Search for collectivity with azimuthal J/ψ-hadron correlations in high multiplicity p–Pb collisions at sNN=5.02 and 8.16 TeV

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Articlehistory:

Received27September2017

Receivedinrevisedform14February2018 Accepted14February2018

Availableonline2March2018 Editor:M.Doser

WepresentameasurementofazimuthalcorrelationsbetweeninclusiveJ/ψandchargedhadronsinp–Pb collisionsrecordedwiththeALICEdetectorattheCERNLHC. TheJ/ψ arereconstructedatforward (p-going, 2.03<y<3.53) and backward(Pb-going,−4.46<y<−2.96) rapidity viatheir

μ

+

μ

− decay channel,whilethechargedhadronsarereconstructedatmid-rapidity(|

η

|<1.8).Thecorrelationsare ex-pressedintermsofassociatedcharged-hadronyieldsperJ/ψtrigger.A rapiditygapofatleast1.5unitsis requiredbetweenthetriggerJ/ψandtheassociatedchargedhadrons.Possiblecorrelationsdueto collec-tiveeffectsareassessedbysubtractingtheassociatedper-triggeryieldsinthelow-multiplicitycollisions fromthoseinthehigh-multiplicitycollisions.Afterthesubtraction,weobserveastrongindicationof re-mainingsymmetricstructuresat

ϕ

≈0 and

ϕ

≈

π

,similartothosepreviouslyfoundintwo-particle correlationsatmiddleand forwardrapidity.Thecorrespondingsecond-orderFouriercoefficient(v2)in

thetransverse momentumintervalbetween3and 6 GeV/c isfound tobepositivewithasignificance ofabout5

σ

.TheobtainedresultsaresimilartotheJ/ψ v2coefficientsmeasuredinPb–Pbcollisionsat

√_s

NN=5.02 TeV,suggestingacommonmechanismattheoriginoftheJ/ψ v2.

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

1. Introduction

The measurement of angular correlations between particles produced in hadron andnucleus collisions is a powerful tool to studytheparticleproductionmechanisms.Usuallythetwo-particle correlation function is expressed in terms of differences in the azimuthal angle (

ϕ

) and pseudorapidity (

η

) of the emitted particles.Inminimum-biasproton–proton(pp)collisions,the dom-inant structuresin the correlation function are a near-side peak at

(ϕ,

η)

≈ (

0

,

0

)

and an away-side ridge located at

ϕ

≈

π

andelongated in

η

[1]. The near-side peak originates from jet fragmentation,resonancedecaysandfemtoscopiccorrelations.The away-sideridge resultsfromfragmentationofrecoiljets. In colli-sionsofheavy ions,the two-particlecorrelation functionexhibits additionallong-rangestructureselongatedin

η

[2].These struc-tures are usually interpreted as signatures of collective particle flowproduced during thehydrodynamic evolution ofthefireball. Theyare analyzedin termsof theFouriercoefficients ofthe rel-ativeangledistributions.Assumingfactorization,thesecoefficients arethenrelatedtotheFouriercoefficients(vn)oftheparticle

az-imuthal distribution relative to the common symmetry plane of thecollidingnuclei’soverlaparea.

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

The discovery of a near-side ridge inhigh-multiplicity pp [3] andp–Pb [4] collisions hasincreased theinterest intwo-particle angular correlations in smallcollision systems.These discoveries werefollowedbytheobservationthatthenear-sideridgeinp–Pb collisions is accompanied by an away-side one [5,6]. Long-range structureshavealsobeen reportedintwo-particle correlationsin d–Aucollisions atRHIC [7,8]. Furtherstudiesusing multi-particle correlations have proven that the observed long-range correla-tions are of a collective origin [9–11]. Moreover, the transverse-momentumandparticle-massdependenciesofthevncoefficients

inp–Pbcollisionshavebeenfoundtobesimilartothosemeasured inA–Acollisions,suggestingacommonhydrodynamicoriginofthe observedcorrelations[12,13].Alternativeinterpretations,including Color-GlassCondensate basedmodels[14] andfinal-stateparton– partonscattering[15],havealsobeenproposed.Long-range corre-lationsofforwardandbackwardmuonswithmid-rapidityhadrons have also been found in p–Pb collisions ata center-of-mass en-ergypernucleonpair

√

sNN

=

5

.

02 TeV[16].Theresultsshowthat

thesecorrelations persistacross wide rapidity ranges andextend intothehighmuontransverse-momentuminterval,whichis dom-inatedbydecaysofheavyflavors.

Inppcollisions,theJ/

ψ

resonanceisformedmainlyfrompairs ofc and

¯

c quarksproducedinhardscatteringreactionsduringthe initialstageofthecollision.Thetheoreticalmodelsdescribingthe

https://doi.org/10.1016/j.physletb.2018.02.039

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

J/

ψ

productioncombinecalculationsoftheproductionofcc pairs

¯

within a perturbative Quantum Chromodynamics approach with thesubsequent non-perturbativeformationofthe c

¯

c boundstate [17]. Inp–Pbcollisions, theproductionis affectedby the modifi-cationof partondistribution functionsinside thenucleus [18] as wellaspossibleenergylossandinelasticscatteringinsidenuclear matter [19,20]. In A–A collisions, there are two additional com-peting phenomena that influencethe J/

ψ

production.First isthe suppressed production dueto the dissociation of the cc pairs

¯

in thequark–gluonplasma [21].Second istheJ/

ψ

enhancementvia recombination of charm quarks thermalized in the medium [22,

23].Therecombinationisexpectedtobecomeprevalentincentral collisionsattheLHCenergies.

Recently,theALICECollaborationhaspublishedaprecise mea-surement of the second-order Fourier coefficient, v2, of the

az-imuthal distribution ofthe J/

ψ

production inPb–Pb collisions at

√

sNN

=

5

.

02 TeV [24]. The results show significant v2 incentral

andsemi-centralcollisions.ThemeasuredJ/

ψ

v2atlowand

inter-mediate transverse momentum can be qualitatively described by a transport model in which the J/

ψ

azimuthal anisotropy is in-heritedfrom that ofrecombined charm quarks[25,26]. However, athighertransversemomentumthedatastill indicatessignificant

v2 while the transport model predicts significantly smaller

val-uescomingmostlyfrompath-lengthdependentsuppressioninthe almond-shapedinteractionregionofthecollidingnucleiandfrom non-prompt J/

ψ

produced from b-hadron decays assuming ther-malizedb quarks.Giventheseresults inPb–Pb collisions, itis of interesttostudytheJ/

ψ

-hadronazimuthalcorrelationsalsointhe smallerp–Pb system. The recombinationofcharm quarks,if any, should havemuch smallerimpact,due tothe smallernumber of initially producedcharm quarks withrespectto Pb–Pb collisions. The small system size should not lead to a sizeable path-length dependentsuppression.Nevertheless,thestudyoftheJ/

ψ

-hadron azimuthal correlations could allow to determine whenever J/

ψ

production is affected by the medium possibly created in these collisions[27–29].

In this Letter, we present results for long-range correlations between forward (p-going, 2

.

03

<

y

<

3

.

53) and backward (Pb-going,

−

4

.

46

<

y

<

−

2

.

96)inclusiveJ/

ψ

andmid-rapiditycharged hadrons in p–Pb collisions at

√

sNN

=

5

.

02 and 8.16 TeV.

Inclu-siveJ/

ψ

referstobothpromptJ/

ψ

(directanddecaysfromhigher mass charmonium states) and non-prompt J/

ψ

(feed down from b-hadrondecays).

2. Experimental setup and data samples

Adetaileddescriptionofthe ALICEapparatuscanbe foundin Ref. [30].Below,webrieflydescribethedetectorsystemsessential forthepresentanalysis.

Inthefollowing,

η

and ylabwilldenotethepseudorapidityand

rapidity in the ALICE laboratory system. The muons are recon-structedinthemuonspectrometercoveringtherangeof

−

4

<

η

<

−

2

.

5.Thespectrometercontainsafrontabsorberlocatedbetween 0.9and5 mfrom thenominalinteraction point. Theabsorber is followed by five tracking stations, each made of two planes of CathodePadChambers.Thethirdstationisplacedinsideadipole magnetwith3Tmfieldintegral.Thetrackingstationsarefollowed byanironwallwithathicknessof7.2interactionlengthsandtwo triggerstations,eachoneconsistingoftwoplanesofResistivePlate Chambers.

Thepositionoftheinteractionpointisobtainedusingthe clus-tersreconstructedin theSiliconPixelDetector(SPD) [31,32].The SPDislocatedinthecentralbarreloftheALICEapparatusand op-eratedinsidealargesolenoidal magnetprovidingauniform0.5 T magneticfield parallel tothebeamline. The SPDconsistsoftwo

cylindricallayerswhichcover

|η|

<

2

.

0 and

|η|

<

1

.

4 withrespect to the nominal interaction-point, for the inner and outer layer, respectively. The associated charged hadrons at mid-rapidity are reconstructedviatheso-called SPDtracklets,shorttracksegments formedfromtheclustersinthetwolayersoftheSPDandthe pri-maryvertex[32].

The V0 detector [33] consists of two rings of 32 scintillator counterseach,covering2

.

8

<

η

<

5

.

1 (V0-A)and

−

3

.

7

<

η

<

−

1

.

7 (V0-C),respectively.Itisusedfortriggeringandevent-multiplicity estimation.

The data samples presented here were collected during the 2013and2016p–PbLHC runs.The collisionenergy was

√

sNN

=

5

.

02 and 8.16 TeV forthe 2013 and 2016 data samples, respec-tively. Part of the 5.02 TeV data were collected during the 2016 p–Pbrun.Datawithbothbeamconfigurations,namelyPb–nucleus momentum(denotedasPb–pcollisions)orprotonmomentum (de-notedasp–Pbcollisions)orientedtowardsthemuonspectrometer, have been analyzed.The asymmetric beamenergies, imposed by the two-in-one LHC magnet design, resulted in collisions whose nucleon–nucleoncenter-of-massreferencesystemisshiftedin ra-pidity by 0.465 inthe directionoftheproton beamwithrespect to theALICElaboratorysystem. The datawere takenwitha trig-gerthatrequiredcoincidence ofminimum-bias(MB)anddimuon triggers.TheMBtriggerwasprovidedbytheV0detector request-ing a signal in both V0-A andV0-C rings. Its efficiency isfound to beabout98%[34].Thedimuon triggerrequiredatleastapair ofopposite-signtracksegmentsinthe muontriggersystem, each withatransversemomentum(pT) abovethethresholdofthe

on-linetriggeralgorithm. Thisthresholdwassetto provide50% effi-ciencyformuontrackswithpT

=

0

.

5 GeV/c.

The collected data samples of p–Pb and Pb–p collisions at 5.02 TeV (8.16 TeV) correspond to integrated luminosities of 8.1 and5.8 (8.7and 12.9) nb−1_{,respectively. The maximum}

interac-tion pile-upprobabilityrangedup to3% and8% during2013and 2016datataking,respectively.

3. Event, track and dimuon selection

Thebeam-inducedbackgroundisrejectedbyrequiringthatthe timing signals from both rings of the V0 detector are compati-blewithparticlescomingfromcollisionevents.Eventscontaining multiple collisions (pile-up) are rejected by requiring one single interaction vertexreconstructedinthe SPDandby exploitingthe correlation betweenthe number of clustersin the two layers of theSPDandthenumberofthereconstructedSPDtracklets.

The longitudinal position ofthe reconstructed primary vertex (zvtx) is required to be within

±

10 cm from the nominal

inter-action point. The reconstructed SPDtracklets are selectedby ap-plying a zvtx-dependent pseudorapidity cut. The cut is adjusted

to exclude the contribution from the edges of the SPD where the detector acceptance is low. For example, we select tracklets within

−

1

.

8

<

η

<

0

.

5,

−

1

.

3

<

η

<

1

.

3 and

−

0

.

5

<

η

<

1

.

8 for events withzvtx

=

10,0 and

−

10 cm, respectively.The

contribu-tion from fake and secondary tracklets is reduced by applying a

| |

<

5 mrad cut onthe difference betweentheazimuthal an-gles ofthe clustersin thetwo layers of theSPD withrespect to the primary vertex. With this cut, the mean pT of the selected

chargedhadronsisfoundtobeapproximately0.75 GeV/c [16]. Thetracksreconstructedinthemuonspectrometerarerequired toemergeataradialtransversepositionbetween17.6and89.5 cm fromtheendofthefrontabsorber inordertoavoidregionswith higher material budget. The tracks reconstructed in the tracking chambers are identified as muons by requiring their matching withcorrespondingtracksegmentsinthetriggerchambers. Back-ground tracks are removed with a selection on the product of

Fig. 1. TheMμμ distributioninthe3<pμμT <6 GeV/c intervalfittedwithacombinationofaCB2functionforthesignalandaVWGfunctionforthebackground,for

high-multiplicity(leftpanel)andlow-multiplicity(rightpanel)p–Pbcollisionsat√sNN=8.16 TeV. the total track momentum and the distance of closest approach

to the primary vertexin the transverse plane [35]. The selected dimuons are defined as pairs of opposite-sign muon tracks hav-ing

−

4

<

yμμ_lab

<

−

2

.

5,transversemomentum pμμ_T between0and 12GeV/c and invariantmass Mμμ between1and5 GeV/c2.Only eventswithatleastonedimuonsatisfyingtheseselection criteria areconsidered.

Thedatasamplesaresplitintomultiplicityclassesbasedonthe totalchargedepositedinthetworings(V0-AandV0-C)oftheV0 detector(V0M)[34].Thehigh-multiplicity(low-multiplicity)event classisdefinedas0–20%(40–100%)oftheMBtriggerevent sam-ple.

4. Analysis

TheMμμ distributionineachevent-multiplicityclassandpμμ_T

binisfit withthecombinationof an extendedCrystal Ball(CB2) functionfortheJ/

ψ

signal andaVariable-WidthGaussian (VWG) functionfor thebackground [36]. Thetail parameters ofthe CB2 function were fixed to the values used in [37,38]. The J/

ψ

peak position and width were obtained from the fit in the 0–100% eventclassandfixedtothesevaluesintheotherevent-multiplicity classes.Examplesof the Mμμ fit in the0–20% andthe 40–100% event classes in the 3

<

pμμ_T

<

6 GeV/c interval are shown in Fig.1.

TheangularcorrelationsbetweenJ/

ψ

andchargedhadronsare obtained from the associated-particle (SPD tracklets) yields per dimuontrigger.Theyieldsaredefinedas

Yi

(

zvtx

,

Mμμ

,

pμμT

,

ϕ

,



η

)

=

1 Ni trig

(

zvtx

,

Mμμ

,

p μμ T

)

d2Ni_assoc

(

zvtx

,

Mμμ

,

pμμT

)

d



ϕ

d



η

=

1 N_trigi

(

zvtx

,

Mμμ

,

pμμT

)

S Ei

(

zvtx

,

Mμμ

,

pμμT

,

ϕ

,



η

)

M Ei

₍

_z vtx

,

Mμμ

,

pμμT

,

ϕ

,



η

)

,

(1)

whereNi_trig

(

zvtx

,

Mμμ

,

pμμ_T

)

isthenumberofdimuons,Niassoc

(

zvtx

,

Mμμ

,

pμμ_T

)

isthenumberofassociatedSPDtrackletscorrectedfor acceptanceandcombinatorialeffects(asshowninthesecondline oftheequationanddescribedbelow),

ϕ

and

η

=

yμμ_lab

−

η

tracklet

are theazimuthal angleand (pseudo)rapiditydifference between the trigger dimuon and the associated SPD tracklet. The yields arecalculatedseparatelyineach event-multiplicityclass (index i)

and 1 cm-widezvtx interval.Thedistribution

S Ei

(

zvtx

,

Mμμ

,

pμμT

,

ϕ

,

η

)

=

d2Ni_same

(

zvtx

,

Mμμ

,

pμμT

)

d



ϕ

d



η

isthe yieldofassociated SPDtrackletsfromthesameevent. The distribution M Ei

(

zvtx

,

Mμμ

,

pμμT

,



ϕ

,



η

)

=

α

i

(

zvtx

,

Mμμ

,

pμμT

)

d2_Ni mixed

(

zvtx

,

Mμμ

,

p μμ T

)

d



ϕ

d



η

is constructed using the event-mixing technique, i.e. combining dimuons from one event with SPD tracklets from other events selected in the same event-multiplicityclass and zvtx interval. It

servesbothtocorrectfordetectoracceptanceandefficiencyandto takeintoaccountthecombinatorialbackground.Thenormalization factor

α

i

₍

_z

vtx

,

Mμμ

,

pμμ_T

)

is defined as 1

/(

d2N_mixedi

(

zvtx

,

Mμμ

,

pμμ_T

)/

d

ϕ

d

η)

in the

η

regioncorresponding to themaximal acceptance[16].

Withineachevent-multiplicityclassandbinofMμμ, pμμ_T ,

ϕ

and

η

,theyieldsYi_{averagedoverz}

vtxareobtainedbyfittingthe

distribution Yi_N

trig

(

zvtx

)

iM Ei

(

zvtx

)

to the distribution S Ei

(

zvtx

)

.

A Poissonlikelihoodfitisusedinordertoproperlydealwiththe casesoflownumberoftracklets.Then,theaverageyieldsare pro-jected on the

ϕ

axis in the rangeof 1

.

5

<

|η|

<

5 using the methoddescribedin[16].

In order to extract the yields per J/

ψ

trigger, the yields per dimuontriggerineach event-multiplicityclass, pμμ_T and

ϕ

bins arefitasafunctionofMμμ usingthefollowingsuperposition Yi

(

Mμμ

)

=

S S

+

BY i J/ψ

+

B S

+

BY i B

(

Mμμ

),

(2)

where S and B are the number of J/

ψ

and the background dimuons in each bin of Mμμ obtained from the invariant mass fit (using a CB2 function for the J/

ψ

signal anda VWG function forthe background)described above, YJ/ψ is theassociatedyield

corresponding to theJ/

ψ

triggerand YB

(

Mμμ

)

is asecond-order polynomial function aimed to describe the associated yields cor-responding to the background. The fit range is chosen between 1.5and4.5 GeV/c2_{.Examplesoffitsinhigh-multiplicityand}

low-multiplicityeventclassesareshowninFig.2.

Fig.3showstheobtainedassociatedtrackletyieldsperJ/

ψ

trig-ger for p–Pb and Pb–p collisions at

√

sNN

=

5

.

02 and 8.16 TeV.

Fig. 2. Exampleofassociatedtrackletyieldsperdimuontriggerinthe3<pμμT <6 GeV/c intervalforhigh-multiplicity(leftpanel)andlow-multiplicity(rightpanel)p–Pb

collisionsat√sNN=8.16 TeV.TheresultofthefitwiththefunctionfromEq. (2) isrepresentedwiththebluesolidline.Thedashedredlinecorrespondstotheassociated

trackletyieldsperbackgrounddimuon.(Forinterpretationofthecolorsinthefigure(s),thereaderisreferredtothewebversionofthisarticle.)

As expected, in low-multiplicity collisions we observe a signifi-cant correlation structure on the away side (Fig. 3, top panels), presumably originating from the fragmentation of recoil jets. In high-multiplicity collisions (Fig. 3, middlepanels), a possible en-hancementon both near(

ϕ

≈

0) andaway (

ϕ

≈

π

) side can be spotted on top of the away-side structure. Inorder to isolate possiblecorrelationsduetocollectiveeffectsbetweentheJ/

ψ

and theassociatedtracklets,weapplythesamesubtractionmethodas inpreviousmeasurements[5,6,12,16],namelysubtractingtheYJ/ψ

yieldsinlow-multiplicitycollisionsfromthoseinhigh-multiplicity collisions (Fig. 3, bottom panels). The subtraction method relies ontheassumptions thatthejetcorrelationsontheaway side re-mainunmodified asafunction oftheeventmultiplicity andthat there are no significant correlations due to collective effects in low-multiplicitycollisions(seediscussioninSection6).

In order to quantify the remaining correlation structures, the subtractedyieldsYsub

J/ψ

(ϕ)

arefitwith

a0

+

2a1cos



ϕ

+

2a2cos 2



ϕ

.

(3)

Thesecond-orderFouriercoefficient V2

{

J

/ψ

−

tracklet

,

sub

}

ofthe

azimuthalcorrelationbetweentheJ/

ψ

andtheassociatedcharged hadronsisfinally calculatedasa2

/

bhigh0 . Thedenominator b

high

0

=

a0

+

blow0 corresponds to the combinatorial baseline of the

high-multiplicity collisions, wherethe parameter blow₀ isthe combina-torial baseline of the low-multiplicity collisions obtained at the minimumoftheper-triggeryields,namelyin

ϕ

<

π/

6.The pa-rameterblow₀ isthenormalizationfactorusedinFig.3.The param-etera1,whichdescribesthe strengthof theremaining away-side

correlationstructure,isfoundtobecompatiblewithzeroin prac-ticallyall pJ_T/ψ intervals, inbothp–PbandPb–pcollisionsatboth 5.02and8.16 TeV.

As an alternative extraction method, the calculation of blow₀ , thesubtractionoflow-multiplicityfromhigh-multiplicitycollision yieldsandthefittoEq. (3) isdoneineachbinofMμμ separately.

Then the V2

{

J

/ψ

−

tracklet

,

sub

}

coefficientisextractedby fitting V2

{μμ

−

tracklet

,

sub

}(

Mμμ

)

witha superposition similar tothe

onedefinedinEq. (2)

V2

{

μμ

−

tracklet

,

sub

}(

Mμμ

)

=

S S

+

BV2

{

J

/ψ

−

tracklet

,

sub

}

+

B S

+

BV B 2

{

μμ

−

tracklet

,

sub

}(

Mμμ

),

(4)

where the V₂B

{

μμ

−

tracklet

,

sub

}(

Mμμ

)

is the second-order Fouriercoefficientoftheazimuthalcorrelation betweenthe back-ground dimuons and associated tracklets. The background co-efficient VB

2

{μμ

−

tracklet

,

sub

}(

Mμμ

)

is parameterized with a

second-order polynomial function. This parameterization is cho-sen since it reproduces the dimuon v2

(

Mμμ

)

constructed from

the measured muon v2 coefficient [16] assuming that the

domi-nant partof thebackground iscombinatorial.An exampleof the

V2

{

μμ

−

tracklet

,

sub

}(

Mμμ

)

fitisshowninFig.4.

Following theprocedure used inRefs. [5,12,16], the V2

{

J

/ψ

−

tracklet

,

sub

}

coefficient is factorized into a product of J/

ψ

and charged-hadronv2 coefficients.Thus,theJ/

ψ

second-orderFourier

azimuthalcoefficient vJ₂/ψ

{

2

,

sub

}

isobtainedas

vJ₂/ψ

{

2

,

sub

} =

V2

{

J

/ψ

−

tracklet

,

sub

}/

vtracklet2

{

2

,

sub

},

(5)

wherethe vtracklet₂

{

2

,

sub

}

isthetrackletsecond-order Fourier az-imuthal coefficient obtained by performing the analysis consid-ering SPD tracklets as both trigger and associated particles. The obtained values of vtracklet

2

{

2

,

sub

}

are between 0.067 and 0.069

depending on the beam configuration and collision energy, with 1–2%relativestatisticaluncertaintyand5–6.5%relativesystematic uncertainty.

5. Systematic uncertainties

The combined statistical and systematic uncertainties of the measured vtracklet₂

{

2

,

sub

}

coefficient for each beam configuration andcollisionenergyaretakenasglobalsystematicuncertaintiesof thecorrespondingvJ₂/ψ

{

2

,

sub

}

coefficients.

Alltheothersystematicuncertaintiesofthe v₂J/ψ

{

2

,

sub

}

coeffi-cientsareobtainedforeachdatasampleandpTintervalseparately.

Thefollowingsourcesareconsidered.

A possibleinaccurate correction for theSPDacceptance is as-sessed by varying the zvtx range between

±

8 and

±

12 cm.

Sys-tematicuncertaintiesareassignedonlyinthecasesofasignificant changeoftheresults.Thesignificanceisdefinedaccordingtothe proceduredescribedinRef. [39].

Thesystematiceffectrelatedtotheuncertaintyoftheshapeof thedimuonbackgroundyields YB

(

Mμμ

)

isestimatedby perform-ing thefitwithEq. (2) usingalinearfunction forthebackground termandvaryingthefitrange.Thesystematiceffectcomingfrom the uncertainty ofthe signal-to-backgroundratio S

/

B is checked

Fig. 3. AssociatedtrackletyieldsperJ/ψ triggerin3<pJT/ψ<6 GeV/c inp–PbandPb–pcollisionsat√sNN=5.02 TeV(leftpanels)and8.16 TeV(rightpanels).Thetop

andthemiddlepanelscorrespondtothelow-multiplicityandthehigh-multiplicityeventclasses,respectively.Thebottompanelsshowtheyieldsafterthesubtractionof thelow-multiplicitycollisionyieldsfromthehigh-multiplicitycollisionones.Thesolidlinerepresentthefittothedataasdescribedinthetext.Thedashed,dot-dashed anddottedlinescorrespondtotheindividualtermsofthefitfunctiondefinedinEq. (3).Alltheyieldsarenormalizedtothevalueinϕ<π/6 inthelow-multiplicity (40–100%)eventclass.Onlythestatisticaluncertaintiesareshown.(Forinterpretationofthecolorsinthefigure(s),thereaderisreferredtothewebversionofthisarticle.)

by employing various invariant mass fit functions, both for the backgroundandfortheJ/

ψ

signal.Themaximal differenceofthe resultsobtainedwiththeabovecheckswithrespecttothedefault approachistakenasthecorrespondingsystematicuncertainty.

The uncertainty arising fromthe employed analysis approach isobtainedasthedifferencebetweenthetwoextractionmethods describedinSection4.

AsdescribedinSection 4,bydefaultthemixed-event distribu-tion M E

(ϕ,

η)

isnormalizedtounityinthe

η

region corre-spondingto themaximal acceptance. Asan alternativeapproach, normalizingtheintegral ofM E

(ϕ,

η)

tounity isused.No

sig-nificant effect on the obtained results is observed and thus no systematicuncertaintyisassigned.

The usedevent-mixingtechnique can introducesystematic bi-ases. The event multiplicity distribution of the selected dimuons (1

<

Mμμ

<

5 GeV/c2_{) differs fromthat of the J/}

_ψ

_{signal. Since}

the charged-hadronspectra andthe charged-hadron densityasa functionof

η

changewitheventmultiplicity[34],thenon-uniform (bothintheazimuthalandlongitudinaldirections)SPDacceptance can introduceabias.The corresponding systematicuncertaintyis evaluated by doing the event mixing in finer event-multiplicity bins.

Table 1

SummaryofabsolutesystematicuncertaintiesofthevJ2/ψ{2,sub}coefficients.Theuncertaintiesvarywithintheindicatedrangesdependingonp J/ψ

T .Thevaluesnotpreceded

byasignrepresentdouble-sideduncertainties.

Source of systematics √sNN=5.02 TeV √sNN=8.16 TeV

p–Pb Pb–p p–Pb Pb–p Acceptance correction 0 to 0.019 0 to 0.057 0 to 0.011 0 to 0.007 Background shape 0.007 to 0.013 0.015 to 0.056 0.011 to 0.013 0.003 to 0.012 Extraction method 0.003 to 0.015 0.010 to 0.040 0.002 to 0.011 0.008 to 0.018 Event mixing 0.003 to 0.015 0.004 to 0.025 0.002 to 0.008 0.004 to 0.012 Residualaway-side jetcorrelation – −0.030 to 0 −0.018 to 0 – Total +0.009 to+0.024 +0.024 to+0.084 +0.013 to+0.019 +0.015 to+0.021 −0.009 to−0.024 −0.024 to−0.090 −0.015 to−0.026 −0.015 to−0.021

Fig. 4. Example ofthe fit from Eq. (4) in the 3<pμμT <6 GeV/c interval for

p–Pbcollisionsat√sNN=8.16 TeV.ThedashedlinecorrespondstotheV2B{μμ−

tracklet,sub}(Mμμ).

Thenon-uniformacceptanceofthemuonspectrometercoupled to sizeable correlations between the dimuons and SPD tracklets can bias azimuthally the sample of SPD tracklets used for event mixing.Inordertocheckforpossibleeffectsonourmeasurement, theevent mixingis performedinintervals ofazimuthal angleof theselecteddimuons.Weobserveno significantsystematiceffect astheobtainedresultsshownegligibledeviationswithrespectto theresultsusingthedefaultevent-mixingtechnique.

The effectof a possibleresidual near-side peak is checkedby varying the rapidity gapbetween the trigger dimuons and asso-ciated charged-hadrons from 1.0to 2.0units. We observe no in-dicationofincreasing v2 withreducedgapandthusconsiderthe

defaultgapof1.5unitssufficienttoeliminateanysignificant resid-ualnear-sidepeakcontribution.

As shown in Section 4, the recoil-jet away-side correlation structureinthehigh-multiplicityeventclassisgreatlydiminished after the subtraction of the low-multiplicity event class. By de-fault,any remaining away-side structureis supposed to be taken intoaccount bythe cos

ϕ

termin Eq. (3).In ordertocheck for residual effects we proceed in the following way. First, the cor-relation function in the low-multiplicityevent class is fitwith a Gaussianfunctioncenteredat

ϕ

=

π

.Then,thecorrelation func-tion in the high-multiplicity event class is fit with the function from Eq. (3), where the cos

ϕ

term is replaced by a Gaussian function with a width fixed to the value obtained from the fit inthelow-multiplicitycollisions.No clearsignature ofsystematic changeoftheresultsisseen,exceptsomehintsofapossibleeffect inthe highest pJ_T/ψ interval. Conservatively,we assign systematic uncertainty as the difference with respect to the default

analy-sis approach. Since the typical values of the Gaussian width are around 1 rad, one-sided (negative) systematic uncertainty is as-signed.

In Table 1 we presenta summary ofthe assigned systematic uncertainties ofthe vJ₂/ψ

{

2

,

sub

}

coefficients. No sizeable correla-tionsbetweenthepJ_T/ψ intervalsareobservedandthereforeinthe followingtheuncertaintiesareconsidereduncorrelated.

OurmeasurementisforinclusiveJ/

ψ

.ThefractionofJ/

ψ

from decaysofb-hadronsreachesuptoabout15%atpJ_T/ψ

≈

6 GeV/c in p–Pb collisions at

√

sNN

=

5

.

02 [40] and 8.16 TeV [41]. Therefore

the feed-down contribution is unlikely to influence significantly ourresults.Inprinciple,apossiblestrongmultiplicitydependence of the feed-down fraction can potentially affect the subtraction approach. However, no evidenceforsuch a strong dependenceis observedinppcollisions[42].

As additionalcross-checks the analysis is done using alterna-tive event-multiplicity estimators, varying the tracklet

| |

cut, applyingacutontheasymmetry oftransversemomentumofthe twomuontracks,removingthepile-upcutsandexcludingtheSPD regionswithnon-uniformacceptanceinpseudorapidity.The corre-sponding resultsare foundto be compatiblewiththoseobtained with the defaultanalysis approach andtherefore no further sys-tematicuncertaintiesareassigned.

6. Results

In Fig. 5 we report the measured v₂J/ψ

{

2

,

sub

}

coefficients as a function of pJ_T/ψ for p–Pb andPb–p collisions at

√

sNN

=

5

.

02

and8.16 TeV.Upto pJ_T/ψ of3 GeV/c,nosignificantdeviationfrom zeroisobservedforeitherp–PborPb–pcollisionsatthetwo colli-sionenergies.Onthecontrary,inthepJ_T/ψ intervalbetween3and 6 GeV/c, the vJ₂/ψ

{

2

,

sub

}

is found to be positive although with largeuncertainties.AsalsoshowninFig.5,thevJ₂/ψ coefficientsin 2

.

5

<

y

<

4 in centralPb–Pb collisions at

√

sNN

=

5

.

02 TeV reach

maximalvaluesinthesamepJ_T/ψ interval[24].

Twomethods are employed inorder toobtain theprobability thatthe vJ₂/ψ

{

2

,

sub

}

iszerointhe3

<

pJ_T/ψ

<

6 GeV/c interval.In thefirstmethod,thevJ₂/ψ

{

2

,

sub

}

valuesinthetwo pJ_T/ψ intervals (3

<

pJ_T/ψ

<

4 GeV/c and 4

<

pJ_T/ψ

<

6 GeV/c) are combined into aweightedaverageforeach rapidityandcollisionenergy.The ob-tainedprobabilitiesare0.13%and0.13%(7.8%and0.23%)forp–Pb and Pb–pcollisions, respectively, at

√

sNN

=

8

.

16 TeV (5.02 TeV).

Combining all eight vJ₂/ψ

{

2

,

sub

}

values yields a total probabil-ity of1

.

7

×

10−7_{.This corresponds to a 5}

_.

₁

_σ

_{significanceof the}

measured positive vJ₂/ψ

{

2

,

sub

}

coefficient. The second method is Fisher’s combinedprobability test[43].Withthismethodone ob-tainsprobabilities of0.14%and0.23% (10.3%and0.41%) forp–Pb and Pb–p collisions at

√

sNN

=

8

.

16 TeV (5.02 TeV), respectively.

Fig. 5. v₂J/ψ{2,sub}inbinsofpTJ/ψ forp–Pb,2.03<y<3.53 (leftpanels), andPb–p,−4.46<y<−2.96 (rightpanels), collisionsat √sNN=5.02 TeV(toppanels)and

8.16 TeV(bottompanels).Theresultsarecomparedtothev2J/ψ{EP}coefficientsmeasuredincentralPb–Pbcollisionsat √

sNN=5.02 TeVinforwardrapidity(2.5<y<4)

usingeventplane(EP)basedmethods[24].Thestatisticalanduncorrelatedsystematicuncertaintiesarerepresentedbylinesandboxes,respectively.Thequotedglobal systematicuncertaintiescorrespondtothecombinedstatisticalandsystematicuncertaintiesofthemeasuredvtracklet

2 {2,sub}coefficient. The total probability is 1

.

4

×

10−6 which corresponds to a 4

.

7

σ

significance.Inthecalculationoftheaboveprobabilities,both sta-tistical and systematic uncertainties of the measured values are takenintoaccount.Theglobalsystematicuncertaintyisnottaken intoaccountasitisirrelevantinthecaseofthezerohypothesis.

Theanalysismethod presentedin thisLetterrelies onthe as-sumptionthattherearenosignificantcorrelationsduetocollective effectsinthelow-multiplicityeventclass.Incaseofapresenceof suchcorrelations,themeasuredV2

{

J

/ψ

−

tracklet

,

sub

}

isequalto

V2

{

J

/ψ

−

tracklet

,

high

} −

blow₀

bhigh₀ V2

{

J

/ψ

−

tracklet

,

low

},

(6) whereV2

{

J

/ψ

−

tracklet

,

high

}

andV2

{

J

/ψ

−

tracklet

,

low

}

arethe

second-orderFouriercoefficientsof theazimuthal correlation be-tween the J/

ψ

and the associated charged hadrons in the high-multiplicity and the low-multiplicity collisions, respectively, and

blow₀

/

bhigh₀

≈

1/3 is the ratio of the combinatorial baseline in the low-multiplicityandhigh-multiplicitycollisions (see Fig.3). Asis demonstratedinRef. [44],theassumptionofnosignificant collec-tivecorrelationsinthelow-multiplicitycollisionsiscertainly ques-tionablefor light-flavor hadrons.Our dataindicates the same,as weobserveastatisticallysignificantincreaseofthemeasured val-uesofvtracklet₂

{

2

,

sub

}

whensubtractingalowerevent-multiplicity, e.g.60–100%,class.Ultimately,thevalueofthevtracklet₂ coefficient isfoundtobe about17%higherincasenosubtractionisapplied. Therefore, replacing the subtracted vtracklet₂

{

2

,

sub

}

coefficient in Eq. (5) bythenon-subtractedcoefficientwouldmeanthatthevJ₂/ψ

coefficients are up to 17% lower with respect to the measured

vJ₂/ψ

{

2

,

sub

}

coefficients. However, assuming that the vJ₂/ψ coeffi-cientsfollowthesametrendasafunctionofeventmultiplicityas the vtracklet₂ coefficient, they wouldbe up to 17% higherwith re-specttothe measured vJ₂/ψ

{

2

,

sub

}

coefficients. Subtracting lower

event-multiplicity classesinthe measurementofthe vJ₂/ψ

{

2

,

sub

}

coefficientdoesnotimprovetheprecisionofourmeasurement, be-causeofthe limitedamountofJ/

ψ

signal in thelow-multiplicity collisions.

Thenuclearmodification factorofJ/

ψ

inp–PbandPb–p colli-sions[37,38] aswellasthecharged-particle v2 coefficient[45–47]

inppcollisionsshow nosignificant

√

sNN dependence.Asseenin

Fig.5,the measured vJ₂/ψ

{

2

,

sub

}

coefficientsat

√

sNN

=

5

.

02 and

8.16 TeValsoappeartobeconsistentwitheachother.Thelargest absolute difference between the results at the two collision en-ergies is observed in Pb–p collisions in the 3

<

pJ_T/ψ

<

6 GeV/c interval. The significance of this difference is rather low (below 1

.

5

σ

), because ofthe large uncertainties of the measurement at

√

sNN

=

5

.

02 TeV. Hence, the data for the two collision energies

arecombinedasaweightedaveragetakingintoaccountboth sta-tistical and systematic uncertainties. In Fig. 6, we present these combinedresultsforp–PbandPb–pcollisionstogetherwith mea-surementsandmodelcalculationsforPb–Pb collisionsat

√

sNN

=

5

.

02 TeV[25].

In Pb–Pb collisions, the positive vJ₂/ψ coefficients at pJ_T/ψ be-low3–4 GeV/c arebelievedtooriginatefromtherecombinationof charmquarksthermalizedinthemedium andaredescribedfairly well by the transport model[25] (seeFig. 6). In p–Pbcollisions, theamountof producedcharmquarksis smallandthereforethe contribution from recombination should be negligible. Our mea-suredvalues at pJ_T/ψ

<

3 GeV/c are compatiblewithzero,in line withthisexpectation.Thereisonepublication[28] whichsuggests that even in p–Pbcollisions a sizeable contributionfrom recom-bination could occur due to canonical enhancement effects. The uncertaintiesofourresultsdonotallowtoconfirmortoruleout thisscenario.

InPb–Pbcollisions,themeasured vJ₂/ψ coefficientsexceed sub-stantiallythetheoreticalpredictionsatpJ_T/ψ

>

4 GeV/c,wherethe

Fig. 6. Combined vJ2/ψ{2,sub} coefficientsinp–Pb andPb–pcollisionscompared

tothe results incentral and semi-central Pb–Pb collisions at √sNN=5.02 TeV

[24] and the transport model calculations for semi-central Pb–Pb collisions at

√

sNN=5.02 TeV[25].Thesolidlinecorrespondstothecontributionfrom

path-lengthdependentsuppressioninsidethe medium.Thebandshowsthe resulting vJ₂/ψ includingalsotherecombinationofthermalizedcharmquarksandthe feed-downfromb-hadrondecaysassumingthermalizationofbquarks.

main contributionto vJ₂/ψ is expectedto come frompath-length dependent suppression inside the medium [25] (see Fig. 6). In p–Pbcollisions,themedium, ifany,hasamuchsmallersize [48] and hence very little, if any, path-length dependent effects are expected. In principle, the feed-down from decays of b-hadrons cangive a positive vJ₂/ψ athightransversemomentum incaseof a positive b quark v2. However, the latter would have to reach

unreasonably high values given the magnitude of the measured

vJ₂/ψ

{

2

,

sub

}

andthesmallfeed-downfraction.Despitethese con-siderations, the measured positive vJ₂/ψ coefficients would imply thattheJ/

ψ

participatesinthecollectivebehaviorofthep–Pb col-lisionsystem.

7. Summary

We presented a measurement of the angular correlations between forward and backward J/

ψ

and mid-rapidity charged hadronsinp–PbandPb–pcollisionsat

√

sNN

=

5

.

02 and8.16 TeV.

The data indicate persisting long-range correlation structures at

ϕ

≈

0 and

ϕ

≈

π

, reminiscentofthe doubleridge previously found in charged-particle correlations at mid- and forward ra-pidity. The corresponding vJ₂/ψ

{

2

,

sub

}

coefficients in 3

<

pJ_T/ψ

<

6 GeV/c are found to be positive with a total significance of 4

.

7

σ

to 5

.

1

σ

. The obtained values, albeit with large uncertain-ties, are comparablewith those measured in Pb–Pb collisions at

√

sNN

=

5

.

02 TeV in forward rapidity. Although the underlying

mechanism is not understood, the comparable magnitudeof the

vJ₂/ψ coefficientsathightransversemomentuminp–PbandPb–Pb collisions indicates that thismechanism could be similarin both collisionsystems.

Acknowledgements

The ALICE Collaboration would like to thank all its engineers andtechnicians fortheir invaluablecontributionstothe construc-tionoftheexperimentandtheCERNacceleratorteamsforthe out-standingperformanceoftheLHCcomplex.TheALICECollaboration

gratefully acknowledges the resources and support provided by all Grid centresandthe WorldwideLHC ComputingGrid (WLCG) collaboration. The ALICE Collaboration acknowledges the follow-ing funding agencies for their 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 Academyof SciencesandNationalstiftung fürForschung, Technologie und Entwicklung, Austria; Ministry of Communica-tions and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Universidade Federal do Rio Grande do Sul (UFRGS), Financiadora de Estudos e Projetos (Finep) and Fun-dação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil; Ministry of Science & Technology of China (MSTC), Na-tional Natural Science Foundation of China (NSFC) and Ministry of Education of China (MOEC), China; Ministry of Science, Edu-cation andSports andCroatian ScienceFoundation, Croatia; Min-istryofEducation,Youth andSportsofthe CzechRepublic, Czech Republic; The Danish Council for Independent Research – Natu-ral Sciences, the Carlsberg Foundation and Danish National Re-search Foundation (DNRF), Denmark; Helsinki Institute ofPhysics (HIP),Finland;Commissariatàl’EnergieAtomique(CEA)and Insti-tut National de Physique Nucléaire et de Physique des Particules (IN2P3) andCentre Nationalde la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and GSI Helmholtzzentrum für Schwe-rionenforschungGmbH,Germany;GeneralSecretariatforResearch and Technology, Ministry of Education, Research and Religions, Greece; National Research, Development and Innovation Office, Hungary; Department of Atomic Energy, Government of India (DAE),DepartmentofScienceandTechnology,GovernmentofIndia (DST), University Grants Commission,Government ofIndia (UGC) andCouncil ofScientificandIndustrialResearch(CSIR), India; In-donesian Institute of Science, Indonesia; Centro Fermi – Museo StoricodellaFisicaeCentroStudieRicercheEnricoFermiand Isti-tutoNazionalediFisicaNucleare(INFN),Italy;Institutefor Innova-tive ScienceandTechnology,NagasakiInstituteofAppliedScience (IIST),Japan SocietyforthePromotion ofScience(JSPS)KAKENHI and Japanese Ministry of Education, Culture, Sports, Science and Technology(MEXT),Japan;ConsejoNacionaldeCiencia(CONACYT) yTecnología,throughFondodeCooperaciónInternacionalen Cien-cia y Tecnología (FONCICYT) and Dirección General de Asuntos delPersonalAcademico(DGAPA),Mexico;NederlandseOrganisatie voor Wetenschappelijk Onderzoek (NWO), 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,Ministeriode Cienciae Innovacion 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

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ALICE Collaboration

S. Acharya

137

,

D. Adamová

94

,

J. Adolfsson

34

,

M.M. Aggarwal

99

,

G. Aglieri Rinella

35

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M. Agnello

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N. Agrawal

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,

Z. Ahammed

137

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S.U. Ahn

79

,

S. Aiola

141

,

A. Akindinov

64

,

M. Al-Turany

106

,

S.N. Alam

137

,

D.S.D. Albuquerque

122

,

D. Aleksandrov

90

,

B. Alessandro

58

,

R. Alfaro Molina

74

,

Y. Ali

15

,

A. Alici

12

,

53

,

27

,

A. Alkin

3

,

J. Alme

22

,

T. Alt

70

,

L. Altenkamper

22

,

I. Altsybeev

136

,

C. Alves Garcia Prado

121

,

C. Andrei

87

,

D. Andreou

35

,

H.A. Andrews

110

,

A. Andronic

106

,

V. Anguelov

104

,

C. Anson

97

,

T. Antiˇci ´c

107

,

F. Antinori

56

,

P. Antonioli

53

,

L. Aphecetche

114

,

H. Appelshäuser

70

,

S. Arcelli

27

,

R. Arnaldi

58

,

O.W. Arnold

105

,

36

_,

I.C. Arsene

21

,

M. Arslandok

104

,

B. Audurier

114

,

A. Augustinus

35

,

R. Averbeck

106

,

M.D. Azmi

17

,

A. Badalà

55

,

Y.W. Baek

60

,

78

,

S. Bagnasco

58

,

R. Bailhache

70

,

R. Bala

101

,

A. Baldisseri

75

,

M. Ball

45

,

R.C. Baral

67

,

88

,

A.M. Barbano

26

,

R. Barbera

28

,

F. Barile

33

,

L. Barioglio

26

,

G.G. Barnaföldi

140

,

L.S. Barnby

93

,

V. Barret

131

,

P. Bartalini

7

,

K. Barth

35

,

E. Bartsch

70

,

N. Bastid

131

,

S. Basu

139

,

G. Batigne

114

,

B. Batyunya

77

,

P.C. Batzing

21

,

J.L. Bazo Alba

111

,

I.G. Bearden

91

,

H. Beck

104

,

C. Bedda

63

,

N.K. Behera

60

,

I. Belikov

133

,

F. Bellini

27

,

35

,

H. Bello Martinez

2

,

R. Bellwied

124

,

L.G.E. Beltran

120

,

V. Belyaev

83

,

G. Bencedi

140

,

S. Beole

26

,

A. Bercuci

87

,

Y. Berdnikov

96

,

D. Berenyi

140

,

R.A. Bertens

127

,

D. Berzano

35

,

L. Betev

35

,

A. Bhasin

101

,

I.R. Bhat

101

,

B. Bhattacharjee

44

,

J. Bhom

118

,

A. Bianchi

26

,

L. Bianchi

124

,

N. Bianchi

51

,

C. Bianchin

139

,

J. Bielˇcík

39

,

J. Bielˇcíková

94

,

A. Bilandzic

36

,

105

,

G. Biro

140

,

R. Biswas

4

,

S. Biswas

4

,

J.T. Blair

119

,

D. Blau

90

,

C. Blume

70

,

G. Boca

134

,

F. Bock

35

,

A. Bogdanov

83

,

L. Boldizsár

140

,

M. Bombara

40

,

G. Bonomi

135

,

M. Bonora

35

,

J. Book

70

,

H. Borel

75

,

A. Borissov

104

,

19

,

M. Borri

126

,

E. Botta

26

,

C. Bourjau

91

,

L. Bratrud

70

,

P. Braun-Munzinger

106

,

M. Bregant

121

,

T.A. Broker

70

,

M. Broz

39

,

E.J. Brucken

46

,

E. Bruna

58

,

G.E. Bruno

35

,

33

,

D. Budnikov

108

,

H. Buesching

70

,

S. Bufalino

31

,

P. Buhler

113

,

P. Buncic

35

,

O. Busch

130

,

Z. Buthelezi

76

,

J.B. Butt

15

,

J.T. Buxton

18

,

J. Cabala

116

,

D. Caffarri

35

,

92

,

H. Caines

141

,

A. Caliva

63

,

106

,

E. Calvo Villar

111

,

P. Camerini

25

,

A.A. Capon

113

,

F. Carena

35

,

W. Carena

35

,

F. Carnesecchi

27

,

12

,

J. Castillo Castellanos

75

,

A.J. Castro

127

,

E.A.R. Casula

54

,

C. Ceballos Sanchez

9

,

S. Chandra

137

,

B. Chang

125

,

W. Chang

7

,

S. Chapeland

35

,

M. Chartier

126

,

S. Chattopadhyay

137

,

S. Chattopadhyay

109

,

A. Chauvin

36

,

105

,

C. Cheshkov

132

,

B. Cheynis

132

,

V. Chibante Barroso

35

,

D.D. Chinellato

122

,

S. Cho

60

,

P. Chochula

35

,

M. Chojnacki

91

,

S. Choudhury

137

,

T. Chowdhury

131

,

P. Christakoglou

92

,

C.H. Christensen

91

,

P. Christiansen

34

,

T. Chujo

130

,

S.U. Chung

19

,

C. Cicalo

54

,

L. Cifarelli

12

,

27

,

F. Cindolo

53

,

J. Cleymans

100

,

F. Colamaria

52

,

33

,

D. Colella

35

,

52

,

65

,

A. Collu

82

,

M. Colocci

27

,

M. Concas

58

,

ii

,

G. Conesa Balbastre

81

,

Z. Conesa del Valle

61

,

J.G. Contreras

39

,

T.M. Cormier

95

,

Y. Corrales Morales

58

,

I. Cortés Maldonado

2

,

P. Cortese

32

,

M.R. Cosentino

123

,

F. Costa

35

,

S. Costanza

134

,

J. Crkovská

61

,

P. Crochet

131

,

E. Cuautle

72

,

L. Cunqueiro

95

,

71

,

T. Dahms

36

,

105

,

A. Dainese

56

,

M.C. Danisch

104

,

A. Danu

68

,

D. Das

109

,

I. Das

109

,

S. Das

4

,

A. Dash

88

,

S. Dash

48

,

S. De

49

,

A. De Caro

30

,

G. de Cataldo

52

,

C. de Conti

121

,

J. de Cuveland

42

,

A. De Falco

24

,

D. De Gruttola

30

,

12

,

N. De Marco

58

,

S. De Pasquale

30

,

R.D. De Souza

122

,

H.F. Degenhardt

121

,

A. Deisting

106

,

104

,

A. Deloff

86

,

C. Deplano

92

,

P. Dhankher

48

,

D. Di Bari

33

,

A. Di Mauro

35

,

P. Di Nezza

51

,

B. Di Ruzza

56

,

M.A. Diaz Corchero

10

,

T. Dietel

100

,

P. Dillenseger

70

,

Y. Ding

7

,

R. Divià

35

,

Ø. Djuvsland

22

,

A. Dobrin

35

,

D. Domenicis Gimenez

121

,

B. Dönigus

70

,

O. Dordic

21

,

L.V.R. Doremalen

63

,

A.K. Dubey

137

,

A. Dubla

106

,

L. Ducroux

132

,

S. Dudi

99

,

A.K. Duggal

99

,

M. Dukhishyam

88

,

P. Dupieux

131

,

R.J. Ehlers

141

,

D. Elia

52

,

E. Endress

111

,

H. Engel

69

,

E. Epple

141

,

B. Erazmus

114

,

F. Erhardt

98

,

B. Espagnon

61

,

G. Eulisse

35

,

J. Eum

19

,

D. Evans

110

,

S. Evdokimov

112

,

L. Fabbietti

105

,

36

,

J. Faivre

81

,

A. Fantoni

51

,

M. Fasel

95

,

L. Feldkamp

71

,

A. Feliciello

58

,

G. Feofilov

136

,

A. Fernández Téllez

2

,

E.G. Ferreiro

16

,

A. Ferretti

26

,

A. Festanti

29

,

35

,

V.J.G. Feuillard

75

,

131

,

J. Figiel

118

,

M.A.S. Figueredo

121

,

S. Filchagin

108

,

D. Finogeev

62

,

F.M. Fionda

22

,

24

,

M. Floris

35

,

S. Foertsch

76

,

P. Foka

106

,

S. Fokin

90

,

E. Fragiacomo

59

,

A. Francescon

35

,

A. Francisco

114

,

U. Frankenfeld

106

,

G.G. Fronze

26

,

U. Fuchs

35

,

C. Furget

81

,

A. Furs

62

,

M. Fusco Girard

30

,

J.J. Gaardhøje

91

,

M. Gagliardi

26

,

A.M. Gago

111

,

K. Gajdosova

91

,

M. Gallio

26

,

C.D. Galvan

120

,

P. Ganoti

85

,

C. Garabatos

106

,

E. Garcia-Solis

13

,

K. Garg

28

,

C. Gargiulo

35

,

P. Gasik

105

,

36

,

E.F. Gauger

119

,

M.B. Gay Ducati

73

,

M. Germain

114

,

J. Ghosh

109

,

P. Ghosh

137

,

S.K. Ghosh

4

,

P. Gianotti

51

,

P. Giubellino

35

,

106

,

58

,

P. Giubilato

29

,

E. Gladysz-Dziadus

118

,

P. Glässel

104

,

D.M. Goméz Coral

74

,

A. Gomez Ramirez

69

,

A.S. Gonzalez

35

,

V. Gonzalez

10

,

P. González-Zamora

10

,

2

,

S. Gorbunov

42

,

L. Görlich

118

,

S. Gotovac

117

,

V. Grabski

74

,

L.K. Graczykowski

138

,

K.L. Graham

110

,

L. Greiner

82

,