Centrality, rapidity and transverse momentum dependence of image suppression in Pb–Pb collisions at image

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Physics

Letters

B

www.elsevier.com/locate/physletb

Centrality,

rapidity

and

transverse

momentum

dependence

of

J

/ψ

suppression

in

Pb–Pb

collisions

at

√

s

_NN

=

2

.

76 TeV

.ALICE

Collaboration

∗

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received3November2013

Receivedinrevisedform15May2014 Accepted20May2014

Availableonline27May2014 Editor:L.Rolandi

Keywords:

Relativisticheavyioncollisions Quarkgluonplasma Quarkonium J/ψsuppression Experimentalresults

The inclusive J/ψ nuclear modification factor (RAA) in Pb–Pb collisions at √sNN=2.76 TeV has been

measured by ALICE as a function of centrality in the e+e− decay channel at mid-rapidity (|y|<0.8) and as a function of centrality, transverse momentum and rapidity in the

μ

+

μ

− decay channel at forward-rapidity (2.5 <y<4). The J/ψ yields measured in Pb–Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The RAAintegrated over a centrality range

corresponding to 90% of the inelastic Pb–Pb cross section is 0.72 ±0.06(stat.)±0.10(syst.)at mid-rapidity and 0.58 ±0.01(stat.)±0.09(syst.)at forward-rapidity. At low transverse momentum, significantly larger values of RAA are measured at forward-rapidity compared to measurements at lower energy. These

features suggest that a contribution to the J/ψ yield originates from charm quark (re)combination in the deconfined partonic medium.

©2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP3_.

1. Introduction

The theory ofQuantum Chromodynamics (QCD) predicts that the hot anddense nuclear matter produced during the collision of ultra-relativisticheavy nucleibehaves asa deconfined Plasma ofQuarksandGluons(QGP). Thisphaseofmatter existsforonly a short time before the fireball cools down and the process of hadronization takes place. Heavy quarks are an important probe oftheQGPsincetheyareexpectedtobeproducedonlyduringthe initialstageofthecollisioninhard partonicinteractions, thus ex-periencingtheentireevolutionofthesystem.Itwaspredictedthat inahotanddensedeconfinedmediumliketheQGP,boundstates of charm (c)and anti-charm (c)

¯

quarks, i.e. charmonia, are sup-pressedduetothescreeningeffectsinducedbythehighdensityof colorcharges[1].Therelativeproductionprobabilitiesof charmo-niumstateswithdifferentbindingenergiesmayprovideimportant informationonthepropertiesofthismediumand,inparticular,on itstemperature[2,3].Among thecharmoniumstates,the strongly boundJ

/ψ

isofparticularinterest.The J

/ψ

productionisa com-bination from prompt andnon-prompt sources. The prompt J

/ψ

yield consists of the sum of direct J

/ψ

(

≈

65%) and excited c

¯

c states such as

χ

c and

ψ(

2S

)

decaying into J

/ψ

+

X (

≈

35%) [4].

Theseexcited stateshavea smallerbinding energythanthe J

/ψ

. Non-prompt J

/ψ

productionis directly relatedto beauty hadron productionwhoserelative contributionincreaseswiththe energy of the collision. Experimentally, J

/ψ

production was studied in

*

Forcorrespondence,pleaseusee-mailaddress:alice-publications@cern.ch.

heavy-ioncollisions attheSuperProton Synchrotron(SPS) andat the RelativisticHeavyIonCollider(RHIC),coveringa largeenergy range from about 20 to 200 GeV center-of-mass energy per nu-cleon pair (

√

sNN). A suppression of the inclusive J

/ψ

yield in nucleus–nucleus(A–A)collisionswithrespecttotheonemeasured in proton–proton (pp) scaled by the number of binary nucleon– nucleon collisions was observed. In the most central events, the suppressionisbeyondtheoneinduced bycoldnuclearmatter ef-fects (CNM), such asshadowing andnuclear absorption, atboth SPS[5,6]andRHIC[7].AttheSPStheJ

/ψ

suppressionis compat-ible withthemeltingoftheexcited stateswhereastheRHICdata suggest a small amount of suppression for the direct J

/ψ

[8,9]. Similar predictions on sequential suppression [3] were madefor thebottomoniumfamily,whichhasbecomeaccessibleattheLarge HadronCollider(LHC)energies. Thesequentialsuppressionofthe

Υ (

1S

)

,

Υ (

2S

)

and

Υ (

3S

)

stateswasfirstobservedbytheCMS ex-perimentinPb–Pbcollisionsat

√

sNN

=

2

.

76 TeV[10].

The first ALICE measurement of the inclusive J

/ψ

production incentralPb–Pbcollisionsat

√

sNN

=

2

.

76 TeV atforward-rapidity has shown lesssuppression compared to PHENIX results in cen-tralAu–Aucollisionsat

√

sNN

=

0

.

2 TeV[11].At

√

sNN

=

2

.

76 TeV, thecharmquarkdensityproducedinthecollisionsincreaseswith respectto SPSandRHICenergies [12].Thismayresultinthe en-hancementoftheprobabilitytocreateJ

/ψ

mesonsfrom (re)com-bination of charm quarks [13,14]. If the J

/ψ

mesons are fully suppressed in the QGP, their creation will take place at chem-ical freeze-out (near the phase boundary) as detailed in [13,15, 16].IfJ

/ψ

mesonssurviveintheQGP,productionmaytakeplace continuously during the QGP lifetime [14,17,18]. Because of the

http://dx.doi.org/10.1016/j.physletb.2014.05.064

0370-2693/©2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/3.0/).Fundedby SCOAP3_.

large increase of the c

¯

c cross-section towards LHC energy the (re)combination mechanismmaybecomedominantthere. Accord-ing to statistical[13] and partonic transport [17,18] models, this contributionleads to an increase ofthe RAA atthe LHCwith re-spect to the one observed at RHIC. In particular, this scenario predicts an increase of the RAA from forward- to mid-rapidity, wherethedensityofcharm quarksis higher.Furthermore,in or-der to (re)combine, two charm quarks need to be close enough inphasespace,sothatlowtransversemomentumJ

/ψ

production isexpected to be favored. The transverse momentum and rapid-itydependence of the J

/ψ

RAA are therefore crucialobservables to sharpen the interpretation of the results, providing a deeper insightonthebalancebetweenJ

/ψ

(re)combinationand suppres-sion.

In thisLetter, we present results on the nuclear modification factorforinclusiveJ

/ψ

inPb–Pbcollisionsat

√

sNN

=

2

.

76 TeV asa functionofcollisioncentrality,transversemomentumandrapidity. Complementarytoourresults,J

/ψ

suppressionatlargetransverse momentum in Pb–Pb collisions, was reported previously by AT-LAS[19]andCMS[20].

2. Experimentalapparatusanddatasample

ALICEisageneralpurposeheavy-ionexperiment.Adetailed de-scriptionof the experimental apparatus can be found in [21]. It consistsof a central barrel covering the pseudo-rapidity interval

|

η

|

<

0

.

9 andamuonspectrometercovering

−

4

<

η

<

−

2

.

5.1 J

/ψ

production is measured in both rapidity ranges: at mid-rapidity in the dielectron decay channel and at forward-rapidity in the dimuondecaychannel.Inboth casestheJ

/ψ

transverse momen-tum(pT)coverageextendsdowntozero.

Atmid-rapidity,thedetectorsusedfortheJ

/ψ

analysisarethe Inner Tracking System(ITS) [22] and the Time Projection Cham-ber (TPC) [23].The ITSis composed of six concentriccylindrical layers of silicon detectors withradii ranging from 3.9 to 43 cm withrespecttothebeamaxis.Itsmainpurposeistoprovidethe reconstruction of the primary interaction vertex as well as sec-ondarydecayverticesofheavy flavoredparticles. Inaddition,the twoinnermostlayerscanprovideaninputatlevelzero(L0)tothe triggersystem.TheTPC,withan activevolumeextendingfrom85 to247 cmintheradialdirection,isthemaintrackingdetectorof thecentralbarrelandalso providesparticleidentificationvia the measurement ofthe specific energy loss (dE

/

dx) in the detector gas.

At forward-rapidity, the J

/ψ

analysis is carried out using the muonspectrometer[24].Thespectrometerconsistsofaten inter-action length front absorber, filtering the muons in front of five tracking stations made of two planes of cathode pad chambers each. The third station is located inside a dipole magnet with a 3 Tmfieldintegral.ThespectrometeriscompletedbyaMuon Trig-gersystem(MTR) madeoftwo stations,each equippedwithtwo planesofresistiveplatechambers.Thetriggerchambersareplaced behind a1.2 m thick iron wall to stop secondaryhadrons escap-ing from the front absorber and low momentum muons coming mainlyfrom

π

andKdecays.Throughoutitsfulllength,aconical absorbermadeoftungsten,leadandsteelprotectsthemuon spec-trometeragainst secondaryparticles generated bythe interaction withthebeampipeofprimaryparticlesproducedatlarge

η

.

Additionalforwarddetectors,theVZERO[25]andtheZero De-gree Calorimeters (ZDC) [26], are used for triggering and event

1 _{IntheALICEreferenceframe,themuonspectrometercoversanegativeηrange} andconsequentlyanegativey range.Wehavechosentopresentourresultswitha positivey notation.

characterization.TheVZEROdetectoriscomposedoftwo scintilla-torarrays,32channelseach,placedonbothsidesoftheInteraction Point(IP).Itcovers2

.

8

≤

η

≤

5

.

1 (VZERO-A)and

−

3

.

7

≤

η

≤ −

1

.

7 (VZERO-C). The ZDCare located ata distance of 114 mon both sidesoftheIPandcandetectspectatorneutronsandprotons.

TheresultspresentedinthisLetterarebasedondatacollected duringthe2010and2011LHCPb–Pbrunsforthedielectron anal-ysis andon data collected in the 2011run forthe dimuon one. Forward-rapidityresultsinthedimuonchannelfromthe2010data set,basedonanintegratedluminosityabout25timessmallerthan the 2011 data set, have been published previously in [11]. The minimumbias(MB)triggerforthe2011datasetisdefinedbythe coincidenceofsignalsinthetwoVZEROarrayssynchronizedwith thepassageoftwo crossingPbbunches.Inthe2010dataset,the MB triggerhadan additionalrequirementon hitsintheITS. The twoMBtriggerdefinitions,however,leadtoverysimilartrigger ef-ficiencies,whicharelargerthan95%forinelasticPb–Pbcollisions. Electromagnetic interactions are rejected atthe level one trigger (L1)byapplyingacutontheminimumenergydepositedby spec-tator neutrons in the ZDC. Beam induced background is further reducedattheofflinelevelbyapplyingtimingcutsonthesignals fromtheVZEROandZDCdetectors.

At mid-rapidity, the 2010 data sample used in the electron analysisconsistsof15millioneventscollectedwiththeMBtrigger, corresponding to an integratedluminosity of2

.

1 μb−1.The 2011 event sample was enriched with central and semi-central Pb–Pb collisionsby usingthresholdsontheVZEROmultiplicityattheL0 trigger.Theinspectedintegratedluminosityamountsto25

.

6 μb−1, out ofwhichweanalyzed20million central(0%–10%ofthe cen-tralitydistribution) and20million semi-central(10%–50%)events. Thesummed2010and2011datasetscorrespondtoan integrated luminosity of

L

int

=

27

.

7

±

0

.

4

(

stat.

)

+₋12..28

(

syst.

σ

Pb–Pb

)

μb−1. At forward-rapidity, the2011data sample ismadeofabout17 mil-lion

μμ

MB triggers.The

μμ

MB trigger is definedas the occur-rence of the MB condition in coincidence with the detection in the MTR of two opposite-sign muons tracks. The MTR is capa-bleof (i) deliveringL0 triggerdecisionsat 40 MHzbasedon the detection of one or two muon trigger tracks, (ii) computing an approximate value ofthe transverse momentum of muon trigger tracks(ptrig_T )and(iii)applyingathreshold2 _ontheptrig

T .A1 GeV/c threshold,appliedonbothmuons, waschosentocollectthisdata sample. A scaling factor Fnorm is used to obtain the number of equivalent MB events fromthe numberof

μμ

MB ones. It is de-fined as the ratio, in a MB data sample, of the number of MB eventsdividedbythenumberofeventsfulfillingthe

μμ

MB trig-ger condition. Its value, averaged over the entire data sample, is

Fnorm

=

30

.

56

±

0

.

01

(

stat.

)

±

1

.

10

(

syst.

)

.Theintegratedluminosity used inthis analysisis therefore

L

int

=

NμμMB

×

Fnorm

/

σ

Pb–Pb

=

68

.

8

±

0

.

9

(

stat.

)

±

2

.

5

(

syst. Fnorm

)

+₋54..55

(

syst.

σ

Pb–Pb

)

μb−1assuming aninelasticPb–Pbcross-section

σ

Pb–Pb

=

7

.

7

±

0

.

1+₋00..65b[26].

The centrality determination is based on a fit to the VZERO amplitude distribution asdescribed in[27]. Thefit, basedon the Glauber model,allows forthe extractionof collision-related vari-ablessuchastheaverageofnumberofparticipantnucleons



Npart



andtheaverageofthenuclearoverlapfunction



TAA



per central-ityclass.Numericalvaluesaregivenin

Table 1

.Boththe electron and muon analyses were carried out on an eventsample corre-sponding to the most central 90% of the inelastic Pb–Pb cross-section. In this centrality range the efficiency of the MB trigger is100% andthecontamination fromelectromagneticprocesses is negligible.

2 _{Thethresholdisdefinedas p}trig

T forwhichthetriggerprobabilityis50%and doesnotleadtoasharpcutinpT.

Table 1

Theaverageofnumberofparticipatingnucleons



Npartandtheaveragevalueof thenuclearoverlapfunction



TAAwiththeirassociatedsystematicuncertaintyfor thecentralityclasses,expressedinpercentagesofthenuclearcross-section[27], usedintheseanalyses.

Centrality Npart TAA(mb−1) 0%–10% 356.0±3.6 23.44±0.76 10%–20% 260.1±3.8 14.39±0.45 20%–30% 185.8±3.3 8.70±0.27 30%–40% 128.5±2.9 5.00±0.18 40%–50% 84.7±2.4 2.68±0.12 50%–60% 52.4±1.6 1.317±0.071 60%–70% 29.77±0.98 0.591±0.036 70%–80% 15.27±0.55 0.243±0.016 80%–90% 7.49±0.22 0.0983±0.0076 0%–20% 308.1±3.7 18.91±0.61 10%–40% 191.5±3.3 9.36±0.30 40%–90% 37.9±1.2 0.985±0.051 0%–90% 124.4±2.2 6.27±0.21 3. Dataanalysis

J

/ψ

candidatesareformedbycombiningpairsofopposite-sign (OS)electronandmuontracksreconstructedinthecentral barrel andinthemuonspectrometer,respectively.

Electron candidates are selected by cutting on the quality of tracks reconstructed in the ITS andthe TPC. The selection crite-riaare very similar tothose used in the previous analysisof pp collisionsat

√

s

=

7 TeV[24] usingatighterselectiononelectron identification.Ahit inoneofthetwoinnermostlayers oftheITS is required. This rejects a large fraction of background resulting fromphoton conversions in thedetector material.The tracks are required to have at least 70 out of a maximum of 159 clusters intheTPCandto passaquality cut basedonthe

χ

2 _{of theTPC} trackfitdivided by thenumberof clustersattachedtothe track. Electronidentificationisdone usingtheTPC, requiringthe dE

/

dx signal to be compatible with the electron expectation within a band of

(

−

2

.

0

;

+

3

.

0

)

σ

or

(

−

1

.

5

;

+

3

.

0

)

σ

for the 2010 or 2011 data, respectively, where

σ

denotes the resolution of the dE

/

dx measurement.Duetoalower dE

/

dx resolutionforthe2011data, for

|

η

|

<

0

.

5 amore restrictiveelectron selection,

(

−

0

.

9

;

+

3

.

0

)

σ

, isapplied.The electron/hadronseparationisfurther improvedby rejecting tracks which are compatible with the pion expectation within3

.

5

σ

andwiththeprotonexpectationwithin3

.

5

σ

or4

.

0

σ

in2010or2011data,respectively.SincetheelectronsfromaJ

/ψ

decayhaveamomentumof1.5 GeV/c inthemotherparticlerest frame,acutofpT

>

0

.

85 GeV

/

c onthecandidatetracksisapplied torejectthecombinatorialbackgroundfromlowmomentum elec-trons.Finally,toensuregoodtrackingandparticleidentificationin theTPC,onlycandidateswithin

|

η

|

<

0

.

8 areselected.

Muontracksarereconstructedinthemuonspectrometeras de-tailed in [24] for pp collisions. This procedure remains basically unchangedfor Pb–Pb collisions. However, to cope withthe large background incentral events, some selection criteriawere tight-ened compared to the pp analysis. The search area for finding clustersassociated to tracks is reducedby a factorof nine, both muon candidates have to match a track segment in the trigger chambers and the track pseudo-rapidity has to be in the range

−

4

<

η

<

−

2

.

5. A further cut on thetrack transverse coordinate atthe endof the front absorber (Rabs) is applied (17

.

6

≤

Rabs

≤

89

.

5 cm) toensurethatmuonsemittedatsmallangles,i.e.those that have crossed a significant fractionof the thick beamshield, are rejected. Finally, to remove events very close to the edge of thespectrometeracceptance,onlymuonpairsintherapidityrange 2

.

5

<

y

<

4 areaccepted.

In the e+e− decay channel, the J

/ψ

yields are extracted by countingthenumberofentriesintheinvariantmassrange2

.

92

<

me+e−

<

3

.

16 GeV

/

c2 after subtracting the combinatorial

back-ground. Due to the radiative decay channel and the energy loss ofthe electronsinthedetectormaterial viabremsstrahlung, only

≈

68% oftheJ

/ψ

arereconstructedwiththemassinthecounting massinterval.Thebackgroundshapeisobtainedusingthe mixed-event(ME) technique.Uncorrelatedlepton pairs arecreatedfrom different Pb–Pb events that have similar global properties such as centrality,primary vertexposition andeventplane angle. The backgroundshapefromMEisscaledtomatchthesame-event(SE) invariantmassdistributionintheranges1

.

5

<

me+e−

<

2

.

5 GeV

/

c2

and 3

.

2

<

me+e−

<

4

.

2 GeV

/

c2. These mass ranges were chosen

such that they are close to the signal region and have equal number of bins on each side of the signal region. The lower (1.5 GeV/c2) andupper(2.5 GeV/c2)limitsofthefirstmassrange are chosen in order to avoid sensitivity to correlated low-mass dielectronpairsandJ

/ψ

bremsstrahlungtail,respectively.The sec-ond massrangeis limitedby theupperlimitofthesignal region (3.2 GeV/c2_{) andextends to4.2 GeV/c}2 _{to matchinsizethe first} massinterval.Heretheinfluenceofthe

ψ(

2S

)

onthebackground matching procedure is neglected since the

ψ(

2S

)

dileptonyields areexpectedtoberoughly60timessmallerthanJ

/ψ

yields (esti-mation basedonLHCbmeasurementsofJ

/ψ

[28]and

ψ(

2S

)

[29]

cross-sectionsinpp collisionsat7 TeV).Agoodmatchingbetween the SEandME distributionsisobservedover abroadmassrange outsidetheJ

/ψ

massregion,asvisibleinthetoppanelsof

Fig. 1

. This is a clear sign that the contribution of correlated pairs to the OS mass spectrum is small withrespect to the uncorrelated background or has a similar shape. The bottom panels of Fig. 1

show thebackground-subtractedinvariantmassspectracompared to theJ

/ψ

signal shapefromaMonte-Carlo (MC)simulation.The bremsstrahlungtail fromtheelectron energylossin thedetector material and theJ

/ψ

radiative decaychannel (J

/ψ

→

e+e−

γ

) is welldescribedintheMC.Asshownin

Fig. 1

,itispossibletostudy theJ

/ψ

productioninthreecentralityintervals(0%–10%,10%–40%, 40%–90%),withasignal-to-backgroundratio(S/B),evaluatedinthe range 2

.

92

<

me+e−

<

3

.

16 GeV

/

c2, increasing from 0.02 to 0.25

fromcentraltoperipheralcollisions.

Inthe

μ

+

μ

− decaychannel,theJ

/ψ

rawyieldisextractedin eachcentralityandkinematicintervalbyusingtwodifferent meth-ods.Inthefirstapproach,theOSdimuoninvariantmass distribu-tionisfittedwiththesumofanextendedCrystalBall(CB2) func-tionto describethesignal,andaVariableWidthGaussian(VWG) function for the background.The CB2 function extends the stan-dardCrystalBall(Gaussianpluspower-lawtailatlowmasses[30]) by an additional power-law tail athigh masses withparameters independent ofthelow massones. The VWGfunction isa Gaus-sian functionwithafourthparametertoallow linearvariationof the widthwith the invariant mass of the dimuon pair. The J

/ψ

signal isclearly visibleinallcentrality, pT or y intervalseven be-fore any background subtraction, as can be observed in the top panels of Fig. 2, where examples of invariant mass spectra fits in selected pT intervals are shown. The signal-to-background ra-tio, evaluated within 3 standard deviations with respect to the J

/ψ

polemass, variesfrom 0.16atlow pT up to 1.2at high pT. The corresponding values incentralityand y intervals are inthe range0.16–6.5 fromcentral toperipheralcollisions and0.19–0.59 from low to high rapidity. In all cases, the significance is larger than 10. In the second approach, the combinatorial background was subtracted usingan event-mixingtechnique.The background shape obtained from ME was normalized to the data through a combinationofthemeasuredlike-signmuonpairsfromSE.

Fig. 2

(bottompanels) showsthe resultingmassdistributionfittedwith the sum of a CB2 andan exponential which accounts for

resid-Fig. 1. (Coloronline.)Top panels:invariantmassdistributionsforopposite-sign(OS)andmixed-events(ME)electronpairs.Bottompanels:OSinvariantmassspectra,after thesubtractionoftheMEdistributions,withacomparisontotheMonteCarlosignal(solidlines)superimposed.TheMCsignalisscaledtomatchtheintegraloftheOS distributionwithinthemasscountingwindow.Fromlefttoright,distributionscorrespondtothecentralityranges0%–10%,10%–40%and40%–90%,respectively.Thepanels forthe0%–10%and10%–40%centralityrangesareobtainedfromthe2011data,whiletheonesforthe40%–90%centralityrangeareobtainedfromthe2010data.Thetwo verticaldashedlinesshownineachpanelindicatethemassintervalusedforsignalcounting.

Fig. 2. (Coloronline.)Top panels:fitsofthedimuoninvariantmassspectrainselectedpTintervals.Bottompanels:idemaftersubtractionofthecombinatorialbackground withtheeventmixingtechnique.Distributionscorrespondtothecentralityclass0%–90%and2.5<y<4.

ualcorrelatedbackground.Inbothapproaches,thepositionofthe peak ofthe CB2 function (mJ/ψ), as well asits width(

σ

J/ψ), are

freeparametersofthefit.Theirvalues,obtainedbyfittingthe in-variant mass spectrum integrated over pT, y and centrality, are

mJ/ψ

=

3

.

103

±

0

.

001 GeV

/

c2 (shiftedup by 0.2%withrespectto

thePDG mass [31]) and

σ

J/ψ

=

0

.

071

±

0

.

001 GeV

/

c2. More

de-tails aboutthefittingprocedures andthe differentparameters of thesignalandbackgroundlineshapesarediscussedinSection4.

The measured number of J

/ψ

(Ni

J/ψ) in a centralityclass i is

normalized tothe corresponding number ofMB events falling in thecentralityclass(Ni

events) andfurthercorrectedforthe branch-ingratio(BR)ofthedileptondecaychannel,theacceptance A and

Table 2

InclusiveJ/ψproductioncross-sectionsatmid-rapidityusedintheinterpolationprocedure.TheJ/ψareassumedunpolarizedandthesystematicuncertaintiesdonotinclude thecontributionfromunknownpolarization.

Experiment Collision energy√s Rapidity range Blldσ/d y at y=0 stat. syst. Reference

(TeV) (nb) (nb) (nb) PHENIX 0.2 |y| <0.35 44.30 1.40 6.80 [38] CDF 1.96 |y| <0.6 201.6 1.0 17.8 −16.3 [39] ALICE 2.76 |y| <0.9 255.8 58.7 45.9 [40] ALICE 7 |y| <0.9 409.9 36.8 59.4 [24,41]

Interpolation 2.76 |y| <0.8 252.6 16.4 25.8 this work

theefficiency

i _{ofthedetector.Inthe}

_μ

+

_μ

− _{analysis, N}i

events is computedby multiplying the number of

μμ

MB triggered events bytheFnormfactor(describedinSection2)scaledbythewidthof thecentralityclass i.The inclusiveJ

/ψ

yieldforthemeasured pT andy rangesisthengivenby:

Y_Ji_/ψ

=

N i J/ψ BR_J/ψ→l+_l−Ni eventsA

×

i

.

(1)

The acceptancetimes efficiency product ( A

×

ε

) isdefined as the ratio between the number of reconstructed J

/ψ

divided by thenumberofgeneratedonesinthe kinematicrangeunderstudy. In the e+e− decay channel, A

×

ε

is calculated fromMC simu-lations. These MC events are a superposition ofPb–Pb collisions generated withan appropriate HIJING [32] tune reproducing the measured charged particle density [33] and J

/ψ

generated from parametrized pT and y distributions (details in Section 4). The J

/ψ

dielectron decays are performed using PHOTOS [34,35]. The particles are then transported through a simulation of the AL-ICE detector using GEANT3.21 [36]. The geometrical acceptance is about 34%. The estimated integrated A

×

ε

for the J

/ψ

emit-tedin

|

y

|

<

0

.

8 amountto0.080,0.085and0.093forthe0%–10%, 10%–40%and40%–90% centralityclassesinthe2010datasample and0.026and0.028forthe0%–10%and10%–40%centralityclasses inthe2011one, respectively.The largedifference inefficiencyis mainlydue toa lower efficiencyofthe two innermostITSlayers andstrongerparticleidentificationcutsusedforthe2011dataset. Inthe

μ

+

μ

−decaychannel,A

×

ε

wascomputedusingan embed-ding technique whereMC J

/ψ

particlesare injected intothe raw dataofrealeventsandthenreconstructed.TheMCJ

/ψ

pT and y parametrizationis takenfrom actual measurements.PYTHIA [37]

takes care of the J

/ψ

decays and the daughter particles signals inthe detector,givenby GEANT3.21, are then addedto the real Pb–Pbevents.When studiedasafunctionofcentrality, A

×

ε

de-creasesby7.9%,from0.127inthe80%–90%centralityclassto0.117 inthe0%–10% one. Thecentralityintegrated A

×

ε

(0%–90% cen-tralityclass)is0.120 witha negligiblestatisticaluncertainty. The geometricalacceptanceisabout18%.Thequantity A

×

ε

showsa non-monotonicdependenceonpT,startingatapproximately0.124 at zero transverse momentum, reaching a minimum of 0.103 at 1.5 GeV/c andthenlinearlyincreasingupto0.264at8 GeV/c.The rapidity dependenceof A

×

ε

reflects thegeometrical acceptance ofthemuon pairswithamaximum of0.189centered at y

=

3

.

3 decreasingtowardstheedgesoftheacceptanceto0.033(0.060)at

y

=

2

.

5 ( y

=

4

.

0).

Finally,thenuclearmodificationfactoriscalculatedastheratio between the corrected J

/ψ

yield in Pb–Pb collisions Y_JPb–Pb_/ψ and theJ

/ψ

cross-sectioninpp collisionsscaledbythenuclearoverlap function:

RAA

=

Y_JPb–Pb_/ψ



TAA

 ×

σ

_Jpp_/ψ

.

(2)

In the dielectron analysis, the pp reference was obtained by interpolatingtheinclusiveJ

/ψ

cross-sectionsatmid-rapidity

mea-suredby PHENIX[8]at

√

s

=

0

.

2 TeV,CDF[39] at

√

s

=

1

.

96 TeV andALICE[40,24,41]at

√

s

=

2

.

76and 7 TeV. Allthedatapoints usedinthisprocedurearelistedin

Table 2

.Theinterpolationwas done by fitting the data points with several functions assuming a linear,an exponential,apower laworapolynomial

√

s

depen-dence. Thevalue oftheinterpolatedppreferenceatmid-rapidity, d

σ

_Jpp_/ψ

/

d y

=

4

.

25

±

0

.

28

(

stat.

)

±

0

.

43

(

syst.

)

μb, is consistent with theonemeasuredbyALICE

[40]

,butthetotaluncertaintyistwice smaller,beingdrivenmainlyby theCDFresult. Thestatistical un-certainty was obtainedfromthe fittingprocedure,while the sys-tematiconewasobtainedbychangingthefitfunctionandby shift-ingthedatapointswithintheirexperimentalsystematic uncertain-ties. Forthe dimuonanalysis, thepp referenceandits associated uncertaintiesareextractedfromtheALICEmeasurement[40]. 4. Systematicuncertainties

The main sources ofsystematic uncertainties forthe J

/ψ

RAA evaluationare thetrackingefficiency,thesignal extraction proce-dure,theparameterizationoftheJ

/ψ

kinematicdistributionsused as input for the MC simulations, the uncertainty on the nuclear overlapfunction andtheuncertaintyonthe J

/ψ

pp cross-section at

√

s

=

2

.

76 TeV.Otheranalysis-dependentsourcesaredetailedin thefollowing.Thesystematicuncertaintieshavebeenevaluatedas afunctionofcentralityand, forthedimuonanalysis,ofpTand y. Anoverviewofsystematicuncertaintiesisgivenin

Table 3

.

In the dielectronanalysis, thesystematic uncertainties on the signalextractionareestimatedbyvaryingthemassregionusedto countthesignal,themassintervalusedformatchingtheME back-groundandtheOSdistribution.Inallthesecases,the background-subtracted OS distribution is compared to the MC signal shape andthe normalized

χ

2 _{obtainedisalways closeto 1.Thisshows} that,afterbackgroundsubtraction,thenumberofcorrelatedpairs not relatedto J

/ψ

decaysissmallanddoesnotinducea sizeable systematicuncertainty.Thecentralitydependentsystematic uncer-taintyonthesignalextraction,takenastheRMSofthedistribution ofthenumberofJ

/ψ

obtainedfromalltheperformedtests,ranges from7%to9%and4%to6%for2010and2011data,respectively. The systematicuncertainties dueto trackreconstructionand par-ticle identification are evaluated by varying all the analysiscuts. For each cut variation, the number of J

/ψ

signal counts is cor-rectedwiththecorresponding A

×

ε

.The RMSofthisquantity is found tovaryinthe range6–9%and4–5%inthe2010and2011 data, respectively. Since the signal extraction procedure must be used for every cut variation, the systematic uncertainties due to analysis cuts and signal extraction cannot be truly disentangled. Thus, aglobalsystematicuncertaintyisintroducedastheRMSof thedistribution ofcorrectedresultswhenvaryingboth signal ex-tractionparametersandcutvalues.Thesesystematicuncertainties range between 8% and11% depending on the centrality interval. The central valuefor thecorrected J

/ψ

yieldis chosen tobe the meanofthedistributionobtainedfromalltheperformedtests.

Inthedimuonanalysis,thesystematicuncertaintyonthesignal extraction is estimatedby fitting the invariant mass distribution

Table 3

SystematicuncertaintiesenteringtheRAAcalculation.ThetypeI(II)standsforcorrelated(uncorrelated)uncertaintieswithinagivensetofdatapoints.Theuncorrelated systematicuncertainties(typeII)aregivenasarange.

Channel μ+μ− e+e−

Centrality pTor y Centrality

value (%) type value (%) type value (%) type

signal extraction 1–3 II 1–5 II 8–11 II

tracking efficiency 11 and 0–1 I and II 1 and 8–14 I and II

trigger efficiency 2 and 0–1 I and II 1 and 2–4 I and II n/a

input MC parameterization 3 I 0–8 II 5 I

matching efficiency 1 I 1 II n/a

centrality limits 0–5 II 0–1 I 0–3 II

TAA 3–8 II 3 I 3–5 II

σJpp/ψ 9 I 6 and 5–6 I and II 12 I

Fnorm 4 I 4 I n/a

withandwithoutbackground subtractionandby varyingthe pa-rametersthatdefinethepowerlawshapesatlowandhighmasses oftheCB2signalfunction.Thesefitparametersarenotconstrained by the data and cannot be let free during the fitting procedure. Theyhavebeenfixedtodifferentvaluesextractedeitherfrom sim-ulationsorfrompp data, wherethesignal-to-backgroundratiois morefavorable. Fits corresponding to thevarious choices forthe CB2tailsare performed,keepingthebackgroundparametersfree, andvarying the invariant mass rangeused forthe fits. The raw J

/ψ

yieldisdeterminedastheaverageoftheresultsobtainedwith theaboveprocedureandthecorrespondingsystematicuncertainty is defined as the RMS of the deviations fromthe average. As a functionofcentrality(pT or y)thesystematicuncertaintyforthe signalextractionvariesfrom1%to3%(1%to5%).Thesinglemuon trackingandtriggerefficiencies,

trk and

trg,are estimatedwith

theembedded J

/ψ

simulation.Thecentralitydependenceofthese quantitiesisweak,since thedecreaseinmostcentralcollisionsis about1%and3.5%for

trk and

trg respectively.A11% systematic

uncertaintyon the tracking efficiencyis estimated by comparing itsdeterminationbased onrealdataandona MCapproach.This estimationreliesonacalculationofthetrackingefficiencyineach stationusingthedetectorredundancy(twoindependentdetection planesper station).Thesingle trackefficiency,definedasproduct ofthe stationefficiencies, is calculated fortracks fromreal data andfromsimulation.Thesingletrackefficienciesaretheninjected inpure J

/ψ

simulationsandthedifferenceusedastheJ

/ψ

track-ingsystematicuncertainty.ThepTandy dependenceoftheformer uncertaintyleads toabintobinuncorrelatedcomponentranging between8%and14%.ThesystematicuncertaintyontheJ

/ψ

A

×

ε

correctionsrelatedtothetriggerefficiencyis2%,mostly givenby theuncertaintyontheintrinsicefficiencyofthetriggerchambers. Thesystematicuncertaintyrelatedtotheresponsefunctionofthe trigger is always below 1% except in the lowest J

/ψ

pT interval where a value of 3% was estimated. As a function of centrality, thesystematicuncertainty ofthe trackingor thetrigger efficien-ciesis1%inthemostcentralcollisionsandbecomesnegligiblefor peripheral collisions. The uncertainty on the matching efficiency betweentracksreconstructedinthetrackingandtriggerchambers amountsto1%.Itiscorrelated asafunction ofthe centralityand uncorrelatedasafunctionofpT andy.

The A

×

ε

calculationdependson the J

/ψ

pT and y distribu-tionsusedasaninputtotheMC,andsystematiceffectsoriginating from different parameterizations of these distributions must be takenintoaccount.Inthee+e− analysis,theJ

/ψ

(pT, y) parame-terizationis basedonan interpolation oftheRHIC, CDFandLHC datainpp andpp collisions

¯

[42]

correctedusingnuclear shadow-ingcalculations

[43]

.Thesystematicuncertaintywas evaluatedby varyingthe slope ofthe pT shape ina wide rangesuch that the averagepTchangesbetween1.5 GeV/c and3.0 GeV/c.TheJ

/ψ

pT

spectrainA–Acollisions measuredbyPHENIX

[9]

atmid-rapidity andALICEatforwardrapidity [40]atall availablecentralities, to-gether withtheir uncertainties, are well covered inthe envelope determined by the considered variations. A centrality correlated systematic uncertainty of 5% was obtained following this proce-dure. In the

μ

+

μ

− analysis, the MC J

/ψ

parameterizations are based onthe pT and y distributions measured fordifferent cen-tralityclasses.The pT– y correlationobservedbyLHCbinpp colli-sions[28] wasalsoincludedinthesystematicstudy.Acorrelated variation in A

×

ε

of3% was observed as a function of central-ity.The pT( y)dependenceofthissystematicuncertaintybringsa maximumcontributionof1%(8%)oneachpoint.

Furthersourcesofsystematicuncertaintiesaffectingthenuclear modification factor are the uncertaintyon the limits of the cen-trality classes [27], on the nuclear overlap function and on the J

/ψ

cross-sectioninppcollisionsat

√

s

=

2

.

76 TeV.Anuncertainty onthenormalizationfactorFnorm,accountingforrunbyrun fluc-tuations onthisquantity, isalsoadded inthemuon analysis. All numericalvaluescanbefoundin

Table 3

.

When computing the A

×

ε

factor, we assumed that J

/ψ

are produced unpolarized and no systematic uncertainty is assigned to a possible polarization. In pp collisions, mid-rapidity (pT

>

10 GeV

/

c) and forward-rapidity (pT

>

2 GeV

/

c) measurements havebeen done at

√

s

=

7 TeV andindeed show that J

/ψ

polar-ization is compatiblewithzero [44–46]. In Pb–Pb collisions, J

/ψ

mesonsproducedfromcharmquarksinthemediumareexpected tobeunpolarized.

5. Results

In the e+e− decay channel, the inclusive J

/ψ

RAA was stud-iedasafunctionofthecollisioncentrality(0%–10%,10%–40%and 40%–90%) for pT

>

0 GeV

/

c and

|

y

|

<

0

.

8. In the

μ

+

μ

− decay channel,theeventsamplecollectedinthe2011runwiththe ded-icated

μμ

MB triggerallowsforthestudyoftheRAA asafunction ofthecentralityofthecollisionsinnineintervals. Furthermore,a differential studyofthe RAA asa functionof transverse momen-tumorrapidityisalsofeasible.Dataareanalyzedinsevenintervals inthepT range0

<

pT

<

8 GeV

/

c rangeandsixintervalsinthe y range 2

.

5

<

y

<

4. The chosen binning matches the one adopted forthe

√

s

=

2

.

76 TeV ppresults,whichareusedasthereference fortheevaluationofthenuclearmodificationfactor.

Fig. 3showstheinclusiveJ

/ψ

RAAatmid- andforward-rapidity asafunctionofthenumberofparticipantnucleons



Npart



. Statis-ticaluncertaintiesareshownasverticalerrorbars,whiletheboxes representthevariousuncorrelatedsystematicuncertainties added in quadrature.The systematicuncertainties correlated bin by bin (typeII in

Table 3

)are summedin quadratureandreferred toas

Fig. 3. (Coloronline.) Centralitydependenceofthenuclearmodificationfactor,RAA, ofinclusiveJ/ψ productioninPb–Pbcollisionsat √sNN=2.76 TeV,measuredat mid-rapidityandat forward-rapidity.The pointtopointuncorrelated systematic uncertainties(typeII)arerepresentedasboxesaroundthedatapoints,whilethe statisticalonesareshownasverticalbars.Globalcorrelatedsystematicuncertainties (typeI)arequoteddirectlyinthelegend.

is observed, independent of centrality for



Npart



>

70. Although withlarger uncertainties, themid-rapidity RAA shows a suppres-sion of the J

/ψ

yield too. The centrality integrated RAA values are R0%–90%

AA

=

0

.

72

±

0

.

06

(

stat.

)

±

0

.

10

(

syst.

)

andR0%–90%AA

=

0

.

58

±

0

.

01

(

stat.

)

±

0

.

09

(

syst.

)

atmid- andforward-rapidity,respectively. Thesystematicuncertaintieson both RAA valuesincludethe con-tributionarising from



TAA



calculations.Thisamounts to3.4% of the computed



TAA



value and is a correlated systematic uncer-tainty common to the mid- and forward-rapidity measurements. PHENIX mid- (

|

y

|

<

0

.

35) andforward-rapidity (1

.

2

<

|

y

|

<

2

.

2) results on inclusive J

/ψ

RAA at

√

sNN

=

0

.

2 TeV exhibit a much strongerdependenceonthecollision centralityandasuppression ofaboutafactorofthreelargerinthemostcentralcollisions[9].

The measured inclusive J

/ψ

RAA includes contributions from prompt and non-prompt J

/ψ

; the first one results from direct J

/ψ

production and feed-down from

ψ(

2S

)

and

χ

c, the second

one arises from beautyhadron decays. Non-prompt J

/ψ

are dif-ferentwithrespecttothepromptones,sincetheirsuppressionor productionisinsensitivetocolorscreeningorregeneration mech-anisms. Beauty hadron decay mostly occurs outside the fireball, anda measurementofthenon-promptJ

/ψ

RAA istherefore con-nectedto thebeauty quark in-mediumenergyloss (see [47] and referencestherein).At mid-rapidity,the contributionfrombeauty hadron feed-down to the inclusive J

/ψ

yield in pp collisions at

√

s

=

7 TeV isapproximately15%

[48]

.ThepromptJ

/ψ

RAAcanbe evaluatedaccordingtoRprompt_AA

= (

RAA

−

Rnon-promptAA

)/(

1

−

FB

)

where

FB is the fraction ofnon-prompt J

/ψ

measured in pp collisions, andRnon-prompt_AA isthenuclearmodificationfactorofbeautyhadrons inPb–Pb collisions. Thus, the prompt J

/ψ

RAA at mid-rapidity is expectedtobe about7%smaller thantheinclusivemeasurement ifthe beauty productionscales with the numberof binary colli-sions (Rnon-prompt_AA

=

1) andabout17% larger ifthebeautyis fully suppressed (Rnon-prompt_AA

=

0). At forward-rapidity, the non-prompt J

/ψ

fractionwasmeasuredbytheLHCbCollaborationtobeabout 11(7)%in pp collisionsat

√

s

=

7

(

2

.

76

)

TeV inthe pT range cov-eredbythisanalysis[28,49].Then,thedifferencebetweentheRAA ofpromptJ

/ψ

andthe oneforinclusiveJ

/ψ

isexpectedtobe of about

−

6% and7% inthe two aforementionedextremecases as-sumedforbeautyproduction.

Fig. 4. (Coloronline.) Toppanel:transversemomentumdependenceofthe central-ityintegratedJ/ψ RAAmeasuredbyALICEinPb–Pbcollisionsat√sNN=2.76 TeV comparedtoCMS[20]resultsatthesame√sNN.Bottompanel:transverse momen-tumdependenceoftheJ/ψ RAAmeasuredbyALICEinthe0%–20%mostcentral Pb–Pbcollisionsat√sNN=2.76 TeV comparedtoPHENIX[9]resultsinthe0%–20% mostcentralAu–Aucollisionsat√sNN=0.2 TeV.

In the top panel of Fig. 4, the J

/ψ

RAA atforward-rapidity is shown as a function of pT for the 0%–90% centrality integrated Pb–Pb collisions. It exhibits a decrease from 0.78 to 0.36, indi-cating that high pT J

/ψ

are more suppressed than low pT ones. Furthermore,athighpTadirectcomparisonwithCMSresults[20] atthe same

√

sNN is possible,themain differencebeingthat the CMS measurement covers a slightly more central rapidity range (1

.

6

<

|

y

|

<

2

.

4). In theoverlapping pT range a similar suppres-sion isfound. One should add herethat thetwo CMSpoints are not independent andcorrespondto differentintervalsof theJ

/ψ

pT (3

<

pT

<

30 GeV

/

c and 6

.

5

<

pT

<

30 GeV

/

c). In the bot-tom panelof

Fig. 4

,theforward-rapidityJ

/ψ

RAA forthe0%–20% mostcentral collisions isshown. The observed pT dependenceof the RAA formostcentralcollisions isveryclosetotheoneinthe 0%–90% centralityclass.Thisisindeedexpectedsincealmost70% of the J

/ψ

yield iscontained inthe 0%–20% centrality class.Our dataarecomparedtoresultsobtainedbyPHENIXin0%–20%most central Au–Au collisions at

√

sNN

=

0

.

2 TeV, in the rapidity re-gion1

.

2

<

|

y

|

<

2

.

2[9].AstrikingdifferencebetweentheJ

/ψ

RAA patterns can be observed.In particular,in thelow pT region the ALICE RAA resultisa factorofup tofourhighercomparedtothe PHENIXone.Thisobservationisinqualitativeagreementwiththe

Fig. 5. (Coloronline.) TherapiditydependenceoftheJ/ψ RAAmeasuredinPb–Pb collisionsat √sNN=2.76 TeV.Bothmid- andforward-rapiditymeasurements in-cludeacommoncorrelatedsystematicuncertaintyof3.4%dueto



TAA.The mid-rapiditymeasurementcoverstherapidityrange

|

y| <0.8 andtheforward-rapidity oneisgiveninintervalsof0.25unitofrapidityfromy=2.5 toy=4.

calculations from[17,50]wherethe(re)combinationdominancein theJ

/ψ

productionleads to a decrease ofthe



p2_T



in A–A colli-sionswithrespect to pp collisions. Althoughatthe two energies the rapidity coverages are not the same andCNM effects might havea different size,our results point tothe presence ofa new contributiontotheJ

/ψ

yieldatlow pT.

Finally,thedependenceoftheJ

/ψ

RAA onrapidityisdisplayed inFig. 5 forthe 0%–90% centralityclass. At forward-rapidity, the J

/ψ

RAAdecreasesbyabout40%from y

=

2

.

5 to y

=

4.Theresult fromtheelectronanalysisisconsistentwithaconstantorslightly increasingRAA towardsmid-rapidity.

6. Conclusions

The inclusive J

/ψ

nuclear modification factor has been mea-suredbyALICEasafunctionofcentrality, pT and y inPb–Pb col-lisionsat

√

sNN

=

2

.

76 TeV,downto zero pT.Atforward-rapidity,

RAA showsa clear suppression ofthe J

/ψ

yield,with no signifi-cantdependenceoncentralityfor



Npart



larger than70.At mid-rapidity,theJ

/ψ

RAAiscompatiblewithaconstantsuppressionas afunction ofcentrality. At forward-rapiditythe J

/ψ

RAA exhibits astrong pT dependenceanddecreases bya factorof2 fromlow

pT to high pT. This behavior strongly differs from that observed byPHENIXat

√

sNN

=

0

.

2 TeV.Thisresultsuggeststhatafraction oftheJ

/ψ

yieldisproducedvia(re)combinationofcharmquarks. Inaddition,theindicationofanon-zeroJ

/ψ

ellipticflowinPb–Pb collisions at

√

sNN

=

2

.

76 TeV observedby ALICE[51] brings an-otherhintinfavorof(re)combinationscenarios.Preciseknowledge ofthecold nuclear effectsis necessaryforfurther understanding ofthe J

/ψ

behavior. The measurement ofthe J

/ψ

productionin p–Pbcollisions at theLHC [52,53] willallow one to sharpen the interpretationoftheseresults.

Acknowledgements

The ALICECollaboration would like to thank all its engineers andtechniciansfortheirinvaluablecontributionstothe construc-tion of the experiment and the CERN accelerator teams for the outstandingperformanceoftheLHCcomplex.

TheALICECollaboration gratefully acknowledgesthe resources andsupportprovided byallGrid centresandtheWorldwideLHC ComputingGrid(WLCG)Collaboration.

The ALICE Collaboration acknowledges the following funding agencies fortheir supportin buildingandrunning theALICE de-tector: StateCommitteeofScience,World FederationofScientists (WFS) andSwiss Fonds Kidagan, Armenia; Conselho Nacional de DesenvolvimentoCientífico eTecnológico (CNPq),Financiadorade EstudoseProjetos(FINEP),FundaçãodeAmparoàPesquisado Es-tado de São Paulo (FAPESP);National NaturalScience Foundation of China (NSFC), the Chinese Ministry of Education (CMOE) and theMinistryofScienceandTechnologyofChina(MSTC);Ministry ofEducationandYouthoftheCzechRepublic;DanishNatural Sci-ence Research Council, the Carlsberg Foundation andthe Danish NationalResearchFoundation;TheEuropeanResearchCouncil un-der the European Community’s Seventh Framework Programme; Helsinki Institute of Physics andthe Academy of Finland; French CNRS-IN2P3,the‘RegionPaysdeLoire’,‘RegionAlsace’,‘Region Au-vergne’ andCEA,France;German BMBFandtheHelmholtz Asso-ciation;GeneralSecretariatforResearchandTechnology,Ministry ofDevelopment, Greece;HungarianOTKA andNationalOfficefor Research and Technology (NKTH); Department of Atomic Energy and Department of Science and Technology of the Government of India; Istituto Nazionale di Fisica Nucleare (INFN) and Cen-tro Fermi – MuseoStorico della Fisica e CentroStudi e Ricerche “Enrico Fermi”, Italy; MEXT Grant-in-Aid for Specially Promoted Research, Japan; JointInstitute forNuclear Research, Dubna; Na-tionalResearchFoundationofKorea(NRF);CONACYT,DGAPA, Méx-ico,ALFA-ECandtheEPLANETProgram(EuropeanParticlePhysics LatinAmericanNetwork); StichtingvoorFundamenteelOnderzoek der Materie(FOM) andtheNederlandse Organisatievoor Weten-schappelijk Onderzoek (NWO), Netherlands; Research Council of Norway (NFR); Polish Ministry of Science and Higher Education; NationalScienceCentre,Poland;MinistryofNational Education/In-stituteforAtomicPhysicsandCNCS-UEFISCDI–Romania;Ministry ofEducationandScience ofRussianFederation, RussianAcademy ofSciences,RussianFederalAgencyofAtomicEnergy,Russian Fed-eralAgencyforScienceandInnovationsandTheRussian Founda-tionforBasicResearch;MinistryofEducationofSlovakia; Depart-mentofScienceandTechnology,SouthAfrica;CIEMAT,EELA, Min-isterio de Economía y Competitividad (MINECO) of Spain, Xunta deGalicia(Conselleríade Educación),CEADEN,Cubaenergía,Cuba, andIAEA(InternationalAtomicEnergyAgency);SwedishResearch Council (VR) and Knut & Alice Wallenberg Foundation (KAW); Ukraine Ministry of Education andScience; United Kingdom Sci-ence and Technology Facilities Council (STFC); The United States DepartmentofEnergy,theUnitedStatesNationalScience Founda-tion,theStateofTexas,andtheStateofOhio.

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ALICECollaboration

B. Abelev

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J. Adam

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D. Adamová

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M.M. Aggarwal

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G. Aglieri Rinella

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A.G. Agocs

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A. Agostinelli

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N. Agrawal

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Z. Ahammed

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N. Ahmad

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A. Ahmad Masoodi

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I. Ahmed

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S.U. Ahn

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S.A. Ahn

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I. Aimo

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cn

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S. Aiola

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M. Ajaz

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A. Akindinov

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D. Aleksandrov

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