Nuclear modification factor of D0mesons in PbPbcollisions at √sNN=5.02 TeV

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Physics

Letters

B

www.elsevier.com/locate/physletb

Nuclear

modification

factor

of

D

mesons

in

PbPb collisions

at

√

s

=

5

.

02

TeV

Receivedinrevisedform19April2018 Accepted28May2018

Availableonline31May2018 Editor:M.Doser

Keywords: Physics Suppression Quarkgluonplasma Shadowing D-meson Openheavy-flavour

The transverse momentum (pT) spectrum of prompt D0 mesons and their antiparticles has been

measuredviathehadronicdecaychannelsD0_→K−_π+_andD0

→K+π−inpp andPbPb collisionsata centre-of-massenergyof5.02 TeV pernucleonpairwiththeCMSdetectorattheLHC.Themeasurement is performedin the D0 _{meson p}

T range of2–100 GeV/c andin the rapidityrangeof |y|<1.The pp

(PbPb)dataset usedfor thisanalysiscorresponds toanintegrated luminosityof 27.4 pb−1 _{(530 μb}−1_).

ThemeasuredD0mesonpTspectruminppcollisionsiswelldescribedbyperturbativeQCDcalculations.

Thenuclearmodificationfactor,comparingD0_{mesonyieldsinPbPb andpp collisions,wasextractedfor}

bothminimum-biasandthe10%mostcentralPbPb interactions.Forcentralevents,theD0_mesonyield

inthePbPb collisionsissuppressedbyafactorof5–6comparedtothepp referenceinthepTrangeof

6–10 GeV/c. ForD0 _{mesonsinthehigh-p}

Trangeof60–100 GeV/c,asignificantlysmallersuppression is

observed.Theresultsarealsocomparedtotheoreticalcalculations.

©2018TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Relativistic heavy ion collisions allow the study of quantum chromodynamics (QCD) at high energy densityand temperature. Lattice QCD calculations predict that under such extreme condi-tionsatransitiontoastronglyinteractinganddeconfinedmedium, calledthe quark-gluonplasma (QGP), occurs [1–3]. Heavyquarks are effective probes to study the properties of the deconfined medium createdin heavy ioncollisions. Thesequarks are mostly produced in primary hard QCD scatterings with a production timescale thatis shorterthanthe formationtime oftheQGP [4]. Duringtheir propagationthroughthe medium,heavy quarkslose energyviaradiative andcollisionalinteractions withthemedium constituents.Quarksareexpectedtolose lessenergythan gluons asaconsequenceoftheirsmallercolourfactor.Inaddition,the so-called“dead-coneeffect”isexpectedto reducesmall-angle gluon radiationofheavyquarkswhencomparedtobothgluonsandlight quarks [5–7]. Energylosscanbe studiedusingthenuclear modi-ficationfactor(RAA), definedastheratioofthe PbPb yieldtothe pp cross-sectionscaledbythenuclearoverlapfunction [8].Precise measurements of the RAA of particles containing both light and heavyquarkscanthusprovideimportanttestsofQCDpredictions atextremedensitiesandtemperaturesandinparticularallowone

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

to test the expected flavour dependence of the energy loss pro-cesses. The comparisonto theoretical calculationsisfundamental in orderto claim anyevidence of flavour dependenceof the en-ergy loss mechanisms since sizeable discrepancies in the RAA of light andheavyparticles canariseasaconsequenceofthe differ-enttransversemomentumspectraandfragmentationfunctionsof beauty,charm,andlightquarksandgluons.

Evidence of open charm suppression at the CERN LHC was observed by the ALICE Collaboration using the RAA of promptly produced D mesons (D0, D+, D∗+ mesons and their conjugates) at mid-rapidity (|y|<0.5) at a nucleon–nucleon centre-of-mass energy √sNN =2.76 TeV. The measurement was performed as a functionofcentrality(i.e. thedegreeofoverlapofthetwo collid-ing nuclei) andtransverse momentum (1<pT<36 GeV/c) [9,10]. Amaximumsuppressionbyafactorof5–6withrespecttothepp reference was observedfor the10% mostcentral collisions at pT ofabout10 GeV/c.Asuppressionby afactorofabout3was mea-suredatthehighestpT rangestudied,from25to35 GeV/c.TheD meson RAA was foundto be consistent with that forall charged particlesforpTfrom6to36 GeV/c.Forlower pT,theDmesonRAA was observedtobe slightlyhigherthanthecharged-particle RAA, althoughstillcompatiblewithintheuncertainties [11,12].AtRHIC, the RAA ofD0 mesonsforthe10%mostcentralAuAucollisionsat

√

sNN=200 GeV was measured by the STAR Collaborationin the rapidityrangeof|y|<1 [13].Asuppressionbyafactorof2–3for

https://doi.org/10.1016/j.physletb.2018.05.074

0370-2693/©2018TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

pTlargerthan3 GeV/c wasseen.Thissuggeststhatasignificant en-ergylossofcharmquarksinthehotmedium alsooccursatRHIC energies.Afirstindicationofasizeabledifferenceinthe RAAofB andDmesonswas observedwhencomparingtheALICEDmeson

RAA with the nonprompt J/ψ meson (i.e. from b-hadron decays)

RAA measurement performed by the CMS Collaboration in PbPb collisionsatthesameenergyandcollisioncentrality [14].The RAA of nonprompt J/ψ mesons in the pT range 6.5–30 GeV/c was in-deed found to be significantly larger than the RAA ofD mesons in the 8–16 GeV/c pT region for central events. The D0 pT range waschosen togive a similarmedian pT valueto thatofthe par-entbhadronsdecayingtoJ/ψ particles [9].Severalmeasurements werealsoperformedtoaddresstherelevanceofcoldnuclear mat-tereffectsforthesuppressionobservedforheavy-flavourparticles. Indeed,thesephenomenacanaffecttheyieldofsuchparticles, in-dependentlyofthepresenceofadeconfinedpartonicmedium.For instance,modifications ofthepartondistributionfunctions(PDFs) inthenucleuswithrespecttonucleonPDFs [15–17] couldchange theproductionrateofheavy-flavourparticles.Toevaluatethe rel-evanceof theseeffects,the productionof prompt Dmesonswas measuredinpPb collisionsatmid-rapidityat5.02 TeV bytheALICE Collaboration [18].ThenuclearmodificationfactorinpPb collisions (RpA) was found to be consistent within the 15–20% uncertain-tieswith unityfor pT from2 to 24 GeV/c. Thissuggests that the suppressionofDmesonsobservedinPbPb collisionscannotbe ex-plainedintermsofinitial-stateeffectsbutismostlyduetostrong final-state effects induced by the QGP. A similar conclusion was obtainedfromthestudyofthe RpA ofBmesonsinpPb collisions at5.02 TeV,wherevaluesconsistentwithunitywithin the uncer-taintieswerefoundforpTfrom10to60 GeV/c [19].

InthisLetter,theproductionofpromptD0mesonsinPbPb col-lisions at 5.02 TeV is measured for the first time up to a pT of 100 GeV/c,allowing one tostudythepropertiesofthein-medium energylossinanewkinematicregime.TheD0 mesonandits an-tiparticlearereconstructedinthecentral rapidityregion(|y|<1) oftheCMSdetectorviathehadronicdecaychannelsD0→K−π+

and D0 →K+π−. The production cross section and yields in pp and PbPb collisions, respectively, and the RAA of prompt D0 mesonsarepresentedasafunctionoftheirpT.TheRAAisreported fortwocentralityintervals:intheinclusivesample(0–100%),and inonecorrespondingtothemostoverlapping10%ofthecollisions.

2. TheCMSdetector

ThecentralfeatureoftheCMSapparatusisasuperconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T.Withinthesolenoidvolumeareasilicontrackerwhich mea-sureschargedparticles withinthepseudorapidity range|η|<2.5, aleadtungstatecrystalelectromagneticcalorimeter(ECAL),anda brass and scintillator hadron calorimeter (HCAL). The ECAL con-sistsofmorethan75 000leadtungstatecrystals,andispartitioned intoabarrelregion(|η|<1.48)andtwoendcapsextendingoutto

|η|=3.0. The HCAL consistsof sampling calorimeters composed ofbrassandscintillatorplates,covering|η|<3.0.Ironhadron for-ward(HF)calorimeters,withquartzfibres readoutby photomulti-pliers,extendthecalorimetercoverageoutto|η|=5.2.Adetailed descriptionoftheCMSexperimentcanbefoundinRef. [20].

3. EventselectionandMonteCarlosamples

The pp (PbPb) dataset used for this analysis corresponds to an integrated luminosity of27.4 pb−1 (530 μb−1). The D0 meson productionis measured from pT of 2 up to 20 GeV/c using large samples of minimum-bias (MB) events (≈2.5 billion pp events

and ≈300 million PbPb events). Minimum-bias events were se-lected onlineusingtheinformationfromtheHFcalorimetersand thebeampickup monitors.For measuringthe D0 meson produc-tion above 20 GeV/c,dedicatedhigh-level trigger (HLT)algorithms weredesignedtoidentifyonlineeventswithaD0 candidate.Since eventswithahigh-pTD0mesonareexpectedtoleavelargeenergy depositsinHCAL,HLTalgorithms were runoneventspreselected by jet triggers in the level-1 (L1) calorimeter trigger system. In PbPb collisions, theD0 triggers with pT thresholdbelow40 GeV/c wererunoneventspassingtheL1MBtriggerselection.Whilethe MB andlower-threshold triggers had to be prescaled because of thehighinstantaneousluminosityoftheLHC,thehighest thresh-old trigger usedin the analysis(pT>60(50)GeV/c for PbPb (pp) datataken)was always unprescaled.The efficiencyofthe HLT al-gorithmswasevaluatedindata,andmodelled byalinearfunction of D0 pT. The efficiency was found to be about100 (90)%in pp (PbPb)collisionsforeventspassingthecorrespondingL1selection. For the offline analysis, events have to pass a set of selec-tion criteriadesignedto rejectevents frombackgroundprocesses (beam-gas collisions and beam scraping events) as described in Ref. [21].Inordertoselecthadroniccollisions,both pp andPbPb eventsarerequiredtohaveatleastonereconstructedprimary in-teraction vertexwith a distance from the centre of the nominal interaction regionoflessthan 15 cm alongthebeamaxis.In ad-dition, in PbPb collisions the shapesof the clustersin the pixel detectorhavetobecompatiblewiththoseexpectedfromparticles produced by a PbPb collision [22]. The PbPb collision eventsare alsorequiredtohaveatleastthreetowersineachoftheHF detec-torswithenergydepositsofmorethan3 GeV pertower.The com-bined efficiency forthis eventselection, andthe remaining non-hadroniccontamination,is(99±2)%.Selectionefficiencies higher than 100% are possible,reflecting thepossible presence of ultra-peripheral (nonhadronic) collisions inthe selected eventsample. Thecollisioncentralityisdeterminedfromthetotaltransverse en-ergy deposition in both the HF calorimeters. Collision centrality binsare giveninpercentagerangesofthetotalinelastichadronic crosssection,withthe0–10%bincorrespondingtothe10%of col-lisionshavingthelargestoverlapofthetwonuclei.

Several Monte Carlo (MC) simulated event samples are used to evaluate background components, signal efficiencies, and de-tector acceptance corrections. The events produced include both promptandnonprompt(frombhadrondecays) D0 _mesonevents. Proton–proton collisions are generated with pythia 8 v212 [23] tune CUETP8M1 [24] and propagated through the CMS detector usingthe Geant4package [25].The D0 mesonsare decayedwith evtgen 1.3.0 [26], andfinal-state photon radiation in the D0 de-caysissimulatedwith photos 2.0 [27].ForthePbPb MCsamples, each pythia 8eventisembeddedintoaPbPb collision event gen-erated with hydjet 1.8 [28], which is tuned to reproduce global eventpropertiessuchasthecharged-hadronpTspectrumand par-ticlemultiplicity.

4. Signalextraction

The D0 _{candidates are reconstructed by combining pairs of} oppositely charged particle tracks with an invariant mass within 0.2 GeV/c2 of the world-average D0 mass [29]. Each track is re-quiredto have pT>1 GeV/c inorderto reduce the combinatorial background.Forhigh-pTD0mesons(above20 GeV/c)inPbPb data, the single trackcutis raised to pT>8.5 GeV/c toaccount forthe selection (pT>8 GeV/c) performedat theHLT. All tracks are also required to be within |η|<1.5. Foreach pair of selected tracks, two D0 candidates are createdby assuming that one ofthe par-ticles hasthe mass ofthe pion whilethe other hasthe mass of thekaon,andvice-versa.TheD0_{mesonsarerequiredtobewithin}

Fig. 1. ExamplesofD0 _{candidateinvariantmassdistributionsinpp (top)andPbPb (bottom)collisionsat5.02 TeV .(Forinterpretationofthecoloursinthefigure(s),the} readerisreferredtothewebversionofthisarticle.)

|y|<1,optimised in conjunctionto the trackpseudorapidity se-lectiontogive thebestsignaltobackgroundratiooverthewhole rangeof D0 pT studied. In orderto further reduce the combina-torial background,the D0 candidates are selectedbased onthree topological criteria: on the three-dimensional (3D) decay length

Lxyznormalisedtoitsuncertainty(requiredtobelargerthan4–6), onthe pointingangleθp (definedasthe anglebetweenthetotal momentumvectorofthetracksandthevectorconnectingthe pri-maryandthesecondaryvertices andrequiredto besmallerthan 0.12), and on the χ2 _{probability, divided by the number of} de-greesof freedom,ofthe D0 vertexfit(required tobe largerthan 0.025–0.05). The selection is optimised in each pT bin using a multivariatetechnique [30] inordertomaximisethestatistical sig-nificanceoftheD0 _{mesonsignals.}

The D0 mesonyields in each pT interval are extractedwitha binnedmaximum-likelihoodfittotheinvariantmassdistributions intherange1.7<mπK<2.0 GeV/c2.SeveralexamplesofD0 candi-dateinvariant massdistributionsare showninFig. 1forpp (top) andPbPb (bottom)collisions. Thecombinatorialbackground, orig-inatingfromrandompairs oftracksnot producedbya D0 meson decay,is modelled bya third-order polynomial.The signal shape was found to be best modelled over the entire pT range mea-suredbytwoGaussianfunctionswiththesamemeanbutdifferent widths. An additional Gaussian function is used to describe the invariantmassshapeofD0_{candidateswithincorrectmass} assign-ment fromthe exchange of thepion andkaon designations. The widthsoftheGaussianfunctionsthatdescribetheD0 signalshape andthe shape of the D0 _{candidates with swapped mass} assign-ment are free parameters in the fit. Also, the ratio betweenthe

yields ofthesignal andofthe D0 candidates withswapped mass assignmentsisfixedtothevalueextractedfromsimulation.

The D0 pT-differential cross section in each pT interval in pp collisionsisdefinedas:

dσpp dpT   |y|<1 =1 2 1 pT 1 B L fpromptNpp

(α )promptβprescaletrigger  

|y|<1

, (1)

where pTisthewidthofthepTinterval,Bisthebranching frac-tionofthedecaychain,Listheintegratedluminosity,(α )prompt representsthecorrectionforacceptanceandefficiencyandNpp is the yield of D0 andD0 mesons extractedin each pT interval. In both pp and PbPb cases, the value of αprompt ranges fromabout 0.3at2–3 GeV/c toabout100%at60–100 GeV/c.Thevalueof prompt rangesforPbPb (pp)fromabout0.02 (0.03)at2–3 GeV/c toabout 0.4(0.6)at60–100 GeV/c.Thefactor1/2accountsforthefactthat thecrosssection isgivenfortheaverageofparticlesand antipar-ticles.Therawyields Npparecorrectedinordertoaccountforthe average prescale factor βprescale and the efficiency trigger of the trigger thatwas usedtoselecteventsinthat specific pT interval. Thefactor fprompt isthefractionofD0mesonsthatcomesdirectly from c quark fragmentation andis measured using control sam-ples in databy exploitingthe differencein thedistributions ofa quantityfoundbymultiplyingthe3DD0decaylengthLxyzbythe sine of the pointing angle sin(θp) of prompt and nonprompt D0 mesons. Inparticular, the value of fprompt (typicallyin therange 0.8–0.9)ismeasuredineach pTintervalbyfittingthedistribution of Lxyzsin(θp) usingthe prompt andnonprompt shapesobtained fromMCsimulation.

The D0 _p

T-differential production yieldin each pT interval in PbPb collisionsisdefinedas:

1 TAA dNPbPb dpT  _| y|<1 = 1 TAA 1 2 1 pT 1 BNMB fpromptNPbPb

(α )promptβprescale trigger  

|y|<1

, (2)

whereNMB isthenumberofMBeventsusedfortheanalysisand

TAAisthenuclearoverlapfunction [8],whichisequaltothe num-berofnucleon–nucleon (NN) binary collisions dividedby theNN cross section and can be interpreted as the NN-equivalent inte-grated luminosity per heavy ion collision. The values of TAA are 5.61 mb−1 forinclusivePbPb collisions and23.2 mb−1 forcentral events [21].TheothertermsweredefinedanalogouslytoEq. (1).

5. Systematicuncertainties

The yields are affected by several sources of systematic un-certainties arising from the signal extraction, acceptance and ef-ficiency corrections, branching fraction, and integrated luminos-ity determination. The uncertainty in the raw yield extraction (1.6–8.2% for pp and 1.3–17.5% for PbPb data, with the highest value at low-pT, which isthe region withthe smallest signal to backgroundratio)isevaluatedbyrepeatingthefitprocedureusing differentbackgroundfitfunctionsandbyforcingthewidthsofthe Gaussianfunctionsthatdescribethesignaltobeequaltothe val-uesextractedinsimulationstoaccountforpossibledifferencesin thesignalresolution indataandinMC. Inthebackground varia-tionstudy,anexponentialplusasecond-orderpolynomialfunction wasconsideredinsteadofthefirstorderpolynomialone,whichis usedasdefault.Thefinaluncertaintyintherawyieldextractionis definedasthesuminquadratureoftherelativedifferencesofthe signalvariationandthemaximumofallthebackgroundvariations. Thesystematicuncertaintyduetotheselection oftheD0 me-soncandidates (0.5–3.6%forpp and 2.7–8.1%forPbPb data, with thehighestvalue atlow-pT) isestimatedby considering the dif-ferencesbetweenMC anddata in thereduction ofthe D0 _yields obtainedby applyingeachoftheD0 _{selectionvariables described} in Sec. 4. The studywas performed by varying one selection at a time,in a range that allowed a robust signal extraction proce-dureandbyconsideringthemaximumrelativediscrepancyinthe yield reduction betweendata andMC. The total uncertainty was thequadraticsumofthemaximumrelative discrepancyobtained byvaryingeachofthethreeselectionvariablesseparately.

TheuncertaintyduetotheD0 triggerefficiency(1%forpp and 2%forPbPb data)isevaluatedasthestatisticaluncertaintyinthe zeroth-ordercoefficientofthelinearfunctionusedtodescribethe plateauoftheefficiencydistribution.Thesystematicuncertaintyin thehadrontrackingefficiency(4.0% forpp and6.0–6.5%forPbPb data) is estimated froma comparisonof two- and four-body D0 mesondecaysindataandsimulatedsamples [31].

ToevaluatethesystematicuncertaintyinthepromptD0_meson fraction,the widthofthe Lxyzsin(θp)MC promptandnonprompt templates are varied in a range that covers the observed differ-encesbetweenthedataandMCvalues.Thesystematicuncertainty (10%forbothpp and PbPb data)was obtainedineach pT binas thedifferencebetweenthe fprompt valueextractedfromthe vari-ation that gives thebest χ2 _{fitto data and thenominal f}

prompt value.Toevaluate thisuncertaintyforthe RAA measurement,the widthsofthe templatedistributions are varied simultaneouslyin pp andPbPb.Thesystematicuncertaintyonthe fprompt correction was evaluatedas thespreadof theratios of fprompt in PbPb and pp toaccountforpartialcancellationsofthesystematiceffectsin thetwoanalyses.

TheuncertaintyrelatedtothesimulatedpTshape(smallerthan 0.5% forboth pp andPbPb data) isevaluated by reweighting the simulatedD0_mesonp

TdistributionaccordingtothepT shape ob-tainedfromafixed-orderplusnext-to-leadinglogarithmic(FONLL) prediction [32].

Thesystematicuncertaintyinthecrosssectionmeasurementis computedasthesuminquadratureofthedifferentcontributions mentioned above.The globaluncertaintyin thepp measurement (2.5%) is the sumin quadrature ofthe systematic uncertainty in the integrated luminosity (2.3% [33]) and in the branching frac-tion B (1.0% [29]). The global uncertainty in the PbPb measure-ment (+3.6%, −4.1% for the centrality range0–100% and +2.9%,

−3.7%for0–10%)isthesuminquadratureoftheuncertainties in the MB selection efficiency(2%), in the branching fraction (1.0%) andinthe TAA(+2.8%,−3.4%forthecentralityrange0–100%and

+1.9%,−3.0% for0–10%). Forthe RAA results,no cancellation of uncertaintiesisassumedbetweenthepp andPbPb results.

6. Results

The pT-differential production cross section in pp collisions measured intheinterval |y|<1 ispresented intheleft panel of Fig. 2. The result is compared to the prediction of FONLL anda general-massvariableflavour numberscheme(GM-VFNS) [34–36] calculation. TheCMSmeasurement liescloseto theupperbound oftheFONLLpredictionandthelowerboundoftheGM-VFNS cal-culation. The D0 pT-differential production yields divided by the nuclear overlap functions TAA in PbPb collisions in the 0–100% and 0–10% centrality ranges are presented in the right panel of Fig. 2and compared to thesame pp cross section shownin the leftpanel.

Thenuclearmodificationfactor,RAAiscomputedas:

RAA= 1 TAA dNPbPb dpT  dσpp dpT . (3)

The RAA inthecentralityrange0–100%isshownintheleftpanel of Fig.3 as a function of pT.The RAA shows a suppression ofa factor3to4atpTof6–8 GeV/c.AthigherpT,thesuppression fac-tordecreasestoavalueofabout1.3inthepTrange60–100 GeV/c. The RAA forthe centralityrange 0–10%is presented inthe right panel of Fig. 3. The D0 _R

AA in central events shows a hint of stronger suppression if compared to the inclusive RAA result for

pT>5 GeV/c.Inthiscomparison,thelargeoverlapbetweenthetwo resultshastobeconsidered.Indeed,roughly40% oftheD0 candi-datesusedinthemeasurementinthecentralityrange0–100% are alsoincludedinthe0–10% result.

The results are also compared to calculations of four types of models: (a) two perturbative QCD-based models that include both collisionalandradiative energyloss,(M. Djordjevic[37] and CUJET 3.0 [38–40])andonethatincludesradiativeenergylossonly (I. Vitev[41,42]),(b) a transportmodelbasedonaLangevin equa-tionthatincludescollisionalenergylossandheavy-quarkdiffusion in the medium (S. Cao et al. [43,44]),(c) a microscopic off-shell transportmodelbasedonaBoltzmannapproachthatincludes col-lisional energy loss only (PHSD [45,46]), and (d) a model based on theanti-de Sitter/conformal field theory (AdS/CFT) correspon-dence, that includes thermal fluctuations in the energy loss for heavy quarksina stronglycoupledplasma [47]. TheAdS/CFT cal-culation is provided for two settings of the diffusion coefficient D of the heavy quark propagation through the medium: depen-dent on, and independent of the quark momentum. For D0 me-son pT>40 GeV/c, the perturbative QCD-based models describe the suppression in both centrality ranges within the uncertain-ties, although the trend suggested by these predictions is typi-cally lower than that inthe experimental data.The model based

Fig. 2. (left)The pT-differentialproductioncrosssectionofD0 mesonsinpp collisionsat√s=5.02TeV.Theverticalbars(boxes)correspondtostatistical(systematic) uncertainties.Theglobalsystematicuncertainty,listedinthelegendandnotincludedinthepoint-to-pointuncertainties,comprisestheuncertaintiesintheintegrated luminositymeasurementandtheD0_{mesonB.ResultsarecomparedtoFONLL [32] andGM-VFNS [34–36] calculations.(right)The p}

T-differentialproductionyieldsofD0 mesonsdividedbythenuclearoverlapfunctionsTAAforPbPb collisionsinthe0–100%(red)and0–10%(blue)centralityrangescomparedtothesamepp crosssections shownintheleftpanel(black).

on a Langevin approach describes the measurement well in the centralityrange 0–100%,while itpredicts slightlytoo much sup-pressionforcentralevents.TheAdS/CFTcalculationsdescribewell both the 0–100% andthe 0–10% measurements. In the interme-diate pT region (10<pT<40 GeV/c), all the theoretical calcula-tionsdescribewelltheRAA resultsinbothcentralityintervals.For

pT<10 GeV/c, the PHSD prediction that includes shadowing can reproducethemeasurementinthe0–100%centralityregion accu-rately, while the Langevin calculation predicts significantly more suppression than seen in data for both centrality ranges. In the samelow-pTregion,theAdS/CFTcalculationliesatthelowerlimit oftheexperimentaluncertaintiesforboth0–10%and0–100% mea-surements.

The D0 _R

AA measured in thecentralityrange 0–100%is com-paredinthetoppanel ofFig.4totheCMSmeasurementsofthe

RAAofchargedparticles [21],B± mesons [48] andnonpromptJ/ψ meson [49] performedatthesameenergyandinthesame central-ityrange.Thesystematicuncertaintiesbetweenthe RAA measure-mentofthe D0 _{mesons,andofthelightandbeautyparticles,are} almost completely uncorrelated. The only common contribution comesfromthesystematicuncertaintyofonetrack(4%),whichis howevernegligiblewhencomparedtothetotaluncertainties.The D0_mesonR

AAvaluesareconsistentwiththoseofchargedparticles for pT>4 GeV/c. For lower pT, a somewhat smaller suppression forD0 mesonsisobserved.The RAA oftheB± mesons,measured inthe pT range7–50 GeV/c andtherapidity rangeof|y|<2.4, is alsoconsistentwiththeD0mesonmeasurementwithinthe exper-imentaluncertainties.TheRAAofnonpromptJ/ψ,whichwasfound tohave almostno rapidity dependence [49], isshownhere mea-suredinthepT ranges6.5–50 GeV/c in|y|<2.4,and3–6.5 GeV/c in 1.8<|y|<2.4. Its RAA is found to be higher than the D0 me-son RAA in almost the entire pT range. The D0 meson RAA in thecentrality range0–10% iscompared in Fig.4 tothe charged-particle RAA. As observed for 0–100% PbPb events, the two re-sults are consistent within uncertainties for pT>4 GeV/c and a somewhatsmallersuppressionforcharmedmesonsisobservedat lower pT.

7. Summary

InthisLetter,thetransversemomentum(pT)spectraofprompt D0 mesons inpp and PbPb collisions andthe D0 meson nuclear modificationfactor(RAA)inthecentralrapidityregion(|y|<1)at

√

sNN=5.02TeV from CMSare presented.The RAA ofpromptD0 mesonsismeasured asafunctionoftheir pT from2to100 GeV/c in two centrality ranges, inclusiveand 10% mostcentral. The D0 meson yield is found to be strongly suppressed in PbPb colli-sions when compared to the measured pp reference data scaled by the numberof binary nucleon–nucleon collisions. These mea-surementsareconsistentwiththeRAA ofchargedhadronsinboth centrality intervalsfor pT>4 GeV/c. Ahint ofa smaller suppres-sion of D0 RAA withrespect to chargedparticle RAA is observed for pT<4 GeV/c.TheD0 RAAwasfoundtobecompatiblewiththe B± RAAintheintermediate pTregionandsignificantlylowerthan the nonpromptJ/ψ meson RAA for pT<10 GeV/c.Comparisons to different theoretical models show that the general trend of the

RAA isqualitativelyreproduced athigh pT.Comparisons to differ-ent theoreticalmodels show thatthe generaltrendofthe RAA is qualitatively reproducedathigh pT,whilequantitative agreement forallcentralityand pTselectionsisyettobeattained.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technical andadministrativestaffs atCERNand atother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentresand personneloftheWorldwideLHCComputingGridfordeliveringso effectively thecomputinginfrastructure essentialto our analyses. Finally, we acknowledge the enduring support for the construc-tion andoperationofthe LHCandtheCMSdetectorprovided by thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIEN-CIAS(Colombia);MSESandCSF(Croatia);RPF(Cyprus);SENESCYT

Fig. 3. RAAasafunctionofpTinthecentralityrange0–100%(top)and0–10% (bot-tom).Theverticalbars(boxes)correspondtostatistical(systematic)uncertainties. Theglobal systematicuncertainty,representedas a greybox at RAA=1, com-prisestheuncertaintiesintheintegratedluminositymeasurementandTAAvalue. TheD0 _R

AAvaluesarealsocomparedtocalculationsfromvarioustheoretical mod-els [37–47].

(Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Fin-land,MEC,andHIP(Finland);CEAandCNRS/IN2P3(France);BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hun-gary);DAEandDST (India);IPM(Iran);SFI(Ireland);INFN (Italy); MSIPandNRF (RepublicofKorea);LAS(Lithuania);MOE andUM (Malaysia); BUAP,CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland);FCT(Portugal);JINR(Dubna);MON,ROSATOM,RAS,RFBR andRAEP (Russia);MESTD(Serbia); SEIDI,CPAN,PCTI andFEDER (Spain);SwissFundingAgencies(Switzerland);MST(Taipei);ThEP Center, IPST, STAR, and NSTDA (Thailand); TUBITAK and TAEK (Turkey);NASUandSFFR(Ukraine);STFC (UnitedKingdom);DOE andNSF(USA).

Individuals have received support from the Marie-Curie pro-gramme and the European Research Council and Horizon 2020 Grant,contract No.675440 (European Union);theLeventis Foun-dation;the Alfred P. Sloan Foundation; the Alexander von Hum-boldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Inno-vatie door Wetenschap en Technologie (IWT-Belgium); the Min-istry of Education, Youth and Sports (MEYS) of the Czech Re-public; the Council of Scientific and Industrial Research, In-dia; the HOMING PLUS programme of the Foundation for

Pol-Fig. 4. (top)Nuclearmodificationfactor RAA asafunctionofpT inthe central-ityrange0–100%(greensquares)comparedtothe RAAofchargedparticles(red circles) [21],B± mesons(bluetriangles) [48] andnonprompt J/ψ meson(purple crossesandstars) [49] inthesamecentralityrangeat5.02 TeV.(bottom)Nuclear modificationfactorRAAasafunctionofpTinthecentralityrange0–10%(green squares)comparedtothe RAAofchargedparticles(redcircles) [21] inthesame centralityrange.

ish Science, cofinanced from European Union, Regional Devel-opment Fund, the Mobility Plus programme of the Ministry of Science and Higher Education, the National Science Cen-tre (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 Clarín-COFUND del Principado de Asturias; the Thalis and Aris-teia programmes cofinanced by EU-ESF andthe Greek NSRF; the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chula-longkornUniversityandtheChulalongkornAcademic intoIts2nd Century Project Advancement Project (Thailand); and the Welch Foundation,contractC-1845.

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TheCMSCollaboration

A.M. Sirunyan,A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, F. Ambrogi, E. Asilar,T. Bergauer, J. Brandstetter, E. Brondolin, M. Dragicevic, J. Erö,M. Flechl, M. Friedl,R. Frühwirth1,V.M. Ghete, J. Grossmann, J. Hrubec, M. Jeitler1, A. König,N. Krammer,

I. Krätschmer,D. Liko,T. Madlener, I. Mikulec, E. Pree,D. Rabady, N. Rad, H. Rohringer, J. Schieck1,

R. Schöfbeck, M. Spanring, D. Spitzbart,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, 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,S. Moortgat, L. Moreels,Q. Python, K. Skovpen, S. Tavernier, W. Van Doninck, P. Van Mulders,

I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

H. Brun, B. Clerbaux, G. De Lentdecker, H. Delannoy, G. Fasanella,L. Favart, R. Goldouzian, A. Grebenyuk,

G. Karapostoli,T. Lenzi,J. Luetic, T. Maerschalk, A. Marinov, A. Randle-conde,T. Seva, C. Vander Velde,

P. Vanlaer,D. Vannerom, R. Yonamine,F. Zenoni, F. Zhang2

UniversitéLibredeBruxelles,Bruxelles,Belgium

A. Cimmino,T. Cornelis, D. Dobur,A. Fagot, M. Gul, I. Khvastunov,D. Poyraz, C. Roskas, S. Salva,

M. Tytgat,W. Verbeke, N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,O. Bondu, S. Brochet,G. Bruno, C. Caputo, A. Caudron, S. De Visscher, C. Delaere,

M. Delcourt,B. Francois, A. Giammanco, A. Jafari,M. Komm, G. Krintiras,V. Lemaitre, A. Magitteri,

A. Mertens, M. Musich, K. Piotrzkowski,L. Quertenmont,M. Vidal Marono, S. Wertz

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium N. Beliy

UniversitédeMons,Mons,Belgium

W.L. Aldá Júnior, F.L. Alves,G.A. Alves,L. Brito, M. Correa Martins Junior,C. Hensel, A. Moraes,M.E. Pol, P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas, W. Carvalho,J. Chinellato3, A. Custódio, E.M. Da Costa, G.G. Da Silveira4,

D. De Jesus Damiao,S. Fonseca De Souza, L.M. Huertas Guativa, H. Malbouisson, M. Melo De Almeida,

C. Mora Herrera,L. Mundim,H. Nogima, A. Santoro, A. Sznajder,E.J. Tonelli Manganote3,

F. Torres Da Silva De Araujo,A. Vilela Pereira UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahujaa, C.A. Bernardesa, T.R. Fernandez Perez Tomeia, E.M. Gregoresb,P.G. Mercadanteb, S.F. Novaesa, Sandra S. Padulaa, D. Romero Abadb,J.C. Ruiz Vargasa

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

A. Aleksandrov, R. Hadjiiska, P. Iaydjiev,M. Misheva, M. Rodozov, M. Shopova,S. Stoykova, G. Sultanov

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

W. Fang5, X. Gao5 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. Shaheen, A. Spiezia, J. Tao, C. Wang,Z. Wang, E. Yazgan, H. Zhang, S. Zhang, J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

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

C. Avila,A. Cabrera, L.F. Chaparro Sierra, C. Florez, C.F. González Hernández,J.D. Ruiz Alvarez UniversidaddeLosAndes,Bogota,Colombia

B. Courbon, N. Godinovic, D. Lelas,I. Puljak, P.M. Ribeiro Cipriano, T. Sculac UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic, M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,D. Ferencek, K. Kadija,B. Mesic, A. Starodumov6, T. Susa InstituteRudjerBoskovic,Zagreb,Croatia

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

UniversityofCyprus,Nicosia,Cyprus M. Finger7, M. Finger Jr.7 CharlesUniversity,Prague,CzechRepublic E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

Y. Assran8,9,M.A. Mahmoud10,9, A. Mahrous11

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

R.K. Dewanjee, M. Kadastik, L. Perrini, M. Raidal, A. Tiko, C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia P. Eerola, J. Pekkanen,M. Voutilainen DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,T. Järvinen, V. Karimäki,R. Kinnunen, T. Lampén, K. Lassila-Perini, S. Lehti,T. Lindén,

P. Luukka, E. Tuominen, J. Tuominiemi,E. Tuovinen

HelsinkiInstituteofPhysics,Helsinki,Finland J. Talvitie,T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon,F. Couderc, M. Dejardin, D. Denegri,J.L. Faure, F. Ferri, S. Ganjour, S. Ghosh,A. Givernaud, P. Gras, G. Hamel de Monchenault,P. Jarry, I. Kucher, E. Locci,M. Machet, J. Malcles, G. Negro,J. Rander,

A. Rosowsky,M.Ö. Sahin, M. Titov

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

A. Abdulsalam,I. Antropov, S. Baffioni, F. Beaudette, P. Busson, L. Cadamuro, C. Charlot,

R. Granier de Cassagnac,M. Jo, S. Lisniak,A. Lobanov, J. Martin Blanco, M. Nguyen, C. Ochando,

G. Ortona,P. Paganini, P. Pigard,S. Regnard, R. Salerno, J.B. Sauvan, Y. Sirois, A.G. Stahl Leiton, T. Strebler, Y. Yilmaz,A. Zabi, A. Zghiche

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

J.-L. Agram12,J. Andrea, D. Bloch,J.-M. Brom, M. Buttignol,E.C. Chabert, N. Chanon, C. Collard, E. Conte12,X. Coubez, J.-C. Fontaine12, D. Gelé, U. Goerlach,M. Jansová, A.-C. Le Bihan, N. Tonon, P. Van Hove

UniversitédeStrasbourg,CNRS,IPHCUMR7178,F-67000Strasbourg,France S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,C. Bernet, G. Boudoul,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, M. Lethuillier,L. Mirabito,

A.L. Pequegnot, S. Perries,A. Popov13,V. Sordini, M. Vander Donckt, S. Viret UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France T. Toriashvili14

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze7

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann,S. Beranek, L. Feld, M.K. Kiesel, K. Klein, M. Lipinski, M. Preuten,C. Schomakers, J. Schulz, T. Verlage,V. Zhukov13

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

A. Albert, E. Dietz-Laursonn,D. Duchardt, M. Endres, M. Erdmann,S. Erdweg, T. Esch, R. Fischer, A. Güth,

M. Hamer,T. Hebbeker,C. Heidemann, K. Hoepfner, S. Knutzen,M. Merschmeyer, A. Meyer,P. Millet,

S. Mukherjee,M. Olschewski, K. Padeken,T. Pook, M. Radziej, H. Reithler,M. Rieger, F. Scheuch,

D. Teyssier,S. Thüer

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

G. Flügge,B. Kargoll, T. Kress,A. Künsken, J. Lingemann, T. Müller, A. Nehrkorn, A. Nowack,C. Pistone,

O. Pooth,A. Stahl15

M. Aldaya Martin,T. Arndt, C. Asawatangtrakuldee, K. Beernaert,O. Behnke, U. Behrens,

A. Bermúdez Martínez, A.A. Bin Anuar, K. Borras16,V. Botta, A. Campbell, P. Connor,

C. Contreras-Campana, F. Costanza, C. Diez Pardos,G. Eckerlin, D. Eckstein, T. Eichhorn, E. Eren,

E. Gallo17,J. Garay Garcia, A. Geiser, A. Gizhko, J.M. Grados Luyando, A. Grohsjean, P. Gunnellini,

M. Guthoff,A. Harb, J. Hauk, M. Hempel18, H. Jung,A. Kalogeropoulos, M. Kasemann,J. Keaveney,

C. Kleinwort,I. Korol, D. Krücker,W. Lange, A. Lelek, T. Lenz, J. Leonard,K. Lipka, W. Lohmann18, R. Mankel, I.-A. Melzer-Pellmann, A.B. Meyer, G. Mittag, J. Mnich, A. Mussgiller, E. Ntomari,D. Pitzl,

A. Raspereza,B. Roland, M. Savitskyi, P. Saxena,R. Shevchenko, S. Spannagel, N. Stefaniuk,

G.P. Van Onsem,R. Walsh, Y. Wen, K. Wichmann,C. Wissing, O. Zenaiev

DeutschesElektronen-Synchrotron,Hamburg,Germany

S. Bein,V. Blobel, M. Centis Vignali, T. Dreyer, E. Garutti, D. Gonzalez, J. Haller, A. Hinzmann,

M. Hoffmann,A. Karavdina, R. Klanner, R. Kogler, N. Kovalchuk,S. Kurz, T. Lapsien, I. Marchesini,

D. Marconi,M. Meyer, M. Niedziela, D. Nowatschin, F. Pantaleo15, T. Peiffer, A. Perieanu,C. Scharf,

P. Schleper, A. Schmidt, S. Schumann,J. Schwandt, J. Sonneveld,H. Stadie,G. Steinbrück, F.M. Stober,

M. Stöver, H. Tholen, D. Troendle,E. Usai, L. Vanelderen,A. Vanhoefer, B. Vormwald

UniversityofHamburg,Hamburg,Germany

M. Akbiyik, C. Barth,S. Baur, E. Butz, R. Caspart, T. Chwalek, F. Colombo, W. De Boer,A. Dierlamm,

B. Freund, R. Friese,M. Giffels, A. Gilbert, D. Haitz,F. Hartmann15,S.M. Heindl, U. Husemann, F. Kassel15,

S. Kudella, H. Mildner, 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

InstitutfürExperimentelleKernphysik,Karlsruhe,Germany

G. Anagnostou, G. Daskalakis,T. Geralis,V.A. Giakoumopoulou, A. Kyriakis, D. Loukas, I. Topsis-Giotis

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

G. Karathanasis,S. Kesisoglou, A. Panagiotou, N. Saoulidou

NationalandKapodistrianUniversityofAthens,Athens,Greece K. Kousouris

NationalTechnicalUniversityofAthens,Athens,Greece

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

UniversityofIoánnina,Ioánnina,Greece

M. Csanad, N. Filipovic,G. Pasztor, G.I. Veres19

MTA-ELTELendületCMSParticleandNuclearPhysicsGroup,EötvösLorándUniversity,Budapest,Hungary

G. Bencze,C. Hajdu, D. Horvath20,Á. Hunyadi, F. Sikler,V. Veszpremi, A.J. Zsigmond

WignerResearchCentreforPhysics,Budapest,Hungary

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

M. Bartók19,P. Raics, Z.L. Trocsanyi, B. Ujvari InstituteofPhysics,UniversityofDebrecen,Debrecen,Hungary

S. Choudhury, J.R. Komaragiri

S. Bahinipati22,S. Bhowmik, P. Mal, K. Mandal, A. Nayak23, D.K. Sahoo22, N. Sahoo,S.K. Swain NationalInstituteofScienceEducationandResearch,Bhubaneswar,India

S. Bansal,S.B. Beri, V. Bhatnagar,R. Chawla, N. Dhingra, A.K. Kalsi,A. Kaur, M. Kaur, R. Kumar, P. Kumari, A. Mehta,J.B. Singh, G. Walia

PanjabUniversity,Chandigarh,India

Ashok Kumar,Aashaq Shah, A. Bhardwaj, S. Chauhan,B.C. Choudhary, R.B. Garg,S. Keshri, A. Kumar,

S. Malhotra,M. Naimuddin, K. Ranjan,R. Sharma

UniversityofDelhi,Delhi,India

R. Bhardwaj,R. Bhattacharya, S. Bhattacharya, U. Bhawandeep, S. Dey,S. Dutt, S. Dutta, S. Ghosh,

N. Majumdar, A. Modak, K. Mondal, S. Mukhopadhyay, S. Nandan,A. Purohit, A. Roy, D. Roy,

S. Roy Chowdhury, S. Sarkar,M. Sharan, S. Thakur

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

IndianInstituteofTechnologyMadras,Madras,India

R. Chudasama,D. Dutta, V. Jha, V. Kumar, A.K. Mohanty15, P.K. Netrakanti,L.M. Pant, P. Shukla,A. Topkar

BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz,S. Dugad, B. Mahakud, S. Mitra, G.B. Mohanty, N. Sur, B. Sutar

TataInstituteofFundamentalResearch-A,Mumbai,India

S. Banerjee, S. Bhattacharya, S. Chatterjee,P. Das, M. Guchait,Sa. Jain, S. Kumar, M. Maity24,

G. Majumder,K. Mazumdar, T. Sarkar24, N. Wickramage25

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, S. Paktinat Mehdiabadi27,F. Rezaei Hosseinabadi, B. Safarzadeh28,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, F. Erricoa,b,L. Fiorea,G. Iasellia,c,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,b,A. Ranieria,G. Selvaggia,b,

A. Sharmaa, L. Silvestrisa,15,R. Vendittia,P. Verwilligena

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

G. Abbiendia,C. Battilanaa,b_{,D. Bonacorsi}a,b_{, S. Braibant-Giacomelli}a,b_{, R. Campanini}a,b_{,P. Capiluppi}a,b_,

A. Castroa,b,F.R. Cavalloa,S.S. Chhibraa, G. Codispotia,b, M. Cuffiania,b,G.M. Dallavallea, F. Fabbria, A. Fanfania,b, D. Fasanellaa,b, P. Giacomellia,C. Grandia, L. Guiduccia,b,S. Marcellinia,G. Masettia, A. Montanaria, F.L. Navarriaa,b,A. Perrottaa, A.M. Rossia,b,T. Rovellia,b, G.P. Sirolia,b,N. Tosia

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

S. Albergoa,b,S. Costaa,b,A. Di Mattiaa,F. Giordanoa,b,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,P. Lenzia,b, M. Meschinia, S. Paolettia,L. Russoa,29_{, G. Sguazzoni}a_{, D. Strom}a_{, L. Viliani}a,b,15

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

L. Benussi, S. Bianco, F. Fabbri,D. Piccolo, F. Primavera15 INFNLaboratoriNazionalidiFrascati,Frascati,Italy

V. Calvellia,b, F. Ferroa, E. Robuttia,S. Tosia,b

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

A. Benagliaa, L. Brianzaa,b,F. Brivioa,b, V. Cirioloa,b, M.E. Dinardoa,b, S. Fiorendia,b, S. Gennaia, A. Ghezzia,b, P. Govonia,b, M. Malbertia,b,S. Malvezzia,R.A. Manzonia,b, D. Menascea, L. Moronia, M. Paganonia,b,K. Pauwelsa,b, D. Pedrinia,S. Pigazzinia,b,30,S. Ragazzia,b,T. Tabarelli de Fatisa,b

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

S. Buontempoa, N. Cavalloa,c, S. Di Guidaa,d,15, F. Fabozzia,c,F. Fiengaa,b, A.O.M. Iorioa,b, W.A. Khana, L. Listaa,S. Meolaa,d,15,P. Paoluccia,15,C. Sciaccaa,b,F. Thyssena

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

P. Azzia,15_{, L. Benato}a,b_{,D. Bisello}a,b_{, A. Boletti}a,b_{, R. Carlin}a,b_{,A. Carvalho Antunes De Oliveira}a,b_,

P. Checchiaa,P. De Castro Manzanoa, T. Dorigoa, U. Dossellia,F. Gasparinia,b,U. Gasparinia,b,

A. Gozzelinoa, S. Lacapraraa,P. Lujan,M. Margonia,b,A.T. Meneguzzoa,b,N. Pozzobona,b,P. Ronchesea,b, R. Rossina,b, F. Simonettoa,b,S. Venturaa, 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,b, P. Montagnaa,b,S.P. Rattia,b, V. Rea, M. Ressegotti, C. Riccardia,b, P. Salvinia, I. Vaia,b, P. Vituloa,b

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

L. Alunni Solestizia,b,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,15,G. Bagliesia,J. Bernardinia,T. Boccalia,L. Borrello, R. Castaldia, M.A. Cioccia,b, R. Dell’Orsoa,G. Fedia, L. Gianninia,c, A. Giassia, M.T. Grippoa,29,F. Ligabuea,c, T. Lomtadzea, E. Mancaa,c,G. Mandorlia,c,L. Martinia,b, A. Messineoa,b, F. Pallaa,A. Rizzia,b, A. Savoy-Navarroa,31, 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, N. Dacia,D. Del Rea,b,15,E. Di Marcoa,b,M. Diemoza,

S. Gellia,b, E. Longoa,b, F. Margarolia,b,B. Marzocchia,b, P. Meridiania,G. Organtinia,b,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, M. Costaa,b,R. Covarellia,b,A. Deganoa,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,F. Raveraa,b,A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b, K. Shchelinaa,b, V. Solaa,A. Solanoa,b,A. Staianoa,P. Traczyka,b

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

c_{UniversitàdelPiemonteOrientale,Novara,Italy}

S. Belfortea,M. Casarsaa, F. Cossuttia,G. Della Riccaa,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. Sekmen,D.C. Son,Y.C. Yang KyungpookNationalUniversity,Daegu,RepublicofKorea

A. Lee

ChonbukNationalUniversity,Jeonju,RepublicofKorea

H. Kim,D.H. Moon,G. Oh

ChonnamNationalUniversity,InstituteforUniverseandElementaryParticles,Kwangju,RepublicofKorea J.A. Brochero Cifuentes,J. Goh, T.J. Kim

HanyangUniversity,Seoul,RepublicofKorea

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

M. Choi,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 Ali32,F. Mohamad Idris33,W.A.T. Wan Abdullah, M.N. Yusli,

Z. Zolkapli

R. Reyes-Almanza,G. Ramirez-Sanchez, M.C. Duran-Osuna, H. Castilla-Valdez, E. De La Cruz-Burelo,

I. Heredia-De La Cruz34, R.I. Rabadan-Trejo, R. Lopez-Fernandez,J. Mejia Guisao, A. Sanchez-Hernandez

CentrodeInvestigacionydeEstudiosAvanzadosdelIPN,MexicoCity,Mexico

S. Carrillo Moreno, C. Oropeza Barrera, F. Vazquez Valencia

UniversidadIberoamericana,MexicoCity,Mexico

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

A. Morelos Pineda

UniversidadAutónomadeSanLuisPotosí,SanLuisPotosí,Mexico D. Krofcheck

UniversityofAuckland,Auckland,NewZealand P.H. Butler

UniversityofCanterbury,Christchurch,NewZealand

A. Ahmad, M. Ahmad, 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, K. Nawrocki, M. Szleper,

P. Zalewski

NationalCentreforNuclearResearch,Swierk,Poland

K. Bunkowski,A. Byszuk35, K. Doroba,A. Kalinowski, M. Konecki,J. Krolikowski, M. Misiura,

M. Olszewski, A. Pyskir,M. Walczak

InstituteofExperimentalPhysics,FacultyofPhysics,UniversityofWarsaw,Warsaw,Poland

P. Bargassa,C. Beirão Da Cruz E Silva, A. Di Francesco, P. Faccioli, B. Galinhas, M. Gallinaro,J. Hollar, N. Leonardo,L. Lloret Iglesias,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. Karjavin, A. Lanev,

A. Malakhov,V. Matveev36,37,V. Palichik, V. Perelygin, S. Shmatov, S. Shulha,N. Skatchkov, V. Smirnov,

N. Voytishin,A. Zarubin

JointInstituteforNuclearResearch,Dubna,Russia

Y. Ivanov, V. Kim38,E. Kuznetsova39,P. Levchenko,V. Murzin, V. Oreshkin,I. Smirnov, 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

InstituteforNuclearResearch,Moscow,Russia

V. Epshteyn, V. Gavrilov, N. Lychkovskaya,V. Popov, I. Pozdnyakov, G. Safronov, A. Spiridonov,

A. Stepennov, M. Toms,E. Vlasov, A. Zhokin

T. Aushev,A. Bylinkin37

MoscowInstituteofPhysicsandTechnology,Moscow,Russia

R. Chistov40, M. Danilov40,P. Parygin,D. Philippov, S. Polikarpov,E. Tarkovskii NationalResearchNuclearUniversity‘MoscowEngineeringPhysicsInstitute’(MEPhI),Moscow,Russia

V. Andreev,M. Azarkin37,I. Dremin37, M. Kirakosyan37,A. Terkulov P.N.LebedevPhysicalInstitute,Moscow,Russia

A. Baskakov,A. Belyaev, E. Boos,A. Ershov, A. Gribushin, A. Kaminskiy41,O. Kodolova,V. Korotkikh, I. Lokhtin,I. Miagkov, S. Obraztsov,S. Petrushanko, V. Savrin, A. Snigirev, I. Vardanyan

SkobeltsynInstituteofNuclearPhysics,LomonosovMoscowStateUniversity,Moscow,Russia V. Blinov42, Y. Skovpen42,D. Shtol42

NovosibirskStateUniversity(NSU),Novosibirsk,Russia

I. Azhgirey,I. Bayshev,S. Bitioukov, D. Elumakhov, V. Kachanov, A. Kalinin, D. Konstantinov,

V. Krychkine, V. Petrov, R. Ryutin, A. Sobol,S. Troshin, N. Tyurin,A. Uzunian, A. Volkov StateResearchCenterofRussianFederation,InstituteforHighEnergyPhysics,Protvino,Russia

P. Adzic43,P. Cirkovic, D. Devetak,M. Dordevic, J. Milosevic,V. Rekovic UniversityofBelgrade,FacultyofPhysicsandVincaInstituteofNuclearSciences,Belgrade,Serbia

J. Alcaraz Maestre,M. Barrio Luna, M. Cerrada,N. Colino, B. De La Cruz,A. Delgado Peris,

A. Escalante Del Valle,C. Fernandez Bedoya, J.P. Fernández Ramos,J. Flix, M.C. Fouz,P. Garcia-Abia,

O. Gonzalez Lopez,S. Goy Lopez, J.M. Hernandez, M.I. Josa, A. Pérez-Calero Yzquierdo, J. Puerta Pelayo,

A. Quintario Olmeda,I. Redondo, L. Romero,M.S. Soares, A. Álvarez Fernández

CentrodeInvestigacionesEnergéticasMedioambientalesyTecnológicas(CIEMAT),Madrid,Spain J.F. de Trocóniz,M. Missiroli, D. Moran

UniversidadAutónomadeMadrid,Madrid,Spain

J. Cuevas,C. Erice, J. Fernandez Menendez, I. Gonzalez Caballero,J.R. González Fernández,

E. Palencia Cortezon,S. Sanchez Cruz, I. Suárez Andrés,P. Vischia, J.M. Vizan Garcia UniversidaddeOviedo,Oviedo,Spain

I.J. Cabrillo, A. Calderon, B. Chazin Quero,E. Curras, J. Duarte Campderros, M. Fernandez,

J. Garcia-Ferrero,G. Gomez, A. Lopez Virto, J. Marco,C. Martinez Rivero, P. Martinez Ruiz del Arbol,

F. Matorras,J. Piedra Gomez, T. Rodrigo,A. Ruiz-Jimeno, L. Scodellaro,N. Trevisani, I. Vila, R. Vilar Cortabitarte

InstitutodeFísicadeCantabria(IFCA),CSIC-UniversidaddeCantabria,Santander,Spain

D. Abbaneo, E. Auffray, P. Baillon, A.H. Ball,D. Barney, M. Bianco, P. Bloch,A. Bocci, C. Botta,

T. Camporesi, R. Castello,M. Cepeda, G. Cerminara, E. Chapon,Y. Chen, D. d’Enterria, A. Dabrowski,

V. Daponte, A. David,M. De Gruttola, A. De Roeck, M. Dobson, B. Dorney, T. du Pree,M. Dünser,

N. Dupont,A. Elliott-Peisert, P. Everaerts,F. Fallavollita,G. Franzoni, J. Fulcher,W. Funk, D. Gigi,K. Gill, F. Glege, D. Gulhan, P. Harris,J. Hegeman, V. Innocente, P. Janot, O. Karacheban18,J. Kieseler,

H. Kirschenmann,V. Knünz,A. Kornmayer15,M.J. Kortelainen, M. Krammer1, C. Lange, P. Lecoq,

C. Lourenço,M.T. Lucchini,L. Malgeri, M. Mannelli,A. Martelli, F. Meijers, J.A. Merlin, S. Mersi, E. Meschi, P. Milenovic44,F. Moortgat, M. Mulders, H. Neugebauer, S. Orfanelli,L. Orsini, L. Pape, E. Perez,

H. Sakulin, C. Schäfer, C. Schwick,M. Seidel, M. Selvaggi,A. Sharma,P. Silva, P. Sphicas46, A. Stakia, J. Steggemann,M. Stoye, M. Tosi,D. Treille, A. Triossi, A. Tsirou,V. Veckalns47, M. Verweij, W.D. Zeuner CERN,EuropeanOrganizationforNuclearResearch,Geneva,Switzerland

W. Bertl†, L. Caminada48, K. Deiters,W. Erdmann, R. Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski,

U. Langenegger, T. Rohe, S.A. Wiederkehr

PaulScherrerInstitut,Villigen,Switzerland

F. Bachmair, L. Bäni, P. Berger, L. Bianchini, B. Casal, G. Dissertori,M. Dittmar, M. Donegà, C. Grab,

C. Heidegger, D. Hits, J. Hoss,G. Kasieczka, T. Klijnsma,W. Lustermann,B. Mangano, M. Marionneau,

M.T. Meinhard,D. Meister, F. Micheli,P. Musella, F. Nessi-Tedaldi, F. Pandolfi, J. Pata, F. Pauss,G. Perrin,

L. Perrozzi,M. Quittnat, M. Reichmann, M. Schönenberger,L. Shchutska, V.R. Tavolaro, K. Theofilatos,

M.L. Vesterbacka Olsson, R. Wallny, D.H. Zhu

InstituteforParticlePhysics,ETHZurich,Zurich,Switzerland

T.K. Aarrestad, C. Amsler49, M.F. Canelli,A. De Cosa, R. Del Burgo, S. Donato, C. Galloni, T. Hreus,

B. Kilminster, J. Ngadiuba,D. Pinna,G. Rauco, P. Robmann, D. Salerno, C. Seitz,Y. Takahashi, A. Zucchetta

UniversitätZürich,Zurich,Switzerland

V. Candelise,T.H. Doan, Sh. Jain,R. Khurana, C.M. Kuo,W. Lin, A. Pozdnyakov,S.S. Yu

NationalCentralUniversity,Chung-Li,Taiwan

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

NationalTaiwanUniversity(NTU),Taipei,Taiwan

B. Asavapibhop, K. Kovitanggoon, G. Singh, N. Srimanobhas

ChulalongkornUniversity,FacultyofScience,DepartmentofPhysics,Bangkok,Thailand

F. Boran, S. Cerci50, S. Damarseckin, Z.S. Demiroglu, C. Dozen, I. Dumanoglu, S. Girgis, G. Gokbulut, Y. Guler, I. Hos51,E.E. Kangal52, O. Kara, A. Kayis Topaksu,U. Kiminsu,M. Oglakci, G. Onengut53, K. Ozdemir54, D. Sunar Cerci50, B. Tali50, S. Turkcapar,I.S. Zorbakir, C. Zorbilmez

ÇukurovaUniversity,PhysicsDepartment,ScienceandArtFaculty,Adana,Turkey

B. Bilin, G. Karapinar55, K. Ocalan56,M. Yalvac, M. Zeyrek MiddleEastTechnicalUniversity,PhysicsDepartment,Ankara,Turkey

E. Gülmez,M. Kaya57,O. Kaya58, S. Tekten, E.A. Yetkin59 BogaziciUniversity,Istanbul,Turkey

M.N. Agaras, S. Atay, A. Cakir,K. Cankocak

IstanbulTechnicalUniversity,Istanbul,Turkey B. Grynyov

InstituteforScintillationMaterialsofNationalAcademyofScienceofUkraine,Kharkov,Ukraine

L. Levchuk,P. Sorokin