Studies of charm and beauty hadron long-range correlations in pp and pPb collisions at LHC energies

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Studies

of

charm

and

beauty

hadron

long-range

correlations

in

pp

and

pPb

collisions

at

LHC

energies

.The CMSCollaboration

CERN,Geneva,Switzerland

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

Articlehistory:

Received15September2020

Receivedinrevisedform30November2020 Accepted14December2020

Availableonline21December2020 Editor:M.Doser Keywords: CMS Ridge Collectivity Smallsystems Heavyflavor Ellipticflow

MeasurementsofthesecondFourierharmoniccoefficient(v2)oftheazimuthaldistributionsofprompt andnonpromptD0_{mesonsproducedinpp andpPb collisionsarepresented.NonpromptD}0_mesonscome frombeautyhadrondecays.ThedatasamplesarecollectedbytheCMSexperimentatnucleon-nucleon center-of-massenergiesof13 and 8.16 TeV, respectively. Inhighmultiplicity pp collisions, v2 signals forpromptcharmhadronsarereportedforthefirsttime,andarefoundtobecomparabletothosefor light-flavor hadronspeciesoveratransverse momentum(pT)rangeof2–6 GeV. Comparedatsimilar eventmultiplicities,thepromptD0mesonv2valuesinpp andpPb collisionsaresimilarinmagnitude. The v2 values for openbeautyhadrons are extracted forthe firsttimevianonprompt D0 mesons in pPb collisions.ForpTintherangeof2–5 GeV,theresultssuggestthatv2fornonpromptD0mesonsis smallerthanthatforpromptD0mesons.Thesenewmeasurementsindicateapositivecharmhadronv2 inpp collisionsandsuggestamassdependenceinv2betweencharmand beautyhadronsinthe pPb system.Theseresultsprovideinsightsintotheoriginofheavy-flavorquarkcollectivityinsmallsystems.

©2020TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Strong collectivity in high-energy nucleus-nucleus (AA) colli-sions at the BNL RHIC [1–4] and atthe CERN LHC [5,6], has in-dicated the formation of a hot, strongly interacting quark gluon plasma (QGP), which exhibits nearly ideal hydrodynamic behav-ior [7–9].Thecollectivephenomena manifestsitselfinlong-range (largepseudorapidity gap) particlecorrelations [10–15]. Although not originally expected, similar long-range collective azimuthal correlations are also being observed in small colliding systems with high final-state particle multiplicity, such as proton-proton (pp) [16–20], proton-nucleus (pA) [21–31], and lighter nucleus-nucleus systems [31–34]. This observation raised the question of whetherafluid-likeQGPmediumwithasizesignificantlysmaller thaninAA collisionsiscreatedintheseothersystems [35–37].At thesametime,thereisnoobservationoflong-rangecorrelationsin e+e− andep collisions,whichareevensmallersystemscompared to pp collisions [38,39]. In the context of hydrodynamic models, the observed azimuthal correlation structure ofemitted particles istypicallycharacterizedby itsFouriercomponents [40].The sec-ondandthirdFourieranisotropycoefficientsareknownaselliptic (v2)andtriangular(v3)flow,whichmostdirectlyreflecttheQGP medium responsetotheinitialcollisiongeometryandits

fluctua- _{E-mailaddress:cms-publication-committee-chair@cern.ch.}

tions,respectively [41–44].Theexperimentalmeasurementsinthe smallsystemsare consistent withthedominance ofstrong final-stateinteractions [35,37,45–47],suchasahydrodynamicexpansion ofatinyQGPdroplet [35,37].Alternativescenariosbasedongluon saturationintheinitialstatecanalsocapturethemainfeaturesof thecorrelation data,andare conjecturedto playa dominantrole astheeventmultiplicitydecreases [35,36].

Heavy-flavorquarks(charmandbottom)areproducedviahard scatteringsin the very early stagesofthe highenergy collisions. These quarks are available to probe both initial- and final-state effects ofthe collision dynamics [48,49]. Strongelliptic flow sig-nalsofelectronsfromthedecayofheavy-flavorhadronsandopen charmD0_{mesonsareobservedinbothgold-gold(AuAu)collisions} atRHIC [50,51] andlead-lead(PbPb)collisionsattheLHC [52–54]. Thesefindings suggestthat charmquarks develop significant col-lectivebehaviorvia their stronginteractions withthe bulkofthe QGPmedium. Measurementsofellipticflowofhidden-charmJ/ψ mesonsprovidefurtherevidenceforstrongrescatteringsofcharm quarks [55,56].

In small colliding systems, the study of heavy-flavor hadron collectivityhasthepotential todisentanglepossiblecontributions fromboth initial- andfinal-state effects. In particular, heavy fla-vorhadronsmaybe moresensitive to possibleinitial-stategluon saturationeffects.Recent observationofa significant ellipticflow signalforpromptD0 [57] andpromptJ/ψ[58,59] mesonsinpPb collisions providedthe firstevidence forcharm quark collectivity

https://doi.org/10.1016/j.physletb.2020.136036

0370-2693/©2020TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

insmallsystems.Surprisingly,despitethemassdifferences,the ob-served v2 signalforpromptJ/ψmesonsinpPb collisionsisfound to be comparable to that of prompt D0 mesons and light-flavor hadronsatagivenparticletransversemomentum(pT).This behav-iorcannotbeexplainedbythefinal-stateeffectsofaQGPmedium, asthecontributionfromrecombinationstoJ/ψproductionisnot expectedtobesignificantinsmallsystems [60].Thisfindingmay implytheexistenceofinitial-statecorrelationeffects [61].Further detailedinvestigationsare importanttoaddressmanyopen ques-tionsforunderstandingtheoriginofheavy-flavorquarkcollectivity in small systems. These include the multiplicity dependence of charmquark collectivityinbothpPb andpp systemsandthe de-tailsofcollectivebehaviorofbeautyquarks.

This Letterpresents thefirst measurementof theelliptic flow (v2)forpromptD0 mesonsinpp collisionsatcenter-of-mass en-ergy √s=13 TeV andfornonpromptD0 mesons(fromdecaysof beauty hadrons) in pPb collisions at nucleon-nucleon center-of-mass energy √s_NN=8.16 TeV,using long-range (|η|>1) two-particle angular correlations. The v2 harmonic coefficient is de-termined over the 2–8 GeV pT range for prompt D0 _{mesons as} a function of multiplicity with results forthe pp and pPb colli-sions. Thenonprompt D0 meson v2 values areextractedin high-multiplicity pPb collisions for two transverse momentum ranges 2–5and5–8 GeV,andarecomparedtopreviousmeasurementsof promptD0_{mesonsandlightflavorhadrons.}

2. Experimental apparatus and data sample

The central feature of the CMS apparatus is a superconduct-ing solenoid of6 m internal diameter, providing a magneticfield of3.8 T.Withinthesolenoidvolume,thereare fourprimary sub-detectorsincludingasiliconpixelandstriptrackerdetector,alead tungstatecrystalelectromagneticcalorimeter,andabrassand scin-tillator hadron calorimeter, each composed of a barrel and two endcapsections.Iron andquartz-fiber Cherenkovhadron forward calorimeters cover the pseudorapidity (ηlab) range 2.9<|ηlab|< 5.2 in laboratory frame. Muons are measured in gas-ionization detectors embedded in the steel flux-return yoke outside the solenoid.Thesilicontrackermeasureschargedparticleswithinthe range |ηlab|<2.5. For charged particles with 1< pT<10 GeV and|ηlab|<1.4,thetrackresolutionsare typically1.5%in pT and 25–90(45–150) μm inthetransverse(longitudinal)impact param-eter [62].AdetaileddescriptionoftheCMSdetector,togetherwith a definitionofthecoordinatesystemusedandtherelevant kine-maticvariables,canbefoundinRef. [63].

TheeventsampleswerecollectedbytheCMSexperimentwith a two-level triggersystem [64]:atlevel-1 eventsare selectedby customhardware processorswhilethehigh-level triggerusesfast versionsoftheofflinesoftware.ThepPb dataat√sNN=8.16 TeV

used in this analysis were collected in 2016, and correspond to an integrated luminosity of 186.0 nb−1 [65]. The beam energies are 6.5 TeV for the protons and 2.56 TeV per nucleon for the lead nuclei. Because of the asymmetric beam conditions, parti-cles selected in this analysis from midrapidity in the laboratory frame (|ylab|<1) correspond to rapidity in the nucleon-nucleon center-of-mass frameof−1.46<ycm<0.54,withpositive rapid-ity corresponding to the proton beam direction. The pp data at

√

s=13 TeV werecollectedin2017and2018withintegrated lu-minosities of 1.27 pb−1 and 10.22 pb−1 during special runs with low beamintensity,resultinginanaveragenumberofconcurrent pp collisionsofabout1perbunchcrossing.Theevent reconstruc-tion,eventselections,andtriggers(minimumbiasandhigh multi-plicity)areidenticaltothosedescribedinRefs. [19,66,67].Similar to previous CMScorrelation measurements, the pPb and pp data areanalyzedforseveralmultiplicity(N_trkoffline)classes,whereNoffline_trk

is the numberof offline selected tracks [19,62] with |ηlab|<2.4 andpT>0.4 GeV.

3. Prompt and nonprompt D0_{meson reconstruction and}

selection

TheD0 (andits charge conjugatestateD0)mesons are recon-structed throughthe hadronicdecaychannel D0_→K−_π+ _(D0_→ K+π−).TheinvariantmassofD0candidatesisrequiredtobefrom 1.725–2.000 GeV tocovertheworld-averageD0mass [68].Inorder to suppress the combinatorial background and improve the mo-mentumandmassresolution,high-purity [62] tracksreconstructed usingthe silicon trackerwith pT>0.7 GeV, |ηlab|<2.4,smaller than10%relative uncertaintyin pT,andthenumberofvalidhits

≥11areused.Foreach pairofselectedtracks,twoD0 candidates are considered by assuming that one of the tracks has the pion masswhiletheothertrackhasthekaonmass,andviceversa.

TheD0 candidatesare selected usinga multivariate technique that employs the boosted decision tree (BDT) algorithm in the ToolkitforMultivariate Data Analysis with ROOT [69].The selec-tionisoptimizedseparately forpp and pPb collisions,andforall

pT ranges,inorder tomaximize thestatisticalsignificanceofthe prompt ornon-prompt D0 meson signals. The Monte Carlo(MC) signalsimulatedsamplesareproducedwith pythia 8.209 [70] tune CUETP8M1 [71] (embeddedinto eposlhc[72] forthecaseofpPb analysis) for both prompt and nonprompt D0 events. The back-groundsamplesforthemultivariate training aretakenfromdata. ThetrainingvariablesrelatedtoD0 mesonsinclude:the χ2 prob-abilityforD0 _{vertexfitting;the three-dimensionaldistance(with} andwithoutbeingnormalizedbyitsuncertainty)betweenthe pri-maryanddecayvertices;andthethree-dimensionalpointingangle (defined as the angle between the line segment connecting the primary anddecayverticesandthemomentum vector ofthe re-constructed particlecandidates). The training variables relatedto the decay products are: pT; pseudorapidity and the longitudinal and transverse track impact parameter significance. In the BDT training for prompt D0 _{signals, same-sign (SS) π}±_K± _candidates areused,whichcontainpredominantlycombinatorialbackground. ForoptimizingnonpromptD0 signals,bothpromptD0 signalsand combinatorialcandidates areconsidered asdominantbackground to be suppressed. For this reason, opposite-sign (OS) candidates (although including fractions <5% of nonprompt D0 signals) are usedforthebackgroundtrainingsample.Thisapproachisfoundto give betterperformance forachieving highernonpromptD0 frac-tionsthanusingSSbackgroundcandidates,especiallyathigherpT. The optimalselection criterion is the workingpoint withthe highestsignal significance of prompt andnonprompt D0 signals. For extracting the nonprompt D0 _{yield, the distributions of} dis-tanceofclosestapproach(DCA)oftheD0 mesonmomentum vec-tor, relative to the primary vertex, are fitted using the template probabilitydistributionfunctions(PDs)forpromptandnonprompt D0 signals derived from MC simulation. The residual nonprompt fractionintheBDTprompt-trainedsampleisfoundtobenomore than7%,whileintheBDTnonprompt-trainedsample,theoptimal selectionyieldsanonpromptfractionupto20%.Thisprocedureis furtheroutlinedinSection4.

4. Data analysis

The azimuthal anisotropies of D0 mesons are extracted from theirlong-range(|η|>1) two-particleazimuthal correlationsof D0 candidateswithchargedparticles,asdescribedinRefs. [19,26]. The two-dimensional (2D) correlation function is constructed by pairingeachD0 candidatewithreferenceprimarycharged-particle trackswith0.3<pT<3.0 GeV (denoted“ref”particles), and cal-culating

1 N_D0 d2Npair dηdφ =B(0,0) S(η,φ) B(η,φ), (1)

whereηandφ are thedifferencesinpseudorapidity ηlab and azimuthal angleφ ofeach pair.The same-event pairdistribution,

S(η,φ),representstheyieldofparticlepairsnormalizedbythe numberofD0 candidates(ND0) fromthesameevent.The

mixed-eventpairyielddistribution,B(η,φ),isconstructedbypairing D0 candidates ineach eventwiththe referenceprimary charged-particle tracks from10 different randomly selected events, from the same N_trkoffline range, andwitha primary vertex falling in the same2cm widerangeofreconstructedz coordinates.The B(0,0) represents the value of B(η,φ) at η=0 andφ=0. It is evaluated byinterpolatingthefournearest binswithabinwidth of0.3 inηand π/16 inφ bilinearly. Theinterpolationshows a negligible effect on the measurements. The analysisprocedure is performed in each D0 _{candidate p}

T range by dividing it into 14 intervals ofinvariant mass.The correction forthe acceptance andefficiency(derived fromsimulations using pythia forpp and pythia+epos for pPb) of the D0 meson yield is found to have a negligibleeffectonthemeasurements,andisnotapplied.The cor-respondingeffects arediscussed inSection5.The φ correlation functionsaveraged over|η|>1 (toremove short-range correla-tions,such asjet fragmentation)areobtainedfromtheprojection of2Dcorrelationfunctionsandfittedbythefirstthreetermsofa Fourierseries: 1 N_D0 dNpair dφ = Nassoc 2π  1+ 3  n=1 2Vncos(nφ)  . (2)

Here, Vn are the Fourier coefficientsand Nassoc represents the totalnumberofpairsperD0 _{candidate.Theinclusionofadditional} Fouriertermstothefithasnegligible effect.Byassuming Vn to be theproductofsingle-particleanisotropies [73], Vn(D0,ref)=

vn(D0)vn(ref),the vn anisotropyharmonicsforD0 candidatescan beextractedfromtheequation:

vn(D0)=Vn(D0,ref)



Vn(ref,ref). (3) Because of the limited statistical precision of the available data, only the ellipticanisotropy harmonicresults are reportedin this analysis.

To extract the V2 values of the inclusive D0 meson sig-nal (V_2S ), a two-step fit to the invariant mass spectrum of D0 candidates and their V2 as a function of the invariant mass,

V_2S+B(minv),isperformedineach pT interval.The massspectrum fitfunctioniscomposedoffivecomponents:thesumoftwo Gaus-sian functionswith the same mean but different widths for the D0 signal,S(minv);anadditionalGaussianfunctiontodescribethe invariant massshapeofD0 _{candidateswithanincorrectmass} as-signment from the exchange of the pion andkaon designations,

S W(minv); Crystal Ball (CB) functions [74] to describe processes D0_→π+_π−_{(S(mπ+π−)) andD}0_→K+_K−_{(S(mK+K−)); and a} third-orderpolynomialtomodelthecombinatorialbackground,B(minv). ThecontributionsfromtheprocessesD0→ π+π−andD0→K+K− are the results of mislabelling K as π, or vice versa. These two componentsareemulated bytwoCB functionsattwo sidesaway from the peak region. The width and the ratio of the yields of

S W(minv)andS(minv)andtheCBfunctionshapearefixed accord-ingtoresultsobtainedfromsimulationstudiesusing pythia forpp collisionsand pythia+epos forpPb collisions.

The V_2S+B(minv)distributionisfitwith

V_2S+B(minv)=α(minv)V2S + [1−α(minv)]V2B (minv), (4) where

Fig. 1. ExampleoffitstotheinvariantmassspectrumandV₂S_+B(minv),fortheBDT

prompt-trainedsampleinpp collisions.

α(minv)=  S(minv)+S W(minv)+S(mK+K−) +S(m_π+_π−)/S(minv)+S W(minv) +S(mK+K−)+S(mπ+_π−)+B(minv)  . (5)

HereV_2B (minv)forthebackgroundD0 candidatesismodeledasa linearfunctionoftheinvariantmass,and α(minv)istheD0 signal fraction.TheK-π swapped,D0_{→ π}+_π− _andD0_→K+_K− compo-nentsareincludedinthesignalfractionbecausethesecandidates arefromgenuineD0 mesonsandshouldhavethesame v2 value asthatoftheD0 _signal.

Fig. 1 shows an example of fits to the mass spectrum and

V_2S+B(minv),fortheBDTprompt-trainedsampleinthe pT interval 4–6 GeV forthe multiplicity range Noffline_trk ≥100 in pp collisions. Similar fitsin pPb datacan be found inRef. [57],which are not repeatedhere.

For extracting the V2 values of nonprompt D0 mesons, the measurementandfitting proceduredescribed above are repeated inthreeseparateDCAranges,containingverydifferentnonprompt D0 fractions.Alinearfitbythefunctionalform,

V_2S = fb→DV_2b→D+ (1−fb→D)V_2prompt D, (6)

to the measured D0 _V

2 values asa function of nonprompt D0 fraction is performedto extrapolate to the V2 value at a non-promptfractionof100%. The fb→Drepresentsthenonprompt D0 fraction. The v2 values of nonprompt D0 are evaluated by us-ing Eq. (3). Fig. 2 shows an example of fits to the mass spec-trumand V_2S+B(minv) forthe BDT nonprompt-trainedsample for DCA<0.008cm and 0.008<DCA<0.014cm, in the pT interval 2–5 GeV, for the multiplicity range 185≤Noffline

trk <250 in pPb collisions. The resultingD0 _{signal V}

2 distributions contain con-tributionsfrombothpromptandnonpromptD0 _mesons.

Fig. 2. ExampleoffitstotheinvariantmassspectrumandV2S+B(minv),fortheBDTnonprompt-trainedsampleinpPb collisions.TheleftplotshowsthefitforDCA<0.008cm

andtherightplotisfor0.008<DCA<0.014cm.

Fig. 3. Left:exampleoftemplatefittotheD0_{mesonDCAdistributioninthe p}

Tinterval3–4 GeV foreventswith185≤Ntrkoffline<250 ofpPb collisions.Right:inclusiveD0

VS

2valuesfromthethreeDCAregionsasafunctionofthecorrespondingnonpromptD

0_{fraction,for2<p}

T<5 GeV and5<pT<8 GeV.TheredlineisalinearfittoV2S data.

Inclusive D0 mesonyields, extracted asa function ofDCA,by fittingtheinvariantmassdistributionineachDCAbin,areshown inFig.3(left).AtemplatefittotheDCAdistributionisperformed usingtemplatedistributionsofpromptandnonpromptD0 mesons obtainedfromMC simulationtoestimatethenonpromptD0 frac-tions in each of the three DCA regions used to extract inclusive D0 _V

2, as described above. The inclusive D0 V2 values from the three DCAregions are then plottedas afunction of the cor-responding nonprompt D0 _{fraction, shown in Fig. 3 (right), for} 2<pT<5 GeV and 5<pT<8 GeV, respectively. The measure-ments arewell describedby alinear-functionfit,whichisshown asaredlineinFig.3.

The residual contribution of back-to-back dijets to the mea-suredv2 resultsiscorrectedbysubtractingcorrelationsfrom low-multiplicityevents,followinganidenticalprocedureestablishedin Refs. [19,73].The Fouriercoefficients, Vn,extractedfromEq. (2) forNoffline_trk <35(20),inpPb (pp)collisions,aresubtractedfromthe

Vncoefficientsobtainedinthehigh-multiplicityregion,with

V_nsub_ =Vn−Vn(Nofflinetrk <35) ×Nassoc(Nofflinetrk <35) Nassoc Yjet Yjet(Noffline_trk <35) . (7)

Here,Yjet representsthejetyield.Itisthedifferencebetween in-tegrals of the short-range (|η|<1) and long-range (|η|>2) event-normalizedassociatedyieldsforeach multiplicityclass.The ratio Yjet/Yjet(Nofflinetrk <35) is introduced to account for the en-hanced jet correlations resulting from the selection of higher-multiplicityevents.Itisobservedthatthevaluesofjet yieldratio showlittledependenceon pT overthefullpTrange.Forthe mea-surement of nonprompt D0 _{mesons, all quantities in Eq. (7) are} first extrapolatedto values ata nonprompt D0 _{fractionof 100%,} followingthesameapproachasinFig.3,beforeapplyingthe sub-traction procedure. Elliptic flow (vsub₂ ), corrected for residual jet correlations,isobtainedfromV_2subusingEq. (3).

Table 1

Summaryofsystematicuncertaintiesonvsub

2 .TherangesofsystematicuncertaintiescorrespondtothepT

rangesofD0_{mesons.Valuesarein10}−3_.

Source Prompt D0_{in pPb Nonprompt D}0_{in pPb Prompt D}0_{in pp}

collisions (×10-3_{) collisions (×10}-3_{) collisions (×10}-3₎

Nonprompt D0_{contamination 3–8 — 4–5}

Nonprompt D0_{fraction estimation — 1–7 —}

Background V2PD 2–4 2 2–5

Efficiency correction 0.1–13 0.2–0.6 0.8–13

Trigger bias 0.6–1 0.1–1 0.4–2

Effect from pileup 2–5 2–5 4–10

BDT selection 2–5 2 3–8

Jet subtraction 2–7 14–16 5–49

Total 5–18 16–17 13–52

5. Systematic uncertainties

Table 1 summarizes the estimate of systematic uncertainties for the vsub₂ of prompt and nonprompt D0 mesons in pPb colli-sions as well asthat ofprompt D0 _{mesons in pp collisions. The} rangesofsystematicuncertainties correspondtothe pT rangesof D0 _mesons.

Systematicuncertainties intheBDT selectionofthe D0 candi-datesareevaluatedbystudyingMCsimulatedsamples.The differ-encebetweenapplyingBDTselectionsandnotapplyingthose cri-teria istakenasthesystematicuncertainty.Thisprocedureyields the v2 uncertainties of 0.002–0.005 for prompt D0 mesons and 0.002fornonpromptD0mesonsinpPb collisions.Inpp collisions, itbringsanuncertaintyof0.003–0.008onthepromptD0 v2 mea-surement.

Othersourcesofsystematicuncertaintyincludethebackground mass PD, the D0 _{meson yield correction (acceptance and} effi-ciency correction), the background V2 PD, and the jet subtrac-tionmethod.ChangingthebackgroundmassPDtoasecond-order polynomial or an exponential function shows negligible system-atic effects. To evaluate the uncertainties arising from the pT -dependentD0 _{mesonyieldcorrection,thev}

2 valuesareextracted from the corrected signal D0 distributions and compared to the uncorrected v2 values as a conservative estimate. This yields an uncertainty of less than 0.013. For most bins, the uncertainties from the yield correction are less than 0.003 and are small (or negligible)comparedtoothersourcesandstatisticaluncertainties. Thesystematicuncertainties fromthebackground v2 PDare eval-uatedbychangingv₂B(minv)toasecond-orderpolynomialfunction of theinvariant mass, yielding an uncertaintyof lessthan0.005. Tostudypotentialtriggerbiases,acomparisontohigh-multiplicity pPb data for a given multiplicity range that were collected us-ing a lower thresholdtrigger with100% efficiencyis performed. Theuncertaintyfromtriggerbiasisquotedas0.001.Thoughdata collected withlowbeamintensityareusedinthisanalysis, there arestilladditionalcollisionsbesidestheoneofinterestper bunch crossing,whichareknownaspileupinteractions.Thepossible con-taminationbyresidualpileupinteractionsisalsostudiedby vary-ing thepileupselectionofeventsintheperformedanalysis,from nopileuprejectionatalltoselectingeventswithonlyone recon-structedvertex.ThevariationofD0 v2valuesisabout0.002–0.005 in pPb collisions, while it is about 0.004–0.010 in pp collisions because of larger pileup.To study the uncertainty from jet sub-traction,theratioYjet/Yjet(Nofflinetrk <35)isvariedbyone standard deviation. It yields an uncertainty of0.002–0.007 for prompt D0 mesonsand0.016–0.017fornonpromptD0inpPb collisions.Inpp collisions, it yields an uncertaintyof 0.013–0.049 for prompt D0 mesons. This effect diminishes towards highmultiplicity regions becauseofthesmallNoffline

trk ratioaccordingtoEq. (7).

For the measurement of prompt D0 _{mesons, the contribution} fromnonpromptD0_{mesonsissignificantlysuppressed.Noexplicit}

Fig. 4. Resultsofvsub

2 forpromptD 0 _{mesons,asafunctionofp} T for|ylab|<1, withNoffline trk ≥100 inpp collisionsat √

s=13 TeV.Publisheddataforcharged par-ticles,K0Smesonsand baryonsarealsoshownforcomparison [19].Thevertical

barscorrespondtothestatisticaluncertainties,whiletheshadedareasdenotethe systematicuncertainties.ThehorizontalbarsrepresentthewidthofthepTbins.

correction is applied and a systematic uncertainty is quoted in-stead.BasedonthepredictionforAAcollisionsthatB mesonshave asmallerv2 thanlight-flavorparticlesbecauseofthelargermass oftheb quark [75–77],thenonpromptD0 _v

2 valuesareassumed toliebetween0andthoseofstrange hadrons.The v2 forprompt D0 isthusreestimatedwiththeboundsofnonpromptD0 v2 and theextractednonpromptD0 _{fractionsandthechangein v}

2 signal isfound to be smaller than 0.008.For the measurementof non-prompt D0 mesons, a major systematic uncertainty comes from thedetermination ofnonprompt D0 fractionin differentDCA re-gions. The DCAtemplate distributions of prompt andnonprompt D0 _{mesonsfromMCsimulationaresmearedviascalingthewidth} ofthesedistributions. Thevariation ofDCAwidthis 2–8%,based onthebest χ2 _{fittodata.Theresultingvariationintheextracted} nonpromptD0 _v

2isquoted asasystematicuncertaintyof0.007. All sources of systematic uncertainties are added in quadra-turetoobtainthetotalsystematicuncertainty.Thetotalsystematic uncertaintiesforprompt andnonpromptD0 mesons inpPb colli-sionsyield0.005–0.018and0.016–0.017, respectively.Forprompt D0 _{mesonsin pp collisions,the totalsystematicuncertainties are} quotedas0.013–0.052.

6. Results

Thevsub₂ resultsofpromptD0 mesonsinpp collisionsat√s =

13 TeV, arepresentedin Fig.4asa functionof pT for |ylab|<1, withNoffline_trk ≥100.Publisheddataforlight-flavorhadrons

includ-Fig. 5. Resultsofvsub

2 forpromptD0 mesons,asafunctionofeventmultiplicity

forthreedifferentpTranges,with|ylab|<1 inpp collisionsat√s =13 TeV and

pPb collisionsat √sNN=8.16 TeV.Theverticalbarscorrespondtostatistical

un-certainties,whiletheshadedareasdenotethesystematicuncertainties.They-axis iszoomedintobetterdisplaythedata;theuncertaintiesaresymmetricwith re-specttotheircentralvalues.ThehorizontalbarsrepresentthewidthoftheNoffline trk

bins.Theright-mostpointswithright-handarrowscorrespondtoNoffline trk ≥100 for

pp collisionsandNoffline

trk ≥250 forpPb collisions.Thev sub

2 valuesinpPb collisions

with185≤Noffline

trk <250 aremeasuredindifferentpTrangesfromRef. [57] and

arefoundtobeconsistentwithRef. [57].

ing inclusivecharged particles (dominated by pions), K0_S mesons and baryonsare also shownforcomparison [19]. The positive

v2 signal (0.061±0.018(stat)±0.013(syst)) over a pT range of

∼2–4 GeV forprompt charmhadronsprovides indicationsof the collectivityofcharmquarksinpp collisions,withadecliningtrend toward higher pT. The v2 magnitude for prompt D0 mesons is found to be compatiblewith light-flavor hadron species, though slightlysmallerbyaboutonestandard deviation.The results sug-gest that collectivityisbeingdevelopedforcharm hadronsinpp collisions,comparable(orslightlyweaker)thanthatforlight-flavor hadrons. This finding is similar to the observation made in pPb collisions at √sNN=8.16 TeV over a similar pT range at higher

multiplicities185≤Noffline

trk <250 [57].

Tofurther investigatepossiblesystem sizedependenceof col-lectivity for charm hadrons in small colliding systems, v2 for prompt D0 mesons in pPb and pp collisions are both measured indifferentmultiplicityclasses.ThepromptD0 v2asafunctionof event multiplicity forthree different pT ranges: 2<pT<4 GeV, 4< pT<6 GeV, and 6<pT<8 GeV are presented in Fig. 5. At similar multiplicities of Noffline_trk ∼100, the prompt D0 _v

2 val-ues are found to be comparable within uncertainties in pp and pPb systems.For2<pT<4 GeV,themeasuredresultsofprompt D0 _{provide indications of positive v}

2 down to Nofflinetrk ∼50 with a significance ofmore than 2.4 standarddeviations in pPb colli-sions, while for 6<pT<8 GeV the prompt D0 v2 signal tends

Fig. 6. Resultsofvsub

2 forpromptandnonpromptD

0_{mesons,aswellasK}0

Smesons,

baryonsfor|ylab|<1,andpromptJ/ψmesonsfor1.2<|ylab|<2.4,asfunctions

ofpT with185≤Noffline_trk <250 inpPb collisionsat√sNN=8.16 TeV [57,59].The

verticalbarscorrespondtostatisticaluncertainties,whiletheshadedareasdenote thesystematicuncertainties.Thehorizontalbarsrepresentthewidthofthe non-promptD0 _p

Tbins.Thedashed,dash-dotted,andsolidlines,showthetheoretical

calculationsofpromptD0_{,J/ψ,andnonpromptD}0_{mesons,respectively,withinthe}

CGCframework [61,78].

to diminishin the low multiplicity regions. No clear multiplicity dependencecanbe determined forpp data,becauseoflarge sta-tisticaluncertaintiesatlowmultiplicities.

Thevsub₂ resultsfornonpromptD0mesonsfrombeautyhadron decays are shown in Fig. 6 as a function of pT for pPb colli-sions at 8.16 TeV with 185≤N_trkoffline<250. The extracted vsub₂

valuesare−0.008±0.028(stat)±0.016(syst) for 2<pT<5 GeV and0.057±0.029(stat)±0.017(syst) for5<pT<8 GeV.Atlow

pT, the nonprompt D0 v2 is consistent with zero, while at high

pT,a hintof a positive v2 value forbeautymesons issuggested butnot significantwithin statistical andsystematicuncertainties. Previously published v2 datafor prompt D0 mesonsand strange hadronsarealsoshown [57].

At pT∼2–5 GeV, the nonprompt D0 meson v2 from beauty hadrondecaysisobserved tobesmaller thanthatforprompt D0 mesons with a significance of 2.7 standard deviations. Based on MC simulations with evtgen and pythia [70,79], nonprompt D0 mesons carry more than 50% of B transverse momenta. The de-viation of nonprompt D0 meson azimuthal distributions from B mesonscouldreducetheextractedv2 valuesatfixedB mesonpT. Takingthe gluon saturation modelasan example, themaximum

v2 value of B mesons is at pT∼6 GeV [78], while the maxi-mum v2 value ofnonprompt D0 mesons is about70% ofthat of B mesons at D0 _p

T∼4 GeV due to the effects discussed above. Thesestudies suggest a flavor hierarchy ofthe collectivity signal thattendstodiminishfortheheavierbeautyhadrons.Thisis qual-itatively consistent with the scenario of v2 being generated via final-state rescatterings,where heavier quarks tend to develop a weaker collective v2 signal [49]. The ordering of muon v2 from charmandbeautydecayatlow pT isalsoobservedinPbPb colli-sionswherefinal-statescatteringsplayanimportantrole [80].

Correlations at the initial stage of the collision between par-tonsoriginating fromprojectile protons and dense gluonsin the leadnucleusare abletogeneratesizableellipticflowinthecolor glasscondensate (CGC)framework [35,61,78].These CGC calcula-tionsofv2 signalsforpromptJ/ψmesons,aswell aspromptand nonprompt(fromB mesondecay)D0 mesons,are comparedwith datainFig.6.Thequalitativeagreementbetweendataandtheory suggeststhatinitial-stateeffectsmayplayanimportantroleinthe

generation ofcollectivityfortheseparticlesin pPb collisions.The CGC framework also predicts a flavor hierarchy between prompt and nonprompt D0 for pT∼2–5 GeV, again consistent with the datawithinuncertainties.

7. Summary

The first measurements of elliptic azimuthal anisotropies for prompt D0 mesons in proton-proton (pp) collisions at center-of-mass energy √s=13 TeV, and for nonprompt D0 _{mesons from} beauty hadron decaysin proton-lead(pPb) collisions at nucleon-nucleon center-of-mass energy √sNN=8.16 TeV are presented.

In pp collisions with multiplicities of Noffline

trk ≥100, the second Fourierharmoniccoefficient(v2)oftheazimuthaldistributionsfor prompt D0 mesonsare measuredover thetransverse momentum (pT)rangeof2–8 GeV,withindicationsofpositive v2 signalsover the pT range of 2–4 GeV.These values are found to be compa-rable (orslightly smaller) to thoseof light-flavor hadron species. Atsimilareventmultiplicities,thepromptD0 mesonv2 signalsin pp and pPb collisions are found tobe comparable inmagnitude. The v2 valuesof open beautyhadronsare extracted forthe first timevianon-promptD0mesonsinpPb collisions,withmagnitudes smallerthan thoseforprompt D0 _{mesonsfor p}

T∼2–5 GeV. The newmeasurementsofcharmhadron v2 inthepp systemandthe indicationsof massdependenceofheavy-flavorhadron v2 inthe pPb system provideinsightsinto theoriginofheavy-flavorquark collectivityinsmallcollidingsystems.

Declaration of competing interest

Theauthorsdeclarethattheyhavenoknowncompeting finan-cialinterestsorpersonalrelationshipsthatcouldhaveappearedto influencetheworkreportedinthispaper.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technical andadministrativestaffsat CERNandat other CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructure essentialto ouranalyses. Finally, we acknowledge the enduring support for the construc-tion andoperation oftheLHC andtheCMSdetectorprovided by the followingfundingagencies:BMBWF andFWF(Austria); FNRS and FWO (Belgium); CNPq, CAPES,FAPERJ, FAPERGS, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RIF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUT, PUT and ERDF (Estonia); AcademyofFinland,MEC,andHIP(Finland);CEAandCNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); NK-FIA (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN(Italy);MSIPandNRF(RepublicofKorea);MES(Latvia);LAS (Lithuania);MOE andUM(Malaysia);BUAP,CINVESTAV,CONACYT, LNS,SEP,andUASLP-FAI(Mexico);MOS(Montenegro);MBIE(New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portu-gal);JINR(Dubna);MON,ROSATOM,RAS, RFBR,andNRCKI (Rus-sia);MESTD(Serbia);SEIDI,CPAN,PCTI,andFEDER(Spain);MoSTR (Sri Lanka); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter,IPST,STAR,andNSTDA(Thailand);TUBITAKandTAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOEand NSF (USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandHorizon2020Grant, contract Nos.675440, 752730,and765710 (EuropeanUnion);the

LeventisFoundation;theA.P.SloanFoundation;theAlexandervon Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap enTechnologie (IWT-Belgium); the F.R.S.-FNRS andFWO(Belgium)underthe“ExcellenceofScience–EOS”–be.h projectn. 30820817; the BeijingMunicipal Science & Technology Commission, No. Z191100007219010; The Ministry of Education, Youth and Sports (MEYS) of the Czech Republic; the Deutsche Forschungsgemeinschaft(DFG) under Germany’s Excellence Strat-egy –EXC 2121“Quantum Universe” –390833306; the Lendület (“Momentum”)ProgramandtheJánosBolyaiResearchScholarship of the Hungarian Academy of Sciences, the New National Excel-lence ProgramÚNKP,the NKFIA research grants 123842, 123959, 124845,124850,125105,128713,128786,and129058 (Hungary); the Council of Science and Industrial Research, India; the HOM-ING PLUS program of the Foundation for Polish Science, cofi-nanced from European Union, Regional Development Fund, the MobilityPlusprogram ofthe Ministryof Scienceand Higher Ed-ucation,theNationalScienceCenter(Poland), contractsHarmonia 2014/14/M/ST2/00428,Opus2014/13/B/ST2/02543,2014/15/B/ST2/ 03998,and2015/19/B/ST2/02861,Sonata-bis2012/07/E/ST2/01406; the National Priorities Research Program by Qatar National Re-searchFund;theMinistryofScienceandHigherEducationofthe RussianFederation, projectno.02.a03.21.0005(Russia);theTomsk PolytechnicUniversityCompetitivenessEnhancementProgram;the ProgramaEstatalde Fomentode laInvestigación Científicay Téc-nicade ExcelenciaMaría de Maeztu, grant MDM-2015-0509 and theProgramaSeveroOchoa delPrincipadode Asturias;theThalis andAristeiaprograms cofinancedbyEU-ESFandtheGreekNSRF; theRachadapisekSompotFundforPostdoctoralFellowship, Chula-longkornUniversity andtheChulalongkornAcademicintoIts 2nd Century Project Advancement Project (Thailand); the Kavli Foun-dation;the Nvidia Corporation; the SuperMicro Corporation; the WelchFoundation,contractC-1845;andtheWestonHavens Foun-dation(USA).

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The CMS Collaboration

A.M. Sirunyan†,A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam, F. Ambrogi, T. Bergauer, M. Dragicevic, J. Erö,A. Escalante Del Valle, M. Flechl,R. Frühwirth1,

M. Jeitler1,N. Krammer, I. Krätschmer,D. Liko, T. Madlener,I. Mikulec, N. Rad, J. Schieck1, R. Schöfbeck,

M. Spanring, W. Waltenberger, C.-E. Wulz1, M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Drugakov, V. Mossolov,J. Suarez Gonzalez

InstituteforNuclearProblems,Minsk,Belarus

M.R. Darwish, E.A. De Wolf,D. Di Croce, X. Janssen,T. Kello2,A. Lelek, M. Pieters, H. Rejeb Sfar,

H. Van Haevermaet, P. Van Mechelen,S. Van Putte, N. Van Remortel

UniversiteitAntwerpen,Antwerpen,Belgium

F. Blekman, E.S. Bols,S.S. Chhibra, J. D’Hondt, J. De Clercq, D. Lontkovskyi,S. Lowette, I. Marchesini,

S. Moortgat, Q. Python, S. Tavernier, W. Van Doninck, P. Van Mulders

VrijeUniversiteitBrussel,Brussel,Belgium

D. Beghin, B. Bilin, B. Clerbaux, G. De Lentdecker, H. Delannoy, B. Dorney, L. Favart, A. Grebenyuk,

A.K. Kalsi, L. Moureaux, A. Popov, N. Postiau, E. Starling, L. Thomas, C. Vander Velde, P. Vanlaer,

D. Vannerom

T. Cornelis, D. Dobur,I. Khvastunov3,M. Niedziela, C. Roskas, K. Skovpen, M. Tytgat, W. Verbeke,

B. Vermassen, M. Vit

GhentUniversity,Ghent,Belgium

G. Bruno,C. Caputo, P. David, C. Delaere, M. Delcourt,A. Giammanco, V. Lemaitre, J. Prisciandaro,

A. Saggio, P. Vischia, J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

G.A. Alves, G. Correia Silva,C. Hensel,A. Moraes

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas, W. Carvalho, J. Chinellato4,E. Coelho, E.M. Da Costa, G.G. Da Silveira5,

D. De Jesus Damiao, C. De Oliveira Martins, S. Fonseca De Souza, H. Malbouisson, J. Martins6,

D. Matos Figueiredo, M. Medina Jaime7,M. Melo De Almeida, C. Mora Herrera,L. Mundim, H. Nogima,

W.L. Prado Da Silva, P. Rebello Teles, L.J. Sanchez Rosas,A. Santoro, A. Sznajder,M. Thiel,

E.J. Tonelli Manganote4, F. Torres Da Silva De Araujo,A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

C.A. Bernardesa,L. Calligarisa,T.R. Fernandez Perez Tomeia, E.M. Gregoresb, D.S. Lemosa,

P.G. Mercadanteb, S.F. Novaesa, Sandra S. Padulaa

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,SãoPaulo,Brazil}

A. Aleksandrov, G. Antchev, R. Hadjiiska, P. Iaydjiev, M. Misheva,M. Rodozov, M. Shopova,G. Sultanov

InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

M. Bonchev, A. Dimitrov, T. Ivanov, L. Litov,B. Pavlov, P. Petkov,A. Petrov

UniversityofSofia,Sofia,Bulgaria

W. Fang2,X. Gao2, L. Yuan

BeihangUniversity,Beijing,China

M. Ahmad, Z. Hu, Y. Wang

DepartmentofPhysics,TsinghuaUniversity,Beijing,China

G.M. Chen8, H.S. Chen8,M. Chen, C.H. Jiang, D. Leggat, H. Liao,Z. Liu, A. Spiezia, J. Tao, E. Yazgan,

H. Zhang, S. Zhang8, J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

A. Agapitos, Y. Ban, G. Chen, A. Levin, J. Li,L. Li, Q. Li, Y. Mao,S.J. Qian, D. Wang, Q. Wang

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China M. Xiao

ZhejiangUniversity,Hangzhou,China

C. Avila, A. Cabrera,C. Florez, C.F. González Hernández, M.A. Segura Delgado

UniversidaddeLosAndes,Bogota,Colombia

J. Mejia Guisao,J.D. Ruiz Alvarez, C.A. Salazar González, N. Vanegas Arbelaez

UniversidaddeAntioquia,Medellin,Colombia

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic, M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic, D. Ferencek,K. Kadija, D. Majumder, B. Mesic, M. Roguljic, A. Starodumov9,T. Susa

InstituteRudjerBoskovic,Zagreb,Croatia

M.W. Ather, A. Attikis, E. Erodotou,A. Ioannou, M. Kolosova,S. Konstantinou, G. Mavromanolakis,

J. Mousa, C. Nicolaou, F. Ptochos,P.A. Razis, H. Rykaczewski, H. Saka,D. Tsiakkouri

UniversityofCyprus,Nicosia,Cyprus

M. Finger10,M. Finger Jr.10, A. Kveton, J. Tomsa

CharlesUniversity,Prague,CzechRepublic E. Ayala

EscuelaPolitecnicaNacional,Quito,Ecuador E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador Y. Assran11,12,E. Salama12,13

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

S. Bhowmik, A. Carvalho Antunes De Oliveira, R.K. Dewanjee, K. Ehataht,M. Kadastik, M. Raidal,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola, L. Forthomme, H. Kirschenmann,K. Osterberg, M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

E. Brücken, F. Garcia, J. Havukainen, J.K. Heikkilä, V. Karimäki, M.S. Kim,R. Kinnunen, T. Lampén,

K. Lassila-Perini, S. Laurila, S. Lehti,T. Lindén, H. Siikonen,E. Tuominen, J. Tuominiemi

HelsinkiInstituteofPhysics,Helsinki,Finland

P. Luukka, T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon, F. Couderc, M. Dejardin,D. Denegri, B. Fabbro, J.L. Faure, F. Ferri, S. Ganjour, A. Givernaud,

P. Gras, G. Hamel de Monchenault, P. Jarry,C. Leloup, B. Lenzi, E. Locci,J. Malcles, J. Rander,

A. Rosowsky, M.Ö. Sahin,A. Savoy-Navarro14, M. Titov,G.B. Yu

IRFU,CEA,UniversitéParis-Saclay,Gif-sur-Yvette,France

S. Ahuja, C. Amendola, F. Beaudette, M. Bonanomi, P. Busson, C. Charlot, B. Diab, G. Falmagne,

R. Granier de Cassagnac, I. Kucher, A. Lobanov, C. Martin Perez, M. Nguyen,C. Ochando, P. Paganini,

J. Rembser, R. Salerno,J.B. Sauvan, Y. Sirois, A. Zabi, A. Zghiche

LaboratoireLeprince-Ringuet,CNRS/IN2P3,EcolePolytechnique,InstitutPolytechniquedeParis,Palaiseau,France

J.-L. Agram15,J. Andrea, D. Bloch, G. Bourgatte, J.-M. Brom,E.C. Chabert, C. Collard,E. Conte15,

J.-C. Fontaine15, D. Gelé, U. Goerlach,C. Grimault, A.-C. Le Bihan, N. Tonon,P. Van Hove

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron, C. Bernet,G. Boudoul, C. Camen, A. Carle, N. Chanon, R. Chierici,D. Contardo, P. Depasse,

H. El Mamouni, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, Sa. Jain, I.B. Laktineh,H. Lattaud, A. Lesauvage,

M. Lethuillier, L. Mirabito,S. Perries, V. Sordini, L. Torterotot,G. Touquet, M. Vander Donckt, S. Viret

UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France G. Adamov

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze10

TbilisiStateUniversity,Tbilisi,Georgia

C. Autermann, L. Feld, K. Klein, M. Lipinski, D. Meuser, A. Pauls, M. Preuten,M.P. Rauch,J. Schulz,

M. Teroerde

RWTHAachenUniversity,I.PhysikalischesInstitut,Aachen,Germany

M. Erdmann, B. Fischer, S. Ghosh, T. Hebbeker,K. Hoepfner,H. Keller, L. Mastrolorenzo,

M. Merschmeyer, A. Meyer,P. Millet, G. Mocellin, S. Mondal, S. Mukherjee,D. Noll, A. Novak, T. Pook,

A. Pozdnyakov, T. Quast,M. Radziej, Y. Rath, H. Reithler,J. Roemer, A. Schmidt, S.C. Schuler, A. Sharma,

S. Wiedenbeck, S. Zaleski

RWTHAachenUniversity,III.PhysikalischesInstitutA,Aachen,Germany

G. Flügge, W. Haj Ahmad16, O. Hlushchenko,T. Kress, T. Müller, A. Nowack,C. Pistone, O. Pooth,D. Roy,

H. Sert, A. Stahl17

RWTHAachenUniversity,III.PhysikalischesInstitutB,Aachen,Germany

M. Aldaya Martin, P. Asmuss,I. Babounikau, H. Bakhshiansohi,K. Beernaert, O. Behnke,

A. Bermúdez Martínez, A.A. Bin Anuar, K. Borras18, V. Botta,A. Campbell, A. Cardini,P. Connor,

S. Consuegra Rodríguez, C. Contreras-Campana, V. Danilov,A. De Wit, M.M. Defranchis, C. Diez Pardos,

D. Domínguez Damiani, G. Eckerlin,D. Eckstein, T. Eichhorn, A. Elwood, E. Eren, L.I. Estevez Banos,

E. Gallo19, A. Geiser,A. Grohsjean, M. Guthoff, M. Haranko,A. Harb, A. Jafari,N.Z. Jomhari, H. Jung,

A. Kasem18,M. Kasemann, H. Kaveh, J. Keaveney, C. Kleinwort,J. Knolle, D. Krücker,W. Lange, T. Lenz,

J. Lidrych, K. Lipka,W. Lohmann20,R. Mankel, I.-A. Melzer-Pellmann,A.B. Meyer, M. Meyer, M. Missiroli,

J. Mnich, A. Mussgiller, V. Myronenko,D. Pérez Adán, S.K. Pflitsch,D. Pitzl, A. Raspereza,A. Saibel,

M. Savitskyi, V. Scheurer,P. Schütze, C. Schwanenberger, R. Shevchenko, A. Singh,R.E. Sosa Ricardo,

H. Tholen, O. Turkot, A. Vagnerini, M. Van De Klundert,R. Walsh, Y. Wen,K. Wichmann, C. Wissing,

O. Zenaiev, R. Zlebcik

DeutschesElektronen-Synchrotron,Hamburg,Germany

R. Aggleton, S. Bein,L. Benato, A. Benecke,T. Dreyer, A. Ebrahimi, F. Feindt, A. Fröhlich, C. Garbers,

E. Garutti, D. Gonzalez, P. Gunnellini, J. Haller, A. Hinzmann,A. Karavdina, G. Kasieczka, R. Klanner,

R. Kogler, N. Kovalchuk,S. Kurz, V. Kutzner, J. Lange,T. Lange, A. Malara, J. Multhaup, C.E.N. Niemeyer,

A. Reimers, O. Rieger,P. Schleper, S. Schumann,J. Schwandt,J. Sonneveld, H. Stadie, G. Steinbrück,

B. Vormwald, I. Zoi

UniversityofHamburg,Hamburg,Germany

M. Akbiyik, M. Baselga, S. Baur, T. Berger,E. Butz, R. Caspart,T. Chwalek, W. De Boer, A. Dierlamm,

K. El Morabit, N. Faltermann, M. Giffels,A. Gottmann, F. Hartmann17, C. Heidecker, U. Husemann,

G. Quast, K. Rabbertz, D. Savoiu, D. Schäfer, M. Schnepf,M. Schröder, I. Shvetsov, H.J. Simonis,R. Ulrich,

M. Wassmer, M. Weber,C. Wöhrmann, R. Wolf,S. Wozniewski

KarlsruherInstitutfuerTechnologie,Karlsruhe,Germany

G. Anagnostou, P. Asenov, G. Daskalakis,T. Geralis, A. Kyriakis,D. Loukas, G. Paspalaki,A. Stakia

InstituteofNuclearandParticlePhysics(INPP),NCSRDemokritos,AghiaParaskevi,Greece

M. Diamantopoulou, G. Karathanasis,P. Kontaxakis,A. Manousakis-katsikakis, A. Panagiotou,

I. Papavergou, N. Saoulidou, K. Theofilatos, K. Vellidis,E. Vourliotis

NationalandKapodistrianUniversityofAthens,Athens,Greece

G. Bakas, K. Kousouris, I. Papakrivopoulos,G. Tsipolitis, A. Zacharopoulou

NationalTechnicalUniversityofAthens,Athens,Greece

I. Evangelou, C. Foudas, P. Gianneios,P. Katsoulis, P. Kokkas, S. Mallios, K. Manitara, N. Manthos,

I. Papadopoulos, J. Strologas,F.A. Triantis, D. Tsitsonis

UniversityofIoánnina,Ioánnina,Greece

M. Bartók21, R. Chudasama, M. Csanad, P. Major, K. Mandal, A. Mehta,G. Pasztor, O. Surányi,G.I. Veres

MTA-ELTELendületCMSParticleandNuclearPhysicsGroup,EötvösLorándUniversity,Budapest,Hungary

G. Bencze, C. Hajdu,D. Horvath22,F. Sikler, V. Veszpremi, G. Vesztergombi†

WignerResearchCentreforPhysics,Budapest,Hungary

N. Beni, S. Czellar,J. Karancsi21, J. Molnar,Z. Szillasi

InstituteofNuclearResearchATOMKI,Debrecen,Hungary

P. Raics, D. Teyssier, Z.L. Trocsanyi,B. Ujvari

InstituteofPhysics,UniversityofDebrecen,Debrecen,Hungary

T. Csorgo, W.J. Metzger, F. Nemes, T. Novak

EszterhazyKarolyUniversity,KarolyRobertCampus,Gyongyos,Hungary

S. Choudhury, J.R. Komaragiri, P.C. Tiwari

IndianInstituteofScience(IISc),Bangalore,India

S. Bahinipati23, C. Kar,G. Kole, P. Mal, V.K. Muraleedharan Nair Bindhu, A. Nayak24,D.K. Sahoo23,

S.K. Swain

NationalInstituteofScienceEducationandResearch,HBNI,Bhubaneswar,India

S. Bansal, S.B. Beri, V. Bhatnagar,S. Chauhan, N. Dhingra25,R. Gupta, A. Kaur, M. Kaur, S. Kaur,

P. Kumari, M. Lohan, M. Meena, K. Sandeep, S. Sharma, J.B. Singh, A.K. Virdi

PanjabUniversity,Chandigarh,India

A. Bhardwaj, B.C. Choudhary, R.B. Garg,M. Gola, S. Keshri,Ashok Kumar, M. Naimuddin,P. Priyanka,

K. Ranjan, Aashaq Shah, R. Sharma

UniversityofDelhi,Delhi,India

R. Bhardwaj26,M. Bharti26,R. Bhattacharya, S. Bhattacharya, U. Bhawandeep26,D. Bhowmik, S. Dutta,

S. Ghosh, B. Gomber27,M. Maity28, K. Mondal, S. Nandan,A. Purohit, P.K. Rout, G. Saha, S. Sarkar,

M. Sharan, B. Singh26,S. Thakur26

P.K. Behera, S.C. Behera, P. Kalbhor, A. Muhammad,P.R. Pujahari, A. Sharma, A.K. Sikdar IndianInstituteofTechnologyMadras,Madras,India

D. Dutta, V. Jha, D.K. Mishra, P.K. Netrakanti,L.M. Pant, P. Shukla

BhabhaAtomicResearchCentre,Mumbai,India

T. Aziz, M.A. Bhat, S. Dugad,G.B. Mohanty, N. Sur, Ravindra Kumar Verma

TataInstituteofFundamentalResearch-A,Mumbai,India

S. Banerjee, S. Bhattacharya, S. Chatterjee, P. Das, M. Guchait,S. Karmakar, S. Kumar, G. Majumder,

K. Mazumdar, N. Sahoo,S. Sawant

TataInstituteofFundamentalResearch-B,Mumbai,India

S. Dube, B. Kansal, A. Kapoor, K. Kothekar, S. Pandey, A. Rane, A. Rastogi,S. Sharma

IndianInstituteofScienceEducationandResearch(IISER),Pune,India

S. Chenarani, S.M. Etesami,M. Khakzad, M. Mohammadi Najafabadi, M. Naseri, F. Rezaei Hosseinabadi

InstituteforResearchinFundamentalSciences(IPM),Tehran,Iran

M. Felcini, M. Grunewald

UniversityCollegeDublin,Dublin,Ireland

M. Abbresciaa,b,R. Alya,b,29,C. Calabriaa,b,A. Colaleoa, D. Creanzaa,c,L. Cristellaa,b, N. De Filippisa,c, M. De Palmaa,b,A. Di Florioa,b,W. Elmetenaweea,b, L. Fiorea, A. Gelmia,b, G. Iasellia,c, M. Incea,b, S. Lezkia,b,G. Maggia,c, M. Maggia,J.A. Merlina,G. Minielloa,b,S. Mya,b,S. Nuzzoa,b,A. Pompilia,b, G. Pugliesea,c, R. Radognaa,A. Ranieria, G. Selvaggia,b, L. Silvestrisa,F.M. Simonea,b, R. Vendittia,

P. Verwilligena

a_{INFNSezionediBari,Bari,Italy} b_{UniversitàdiBari,Bari,Italy} c_{PolitecnicodiBari,Bari,Italy}

G. Abbiendia, C. Battilanaa,b, D. Bonacorsia,b, L. Borgonovia,b, S. Braibant-Giacomellia,b,

R. Campaninia,b,P. Capiluppia,b, A. Castroa,b,F.R. Cavalloa,C. Cioccaa,G. Codispotia,b,M. Cuffiania,b, G.M. Dallavallea, F. Fabbria,A. Fanfania,b,E. Fontanesia,b, P. Giacomellia, L. Giommia,b, C. Grandia, L. Guiduccia,b, F. Iemmia,b,S. Lo Meoa,30, S. Marcellinia, G. Masettia,F.L. Navarriaa,b,A. Perrottaa, F. Primaveraa,b,T. Rovellia,b, G.P. Sirolia,b,N. Tosia

a_{INFNSezionediBologna,Bologna,Italy} b_{UniversitàdiBologna,Bologna,Italy}

S. Albergoa,b,31, S. Costaa,b, A. Di Mattiaa,R. Potenzaa,b,A. Tricomia,b,31, C. Tuvea,b

a

INFNSezionediCatania,Catania,Italy

b_{UniversitàdiCatania,Catania,Italy}

G. Barbaglia,A. Cassesea,R. Ceccarellia,b,V. Ciullia,b,C. Civininia, R. D’Alessandroa,b, F. Fioria, E. Focardia,b, G. Latinoa,b,P. Lenzia,b, M. Lizzoa,b,M. Meschinia,S. Paolettia, R. Seiditaa,b,

G. Sguazzonia,L. Viliania

a_{INFNSezionediFirenze,Firenze,Italy} b_{UniversitàdiFirenze,Firenze,Italy}

L. Benussi, S. Bianco, D. Piccolo

INFNLaboratoriNazionalidiFrascati,Frascati,Italy

M. Bozzoa,b, F. Ferroa, R. Mulargiaa,b, E. Robuttia,S. Tosia,b