Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at √s = 13 TeV

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Physics Letters B

www.elsevier.com/locate/physletb

Pseudorapidity and transverse-momentum distributions of charged particles in proton–proton collisions at √

s = ^{13 TeV}

.ALICE Collaboration

a r t i c l e i n f o a b s t ra c t

Articlehistory:

Received5October2015

Receivedinrevisedform20November2015 Accepted9December2015

Availableonline15December2015 Editor:W.-D.Schlatter

The pseudorapidity(η) and transverse-momentum (pT) distributions ofchargedparticlesproduced in proton–proton collisions are measuredatthe centre-of-massenergy √

s=^{13 TeV.} ^The pseudorapidity distributionin|η_|<1.8 isreportedforinelasticeventsandforeventswithatleastonechargedparticle in|η_|<1.Thepseudorapiditydensityofchargedparticlesproducedinthepseudorapidityregion|η_|<

0.5 is5.31±⁰.18 and 6.46±⁰.19 for thetwo event classes,respectively. Thetransverse-momentum distributionofchargedparticlesismeasuredintherange0.15<pT<20 GeV/cand|η_|<0.8 forevents with atleast one charged particlein |η_|<1.The evolution of the transverse momentumspectra of chargedparticlesisalsoinvestigatedasafunctionofeventmultiplicity.Theresultsare comparedwith calculationsfromPYTHIAandEPOSMonteCarlogenerators.

©²⁰¹⁵^CERN^for^the^benefitôf^theÂLICECollaboration.PublishedbyElsevierB.V.Thisisanopen accessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP³.

1. Introduction

After a two-year long shutdown, the Large Hadron Collider (LHC)atCERNrestartedits physicsprogrammeinJune2015with proton–proton collisions at √

s=^{13 TeV,} ^the ^highest ^centre-of- massenergyreachedsofarinlaboratory.Themeasurementofthe inclusive production of charged hadrons in high-energy proton–

protoninteractions is a key observable to characterise the global properties of the collision, in particular whenever the collision energyincreasessigniﬁcantly. Particleproductionatcolliderener- giesoriginatesfromtheinterplayofperturbative(hard)andnon- perturbative (soft) QCD processes. Soft scattering processes and partonhadronisation dominatethebulk of particleproductionat low transverse momentaand canonly be modelled phenomeno- logically.Hence,thesemeasurementsprovideconstraintsforabet- tertuningofmodelsandeventgeneratorsforhadron-colliderand cosmic-rayphysics[1].

We present the pseudorapidity (

η

) and transverse-momentum (pT) distributions of primary chargedparticles measured in proton–protoncollisionsatthecentre-of-massenergy√

s=^{13 TeV} withthe ALICEdetector[2]at theLHC [3].Primary particles are deﬁnedas prompt particles produced in the collisions, including alldecayproducts,withtheexception ofthosefromweakdecays of strange particles. Similar measurements have been performed byALICEinproton–proton(pp),proton–lead(p–Pb)andlead–lead (Pb–Pb)collisions collectedduring theprevious LHCrun atlower

E-mailaddress:[email protected].

energies [4–14]. The pseudorapidity distribution is measured at centralrapidityin|

η

|<1.8.Themeasurementsreportedherehave beenobtainedforinelasticevents(INEL)andeventshavingatleast one chargedparticleproduced with pT>0 in thepseudorapidity interval|

η

|<1 (INEL>0).Similarresultswererecentlypublished by the CMS Collaboration for INEL events [15]. The transverse- momentum distribution of charged particles is measured in the range0.15<p_T<20 GeV/c and|

η

|<0.8 forINEL>0 events.The evolutionofthetransversemomentumspectraofchargedparticles is also investigated asa function of event multiplicity. The data havebeencomparedtocalculationsfrommodels commonlyused attheLHC.

2. TheALICEdetectoranddatacollection

A comprehensivedescription of the ALICEexperimental setup canbe foundin [2,16].Themain detectorsutilisedfortheanaly- sis presentedherearethe InnerTrackingSystem(ITS), theTime- ProjectionChamber(TPC), theV0countersandtheALICEDiffrac- tive (AD) detector. The ITSand TPC detectors,which are located insideasolenoidalmagnetprovidingamagneticﬁeldof0.5 T,are usedforprimary-vertexandtrackreconstruction.TheV0counters and the AD detector are employed for triggering and for back- groundsuppression.

TheITSiscomposedofsixcylindricallayers ofhigh-resolution silicontrackingdetectors.The innermostlayersconsist oftwoar- raysofhybridSiliconPixelDetectors(SPD)locatedatradii3.9and 7.6 cm from the beam axis and covering respectively |

η

_|<2.0 and |

η

_|<1.4 for particles emerging from the nominal interac- http://dx.doi.org/10.1016/j.physletb.2015.12.030

0370-2693/©²⁰¹⁵^CERN^for^the^benefitôf^theÂLICECollaboration.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP³.

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tion point (z =^{0 cm).} ^The ^TPC îs â ^large cylindrical drift detector of radial and longitudinal size of about 85<r<250 cm and−²⁵⁰<z<250 cm,respectively.Theactivevolumeofnearly 90 m³ isfilled with an Ar–CO₂ (88–12%) gas mixture andis di- videdinto twohalvesby acentral high-voltagemembranemain- tainedat−^{100 kV.} ^The^two ênd-capsâreêach êquipped^with³⁶ multi-wireproportionalchamberswithcathodepadreadout,com- prising a total of 558 000 readoutchannels. The V0 countersare twoscintillatorhodoscopesplacedoneithersideoftheinteraction regionat z=³.3 m and z= −⁰.9 m, coveringthepseudorapidity regions 2.8<

η

<5.1 and −³.7<

η

<−¹.7, respectively.The AD detectorwas integratedinALICEduringtheLHCshutdownbefore Run2toenhancethecapabilitiesoftheexperimenttotagdiffrac- tive processes and low pT events [17]. It consists oftwo double layers ofscintillationcounters placedfarfromthe interactionre- gion, on both sides: one in the ALICE cavern at z=17.0 m and oneintheLHCtunnelatz= −¹⁹.5 m. Thepseudorapiditycover- ageof thetwo AD arraysis 4.8<

η

<6.3 and −⁷.0<

η

<−⁴.9, respectively.

Thedatawere collectedafterthestartupofLHCRun2inJune 2015.Beamsconsistingof39buncheswerecirculatinginthema- chine,withabout8×¹⁰⁹^protons^per^bunch.În^theÂLICEînterac- tionregion,15pairsofbuncheswere colliding,leadingtoalumi- nosityofabout5×¹⁰²⁷^cm⁻²^s⁻¹^.^This^valuecorrespondstoarate ofabout350 Hzforinelasticproton–protoncollisions.The proba- bilitythata recordedeventcontains morethanone collisionwas estimatedtobearound10⁻³,whichisconsistentwiththefraction ofeventscontaining morethanone distinctvertexandtaggedas pileup.Theluminous regionhadanRMSwidthofabout5 cm in the z directionandabout85 μm inthe transversedirection. The datawere collected usinga minimum-biastriggerrequiringa hit ineithertheV0scintillatorsorintheADarrays.Theeventswere recorded incoincidence with the arrival of protonbunches from both directions. Control triggers taken for various combinations ofbeamandemptybuckets wereusedtomeasurebeam-induced andaccidental backgrounds. The contamination frombackground events is removed offline by using the timing information from theV0andtheADdetectors,whichhaveatimeresolutionbetter than 1 ns. Backgroundevents are also rejectedby exploitingthe correlation betweenthe numberof clustersofpixel hitsandthe numberoftracklets(shorttracksegmentspointingtotheprimary vertex) inthe SPD. From the analysisof control triggers itis estimated that the remaining backgroundfraction inthe sample is lessthan10⁻⁴ andcanbeneglected.

3. Eventselectionanddataanalysis

About1.5million eventspassthe minimum-biasselectioncri- teria.Eventsusedforthedataanalysisarefurtherrequiredtohave avalidreconstructedvertexwithin|^z|<10 cm.Allcorrectionsare calculatedusing a sample ofabout4 million MonteCarlo events fromthePYTHIA 6[18](Perugia-2011 [19]) eventgeneratorwith particletransportperformedvia aGEANT3 [20]simulationofthe ALICEdetector.

The analysistechnique employed for the measurement ofthe charged-particlepseudorapiditydistributionisbasedontherecon- struction of tracklets, which are built using the position of the reconstructedprimaryvertexandtwohits,oneoneachSPDlayer.

Detailson thealgorithm fortrackletreconstruction are described in[4].Thistechniqueeffectivelyallowstoreconstructchargedpar- ticles with pT above the 50 MeV/c cut-off determined by parti- cleabsorptioninthematerial.Thecharged-particlepseudorapidity density is obtained from the measured distribution of tracklets dNtracklets/d

η

asdNch/d

η

₌

α

(1−β)dNtracklets/d

η

.Thecorrection

α

accountsforthe acceptanceandeﬃciencyforaprimary parti-

Table 1

Summaryoftherelativesystematicuncertainties(expressedin%)contributingto themeasurementofthecharged-particlepseudorapidityandtransverse-momentum distributions.ThevaluesforthedNch/dηanalysisarereportedseparatelyforthe INELandINEL>0 classes.ForthedNch/dpTanalysisthepTdependenceissum- marisedwiththevaluesat0.15and20 GeV/cfortheINEL>0 class.

dNch/dη dNch/dpT INEL INEL>0 0.15 20 GeV/c Background events and pileup Negligible Negligible

Normalisation 2.8 2.3 2.3

Detector acceptance and eﬃciency 1.5 1.8 5.6

Material budget 0.1 1.5 0.2

Track(let) selection criteria Negligible 1.5 3.0

Particle composition 0.2 0.3 2.4

Weak decays of strange hadrons 0.5 3.4 0.4

Zero-pTextrapolation 1.0 Not applicable

Total (η,pTdependent) 1.9 4.4 6.8

Total 3.4 3.0 5.0 7.2

cleto producea tracklet,while β isthe contamination ofrecon- structed tracklets fromcombinationsofhitsnot produced by the same primary particle. Both correction factors are determined as a function ofthe z positionof theprimary vertexandthe pseu- dorapidityofthetrackletfromdetectorsimulationsandarefound tobeonaverage1.5and0.01,respectively.Thevertexpositionre- quirementresultsinaneffective|

η

|<1.8 coverage.Differencesin strange-particle content between data and simulations, observed atlower beamenergies [21,22],aretakenintoaccountby scaling thestrangenessproductionintheMonteCarloeventsampleby a factor1.85(strangenesscorrection),resultinginafurthercontami- nationcorrectionofabout1%.

Thetransverse-momentumdistributionismeasuredfromtracks reconstructed usingthe informationfromthe ITSandTPCdetec- tors. Candidate tracks are selected with cuts on the number of spacepoints usedfortrackingandonthe qualityofthetrackﬁt, aswellasonthedistanceofclosestapproachtothereconstructed vertex. Details on the track-reconstruction algorithm andquality cutscanbefoundin[10,11,14].Therequirementsappliedfortrack selectionresultinaneffective|

η

|<0.8 acceptance.Theeﬃciency fortrackreconstructionandselectiondependsontheparticletype and it isknown that PYTHIA 6 does not reproduce correctlythe particle fractions measured at √

s=7 TeV.A reweighting of the Monte Carloeﬃciencies foreach species withthe relative abun- dances measured in minimum-bias pp collisions at √

s=^{7 TeV} [21,22] is performed.The overall primary charged-particle reconstruction eﬃciency for |

η

|<0.8 increases sharply from 34% at 150 MeV/c, reaches 73% at 0.8 GeV/c, decreases moderately to 67% for pT=^{2 GeV}/c andrisesagainto reacha saturationvalue of74% at10 GeV/c. Theminimumaround 2 GeV/c arisesdueto the azimuthal segmentation oftheTPCreadout chambers. Tracks of moderate pT, which may not have enough hits in adjacent azimuthal sectors, do not pass the selection criteria. Finally, the residualcontaminationfromsecondaryparticlesissubtractedfrom the spectrum; this contamination, estimated from Monte Carlo simulations, is 7% forourlowest pT binanddecreases below 1%

forp_T>2 GeV/c.

4. Systematicuncertainties

Asummary ofthecontributions totherelative systematicuncertainties ofthe charged-particle pseudorapidity andtransverse- momentumdistributionsisreportedinTable 1.

One ofthe maincontributions tothe normalisationofthe results comes from the limited knowledge of cross-sections and

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kinematics of diffractive processes. For proton–proton collisions at √

s=13 TeV there is not yet any experimental information available aboutdiffractive processes, thereforetrigger and event- selection efficiency corrections are solely based on previous ex- perimentaldata atlower collision energies andsimulations with Monte Carloevent generators. The corresponding systematic uncertainty has been evaluated by varying the fractions of single- diffractive (SD) and double-diffractive (DD) events produced by PYTHIA 6(Perugia-2011)by±^50%ôf^their^nominal^valuesât√

s= 13 TeV.The resultingcontributiontothe systematicuncertainties forINELandINEL>0 eventsisestimatedtobeabout2%and1.2%, respectively.Toestimatesystematicuncertaintiesassociatedtothe modeldependence of the normalisation correction we employed PYTHIA 8[23](Monash-2013[24]),whichshowslargedifferences bothinthemultiplicityandtransverse-momentumdistributionsof chargedparticleswithrespecttoPYTHIA 6,especiallyindiffractive events[25].A differenceofabout0.4%and2%isobservedforINEL andINEL>0 events,respectively.Finally,anuncertaintyof2%has beenestimatedby varying the oﬄineevent-selection criteriaap- pliedtothetriggerdetectorswhichonlyaffectsthenormalisation oftheINELsample.

Thesystematicuncertaintiesforthetransverse-momentumdis- tribution analysis are evaluated in a similar way as in previous analysesofpp[9,10],p–Pb[11,12],andPb–Pb[14]data.Thedom- inantsourcesofuncertaintyarethetrackselections,theeﬃciency correctionsand, forlow p_T,thecontamination fromweakdecays ofstrange hadrons. The systematicuncertainties forthe pseudorapidity distribution analysisare discussed in the following. The uncertaintyin detector acceptanceand eﬃciency isestimated to beabout1.5%, determinedfromthe changeofthemultiplicity at a given

η

by varying the range of the z position of the vertex andperforming the measurement in differentruns. The material budgetintheALICEcentralbarrel|

η

|<1 is knownwitha preci- sionof about 5% [16]. The corresponding systematicuncertainty, obtainedby varyingthe materialbudget inthe simulation,is es- timatedtobe about0.1% andisnegligibly smallcompared tothe othersources. Thesensitivitytotrackletselectioncriteriawas es- timatedvarying the selectionrequirements andisnegligible. The uncertainty due to the particle composition is estimated to be about0.2%andwas determinedbychangingtherelativefractions ofchargedkaonsandprotonswithrespect tochargedpionspro- duced by the Monte Carlo generator by ±^30%. ^The uncertainty resultingfromthesubtractionofthecontaminationfromweakde- caysof strangehadronsis estimatedtoamount toabout0.5% by varyingthe strangenesscorrection by ±^30%. ^Theuncertainty due tothecorrection downtozerop_Tisestimatedtobeabout1% by varyingtheamountofparticlesbelowthe50 MeV/clow-pTcutoff by⁺₋¹⁰⁰₅₀ %.

5. Results

Fig. 1shows the average charged-particle density distribution ^dNch/d

η

^measuredⁱⁿÎNELândÎNEL>0 eventsinthepseudora- pidityrange|

η

_|<1.8.Thedatapointshavebeensymmetrisedav- eragingtheresultsobtainedin ±

η

,whichwereconsistent within statisticaluncertainties. The corresponding pseudorapidity densi- tiesin|

η

_|<0.5 are5.31±⁰.18 and6.46±⁰.19,respectively.The pseudorapidity densityfor the INEL>0 events is also measured in |

η

|<1 for direct comparison with INEL>0 results reported byALICEatlower energies [5]andis 6.61±⁰.20.Alsoshownin Fig. 1aretheresultsrecentlypublishedby theCMSCollaboration forinelastic collisions[15],whichagree,within theuncertainties, with the measurement presented here. We compared our mea- surementto Monte Carlo calculations performedwith PYTHIA 6 [18] (Perugia-2011 [19]), PYTHIA 8 [26] (Monash-2013 [24]) and

Fig. 1.Averagepseudorapiditydensityofchargedparticlesasafunctionofηpro- ducedinppcollisionsat√

s=^{13 TeV.}^The^ALICE^results^are^shownⁱⁿ^the^normali- sationclassesINELandINEL>0 andcomparedtoMonteCarlocalculations[18,19, 24,26–28]andtotheresultsfromtheCMSCollaboration[15].Theuncertaintiesare thequadraticsumofstatisticalandsystematiccontributions.

Fig. 2.Charged-particlepseudorapiditydensitymeasuredinthecentral pseudora- pidityregion|η|<0.5 forINELandINEL>0 events[4–6,15,29–33].Theuncertain- tiesarethequadraticsumofstatisticalandsystematiccontributions.Thelinesare power-lawﬁtsoftheenergydependenceofthedataandthegreybandsrepresent thestandarddeviationoftheﬁts.

EPOS LHC¹ [27,28] in both the INEL and INEL>0 event classes.

PYTHIA 6calculationsareinbetteragreementwiththedatathan PYTHIA 8 in both classes, with PYTHIA 8 beinghigher than the data by about 12% (7%) in INEL events and about 7% (3%) in INEL>0 events at

η

_∼0 (

η

_∼1.5). EPOS LHC calculations are about7%(4%)andabout7%(5%)higherthanthedatainINELand INEL>0 events,respectively,at

η

∼^{0 (}

η

∼¹.5).InFig. 2weshow

1 CalculationsperformedwithCRMCpackageversion1.5.3.

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Fig. 3.Invariantcharged-particleyieldasafunctionofpTnormalisedtoINEL>0 events.ThedataarecomparedtoMonteCarlocalculations[18,19,24,26–28].Forthe ratioofmodels(MC)anddata(lowerpanel)thesystematicandtotaluncertainties ofthedataareshownasgreybands.

acompilationofresultsonpseudorapiditydensityofchargedpar- ticlesmeasured in |

η

|<0.5 for theINEL andINEL>0 results at differentproton–proton colliderenergies [4–6,15,29–33]. The en- ergydependenceof ^dNch/d

η

is parametrisedby thepower law as^b ﬁtted to data, where a and b are free parameters. By com- biningthe data atlower energies withALICEandCMSresults at

√s=^{13 TeV,} ^we^obtain^b=⁰.103±⁰.002 andb=⁰.111±⁰.004 forINELandINEL>0 eventclasses,respectively.Noticethattheﬁt resultsassumethatuncertainties atdifferentcentre-of-massener- giesareindependent,whichisnotstrictlythecase.

Fig. 3 presents the measured pT spectrum and its comparison with calculations with PYTHIA 6 (Perugia-2011), PYTHIA 8 (Monash-2013) and EPOS LHC. For bulk particle production, the mechanism of colour reconnection is an important one in the PYTHIA models (see discussion below and in Ref. [34]). EPOS is a model based on the Gribov–Regge theory atparton level [27].

Collective(ﬂow-like)effectsareincorporatedintheEPOS3version [35]andtreatedviaparametrisationsintheEPOS LHCversion[28].

Theseeventgenerators,beneﬁttingfromthetuningperformedon theLHCdatainRun1,describethe p_T spectrumreasonablywell, althoughnotindetail.ItisinterestingtonotethatbothPYTHIA 8 andEPOS LHCmodelsshow asimilar patternintheratiotodata withdiscrepanciesupto20%andthatPYTHIA 6overestimatespar- ticleproductionathighp_T.

Fig. 4 shows the ratio of transverse-momentum spectra of charged particles at √

s=13 TeV and 7 TeV. The published data at √

s=^{7 TeV} ^[10] ^were ^for ^INEL ^events. ^We ^have recalculated the normalisation of the spectrum to correspond to INEL>0 eventsin asimilar manner asdone for√

s=^{13 TeV.} ^The ^trigger andevent-selection eﬃciencyfor INEL>0 eventsat √

s=^{7 TeV} was estimated using thesame Monte Carlosimulations used for thepublication [10].The systematicuncertainties oftheratioare the quadratic sum of uncertainties at the two energies. As ex- pected,the spectrum is signiﬁcantlyharder at√

s=13 TeV than at√

s=^{7 TeV.}^{PYTHIA 6,}^{PYTHIA 8}^and^{EPOS LHC}^reproduce ^the

Fig. 4. Ratio of transverse-momentum spectra in INEL>0 events at √ s= 13 and 7 TeV.Theboxesrepresentthesystematicuncertainties.Thedataarecom- paredtoMonteCarlocalculations[18,19,24,26–28].

trendobservedinthedata,butexhibitaslightlymorepronounced hardening with energy inthe transverse momentum region of a few GeV/c.Theeffectappearstobe moresigniﬁcant inPYTHIA 8 thaninPYTHIA 6andEPOS LHC.

The correlation of the particle mean transverse momentum (^pT⁾ ^with ^the multiplicity of the event (N_ch) ﬁrst observed at the SppS collider¯ [36] has been studied by many experimentsat hadron colliders in pp(¯p) covering collision energies from √

s= 31 GeV up to7 TeV [9,37–44]. The increase of ^pT^with ^Nch in the central rapidity region observed in all experiments could be reproduced in the PYTHIA event generator only if a mechanism ofhadronisationwithcolourreconnections(CR)isconsidered[34, 45–47]. A connectionbetween CRandfeatures of collective flow has been conjectured in [48]. In heavy-ion collisions, collective flowisestablishedasagenuinespace–timeevolutionofafireball, whileCRinPYTHIAisamechanisminvokedforhadronisation.The relevance ofthe CR-flow conjecture is currently investigated fur- ther[49].A mechanisminvolvingcollectivestringhadronisationis alsousedintheEPOSmodel[28].

Fig. 5 shows the ratio of spectra measured in three inter- vals of multiplicity tothe inclusive(INEL>0) spectrum. Forthis ratio, the spectra were normalised by the integral prior to di- viding. The selection is performed on the multiplicity measured in the same kinematic region as the spectrum, |

η

|<0.8 and 0.15<p_T<20 GeV/c,usingthemeasuredtrackmultiplicity N_ch^acc fordataandthetrue valueof N_ch knowninMonte Carloevents.

For INEL>0 events, ^Nâcc_ch=⁶.73 (and, from the spectrum in Fig. 3,^Nch=⁹.41±⁰.38)fordataand^Nch=¹⁰.13 forPYTHIA 8 and ^Nch=⁹.97 for EPOS LHC events. The low-multiplicity interval corresponds to N_ch (N_châcc) smaller than the average value in INEL>0 events,^Nch ⁽^Nâcc_ch^), ^themedium-multiplicityinter- val coversbetween^Nch⁽^Nâcc_ch^{) and}^twice ^Nch⁽^Nâcc_ch^),^while thehigh-multiplicityintervalincludesalleventswithNch(Nâcc_ch)≥ 2^Nch (^Nâcc_ch)^. ^Given^that ^themeasurement efficiencyofthe p_T spectrumforINEL>0 eventswithN_ch=^{1 is}âbout^50%,^the^data isslightlybiasedforthelowestmultiplicityinterval.Thisleadstoa slighthardeningofthemeasuredspectrum,butthemagnitudeof thespectralshapechange,ofafewpercent,isclearlysmallerthan theobserveddifferencebetweendataandmodels.Thesystematic

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Fig. 5.Ratiosoftransverse-momentumdistributionsofchargedparticlesinthreein- tervalsofmultiplicitiestotherespectiveoneforinclusive(INEL>0)collisions.The spectrawerenormalised bytheintegralpriortodivision.Thedataarecomparedto MonteCarlocalculations[24,26–28].

uncertaintiesofthemeasuredspectracanceloutcompletelyinthe ratios.A residualcontribution,notestimatedatthisstage,is that ofthecontaminationfromstrange-particledecays.

It is known that the increase of ^pT âs â ^function ôf ^multi- plicityismoderate[44].ThedatainFig. 5showthat thecorrela- tionofthespectrumwithmultiplicity isprominentforthewhole pT range andin particular that it is stronger athigh pT.In first order, thiscorrelation arises naturally fromjets, giving the lead- ing high-pT hadron anda significant contribution tomultiplicity.

Thegeneralfeatures seen inthedata, whichare similarto those ﬁrst seen at √

s=⁰.9 TeV[9], are reproduced by PYTHIA 8 and EPOS LHCfairlywell, butsome disagreements arenoticeabletoo, inparticularinthe p_TregionofafewGeV/c.Thisismorepromi- nentforEPOS LHC. Itwasshownearlier[44]thatboth EPOS LHC andPYTHIA 8reproducewell,althoughslightlyoverpredicting,the correlation of^pT ^with ^Nch.The presentdata on spectral shape highlightsomedeﬁcienciesinbothmodelsconcerningthedescrip- tionofspectralshapesasafunctionofmultiplicity.

6. Conclusions

Wehavereportedthemeasurement ofthepseudorapidity and transverse-momentumdistributionsofchargedparticlesproduced inproton–protoncollisions at√

s=13 TeV with theALICEdetec- tor at LHC. The pseudorapidity distribution is measured for two normalisationclasses:inelasticevents(INEL)andeventshavingat least one charged particle in the pseudorapidity interval |

η

_|<1 (INEL>0). The charged-particle densities in |

η

|<0.5 are5.31± 0.18 and6.46±⁰.19,respectively.Thetransverse-momentumdis- tribution is measured in the range 0.15<p_T<20 GeV/c and

|

η

_|<0.8 forINEL>0 events.Thespectrumissigniﬁcantly harder thanat√

s=^{7 TeV and}^shows^rich^features^when^correlated^with thecharged-particle multiplicitymeasured inthesamekinematic region. The results are found to be in fair agreement with the expectationsfromlowerenergyextrapolationsandwiththecalcu- lationsfromPYTHIAandEPOSMonteCarlogenerators,butnotin alldetails. Bothmodels exhibit aslightlymorepronounced hard- eningofthe pT distributions withcollision energythanthe data fortransversemomentaaboveafewGeV/c.

Acknowledgements

The ALICE Collaboration would like to thank all its engineers andtechniciansfortheir invaluablecontributions totheconstruc- tionoftheexperimentandtheCERNacceleratorteamsfortheout- standingperformanceoftheLHCcomplex.TheALICECollaboration gratefully acknowledges the resources and support provided by all Gridcentres andtheWorldwide LHC ComputingGrid (WLCG) Collaboration. The ALICE Collaboration acknowledges the following funding agencies for their support in building and running theALICEdetector:StateCommittee ofScience,WorldFederation of Scientists (WFS)and SwissFonds Kidagan, Armenia; Conselho Nacional de DesenvolvimentoCientíﬁco e Tecnológico (CNPq), Fi- nanciadorade Estudos eProjetos(FINEP),Fundação de Amparoà Pesquisa do Estado de São Paulo (FAPESP); National Natural Sci- enceFoundation ofChina (NSFC), theChinese Ministryof Educa- tion(CMOE)andtheMinistryofScienceandTechnologyofChina (MSTC); Ministry of Education andYouth ofthe Czech Republic;

Danish Natural Science Research Council, the Carlsberg Founda- tion andthe DanishNationalResearch Foundation;TheEuropean ResearchCouncilundertheEuropeanCommunity’sSeventhFrame- work Programme; Helsinki Institute of Physics andthe Academy of Finland; French CNRS-IN2P3, the ‘Region Pays de Loire’, ‘Re- gion Alsace’, ‘Region Auvergne’ and CEA, France; German Bun- desministerium für Bildung, Wissenschaft, Forschung und Tech- nologie(BMBF)andtheHelmholtzAssociation;GeneralSecretariat forResearchandTechnology,MinistryofDevelopment,Greece;Na- tionalResearch,DevelopmentandInnovationOﬃce(NKFIH),Hun- gary;DepartmentofAtomicEnergyandDepartmentofScienceand TechnologyoftheGovernmentofIndia;IstitutoNazionalediFisica Nucleare (INFN) and Centro Fermi – Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”,Italy; Japan Societyfor the PromotionofScience (JSPS)KAKENHIandMEXT, Japan;Joint Institute forNuclear Research, Dubna; NationalResearchFounda- tion of Korea (NRF); Consejo Nacional de Ciencia y Tecnología (CONACYT),DireccionGeneraldeAsuntosdelPersonalAcademico (DGAPA),México,AmeriqueLatineFormationacademique–Euro- peanCommission(ALFA-EC)andtheEPLANETProgram(European Particle Physics Latin American Network); Stichting voor Funda- menteelOnderzoekderMaterie(FOM)andtheNederlandseOrgan- isatie voor WetenschappelijkOnderzoek (NWO),Netherlands; Re- search CouncilofNorway (NFR);NationalScience Centre,Poland;

Ministry of National Education/Institute for Atomic Physics and NationalCouncilofScientificResearchinHigherEducation(CNCSI- UEFISCDI),Romania;MinistryofEducationandScienceofRussian Federation, Russian Academy of Sciences, RussianFederal Agency of Atomic Energy, Russian Federal Agency for Science and Inno- vations andThe Russian Foundation for Basic Research; Ministry of Education ofSlovakia; Department of Science andTechnology, South Africa; Centro de Investigaciones Energeticas, Medioambi- entales yTecnologicas (CIEMAT),E-Infrastructureshared between EuropeandLatin America(EELA),MinisteriodeEconomíayCom- petitividad (MINECO) of Spain, Xunta de Galicia (Consellería de Educación), Centro de Aplicaciones TecnológicasyDesarrollo Nu- clear(CEADEN),Cubaenergía,Cuba,andIAEA(InternationalAtomic EnergyAgency);SwedishResearch Council(VR)andKnut&Alice WallenbergFoundation (KAW);UkraineMinistryofEducationand Science;UnitedKingdomScienceandTechnologyFacilitiesCouncil (STFC);TheUnitedStatesDepartmentofEnergy,theUnitedStates NationalScience Foundation, the State of Texas, andthe State of Ohio; Ministry of Science, Education and Sports of Croatia and Unity throughKnowledge Fund, Croatia; Council ofScientific and IndustrialResearch(CSIR),NewDelhi,India;PontificiaUniversidad CatólicadelPerú.

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ALICECollaboration

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, A. Akindinov

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, S.N. Alam

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, I. Altsybeev

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, A. Andronic

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, V. Anguelov

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, J. Anielski

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, T. Antiˇci ´c

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, F. Antinori

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