J/ψ suppression at forward rapidity in Pb–Pb collisions at sNN=5.02 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

J/ψ

suppression

at

forward

rapidity

in

Pb–Pb

collisions

at

√

_s

NN

=

5.02 TeV

ALICE Collaboration

⋆

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory: Received29July2016

Receivedinrevisedform5December2016 Accepted26December2016

Availableonline10January2017 Editor:L.Rolandi

TheinclusiveJ/ψ productionhasbeenstudiedinPb–Pbandppcollisionsatthecentre-of-massenergy per nucleon pair √sNN=5.02 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is

reconstructed, in the centre-of-mass rapidity interval 2.5<y<4 and in the transverse-momentum range pT<12 GeV/c,viaitsdecaytoamuonpair.InthisLetter,wepresent resultsontheinclusive J/ψ cross sectionin ppcollisions at √s=5.02 TeV and onthe nuclear modification factor RAA. The latterispresentedasafunctionofthecentralityofthecollisionand,forcentralcollisions,asafunction of the transverse momentum pT ofthe J/ψ.The measured RAA values indicate asuppression of the J/ψ innuclear collisions and are thencomparedto ourprevious resultsobtained inPb–Pbcollisions

at√sNN=2.76 TeV.The ratioofthe RAA values atthe twoenergiesisalsocomputed andcompared tocalculationsofstatisticaland dynamicalmodels.Thenumericalvalueoftheratioforcentral events (0–10% centrality) is 1.17±0.04(stat)±0.20(syst). In central events, as a function of pT, a slight increaseofRAAwithcollisionenergyisvisibleintheregion2<pT<6 GeV/c.Theoreticalcalculations qualitativelydescribethemeasurements,withinuncertainties.

©2017TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Whenheavynucleicollideatultrarelativisticenergies,astateof strongly-interacting matter is formed,characterised by high tem-perature anddensity, where quarks andgluons are not confined into hadrons (Quark–Gluon Plasma, QGP [1]). A detailed charac-terisation of the QGP is the object, since more than 25 years, of an intense research activity at the CERN/SPS [2] and at the BNL/RHIC [3–6] and CERN/LHC [7] ion colliders. Charmonia and bottomonia, which are bound states of charm–anticharm (cc) or bottom–antibottom (bb) quarks, respectively [8], are among the most sensitive probes of the characteristics of the QGP. A sup-pression of their yields in nucleus–nucleus (A–A) collisions with respecttoexpectationsfromproton–proton(pp)collisionswas ex-perimentallyobserved.FortheJ/

ψ

meson,thegroundcc statewith quantumnumbersJPC

₌

₁−−_{,asuppressionwasfoundattheSPS,}

inPb–Pb andIn–Ininteractions atthecentre-of-mass energyper nucleonpair

√

sNN

=

17

.

2 GeV[9,10],RHIC,inAu–Auinteractions at

√

sNN

=

200 GeV[11,12],andfinally attheLHC,in Pb–Pb

col-lisions at

√

sNN

=

2

.

76 TeV [13,14]. Early theoretical calculations predictedJ/

ψ

suppressionto be induced by thescreening ofthe colourforce ina deconfined medium andto become stronger as theQGPtemperatureincreases[15,16].Inacomplementarywayto

⋆ _{E-mailaddress:alice-publications@cern.ch.}

thisstaticapproach,J/

ψ

suppressioncanalsobeseenastheresult of dynamical interactions with the surrounding partons [17–19]. TheLHCresults,integratedovertransversemomentum(pT)down

to pT

=

0,show asuppression ofthe J/

ψ

, quantifiedthrough the ratio betweenitsyields in Pb–Pbandthose inpp, normalised to thenumberofnucleon–nucleoncollisionsinPb–Pb(nuclear modi-ficationfactor, RAA).However,theobservedsuppressionissmaller

thanatSPSandRHIC[20,21],inspiteofthehigherinitial temper-atureoftheQGPformedattheLHC[22].Theeffectisparticularly evident for head-on(central) collisions.In orderto explain these observations, theoretical models require a contribution from J/

ψ

regeneration viaarecombinationmechanism[23,24]betweenthe c and c quarks,during thedeconfinedphaseand/oratthe hadro-nisation of the system, which occurs when its temperature falls below the critical value Tc

∼

155 MeV [25].The strength ofthis

regeneration effectincreaseswiththeinitial numberofproduced cc pairs relativeto thetotalnumberofquarks and,therefore, in-creaseswiththecollisionenergy,explainingthereduced suppres-sionattheLHC.Sincethebulkofcharm–quark productionoccurs at small momenta, recombination should be more important for low-pTJ/

ψ

,asobservedintheLHCresults[21].

An important test of the suppression and regeneration pic-tureof J/

ψ

productionattheLHC canbe obtainedby comparing the centrality and pT dependence of the J/

ψ

RAA, measured at

√

_s

NN

=

2

.

76 TeV,tothatobtainedat

√

sNN

=

5

.

02 TeV,thehighest energyavailable up tonow innuclearcollisions. The suppression

http://dx.doi.org/10.1016/j.physletb.2016.12.064

0370-2693/©2017TheAuthor.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

effectsrelated tocolour screening shouldbecome stronger when increasingthecollisionenergy,duetothehigherQGPtemperature, andalsotherecombinationeffectsshouldbecomestronger,dueto theexpectedincrease ofthecc productioncrosssection. Thetwo effectsactinoppositedirectionsandthecomparisonoftheRAA at

thedifferentenergies canprovideinsightsintheevolutionofthe relativecontributionofthetwoprocesses.

InthisLetter,wepresentthefirstresultsontheJ/

ψ

RAA

mea-sured by the ALICECollaboration in Pb–Pb collisions at

√

sNN

=

5

.

02 TeV and the integrated and pT differential J/

ψ

production crosssection inpp collisions atthe same energy. In both Pb–Pb andpp collisions, the J/

ψ

is reconstructed via its dimuon decay channel at forwardrapidity, 2

.

5

<

y

<

4 and for pT

<

12 GeV

/

c. ThemeasurementsrefertoinclusiveJ/

ψ

production,thatincludes bothpromptJ/

ψ

(directJ/

ψ

andfeed-downfromhigher-mass res-onances) and non-prompt J/

ψ

(from decay of beauty hadrons). ThenuclearmodificationfactorisobtainedbynormalisingtheJ/

ψ

yield in Pb–Pb collisions to the product of the nuclear overlap function times the corresponding J/

ψ

cross section measured in pp, atthe sameenergy andin the samekinematic window. The resultson RAA are presentedasa function of the J/

ψ

pT andof

thecentralityofthecollision.

2. Experimentalapparatusanddatasample

TheALICEdetectordesignandperformance areextensively de-scribedin[26] and[27].Theanalysispresentedhereis basedon the detection ofmuons in the forward muon spectrometer [28], whichcoversthepseudo-rapidityrange

−

4

<

η

<

−

2

.

5.1 In addi-tion, the Silicon PixelDetector (SPD) [29] is used to reconstruct the primary vertex. The V0 detectors [30] provide a minimum-bias(MB) triggerandareused todetermine thecentralityofthe collision,while the T0 Cherenkovcounters [31] are used forthe luminositydeterminationinppcollisions. Finally,theZeroDegree Calorimeters(ZDC)areusedtorejectelectromagneticPb–Pb inter-actions [32]. Abrief descriptionof thesedetectors isgiven here-after.

Themuonspectrometercontainsafrontabsorber,madeof car-bon, concrete and steel, placed between 0.9 and 5 m from the Interaction Point (IP), which filters out hadrons, thus decreasing the occupancy in the downstream tracking system. The latter is composed of five stations, each one consisting of two planes of CathodePadChambers (CPC).The thirdtrackingstation isplaced inside the gap of a dipole magnet with a 3 T m field integral. Twotrigger stations, each one equipped with two planes of Re-sistive Plate Chambers (RPC), are located behind a 7.2 interac-tionlength iron wall, which absorbs secondary hadronsescaping the front absorber and low-momentum muons. The muon trig-gersystemdeliverssingle-muonanddimuontriggerswitha pro-grammable transverse-momentum threshold. Finally, throughout itsentirelength,aconicalabsorberaroundthebeampipe(

θ <

2◦) madeof tungsten, lead andsteel shields the muon spectrometer againstsecondaryparticlesproducedbytheinteractionoflarge-

η

primaryparticlesinthebeampipe.

Theprimary vertexis reconstructedusinghitpairs inthetwo cylindricallayers ofthe SPD[26,29], whichhave average radiiof 3.9and7.6cm,andcoverthepseudo-rapidityintervals

|

η

|

<

2 and

|

η

|

<

1

.

4,respectively.

The two V0detectors [30],with 32 scintillator tiles each, are placedoneach sideoftheIP,coveringthepseudo-rapidityranges

1 _{IntheALICEreferenceframe,themuonspectrometercoversanegativeηrange} andconsequentlyanegativeyrange.Wehavechosentopresentourresultswitha positiveynotation.

2

.

8

<

η

<

5

.

1 and

−

3

.

7

<

η

<

−

1

.

7.Thecoincidenceofthesignals from the two hodoscopes defines the MB trigger. Beam-induced backgroundisreducedbyapplyingtimingcutsonthesignalsfrom the V0s and ZDCs. The latter are positioned along the beam di-rection at

±

112.5 m from the IP. Finally, the T0 detectors [31], madeof two arraysof quartz Cherenkovcounters, are placed on bothsidesoftheIP,coveringthepseudo-rapidityintervals

−

3

.

3

<

η

<

−

3 and4

.

6

<

η

<

4

.

9.

In Pb–Pb collisions, the centrality determination is based on a Glauber fit ofthe total V0signal amplitude distribution as de-scribed in [33,34].A selection corresponding to the mostcentral 90% of the hadronic cross section was applied; for these events theMBtriggerisfullyefficient.

ForbothPb–Pb andpp datataking, thetriggercondition used inthe analysisis a

µµ

-MBtrigger formed by thecoincidence of the MB trigger and an unlike-sign (US) dimuon trigger. The lat-terhasatriggerprobability foreach ofthetwomuon candidates that increaseswiththe muon pT,is 50%at1.0 GeV/c (0.5GeV/c)

in Pb–Pb (pp) collisions, andsaturates at pT

≈

2

.

5 GeV

/

c, where

it reaches a value of about 98%. Like-sign dimuon triggers were also collected, mainly for background normalisation purposes in thePb–Pbanalysis.

The data samples used in this analysis correspond to an in-tegrated luminosity LPb–Pb

int

≈

225 µb−1 for Pb–Pb and L pp int

≈

106 nb−1 forppcollisions.

3. Dataanalysis

Theanalysisprocedurewasverysimilarforthetwodata sam-ples describedinthisLetter.Inthefollowingparagraphs, thePb– Pbanalysisisfirstpresented,followedbythedescriptionofthepp one.

The J/

ψ

candidates were formed by combining pairs of US tracks reconstructed in the geometrical acceptance of the muon spectrometer using the trackingalgorithm described in [28].The same single-muon and dimuon selection criteria as in previous analyses[21]wereapplied,andtracksinthetrackingsystemwere required to match a track segment in the muon trigger system (triggertracklet).

The J/

ψ

rawyields were determined fromthe invariant mass distributionofUSdimuonsusingtwomethods.Inthefirstone,the USdimuoninvariant massdistributions werefittedwiththesum of a signal and a background function. In the second approach, the background, estimated using an event-mixing technique and normalisedusingthelike-signdimuondistributions[21],was sub-tracted and the resulting spectra were fitted with the sum of a signalfunctionanda(small)residualbackgroundcomponent.

Variousshapeswere consideredforthesignalandbackground contributions. For the J/

ψ

signal either an extended Crystall Ball (CB2)functionorapseudo-Gaussianwithamass-dependentwidth wereused[35].Thenon-Gaussiantailsofthesignalfunctionswere fixed either (i) to the values obtainedin MonteCarlo (MC) sim-ulations, where simulated J

/ψ

→

µ

+

µ

− are embedded into real eventsto accountfor theeffectofthe detectoroccupancy, or(ii) to the values obtainedin a high-statisticspp collision sample at

√

_s

=

13 TeV, collected undersimilardetectorconditions.The tail parameters exhibit a dependence on the pTand rapidity of the

J/

ψ

andamild dependenceonthecentralityofthecollision.The smallcontributionofthe

ψ (

2S

)

signal was takenintoaccount in the fits, its mass and widthbeing tied to those ofthe J/

ψ

[36]. Forthebackground,whentheUSdimuonmassspectrumwas fit-ted, a variable-width-Gaussian with a mass-dependent width or the ratio of a 2nd to a 3rd order polynomial were used. When considering the US dimuon distributions after subtraction of the background obtained with the event-mixing procedure, a small

Fig. 1. (Colouronline.) InvariantmassdistributionsofUSdimuonswith2.5<y<4 andpT<12 GeV/c.Thetop(bottom)rowshowsthedistributionbefore(after)background subtractionwiththeevent-mixingtechnique.Theleftpanelscorrespondtothemostcentralevents(0–10%)whiletherightpanelstoaperipheral(70–80%)centralityrange. Thefitcurvesshowninbluerepresentthesumofthesignalandbackgroundshapes,whiletheredlinescorrespondtotheJ/ψsignalandthegreyonestothebackground.

dimuoncontinuum component isstill presentandwas fitted us-ingthesumoftwoexponentials.Severalfittingsub-ranges,within the interval 2

<

mµµ

<

5 GeV

/

c2, were used for both signal ex-tractionprocedures.

Fig. 1showsexamplesoffitstotheUSdimuoninvariantmass distributions withand without backgroundsubtraction usingthe event-mixing technique, fordifferent selectionsin centrality. The raw J/

ψ

yield in each centrality or pT interval was determined

as the average of the results obtained with the two fitting ap-proaches,the variousparameterisations of signal andbackground andthedifferentfittingranges,whilethecorrespondingsystematic uncertainties weredefinedasthe RMSoftheseresults.Afurther contributiontothesystematicuncertaintywasestimatedbyusing adifferent setofresonancetails obtainedusingintheMC simu-lationadifferentparticletransportmodel(GEANT4[37]insteadof GEANT3[38]).ThetotalnumberofJ

/ψ

,integratedovercentrality,

pTandy,isNJ/ψ

=

2

.

77

±

0

.

02

(

stat

)

±

0

.

05

(

syst

)

·

105.The

system-aticuncertaintyrangesfrom1.6%to2.8%asafunctionofcentrality andfrom1.2%to3.1%asafunctionofpT.

Thenuclear modificationfactor,asa functionofthecentrality class i of thecollision andforthe J/

ψ

transverse-momentum in-terval

%

pT,iscalculatedas Ri_AA

(%

pT

)

=

N i J/ψ

(%

pT

)

BRJ/ψ→µ+µ−NMBi A

ε

i

(%

pT

)

⟨

TAAi

⟩

σ

Jpp/ψ

(%

pT

)

,

(1) where Ni

J/ψ

(%

pT

)

isthe numberofextractedJ/

ψ

in agiven

cen-tralityandpTrange,BRJ/ψ→µ+µ−

=

5

.

96

±

0

.

03% isthebranching ratio of the dimuon decay channel [39], Ni

MB is the number of

equivalent minimum-biasevents, A

ε

i

(%

pT

)

is theproduct ofthe detector acceptance times the reconstruction efficiency,

⟨

Ti

AA

⟩

is

theaverageofthenuclearoverlapfunction,and

σ

pp

J/ψ

(%

pT

)

isthe

inclusiveJ/

ψ

crosssectionforppcollisionsatthesameenergyand inthesamekinematicrangeasthePb–Pbdata.

The A

ε

valuesweredeterminedfromMCsimulations,withthe generated pTand y distributions for the J/

ψ

adjusted on data, and separately tuned for each centrality class using an iterative approach.Unpolarised J/

ψ

productionwas assumed[21].Forthe

tracking chambers, the time-dependent status of each electronic channel during the datatakingperiod was takenintoaccount as well asthemisalignment ofthedetectionelements. The efficien-ciesofthemuontriggerchambersweredeterminedfromdataand were then applied inthe simulations. Finally, thedependence of the efficiency on thedetector occupancy was taken into account by embedding MC-generated J/

ψ

into real minimum-bias Pb–Pb events.

For J/

ψ

produced within 2

.

5

<

y

<

4 and pT

<

12 GeV

/

c, in 0–90%mostcentralcollisions,the A

ε

valueis0

.

136

±

0

.

007

(

syst

)

. A relative decrease of the efficiencyby 14% was observed when going from peripheral to central collisions. As a function of pT, A

ε

has a minimum value of about0

.

12 at pT

≈

1

.

5 GeV

/

c, and

then steadilyincreases up to about 0.4at the upper end of the considered range.The followingsourcesofsystematicuncertainty on A

ε

were considered.A firstcontribution of2% dueto the in-put MC pTand y distributions was estimated by (i) varying the

input shapesthat were tuned ondatawithin their statistical un-certaintiesand(ii)takingintoaccounttheeffectofpossible pT

−

y

correlationsbycomparing,asafunctionofcentrality,the A

ε

val-ueswiththecorrespondingresultofa 2-Dacceptancecalculation in classes of pT and y. A second contribution comes from the

trackingefficiencyanditwas estimatedby comparingthe single-muon tracking efficiency values obtained, in MC and data, with aprocedurethatexploitstheredundancyofthetracking-chamber information[21].A3%systematicuncertaintyonthedimuon track-ingefficiencyisobtainedandisapproximatelyconstantasa func-tion of centrality and kinematics. The systematic uncertainty on thedimuontriggerefficiencyrepresentsthethirdcontributionand it has two origins: the intrinsic efficiencies of the muon trigger chambersandtheresponse ofthetriggeralgorithm.Thefirstone wasdeterminedfromtheuncertaintiesonthetriggerchamber ef-ficiencies measured from data andapplied to simulations and it amountsto1.5%.Thesecondonewasestimatedbycomparingthe

pT dependence,at thesingle-muon level,ofthe trigger response

functionbetweendataandMCanditvariesbetween0.2%and4.6% asafunction of pT.Combiningthe twosources,a systematic

un-certainty rangingfrom1.5% to4.8%asa functionoftheJ/

ψ

pT is

Table 1

Summaryofsystematicuncertainties,inpercentage,onRAAandd2σ_Jpp_/ψ/dydpT.ValuesmarkedwithanasteriskcorrespondtocorrelateduncertaintiesasafunctionofpT (secondandfifthcolumn)orcentrality(thirdcolumn).ThereisnocorrelationbetweentheuncertaintiesrelatedtotheanalysisofthePb–Pbandoftheppsample.The contentsofthe“ppreference”rowcorrespondtothequadraticsumofthecontributionsindicatedford2_σpp

J/ψ/dydpT,excludingonlytheBRuncertaintywhichcancelsout

whenformingtheRAA.

Source RAA d2σ_Jpp_/ψ/dydpT 0–90% pT<12 GeV/c vspT (0–20%) vscentrality (pT<8 GeV/c) pT<12 GeV/c vs pT Signal extr. 1.8 1.2–3.1 1.6–2.8 3 1.5–9.3 MC input 2 2 2∗ _{2 0.7–1.5} Tracking eff. 3 3 3∗ _{1 1} Trigger eff. 3.6 1.5–4.8 3.6∗ _{1.8 1.5–1.8} Matching eff. 1 1 1∗ _{1 1} F(Lpp_int) 0.5 0.5∗ ₀.5∗ _{(2.1) (2}.1∗₎ BR – – – 0.5 0.5∗ ⟨TAA⟩ 3.2 3.2∗ _3.1–7.6 Centrality 0 0.1∗ _0–6.6 pp reference 5.0 3–10!2.1∗_(Lpp int) 4.9∗

ofthe

χ

2 _{cut used indefining thematching betweenthe}

recon-structedtracksandthetriggertracklets.

ThenormalisationfactortothenumberofequivalentMBevents wasobtainedasNi

MB

=

Fi

·

Nµµ-MB,where Nµµ-MBisthenumber

of

µµ

-MB triggered events, and Fi _{is the inverse of the}

proba-bilityofhaving adimuon triggerin a MBevent inthecentrality rangei.The Fi _{values were calculated withtwo different}

meth-ods,by applying thedimuon triggercondition inthe analysison minimum-biasevents,orfromtherelativecountingrateofthetwo triggers[40].Theobtainedvalue, inthe0–90% centralityclass,is

F

₌

11

.

84

±

0

.

06,where the uncertainty is dominated by a sys-tematiccontribution correspondingto thedifferencebetweenthe resultsobtained with the two approaches. As a function of cen-trality, Fi

₌

_F

_{· %}

i_,where

_%

i _{isthefractionof theinelasticcross}

sectionofagivencentralityclasswithrespecttothewhole0–90% centralityrange(e.g.0.1/0.9for0–10%centralityandsoon).

The values for

⟨

Ti

AA

⟩

and for the average number of

partici-pantnucleons

⟨

Ni

part

⟩

wereobtainedviaaGlaubercalculation[33, 34,41]. The systematicuncertainty is3.2% forthe 0–90% central-ity range and was obtained by varying within uncertainties the densityparametersofthePbnucleusandthenucleon–nucleon in-elasticcrosssection[34,41].

Finally,the effects of the uncertainty on the value of the V0 signalamplitudecorrespondingto90%ofthehadronicPb–Pbcross sectionwereestimatedbyvaryingsuchavalueby

±

0

.

5%[33]and redefiningcorrespondingly thecentralityintervals.The systematic effecton RAA ranges from0.1% to6.6%fromcentraltoperipheral

collisions.

TheJ/

ψ

cross-sectionvaluesinpp collisionsat

√

s

=

5

.

02 TeV, bothintegratedandpTdifferential,wereobtainedwithananalysis

proceduresimilartotheonedescribedinthepreviousparagraphs for Pb–Pb. In particular, the same criteria for single-muon and dimuonselectionwereadopted.

Thesignal extraction was then performedby fittingthe spec-trawiththesumofasignalandabackgroundcontribution,using shapessimilarto thoseadoptedforthePb–Pb analysis.The back-groundsubtractionvia theevent-mixing technique wasnot used, asthe signal-over-background ratiois largerby afactor

∼

40,in thepT-integratedspectra,withrespecttocentralPb–Pbcollisions,

making the influence of the backgroundestimate much less im-portantinthedeterminationoftheuncertaintyonNpp_J/ψ.Thevalue

Npp_J/ψ

=

8649

±

123

(

stat

)

±

297

(

syst

)

isobtained,withthe system-aticuncertaintydeterminedasforthePb–Pbanalysis.

ThedeterminationofA

ε

ppwascarriedoutviaMCsimulations.

Since no appreciable dependence of the tracking efficiency as a function of the hadronic multiplicity can be seen in pp, a pure MC (i.e.,withoutembedding)was used. The input pT and y

dis-tributions wereobtainedfromthemeasuredonesviaan iterative procedure,andunpolarisedJ/

ψ

productionwasassumed[42].The obtainedvalueis A

ε

pp

=

0

.

243

±

0

.

007

(

syst

)

,withthesystematic uncertainties onthetracking,triggerandmatchingefficiency cal-culatedasinthePb–Pbanalysis.Becauseofthelimitedpp statis-tics,thesystematicuncertaintyontheMCinputswasnotobtained througha2-Dacceptancecalculation,asdoneinthePb–Pb analy-sis,butitwasdeterminedcomparingtheA

ε

valuesobtainedusing J/

ψ

pT (y)distributionsevaluatedinvariousy (pT)intervalsinpp

collisionsat

√

s

₌

7 TeV[43].

The integrated luminosity was calculated as Lpp_int

= (

Npp_µµ-MB

·

Fpp

_)/

_σ

pp

ref,where

σ

pp

ref isareference-triggercrosssectionmeasured

ina vander Meerscan,following theproceduredetailedin[44], and Fpp _{is the ratio of the reference-trigger probability to the}

µµ

-MB trigger probability.The corresponding numerical value is

Lpp_int

₌

106

.

3

±

2

.

2

(

syst

)

nb−1, where the quoted uncertainty re-flectsthevanderMeerscanuncertainty.

Finally,theinclusiveJ/

ψ

crosssectioninppcollisions at

√

s

=

5

.

02 TeV wasobtainedas

d2

_σ

pp J/ψ dydpT

=

N_Jpp_/ψ

(%

pT

)

BRJ/ψ→µ+µ−LppintA

ε

pp

(%

pT

)%

pT

%

y

.

(2)

Table 1 summarises the systematicuncertainties on the mea-surementofthenuclearmodificationfactorsandd2

_σ

pp

J/ψ

/

dydpT.

TheRAAvaluespresentedinthefollowingrefertoinclusiveJ/

ψ

production, i.e. include both prompt and non-prompt J/

ψ

. Since beauty-hadrondecaysoccur outsidetheQGP, thenon-promptJ/

ψ

RAA is related to the nuclear modification of the beauty-hadron pT distributions. The difference betweenthe RAA of prompt and

inclusive J/

ψ

can be estimated as in [21], using the fraction FB

ofnon-prompttoinclusiveJ/

ψ

inppcollisionsandassumingtwo extreme casesfor the Rnon-prompt_AA ofnon-prompt J/

ψ

, namely no medium effects on b-quarks (Rnon-prompt_AA

=

1) or their complete suppression(Rnon-prompt_AA

=

0). FB wasobtainedbyaninterpolation

oftheLHCbmeasurementsinppcollisionsat

√

s

₌

2

.

76 and7 TeV

[43,45,46].ThequantitativeeffectontheinclusiveJ/

ψ

RAAis

pro-videdinthefollowingalongwiththeresults.

4. Results

The pT-differential inclusive J/

ψ

cross section in pp collisions at

√

s

₌

5

.

02 TeV, in the region 2

.

5

<

y

<

4, isshown in Fig. 2. The cross section value, integratedover the interval 2

.

5

<

y

<

4,

pT

<

12 GeV

/

c is

σ

_Jpp_/ψ

=

5

.

61

±

0

.

08

(

stat

)

±

0

.

28

(

syst

)

µb. These results are used as a reference in the determination of the nu-clearmodificationfactorforPb–Pbcollisions.Boththedifferential

Fig. 2. (Colouronline.) Thedifferentialcrosssectiond2_σpp

J/ψ/dydpTforinclusiveJ/ψ

productioninppcollisionsat√s₌5.02 TeV.Theerrorbarsrepresentthestatistical uncertainties,theboxesaroundthepointstheuncorrelatedsystematic uncertain-ties.Theuncertaintyontheluminositymeasurementrepresentsacorrelatedglobal uncertainty.

Fig. 3. (Colouronline.) Thenuclearmodificationfactor for inclusiveJ/ψ produc-tion,asafunctionofcentrality,at √sNN=5.02 TeV,comparedtopublished re-sultsat√sNN=2.76 TeV[20].Theerrorbarsrepresentstatisticaluncertainties,the boxesaroundthepointsuncorrelatedsystematicuncertainties,whilethe centrality-correlatedglobaluncertaintiesareshownasafilledboxaroundRAA=1.Thewidths ofthecentralityclassesusedintheJ/ψanalysisat√sNN=5.02 TeV are2%from0

to12%,then3%upto30%and5%formoreperipheralcollisions.

andintegrated pp cross section valuesare consistent withthose obtained via an interpolation [45,47] of the measured values at

√

_s

=

2

.

76 and 7 TeV [48,49], which were used for the deter-mination of the nuclear modification factorin p–Pb collisions at

√

_s

NN

=

5

.

02 TeV[40,47,50].

ThenuclearmodificationfactorforinclusiveJ/

ψ

productionin Pb–Pb collisions at

√

sNN

=

5

.

02 TeV, integratedover the central-ityrange0–90%,andforthe interval 2

.

5

<

y

<

4, pT

<

12 GeV

/

c isRAA(pT

<

12 GeV

/

c)

=

0

.

65

±

0

.

01

(

stat

)

±

0

.

05

(

syst

)

,showinga significantsuppression oftheJ/

ψ

withrespecttopp collisions at thesame energy.When restrictingthe pT rangeto 8GeV/c,

cor-respondingtotheintervalcoveredinthe

√

sNN

=

2

.

76 TeV results, one obtains RAA(pT

<

8 GeV

/

c)

=

0

.

66

±

0

.

01

(

stat

)

±

0

.

05

(

syst

)

. The ratio between the latter value and the corresponding one at

√

sNN

=

2

.

76 TeV, RAA(pT

<

8 GeV

/

c)

=

0

.

58

±

0

.

01

(

stat

)

±

0

.

09

(

syst

)

[20],is1

.

13

±

0

.

02

(

stat

)

±

0

.

18

(

syst

)

.Whencalculating theratio,the quoted uncertainties onthe two valuesare consid-eredasuncorrelated,exceptforthe

⟨

TAA

⟩

contribution.

Fig. 3 shows the centrality dependence of RAA at

√

sNN

=

5

.

02 TeV. The results are compared to the values obtained at

√

_s

NN

=

2

.

76 TeV [20], and correspond to the same

transverse-Fig. 4. (Colouronline.) Comparisonofthecentralitydependence(with10%width centralityclasses)oftheinclusiveJ/ψ RAAfor0.3<pT<8 GeV/cwith theoreti-calmodels[17–19,52–55].ThemodelcalculationsdonotincludethepTcut(except forTM1),whichwasanywayfoundtohaveanegligibleimpact,sincetheyonly in-cludehadronicJ/ψproduction.Theerrorbarsrepresentthestatisticaluncertainties,

theboxesaroundthedatapointstheuncorrelatedsystematicuncertainties,while thecentrality-correlatedglobaluncertaintyisshownasafilledboxaroundRAA=1. Thebracketsshowninthethreemostperipheralcentralityintervalsrepresentthe rangeofvariationofthehadronicJ/ψ RAAunderextremehypothesisonthe photo-productioncontaminationontheinclusiveRAA.

momentumrange,pT

<

8 GeV

/

c.Thecentralitydependence, char-acterised by an increasing suppression with centrality up to

Npart

∼

100,followedby an approximatelyconstant RAA value, is

similar atthe twoenergies.Asystematicdifferenceby about15% is visiblewhencomparingthe twosets ofresults,evenifthe ef-fect iswithin thetotaluncertaintyofthemeasurements.The RAA

of promptJ/

ψ

wouldbe about10% higher if Rnon-prompt_AA

=

0 and about 5% (1%) smaller if Rnon-prompt_AA

₌

1 for central (peripheral) collisions.

An excessofvery-low pT J/

ψ

,compared totheyieldexpected assumingasmoothevolutionoftheJ/

ψ

hadro-productionand nu-clear modification factorwas observed in peripheral Pb–Pb colli-sions at

√

sNN

=

2

.

76 TeV [51]. This excess might originate from the photo-production of J/

ψ

andcould influence the RAA in

pe-ripheral collisions. To quantify the expected difference between the hadronicJ/

ψ

RAA andthe measured values the method

de-scribed in[21] was adopted.The hadronicJ/

ψ

RAA,for 0

<

pT

<

8 GeV

/

c,is estimatedtobe about 34%,17% and9% smaller than the measured values in the 80–90%, 70–80% and 60–70% cen-trality classes, respectively. The variation decreases to about 9%, 4% and2%, respectively, when considering the RAA forJ/

ψ

with

0

.

3

<

pT

<

8 GeV

/

c, due to the remaining small contribution of photo-produced J/

ψ

.Fig. 4 showsRAA asafunction ofcentrality,

for0

.

3

<

pT

<

8 GeV

/

c.

ComparingtheresultsofFig. 3andFig. 4,alesspronounced in-creaseof RAA forperipheraleventscanindeedbeseenwhensuch

aselectionisintroduced.Thesameextremehypothesesasin[21]

were made to define upper and lower limits, represented with bracketsonFig. 4.Thus,theselectionofJ/

ψ

with pT

>

0

.

3 GeV

/

c makestheresultsmoresuitable foracomparisonwiththeoretical modelsthatonlyincludehadronicJ/

ψ

production.

We start by comparing the results to a calculation based on a statistical model approach [52], where J/

ψ

are created, like all other hadrons, only atchemical freeze-out accordingto their statistical weights. In this model, the nucleon–nucleon cc pro-duction cross section is extrapolated from LHCb pp measure-mentsat

√

s

₌

7 TeV[56]usingFONLL calculations[57],obtaining d

σ

cc

/

dy

=

0

.

45 mb inthe y rangecovered bythedata.Then,the

nuclearmodificationofthepartondistributionfunctions (shadow-ing) is accounted for via the EPS09 NLO parameterisation [58].

Fig. 5. (Colouronline.) TheratiooftheinclusiveJ/ψRAAfor0.3<pT<8 GeV/c be-tween√sNN=5.02 and2.76TeV,comparedtotheoreticalmodels[17–19,52–55],

shownasafunctionofcentrality.Themodelcalculations donotinclude the pT cut(exceptforTM1),whichwasanywayfoundtohaveanegligibleimpact,since theyonlyinclude hadronicJ/ψ production.Theerrorbarsrepresentthe statisti-caluncertaintiesandtheboxesaroundthedatapointstheuncorrelatedsystematic uncertainties.Thecentrality-correlatedglobaluncertaintyisshownasafilledbox aroundr=1 andisobtainedasthequadraticsumofthecorrespondingglobal un-certaintiesat√sNN=2.76 and5.02 TeV.

The corresponding 17% uncertainty on the extrapolated d

σ

cc

/

dy plusshadowingisusedwhencalculatingtheuncertaintybandsfor thismodel.Theresultsarealsocomparedtothecalculationsofa transport model(TM1) [18,54,55]based on a thermalrate equa-tion, which includes continuous dissociation and regeneration of theJ/

ψ

both intheQGPandinthehadronicphase.Theinclusive cc cross section is taken as d

σ

cc

/

dy

=

0

.

57 mb, consistent with

FONLL calculations,while the J/

ψ

productioncross section value inN–Ncollisions isd

σ

J/ψ

/

dy

=

3

.

14 µb.Theresultsofthismodel

areshownasa bandincludinga variationoftheshadowing con-tribution between 10% and 25% and a 5% uncertainty on the cc crosssection.Theresultsarethencomparedtothecalculationsof asecondtransportmodel(TM2)[19],whichimplementsa hydro-dynamicdescriptionofthemediumevolution.Theinputnucleon– nucleon cross sections for cc and J/

ψ

are taken as d

σ

cc

/

dy

=

0

.

82 mb, corresponding to theupper limit ofFONLL calculations, andd

σ

J/ψ

/

dy

=

3

.

5 µb.Alsoforthismodeltheband corresponds

tothechoice ofeithernoshadowing, orashadowingeffect esti-matedwiththeEPS09NLO parameterisation.Finally,thedataare comparedtoa‘co-mover’model[17,53],wheretheJ/

ψ

are disso-ciated via interactions withthe partons/hadrons producedin the same rapidity range, using an effective interaction cross section

σ

co-J/ψ

₌

₀

_.

_{65 mb,basedoncalculationsthatdescribedlower}

en-ergyexperimentalresults.Regenerationeffectsareincluded,based ond

σ

cc

/

dy valuesrangingfrom0.45to0.7mb,whichcorrespond totheuncertainty bandshownforthe model.Shadowingeffects, calculatedwithintheGlauber–Gribovtheory[59],areincludedand are consistent with EKS98/nDSg predictions [60,61]. Finally, the contributionofnon-promptproductionistakenintoaccountinthe transportmodelsTM1andTM2,whileitisnot consideredinthe othercalculations.

The data are described by the various calculations, the latter havingrather largeuncertainties, due tothe choice ofthe corre-sponding input parameters, and in particular of d

σ

cc

/

dy. It can

be notedthat for mostcalculationsa better description is found whenconsideringtheirupperlimit.Fortransportmodelsthis cor-respondsto a minimum contributionor even absenceof nuclear shadowing, which can be clearly considered as an extreme as-sumptionfor primary J/

ψ

, considering the J/

ψ

measurements in p–Pbcollisions[47,50].

Fig. 6. (Colouronline.) The pT dependenceofthe inclusiveJ/ψ RAA at √sNN= 5.02 TeV,comparedtothecorrespondingresultat√sNN=2.76 TeV[20]andtothe calculationofatransportmodel[18,54,55](TM1),inthecentralityinterval0–20%. The pTdependence ofrisalso shownforbothdataandtheory.Theerrorbars representstatisticaluncertainties,theboxesaroundthepointsuncorrelated system-aticuncertainties,whilepT-correlatedglobaluncertaintiesareshownasafilledbox aroundRAA=1.

Acorrelationbetweentheparametersofthemodelsispresent whencomparingtheir calculationsfor

√

sNN

=

2

.

76 and5.02TeV. Therefore, the theoretical uncertainties can be reducedby form-ing the ratio r

₌

RAA

(

5

.

02 TeV

)/

RAA

(

2

.

76 TeV

)

. Concerning data, the uncertainties on

⟨

TAA

⟩

cancel. In Fig. 5 the centrality

de-pendence of r, calculated for 0

.

3

<

pT

<

8 GeV

/

c, is shown and compared tomodels. Forprompt J/

ψ

the ratior wouldbe about 2% (1–2%) higher if beauty hadrons were fully (not) suppressed by the medium. The transport model of Ref. [18,54,55] (TM1) showsadecreaseofrwithincreasing centrality,duetothelarger suppression effects at high energy, followed by an increase, re-lated to the effect of regeneration, which acts in the opposite directionand becomes dominantfor central collisions. The other transport model (TM2)[19] also exhibits an increase forcentral collisions, while for peripheral collisions the behaviour is differ-ent. In the co-mover model [17,53], no structure is visible as a functionofcentrality,andthecalculationfavours r-valuesslightly belowunity,implying thatinthismodeltheincrease ofthe sup-pression effects withenergy maybe dominant over the regener-ation effects forall centralities. Finally,the statisticalmodel [52]

shows a continuous increase of r with centrality, dominated by the increase inthe cc crosssection with energy.The uncertainty bands shown in Fig. 5 correspond to variations of about 5% in thecc crosssectionat

√

sNN

=

5

.

02 TeV,plusa10%relative varia-tion of the shadowingcontribution between thetwo energies in the case of TM1. The data are, within uncertainties, compatible withthetheoretical models,andshow noclearcentrality depen-dence. The ratiofor central collisions and 0

.

3

<

pT

<

8 GeV

/

c is

r0–10%

₌

₁

_.

₁₇

_±

₀

_.

₀₄

₍

_stat

₎

_±

₀

_.

₂₀

₍

_syst

₎

_.

Finally,the studyofthe pT dependenceof RAA has proven to

be a sensitive test of the presence ofa regeneration component which,incalculations,leadstoanincreaseatlow pT.Fig. 6shows,

forthe centralityinterval 0–20%, RAA asa function oftransverse

momentum, compared to the corresponding results obtained at

√

_s

NN

=

2

.

76 TeV, andto a theoretical modelcalculation. The re-gion pT

<

0

.

3 GeV

/

c was not excluded, because the contribution ofJ/

ψ

photo-productionisnegligiblewithrespecttothehadronic oneforcentralevents[51].Inthesamefigurethe pT dependence

ofrisalsoshown.AhintforanincreaseofRAA with

√

sNN is

withunityelsewhere.Thisfeatureisqualitativelydescribedbythe theoreticalmodel(TM1)alsoshowninthefigure.ThepromptJ/

ψ

RAAisexpectedtobe7%larger(2%smaller)forpT

<

1 GeV

/

c and 30%larger(55%smaller)for10

<

pT

<

12 GeV

/

c whenthebeauty contribution is fully (not) suppressed. Assuming that Rnon-prompt_AA

does not vary significantly between the two collision energies, the ratio r appears to be less sensitive to the non-prompt J/

ψ

contribution.The effectis negligible forthe caseoffull suppres-sion of beauty hadrons, while it varies from no increase at low transverse momentum up to a maximum increase of about 15% for5

<

pT

<

6 GeV

/

c ifnosuppressionisassumed. Thetransport modelofRef.[18,54,55](TM1)fairlydescribestheoverallshapeof theRAA pTdependence.

5. Conclusion

We reportedthe ALICEmeasurement ofinclusiveJ/

ψ

produc-tion in pp and Pb–Pb collisions at

√

sNN

=

5

.

02 TeV at the LHC.

A systematic difference by about15% isvisible when comparing the RAA measured at

√

sNN

=

5

.

02 TeV to the one obtained at

√

_s

NN

=

2

.

76 TeV, even if such an effect is within the total un-certainty of themeasurements. When removing very-low pT J/

ψ

(pT

<

0

.

3 GeV/c), the RAA showsa lesspronounced increase for

peripheralevents,whichcanbeascribedtotheremovalofalarge fractionof electromagnetic J/

ψ

production [51]. Theseresults, as well as those on the ratio of the nuclear modification factors between

√

sNN

=

5

.

02 and 2.76 TeV, are described by theoreti-cal calculations, and closerto their upper limits. The pT

depen-dence of RAA exhibits an increase at low pT, a feature that in

the model which is compared to the data is related to an im-portantcontributionofregenerated J/

ψ

.A hintforan increase of

RAA between

√

sNN

=

2

.

76 and 5.02 TeV is visible in the region 2

<

pT

<

6 GeV

/

c,whiletheresultsareconsistentelsewhere.The resultspresentedinthispaperconfirmthatalsoatthehighest en-ergiesreachedtodayattheLHC,dataonJ/

ψ

productionsupporta picturewhereacombinationofsuppressionandregenerationtakes placeintheQGP,thetwomechanismsbeingdominantathighand low pT,respectively.

Acknowledgements

The ALICE Collaboration would like to thank all its engineers andtechnicians fortheir invaluablecontributionstothe construc-tion of the experiment and the CERN accelerator teams for the outstanding performance of the LHC complex. The ALICE Collab-oration gratefully acknowledges the resources and support pro-vided by all Grid centres and the Worldwide LHC Computing Grid(WLCG)Collaboration.The ALICECollaborationacknowledges the following funding agencies fortheir support in building and running the ALICE detector: A. I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS), Armenia; Austrian Academy of Sciences and Nationalstiftung für Forschung, Technologie und Entwicklung, Austria; Conselho Na-cional de Desenvolvimento Científico e Tecnológico (CNPq), Uni-versidadeFederal doRioGrande doSul(UFRGS), Financiadorade Estudos e Projetos (Finep) and Fundação de Amparo à Pesquisa doEstado de São Paulo (FAPESP),Brazil; Ministryof Science and Technology of the People’s Republic of China (MOST), National Natural Science Foundation of China (NSFC) and Ministry of Ed-ucation of China (MOE), China; Ministry of Science, Education and Sport and Croatian Science Foundation, Croatia; Ministry of Education, Youth and Sports of the Czech Republic, Czech Re-public; The Danish Council for Independent Research – Natural Sciences, the CarlsbergFoundation andDanish NationalResearch

Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat à l’Énergie Atomique et aux Énergies Al-ternatives (CEA) and Institut National de Physique Nucléaire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique(CNRS),France;Bundesministeriumfür Bil-dung, Wissenschaft, Forschung und Technologie (BMBF) and GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany; Ministry of Education, Research and Religious Affairs, Greece; National Research, Development and Innovation Office, Hungary; Department of Atomic Energy, Government of India (DAE) and Council of Scientific and Industrial Research (CSIR), New Delhi, India; IndonesianInstitute of Science, Indonesia; Centro Fermi – MuseoStorico dellaFisica eCentroStudi e RicercheEnricoFermi andIstitutoNazionalediFisicaNucleare (INFN),Italy;Institutefor Innovative Science and Technology, Nagasaki Institute of Applied Science (IIST), Japan Society for the Promotion of Science (JSPS), KAKENHIandJapaneseMinistryofEducation,Culture, Sports, Sci-enceand Technology (MEXT),Japan; Consejo Nacionalde Ciencia y Tecnología (CONACYT), through Fondo de Cooperación Interna-cional enCiencia yTecnología(FONCICYT)andDirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nationaal instituut voor subatomaire fysica (Nikhef), Netherlands; The Re-search Council of Norway, Norway; Commission on Science and Technology forSustainableDevelopmentintheSouth(COMSATS), Pakistan;PontificiaUniversidadCatólicadelPerú,Peru;Ministryof ScienceandHigherEducationandNationalScienceCentre,Poland; KoreaInstituteofScienceandTechnologyInformationandNational ResearchFoundationofKorea(NRF),RepublicofKorea;Ministryof Education andScientific Research,Institute ofAtomicPhysicsand Romanian National Agency for Science, Technology and Innova-tion,Romania;JointInstituteforNuclearResearch(JINR),Ministry of Education andScience of theRussian Federation andNational Research Centre Kurchatov Institute, Russia; Ministry of Educa-tion,Science,ResearchandSportoftheSlovakRepublic,Slovakia; National ResearchFoundation ofSouth Africa, South Africa; Cen-tro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía,Cuba; Ministerio deCienciaeInnovación andCentro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT),Spain;SwedishResearchCouncil(VR) andKnut&Alice WallenbergFoundation(KAW),Sweden;EuropeanOrganizationfor Nuclear Research, Switzerland; National Science and Technology Development Agency (NSDTA), Suranaree University of Technol-ogy (SUT) andOffice of theHigher EducationCommission under NRU projectofThailand,Thailand;TurkishAtomicEnergy Agency (TAEK),Turkey;NationalAcademyofSciencesofUkraine,Ukraine; ScienceandTechnologyFacilitiesCouncil(STFC),UnitedKingdom; NationalScienceFoundationoftheUnitedStatesofAmerica(NSF) andUnitedStatesDepartmentofEnergy,OfficeofNuclear Physics (DOENP),UnitedStatesofAmerica.

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ALICECollaboration

J. Adam

39

,

D. Adamová

85

,

M.M. Aggarwal

89

,

G. Aglieri Rinella

35

,

M. Agnello

112

,

31

_,

_{N. Agrawal}

48

_,

D.S.D. Albuquerque

123

,

D. Aleksandrov

81

,

B. Alessandro

112

,

D. Alexandre

103

,

R. Alfaro Molina

64

,

A. Alici

12

,

106

_,

_{A. Alkin}

3

_,

_{J. Alme}

37

,

22

_,

_{T. Alt}

42

_,

_{S. Altinpinar}

22

_,

_{I. Altsybeev}

135

_,

_{C. Alves Garcia Prado}

122

_,

M. An

7

,

C. Andrei

79

,

H.A. Andrews

103

,

A. Andronic

99

,

V. Anguelov

95

,

C. Anson

88

,

T. Antiˇci´c

100

,

F. Antinori

109

,

P. Antonioli

106

,

L. Aphecetche

115

,

H. Appelshäuser

61

,

S. Arcelli

27

,

R. Arnaldi

112

,

O.W. Arnold

36

,

96

_,

_{I.C. Arsene}

21

_,

_{M. Arslandok}

61

_,

_{B. Audurier}

115

_,

_{A. Augustinus}

35

_,

_{R. Averbeck}

99

_,

M.D. Azmi

18

,

A. Badalà

108

,

Y.W. Baek

68

,

S. Bagnasco

112

,

R. Bailhache

61

,

R. Bala

92

,

S. Balasubramanian

140

_,

_{A. Baldisseri}

15

_{, R.C. Baral}

58

_,

_{A.M. Barbano}

26

_,

_{R. Barbera}

28

_,

_{F. Barile}

33

_,

G.G. Barnaföldi

139

,

L.S. Barnby

35

,

103

_,

_{V. Barret}

71

_,

_{P. Bartalini}

7

_,

_{K. Barth}

35

_,

_{J. Bartke}

119

,i

_,

_{E. Bartsch}

61

_,

M. Basile

27

_,

_{N. Bastid}

71

_,

_{S. Basu}

136

_,

_{B. Bathen}

62

_{, G. Batigne}

115

_,

_{A. Batista Camejo}

71

_,

_{B. Batyunya}

67

_,

P.C. Batzing

21

,

I.G. Bearden

82

,

H. Beck

61

,

95

_,

_{C. Bedda}

112

_,

_{N.K. Behera}

51

_,

_{I. Belikov}

65

_,

_{F. Bellini}

27

_,

H. Bello Martinez

2

,

R. Bellwied

125

,

R. Belmont

138

,

E. Belmont-Moreno

64

,

L.G.E. Beltran

121

,

V. Belyaev

76

,

G. Bencedi

139

,

S. Beole

26

,

I. Berceanu

79

,

A. Bercuci

79

,

Y. Berdnikov

87

,

D. Berenyi

139

,

R.A. Bertens

54

,

D. Berzano

35

,

L. Betev

35

,

A. Bhasin

92

,

I.R. Bhat

92

,

A.K. Bhati

89

, B. Bhattacharjee

44

,

J. Bhom

119

,

L. Bianchi

125

_,

_{N. Bianchi}

73

_{, C. Bianchin}

138

_,

_{J. Bielˇcík}

39

_,

_{J. Bielˇcíková}

85

_{, A. Bilandzic}

82

,

36

,

96

_,

_{G. Biro}

139

_,

R. Biswas

4

,

S. Biswas

80

,

4

_,

_{S. Bjelogrlic}

54

_,

_{J.T. Blair}

120

_{, D. Blau}

81

_,

_{C. Blume}

61

_,

_{F. Bock}

75

,

95

_,

A. Bogdanov

76

_,

_{H. Bøggild}

82

_,

_{L. Boldizsár}

139

_,

_{M. Bombara}

40

_,

_{M. Bonora}

35

_,

_{J. Book}

61

_,

_{H. Borel}

15

_,

A. Borissov

98

,

M. Borri

127

,

84

_,

_{F. Bossú}

66

_,

_{E. Botta}

26

_,

_{C. Bourjau}

82

_,

_{P. Braun-Munzinger}

99

_,

_{M. Bregant}

122

_,

T. Breitner

60

,

T.A. Broker

61

,

T.A. Browning

97

, M. Broz

39

, E.J. Brucken

46

,

E. Bruna

112

,

G.E. Bruno

33

,

D. Budnikov

101

,

H. Buesching

61

,

S. Bufalino

31

,

26

_,

_{S.A.I. Buitron}

63

_,

_{P. Buncic}

35

_,

_{O. Busch}

131

_,

Z. Buthelezi

66

,

J.B. Butt

16

,

J.T. Buxton

19

,

J. Cabala

117

,

D. Caffarri

35

,

X. Cai

7

, H. Caines

140

,

L. Calero Diaz

73

_{, A. Caliva}

54

_,

_{E. Calvo Villar}

104

_{, P. Camerini}

25

_,

_{F. Carena}

35

_{, W. Carena}

35

_,

F. Carnesecchi

12

,

27

_,

_{J. Castillo Castellanos}

15

_,

_{A.J. Castro}

128

_,

_{E.A.R. Casula}

24

_,

_{C. Ceballos Sanchez}

9

_,

J. Cepila

39

_{, P. Cerello}

112

_{, J. Cerkala}

117

_,

_{B. Chang}

126

_,

_{S. Chapeland}

35

_,

_{M. Chartier}

127

_,

_{J.L. Charvet}

15

_,

S. Chattopadhyay

136

,

S. Chattopadhyay

102

,

A. Chauvin

96

,

36

_,

_{V. Chelnokov}

3

_,

_{M. Cherney}

88

_,

C. Cheshkov

133

,

B. Cheynis

133

, V. Chibante Barroso

35

,

D.D. Chinellato

123

,

S. Cho

51

,

P. Chochula

35

,

K. Choi

98

,

M. Chojnacki

82

,

S. Choudhury

136

,

P. Christakoglou

83

,

C.H. Christensen

82

,

P. Christiansen

34

,

T. Chujo

131

,

S.U. Chung

98

,

C. Cicalo

107

,

L. Cifarelli

12

,

27

_,

_{F. Cindolo}

106

_,

_{J. Cleymans}

91

_,

_{F. Colamaria}

33

_,

D. Colella

56

,

35

_{, A. Collu}

75

_,

_{M. Colocci}

27

_{, G. Conesa Balbastre}

72

_,

_{Z. Conesa del Valle}

52

_{, M.E. Connors}

140

,ii

_,

J.G. Contreras

39

, T.M. Cormier

86

,

Y. Corrales Morales

26

,

112

_,

_{I. Cortés Maldonado}

2

_,

_{P. Cortese}

32

_,

M.R. Cosentino

122

,

124

_,

_{F. Costa}

35

_,

_{J. Crkovská}

52

_,

_{P. Crochet}

71

_,

_{R. Cruz Albino}

11

_{, E. Cuautle}

63

_,

L. Cunqueiro

35

,

62

_,

_{T. Dahms}

36

,

96

_,

_{A. Dainese}

109

_,

_{M.C. Danisch}

95

_,

_{A. Danu}

59

_,

_{D. Das}

102

_,

_{I. Das}

102

_,

S. Das

4

, A. Dash

80

,

S. Dash

48

, S. De

122

,

A. De Caro

30

, G. de Cataldo

105

,

C. de Conti

122

,

J. de Cuveland

42

,

A. De Falco

24

,

D. De Gruttola

30

,

12

_,

_{N. De Marco}

112

_,

_{S. De Pasquale}

30

_,

_{R.D. De Souza}

123

_,

_{A. Deisting}

99

,

95

_,

A. Deloff

78

, C. Deplano

83

,

P. Dhankher

48

,

D. Di Bari

33

,

A. Di Mauro

35

,

P. Di Nezza

73

, B. Di Ruzza

109

,

M.A. Diaz Corchero

10

_,

_{T. Dietel}

91

_,

_{P. Dillenseger}

61

_,

_{R. Divià}

35

_{, Ø. Djuvsland}

22

_,

_{A. Dobrin}

83

,

35

_,

D. Domenicis Gimenez

122

,

B. Dönigus

61

,

O. Dordic

21

,

T. Drozhzhova

61

,

A.K. Dubey

136

,

A. Dubla

99

,

54

_,

L. Ducroux

133

_{, P. Dupieux}

71

_,

_{R.J. Ehlers}

140

_,

_{D. Elia}

105

_,

_{E. Endress}

104

_,

_{H. Engel}

60

_,

_{E. Epple}

140

_,

B. Erazmus

115

,

I. Erdemir

61

,

F. Erhardt

132

,

B. Espagnon

52

,

M. Estienne

115

,

S. Esumi

131

,

G. Eulisse

35

,

J. Eum

98

,

D. Evans

103

, S. Evdokimov

113

,

G. Eyyubova

39

,

L. Fabbietti

36

,

96

_,

_{D. Fabris}

109

_,

_{J. Faivre}

72

_,

A. Fantoni

73

,

M. Fasel

75

,

L. Feldkamp

62

,

A. Feliciello

112

,

G. Feofilov

135

,

J. Ferencei

85

,

A. Fernández Téllez

2

,

E.G. Ferreiro

17

, A. Ferretti

26

,

A. Festanti

29

, V.J.G. Feuillard

71

,

15

_{, J. Figiel}

119

_,

M.A.S. Figueredo

122

_,

_{S. Filchagin}

101

_{, D. Finogeev}

53

_,

_{F.M. Fionda}

24

_,

_{E.M. Fiore}

33

_,

_{M. Floris}

35

_,

S. Foertsch

66

,

P. Foka

99

,

S. Fokin

81

,

E. Fragiacomo

111

,

A. Francescon

35

,

A. Francisco

115

,

U. Frankenfeld

99

,

G.G. Fronze

26

_,

_{U. Fuchs}

35

_,

_{C. Furget}

72

_,

_{A. Furs}

53

_{, M. Fusco Girard}

30

_{, J.J. Gaardhøje}

82

_,

_{M. Gagliardi}

26

_,

A.M. Gago

104

,

K. Gajdosova

82

,

M. Gallio

26

,

C.D. Galvan

121

,

D.R. Gangadharan

75

,

P. Ganoti

90

,

C. Gao

7

,

C. Garabatos

99

,

E. Garcia-Solis

13

,

K. Garg

28

,

C. Gargiulo

35

,

P. Gasik

96

,

36

_,

_{E.F. Gauger}

120

_,

_{M. Germain}

115

_,

M. Gheata

59

,

35

_,

_{P. Ghosh}

136

_{, S.K. Ghosh}

4

_,

_{P. Gianotti}

73

_,

_{P. Giubellino}

35

,

112

_,

_{P. Giubilato}

29

_,

E. Gladysz-Dziadus

119

,

P. Glässel

95

, D.M. Goméz Coral

64

, A. Gomez Ramirez

60

,

A.S. Gonzalez

35

,

V. Gonzalez

10

_,

_{P. González-Zamora}

10

_{, S. Gorbunov}

42

_,

_{L. Görlich}

119

_,

_{S. Gotovac}

118

_,

_{V. Grabski}

64

_,

O.A. Grachov

140

,

L.K. Graczykowski

137

,

K.L. Graham

103

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A. Grelli

54

,

A. Grigoras

35

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C. Grigoras

35

,

V. Grigoriev

76

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1

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67

_,

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3

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111

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99

_,