J. Hegeman, C. Heidegger,

V. Innocente, A. Jafari,P. Janot, O. Karacheban18,J. Kieseler, A. Kornmayer, M. Krammer1,C. Lange, P. Lecoq,C. Lourenço,L. Malgeri, M. Mannelli,F. Meijers, J.A. Merlin,S. Mersi, E. Meschi, P. Milenovic43, F. Moortgat,M. Mulders, J. Ngadiuba, S. Nourbakhsh,S. Orfanelli, L. Orsini,F. Pantaleo15, L. Pape, E. Perez,M. Peruzzi, A. Petrilli, G. Petrucciani,A. Pfeiffer,M. Pierini, F.M. Pitters,D. Rabady, A. Racz, T. Reis,G. Rolandi44, M. Rovere, H. Sakulin, C. Schäfer, C. Schwick,M. Seidel, M. Selvaggi,A. Sharma, P. Silva,P. Sphicas45,A. Stakia, J. Steggemann,M. Tosi,D. Treille, A. Tsirou, V. Veckalns46,M. Verzetti, W.D. Zeuner

CERN,EuropeanOrganizationforNuclearResearch,Geneva,Switzerland

L. Caminada47, K. Deiters,W. Erdmann, R. Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski, U. Langenegger,T. Rohe, S.A. Wiederkehr

PaulScherrerInstitut,Villigen,Switzerland

M. Backhaus,L. Bäni, P. Berger,N. Chernyavskaya, G. Dissertori, M. Dittmar, M. Donegà, C. Dorfer, T.A. Gómez Espinosa, C. Grab, D. Hits, T. Klijnsma,W. Lustermann, R.A. Manzoni, M. Marionneau,

M.T. Meinhard,F. Micheli,P. Musella, F. Nessi-Tedaldi, J. Pata, F. Pauss, G. Perrin,L. Perrozzi, S. Pigazzini, M. Quittnat,C. Reissel, D. Ruini,D.A. Sanz Becerra, M. Schönenberger, L. Shchutska, V.R. Tavolaro, K. Theofilatos,M.L. Vesterbacka Olsson, R. Wallny, D.H. Zhu

ETHZurich–InstituteforParticlePhysicsandAstrophysics(IPA),Zurich,Switzerland

T.K. Aarrestad, C. Amsler48, D. Brzhechko, M.F. Canelli,A. De Cosa, R. Del Burgo, S. Donato, C. Galloni, T. Hreus,B. Kilminster, S. Leontsinis, I. Neutelings, G. Rauco, P. Robmann, D. Salerno,K. Schweiger, C. Seitz,Y. Takahashi, A. Zucchetta

UniversitätZürich,Zurich,Switzerland

Y.H. Chang,K.y. Cheng, T.H. Doan,R. Khurana, C.M. Kuo,W. Lin, A. Pozdnyakov,S.S. Yu NationalCentralUniversity,Chung-Li,Taiwan

P. Chang, Y. Chao,K.F. Chen, P.H. Chen, W.-S. Hou, Arun Kumar, Y.F. Liu,R.-S. Lu, E. Paganis, A. Psallidas, A. Steen

NationalTaiwanUniversity(NTU),Taipei,Taiwan

B. Asavapibhop,N. Srimanobhas, N. Suwonjandee ChulalongkornUniversity,FacultyofScience,DepartmentofPhysics,Bangkok,Thailand

A. Bat,F. Boran, S. Cerci49,S. Damarseckin, Z.S. Demiroglu, F. Dolek, C. Dozen,I. Dumanoglu, S. Girgis, G. Gokbulut,Y. Guler, E. Gurpinar, I. Hos50,C. Isik, E.E. Kangal51, O. Kara, A. Kayis Topaksu,U. Kiminsu, M. Oglakci,G. Onengut, K. Ozdemir52,S. Ozturk53, D. Sunar Cerci49,B. Tali49, U.G. Tok, S. Turkcapar, I.S. Zorbakir,C. Zorbilmez

ÇukurovaUniversity,PhysicsDepartment,ScienceandArtFaculty,Adana,Turkey B. Isildak54, G. Karapinar55, M. Yalvac, M. Zeyrek MiddleEastTechnicalUniversity,PhysicsDepartment,Ankara,Turkey

I.O. Atakisi,E. Gülmez,M. Kaya56, O. Kaya57,S. Ozkorucuklu58,S. Tekten, E.A. Yetkin59 BogaziciUniversity,Istanbul,Turkey

M.N. Agaras, A. Cakir,K. Cankocak, Y. Komurcu, S. Sen60 IstanbulTechnicalUniversity,Istanbul,Turkey

B. Grynyov

InstituteforScintillationMaterialsofNationalAcademyofScienceofUkraine,Kharkov,Ukraine L. Levchuk

NationalScientificCenter,KharkovInstituteofPhysicsandTechnology,Kharkov,Ukraine

F. Ball,L. Beck, J.J. Brooke,D. Burns, E. Clement, D. Cussans,O. Davignon, H. Flacher,J. Goldstein, G.P. Heath, H.F. Heath,L. Kreczko, D.M. Newbold61,S. Paramesvaran, B. Penning,T. Sakuma, D. Smith, V.J. Smith,J. Taylor, A. Titterton

UniversityofBristol,Bristol,UnitedKingdom

A. Belyaev62, C. Brew, R.M. Brown, D. Cieri, D.J.A. Cockerill, J.A. Coughlan, K. Harder,S. Harper, J. Linacre, E. Olaiya,D. Petyt, C.H. Shepherd-Themistocleous, A. Thea, I.R. Tomalin, T. Williams, W.J. Womersley RutherfordAppletonLaboratory,Didcot,UnitedKingdom

R. Bainbridge,P. Bloch, J. Borg,S. Breeze, O. Buchmuller, A. Bundock, D. Colling, P. Dauncey, G. Davies, M. Della Negra, R. Di Maria, Y. Haddad, G. Hall,G. Iles, T. James, M. Komm, C. Laner, L. Lyons,

A.-M. Magnan, S. Malik,A. Martelli, J. Nash63,A. Nikitenko7,V. Palladino, M. Pesaresi, D.M. Raymond, A. Richards,A. Rose, E. Scott,C. Seez,A. Shtipliyski, G. Singh, M. Stoye, T. Strebler, S. Summers,

A. Tapper,K. Uchida, T. Virdee15, N. Wardle, D. Winterbottom, J. Wright,S.C. Zenz ImperialCollege,London,UnitedKingdom

J.E. Cole, P.R. Hobson, A. Khan,P. Kyberd, C.K. Mackay, A. Morton,I.D. Reid, L. Teodorescu,S. Zahid BrunelUniversity,Uxbridge,UnitedKingdom

K. Call,J. Dittmann, K. Hatakeyama, H. Liu, C. Madrid,B. Mcmaster,N. Pastika, C. Smith BaylorUniversity,Waco,USA

R. Bartek, A. Dominguez CatholicUniversityofAmerica,Washington,DC,USA

A. Buccilli, S.I. Cooper, C. Henderson, P. Rumerio,C. West TheUniversityofAlabama,Tuscaloosa,USA

D. Arcaro, T. Bose, D. Gastler, D. Pinna,D. Rankin, C. Richardson, J. Rohlf, L. Sulak,D. Zou BostonUniversity,Boston,USA

G. Benelli, X. Coubez, D. Cutts, M. Hadley, J. Hakala, U. Heintz, J.M. Hogan64, K.H.M. Kwok, E. Laird, G. Landsberg, J. Lee,Z. Mao, M. Narain, S. Sagir65, R. Syarif, E. Usai, D. Yu

BrownUniversity,Providence,USA

R. Band,C. Brainerd, R. Breedon, D. Burns,M. Calderon De La Barca Sanchez, M. Chertok, J. Conway, R. Conway, P.T. Cox, R. Erbacher,C. Flores, G. Funk, W. Ko, O. Kukral, R. Lander,M. Mulhearn, D. Pellett, J. Pilot, S. Shalhout, M. Shi,D. Stolp, D. Taylor,K. Tos, M. Tripathi,Z. Wang, F. Zhang