Multiplicity dependence of inclusive J/ψ production at midrapidity in pp collisions at s=13 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Multiplicity

dependence

of

inclusive

J/

ψ

production

at

midrapidity

in

pp

collisions

at

√

s

=

13 TeV

.

ALICE

Collaboration



a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory: Received 9 June 2020

Received in revised form 26 August 2020 Accepted 31 August 2020

Available online 3 September 2020 Editor: L. Rolandi

MeasurementsoftheinclusiveJ/ψyieldasafunctionofcharged-particlepseudorapiditydensitydNch/d

η

inppcollisions at√s=13 TeV withALICEattheLHCarereported.The J/ψ mesonyieldismeasured

atmidrapidity(|y|<0.9)inthe dielectronchannel,forevents selectedbasedonthe charged-particle multiplicityatmidrapidity(|

η

|<1)andatforwardrapidity(−3.7<

η

<−1.7 and2.8<

η

<5.1);both

observablesarenormalizedtotheircorrespondingaveragesinminimumbiasevents.Theincreaseofthe

normalizedJ/ψyieldwithnormalizeddNch/d

η

issignificantlystrongerthanlinearanddependentonthe

transversemomentum. Thedataare comparedtotheoreticalpredictions,whichdescribetheobserved

trendswell,albeitnotalwaysquantitatively.

©2020EuropeanOrganizationforNuclearResearch.PublishedbyElsevierB.V.Thisisanopenaccess

articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Hadroniccharmoniumproductionatcolliderenergiesisa com-plex and not yet fully understood process, involving hard-scale processes, i.e.the initial heavy-quarkpair production, which can be describedby meansofperturbativequantum chromodynamics (pQCD), aswell assoft-scaleprocesses, i.e.the subsequent bind-ing intoa color-neutralcharmoniumstate. Thelatterstage is ad-dressed via models which assume that it factorizes with respect to the perturbative early stage. The widely used non-relativistic QCD(NRQCD) effectivetheory [1] incorporatescontributionsfrom severalhadronizationmechanisms,likecolor-singletorcolor-octet models(seeRef. [2] forarecentreviewonmodelsandRef. [3] for acomparisonwithdataofRun1attheLHC).TheNRQCD formal-ismcombinedwithaColorGlassCondensate(CGC)descriptionof theincomingprotons [4] isa recentexampleofacomprehensive treatmentofthetransversemomentumpTandrapiditydependent

production, in particular extended down to zero transverse mo-mentum.MeasurementsofinclusiveJ/

ψ

production,asreportedin thispublication,containa non-promptcontributionfrom bottom-hadrondecaysandtheproductionofbottomquarkscanbe calcu-latedinQCDpertubatively.

The event-multiplicity dependent production of charmonium and open charm hadrons in pp and p–Pb collisions are observ-ableshavingthepotentialtogivenewinsightsonprocessesatthe partonlevelandontheinterplaybetweenthehardandsoft mech-anisms in particle production andis widely studied at the LHC. ALICEhasstudied themultiplicity dependenceinpp collisions at

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

√

s

=

7 TeV of inclusive J/

ψ

production at mid- and forward ra-pidity [5],andpromptJ/

ψ

(includingfeeddownfrom

ψ(

2S

)

and

χ

c),non-prompt J/

ψ

andD-meson productionatmidrapidity [6].

Thegeneralobservationisan increaseofopen andhiddencharm productionwithcharged-particle multiplicity measuredat midra-pidity.FortheJ/

ψ

production,multiplicitiesofabout4timesthe meanvalue were reached. Theresults areconsistent withan ap-proximately linearincrease ofthe normalizedyield asa function of the normalized multiplicity (both observables are normalized totheircorresponding averagesinminimumbiasevents).Forthe D-meson production, normalized event multiplicities of about 6 werereached;astrongerthanlinearincreaseofD-meson produc-tionwasobservedatthehighestmultiplicities.Observationsmade by theCMSCollaboration for

ϒ(

nS

)

production atmidrapidity at

√

s

=

2

.

76 TeV indicate a linear increase with the eventactivity, when measuring it at forwardrapidity, and a stronger than lin-ear increase withtheevent activitymeasured atmidrapidity [7]. AtRHIC, ameasurement ofJ/

ψ

productionasa functionof mul-tiplicitywas recentlyperformedbytheSTARCollaboration [8] for

√

s

=

0

.

2 TeV,showingsimilartrendsasobservedintheLHCdata. The J/

ψ

production asa function ofcharged-particle multiplicity was studied also in p–Pb collisions, exhibiting significant differ-ences for different ranges of rapidity of the J/

ψ

meson [9,10]. Aclear correlation withtheevent multiplicity (andevent shape) was experimentally established for the inclusive charged-particle production [11] aswellasforidentifiedparticles,including multi-strangehyperons [12].

Severaltheoreticalmodels, described briefly inSection 4, pre-dictacorrelationofthenormalizedJ/

ψ

productionwiththe nor-malized event multiplicity which is stronger than linear. These includeacoherentparticleproductionmodel [13],thepercolation

https://doi.org/10.1016/j.physletb.2020.135758

0370-2693/©2020 European Organization for Nuclear Research. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3_.

Table 1

Number of selected events and corresponding integrated luminosities for the different triggers used in this anal-ysis.

MB and HM triggers EMCal triggers

MB HM EG1 EG2

Number of events 1.25×109 ₀

.64×109 ₈₂

.4×106 _120×106 Integrated luminosity 21.6±1.1 nb−1 5.4±0.1 pb−1 7.2±0.1 pb−1 0.82±0.02 pb−1

model [14],theEPOS3eventgenerator [15],aCGC-complemented NRQCD model [16], the PYTHIA8.2 eventgenerator [17,18], and the3-PomeronCGCmodel [19].Whileforinstancemultiparton in-teractions(as implemented inPYTHIA) playan important role in charm(onium) production,it is importantto notice that the pre-dicted correlationis,inall themodelstofirst order,theresultof a (Nch-dependent) reduction of the charged-particle multiplicity.

Well known is the color string reconnection mechanism imple-mented inPYTHIA,butinitial-stateeffectsasinCGCmodelslead, withverydifferentphysics,similarlytoareductioninparticle mul-tiplicity.

InthisLetter,themeasurementsoftheinclusiveJ/

ψ

yieldasa functionofcharged-particlepseudorapiditydensityinppcollisions at

√

s

=

13 TeV are presented. The measurements are performed inthedielectronchannelatmidrapiditywiththeALICEdetectorat the LHC. The pT-integrated anddifferential results are presented

forminimum biasevents aswell asforevents triggeredon high multiplicity,whichextendthemultiplicityrangeupto7timesthe average multiplicity, and on the electromagnetic calorimeter sig-nals,whichallowtoaccesspTvaluesupto15-40 GeV/c.Section2

outlines the experimental setup and the data sample; Section 3

describestheanalysis,whileSection4presentstheresults;abrief summaryandoutlookaregiveninSection5.

2. Experimentanddatasample

ThereconstructionofJ/

ψ

inthee+e− decaychannelat midra-pidity is performed using the ALICE central barrel detectors, described in detail in Refs. [20,21]. The setup is located in a solenoidal magnet providing a field of 0.5 T oriented along the beamdirection.

For this analysis, a minimum bias (MB) trigger, a high mul-tiplicity (HM) trigger, and two triggers based on the deposited energyinthecombinedElectromagnetic Calorimeter(EMCal)and the Di-jetCalorimeter (DCal) [22–24] are employed.Both theMB andHMtriggers areprovidedby theV0detector,thatconsistsof two forward scintillator arrays [25] covering the pseudorapidity ranges

−

3

.

7

<

η

<

−

1

.

7 and 2

.

8

<

η

<

5

.

1. The MB trigger sig-nal consists of a coincident signal in both arrays, while the HM triggerrequiresasignalamplitudeintheV0arraysabovea thresh-oldwhichcorrespondstothe0.1%highestmultiplicityevents.The EMCal andDCalare located back-to-back in azimuthandform a two-arm electromagnetic calorimeter. While the EMCal detector covers

|

η

|

<

0

.

7 overan azimuthal angle of80◦

<

ϕ

<

187◦, the DCalcovers0

.

22

<

|

η

|

<

0

.

7 for260◦

<

ϕ

<

320◦ and

|

η

|

<

0

.

7 for 320◦

<

ϕ

<

327◦.Asaconsequenceofidenticalconstruction,both have identical granularity andintrinsic energyresolution. In this paper,EMCalandDCalwillbe referredto togetherasEMCal.The EMCaltriggerconsistsofthesumofenergyinaslidingwindowof 4

×

4 towersaboveagiventhreshold(atoweristhesmallest seg-mentation ofthe EMCal).Inthisdataset,the triggerrequiresthe presenceofaclusterwithaminimumenergyof9GeV(EG1)or4 GeV(EG2)incoincidencewiththeMBtriggercondition.

Tracksare reconstructed inthepseudorapidity range

|

η

|

<

0

.

9 using the Inner TrackingSystem (ITS) [26], which consists ofsix layers of silicon detectors around the beam pipe, and the Time Projection Chamber (TPC) [27], a large cylindrical gas detector

providing tracking and particle identification via specific ioniza-tion energyloss dE

/

dx. The first two layers of the ITS (covering

|

η

| <

2

.

0 and

|

η

| <

1

.

4), theSiliconPixelDetector (SPD),areused forthe charged-particle multiplicity measurement at midrapidity bycountingtracklets, reconstructedfrompairsofhitsin thetwo SPDlayerspointingtothecollisionvertex.

The results presented in this Letter are obtained using data recordedbyALICEduringtheLHCRun 2datatakingperiodforpp collisionsat

√

s

=

13 TeV.The numberofselected eventsandthe correspondingintegratedluminosities [28] arelistedinTable1for thedifferent triggersused in thisanalysis. Forthe analyzeddata set, the maximum interaction rate was 260 kHz, and the maxi-mumpileupprobabilitywasabout5

×

10−3_.

3. Analysis

InthisworktheinclusiveproductionofJ/

ψ

mesonsisstudied asafunctionofthepseudorapiditydensityofchargedparticlesat midrapidity, dNch/dη.The J/

ψ

yield ina givenmultiplicity inter-val andin a given rapidity ( y) range dNJ/ψ

/

d y is normalized to

theJ/

ψ

yieldinthe INEL

>

0eventclass,



dNJ/ψ

/

d y



.The INEL

>

0

eventclasscontains all eventswithatleast1chargedparticlein

|

η

|

<

1.In thisratio,mostofthe systematicuncertainties related totrackingandparticleidentificationcancel.

3.1. Eventselection

Alleventsselectedinthisanalysisarerequiredtohavea recon-structed collision vertex within the longitudinal interval

|

zvtx

|

<

10 cm inorderto ensureuniform detectorperformance andone SPDtracklet in

|

η

|

<

1. Beam-gas events are rejectedusing tim-ing cuts with the V0 detector. Pileup events are rejected using a vertex finding algorithm based on SPD tracklets [21], allowing the removal of events with 2 vertices. Because of the relatively smallin-bunchpileup probability andthefurther eventselection performedintheanalysis,thefractionofremainingpileupis neg-ligibleintheminimumbiaseventssampleandatmost2%inthe highmultiplicitytriggeredsample.

Events are binned in multiplicity classes based on either the SPD or the V0 detector signals, as shown in Fig. 1. Events cor-respondingto the onsetofthe V0 HMtrigger are excluded;that onsetisrathersharp.Thesmearingseeninthedistributioninthe rightpanel of Fig.1 isdue tothe different thresholdsused dur-ingoperation. Toillustratethis, theV0-amplitude distributionfor asingledatatakingperiodisincludedinFig.1(rightpanel,open squares).

For the measurement of the charged-particle pseudorapidity density dNch/dη at midrapidity,

|

η

|

<

1, the SPD tracklets are used [29]. Giventhe close proximity of the SPD detector to the interactionpoint(thetwolayersareatradialdistancesof3.9and 7.6cm), its geometrical acceptance changes by up to 50% in the zvtx interval selected for analysis. In addition, the meannumber

ofSPD trackletsalso varied during the3-year Run2 datataking period dueto changes in the number of active SPD detector el-ements. In order to compensate forthese detectoreffects, a zvtx

andtime-dependentcorrectionfactorisappliedsuchthatthe mea-suredaverage multiplicity is equalized to a referencevalue. This

Fig. 1. Distribution

of the corrected SPD tracklets

Ncorr

trk (left) and V0 amplitude (right) for the MB events as well as the HM- and EMCal-triggered events used in the analysis. The vertical lines indicate the used multiplicity intervals (see Table2; the first bin spans from 0 to the position of the first line). For the HM-triggered events, the V0 amplitude distribution for a single data taking period is included for illustration (open squares).

reference was chosen to be the largest mean SPD tracklet mul-tiplicityobserved overtime andzvtx.Thisprocedure issimilar to

whatwasdonepreviouslyinRef. [5].Thecorrectionfactorforeach eventisrandomlysmearedusingaPoissondistributiontotakeinto accountevent-by-eventfluctuations.Inthecaseoftheevent selec-tion basedontheforwardmultiplicity measurement withthe V0 detector,thesignalamplitudesareequalizedtocompensatefor de-tectoraging andforthesmallacceptancevariationwiththeevent vertexposition.

The overall inefficiency,the productionof secondary particles duetointeractionswiththedetectormaterial andparticledecays lead to a difference betweenthe number ofreconstructed track-lets and the true primary charged-particle multiplicity Nch (see

details in Ref. [29]).Usingevents simulatedwiththe PYTHIA8.2 event generator [30] (Monash 2013 tune, Ref. [31]), the correla-tion between the tracklet multiplicity (after the zvtx-correction),

Ncorr_trk , and the generated primary charged particles Nch is

de-termined. The propagationof the simulated particles is done by GEANT 3 [32] with a full simulation of the detector response, followed by the same reconstruction procedure as for real data. The correction factor

β(

Ncorr

trk

)

=

Nch/Ncorrtrk to obtain the average

dNch

/

dη value corresponding to a given Ncorrtrk bin is computed

from the N_trkcorr–Nch correlation, shown in Fig. 2 for events

sim-ulated withPYTHIA8.2 andparticle transport through GEANT 3. As thegeneratedcharged-particlemultiplicity inMonteCarlo dif-fers from data, a corrected Nch distribution is constructed from

themeasured Ncorr_trk distributionusingBayesianunfolding.Fromit, thecorrected

β

factorsareobtained.AMonteCarloclosuretestin PYTHIA 8.2withunfolding basedon EPOS-LHC eventsis used to validatetheprocedure.

Thenormalizedcharged-particlepseudorapiditydensityineach eventclassiscalculatedas:

dNch

/

d

η



dNch

/

d

η

INEL

>0

=

β

× 

Ncorr_trk



η

× 

dNch

/

d

η

INEL

>0

,

(1) where



Ncorr

trk



is the averaged value of Ncorrtrk in each

multiplic-ity class,corrected for thetrigger andvertex finding efficiencies. The former is estimated from Monte Carlo simulations and the latter with a data driven approach. They are below unity only for the low-multiplicity events. The value corresponding to INEL

>

0 events,



dNch/dη



INEL>0, was cross-checked with the

pub-lished ALICEmeasurement [29], andis found tobe in very good agreement. A similar procedure is also used for the event se-lection based on the V0 amplitude, measured as a sum of sig-nals fromchargedparticlesinthe intervals

−

3

.

7

<

η

<

−

1

.

7 and

Fig. 2. Correlation

between the number of generated primary charged particles,

Nch, and the number of reconstructed SPD tracklets, Ncorr

trk, in |η|<1, from PYTHIA 8.2 simulated collisions with detector transport through GEANT 3. The black points rep-resent the mean values of Nch.

Table 2

Average normalized charged-particle pseudorapidity density in |η|<1 for each

event class selected in Ncorr

trk measured in SPD (|η|<1; left part) and in V0 am-plitude (−3.7 <η<−1.7 and 2.8 <η<5.1; right part). The values correspond to

the data sample used for the pT-integrated analysis. Only systematic uncertainties are shown since the statistical ones are negligible. The corresponding fraction of the INEL>0 cross section for each event class is also indicated.

SPD selection V0 selection dNch/dη dNch/dηINEL>0 σ/σINEL>0 dNch/dη dNch/dηINEL>0 σ/σINEL>0 0.23±0.01 32% 0.40±0.01 37% 0.60±0.01 25% 0.76±0.01 26% 1.23±0.02 25% 1.41±0.02 25% 2.11±0.03 11% 2.26±0.03 9.0% 2.98±0.05 4.7% 3.03±0.04 2.5% 3.78±0.06 1.8% 3.92±0.06 0.5% 4.58±0.08 0.6% 4.33±0.07 0.08% 5.37±0.09 0.2% 4.96±0.08 0.01% 6.17±0.11 0.05% 7.13±0.12 0.02%

2

.

8

<

η

<

5

.

1.The resultingvaluesofthe normalizedmultiplicity fortheeventclassesconsideredintheanalysisaresummarized in Table 2 alongsidethe respective fractions of the INEL

>

0 cross section.

Fig. 3. Top:

Invariant mass distribution of electron-positron pairs for MB (left), HM (middle) and EMCal (right) triggers, together with combinatorial background estimation

from the track-rotation method (blue lines in the left and middle panels) and the full background estimation (black squares). In the lower panels, the J/ψ signal obtained

after background subtraction is shown together with the J/ψsignal shape from Monte Carlo simulations. The entries contain a correction for the relative efficiency (see text).

The vertical lines indicate the mass range for the signal counting.

3.2. J/

ψ

signalextraction

The J/

ψ

meson is measured in the dielectron decay channel at midrapidity. Electrons and positrons are reconstructed in the centralbarreldetectorsbyrequiringaminimumof70outof max-imally 159trackpointsintheTPCandavalueofthetrackfit

χ

2

over thenumber oftrackpoints smallerthan 4[27].Only tracks with atleast two associated hitsin the ITS, andone of them in the twoinnermostlayers, areaccepted.Thisrequirementensures bothagoodtrackingresolutionandtherejectionofelectronsand positronsproducedfromphotonsconvertinginthedetector mate-rial.IntheMBandHMtriggeranalysis,afurthervetoonthetracks belonging to identified photon conversion topologies is applied. Theelectronidentificationisachievedbythemeasurementofthe specific energyloss ofthe trackin theTPC, which isrequired to be compatiblewiththat expectedforelectrons within3standard deviations.Trackswithaspecificenergylossbeingconsistentwith that of thepion orproton hypothesis within 3.5standard devia-tions arerejected. Fortheanalysisofthe EMCal-triggeredevents, the energy deposition of the track in the TPC is required to be in arange between

−

2.25to

+

3standard deviations around the mean expected value for the electrons. In addition, at least one of the J/

ψ

decay electrons is required to be matched to a clus-terintheEMCal,withaclusterenergyabovethetriggerthreshold andan energy-to-momentum ratiointhe range0

.

8

<

E

/

p

<

1

.

3. Electrons and positrons are selected in the pseudorapidity range

|

η

|

<

0

.

9 andinthetransversemomentumrangepT

>

1 GeV/c.

The numberof reconstructedJ/

ψ

isobtained fromthe invari-ant mass distribution of all the opposite-sign (OS) pairs, which contains e+e−pairsfromJ/

ψ

decaysaswellascombinatoricsand other sources. In the MB andHM trigger analysis, the combina-torialbackgroundisestimatedusingatrackrotationprocedurein which one of thetracks is rotatedby a randomazimuthal angle multiple times to obtain a high statistics invariant mass distri-bution. Thisdistributionis then normalizedsuch thatits integral over arangeoftheinvariant masswell abovetheJ/

ψ

masspeak matchestheoneofrealOSpairs,andissubtractedfromthelatter distribution.Theremainingresidualbackground,whichcanbe at-tributedtophysicalsources,e.g.correlatedsemileptonicdecaysof heavy-quark pairs, is estimated using a second-order polynomial

function. For the analysis of the EMCal-triggered events, a fit to theOSinvariantmassdistributionisperformedusingaMCshape forthesignal addedto apolynomial todescribe thebackground. Asecond- or third-order polynomial function is used, depending onthe pT range.ThenumberofJ/

ψ

isextractedbysummingthe

dielectronyield inthebackground-subtracted invariant mass dis-tribution in the mass interval 2

.

92

<

mee

<

3

.

16 GeV/c2, which

contains approximately 2/3 of the total reconstructed yield. The yieldfallingoutsideofthecountingwindowatlowinvariantmass isduetotheelectronbremsstrahlunginthedetectormaterialand totheradiativeJ/

ψ

decay,andiscorrectedforusingMonteCarlo simulations. Also, a correction forthe yield loss due to the lim-ited triggerandvertexfinding efficiencies atlow multiplicitiesis applied.

Duetothetriggerenhancement,theyields obtainedusingthe EMCal-triggeredeventswerecorrectedbythetriggerscalingfactor, whichisobservedtobeidenticalforalleventclasses.This correc-tionis necessaryto converttheyield per EMCal-triggered events intoayieldperMB-triggeredeventandisaccomplishedbya data-drivenmethodusingtheratiooftheclusterenergydistributionin triggereddata dividedby thecluster energydistribution in mini-mumbiasdata.Theratioflattensabove thetriggerthresholdand thescalingfactoristhenobtainedby fittingaconstanttotheflat interval.

InthetoppanelsofFig.3areshowntheOSinvariantmass dis-tributionforMBevents(left),ahighmultiplicityintervalfromthe HM- (middle) and EMCal-triggered events (right), together with the estimated background distribution. The combinatorial back-ground distribution from the track rotation method is shown in the left and middle panels with the blue lines, while the total backgroundis shownasblack squaresin all thepanels. The sig-nalobtainedafterbackgroundsubtractionisdescribedwellbythe signalshapeobtainedfromMonteCarlosimulations(discussed be-low); these MC templates havebeen scaled and overlaid on the datapointsinthebottompanelsofFig.3.

The J/

ψ

measurement is performed integrated in transverse momentum and in the pT intervals 0

<

pT

<

4 GeV/c and 4

<

pT

<

8 GeV/c, using the MB and HM triggers. At higher pT, the

J/

ψ

mesons are reconstructed using the EMCal triggered events in the transverse momentum intervals 8

<

pT

<

15 GeV/c and

15

<

pT

<

40 GeV/c.It was checkedthat theacceptance and

ef-ficiency for J/

ψ

reconstruction are not dependent on the event multiplicity.Thiswasperformedusingppcollisionssimulatedwith the PYTHIA 8.2event generator withan injected J/

ψ

signal. The dielectrondecayissimulatedwiththeEvtGenpackage [33] using PHOTOS [34] todescribethefinal-stateradiation.TheJ/

ψ

mesons are assumed tobe unpolarized consistentwith measurements in ppcollisionsattheLHC [35].

Toaccountforthemultiplicitydependenceofthe pT spectrum

oftheJ/

ψ

mesons,acorrection fortherelativeefficiency,namely the efficiency for a given pT value relative to the pT-integrated

value, is applied toeach dielectronpair. Thisis containedin the invariantmassdistributionsshowninFig.3.

3.3. Systematicuncertainties

Normalizedmultiplicity: Thesystematic uncertaintyon the nor-malizedmultiplicitycontainscontributionsfromthetrigger,vertex finding, andSPDefficiencies.The firsttwo contributionsare esti-mated using alternative approaches:the trigger efficiencyis cal-culated inadata-drivenway,andforthevertexfindingefficiency Monte Carlo simulations are used. The differences to the values obtainedwiththedefaultmethodsaretakenasthesystematic un-certainties. The contribution fromthe vertexfinding efficiency is below1% (relativeuncertainty) inall eventclasses,theone from thetriggerefficiencyreachesamaximumvalueof1.3%forthe low-estmultiplicityclass.

In order toestimate uncertainties dueto the SPDtracklet re-constructionefficiency,thenumberofcorrectedtrackletsisscaled upanddownby3%,whichisthemaximumobserveddiscrepancy ofthe averagenumber ofSPDtrackletsbetweendata andMonte Carlosimulations.Thisuncertaintyamountsto3.6%inthelowest multiplicity class, and to less than 1.5% in all other classes.The uncertainty fromthe unfolding of the charged-particle multiplic-ity distribution is estimatedby varying the numberof iterations usedintheBayesianunfolding,aswellasbyusingan alternative unfolding method [36]. Theuncertainty isfound tobe negligible. All theaforementioned uncertainty sources are addedin quadra-ture, leadingtoatotal uncertaintyonthenormalizedmultiplicity of3.7%forthelowestmultiplicityclass,andtolessthan2%forall otherclasses.

NormalizedJ/

ψ

yield: Thesystematicuncertaintiesofthe normal-izedJ/

ψ

yieldareduetothesignalextraction,bin-flowcausedby thePoissoniansmearingappliedforthe zvtx-dependentcorrection

of the SPD acceptance and vertex finding, trigger and SPD effi-ciencies. For the analysis of the EMCal-triggered events, there is an additionalcomponentduetothe matchingoftracksto EMCal clustersandtheelectron identificationvia the E

/

p measurement, which hasa non-negligible multiplicity dependence.The E

/

p in-terval andthevalue of E used toselectonlyelectrons above the EMCaltriggerthresholdarevariedtodeterminethesystematic un-certainty oftheelectronidentificationwiththeEMCal,leading to valuesfrom1%to12%,dependingonthemultiplicitybin.

The uncertainty ofthe J/

ψ

signal extraction isdetermined by varyingthefunctionsusedtofitthebackground(first- or second-degreepolynomialsorexponential)andthefittingranges,withthe RMSofthe distributionofnormalizedyieldsobtainedfromthese variationsbeingtakenasasystematicuncertainty(thenormalized yield corresponds to thedefault selection). The bin-floweffect is estimatedfromthe RMSofthe resultsobtainedby repeating the analysis severaltimes withdifferent seeds forthe random num-bergenerator.Theuncertaintiesfromthesignalextractionandthe bin-floweffectarethedominantones.Theyareofcomparablesize, withvaluesbetween1%and8%dependingonthemultiplicityand pT interval. The uncertainties of the vertex finding, trigger and

Fig. 4. Normalized

inclusive

pT-integrated J/ψ yield at midrapidity as a function of normalized charged-particle pseudorapidity density at midrapidity (|η|<1) with

the event selection based on SPD tracklets at midrapidity and on V0 amplitude at forward rapidity in pp collisions at √s=13 TeV. Top: normalized J/ψyield

(diag-onal drawn for reference). Bottom: double ratio of the normalized J/ψ yield and

multiplicity. The error bars show statistical uncertainties and the boxes systematic uncertainties.

SPD tracklet efficiencies affect the estimated number of INEL

>

0 collisions,andhence theevent-averagedminimumbias J/

ψ

yield



dNJ/ψ

/

d y



,aswellastheJ/

ψ

yieldinthelowmultiplicityclasses.

TheuncertaintiesofthevertexfindingandSPDefficienciesare be-low 1% in mostclasses,while the uncertaintydue tothe trigger efficiencyreachesupto4%,dependingonthemultiplicityclass.

All the mentioned sources are added in quadrature to obtain the totalsystematic uncertainty, which,for the pT-integrated

re-sults, varies between 3% and 7% with the multiplicity class. For theselected pT intervals,the uncertaintiesare larger, varying

be-tween 3% and10% withmultiplicity and pT interval, mainly due

tothesignalextraction,whichisaffectedbystatisticalfluctuations ofthe background.The results athigh pT, employing the EMCal,

haveuncertainties upto13%,whicharelargerbecauseofthe ad-ditionalselection requirementsonthe track-clustermatching and theEMCalelectronidentificationselections.

4. Resultsanddiscussion

The top panel of Fig. 4 shows the normalized J/

ψ

yield as a functionofthenormalizedcharged-particlepseudorapiditydensity atmidrapidity,dNch/dη

/



dNch/dη



.Thedashedlinealsoshownin thefigureisalinearfunctionwiththeslopeofunity.

These results include both the MB and HM triggered events, whichallowfora coverageofupto7timestheaverage charged-particlemultiplicity,wheneventsareselectedbasedon the mea-suredmidrapidity multiplicity.Thisisasignificantextension with respecttoourprevious resultsinpp collisionsat

√

s

=

7 TeV [5], where only the range up to 4 was covered and with larger un-certainties. Using the event selection based on the V0 forward multiplicity (green squares), whichshould largely remove a pos-sibleauto-correlationbias,themeasurementextendsonlyupto5 timesthe



dNch/dη



.Theresultsforthetwoeventselection meth-ods are in very good agreement. In both cases, the normalized

Fig. 5. Normalized

inclusive J/

ψyield at midrapidity as a function of normalized charged-particle multiplicity in pp collisions at √s=13 TeV, for different ranges of pTof the J/ψ meson. Left: event selection based on multiplicity at midrapidity. Right: event selection based on multiplicity at forward rapidity. The error bars show statistical

uncertainties and the boxes systematic uncertainties.

J/

ψ

yield grows significantly fasterthan linearwith the normal-izedmultiplicity.

IncludedinFig.4isalsothedoubleratioofthenormalizedJ/

ψ

yield tothe normalizedmultiplicity (bottompanel).Tworegimes could be identified, with a stronger increase of the double ra-tio for events with small multiplicity and a weaker increase for high-multiplicityevents.Itisnotedthat the“energycost”forthe production of a J/

ψ

meson, characterized by a transverse mass mT

=



m2_J/ψ

+

p2_T

/

c2

_

_{5 GeV/c}2_{,issimilartotheoneforparticle}

productionperunitrapidityoftheunderlyingMBevent,estimated as



dNch/dη

 ·

pT



.Alinear(diagonal)correlationwith

multiplic-ity is then expected to first order and observed in PYTHIA 8.2 simulations[18].AsseeninFig.4,thedataexhibitricherfeatures thanthisbaselineexpectation.

ThedatainintervalsofpToftheJ/

ψ

mesonareshowninFig.5.

ThedataexhibitasignificantincreaseofthenormalizedJ/

ψ

yield withthenormalizedmultiplicitybetweentheJ/

ψ

pTintervals0–4

and4–8GeV/c.Thiseffectcouldbeattributedtovarious contribu-tions [18],likeassociatedJ/

ψ

productionwithotherhadronsinjet fragmentationorfrombeauty-quarkfragmentation,asthefraction ofJ/

ψ

fromb-hadrondecaysincreaseswithpT [37].

Measurements of the correlation with the event multiplicity for inclusive charged-particle production have identified similar trends [11] asfortheJ/

ψ

pTdependence.Thestrengthofthis

cor-relationissimilarforJ/

ψ

andforinclusivechargedparticles (dom-inatedby pions)for pT valuesgivingacomparable mT value. The

production ofstrange hyperonsatmidrapidity was also observed to exhibit a correlation with event multiplicity in proportion to theirmass [38];astrongcorrelationwas alsomeasuredforthe

ϒ

mesons [7].

The theoretical models currently available attribute the ob-served behavior todifferent underlying processes.In the PYTHIA 8.2eventgenerator [17],multipartoninteractions(MPI)arean im-portantfactorincharm-quarkproduction.Indeed,fromMPIsalone astrongerthanlinearscalingisexpectedforopen-charm produc-tion, as was demonstrated in Ref. [6] with PYTHIA8.157. Taking into account all sources of heavy-quark production, however, a

closeto linear increase is predicted [18]. PYTHIA8.2 reproduces well theobservationin datawitha very similar correlation with multiplicityforthetwodifferentrapidityintervalsusedfor multi-plicitymeasurement,asseen intheleft panel ofFig. 6,although theoverall slopeof thetrendis underestimated.Toillustrate the effectofnon-promptJ/

ψ

intheinclusiveproduction,inFig.6the caseofpromptJ/

ψ

mesonproductionaspredictedbyPYTHIA8.2 isshowninaddition. Asignificant reduction ofthecorrelation is observed,whichappearstobestrongerfortheSPDeventselection case.

IntheEPOS3eventgenerator [15,39],initialconditionsare gen-eratedaccordingtotheparton-basedGribov-Reggeformalism [40]. Sources of particle productionin this framework are parton lad-ders, each composed of a pQCD hard process with initial- and final-state radiation. This model already predicted the stronger than linear increase with multiplicity observed for open-charm mesons [6], originating from a collective (hydrodynamical) evo-lution of the system. The predictions from EPOS3, here without thehydrodynamic component, are similar in magnitudeto those fromPYTHIA8.In thepercolationmodel [14],spatially extended colorstringsarethesources ofparticleproductioninhigh-energy hadronic collisions. In a high-density environment they overlap; such a decrease in the effective number of strings leads to a reduction in particle production. Since the transverse size of a string is determined by its transverse mass, lighter particles are affected in a stronger way than heavier ones. This results in a linearincrease ofheavy-particle productionat low multiplicities, gradually changing to a quadratic one athigh multiplicities. The coherent particle production (CPP) model [13,41] employs phe-nomenologicalparametrizationsforlight hadronsandJ/

ψ

derived fromp–Pb collisions, andpredicts a strongerthan linear relative increase of J/

ψ

production with the normalized event multiplic-ity. In the Color Glass Condensate (CGC) approach, the NRQCD framework is employed for J/

ψ

production. This effective field theory predicts, both for J/

ψ

and D mesons, a relative increase with the normalized multiplicity that is faster than linear, both for pp and p–Pb collisions [16]. In a CGC saturation model, a

Fig. 6. Left:

Comparison of data and PYTHIA 8.2 predictions for the two methods of event selection. For PYTHIA 8.2, the case of prompt J/

ψmeson production is included

for illustration. Right: comparison of data (with SPD event selection) with model predictions from the coherent particle production model [13], the percolation model [14], the EPOS3 event generator [15], the CGC model [16], the 3-Pomeron CGC model [19], and PYTHIA 8.2 predictions. Except for the latter, none of the models include the non-prompt component.

Fig. 7. Normalized

inclusive J/

ψ yield at midrapidity as a function of normalized charged-particle pseudorapidity density at midrapidity for different pTintervals; the data are compared to theoretical model predictions from PYTHIA 8.2.

faster thanlinear trendgenerically arisesfromthe Bjorken-x de-pendent saturation scale which would suppress more the soft-particlemultiplicity,produced atlow-x,compared toJ/

ψ

produc-tion which is sensitive to larger values of x. In the 3-Pomeron fusion model[19],the correlationarisesasJ/

ψ

productionvia 3-gluon fusion processes from various Pomeron configurations are considered. The larger configurationspace forthe particularcase of the overlapping rapidity interval for J/

ψ

and charged parti-cles leads to a significantly stronger correlation. Gluon satura-tion is implemented in this model; its effect, interestingly a re-duced correlation, becomes significant for normalized multiplici-tiesabove 7.

All models predict an increase which is faster than linear, as shownintherightpanelofFig.6.Inall modelsthisiseffectively the resultofa (Nch-dependent) reductionof thecharged-particle

multiplicity,realizedthroughratherdifferentphysics mechanisms in the various approaches (color string reconnection or percola-tion,gluonsaturation,coherentparticleproduction,3-gluonfusion

in gluon ladders/Pomerons). The PYTHIA 8.2 and EPOS3 models underpredictthe data,whilethe percolationmodelslightly over-predictsthemathighmultiplicity;goodagreementisseenforthe CGC,the coherentparticle production,and the 3-Pomeron mod-els.

Theseobservationsneedtobeconsidered havinginmindthat inall models exceptPYTHIA8.2only the promptJ/

ψ

production isincluded.AsillustratedinFig.6forPYTHIA8.2,thepromptJ/

ψ

mesonproductionexhibitsaweaker relativeincrease with multi-plicitycompared totheinclusiveproduction.The agreementwith data will improvein case of EPOS3 and will degrade for all the other models, ina consistent comparison. Thatcould be realized eitheroncethedataforthepromptcomponentwillbecome avail-able oras soon asthe non-prompt component will be added to thecurrentmodelpredictions.

Thecontributionfromdecaysofbeautyhadronsincreases sig-nificantly with pT [37] and might also have a different

beautyproduction [6] isnotpreciseenoughtobeconclusive,buta studyinPYTHIA8.2 [18] showedthat thefeed-downfrombeauty hadronsinfluencestheresult.Thetrendofstrongerincreaseinthe pT intervalsabove4GeV/c seeninthedataisqualitatively

repro-ducedbyPYTHIA8.2,which,however,underestimatesthedatafor pT

<

8 GeV/c,asshowninFig.7.

5. Summaryandconclusions

Wehavepresentedacomprehensivemeasurementofinclusive production ofJ/

ψ

mesons asa function ofthe eventmultiplicity in pp collisions at

√

s

=

13 TeV performed withthe ALICE appa-ratus. The J/

ψ

production at midrapidity is studied using a data sample including minimum bias, high event activity, and EMCal triggered events. The event selection is performedbased on the charged-particle measurement atmidrapidity andin the forward region. The J/

ψ

yield in a given multiplicity interval normalized to the J/

ψ

yield in INEL

>

0 collisions is presented as a func-tion ofthecharged-particle multiplicitysimilarly normalized.The advantageofsucharepresentationisthatmostofthe experimen-tal systematic uncertainties cancel; also, some of the theoretical modeluncertaintiesaremitigatedforsuchnormalizedyields.

AstrongerthanlinearincreaseoftherelativeproductionofJ/

ψ

asa function ofmultiplicity is observed for pT-integratedyields;

this increase is stronger for high-pT J/

ψ

mesons. The trends are

qualitatively, and for some of the models quantitatively, repro-duced by theoretical models, buta critical appraisal of the sim-ilarity or difference between the physics mechanisms at play in variousmodelsisyettobeperformed.Morestringenttestsofthe modelsare neededtoo.Disentanglingthefeed-downfrombeauty hadrons, not included in mostof the current theoretical predic-tions, will be an important step towards shedding light on the mechanismofhadronizationofcharm(andbeauty)quarks,in par-ticularintheenvironmentofahighdensityofcolorstringscreated inhigh-multiplicity pp collisions.Data which willbe collected in Run3attheLHCwillbeasignificantadditionforsuchstudies.

Declarationofcompetinginterest

Theauthorsdeclarethattheyhavenoknowncompeting finan-cialinterestsorpersonalrelationshipsthatcouldhaveappearedto influencetheworkreportedinthispaper.

Acknowledgements

We aregratefulto E.Ferreiro,B. Kopeliovich,E.Levin, M. Sid-dikov,R.Venugopalan,K.Watanabe,andK.Wernerforsendingus thepredictionsofandclarificationsabouttheirmodels.

The ALICE Collaboration would like to thank all its engineers andtechniciansfortheirinvaluablecontributionstothe 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-videdbyallGridcentresandtheWorldwideLHCComputingGrid (WLCG) collaboration. The ALICE Collaboration acknowledges the following fundingagenciesfortheir supportinbuildingand run-ningthe ALICEdetector:A.I. AlikhanyanNationalScience Labora-tory(YerevanPhysicsInstitute)Foundation (ANSL),State Commit-teeofScienceandWorldFederationofScientists(WFS),Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M 2467-N36] and Nationalstiftung für Forschung, Technologie und Entwicklung,Austria;MinistryofCommunicationsandHigh Tech-nologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de DesenvolvimentoCientífico e Tecnológico (CNPq), Fi-nanciadora de Estudose Projetos(Finep), Fundação de Amparoà

Pesquisa doEstado de São Paulo (FAPESP)andUniversidade Fed-eraldoRioGrandedoSul(UFRGS),Brazil;MinistryofEducationof China (MOEC),MinistryofScience & Technologyof China(MSTC) andNational NaturalScience Foundation ofChina (NSFC),China; Ministry of Science and Education and Croatian Science Foun-dation, Croatia; Centro de Aplicaciones Tecnológicas yDesarrollo Nuclear (CEADEN),Cubaenergía,Cuba;The Ministryof Education, Youth and Sports of the Czech Republic, Czech Republic; Dan-ishCouncilforIndependentResearchNaturalSciences,theVillum Fonden and Danish National Research Foundation (DNRF), Den-mark;Helsinki InstituteofPhysics (HIP),Finland; Commissariatà l’Énergie Atomique (CEA) and Institut National de Physique Nu-cléaire etdePhysique desParticules (IN2P3)andCentre National de la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum fürSchwerionenforschungGmbH,Germany;GeneralSecretariatfor ResearchandTechnology,MinistryofEducation,Researchand Re-ligions,Greece;NationalResearchDevelopmentandInnovation Of-fice,Hungary;DepartmentofAtomicEnergy,GovernmentofIndia (DAE),DepartmentofScienceandTechnology,GovernmentofIndia (DST),University Grants Commission, Governmentof India(UGC) andCouncil ofScientificandIndustrial Research(CSIR),India; In-donesian Institute of Science, Indonesia; Centro Fermi - Museo StoricodellaFisicaeCentroStudieRicercheEnricoFermiand Isti-tutoNazionalediFisicaNucleare(INFN),Italy;Institutefor Innova-tiveScienceandTechnology,NagasakiInstitute ofAppliedScience (IIST),JapaneseMinistryofEducation,Culture,Sports,Scienceand Technology(MEXT)andJapanSocietyforthePromotionofScience (JSPS)KAKENHI, Japan;ConsejoNacionalde Ciencia(CONACYT) y Tecnología, through Fondode Cooperación Internacional en Cien-ciayTecnología(FONCICYT)andDirecciónGeneraldeAsuntosdel PersonalAcademico(DGAPA,UNAM),Mexico;Nederlandse Organ-isatievoor WetenschappelijkOnderzoek(NWO),Netherlands; The ResearchCouncilofNorway, Norway;CommissiononScience and TechnologyforSustainableDevelopmentintheSouth(COMSATS), Pakistan;PontificiaUniversidadCatólicadelPerú,Peru;Ministryof Science andHigher Education,National Science Centre and WUT ID-UB,Poland;KoreaInstituteofScienceandTechnology Informa-tion and National Research Foundation of Korea (NRF), Republic of Korea;Ministry of Education and Scientific Research, Institute of Atomic Physics and Ministry of Research and Innovation and InstituteofAtomicPhysics,Romania;JointInstituteforNuclear Re-search (JINR), Ministry of Education and Science of the Russian Federation, National Research Center “Kurchatov Institute”, Rus-sianScienceFoundationandRussianFoundationforBasicResearch, Russia;Ministry ofEducation, Science,Research andSportofthe Slovak Republic, Slovakia; National ResearchFoundation ofSouth Africa,SouthAfrica;SwedishResearchCouncil(VR)andKnut& Al-iceWallenbergFoundation(KAW),Sweden;EuropeanOrganization forNuclearResearch,Switzerland;SuranareeUniversityof Technol-ogy(SUT), NationalScience andTechnology DevelopmentAgency (NSDTA) and Office of the Higher Education Commission under NRUprojectofThailand,Thailand;Turkish AtomicEnergyAgency (TAEK),Turkey;NationalAcademyofSciencesofUkraine,Ukraine; ScienceandTechnology FacilitiesCouncil (STFC),UnitedKingdom; NationalScienceFoundationoftheUnitedStatesofAmerica(NSF) andUnitedStatesDepartmentofEnergy, OfficeofNuclearPhysics (DOENP),UnitedStatesofAmerica.

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N. Bianchi

52

,

J. Bielˇcík

37

,

J. Bielˇcíková

95

,

A. Bilandzic

105

,

G. Biro

145

,

R. Biswas

3

,

S. Biswas

3

,

J.T. Blair

119

,

D. Blau

88

,

C. Blume

68

,

G. Boca

139

,

F. Bock

96

,

A. Bogdanov

93

,

S. Boi

23

,

J. Bok

61

,

L. Boldizsár

145

,

A. Bolozdynya

93

,

M. Bombara

38

,

G. Bonomi

140

,

H. Borel

137

,

A. Borissov

93

,

H. Bossi

146

,

E. Botta

25

,

L. Bratrud

68

,

P. Braun-Munzinger

107

,

M. Bregant

121

,

M. Broz

37

,

E. Bruna

59

,

G.E. Bruno

33

,

106

,

M.D. Buckland

127

,

D. Budnikov

109

,

H. Buesching

68

,

S. Bufalino

30

,

O. Bugnon

115

,

P. Buhler

114

,

P. Buncic

34

,

Z. Buthelezi

72

,

131

,

J.B. Butt

14

,

S.A. Bysiak

118

,

D. Caffarri

90

,

A. Caliva

107

,

E. Calvo Villar

112

,

J.M.M. Camacho

120

,

R.S. Camacho

45

,

P. Camerini

24

,

F.D.M. Canedo

121

,

A.A. Capon

114

,

F. Carnesecchi

26

,

R. Caron

137

,

J. Castillo Castellanos

137

,

A.J. Castro

130

,

E.A.R. Casula

55

,

F. Catalano

30

,

C. Ceballos Sanchez

75

,

P. Chakraborty

49

,

S. Chandra

141

,

W. Chang

6

,

S. Chapeland

34

,

M. Chartier

127

,

S. Chattopadhyay

141

,

S. Chattopadhyay

110

,

A. Chauvin

23

,

C. Cheshkov

135

,

B. Cheynis

135

,

V. Chibante Barroso

34

,

D.D. Chinellato

122

,

S. Cho

61

,

P. Chochula

34

,

T. Chowdhury

134

,

P. Christakoglou

90

,

C.H. Christensen

89

,

P. Christiansen

81

,

T. Chujo

133

,

C. Cicalo

55

,

L. Cifarelli

10

,

26

,

L.D. Cilladi

25

,

F. Cindolo

54

,

M.R. Ciupek

107

,

G. Clai

54

,

ii

,

J. Cleymans

124

,

F. Colamaria

53

,

D. Colella

53

,

A. Collu

80

,

M. Colocci

26

,

M. Concas

59

,

iii

,

G. Conesa Balbastre

79

,

Z. Conesa del Valle

78

,

G. Contin

24

,

60

,

J.G. Contreras

37

,

T.M. Cormier

96

,

Y. Corrales Morales

25

,

P. Cortese

31

,

M.R. Cosentino

123

,

F. Costa

34

,

S. Costanza

139

,

P. Crochet

134

,

E. Cuautle

69

,

P. Cui

6

,

L. Cunqueiro

96

,

D. Dabrowski

142

,

T. Dahms

105

,

A. Dainese

57

,

F.P.A. Damas

115

,

137

,

M.C. Danisch

104

,

A. Danu

67

,

D. Das

110

,

I. Das

110

,

P. Das

86

,

P. Das

3

,

S. Das

3

,

A. Dash

86

,

S. Dash

49

,

S. De

86

,

A. De Caro

29

,

G. de Cataldo

53

,

J. de Cuveland

39

,

A. De Falco

23

,

D. De Gruttola

10

,

N. De Marco

59

,

S. De Pasquale

29

,

S. Deb

50

,

H.F. Degenhardt

121

,

K.R. Deja

142

,

A. Deloff

85

,

S. Delsanto

25

,

131

,

W. Deng

6

,

P. Dhankher

49

,

D. Di Bari

33

,

A. Di Mauro

34

,

R.A. Diaz

8

,

T. Dietel

124

,

P. Dillenseger

68

,

Y. Ding

6

,

R. Divià

34

,

D.U. Dixit

19

,

Ø. Djuvsland

21

,

U. Dmitrieva

62

,

A. Dobrin

67

,

B. Dönigus

68

,

O. Dordic

20

,

A.K. Dubey

141

,

A. Dubla

90

,

107

,

S. Dudi

100

,

M. Dukhishyam

86

,

P. Dupieux

134

,

R.J. Ehlers

96

,

V.N. Eikeland

21

,

D. Elia

53

,

B. Erazmus

115

,

F. Erhardt

99

,

A. Erokhin

113

,

M.R. Ersdal

21

,

B. Espagnon

78

,

G. Eulisse

34

,

D. Evans

111

,

S. Evdokimov

91

,

L. Fabbietti

105

,

M. Faggin

28

,

J. Faivre

79

,

F. Fan

6

,

A. Fantoni

52

,

M. Fasel

96

,

P. Fecchio

30

,

A. Feliciello

59

,

G. Feofilov

113

,

A. Fernández Téllez

45

,

A. Ferrero

137

,

A. Ferretti

25

,

A. Festanti

34

,

V.J.G. Feuillard

104

,

J. Figiel

118

,

S. Filchagin

109

,

D. Finogeev

62

,

F.M. Fionda

21

,

G. Fiorenza

53

,

F. Flor

125

,

A.N. Flores

119

,

S. Foertsch

72

,

P. Foka

107

,

S. Fokin

88

,

E. Fragiacomo

60

,

U. Frankenfeld

107

,

U. Fuchs

34

,

C. Furget

79

,

A. Furs

62

,

M. Fusco Girard

29

,

J.J. Gaardhøje

89

,

M. Gagliardi

25

,

A.M. Gago

112

,

A. Gal

136

,

C.D. Galvan

120

,

P. Ganoti

84

,

C. Garabatos

107

,

J.R.A. Garcia

45

,

E. Garcia-Solis

11

,

K. Garg

115

,

C. Gargiulo

34

,

A. Garibli

87

,

K. Garner

144

,

P. Gasik

105

,

107

,

E.F. Gauger

119

,

M.B. Gay Ducati

70

,

M. Germain

115

,

J. Ghosh

110

,

P. Ghosh

141

,

S.K. Ghosh

3

,

M. Giacalone

26

,

P. Gianotti

52

,

P. Giubellino

59

,

107

,

P. Giubilato

28

,

A.M.C. Glaenzer

137

,

P. Glässel

104

,

A. Gomez Ramirez

74

,

V. Gonzalez

107

,

143

,

L.H. González-Trueba

71

,

S. Gorbunov

39

,

L. Görlich

118

,

A. Goswami

49

,

S. Gotovac

35

,

V. Grabski

71

,

L.K. Graczykowski

142

,

K.L. Graham

111

,

L. Greiner

80

,

A. Grelli

63

,

C. Grigoras

34

,

V. Grigoriev

93

,

A. Grigoryan

1

,

S. Grigoryan

75

,

O.S. Groettvik

21

,

F. Grosa

30

,

59

,

J.F. Grosse-Oetringhaus

34

,

R. Grosso

107

,

R. Guernane

79

,

M. Guittiere

115

,

K. Gulbrandsen

89

,

T. Gunji

132

,

A. Gupta

101

,

R. Gupta

101

,

I.B. Guzman

45

,

R. Haake

146

,

M.K. Habib

107

,

C. Hadjidakis

78

,

H. Hamagaki

82

,

G. Hamar

145

,

M. Hamid

6

,

R. Hannigan

119

,

M.R. Haque

63

,

86

,

A. Harlenderova

107

,

J.W. Harris

146

,

A. Harton

11

,

J.A. Hasenbichler

34

,

H. Hassan

96

,

Q.U. Hassan

14

,

D. Hatzifotiadou

10

,

54

,

P. Hauer

43

,

L.B. Havener

146

,

S. Hayashi

132

,

S.T. Heckel

105

,

E. Hellbär

68

,

H. Helstrup

36

,

A. Herghelegiu

48

,

T. Herman

37

,

E.G. Hernandez

45

,

G. Herrera Corral

9

,

F. Herrmann

144

,

K.F. Hetland

36

,

H. Hillemanns

34

,

C. Hills

127

,

B. Hippolyte

136

,

B. Hohlweger

105

,

J. Honermann

144

,

D. Horak

37

,

A. Hornung

68

,

S. Hornung

107

,

R. Hosokawa

15

,

133

,

P. Hristov

34

,

C. Huang

78

,

C. Hughes

130

,

P. Huhn

68

,

T.J. Humanic

97

,

H. Hushnud

110

,

L.A. Husova

144

,

N. Hussain

42

,

S.A. Hussain

14

,

D. Hutter

39

,

J.P. Iddon

34

,

127

,

R. Ilkaev

109

,

H. Ilyas

14

,

M. Inaba

133

,

G.M. Innocenti

34

,

M. Ippolitov

88

,

A. Isakov

95

,

M.S. Islam

110

,

M. Ivanov

107

,

V. Ivanov

98

,

V. Izucheev

91

,

B. Jacak

80

,

N. Jacazio

34

,

54

,

P.M. Jacobs

80

,

S. Jadlovska

117

,

J. Jadlovsky

117

,

S. Jaelani

63

,

C. Jahnke

121

,

M.J. Jakubowska

142

,

M.A. Janik

142

,

T. Janson

74

,

M. Jercic

99

,

O. Jevons

111

,

M. Jin

125

,

F. Jonas

96

,

144

,

P.G. Jones

111

,

J. Jung

68

,

M. Jung

68

,

A. Jusko

111

,

P. Kalinak

64

,

A. Kalweit

34

,

V. Kaplin

93

,

S. Kar

6

,

A. Karasu Uysal

77

,

D. Karatovic

99

,

O. Karavichev

62

,

T. Karavicheva

62

,