Measurement Of Electrons From Heavy-flavour Hadron Decays In P-pb Collisions At Root S(nn)=5.02 Tev

SISTEMA DE BIBLIOTECAS DA UNICAMP

REPOSITÓRIO DA PRODUÇÃO CIENTIFICA E INTELECTUAL DA UNICAMP

Versão do arquivo anexado / Version of attached file:

Versão do Editor / Published Version

Mais informações no site da editora / Further information on publisher's website:

https://www.sciencedirect.com/science/article/pii/S0370269315010151

DOI: 10.1016/j.physletb.2015.12.067

Direitos autorais / Publisher's copyright statement:

©2016

by Elsevier. All rights reserved.

DIRETORIA DE TRATAMENTO DA INFORMAÇÃO

Cidade Universitária Zeferino Vaz Barão Geraldo

CEP 13083-970 – Campinas SP

Fone: (19) 3521-6493

http://www.repositorio.unicamp.br

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

electrons

from

heavy-flavour

hadron

decays

in

p–Pb

collisions

at

√

s

_NN

=

5

.

02

TeV

.

ALICE

Collaboration



a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received12October2015

Receivedinrevisedform12November2015 Accepted21December2015

Availableonline31December2015 Editor:L.Rolandi

Theproductionofelectronsfromheavy-flavourhadrondecayswasmeasuredasafunctionoftransverse

momentum(pT)inminimum-biasp–Pb collisions at√sNN=5.02 TeV using theALICEdetectoratthe

LHC. The measurementcoversthe pTinterval 0.5<pT<12 GeV/c andthe rapidityrange −1.065<

ycms<0.135 in the centre-of-mass reference frame. The contribution of electrons from background

sources was subtractedusing an invariant mass approach. The nuclear modification factor RpPb was

calculatedbycomparingthepT-differentialinvariantcrosssectioninp–Pbcollisionstoappreferenceat

thesamecentre-of-massenergy,whichwasobtainedbyinterpolatingmeasurements at√s=2.76 TeV

and √s₌7 TeV. The RpPb is consistentwithunity withinuncertainties ofabout 25%,whichbecome

largerforpTbelow1 GeV/c.Themeasurementshowsthatheavy-flavourproductionisconsistentwith

binary scaling,sothat asuppression inthe high-pT yieldin Pb–Pbcollisions hasto beattributed to

effectsinducedbythehotmediumproducedinthefinalstate.Thedatainp–Pbcollisionsaredescribed

byrecentmodelcalculationsthatincludecoldnuclearmattereffects.

©2015CERNforthebenefitoftheALICECollaboration.PublishedbyElsevierB.V.Thisisanopen

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

1. Introduction

TheQuark-GluonPlasma(QGP)[1,2],acolour-deconfined state of strongly-interacting matter, is predicted to exist at high tem-peratureaccordingtolatticeQuantumChromodynamics(QCD) cal-culations[3].Theseconditionscan bereachedinultra-relativistic heavy-ion collisions [4–10]. Charm and beauty (heavy-flavour) quarks are mostly produced in initial hard scattering processes on a very short time scale, shorter than the formation time of theQGPmedium[11],andthus experiencethefulltemporaland spatial evolutionof thecollision. Whileinteracting withtheQGP medium, heavy quarks lose energy via elastic andradiative pro-cesses [12–14]. Heavy-flavour hadrons are therefore well-suited probestostudythepropertiesoftheQGP.Theeffectofenergyloss onheavy-flavourproduction canbe characterised viathe nuclear modificationfactor(RAA)ofheavy-flavourhadrons.The RAAis

de-fined as the ratio of the heavy-flavour hadron yield in nucleus– nucleus (A–A)collisions to that in proton–proton (pp) collisions scaled by the average number of binary nucleon–nucleon colli-sions.The RAA isstudieddifferentiallyasafunctionoftransverse

momentum(pT), rapidity( y)andcollisioncentrality.Itwas

mea-sured at the Relativistic Heavy Ion Collider (RHIC) [15–18] and at the Large Hadron Collider (LHC) [19–22]. At RHIC, in central

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

Au–Au collisionsat

√

sNN

=

200 GeV the RAA of charmed mesons

and of electrons from heavy-flavour hadron decays shows that their productionisstronglysuppressedby afactorofabout5for

pT

>

3 GeV

/c at

mid-rapidity. For the mostcentral Pb–Pb

colli-sions at

√

sNN

=

2

.

76 TeV at the LHC, a suppression by a factor

of5–6isobservedforcharmedmesonsfor pT

>

5 GeV

/c at

mid-rapidity[22].

The interpretation of the measurements in A–A collisions re-quires the study of heavy-flavour production in p–A collisions, whichprovidesaccesstocoldnuclearmatter(CNM)effects.These effects are not related to the formation of a colour-deconfined medium, but are present in case of colliding nuclei (or proton– nucleus). An important CNM effect inthe initial state is parton-density shadowing or saturation, which can be described using modified parton distribution functions (PDF) in the nucleus [23] or using the Color Glass Condensate (CGC) effective theory [24]. FurtherCNMeffects includeenergyloss[25] intheinitial and fi-nalstatesandaCronin-likeenhancement[26]asaconsequenceof multiplescatterings[25,27].

The influence of the CNM effects can be studied by measur-ing the nuclearmodification factor RpA. Like the RAA,the RpA is

defined such that it is unity if there are no nuclear effects. For minimum-biasp–Acollisions,itcanbeexpressedas[28]

RpA

=

1 A dσpA

/

dpT dσpp

/

dpT

,

(1) http://dx.doi.org/10.1016/j.physletb.2015.12.067

0370-2693/©2015CERNforthebenefitoftheALICECollaboration.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

wheredσpA

/

dpT anddσpp

/

dpT arethe pT-differential production

crosssectionsofagivenparticlespeciesinp–Aandppcollisions, respectively,and A isthenumberofnucleonsinthenucleus.

Cold nuclear matter effects were recently investigated at the

RHIC and the LHC [29–44]. At RHIC, the nuclear modification

factor of electrons from heavy-flavour hadron decays in central d–Au collisions (0–20%) at

√

sNN

=

200 GeV is larger than unity

atmid-rapidity in thetransverse momentum interval 1

.

5

<

pT

<

5 GeV

/c

[42]. The corresponding measurement for muons from heavy-flavour hadron decays in central d–Au collisions shows a suppressionatforwardrapidityandanenhancementatbackward rapidity [43]. Theoretical modelsthat includethe modificationof thePDF inthe nucleuscanneitherexplain the enhancementnor thelargedifferencebetweenforwardandbackwardrapidity. Possi-bleexplanationsincludetheCronin-likeenhancement[26] dueto radial flow ofheavy mesons[45].At the LHC,the pT-differential

nuclear modification factor RpPb of D mesons measured in p–Pb

collisions at

√

sNN

=

5

.

02 TeV [44] is consistent with unity for

pT

>

1 GeV

/c and

isdescribedbytheoretical calculationsthat

in-clude gluon saturation effects. Both atRHIC andat theLHC, the p/d–Ameasurementsindicatethatinitial-stateeffectsalonecannot explainthestrongsuppressionseenathigh-pTinnucleus–nucleus

collisions.

In this Letter, the pT-differential invariant cross section and

the nuclear modification factor RpPb of electrons from

heavy-flavourhadron decaysmeasuredinminimum-biasp–Pbcollisions at

√

sNN

=

5

.

02 TeV withALICEattheLHCarepresented.The

mea-surementcoverstherapidityrange

−

1

.

065

<

ycms

<

0

.

135 inthe

centre-of-masssystem(cms)forelectronswithtransverse momen-tum0

.

5

<

pT

<

12 GeV

/c.

Thisrapidity coverage resultsfromthe

samerigidityofthepandPbbeamsattheLHC,leadingtoa rapid-ityshiftof

|

yNN

|

=

0

.

465 between the nucleon–nucleoncms and

thelaboratoryreferenceframe,inthedirectionofthepbeam.At low pT,themeasurementprobestheproductionofcharm-hadron

decays[46],providingsensitivitytothegluonPDFintheregimeof Bjorken-x oftheorderof10−4_{[47],whereasubstantialshadowing}

effectisexpected[48].

ToobtainthenuclearmodificationfactorRpPbofelectronsfrom

heavy-flavour hadron decays, the pT-differential invariant cross

section in p–Pb collisions at

√

sNN

=

5

.

02 TeV was compared to

a pp reference multiplied by 208, the Pb mass number. The pp reference was obtained by interpolating the pT-differential cross

sectionmeasurementsat

√

s

=

2

.

76 TeV and7 TeV.

The Letter is organised as follows. The experimental appara-tus, data sample and event selection are described in Section 2. The electron reconstruction strategy and the pp reference spec-trumareexplainedinSections3and4,respectively.Themeasured

pT-differentialinvariantcrosssection,thenuclearmodification

fac-tor RpPb ofelectronsfromheavy-flavourhadrondecaysand

com-parisonofRpPbtomodelcalculationsarereportedinSection5. 2. Experimentalapparatus,datasampleandeventselection

A detailed description of the ALICE apparatus can be found in [49,50]. Electrons are reconstructed at mid-rapidity using the centralbarreldetectors(describedbelow)locatedinsideasolenoid magnet, which generates a magnetic field B

=

0

.

5 T along the beamdirection.

TheInnerTrackingSystem(ITS),theclosestdetectortothe in-teraction point, includes sixcylindricallayers of silicondetectors withthreedifferenttechnologies(pixel,driftandstrip)atradii be-tween 3.9 cm and 43 cmwith a pseudorapidity coverage inthe laboratoryreferenceframeinthefullazimuthbetween

|

η

lab

|

<

2.0

atsmallradiiand

|

η

lab

|

<

0.9atlargeradii[49,51].Thetwo

inner-mostlayers formthe Silicon Pixel Detector (SPD), which plays a

keyroleinprimaryandsecondaryvertexreconstruction.Atan in-cidentangleperpendiculartothedetectorsurfaces,thetotal mate-rialbudgetoftheITScorrespondsonaverageto7.7%ofaradiation length [51].The maintracking device inthecentral barrelis the TimeProjectionChamber(TPC) [52],whichsurroundstheITSand covers a pseudorapidity rangeof

|

η

lab

|

<

0.9 inthefull azimuth.

Thetrackreconstructionproceedsinwardfromtheouterradiusof the TPCto theinnermostlayer ofthe ITS[50]. The TPCprovides particle identificationviathe measurementofthespecific energy lossdE

/

dx.TheTime-Of-Flightarray(TOF),basedonMulti-gap Re-sistivePlateChambers,coversthefullazimuthand

|

η

lab

|

<

0.9at

a radial distanceof 3.7 mfrom the interaction point [53]. Using the particle time-of-flight measurement, electrons can be distin-guishedfromhadronsfor pT

≤

2

.

5 GeV

/c.

Thecollisiontime,used

forthecalculationofthetime-of-flighttotheTOFdetector,is mea-suredby anarray ofCherenkovcounters,theT0detector,located at

+

350 cm and

−

70 cm from the interaction point along the beamdirection[54].TheElectromagneticCalorimeter(EMCal), sit-uatedbehindtheTOF,isasamplingcalorimeterbasedonShashlik technology[55].Itsgeometricalacceptanceis107◦inazimuthand

|

η

lab

|

<

0.7. Inthis analysis, theazimuthal angleand

η

coverage

were limitedto100◦ and0.6, respectively,toensure uniform de-tectorperformance.

The minimum-bias (MB) p–Pb datasample used inthis anal-ysis was collected in 2013. The trigger condition required a co-incidence of signalsbetween thetwo V0scintillator hodoscopes, placed on either side ofthe interaction point at2

.

8

<

η

lab

<

5

.

1

and

−

3

.

7

<

η

lab

<

−

1

.

7,synchronisedwiththepassageofbunches

frombothbeams[54].The backgroundduetointeractions ofone ofthetwobeamsandresidualparticlesinthebeamvacuumtube was rejectedintheofflineeventselectionbycorrelating thetime informationofthe V0detectorswiththatfromthe twoZero De-greeCalorimeters(ZDC) [50],thatarelocated112.5 mawayfrom the interaction point along the beam pipe, symmetrically on ei-therside.Theprimaryvertexwasreconstructedwithtracksinthe ITSandtheTPC[50].Eventswithaprimaryvertexlocatedfarther than

±

10 cm from thecentreoftheinteraction regionalong the beamdirectionwererejected.About10%oftheeventsdonotfulfil thisselectioncriterion.Asampleof100millioneventspassedthe offline eventselection, corresponding toan integrated luminosity

Lint

=

47

.

8

±

1

.

6 μb−1,giventhecrosssection

σ

_MBV0

=

2

.

09

±

0

.

07 b

fortheminimum-biasV0triggercondition [56].Theefficiencyfor thetriggerconditionandofflineeventselectionislargerthan99% fornon-single-diffractive(NSD)p–Pbcollisions [57].

3. Analysis

A combination of electron identification (eID) strategies with different detectors offers the largest pT reach for the

measure-mentofelectronsfromheavy-flavourhadrondecays.Inparticular, it ensures that thesystematic uncertainties andthe hadron con-taminationaresmalloverthewholetransversemomentumrange. Throughoutthepaper,theterm‘electron’isusedforelectronsand positrons. The capabilityofthe TPCtoidentifyelectrons via spe-cific energy loss dE

/

dx in thedetector was usedover the whole momentum range 0

.

5

<

pT

<

12 GeV

/c.

However, itis subjectto

ambiguous identification of hadrons (pions, kaons, protons and deuterons)below2

.

5 GeV

/c and

above6 GeV

/c in

transverse mo-mentum. At low transverse momentum (0

.

5

<

pT

<

2

.

5 GeV

/c),

these ambiguities were resolved by measuring the time-of-flight oftheparticlefromtheinteractionregiontotheTOFdetectorand combiningitwiththemomentummeasurement,todeterminethe particlemass.Inthehighmomentumregion(6

<

pT

<

12 GeV

/c),

theEMCalwasusedtoreducethehadroncontamination.Electrons are separatedfromhadronsbycalculatingtheratiooftheenergy

Fig. 1. (a):MeasureddE/dx intheTPCasfunctionofmomentump expressedasadeviationfromtheexpectedenergylossofelectrons, normalisedbytheenergy-loss resolution(σTPC) aftereIDwithTOF.ThesolidlinesindicatethenTPCσ selectioncriteriafortheTPCandTOFeIDstrategy.(b):E/p distributionofelectrons(−1<nTPCσ <3)

andhadrons(nTPC

σ <−3.5)inthetransversemomentuminterval6<pT<8 GeV/c.TheE/p distributionofhadronswasnormalisedtothatofelectronsinthelowerE/p

range(0.4–0.6),wherehadronsdominate.Thesolidlinesindicatetheappliedelectronselectioncriteria.(Forinterpretationofthereferencestocolorinthisfigurelegend, thereaderisreferredtothewebversionofthisarticle.)

deposited(E) intheEMCaltothemomentum(p).Sinceelectrons depositall oftheir energyin theEMCal,the ratio E/p isaround unity forelectrons, while the ratio for charged hadronsis much smalleronaverage.

Theselection criteriaforcharged-particle tracksare similar to those applied in previous analyses measuring the production of electrons from heavy-flavour hadron decays in pp collisions [58, 59].In orderto haveoptimaleIDperformance with theTPC, the analysis was restricted to the pseudorapidity range

|

η

lab

|

<

0

.

6

inthe laboratoryframe forelectrons withtransverse momentum 0

.

5

<

pT

<

12 GeV

/c.

Up to a pT of6 GeV

/c,

a signal in the

in-nermost layer of the SPD was required in order to reduce the background from photon conversions. In addition, this selection was further constrained by requiring hits in both SPD layers, to reducethenumberofincorrectmatchesbetweencandidatetracks andhits reconstructed in the first layer of the SPD. At high pT,

wheretheEMCal was used,trackswithhitsin eitheroftheSPD layerswereselectedinordertominimisetheeffectofdeadareas ofthefirst SPDlayer withinthe acceptanceregion ofthe EMCal, asinpreviousanalyses[58,59].

TheelectronidentificationwithTPCandTOFwasbasedonthe numberofstandard deviations(nTPC

σ ornTOFσ ) forthe specific

en-ergy loss and time-of-flight measurements, respectively. The nσ

variable is computedas a difference betweenthe measured sig-nal and the expected one for electrons divided by the energy loss (σTPC) or time-of-flight (σTOF) resolution. The expected

sig-nal and resolution originate from parametrisations of the detec-tor signal, which are described in detail in [50]. In the trans-verse momentum interval 0

.

5

<

pT

<

2

.

5 GeV

/c, particles

were

identified as electrons if they satisfied

−

0

.

5

<

nTPC_σ

<

3, which yields an identification efficiency of 69%. In the transverse mo-mentuminterval 2

.

5

<

pT

<

6 GeV

/c,

a tighterselection criterion

of 0

<

nTPC_σ

<

3 was applied (with an eID efficiency of 50%) to reduce the hadron contamination at higher transverse momen-tum.Toresolvetheaforementionedambiguitiesatlowtransverse momentum (pT

≤

2

.

5 GeV

/c),

only tracks with

|

nTOFσ

|

<

3 were

accepted. Fig. 1(a) shows the measured dE

/

dx in the TPC with respecttotheexpecteddE

/

dx forelectronsnormalisedtothe ex-pectedresolution

σ

TPCaftertheeIDwithTOF.Thesolidlines

indi-catetheselectioncriteriausedforthetransversemomentum

inter-val0

.

5

<

pT

<

2

.

5 GeV

/c,

indicatingthatthehadroncontamination

withintheresultingelectroncandidatesampleissmall.Inthehigh momentumregion(6

<

pT

<

12 GeV

/c),

electronswereselectedif

theysatisfied

−

1

<

nTPC_σ

<

3 and0

.

8

<

E/p

<

1

.

2 (seeFig. 1(b)). The hadron contamination in the electron candidate sample was determined by parametrising the TPC signal in momentum slicesforpT

≤

6 GeV

/c as

doneinpreviousanalyses[58,59].In the

transverse momentum interval 6

<

pT

<

12 GeV

/c,

the E/p

dis-tribution forhadronsidentified via the specific energyloss mea-suredinthe TPC(nTPC_σ

<

−

3

.

5) wasnormalised inthelower E/p

range(0.4–0.6)tothecorrespondingE/p distributionforidentified electrons (

−

1

<

nTPC

σ

<

3) (see Fig. 1(b)).The number ofhadrons

with an E

/p ratio

between 0.8 and 1.2was thus determined in momentum slices. The hadron contamination ranged from2% at 5

<

pT

<

6 GeV

/c to

15% at10

<

pT

<

12 GeV

/c and

was

corre-spondingly subtracted. For pT

<

5 GeV

/c,

the contamination was

foundtobenegligible.

Theresultingelectroncandidatesample,alsoreferredtoasthe ‘inclusiveelectronsample’inthefollowing,stillcontainselectrons fromsourcesotherthanheavy-flavourhadrondecays.Themajority of theremaining backgroundoriginates fromphoton conversions inthedetectormaterial(γ

→

e+e−) andDalitzdecaysofneutral mesons,e.g.

π

0

_→

_γ

_e+_e− _and

_η

_→

_γ

_e+_e−_{.Theseelectronsare} hereafterdenotedas‘photonicelectrons’.

Inpreviousanalysesofelectronsfromheavy-flavourhadron de-caysinppcollisionsbytheALICECollaboration,thecontributionof electronsfrombackgroundsourceswasestimatedviaadata-tuned Monte Carlo cocktail and subtracted from the inclusive electron sample [58,59].Thepioninput tothecocktail wasbasedon pion measurementswithALICE[60,61],whileheaviermesonswere im-plemented via mT scaling[62],andphotonsfromhard scattering

processes(direct

γ

,

γ

∗)wereobtainedfromnext-to-leadingorder (NLO)calculations[63].Theresultingsystematicuncertaintyofthe sumofall backgroundsourceswas large, inparticularatlow pT,

wherethesignal-to-background ratioissmall[58,59].Inorder to reduce this uncertainty, in this analysis an invariant mass tech-nique[16] was usedto estimatethe numberofelectrons coming frombackgroundsources.

Photonicelectronsareproducedine+e−pairsandcanthusbe identified using an invariant mass technique (photonic method).

Fig. 2. Invariantmassdistributionsofunlike-sign andlike-signelectronpairsfor theinclusiveelectronpTinterval0.5<pT<0.6 GeV/c.Thedifferencebetweenthe distributionsyieldsthephotoniccontribution.

Allinclusiveelectrons were paired withother tracks inthe same eventpassingloosertrackselectionandelectronidentification cri-teria(e.g.

−

3

<

nTPC

σ

<

3).Looserselectioncriteriawereappliedto

increase the efficiencyto findthe photonic partner. Fig. 2shows theinvariant massdistributions ofunlike-sign andlike-sign elec-tron pairs for the inclusive electron in the interval 0

.

5

<

pT

<

0

.

6 GeV

/c.

The like-sign distribution estimates the uncorrelated pairs.Subtractingthesefromtheunlike-signpairsyieldsthe num-ber of electrons with a photonic partner N_photraw (see Fig. 2). An invariant mass smaller than 0.14 GeV/c2 was required. Accord-ing to simulations, the peak around zero in the photonic elec-tronpairdistribution isdueto photonconversions; the exponen-tialtail to higher valuesoriginates fromDalitz decays of neutral mesons.

The efficiency

ε

phot to find photonic electron pairs was

esti-matedusingMonteCarlosimulations.Asampleofp–Pbcollisions was generated with HIJING v1.36 [64]. Toincrease the statistical precision at high pT, one cc or bb pair decaying

semileptoni-cally usingthe generatorPYTHIAv6.4.21 [65] withthePerugia-0 tune[66] was added ineach event.The generatedparticles were propagated throughtheapparatususingGEANT3 [67]anda real-isticdetectorresponse wasappliedto reproducetheperformance of the detector systemduring data taking period.The simulated transversemomentumdistributionsofthe

π

0 _and

_η

_mesonswere

weighted to match the measured shapes, where the

π

0 _input

was basedon themeasured charged-pion spectra [68,69] assum-ing _Nπ0

=

1

/

2

(

Nπ+

+

_Nπ−

)

andthe

η

input was derived via mT

scaling.Theefficiency

ε

phot isdefinedasthefractionofelectrons

fromphotonicoriginforwhichthepartnercouldbefoundwithin the defined acceptance of the analysis, i.e. the geometrical ac-ceptanceof theALICEapparatustogether with thesuperimposed track selection and electron identification criteria. The efficiency

ε

phot increasessharplywithpT from35%to80%between0.5and

3 GeV

/c and

remains at 80% up to 12 GeV

/c.

The raw photonic electron distribution Nraw_phot was then corrected by the efficiency

ε

phot as Nphot

(p

T

)

=

Nraw_phot

(p

T

)/

ε

phot

(p

T

)

andsubtracted fromthe

inclusiveelectronyieldtoobtaintheyieldofelectronsfrom heavy-flavour hadron decays. The signal-to-background ratio (ratio of non-photonic to photonicyield) ranges from0.2 at 0.5 GeV/c to 4at10 GeV/c.

The remaining electrons are then those from semileptonic heavy-flavourhadrondecays(N_hferaw),besidesasmallresidual back-ground contribution originating from semileptonic kaon decays

anddielectron decaysofJ

/ψ

mesons. Thelatteris theonly non-negligible contribution from quarkonia.These contributions were subtractedfromthecorrectedinvariantcrosssection,asdescribed lateroninthissection.

ThepT-differentialinvariantcrosssection

σ

hfeofelectronsfrom

heavy-flavourhadrondecays,1

/

2

(

e+

+

e−

)

,wascalculatedas

1 2πpT d2

σ

hfe dpTd y

=

1 2 1

ϕ

pcentre_T 1

y

pT

cunfoldNraw_hfe

(



geo

_×



reco

_×



eID

₎

σ

V0

MB

NMB

,

(2)

where pcentre

T arethecentresofthe pTbinswithwidths

p

T,and

ϕ

and

y denote

thegeometricalacceptanceinazimuthand ra-piditytowhichtheanalysiswasrestricted,respectively.NMBisthe

numberofeventsthatpasstheselectioncriteriadescribedin Sec-tion 2 and

σ

V0

MB is the p–Pb cross section for the minimum-bias

V0 trigger condition. The rawspectrum ofelectrons from heavy-flavour hadron decays(Nraw_hfe) wascorrected fortheacceptanceof the detectors in the selected geometrical region of the analysis (geo_{),thetrackreconstructionandselectionefficiency(}reco_),and

the eID efficiency(eID_{). These correctionswere computedusing}

theaforementionedMonteCarlosimulations.Onlytheefficiencyof theTPCelectronidentificationselectioncriterionforpT

<

6 GeV

/c

was determined usinga data-driven approach based on thenTPC_σ

distribution [59]. Themeasurement oftheelectron pT isaffected

by the finite momentum resolution and by electron energy loss duetobremsstrahlunginthedetectormaterial[49],whichisnot corrected for in the trackreconstruction algorithm. These effects distort theshape of the pT distribution,which fallssteeply with

increasingmomentum.Todeterminethiscorrection(cunfold),an

it-erativeunfoldingprocedurebasedonBayes’theoremwas applied [70,71].

The aforementioned residual background contributions, elec-tronsfromsemileptonickaondecaysanddielectrondecaysofJ

/ψ

mesons,were estimatedasan invariant crosssectionwithMonte Carlosimulationsandfoundtobelessthan3%perpTbinand

sub-tractedfromthecorrectedinvariant crosssection ofnon-photonic electrons.Morespecifically,thecontributionfromJ

/ψ

mesonswas implemented by using a parametrisation for pp collisions based on the interpolation of J

/ψ

measurements from RHIC at

√

s

=

200 GeV,Tevatron at

√

s

=

1

.

96 TeV,andthe LHCat

√

s

=

7 TeV accordingto [72].Decays ofJ

/ψ

mesonswithin

|

ylab

|

<

1.0were

considered. Theparametrisationandits associatedsystematic un-certainty werescaled frompptop–Pbcollisions assumingbinary collision scaling.Potentialdeviationsfrombinary collision scaling wereconsideredbyassigning a50%systematicuncertaintyonthe normalisation. The parametrisationwithits uncertainties usedas inputfortheMonteCarlosimulationsisconsistentwiththe mea-suredJ

/ψ

crosssectioninp–Pbcollisions[38].

The systematic uncertainties were estimated as a function of

pT by repeating theanalysis withdifferentselection criteria. The

systematicuncertaintieswereevaluatedforthespectrumobtained afterthesubtractionofthephotonicyieldNphotfromtheinclusive

spectrum andbefore removing the remaining background contri-butions originatingfromsemileptonickaondecaysanddielectron decays of J

/ψ

mesons. The sources of systematic uncertaintyfor theinclusiveanalysisandthedeterminationoftheelectron back-groundarelistedinTable 1.

The systematic uncertainties for tracking and eID are pT

de-pendentduetotheusageofthevariousdetectorsinthedifferent momentumintervals.Thelatteralsoincludestheuncertaintiesdue tothedeterminationofthehadroncontamination.The3% system-aticuncertaintyforthematchingbetweenITSandTPCwastaken from [73], where the matching efficiency of charged particles in

Table 1

Systematicuncertaintiesforthedifferentmomentumintervals.

Variable 0.5<pT<2.5 GeV/c 2.5<pT<6 GeV/c 6<pT<12 GeV/c

Tracking 4.3% 2.2% 3% Matching 4.2% 3% 3.2% eID 3.6% 3.6% 3.2% (6–8 GeV/c) 5.1% (8–10 GeV/c) 15.1% (10–12 GeV/c) Photonic method 6.9% (0.5–1 GeV/c) 2.4% 4.5% 3.7% (1–2.5 GeV/c) Unfolding 1% 1% <1%

Total 9.9% (0.5–1 GeV/c) 5.8% 7.1% (6–8 GeV/c)

8.0% (1–2.5 GeV/c) 8.1% (8–10 GeV/c)

16.4% (10–12 GeV/c)

data was compared to Monte Carlosimulations. The uncertainty ofthe TOF-TPC matching efficiencywas estimatedby comparing thematching efficiency indata andMonte Carlosimulations us-ingelectrons fromphoton conversions, whichwere identified via topological cuts. The uncertainty amounts to 3%. The TPC-EMCal matching uncertainty was assigned to be 1%, as determined by varyingthesizeofthematchingwindowin

η

andazimuth

ϕ

for charged-particle tracksthat were extrapolatedto thecalorimeter. Theresultingmatchinguncertaintieswerecombinedinquadrature forthevarious pTintervalsshowninTable 1.

The listed uncertainties for the photonic method include the uncertainties on eID and tracking. In addition, the Monte Carlo sample was divided into two halves. The first was treated as realdataand thesecond was used tocorrect theresulting spec-trum.Deviationsfromtheexpected pTspectrumofelectronsfrom

heavy-flavour hadron decays resulted in a 2% systematic uncer-tainty for pT

≤

6 GeV

/c and

4% above. The uncertainty on the

re-weighting of the

π

0_{- and}

_η

_{-meson p}

T distributions inMonte

Carlosimulationswasestimatedbychangingtheweightsby

±

10%. The variation yielded a 2% uncertainty for pT

≤

2

.

5 GeV

/c on

thepT-differentialinvariantcrosssectionofelectronsfrom

heavy-flavour hadron decays.This source ofuncertainty isnegligible at higherpT.Theinvariantmasstechniquegivesasystematic

uncer-taintysmallerbyafactorof

≥

4 andofabout1.4forpT

≤

1 GeV

/c

and3

<

pT

<

12 GeV

/c,

respectively, comparedto theone ofthe

cocktailsubtractionmethod[59].Thereduction inuncertainty,in particularatlow pT,proves the advantageof usingthe invariant

mass technique for the estimation of electrons from background sources.

Theuncertaintyofthe pTunfoldingprocedurewasdetermined

by employing an alternativeunfolding method (matrix inversion) and,asdescribedin[59],bycorrectingthedatawithtwodifferent MonteCarlosamplescorrespondingtodifferentpTdistributions.In

additiontotheaforementionedsignal-enhancedMonteCarlo sam-ple,aminimum-biassample wasused.Thecomparisonofthe re-sultingpT spectrarevealedanuncertaintyof1%forpT

≤

6 GeV

/c,

andsmaller than1% above6 GeV

/c.

The systematicuncertainties ofthe heavy-flavour electron yield dueto the subtractionof the remaining backgroundoriginatingfromsemileptonic kaondecays anddielectrondecaysfromJ

/ψ

mesonsaresmallerthan0.5%.This wasestimatedbychangingtheparticleyieldsby

±

50% and

±

100% fortheJ

/ψ

mesonandthesemileptonickaondecays,respectively. The individual sources of systematic uncertainties are uncor-related. Therefore,they were added in quadratureto give a total systematicuncertainty rangingfrom 5.8% to 16.4% depending on the pT bin. The normalisation uncertainty on the luminosity is

of 3.7%[56].

Fig. 3showstheinterval2

.

5

<

pT

<

8 GeV

/c of

thepT

-differen-tialinvariant crosssection ofelectrons fromheavy-flavourhadron decaysinminimum-biasp–Pbcollisionsat

√

sNN

=

5

.

02 TeV,

com-Fig. 3. The pT-differentialinvariant crosssectionofelectronsfromheavy-flavour hadron decaysinminimum-biasp–Pbcollisions at√sNN=5.02 TeV,comparing theresultsoftheeIDstrategiesinthetwotransitionregionsat2.5and6 GeV/c.

ThecentrevaluesareslightlyshiftedalongthepT-axisinthetransitionregionsfor bettervisibility.Theresultsagreewithin1%.DetailsontheeIDstrategiescanbe foundinthetext.

paringtheresultsofthevariouseIDstrategiesinthetwotransition regions at 2

.

5 GeV

/c and

6 GeV

/c.

A consistency within 1% is found.

4. ppreference

In order to calculate the nuclear modification factor RpPb,

a reference cross section forpp collisions at the same centre-of-mass energyis needed. Since pp dataat

√

s

=

5

.

02 TeV are cur-rently not available, the reference was obtained by interpolating the pT-differential cross sections of electrons from heavy-flavour

hadrondecaysmeasuredinpp collisionsat

√

s

=

2

.

76 TeV andat

√

s

=

7 TeV [58,59].Theanalysisdescribed in thispaperrequires a referenceinthe interval0

.

5

<

pT

<

12 GeV

/c.

While the

√

s

=

2

.

76 TeV analysiswascarriedoutinthispTrange,the

√

s

=

7 TeV measurement is limited to the pT interval 0

.

5

<

pT

<

8 GeV

/c.

Thus, to extendthe pT interval up to 12 GeV

/c a

measurement

by theATLAS Collaborationin the pT interval 7

<

pT

<

12 GeV

/c

was used [74]. The published ATLAS measurement, dσ

/

dpT, was

dividedby1

/(

2πpcentre

T

y)

,wherepcentreT denotesthecentral

val-ues of the pT bins, and

y the

rapidity range covered by the

measurement.Intheoverlapinterval7

<

pT

<

8 GeV

/c the

ALICE

andATLASmeasurements,whichagreewithinuncertainties,were combined as a weighted average. The inverse quadratic sum of statistical and systematic uncertainties of the two spectra were used as weights. Perturbative QCD (pQCD) calculations at fixed order withnext-to-leading-log (FONLL) resummation[75–77] de-scribe all aforementioned pp results [58,59] within experimental and theoretical uncertainties. The pp references are measured in asymmetric rapiditywindow(

|

ycms

|

<

0

.

8 at

√

s

=

2

.

76 TeV and

|

ycms

|

<

0

.

5 at

√

s

=

7 TeV).Theeffectduetothedifferent asym-metricrapiditywindowinthisanalysiswasestimatedwithFONLL andismuchsmallerthanthesystematicuncertaintiesofthedata, thereforeiswasneglected.

Anassumption aboutthe

√

s dependence oftheheavy-flavour productioncross sectionsisrequired fortheinterpolation. Calcu-lationsbasedonpQCDareconsistentwithapower-lawscalingof theheavy-flavourproductioncrosssectionwith

√

s[78]. Therefore,

Fig. 4. The pT-differentialinvariantcross sectionofelectronsfromheavy-flavour hadrondecaysinminimum-biasp–Pbcollisionsat√sNN=5.02 TeV.Thepp refer-enceobtainedviatheinterpolationmethodisshown,notscaledbyA,for compar-ison.Thestatisticaluncertaintiesareindicatedforbothspectrabyerrorbars,the systematicuncertaintiesareshownasboxes.

thisscalingwasusedtocalculatetheinterpolateddatapoints.The statisticaluncertainties ofthespectraat

√

s

=

2

.

76 TeV and

√

s

=

7 TeV were added in quadrature with weights according to the

√

s interpolation.Theweightedcorrelatedsystematicuncertainties (tracking,matchingandeID)ofthespectraat

√

s

=

2

.

76 TeV and

√

s

=

7 TeV wereaddedlinearly,whiletheweighted uncorrelated uncertainties(ITS layerconditions,unfolding andcocktail system-atics) were added in quadrature. The weights were determined accordingtothe

√

s interpolation.Theuncorrelatedandcorrelated uncertaintieswerethenaddedinquadrature.

Thesystematicuncertaintyofthebin-by-bininterpolation pro-cedurewasaddedinquadraturetothepreviousones.Itwas esti-matedbyusingalinearorexponentialdependenceon

√

s instead

ofapowerlaw.Theratiosoftheresulting pT spectratothe

base-linepp reference were usedto estimate asystematic uncertainty of+₋₁₀5%.

The resulting pp reference cross section is well described by FONLLcalculations.Thesystematicuncertaintiesofthe normalisa-tionsrelatedtothedeterminationoftheminimum-biasnucleon– nucleon cross sections of the input spectra were likewise inter-polated, yielding a normalisation uncertainty of 2.3% for the pp referencespectrum,assumingthattheyareuncorrelated.

5. Results

The pT-differential invariant cross section of electrons from

heavy-flavour hadron decays in the rapidity range

−

1

.

065

<

ycms

<

0

.

135 for p–Pbcollisions at

√

sNN

=

5

.

02 TeV isshown in Fig. 4andcomparedwiththeppreferencecrosssection. The ver-tical bars represent the statistical uncertainties, while the boxes indicate the systematic uncertainties. The systematic uncertain-ties of the p–Pb cross section are smaller than those of the pp cross section, in particularat low transverse momentum, mainly as a consequence of the estimation of the electron background via the invariant mass technique. For the pp analysis, the back-ground was subtracted via the cocktail method. At low pT, the

electrons mainly originate from charm-hadron decays, while for

pT

≥

4 GeV

/c beauty-hadron

decays are the dominant source in

ppcollisions[46].

Fig. 5. NuclearmodificationfactorRpPbofelectronsfromheavy-flavourhadron de-caysasafunctionoftransversemomentumforminimum-biasp–Pbcollisionsat

√_sNN=5

.02 TeV,comparedwiththeoreticalmodels[25,27,45,48,75],asdescribed inthetext.Theverticalbarsrepresentthestatisticaluncertainties,andtheboxes indicatethesystematicuncertainties.Thesystematicuncertaintyfromthe normali-sation,commontoallpoints,isshownasafilledboxathighpT.

The nuclear modificationfactor RpPb ofelectrons from

heavy-flavour hadron decays asa function of transverse momentum is showninFig. 5.Thestatisticalandsystematicuncertaintiesofthe spectra in p–Pb andpp were propagated as independent uncer-tainties. The normalisation uncertainties ofthe pp referenceand thep–Pbspectrumwereaddedinquadratureandareshownasa filledboxathightransversemomentuminFig. 5.

The RpPbisconsistentwithunitywithinuncertaintiesoverthe

whole pT rangeofthe measurement.Theproductionofelectrons

from heavy-flavourhadron decays isthus consistent withbinary collisionscaling ofthereferencespectrumforpp collisionsatthe samecentre-of-massenergy.Thesuppressionoftheyieldof heavy-flavour production in Pb–Pb collisions at high-pT is therefore a

finalstateeffectinducedbytheproducedhotmedium.

Given the large systematic uncertainties, our measurement is also compatiblewithan enhancement in the transverse momen-tum interval 1

<

pT

<

6 GeV

/c as

seen at mid-rapidity in d–Au

collisionsat

√

sNN

=

200 GeV[42].Suchanenhancementmightbe

causedbyradialflowassuggestedbystudiesonthemeanpT asa

functionoftheidentifiedparticlemultiplicity[68].

The data are described within the uncertainties by pQCD cal-culations including initial-state effects (FONLL [75]

+

EPS09NLO [48] nuclear shadowingparametrisation).The resultssuggestthat initial-state effects are small at high transverse momentum in Pb–Pb collisions.CalculationsbySharmaet al.whichincludeCNM energy loss, nuclear shadowing andcoherent multiple scattering atthepartoniclevelalsodescribethedata[27].Calculationsbased on incoherent multiple scatterings by Kang et al. predict an en-hancement atlow pT [25]. The formation of a hydrodynamically

expanding medium and consequently flow of charm and beauty quarks are expectedto result in an enhancement in the nuclear modification factor RpPb [45]. To quantify the possible effect on

RpPb,a blastwavecalculationwithparameters extractedfromfits

to the pT spectraoflight-flavourhadrons[68] measured inp–Pb

collisions was employed. The model calculation agrees with the data. However, the present uncertainties of the measurement do not allowusto discriminateamongthe aforementioned theoreti-calapproaches.

6. Summaryandconclusions

The pT-differential invariant cross section for electrons from

heavy-flavourhadron decaysin minimum-bias p–Pb collisions at

√

sNN

=

5

.

02 TeV was measured in the rapidity range

−

1

.

065

<

ycms

<

0

.

135 and the transverse momentum interval 0

.

5

<

pT

<

12 GeV

/c using

the combination of three electron identification methods.Theapplicationofthe invariantmass techniqueto sub-tractelectronsnotoriginatingfromopenheavy-flavourhadron de-cays largely reducedthe systematicuncertainties withrespect to the cocktail subtraction method, in particular at low transverse momentum.The pp reference forthe nuclearmodification factor

RpPb was obtained by interpolating the measured pT-differential

cross sections of electrons from heavy-flavour hadron decays at

√

s

=

2

.

76 TeV and

√

s

=

7 TeV.The RpPb isconsistent withunity

withinuncertaintiesofabout25%,whichbecomelargerforpT

be-low1 GeV

/c.

Thepresentedcalculationsdescribethe datawithin uncertainties.Theresultssuggestthatheavy-flavourproductionin minimum-bias p–Pbcollisions scales withthe number of binary collisions,although within uncertainties thedata are also consis-tentwithanenhancementabovethisscaling.Theconsistencywith unity of the RpPb at high pT indicates that the suppression of

heavy-flavourproductioninPb–Pb collisions isofdifferentorigin thancoldnuclearmattereffects.

Acknowledgements

The ALICECollaboration wouldlike to thank all its engineers andtechniciansfortheirinvaluablecontributionstothe construc-tionoftheexperimentandtheCERNacceleratorteamsforthe out-standingperformanceoftheLHCcomplex.TheALICECollaboration gratefully acknowledges the resources and support provided by allGrid centresandthe Worldwide LHCComputing Grid(WLCG) Collaboration. The ALICE Collaboration acknowledges the follow-ing funding agencies for their support in building and running theALICEdetector:State CommitteeofScience,World Federation ofScientists (WFS) andSwiss Fonds Kidagan, Armenia; Conselho Nacionalde Desenvolvimento Científico e Tecnológico(CNPq), Fi-nanciadorade Estudose Projetos(FINEP),Fundação de Amparoà Pesquisa do Estado de São Paulo (FAPESP); NationalNatural Sci-enceFoundation ofChina (NSFC),the Chinese Ministryof Educa-tion(CMOE)andtheMinistryofScienceandTechnology ofChina (MSTC); Ministry ofEducation and Youth of the Czech Republic; Danish Natural Science Research Council, the Carlsberg Founda-tionandtheDanish NationalResearchFoundation;The European ResearchCouncilundertheEuropeanCommunity’sSeventh Frame-work Programme; Helsinki Institute of Physics and the Academy of Finland; French CNRS-IN2P3, the ‘Region Pays de Loire’, ‘Re-gion Alsace’, ‘Region Auvergne’ and CEA, France; German Bun-desministerium fur Bildung, Wissenschaft, Forschung und Tech-nologie(BMBF)andtheHelmholtzAssociation;GeneralSecretariat for Research and Technology, Ministry of Development, Greece; HungarianOrszagos Tudomanyos KutatasiAlappgrammok (OTKA) andNationalOfficeforResearchandTechnology (NKTH); Depart-mentofAtomicEnergyandDepartmentofScienceandTechnology of the Government of India; Istituto Nazionale di Fisica Nucle-are (INFN) andCentroFermi –Museo Storico dellaFisica e Cen-troStudi e Ricerche “Enrico Fermi”,Italy; MEXT Grant-in-Aid for SpeciallyPromotedResearch,Japan;JointInstituteforNuclear Re-search,Dubna;NationalResearchFoundationofKorea(NRF); Con-sejoNacionaldeCiencayTecnologia(CONACYT),DirecciónGeneral de Asuntos del Personal Academico (DGAPA), México, Amerique Latine Formation academique – European Commission (ALFA-EC) andtheEPLANETProgram (EuropeanParticlePhysicsLatin Ameri-canNetwork);StichtingvoorFundamenteelOnderzoekderMaterie

(FOM)andtheNederlandseOrganisatievoorWetenschappelijk On-derzoek (NWO), Netherlands; Research Council ofNorway (NFR); NationalScienceCentre,Poland;MinistryofNational Education/In-stitute for Atomic Physics and National Council of Scientific Re-search in Higher Education (CNCSI-UEFISCDI), Romania; Ministry ofEducationandScience ofRussianFederation, RussianAcademy ofSciences,RussianFederalAgencyofAtomicEnergy,Russian Fed-eral Agency for Science and Innovations and The Russian Foun-dation for BasicResearch; Ministry ofEducation of Slovakia; De-partment of Science and Technology, Republic of South Africa, South Africa; Centro de Investigaciones Energeticas, Medioambi-entales yTecnologicas (CIEMAT),E-Infrastructureshared between EuropeandLatin America(EELA),MinisteriodeEconomíay Com-petitividad (MINECO) of Spain, Xunta de Galicia (Consellería de Educación), Centro de Aplicaciones TecnológicasyDesarrollo Nu-clear(CEADEN),Cubaenergía,Cuba,andIAEA(InternationalAtomic EnergyAgency);SwedishResearchCouncil (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.

References

[1]J.D.Bjorken,Highlyrelativisticnucleus–nucleuscollisions:thecentralrapidity region,Phys.Rev.D27(1983)140–151.

[2]F.Karsch,LatticeQCDathightemperatureanddensity,Lect.NotesPhys.583 (2002)209–249,arXiv:hep-lat/0106019.

[3]S.Borsanyi,Z.Fodor,C.Hoelbling,S.D.Katz,S.Krieg,K.K.Szabo,Fullresultfor theQCDequationofstatewith2+1 flavors,Phys.Lett.B730(2014)99–104, arXiv:1309.5258[hep-lat].

[4]BRAHMSCollaboration,I.Arsene, etal.,Quarkgluonplasmaandcolorglass condensateatRHIC?TheperspectivefromtheBRAHMSexperiment,Nucl.Phys. A757(2005)1–27,arXiv:nucl-ex/0410020.

[5]B.B.Back,etal.,ThePHOBOSperspectiveondiscoveriesatRHIC,Nucl.Phys.A 757(2005)28–101,arXiv:nucl-ex/0410022.

[6]STARCollaboration,J.Adams,etal.,Experimentalandtheoreticalchallengesin thesearchforthequarkgluonplasma:theSTARcollaboration’scritical assess-mentoftheevidencefromRHICcollisions,Nucl.Phys.A757(2005)102–183, arXiv:nucl-ex/0501009.

[7]PHENIX Collaboration, K. Adcox,et al., Formation ofdensepartonicmatter inrelativisticnucleus–nucleuscollisionsatRHIC:experimentalevaluationby the PHENIXcollaboration,Nucl. Phys.A757(2005)184–283,arXiv:nucl-ex/ 0410003.

[8]ALICECollaboration,K.Aamodt,etal.,Charged-particlemultiplicitydensityat mid-rapidityincentralPb–Pbcollisionsat√sNN=2.76 TeV,Phys.Rev.Lett. 105(2010)252301,arXiv:1011.3916[nucl-ex].

[9]ALICECollaboration,K.Aamodt,etal.,EllipticflowofchargedparticlesinPb– Pbcollisionsat2.76 TeV,Phys.Rev.Lett.105(2010)252302,arXiv:1011.3914 [nucl-ex].

[10]ALICE Collaboration,K. Aamodt,et al., Suppressionofchargedparticle pro-ductionatlargetransversemomentumincentralPb–Pbcollisionsat√sNN= 2.76 TeV,Phys.Lett.B696(2011)30–39,arXiv:1012.1004[nucl-ex].

[11]F.-M.Liu,S.-X. Liu,Quark-gluon plasmaformationtime anddirect photons fromheavyioncollisions,Phys.Rev.C89 (3)(2014)034906,arXiv:1212.6587 [nucl-th].

[12]E.Braaten,M.H.Thoma,Energylossofaheavyfermioninahotplasma,Phys. Rev.D44(1991)1298–1310.

[13]R.Baier,Y.L.Dokshitzer,A.H.Mueller,S.Peigne,D.Schiff,Radiativeenergyloss ofhigh-energyquarksandgluonsinafinitevolumequark-gluon plasma,Nucl. Phys.B483(1997)291–320,arXiv:hep-ph/9607355.

[14]S.Wicks,W.Horowitz,M.Djordjevic,M.Gyulassy,Heavyquarkjetquenching withcollisionalplusradiativeenergylossandpathlengthfluctuations,Nucl. Phys.A783(2007)493–496,arXiv:nucl-th/0701063.

[15]PHENIXCollaboration,A.Adare,etal.,Energylossandflowofheavyquarks inAu+Au collisionsat√sNN=200 GeV, Phys.Rev.Lett.98(2007)172301,

arXiv:nucl-ex/0611018.

[16]STARCollaboration,B.I.Abelev,etal.,Transversemomentumandcentrality de-pendenceofhigh-pT non-photonicelectronsuppressioninAu+Aucollisions at√sNN=200 GeV,Phys.Rev.Lett.98(2007)192301,arXiv:nucl-ex/0607012;

STARCollaboration,B.I.Abelev,etal.,Transversemomentumandcentrality de-pendenceofhigh-pT non-photonicelectronsuppressioninAu+Aucollisions at√sN N=200 GeV,Phys.Rev.Lett.106(2011)159902(Erratum).

[17]PHENIXCollaboration, A.Adare,et al.,Nuclear-modificationfactorfor open-heavy-flavorproductionatforwardrapidityinCu+Cucollisionsat√sNN= 200 GeV,Phys.Rev.C86(2012)024909,arXiv:1204.0754[nucl-ex].

[18]STARCollaboration,L.Adamczyk,etal.,ObservationofD0_mesonnuclear

mod-ificationsinAu+Aucollisionsat√sNN=200 GeV,Phys.Rev.Lett.113 (14) (2014)142301,arXiv:1404.6185[nucl-ex].

[19]ALICECollaboration,B.Abelev,etal.,Productionofmuonsfromheavyflavour decaysatforwardrapidityinppandPb–Pbcollisionsat√sNN=2.76TeV,Phys. Rev.Lett.109(2012)112301,arXiv:1205.6443[hep-ex].

[20]CMS Collaboration, S. Chatrchyan, et al., Suppression ofnon-prompt J/ψ, prompt J/ψ,andY(1S)inPbPbcollisionsat√sNN=2.76 TeV,J.HighEnergy Phys.05(2012)063,arXiv:1201.5069[nucl-ex].

[21]ALICECollaboration,J.Adam,etal.,Inclusive,promptandnon-promptJ/ψ pro-ductionatmid-rapidityinPb–Pbcollisionsat√sNN=2.76 TeV,J.HighEnergy

Phys.07(2015)051,arXiv:1504.07151[nucl-ex].

[22]ALICECollaboration,J.Adam,etal.,Centralitydependenceofhigh-pTDmeson

suppressioninPb–Pbcollisionsat√sNN=2.76 TeV,arXiv:1506.06604

[nucl-ex].

[23]N.Armesto,Nuclearshadowing,J.Phys.G32(2006)R367–R394,arXiv:hep-ph/ 0604108.

[24]H. Fujii,F.Gelis,R. Venugopalan,Quarkpair production inhighenergypA collisions:generalfeatures,Nucl.Phys.A780(2006)146–174,arXiv:hep-ph/ 0603099.

[25]Z.-B.Kang,I.Vitev,E.Wang,H.Xing,C.Zhang,Multiplescatteringeffectson heavymesonproductioninp+Acollisionsatbackwardrapidity,Phys.Lett.B 740(2015)23–29,arXiv:1409.2494[hep-ph].

[26]J.W.Cronin,H.J.Frisch,M.J.Shochet,J.P.Boymond,R.Mermod,P.A.Piroue,R.L. Sumner,Productionofhadronswithlargetransversemomentumat200-GeV, 300-GeV,and400-GeV,Phys.Rev.D11(1975)3105.

[27]R.Sharma,I.Vitev,B.-W.Zhang,Light-conewavefunctionapproachtoopen heavyflavordynamicsinQCDmatter,Phys.Rev.C80(2009)054902,arXiv: 0904.0032[hep-ph].

[28]D.G.d’Enterria,Hardscatteringcross-sectionsatLHCintheGlauberapproach: frompptopAandAAcollisions,arXiv:nucl-ex/0302016.

[29]STAR Collaboration, J. Adams, et al., Open charm yields in d

+

Au colli-sionsat √sNN=200 GeV, Phys.Rev.Lett.94(2005)062301, arXiv:nucl-ex/ 0407006.

[30]PHENIXCollaboration,A.Adare,etal.,υ(1S+2S+3S)productionind+Au andp+p collisionsat√sNN=200 GeV andcold-nuclearmattereffects,Phys. Rev.C87(2013)044909,arXiv:1211.4017[nucl-ex].

[31]PHENIXCollaboration,A.Adare,etal.,Transverse-momentumdependenceof the J/ψ nuclearmodificationind

+

Au collisionsat√sNN=200 GeV,Phys. Rev.C87 (3)(2013)034904,arXiv:1204.0777[nucl-ex].

[32]PHENIXCollaboration,A.Adare,etal.,Nuclearmodificationofψ,χc,andJ/ψ productionind+Aucollisionsat√sNN=200 GeV,Phys.Rev.Lett.111 (20) (2013)202301,arXiv:1305.5516[nucl-ex].

[33]PHENIXCollaboration,A.Adare,etal.,Heavy-flavorelectron–muoncorrelations inp

+

p andd

+

Au collisionsat√sNN=200 GeV,Phys.Rev.C89 (3)(2014) 034915,arXiv:1311.1427[nucl-ex].

[34]STARCollaboration,L.Adamczyk,etal.,Suppressionofϒproductionind+Au andAu+Aucollisionsat√sNN=200 GeV,Phys.Lett.B735(2014)127–137, arXiv:1312.3675[nucl-ex];

STARCollaboration,L.Adamczyk,etal.,Suppressionofϒproductionind+Au andAu+Aucollisionsat√sNN=200 GeV,Phys.Lett.B743(2015)537 (Erra-tum).

[35]PHENIXCollaboration,A.Adare,etal.,Crosssectionforbb production¯ via di-electronsind+Aucollisionsat√sNN=200 GeV,Phys.Rev.C91 (1)(2015) 014907,arXiv:1405.4004[nucl-ex].

[36]ALICE Collaboration,B.B. Abelev,etal., Suppression ofψ(2S)production in p–Pb collisionsat√sNN=5.02 TeV,J.HighEnergyPhys.12(2014)073,arXiv: 1405.3796[nucl-ex].

[37]ALICE Collaboration, B.B. Abelev,et al., Production of inclusive ϒ(1S) and

ϒ(2S)inp–Pb collisionsat√sNN=5.02 TeV,Phys.Lett.B740(2015)105–117,

arXiv:1410.2234[nucl-ex].

[38]ALICECollaboration, J.Adam,etal.,Rapidityand transverse-momentum de-pendenceoftheinclusiveJ/ψ nuclearmodificationfactorinp–Pbcollisions at √sN N=5.02 TeV,J.HighEnergyPhys. 06(2015)055,arXiv:1503.07179 [nucl-ex].

[39]ATLASCollaboration,G.Aad,etal.,MeasurementofdifferentialJ/ψproduction crosssectionsandforward-backwardratiosinp

+

PbcollisionswiththeATLAS detector,Phys.Rev.C92 (3)(2015)034904,arXiv:1505.08141[hep-ex].

[40]CMSCollaboration,S. Chatrchyan,et al.,EventactivitydependenceofY(nS) productionin√sNN=5.02 TeV pPband√s=2.76 TeV ppcollisions,J.High EnergyPhys.04(2014)103,arXiv:1312.6300[nucl-ex].

[41]CMSCollaboration,V.Khachatryan,etal.,StudyofBmesonproductioninpPb collisionsat√sNN=5.02 TeV,arXiv:1508.06678[nucl-ex].

[42]PHENIXCollaboration,A.Adare,etal.,Cold-nuclear-mattereffectson heavy-quarkproduction ind

+

Au collisionsat √sNN=200 GeV, Phys. Rev.Lett. 109 (24)(2012)242301,arXiv:1208.1293[nucl-ex].

[43]PHENIXCollaboration,A.Adare,etal.,Cold-nuclear-mattereffectson heavy-quarkproduction at forwardand backwardrapidityind+Aucollisionsat √

sNN=200 GeV,Phys. Rev.Lett. 112 (25) (2014) 252301, arXiv:1310.1005 [nucl-ex].

[44]ALICECollaboration,B.B.Abelev,etal.,MeasurementofpromptD-meson pro-ductioninp–P b collisionsat√sNN=5.02 TeV,Phys.Rev.Lett.113 (23)(2014) 232301,arXiv:1405.3452[nucl-ex].

[45]A.M.Sickles,Possibleevidenceforradialflowofheavymesonsind+Au colli-sions,Phys.Lett.B731(2014)51–56,arXiv:1309.6924[nucl-th].

[46]ALICECollaboration,B.Abelev,et al.,Measurementofelectronsfrombeauty hadrondecaysinpp collisionsat√s=7 TeV,Phys.Lett.B721(2013)13–23, arXiv:1208.1902[hep-ex].

[47]A.Dainese,Charmproductionand in-mediumQCDenergylossinnucleus– nucleus collisionswithALICE:aperformancestudy,PhDthesis,PaduaU.,2003, arXiv:nucl-ex/0311004.

[48]K.J.Eskola,H.Paukkunen,C.A.Salgado,EPS09:anewgenerationofNLOand LOnuclearpartondistributionfunctions,J.HighEnergyPhys.04(2009)065, arXiv:0902.4154[hep-ph].

[49]ALICECollaboration,K.Aamodt,etal.,TheALICEexperimentattheCERNLHC, J.Instrum.3(2008),S08002.

[50]ALICECollaboration,B.B.Abelev,etal.,PerformanceoftheALICEexperimentat theCERNLHC,Int.J.Mod.Phys.A29(2014)1430044,arXiv:1402.4476 [nucl-ex].

[51]ALICECollaboration,K.Aamodt,etal.,AlignmentoftheALICEinnertracking systemwithcosmic-raytracks,J.Instrum.5(2010)P03003,arXiv:1001.0502 [physics.ins-det].

[52]J.Alme,etal.,TheALICETPC,alarge3-dimensionaltrackingdevicewithfast readoutforultra-highmultiplicityevents,Nucl.Instrum.MethodsA622(2010) 316–367,arXiv:1001.1950[physics.ins-det].

[53] ALICECollaboration,P.Cortese,etal.,ALICE:addendumtothetechnicaldesign reportofthetimeofflightsystem(TOF),CERN-LHCC-2002-016(2002)(URL:

https://cds.cern.ch/record/545834).

[54] ALICECollaboration,P.Cortese,etal.,ALICEtechnicaldesignreportonforward detectors:FMD, T0and V0, CERN-LHCC-2004-025 (2004)(URL: https://cds. cern.ch/record/781854).

[55] ALICE Collaboration, P. Cortese, et al., ALICE electromagnetic calorime-ter technical design report, CERN-LHCC-2008-014 (2008) (URL: https://cds. cern.ch/record/1121574).

[56]ALICECollaboration,B.B.Abelev,etal.,Measurementofvisiblecrosssections inproton-leadcollisionsat√sNN=5.02 TeV invanderMeerscanswiththe

ALICEdetector,J.Instrum.9 (11)(2014)P11003,arXiv:1405.1849[nucl-ex].

[57]ALICECollaboration,B.Abelev,etal.,Pseudorapiditydensityofcharged par-ticlesinp–Pbcollisionsat √sNN=5.02 TeV,Phys. Rev.Lett.110 (3)(2013) 032301,arXiv:1210.3615[nucl-ex].

[58]ALICECollaboration,B.B.Abelev,etal.,Measurementofelectronsfrom semilep-tonicheavy-flavorhadrondecaysinpp collisionsat√s=2.76 TeV,Phys.Rev. D91 (1)(2015)012001,arXiv:1405.4117[nucl-ex].

[59]ALICECollaboration,B.Abelev,etal.,Measurementofelectronsfrom semilep-tonicheavy-flavourhadrondecaysinppcollisionsat√s=7 TeV,Phys.Rev.D 86(2012)112007,arXiv:1205.5423[hep-ex].

[60]ALICECollaboration,B.Abelev,etal.,Neutralpionandηmesonproductionin proton–protoncollisionsat√s=0.9 TeV and√s=7 TeV,Phys. Lett.B717 (2012)162–172,arXiv:1205.5724[hep-ex].

[61]ALICECollaboration,B.B.Abelev,etal.,Neutralpionproductionatmidrapidity inppandPb–Pbcollisionsat√sNN=2.76 TeV,Eur.Phys.J.C74 (10)(2014)

3108,arXiv:1405.3794[nucl-ex].

[62]PHENIXCollaboration,A.Adare,etal.,Detailedmeasurementofthee+e−pair continuumin p

+

p and Au+Aucollisionsat√sNN=200 GeV and impli-cationsfor directphoton production,Phys.Rev.C81(2010)034911, arXiv: 0912.0244[nucl-ex].

[63]L.E.Gordon,W.Vogelsang,Polarizedandunpolarizedisolatedpromptphoton productionbeyondtheleadingorder,Phys.Rev.D50(1994)1901–1916.

[64]M.Gyulassy,X.-N.Wang,HIJING1.0:aMonteCarloprogramforpartonand particleproduction inhigh-energyhadronicandnuclearcollisions, Comput. Phys.Commun.83(1994)307,arXiv:nucl-th/9502021.

[65]T.Sjostrand, S.Mrenna, P.Z.Skands,PYTHIA6.4physicsandmanual,J.High EnergyPhys.05(2006)026,arXiv:hep-ph/0603175.

[66]P.Z.Skands,TuningMonteCarlogenerators:thePerugiatunes,Phys.Rev.D82 (2010)074018,arXiv:1005.3457[hep-ph].

[67] R.Brun,F.Carminati,S.Giani,GEANTdetectordescriptionandsimulationtool, CERNProgramLibrarylongwriteupW5013(1994).

[68]ALICECollaboration,B.B.Abelev,etal.,Multiplicitydependenceofpion,kaon, protonandlambdaproductioninp–Pbcollisionsat √sNN=5.02 TeV, Phys. Lett.B728(2014)25–38,arXiv:1307.6796[nucl-ex].

[69]ALICECollaboration,J.Adam,etal.,Multiplicitydependenceofchargedpion, kaon,and(anti)protonproductionatlargetransversemomentuminp–Pb col-lisionsat√sNN=5.02 TeV,arXiv:1601.03658[nucl-ex].

[70] G.D’Agostini,Bayesianreasoninginhigh-energyphysics:principlesand appli-cations,CERN-YELLOW-99-03(1999)(URL:http://cds.cern.ch/record/395902). [71] J.F.Grosse-Oetringhaus, Measurementofthecharged-particle multiplicity in

proton–protoncollisionswiththeALICEdetector,PhDthesis,MunsterU.,2009,

https://inspirehep.net/record/887184/files/CERN-THESIS-2009-033.pdf. [72]F.Bossu,Z.C.delValle, A.deFalco,M.Gagliardi, S.Grigoryan,G. Martinez

Garcia,PhenomenologicalinterpolationoftheinclusiveJ/psicrosssectionto proton–protoncollisionsat2.76 TeVand5.5 TeV,arXiv:1103.2394[nucl-ex].

[73]ALICECollaboration,B.B.Abelev,etal.,Transversemomentumdependenceof inclusiveprimary charged-particleproduction inp–Pb collisionsat √sNN=

5.02 TeV,Eur.Phys.J.C74 (9)(2014)3054,arXiv:1405.2737[nucl-ex].

[74]ATLASCollaboration,G.Aad,etal.,Measurementsoftheelectron andmuon

inclusive cross-sectionsinproton–protoncollisions at √s=7 TeV withthe ATLAS detector,Phys.Lett.B707(2012)438–458,arXiv:1109.0525[hep-ex].

[75]M.Cacciari,M.Greco,P.Nason,TheP(T)spectruminheavyflavor hadropro-duction,J.HighEnergyPhys.05(1998)007,arXiv:hep-ph/9803400.

[76]M.Cacciari,S.Frixione,P.Nason,Thep(T)spectruminheavyflavor photopro-duction,J.HighEnergyPhys.03(2001)006,arXiv:hep-ph/0102134.

[77]M.Cacciari,S.Frixione,N.Houdeau,M.L.Mangano,P.Nason,G.Ridolfi, Theo-reticalpredictionsforcharmandbottomproductionattheLHC,J.HighEnergy Phys.10(2012)137,arXiv:1205.6344[hep-ph].

[78]ALICECollaboration,B.Abelev,etal.,Measurementofcharmproductionat cen-tralrapidityinproton–protoncollisionsat√s=2.76 TeV,J.HighEnergyPhys. 07(2012)191,arXiv:1205.4007[hep-ex].

ALICECollaboration

J. Adam

40

,

D. Adamová

83

,

M.M. Aggarwal

87

,

G. Aglieri Rinella

36

,

M. Agnello

110

,

N. Agrawal

48

,

Z. Ahammed

132

,

S.U. Ahn

68

,

S. Aiola

136

,

A. Akindinov

58

,

S.N. Alam

132

,

D. Aleksandrov

99

,

B. Alessandro

110

,

D. Alexandre

101

,

R. Alfaro Molina

64

,

A. Alici

12

,

104

,

A. Alkin

3

,

J.R.M. Almaraz

119

,

J. Alme

38

,

T. Alt

43

,

S. Altinpinar

18

,

I. Altsybeev

131

,

C. Alves Garcia Prado

120

,

C. Andrei

78

,

A. Andronic

96

,

V. Anguelov

93

,

J. Anielski

54

,

T. Antiˇci ´c

97

,

F. Antinori

107

,

P. Antonioli

104

,

L. Aphecetche

113

,

H. Appelshäuser

53

,

S. Arcelli

28

,

R. Arnaldi

110

,

O.W. Arnold

37

,

92

,

I.C. Arsene

22

,

M. Arslandok

53

,

B. Audurier

113

,

A. Augustinus

36

,

R. Averbeck

96

,

M.D. Azmi

19

,

A. Badalà

106

,

Y.W. Baek

67

,

S. Bagnasco

110

,

R. Bailhache

53

,

R. Bala

90

,

A. Baldisseri

15

,

R.C. Baral

61

,

A.M. Barbano

27

,

R. Barbera

29

,

F. Barile

33

,

G.G. Barnaföldi

135

,

L.S. Barnby

101

,

V. Barret

70

,

P. Bartalini

7

,

K. Barth

36

,

J. Bartke

117

,

E. Bartsch

53

,

M. Basile

28

,

N. Bastid

70

,

S. Basu

132

,

B. Bathen

54

,

G. Batigne

113

,

A. Batista Camejo

70

,

B. Batyunya

66

,

P.C. Batzing

22

,

I.G. Bearden

80

,

H. Beck

53

,

C. Bedda

110

,

N.K. Behera

50

,

I. Belikov

55

,

F. Bellini

28

,

H. Bello Martinez

2

,

R. Bellwied

122

,

R. Belmont

134

,

E. Belmont-Moreno

64

,

V. Belyaev

75

,

G. Bencedi

135

,

S. Beole

27

,

I. Berceanu

78

,

A. Bercuci

78

,

Y. Berdnikov

85

,

D. Berenyi

135

,

R.A. Bertens

57

,

D. Berzano

36

,

L. Betev

36

,

A. Bhasin

90

,

I.R. Bhat

90

,

A.K. Bhati

87

,

B. Bhattacharjee

45

,

J. Bhom

128

,

L. Bianchi

122

,

N. Bianchi

72

,

C. Bianchin

57

,

134

,

J. Bielˇcík

40

,

J. Bielˇcíková

83

,

A. Bilandzic

80

,

R. Biswas

4

,

S. Biswas

79

,

S. Bjelogrlic

57

,

J.T. Blair

118

,

D. Blau

99

,

C. Blume

53

,

F. Bock

93

,

74

,

A. Bogdanov

75

,

H. Bøggild

80

,

L. Boldizsár

135

,

M. Bombara

41

,

J. Book

53

,

H. Borel

15

,

A. Borissov

95

,

M. Borri

82

,

124

,

F. Bossú

65

,

E. Botta

27

,

S. Böttger

52

,

C. Bourjau

80

,

P. Braun-Munzinger

96

,

M. Bregant

120

,

T. Breitner

52

,

T.A. Broker

53

,

T.A. Browning

94

,

M. Broz

40

,

E.J. Brucken

46

,

E. Bruna

110

,

G.E. Bruno

33

,

D. Budnikov

98

,

H. Buesching

53

,

S. Bufalino

27

,

36

,

P. Buncic

36

,

O. Busch

93

,

128

,

Z. Buthelezi

65

,

J.B. Butt

16

,

J.T. Buxton

20

,

D. Caffarri

36

,

X. Cai

7

,

H. Caines

136

,

L. Calero Diaz

72

,

A. Caliva

57

,

E. Calvo Villar

102

,

P. Camerini

26

,

F. Carena

36

,

W. Carena

36

,

F. Carnesecchi

28

,

J. Castillo Castellanos

15

,

A.J. Castro

125

,

E.A.R. Casula

25

,

C. Ceballos Sanchez

9

,

J. Cepila

40

,

P. Cerello

110

,

J. Cerkala

115

,

B. Chang

123

,

S. Chapeland

36

,

M. Chartier

124

,

J.L. Charvet

15

,

S. Chattopadhyay

132

,

S. Chattopadhyay

100

,

V. Chelnokov

3

,

M. Cherney

86

,

C. Cheshkov

130

,

B. Cheynis

130

,

V. Chibante Barroso

36

,

D.D. Chinellato

121

,

S. Cho

50

,

P. Chochula

36

,

K. Choi

95

,

M. Chojnacki

80

,

S. Choudhury

132

,

P. Christakoglou

81

,

C.H. Christensen

80

,

P. Christiansen

34

,

T. Chujo

128

,

S.U. Chung

95

,

C. Cicalo

105

,

L. Cifarelli

12

,

28

,

F. Cindolo

104

,

J. Cleymans

89

,

F. Colamaria

33

,

D. Colella

59

,

33

,

36

,

A. Collu

74

,

25

,

M. Colocci

28

,

G. Conesa Balbastre

71

,

Z. Conesa del Valle

51

,

M.E. Connors

136

,

ii

,

J.G. Contreras

40

,

T.M. Cormier

84

,

Y. Corrales Morales

110

,

I. Cortés Maldonado

2

,

P. Cortese

32

,

M.R. Cosentino

120

,

F. Costa

36

,

P. Crochet

70

,

R. Cruz Albino

11

,

E. Cuautle

63

,

L. Cunqueiro

36

,

T. Dahms

92

,

37

,

A. Dainese

107

,

A. Danu

62

,

D. Das

100

,

I. Das

51

,

100

,

S. Das

4

,

A. Dash

121

,

79

,

S. Dash

48

,

S. De

120

,

A. De Caro

31

,

12

,

G. de Cataldo

103

,

C. de Conti

120

,

J. de Cuveland

43

,

A. De Falco

25

,

D. De Gruttola

12

,

31

,

N. De Marco

110

,

S. De Pasquale

31

,

A. Deisting

96

,

93

,

A. Deloff

77

,

E. Dénes

135

,

i

,

C. Deplano

81

,

P. Dhankher

48

,

D. Di Bari

33

,

A. Di Mauro

36

,

P. Di Nezza

72

,

M.A. Diaz Corchero

10

,

T. Dietel

89

,

P. Dillenseger

53

,

R. Divià

36

,

Ø. Djuvsland

18

,

A. Dobrin

57

,

81

,

D. Domenicis Gimenez

120

,

B. Dönigus

53

,

O. Dordic

22

,

T. Drozhzhova

53

,

A.K. Dubey

132

,

A. Dubla

57

,

L. Ducroux

130

,

P. Dupieux

70

,

R.J. Ehlers

136

,

D. Elia

103

,

H. Engel

52

,

E. Epple

136

,

B. Erazmus

113

,

I. Erdemir

53

,

F. Erhardt

129

,

B. Espagnon

51

,

M. Estienne

113

,

S. Esumi

128

,

J. Eum

95

,

D. Evans

101

,

S. Evdokimov

111

,

G. Eyyubova

40

,

L. Fabbietti

92

,

37

,

D. Fabris

107

,

J. Faivre

71

,

A. Fantoni

72

,

M. Fasel

74

,

L. Feldkamp

54

,

A. Feliciello

110

,

G. Feofilov

131

,

J. Ferencei

83

,

A. Fernández Téllez

2

,

E.G. Ferreiro

17

,

A. Ferretti

27

,

A. Festanti

30

,