Dielectron production in proton-proton and proton-lead collisions at s NN − − − √ = 5.02 TeV
EEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN-EP-2020-08119 May 2020c (cid:13)
Dielectron production in proton–proton and proton–lead collisions at √ s NN = 5.02 TeV ALICE Collaboration ∗ Abstract
The first measurements of dielectron production at midrapidity ( | η e | < .
8) in proton–proton andproton–lead collisions at √ s NN = .
02 TeV at the LHC are presented. The dielectron cross sectionis measured with the ALICE detector as a function of the invariant mass m ee and the pair transversemomentum p T , ee in the ranges m ee < . c and p T , ee < c , in both collision systems. Inproton–proton collisions, the charm and beauty cross sections are determined at midrapidity from afit to the data with two different event generators. This complements the existing dielectron measure-ments performed at √ s = 7 and 13 TeV. The slope of the √ s dependence of the three measurementsis described by FONLL calculations. The dielectron cross section measured in proton–lead colli-sions is in agreement, within the current precision, with the expected dielectron production withoutany nuclear matter effects for e + e − pairs from open heavy-flavor hadron decays. For the first timeat LHC energies, the dielectron production in proton–lead and proton–proton collisions are directlycompared at the same √ s NN via the dielectron nuclear modification factor R pPb . The measurementsare compared to model calculations including cold nuclear matter effects, or additional sources ofdielectrons from thermal radiation. ∗ See Appendix A for the list of collaboration members a r X i v : . [ nu c l - e x ] M a y ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration ALICE [1], located at the Large Hadron Collider (LHC) at CERN, was designed to study the quark–gluonplasma (QGP), a state of matter which consists of deconfined quarks and gluons. The QGP is created atthe high-energy densities and temperatures reached in ultra-relativistic heavy-ion collisions. Under theseconditions, the chiral symmetry is expected to be restored in the QGP phase [2, 3]. Dileptons (l + l − , i.e.e + e − or µ + µ − ) are emitted during all stages of the heavy-ion collision and carry information about themedium properties at the time of their emission, as they do not interact strongly. This makes them a verypromising tool to understand the chiral symmetry restoration and the thermodynamical properties of theQGP. In particular, the measurement of the dilepton invariant mass ( m ll ) allows for the separation of thedifferent stages of the medium evolution. For m ee < . c , the main dilepton sources are Dalitzdecays of pseudoscalar mesons ( π , η , η ’) as well as Dalitz and two-body decays of vector mesons( ρ , ω , φ ). In this mass range, the dilepton spectrum is sensitive to the in-medium modification of the ρ meson spectral function, which is connected to the partial restoration of chiral symmetry in the hothadronic phase [3, 4]. At the same time, thermal radiation from the medium, contributing over a broadmass range, provides insight into the temperature of the medium and its space–time evolution.Measurements of dilepton production in nucleus–nucleus collisions were performed at the Super ProtonSynchroton at CERN, among others, by CERES [5, 6] and NA60 [7] at a center-of-mass energy pernucleon–nucleon pair, √ s NN ≤ . ρ mesons for m ll < c with a strongly broadened ρ spectral function [7], as well aspartonic thermal radiation for m ll > c [8]. At higher energies √ s NN =
200 GeV, results fromPHENIX [9] and STAR [10] at the Relativistic Heavy Ion Collider (RHIC) are also compatible with mod-els involving a broadening of the ρ spectral function. The study of thermal radiation from the QGP in theintermediate-mass region (IMR), 1 . < m ll < . c , is however challenging at these center-of-massenergies due to the large background from correlated l + l − pairs originating from open heavy-flavorhadron decays. The first measurement of low- m ll dileptons at the LHC, performed by ALICE in Pb–Pbcollisions at √ s NN = .
76 TeV [11], does not provide data sensitive to a thermal signal due to the limitedstatistical precision and the limited knowledge of the charm contribution. Consequently, it is crucial tounderstand the dilepton production in proton–proton (pp) collisions, in particular the contribution fromheavy-flavor hadron decays, in order to single out the characteristic signals of the QGP.In pp collisions, the production of charm and beauty quarks can be estimated with perturbative quantumchromodynamics (pQCD) calculations in vacuum without any initial- and final-state effects. Owing toflavor conservation, the heavy quarks can only be produced in pairs. The resulting lepton pairs origi-nating from charm hadron decays reflect the initial kinematic correlations between the charm and theanti-charm quarks, whereas in the case of beauty hadron decays the correlation is weakened because oftheir large masses. In pp collisions, where no thermal dilepton sources are expected, the l + l − -pairs aris-ing from heavy-flavor hadron decays are the main contribution to the dilepton yield in the IMR. Hence,dileptons can be used to study the heavy-quark production mechanisms. Together with the measurementsof single heavy-flavor hadrons and their decay products, accurate results on dilepton production can pro-vide constraints on the Monte Carlo (MC) event generators aiming to describe heavy-flavor production.In studies with dielectrons by PHENIX in pp collisions at √ s NN =
200 GeV [12, 13], and more recentlyby ALICE in pp collisions at √ s = 7 and 13 TeV [14, 15] the charm and beauty cross sections at midra-pidity and in the full phase space were extracted by means of the analysis of the dielectron invariant mass( m ee ) and pair transverse momentum ( p T , ee ) spectra. The measured cross sections at the LHC and RHICwere found to be consistent with fixed order plus next-to-leading logarithms (FONLL) calculations [16].The production of dileptons in heavy-ion collisions can be modified with respect to pp collisions notonly by the presence of hot nuclear matter but also by the presence of cold nuclear matter (CNM). TheCNM effects include the modification of the quark and gluon content in the initial state, that is described2ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationby means of parton distribution functions (PDFs) of the incoming nucleons in the collinear factorizationframework. In nucleons that are bound in the nucleus, the PDFs are altered by the presence of additionalnuclear matter with respect to free nucleons. This modification depends on the parton momentum fraction x , the atomic mass number of the nucleus A , and the momentum transfer Q in the hard scattering process.Nuclear PDFs are obtained from a global fit to data from different experiments [17–19]. When the phasespace density of gluons within the hadron is high due to gluon self-interactions, reaching a saturationregime, an appropriate theoretical description is the Color Glass Condensate (CGC) theory [20–23]. AtLHC energies at midrapidity, where small values of x are probed by the charm and beauty production( x ≤ − ), the most relevant effect on the PDFs is shadowing [24]. The modification of the initial state inhadronic collisions can significantly reduce the heavy-flavor production cross sections at low transversemomentum ( p T ). In addition, multiple scattering of partons in the nucleus, before and/or after the hardscattering, can change the kinematic distribution of the produced hadrons and affect their azimuthalcorrelation, such that the m ee and p T , ee distributions from correlated heavy-flavor hadron decays couldbe modified [25, 26].Initially, hot matter effects were not expected in proton–nucleus (pA) collisions, so they were used asa baseline for measurements in heavy-ion collisions to study possible CNM effects. At LHC energiesin minimum bias (MB) p–Pb collisions at midrapidity, the measured p T differential production crosssections of single open-charm hadrons [27, 28] and their decay electrons [29, 30], as well as resultson azimuthal correlations of D mesons and charged particles [31], are compatible over the whole p T range probed with the results in pp collisions scaled with the atomic mass number A of the Pb nucleus.Moreover, the yields of J / ψ from B hadron decays as well as prompt J / ψ are found to be suppressedat low p T at midrapidity in MB p–Pb collisions at √ s NN = .
02 TeV [32], but the measurements of Bhadron production cross sections at high p T show no significant modification of the spectra compared toperturbative QCD calculations of pp collisions scaled with A . All of these results indicate that possibleCNM effects are small compared to the current uncertainties of the measurements for open heavy-flavorproduction at midrapidity at the LHC. However, at forward and backward rapidities, the measured p T differential cross sections of D [33] and B mesons [34], and of muons originating from heavy-flavorhadron decays [35] in minimum bias p–Pb collisions at √ s NN = .
02 TeV demonstrate the presenceof CNM effects and support shadowing as possible explanation. The forward and backward results setconstraints on models that also aim at reproducing the midrapidity measurements. Accurate measure-ments in pA collisions provide important inputs for the parametrizations of the nuclear PDFs, which arecurrently suffering from large uncertainties [18, 19].On the other hand, final-state effects may also play an important role in pA collisions. In particular, inthose with large multiplicities of produced particles, as suggested by results from azimuthal anisotropymeasurements through two-particle [36–42] and multi-particle correlations [43, 44], modifications of the p T distributions of identified hadrons with respect to the charged-particle multiplicity in the event [45,46], multiplicity dependence of strangeness production [47], and ψ (2S) production [48–50]. Shouldsuch observations be linked to the creation of a small volume of hot medium in high-multiplicity pAcollisions, the corresponding thermal radiation could lead to an enhanced dilepton production [51–53].At RHIC energies, results on dilepton production at midrapidity in minimum bias d–Au collisions at √ s NN = 200 GeV [12, 13] show no evidence of neither an additional source of lepton pairs, nor of nuclearmodification of the charm and beauty production. At the LHC, where the density of final-state particlesis larger, dilepton measurements in p–Pb collisions can give more insight into the possible formation ofa hot medium in small systems and CNM effects.In this article, the first measurements of e + e − production in pp and p–Pb collisions at √ s NN = .
02 TeVat the LHC are presented. The results are obtained with the ALICE detector. The data are compared, interms of the m ee and p T , ee distributions, to the sum of the expected sources of e + e − pairs from knownhadron decays, the so-called hadronic cocktail. The spectra are shown after the application of fiducial3ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationrequirements on single electrons ( | η e | < . . < p T , e <
10 GeV/ c ) without an extrapolation tothe full phase space. In addition, for the first time at LHC energies, a direct comparison between thedielectron cross section obtained in pp and p–Pb collisions is possible since both data sets were recordedat the same √ s NN . In particular, the analysis of the pp data resolves the model dependence on theexpected m ee and p T , ee distributions of correlated e + e − pairs from open heavy-flavor hadron decays inpp collisions, used as reference for the p–Pb study. This allows for the research of possible modificationsto the dielectron production in p–Pb collisions due to CNM or additional final-state effects.The article is organized as follows. The experimental setup and the used data samples are described inSec. 2. The analysis steps, including track selection criteria, electron identification, signal extraction andefficiency corrections, are described in Sec. 3, together with the corresponding systematic uncertainties.The method to calculate the expected dielectron cross section from known hadron decays is explainedin Sec. 4. In Sec. 5, the results are presented, covering the charm and beauty cross section extractedin pp collisions, comparisons of the dielectron production in pp and p–Pb collisions to the expectationsfrom known hadron decays, and the resulting dielectron nuclear modification factors. The ALICE detector and its performance are described in [1, 54]. Electrons are measured in the ALICEcentral barrel covering the midrapidity range | η | < .
9. (Note that the term ‘electron’ is used for bothelectrons and positrons throughout this paper.) The relevant subsystems used in the dielectron analysisare the Inner Tracking System (ITS) [55], the Time Projection Chamber (TPC) [56], and the Time-Of-Flight (TOF) [57] detector.The innermost detector of the ALICE apparatus, closest to the nominal interaction point, is the ITS. Itconsists of six silicon tracking layers based on three different technologies. The two inner layers areSilicon Pixel Detectors (SPD), the two middle layers are Silicon Drift Detectors, and the two outer layersare Silicon Strip Detectors. About half of the pp and p–Pb data samples were recorded without the SiliconDrift Detector information in order to reach maximal data acquisition rates. For this reason, even whenavailable, the information from this detector is not used so as to have uniform detector conditions overthe entire data sets. The main detector for particle identification (PID) and tracking is the TPC. This 500cm long cylindrical detector, with an outer radius of 247 cm, is located around the ITS. The TPC readoutis based on multi-wire proportional chambers and provides up to 159 three-dimensional space points aswell as the specific energy loss of the particle. The outermost detector used in this analysis is the TOF.It provides a time-of-flight measurement for particles from the interaction point to its active volume, ata radius of 370 cm. The combined information from the ITS, TPC, and TOF is used to reconstruct thetrack of a charged particle using a Kalman-filter based algorithm [54].The data used in this paper were recorded in collisions at √ s NN = .
02 TeV, with the p–Pb data takenin 2016, and the pp data taken in 2017. Due to the asymmetric beam energies in the p–Pb configu-ration, 4 TeV for the proton beam and 1.59 TeV per nucleon for the Pb beam, the rapidity ( y ) of thecenter-of-mass system is shifted by ∆ y = .
465 in the laboratory frame in the direction of the protonbeam. For both collision systems, events were recorded when a coincident signal in the V0 detectorsystem [58] was registered. The V0 detector consists of two segmented scintillators located at +
340 cmand −
70 cm along the beam axis from the nominal interaction point. Additional selections are applied tothe recorded events. The background from beam–gas interactions and pileup events are rejected by usingthe correlations between the V0 detector and ITS signals. Only events with at least one track segmentreconstructed in the ITS contributing to the vertex reconstruction with the SPD are used. To assure auniform detector coverage at midrapidity, the vertex position along the beam direction is restricted to ±
10 cm with respect to the nominal interaction point. A summary of the number of events N ev passingthe event selection criteria and the corresponding integrated luminosity L int is given in Table 1. These4ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationrequirements are fulfilled by 77% (75%) of the recorded events for the pp (p–Pb) data samples. The L int is calculated as L int = N MB / σ MB , with the number of analyzed events after the vertex reconstructionefficiency correction N MB , and the minimum bias trigger cross section σ MB measured via a van der Meerscan in the corresponding collision system [59, 60]. Table 1:
The integrated luminosity ( L int ) and the number of events ( N ev ) after event selection criteria are appliedfor the pp and p–Pb data samples. Data set L int N ev pp 19.93 ± − × p–Pb 299 ± µ b − × The same track selection criteria are applied in the analysis of the pp and p–Pb data samples. Elec-tron candidates are selected from charged tracks reconstructed in the ITS and TPC in the transverse-momentum range 0 . < p T , e <
10 GeV/ c and pseudorapidity range | η e | < .
8. The tracks are requiredto have at least 80 space points reconstructed in the TPC and at least three hits in the ITS assigned tothem. The maximum χ per space point measured in the TPC (ITS) is required to be smaller than 4 (4.5).To reduce the contribution from secondary tracks, the distance-of-closest approach of the track to the re-constructed primary vertex is required to be smaller than 1 cm in the transverse plane to the collidingbeams and smaller than 3 cm in the longitudinal direction. In order to further suppress the contributionof electrons from photon conversions in the detector material, only tracks with a hit in the first layer ofthe SPD and no ITS cluster shared with any other reconstructed track are used in the analysis. Electrons are identified by measuring their specific energy loss d E / d x in the TPC and their velocity withthe TOF as a function of their momentum. The momentum is estimated from the curvature of the trackmeasured in the ITS and TPC. The PID is based on the detector PID response n ( σ Det i ) . This is expressedas the deviation between the measured PID signal of the track in the detector (Det) and its expectedmost probable value for a given particle hypothesis i at the measured track momentum. This deviation isnormalized to the detector resolution σ . Electrons are selected over the whole investigated momentumrange in the interval | n ( σ TPC e ) | <
3, while the charged pion ( π ± ) contribution is suppressed by requiring n ( σ TPC π ) > .
5. Furthermore, the track must also fulfill at least one of the two following conditions:1. The track is outside the hadron bands in the TPC, defined by | n ( σ TPCK ) | < | n ( σ TPCp ) | < | n ( σ TOF e ) | < p T , e . The largest hadron contamination, up to 9%, is observed where kaons ( p T ≈ c ),protons ( p T ≈ c ) or charged pions ( p T > c ) have a similar d E / d x as electrons in the TPC.The final hadron contamination in the dielectron signal is negligible, as pairs containing a misidentifiedhadron are further removed during the signal extraction. A statistical approach is used to extract the true signal pairs ( S ) as a function of m ee and p T , ee , in whichall electrons and positrons in an event are combined to create an opposite-sign spectrum ( OS ). The OS √ s NN = 5.02 TeV ALICE Collaboration ) c (GeV/ ee m - -
10 110 S / B ALICE = 5.02 TeV NN s | < 0.8 e h , | c < 10 GeV/ T,e p c < 8 GeV/ T,ee p ppp-Pb ) c (GeV/ ee m S + BS / ALICE = 5.02 TeV NN s | < 0.8 e h , | c < 10 GeV/ T,e p c < 8 GeV/ T,ee p ppp-Pb Figure 1: (Color online) Signal-to-background ratio (left) and statistical significance (right) of the dielectronmeasurements as a function of m ee in pp and in p–Pb collisions at √ s NN = .
02 TeV. contains not only signal, but also background ( B ) from combinatorial pairs, as well as residual corre-lations from jets and conversions of correlated decay photons originating from the same particle. Thebackground is estimated from the distribution of same-sign pairs ( SS ) from the same event, as explainedin [14]. The advantages of the same-sign technique, with respect to an event-mixing approach, are theintrinsic correct normalization of the SS spectrum, and the inclusion of charge-symmetric backgroundsources, e.g. electrons from fragmentation in jets. The signal is then extracted as S = OS − R acc × SS ,where R acc is a correction factor needed to account for the different acceptance of opposite-sign andsame-sign pairs. It is estimated using an event-mixing technique detailed in [14].For pairs with m ee < .
14 GeV/ c , the angle ϕ V , which quantifies the orientation of the opening angleof the pairs relative to the magnetic field [14] and allows for the rejection of e + e − pairs from photonconversions, is required to be smaller than 2 rad. After applying this criterion, the remaining contributionfrom e + e − pairs from photon conversions in the detector material is less than 1.4%.The signal-to-background ratio ( S / B ) and statistical significance ( S / √ S + B ) are depicted in the left andright panels of Fig. 1, respectively, for the pp and p–Pb samples. Despite a worse S / B in p–Pb collisions,mostly due to the larger particle multiplicity, the statistical significance of the measurement is similar inboth collision systems. The efficiency of the single-electron and pair selection is calculated with dedicated MC simulations. Thesimulated events are propagated through the ALICE detector using the GEANT 3 [61, 62] transport code.The same strategy is used for the pp and p–Pb analyses. Since the full kinematic range cannot be fullypopulated by pairs originating only from the same-mother particle (SM) or only from open heavy-flavorhadron decays (HF), the final efficiency correction is estimated separately for each source. For SM pairs,pp and p–Pb collisions are generated with the Monash2013 [63] tune of PYTHIA 8.1 [64] (denoted asPYTHIA 8 from now on) and with DPMJET [65], respectively. In the case of HF pairs, MC simulationsof open heavy-flavor hadrons using PYTHIA 6 [66] are performed. In the p–Pb case, heavy-flavor eventsare embedded into realistic p–Pb collisions simulated with EPOS-LHC [67]. The efficiency as a function6ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationof m ee and p T , ee is calculated as ε ee ( m ee , p T , ee ) = w SM × ε SM → ee ( m ee , p T , ee ) + w HF × ε HF → ee ( m ee , p T , ee ) . (1)The weights w SM and w HF represent the relative cross sections of the SM and HF sources, respectively.They are estimated with the expected dielectron cross section from known hadron decays, explained inSec. 4. The average reconstruction efficiency of a signal e + e − pair is very similar in pp and p–Pb colli-sions and ranges from 25% to 30%.The corrected differential dielectron cross section is calculated asd σ ee d m ee d p T , ee = L int ∆ m ee ∆ p T , ee S ( m ee , p T , ee ) ε ee ( m ee , p T , ee ) , (2)with ∆ m ee and ∆ p T , ee being the width of the m ee and p T , ee intervals, respectively, and L int the integratedluminosity. In pp collisions, the spectra are corrected for the vertex reconstruction efficiency and for theefficiency of the minimum bias trigger to select inelastic events with an e + e − pair, which are found to be96% and 98%, respectively. In p–Pb collisions both efficiencies are unity. Different sources of systematic uncertainties are taken into account. On the single track level the effectsof the required hit in the first ITS layer, the ITS-TPC matching efficiency, and the selection of trackswithout shared clusters are studied. These uncertainties are calculated as a function of m ee and p T , ee .Effects from the track and PID selection as well as the requirement on ϕ V are estimated on the pair level.For these uncertainties negligible p T , ee dependence is found and they are applied only as a function of m ee . In order to suppress statistical fluctuations, that could influence the estimated systematic uncertain-ties, they are evaluated in both analyses in wide mass intervals. The resulting systematic uncertaintiesfrom the different sources are summarized in Table 2 for the p–Pb and pp analyses.The systematic uncertainties that arise from the limited knowledge of the matching efficiency of the tracksegments reconstructed in the ITS and the TPC, and from the requirement of a hit in the innermost ITSlayer, are determined with a two-step procedure. First, on the single-track level, the efficiencies of thesetwo track selection criteria are estimated for charged pions in data and in MC as a function of p T . Second,the observed difference is taken as input to a toy MC simulation, which generates particles in the full m ee and p T , ee phase space decaying them into e + e − pairs and applying the fiducial selection. The finalsystematic uncertainty at the pair level is then calculated as the sum of the uncertainties of the decayproducts, corresponding to the input.The systematic uncertainty from the requirement of no shared clusters in the ITS is evaluated by varyingthe maximum number of allowed shared ITS clusters for the selected electron candidates. This provides atest of the understanding of the background since it not only probes different single-electron efficienciesbut also different S / B ratios. When no requirement is applied the S / B decreases by a factor two, whichis due to the increased contribution of electrons from photon conversions in the detector material in theselected electron sample. The resulting dielectron spectra are compared after the efficiency correction.The maximum deviation of the variations that are considered statistically significant according to theBarlow criterion [68] is used to assign the systematic uncertainty.Similarly, the uncertainty from the remaining single-electron selection criteria is determined by varyingthem simultaneously within reasonable values. By changing the selection criteria for the tracks in theITS and the hadron rejection criteria, the evaluated systematic uncertainties are sensitive to estimationsof the background as well as a possible bias due to the hadron contamination in the electron sample.The systematic uncertainty is calculated as the root mean square of the variation of the final data points.Finally, a possible bias due to the efficiency correction of the ϕ V selection is estimated. For this purpose,7ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationthe maximum ϕ V requirement for e + e − pairs with m ee < .
14 GeV/ c is varied around its default valuefrom 1.5 to 2.7 rad.Two additional sources of uncertainty are taken into account for the pp analysis, namely the correction forthe primary vertex reconstruction efficiency and the trigger efficiency. Both are evaluated to be 2% basedon MC simulations. A priori, the reconstruction efficiency of an e + e − pair at a given m ee and p T , ee shouldnot depend on its source. However, in the p–Pb analysis, a difference in the efficiencies of e + e − pairsoriginating from either light-flavor decays or heavy-flavor decays is observed. Therefore, an additionaluncertainty of 3% is assigned to cover a possible bias in the spectra. The total systematic uncertaintyis calculated as the quadratic sum of the individual contributions assuming they are all uncorrelated.The total uncertainty varies between 11% and 4%, being equal to 5% in most of the m ee range. Theuncertainties are partially correlated between different m ee intervals. Table 2:
Systematic uncertainties on the requirement of a hit in the first ITS layer, the ITS-TPC matching efficiency(ME), the allowed number of shared clusters in the ITS, the variation of the ϕ V selection, and the tracking and PIDvariations in coarse m ee intervals for the p–Pb (pp) analysis. The uncertainties on the vertex reconstruction (2%)and trigger (2%) efficiencies in the pp analysis, as well as the uncertainty of the light- and heavy-flavor efficiencydifferences (3%) in the p–Pb analysis, are not listed. They are applied over the whole range of the measurement andincluded in the total uncertainty. The total systematic uncertainty is the quadratic sum of the single contributionsassuming they are all uncorrelated. m ee (GeV/ c ) 1st ITS layer ITS-TPC ME Shared ITS cls. ϕ V Tracking & PID Total < .
14 2 (1)% 2 (2)% 2 (1)% 2 (1)% 10 (6)% 11 (7)%0 . − . . − . . − . The measured dielectron spectra in pp and p–Pb collisions are compared to a hadronic cocktail, whichrepresents the sum of the expected contributions of dielectrons from known hadron decays, after thefiducial selection criteria on single electrons are employed. A fast MC simulation of the ALICE centralbarrel is performed, including realistic momentum and angular resolutions as well as Bremsstrahlungeffects, which are applied to the decay electrons as a function of p T , e , azimuthal angle ( ϕ e ) and η e [69].The Dalitz and dielectron decays of light neutral mesons are simulated with the phenomenologicalevent generator EXODUS [70], following the approach described in [14]. The p T spectra of lightneutral mesons measured at midrapidity in pp collisions at different center-of-mass energies and inp–Pb collisions at √ s NN = .
02 TeV are parametrized and taken as input to the calculations. Sincethe measured p T distributions of π ± mesons extend to lower p T , they are used to determine the π input parametrizations. The p T spectra of π ± mesons measured by ALICE in pp and p–Pb colli-sions at √ s NN = .
02 TeV [71, 72] are first parametrized with a modified Hagedorn function [73].A p T -dependent scaling factor is then applied to the π ± parametrization in order to account for thedifference between π and π ± due to isospin-violating decays, mainly of the η mesons. This factoris estimated using an effective model that describes measured hadron spectra at low p T and includesstrong and electromagnetic decays. The measured p T spectra of φ mesons in pp and p–Pb collisions at √ s NN = .
02 TeV [74, 75] are fitted to obtain the φ input parametrizations. The p T spectra of the otherlight mesons, η , η (cid:48) , ρ , and ω are derived from the π ± spectrum. The p T spectrum of the η meson isestimated from a common fit to the ratios of the η to π p T spectra in pp collisions at √ s = 7 TeV [76],8ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration ) c (GeV/ ee m - - - -
10 110 ) c ( m b / G e V / ee m d ee s d ALICE Simulation, pp| < 0.8 e h = 5.02 TeV, | s c < 10 GeV/ T,e p c < 8 GeV/ T,ee p LF Cocktail sum - e + e g fi p - e + e g fi h - e + e w fi ` h , - e + e g fi ` h - e + e p fi w , - e + e fi w - e + e fi r - e + e p fi f , - e + e h fi f , - e + e fi f Figure 2: (Color online) Expected cross section for dielectron production from light-flavor hadron decays inpp collisions at √ s NN = .
02 TeV as a function of m ee . The sum of the single light-flavor (LF) contributions isshown (solid black line) with its uncertainties (gray band). √ s NN = .
02 TeV [78] measured by ALICE as well measure-ments by CERES/TAPS in p–Au and p–Be collisions at √ s NN = 29.1 GeV which extend to lower p T ( p T < c ) [79]. The p T distributions of ω and ρ are obtained from the respective ratios to the π ± p T distributions in simulated pp collisions at √ s = .
02 TeV with PYTHIA 8. The η / π , ρ / π ± and ω / π ± ratios as a function of p T are assumed to be independent of the pA or pp collision systemand of the energy, as suggested by the measurements [76–79]. Therefore, common parametrizations ofthese ratios are used for the pp and p–Pb cocktails. Finally, the η (cid:48) meson is generated assuming m T scaling [80–82], implying that the spectra of all light mesons as a function of m T = (cid:113) m + p , where m is the pole mass of the considered mesons, follow the same shape and only differ by a normalizationfactor. All contributions from the decays of light-flavor hadrons as a function of m ee are shown in Fig. 2.In order to estimate the J / ψ contribution, the measured J / ψ p T spectra in pp and p–Pb collisions at √ s NN = .
02 TeV [83, 84] are parametrized and used as inputs for the simulations. The J / ψ mesonsare decayed using PHOTOS [85] via the dielectron channel, which also includes the full QED radiativechannels.The contributions of correlated semileptonic decays of open charm and beauty hadrons are calculatedwith two different MC event generators. They are identical to the ones used in the dielectron analysesperformed by ALICE in pp collisions at √ s = 7 TeV [14] and √ s = 13 TeV [15]: PYTHIA 6.4 [66]with the Perugia2011 tune [86] and the next-to-leading order event generator POWHEG [87–90] withPYTHIA 6 to evolve the parton shower. Only the shapes of the expected m ee and p T , ee dielectron spectraare estimated with the MC event generators. The absolute normalization is obtained from a fit of themeasured dielectron cross sections in pp collisions at √ s = .
02 TeV, as shown in Sec. 5.1. Forp–Pb collisions, the cc and bb cross sections, extracted in pp collisions, are scaled with the atomic massnumber A of the Pb nucleus (208). This approach neglects any cold nuclear matter effects, which will bediscussed in Sec. 5.2.The following sources of systematic uncertainties are taken into account: the input parametrizations ofthe measured π ± , φ and J / ψ p T spectra and η / π ratios, the scaling factor applied to the π ± parametriza-tions, the m T scaling parameters, and the different decay branching ratios. The uncertainty of the π ± √ s NN = 5.02 TeV ALICE Collaboration c (GeV/ ee m - - - - ) c ( m b / G e V / ee m d ee s d DataCocktail sum (POWHEG) (POWHEG) - e + e fi cc (POWHEG) - e + e fi bbCocktail sum (PYTHIA 6) (PYTHIA 6) - e + e fi cc (PYTHIA 6) - e + e fi bbALICE, pp | < 0.8 e h = 5.02 TeV, | s c < 10 GeV/ T,e p c < 8 GeV/ T,ee p c (GeV/ T,ee p - - - - ) c ( m b / G e V / T , ee p d ee s d DataCocktail sum (POWHEG) (POWHEG) - e + e fi cc (POWHEG) - e + e fi bbCocktail sum (PYTHIA 6) (PYTHIA 6) - e + e fi cc (PYTHIA 6) - e + e fi bbALICE, pp | < 0.8 e h = 5.02 TeV, | s c < 10 GeV/ T,e p c < 2.70 GeV/ ee m Figure 3: (Color online) Projections of the heavy-flavor dielectron fits as a function of m ee (left) and p T , ee (right)using POWHEG (solid black line) and PYTHIA 6 (dashed gray line) as event generators. The colored lines showthe charm (red) and beauty (magenta) contributions for both event generators after the fit. scaling factor is estimated from variations of the model parameters. For the ρ and ω mesons, the uncer-tainty of the ω / π and ρ / π ratios are estimated by comparing the measured and simulated ratios in ppcollisions at √ s = 7 TeV [91] and √ s = 2.76 TeV [92], respectively. The total uncertainties of the pp andp–Pb cocktails vary from 5% to 20% depending on the m ee and p T , ee interval. The dielectron cross sections in pp and p–Pb collisions as well as the nuclear modification factor arepresented differentially as a function of m ee for p T , ee < c and as a function of p T , ee in two differentmass regions, the low-mass region (LMR), 0 . < m ee < . c , and the intermediate-mass region(IMR), 1 . < m ee < . c . The differential e + e − production cross sections d σ ee /d m ee and d σ ee /d p T , ee in pp collisions, measured inthe IMR and in the range p T , ee < c at √ s = .
02 TeV are presented in Fig. 3. The data in theIMR are fitted in m ee and p T , ee with PYTHIA 6 and POWHEG templates of open-charm (red) and open-beauty (magenta) production, keeping the light-flavor and J / ψ contributions fixed. In this mass range,most of the e + e − pairs originate from open heavy-flavor hadron decays. The χ /ndf between the dataand the cocktail sum is 110.9/123 for the POWHEG cocktail and 113.4/123 for the PYTHIA 6 cocktail.Both calculations are able to reproduce the measured spectra well over the full kinematic range probed,however the full cocktail obtained with POWHEG leads to a slightly better description of the data atlow m ee around m ee = 0.5 GeV/ c . The resulting cross sections are listed in Table 3. The systematicuncertainties originating from the data were determined by repeating the fit after moving the data pointscoherently up- and downward by their systematic uncertainties. Additional uncertainties on the effectivebeauty- and charm-to-electron branching ratios, arising from the semi-leptonic decay branching ratios ofopen heavy-flavor hadrons and the fragmentation functions of charm (beauty) quarks, amounting to 22%and 6% for the charm and beauty cross sections, respectively, are also listed in the table. All uncertaintiesare fully correlated between the two generators, which differ only in the implementation of the heavy-10ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationquark production mechanisms. In both calculations, the hadronization of the c- and b-quarks, and thedecays of the open heavy-flavor hadrons, are performed using PYTHIA 6. For the following results,only calculations where the heavy-flavor contribution is evaluated with POWHEG are presented, sincethe cocktail using POWHEG and fitted to the data in the IMR can slightly better describe the measureddielectron cross sections over the full m ee and p T , ee range in pp collisions at √ s = .
02 TeV.
Table 3:
Heavy-flavor cross sections extracted via double differential fits in m ee and p T , ee to the measured di-electron spectra in pp collisions at √ s = .
02 TeV using PYTHIA 6 and POWHEG. The statistical (stat.) andsystematic (syst.) uncertainties on the data are quoted together with the 22% (6%) uncertainty on the branchingratio (BR) of the semi-leptonic decays of the open heavy-flavor hadrons and the fragmentation functions of charm(beauty) quarks is not listed.
PYTHIA POWHEGd σ cc /d y | y = ±
61 (stat.) ±
26 (syst.) ±
115 (BR) µ b 756 ±
80 (stat.) ±
38 (syst.) ±
166 (BR) µ bd σ bb /d y | y = ± ± ± µ b 28 ± ± ± µ b (TeV) s b ) m ( = y | y / d cc s d Dielectron measurements:) fit with PYTHIA 6
T,ee p , ee m ( ) fit with POWHEG T,ee p , ee m ( ALICEpp collisions = 5.02 TeV: ALICE this result s = 7 TeV: ALICE, JHEP 1809 (2018) 064 s = 13 TeV: ALICE Phys. Lett. B788 (2019) 505 s not shown - e + e fi c22% syst. c mesons: Measurement based on prompt DALICE, Eur. Phys. J. C77 (2017) 550FONLL, M. Cacciari et al.FONLL uncertainties (TeV) s b ) m ( = y | y / d bb s d Dielectron measurements:) fit with PYTHIA 6
T,ee p , ee m ( ) fit with POWHEG T,ee p , ee m ( ALICEpp collisions = 5.02 TeV: ALICE this result s = 7 TeV: ALICE, JHEP 1809 (2018) 064 s = 13 TeV: ALICE Phys. Lett. B788 (2019) 505 s not shown - e + e fi b6% syst. bSingle heavy-flavor hadron measurements:ALICE, PLB 763 (2016) 507FONLL, M. Cacciari et al.FONLL uncertainties Figure 4: (Color online) Cross sections at midrapidity for cc (left) and bb (right) as a function of √ s in pp colli-sions. The colored markers represent the measured midrapidity cross sections at √ s = 5.02, 7, and 13 TeV whichare derived using either PYTHIA 6 (blue circles) or POWHEG (red squares) simulations. The systematic and sta-tistical uncertainty of the data points are summed in quadrature and represented by vertical bars. The measurementsare compared with FONLL calculations (black solid line), with model uncertainties (dashed lines), and to singleheavy-flavor hadron measurements (open markers). The referenced cc cross section at √ s = 7 TeV was obtainedfrom a measurement of prompt D meson production with p T > c and | y | < . ( c → D ) = . ± .
024 from e + e − LEP data [93].
A compilation of the measured d σ cc /d y | y = (left) and d σ bb /d y | y = (right) in pp collisions at LHC energiesis shown in Fig. 4 as a function of √ s . The difference in the cross sections obtained with the two MCevent generators in the present analysis at √ s = 5.02 TeV is comparable with the results of previous ob-servations at √ s = 7 [14] and 13 TeV [15] performed with the same models. This reflects the sensitivityof the dielectron measurement to the implementation of the heavy-quark production mechanisms, in par-ticular to the initial correlation of charm quarks, which is not accessible with conventional measurementsof single open-charm hadrons and their decay products. Nevertheless, the cross sections measured usingPOWHEG or PYTHIA are all in agreement, within the current precision, with results from single heavy-11ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationflavor hadron measurements [94, 95]. The measured total cc production cross section in pp collisionsat √ s = meson production with p T > c and | y | < . ( c → D ) = . ± .
024 from e + e − LEP data [93].Recent measurements of f ( c → D ) suggest that this value is smaller in pp collisions at the LHC [96],which would result in a larger cross section of charm production than assumed in [95]. FONLL calcula-tions [16] are able to reproduce the measurements within the model uncertainties that are dominated byscale uncertainties, but also include PDF and mass uncertainties. The slope of the center-of-mass energydependence of the cross sections is described by the calculations. The measured charm production crosssections are however on the upper edge of the large systematic uncertainties of the theory calculationsfor all three measurements. The m ee -differential production cross sections of e + e − pairs measured in pp and p–Pb collisions at √ s NN = .
02 TeV are compared to the expected dielectrons from known hadron decays in Fig. 5.The light-flavor contributions, summarized as "Light flavor" for readability, are based on measurementsin pp and p–Pb collisions as explained in detail in Sec. 4. The correlated pairs from heavy-flavor hadron - - - - -
10 110 ) c ( m b / G e V / ee m d ee s d DataCocktail sumLight flavor (POWHEG) - e + e fi cc (POWHEG) - e + e fi bb - e + e g fi y , J/ - e + e fi y J/ALICE, pp | < 0.8 e h = 5.02 TeV, | s c < 10 GeV/ T,e p c < 8 GeV/ T,ee p – ) c (GeV/ ee m C o ck t a il D a t a - -
10 110 ) c ( m b / G e V / ee m d ee s d DataCocktail sumLight flavor A) · (POWHEG - e + e fi cc A) · (POWHEG - e + e fi bb - e + e g fi y , J/ - e + e fi y J/ALICE, p-Pb | < 0.8 e h = 5.02 TeV, | NN s c < 10 GeV/ T,e p c < 8 GeV/ T,ee p – ) c (GeV/ ee m C o ck t a il D a t a Figure 5: (Color online) Differential e + e − cross section as a function of m ee measured in pp (left) and p–Pb (right)collisions at √ s NN = .
02 TeV. The data are compared to the hadronic cocktail, where the heavy-flavor contribu-tions are fitted to the pp spectrum in the intermediate-mass region, and for p–Pb collisions scaled with the atomicmass number of the Pb nucleus A = 208. The gray band represents the total uncertainty on the hadronic cocktail. decays are calculated with POWHEG. Their contributions are normalized to the d σ cc /d y | y = and thed σ bb /d y | y = in pp collisions obtained from the fit to the pp data, as discussed in the previous section.For p–Pb collisions, the heavy-flavor contributions are further scaled with the atomic mass number ofthe Pb nucleus. This assumes that the production of heavy-flavor quarks in p–Pb collisions scales withthe number of binary nucleon–nucleon collisions. The total systematic uncertainty of the cocktails isindicated by the gray band. The pp cocktail uncertainty in the IMR is zero by construction since theheavy-flavor contribution is directly fitted to the measured spectrum in pp collisions. The systematicuncertainties of the heavy-flavor contribution in the p–Pb cocktail originate from the statistical and sys-tematic uncertainties of the extracted production cross sections in the pp analysis listed in Table 3. Sincethe cross section is based on the measurement of final state e + e − pairs, the uncertainties related to branch-ing ratios of the semi-leptonic decays of open heavy-flavor hadrons and the fragmentation functions of12ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaborationcharm and beauty quarks can be omitted, under the assumption that these do not change from pp top–Pb collisions. This is confirmed by the latest measurements of open heavy-flavor hadrons in pp andp–Pb collisions at √ s NN = .
02 TeV by ALICE [96]. The bottom panels in Fig. 5 show the ratios ofthe data to the cocktail. The data are described by the hadronic cocktails over the whole mass range( m ee < . c ) in both pp and p–Pb collisions, within the systematic and statistical uncertainties.As seen in previous measurements in pp collisions [14, 15], the heavy-flavor contribution dominates thespectrum for m ee > . c . In p–Pb collisions, the heavy-flavor contribution to the hadronic cocktaildoes not include any modification beyond scaling with binary nucleon–nucleon collisions with respect tothe pp cocktail. No significant deviation of the data from the vacuum expectation of the heavy-flavor con-tributions can be observed in the mass spectrum. This suggests that the CNM effects are small comparedto the current uncertainties of the measurements, as observed by other open heavy-flavor measurementsat the LHC at midrapidity [28], or compensated by an additional source of dielectrons in p–Pb collisionscompared with pp collisions, possibly related to the formation of a hot medium in such collisions.The p T , ee spectra for pp and p–Pb collisions in the LMR and IMR are compared to the hadronic cocktailin Figs. 6 and 7, respectively. In the LMR, the hadronic cocktails in pp and p–Pb collisions are both - - - - - ) c ( m b / G e V / T , ee p d ee s d DataCocktail sumLight flavor (POWHEG) - e + e fi cc (POWHEG) - e + e fi bbALICE, pp | < 0.8 e h = 5.02 TeV, | s c < 10 GeV/ T,e p c < 1.10 GeV/ ee m – ) c (GeV/ T,ee p C o ck t a il D a t a - - -
10 110 ) c ( m b / G e V / T , ee p d ee s d DataCocktail sumLight flavor A) · (POWHEG - e + e fi cc A) · (POWHEG - e + e fi bbALICE, p-Pb | < 0.8 e h = 5.02 TeV, | NN s c < 10 GeV/ T,e p c < 1.10 GeV/ ee m – ) c (GeV/ T,ee p C o ck t a il D a t a Figure 6: (Color online) Differential e + e − cross section as a function of p T , ee in the low-mass region measured inpp (left) and p–Pb (right) collisions at √ s NN = .
02 TeV. The data are compared to the hadronic cocktail, wherethe heavy-flavor contributions are fitted to the pp spectrum in the intermediate-mass region, and for p–Pb collisionsscaled with the atomic mass number of the Pb nucleus A = 208. The gray band represents the total uncertainty onthe hadronic cocktail. composed of e + e − pairs from light-flavor, open-charm, and open-beauty hadron decays. Most of thepairs in this mass interval are produced from the decays of light-flavor hadrons, whose production at low p T does not scale with A in p–Pb collisions. Therefore, the relative expected contribution of dielectronsfrom light-flavor hadron decays is smaller in p–Pb collisions compared with pp collisions at the same √ s NN . In p–Pb collisions, the open-charm hadron decays are expected to contribute significantly to thee + e − cross section for p T , ee < c . The open-beauty contribution only plays a significant role for p T , ee > c in both collision systems. In the IMR, correlated e + e − pairs from open-charm hadrondecays are the dominant dielectron source for p T , ee < . c in pp as well as in p–Pb collisions,whereas most of the e + e − pairs originate from open-beauty hadron decays for p T , ee > . c . Thecontribution from J / ψ decays is small over the whole p T , ee range. The dielectron production in pp andp–Pb collisions at √ s NN = .
02 TeV is well described by the hadronic cocktail, utilizing heavy-flavor13ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration - - - - ) c ( m b / G e V / T , ee p d ee s d DataCocktail sum (POWHEG) - e + e fi cc (POWHEG) - e + e fi bb - e + e g fi y , J/ - e + e fi y J/ALICE, pp | < 0.8 e h = 5.02 TeV, | s c < 10 GeV/ T,e p c < 2.70 GeV/ ee m – ) c (GeV/ T,ee p C o ck t a il D a t a - - -
10 1 ) c ( m b / G e V / T , ee p d ee s d DataCocktail sum A) · (POWHEG - e + e fi cc A) · (POWHEG - e + e fi bb - e + e g fi y , J/ - e + e fi y J/ALICE, p-Pb | < 0.8 e h = 5.02 TeV, | NN s c < 10 GeV/ T,e p c < 2.70 GeV/ ee m – ) c (GeV/ T,ee p C o ck t a il D a t a Figure 7: (Color online) Differential e + e − cross section as a function of p T , ee in the intermediate-mass regionmeasured in pp (left) and p–Pb (right) collisions at √ s NN = .
02 TeV. The data are compared to the hadroniccocktail, where the heavy-flavor contributions are fitted to the pp spectrum in the intermediate-mass region, andfor p–Pb collisions scaled with the atomic mass number of the Pb nucleus A = 208. The gray band represents thetotal uncertainty on the hadronic cocktail. cross sections fitted to the pp data and assuming a scaling of the heavy-flavor cross sections with the A ofthe Pb nucleus. In particular, no significant modification of the heavy-flavor production in the measuredkinematic regions is justified by the analysis of the p–Pb collisions data. The nuclear modification factor, R pPb , is calculated as R pPb ( m ee ) = A d σ pPbee / d m ee d σ ppee / d m ee , (3)with σ pPbee and σ ppee representing the cross sections of dielectron production in p–Pb and pp collisions,respectively, and A denoting the mass number of the Pb nucleus (208). The R pPb allows for a directcomparison of the measurements in the pp and p–Pb collision systems. The systematic uncertainties ofthe p–Pb and pp measurements are treated as independent and, thus, added in quadrature. The dielectron R pPb as a function of m ee for p T , ee < c is shown in Fig. 8. The data are compared to the R pPb ofthe hadronic cocktails as described in Sec. 4 (solid black line). In the cocktail R pPb , the uncertaintiesfrom the open heavy-flavor contributions as well as those from the scaling factor applied to the π ± parametrizations, the ρ / π ± , ω / π ± , and η / π p T ratios are fully correlated, and therefore cancel out.The uncertainties on the parametrized π , φ , and J / ψ spectra are propagated to the R pPb . Since theyare based on independent measurements they are added quadratically. The measured R pPb is below theexpectation of binary collision scaling for m ee < . c , where the fraction of dielectrons from light-flavor hadron decays to the total expected e + e − cross section in p–Pb collisions, denoted by the greenarea, is not negligible. The R pPb is consistent with unity in the IMR within uncertainties, displaying astep between the two mass regions. The behavior is reproduced, within uncertainties, by the hadroniccocktail assuming no further modification of the open heavy-flavor cross sections beyond binary collisionscaling. This suggests a different scaling behavior of the light-flavor production from binary collisionscaling, as already indicated in previous measurements [97].14ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration ) c (GeV/ ee m p P b R DataCocktailCocktail (EPS09)Cocktail (HG+QGP)Light flavor fractionALICE = 5.02 TeV NN s c < 10 GeV/ T,e p c < 8 GeV/ T,ee p
5% normalization uncertainty – ) c (GeV/ ee m F r a c t i on o f c o ck t a il Figure 8: (Color online) Measured dielectron nuclear modification factor as a function of m ee at √ s NN = .
02 TeV. The data are shown in blue, with their statistical and systematic uncertainties depicted asvertical bars and boxes. The baseline expectation, calculated from the pp and p–Pb cocktails outlined in Sec. 4, isshown as a black line with a gray band indicating its uncertainties. Two additional cocktails, one incorporating amodified charm production due to CNM effects and another one including thermal radiation from the hadronic andpartonic phases, are shown as red and orange dashed lines, respectively.
An additional cocktail calculation incorporating a modification of the open-charm contribution via CNMeffects is shown by a dashed red line in Fig. 8. The CNM effects on the production of dielectrons fromopen-charm hadron decays are incorporated by using the EPS09 nPDF [18] in the POWHEG calcula-tions. In the mass region below 1 GeV/ c , where the admixture of charm is significant, the modificationof the charm contribution improves the description of the measured R pPb . In the IMR, the data are justbeyond the upper edge of the systematic uncertainties of the calculations including CNM for the charmproduction. On one hand, it suggests negligible CNM effects compared to the current precision of themeasurement in this mass range, where the p T of D mesons, from which the dielectrons originate, islarger than 2 GeV/ c according to calculations performed with PYTHIA 6. This is in agreement withprevious results on the D meson R pPb at √ s NN = .
02 TeV by ALICE, which show no significant modi-fication of the p T spectra above 2 GeV/ c [27, 28] compared to pp collisions. The dielectron cross sectionfrom charm at lower m ee however is sensitive to the production of low p T D mesons ( p T < c ). Onthe other hand, a possible additional source of electron pairs in p–Pb collisions compared to pp collisionscould compensate CNM effects on the heavy-flavor production.The measured R pPb is further compared to calculations including thermal radiation from the hadronicand partonic phases, based on a model which describes the dilepton enhancement measured in heavy-ion collisions at the SPS and RHIC [7, 51, 52, 98]. The contribution of thermal dielectrons is obtainedfrom an expanding thermal fireball model for p–Pb collisions at √ s NN = .
02 TeV, corresponding toa mean charged-particle multiplicity at midrapidity of (cid:104) d N ch / d y (cid:105) = 20, corrected for weak decay feed-down. The equation of state was extracted from lattice QCD computations with a crossover transitionaround the critical temperature T c = 170 MeV. A broadening of the ρ electromagnetic spectral functionis expected as an effect of interactions in the hot hadronic phase. The thermal emission rate of dielec-trons from the hadronic phase is calculated based on the hadronic many-body theory. The effects of thedetector resolution are not included in the calculations and no modification of the heavy-flavor contribu-tion is considered. A hadronic cocktail including these calculations is shown as the orange dotted line15ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration(HG+QGP). In the range 0 . < m ee < . c , the model tends to slightly overestimate the measured R pPb , whereas in the IMR it agrees with the data within their uncertainties. An additional thermal sourceof dielectrons in p–Pb collisions compared to pp collisions can not be excluded by the data.To further investigate the modifications of the open-charm contribution to the e + e − spectrum, the dielec-tron R pPb as a function of p T , ee is shown in the LMR and IMR in Fig. 9. ) c (GeV/ T,ee p p P b R DataCocktailCocktail (EPS09)Cocktail (HG+QGP)ALICE = 5.02 TeV NN s c < 10 GeV/ T,e p c < 1.10 GeV/ ee m – ) c (GeV/ T,ee p p P b R DataCocktailCocktail (EPS09)Cocktail (HG+QGP)ALICE = 5.02 TeV NN s c < 10 GeV/ T,e p c < 2.70 GeV/ ee m – Figure 9: (Color online) Measured dielectron nuclear modification factor as a function of p T , ee in the low-massregion (left) and intermediate-mass region (right) at √ s NN = .
02 TeV. The data are shown in blue, with theirstatistical and systematic uncertainties depicted as vertical bars and boxes. The baseline expectation, calculatedfrom the pp and p–Pb cocktails outlined in Sec. 4, is shown as a black line with a gray band indicating its uncer-tainties. Two additional cocktails, one incorporating a modified charm production due to CNM effects and anotherone including thermal radiation from the hadronic and partonic phases, are shown as red and orange dashed lines,respectively.
In the LMR, the fraction of e + e − pairs from light-flavor hadron decays ranges from about 40% to 60%depending on p T , ee . For p T , ee larger than about 1 GeV/ c the data are compatible with binary collisionscaling, indicating that the production of light-flavor hadrons is driven by the initial hard scatteringsof the incoming partons and is not affected by CNM effects. This no longer holds true for p T , ee < c , pointing to a change in the production mechanism of the light-flavor hadrons. These featurescan be reproduced by the hadronic cocktail. Inclusion of CNM effects for the charm contribution in thehadronic cocktail only have a small effect. The uncertainties on the data as well as the CNM calculationsthemselves are too large to draw any conclusion. The addition of the thermal contributions in the LMRis disfavored by the data at low- p T , ee ( p T , ee < c ), whereas at higher p T , ee the uncertainties on thedata do not allow for any discrimination between the three models.In the IMR, the contribution from light-flavor hadron decays is negligible. The R pPb is consistent withunity, indicating that the heavy-flavor cross sections approximately scale with the number of binarycollisions in this range. According to the calculations using EPS09 nPDFs, a suppression of the totale + e − cross section is expected for p T , ee < . c due to CNM effects on dielectrons from open-charmhadron decays. Nevertheless, it is disfavored by these data. On the contrary, the cocktail calculationincluding thermal contributions would be preferred by the data. In particular, for p T , ee < c athermal contribution significantly helps to improve the description of the data.16ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE CollaborationFinally, a potential interplay between CNM effects and the thermal contribution cannot be ruled out.Therefore, it is mandatory to separate the dielectrons from heavy-flavor hadron decays and those fromthermal radiation. This could be achieved by an analysis as a function of the distance-of-closest approachof the e + e − pairs to the collision vertex [14]. The dielectron production at midrapidity ( | η e | < .
8) was measured with the ALICE detector as afunction of invariant mass and pair transverse momentum in pp and p–Pb collisions at √ s NN = .
02 TeV.In pp collisions, the dielectron continuum can be well described by the expected contributions fromlight-flavor hadron decays and calculations of e + e − pairs from heavy-flavor hadron decays fitted to thedata. The cross sections of cc and bb production at midrapidity are extracted from the measurement by adouble-differential fit to the m ee and p T , ee spectrum in the intermediate-mass region. Templates from twodifferent event generators, PYTHIA 6 [66] and POWHEG [87–90], are used. Both calculations can de-scribe the data well, yet they yield significantly different results for the cross sections of the single cc andbb contributions. The hadronization of c- and b-quarks as well as the decay of the heavy-flavor hadrons isdone in both PYTHIA 6 and POWHEG simulations with the Perugia 2011 tune of PYTHIA 6.4 [66, 86].Therefore, the model dependence of the extracted cross sections directly reflects the sensitivity of thedielectron measurement to the different implementation of the heavy-quark production mechanisms inthe Monte Carlo event generators. The measured d σ cc / d y | y = and d σ bb / d y | y = are compared to existingresults from dielectron measurements, as well as measurements of identified charm hadrons and semi-leptonic decays of beauty hadrons, in pp collisions at different √ s . The difference between the crosssections extracted in this analysis with the two event generators is comparable to those reported in previ-ous observations at √ s = 7 and 13 TeV. The slope of the center-of-mass energy dependence of the crosssections can be described by FONLL calculations.The dielectron m ee and p T , ee spectra in p–Pb collisions at √ s NN = .
02 TeV, reported here for the firsttime, are compared to a hadronic cocktail composed of the expected dielectron cross sections from theknown hadron decays. Whereas e + e − pairs from light-flavor and J / ψ hadron decays are estimated usingindependent measurements of hadrons, the contributions of dielectrons from open heavy-flavor hadrondecays are determined from the dielectron measurement in pp collisions at the same center-of-massenergy using POWHEG as the event generator. The heavy-flavor cross sections are assumed to scalewith the atomic mass number of the Pb nucleus in p–Pb collisions, with respect to the measured ppreference. Good agreement is observed between the measured and expected total e + e − cross section.The dielectron R pPb as a function of m ee highlights the different scaling behavior of the light- and heavy-flavor dielectron sources. While the measured R pPb is below one for m ee < c , it is consistentwith unity within uncertainties in the IMR where most of the e + e − pairs originate from correlated openheavy-flavor hadron decays. On the one hand, calculations including a suppression of the charm produc-tion using the nPDF EPS09 do not describe the data as well as the hadronic cocktail using the atomicmass number scaling hypothesis in the intermediate-mass region. The central value of the computationsincluding CNM effects is nevertheless closer to the measured R pPb at masses around 0.5 GeV/ c . On theother hand, including a thermal contribution from a hot hadronic and partonic phase to the dielectroncocktail helps in the description of the data in the IMR. The thermal radiation calculations seem howeverto overestimate the production of dielectrons in the LMR. The hadronic cocktail calculations includingCNM effects and thermal radiation show that both play a role at low p T , ee with opposite trends, althoughthe current uncertainties on the measured p T , ee dependence of R pPb are still too large to reject any of thecalculations presented. Moreover, CNM effects on the charm production and thermal radiation from ahot medium possibly formed in p–Pb collisions could cancel each other, if both are present, which makesit necessary to disentangle them in a more sophisticated approach.17ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE CollaborationA more detailed study of the dielectron production in p–Pb collisions requires the separation of e + e − pairsfrom prompt sources and those from the displaced open heavy-flavor hadron decays. The distance-of-closest approach of the e + e − pair to the collision vertex, pioneered at the LHC by ALICE in thedielectron analysis of the pp data at √ s = Acknowledgements
The ALICE Collaboration would like to thank all its engineers and technicians for their invaluable con-tributions to the construction of the experiment and the CERN accelerator teams for the outstandingperformance of the LHC complex. The ALICE Collaboration gratefully acknowledges the resources andsupport provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG) collaboration.The ALICE Collaboration acknowledges the following funding agencies for their support in buildingand running the ALICE detector: A. I. Alikhanyan National Science Laboratory (Yerevan Physics In-stitute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS),Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M 2467-N36] and National-stiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and HighTechnologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de DesenvolvimentoCientífico e Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo àPesquisa do Estado de São Paulo (FAPESP) and Universidade Federal do Rio Grande do Sul (UFRGS),Brazil; Ministry of Education of China (MOEC) , Ministry of Science & Technology of China (MSTC)and National Natural Science Foundation of China (NSFC), China; Ministry of Science and Educationand Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear(CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, CzechRepublic; The Danish Council for Independent Research | Natural Sciences, the VILLUM FONDEN andDanish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland;Commissariat à l’Energie Atomique (CEA) and Institut National de Physique Nucléaire et de Physiquedes Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesmin-isterium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für SchwerionenforschungGmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Researchand Religions, Greece; National Research, Development and Innovation Office, Hungary; Departmentof Atomic Energy Government of India (DAE), Department of Science and Technology, Governmentof India (DST), University Grants Commission, Government of India (UGC) and Council of Scientificand Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; Centro Fermi - MuseoStorico della Fisica e Centro Studi e Ricerche Enrico Fermi and Istituto Nazionale di Fisica Nucleare(INFN), Italy; Institute for Innovative Science and Technology , Nagasaki Institute of Applied Science(IIST), Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Japan So-ciety for the Promotion of Science (JSPS) KAKENHI, Japan; Consejo Nacional de Ciencia (CONACYT)y Tecnología, through Fondo de Cooperación Internacional en Ciencia y Tecnología (FONCICYT) andDirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatievoor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway;Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pak-istan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education, NationalScience Centre and WUT ID-UB, Poland; Korea Institute of Science and Technology Information and18ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE CollaborationNational Research Foundation of Korea (NRF), Republic of Korea; Ministry of Education and ScientificResearch, Institute of Atomic Physics and Ministry of Research and Innovation and Institute of AtomicPhysics, Romania; Joint Institute for Nuclear Research (JINR), Ministry of Education and Science ofthe Russian Federation, National Research Centre Kurchatov Institute, Russian Science Foundation andRussian Foundation for Basic Research, Russia; Ministry of Education, Science, Research and Sport ofthe Slovak Republic, Slovakia; National Research Foundation of South Africa, South Africa; SwedishResearch Council (VR) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organi-zation for Nuclear Research, Switzerland; Suranaree University of Technology (SUT), National Scienceand Technology Development Agency (NSDTA) and Office of the Higher Education Commission underNRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; National Academyof Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom;National Science Foundation of the United States of America (NSF) and United States Department ofEnergy, Office of Nuclear Physics (DOE NP), United States of America. References [1]
ALICE
Collaboration, K. Aamodt et al. , “The ALICE experiment at the CERN LHC”,
JINST (2008) S08002. [doi] 10.1088/1748-0221/3/08/S08002.[2] F. Karsch and M. Lutgemeier, “Deconfinement and chiral symmetry restoration in an SU(3)gauge theory with adjoint fermions”, Nucl. Phys.
B550 (1999) 449–464, arXiv:hep-lat/9812023 [hep-lat] .[3] R. Rapp, J. Wambach, and H. van Hees, “The Chiral Restoration Transition of QCD and LowMass Dileptons”,
Landolt-Bornstein (2010) 134, arXiv:0901.3289 [hep-ph] .[4] I. Tserruya, “Electromagnetic Probes”, Landolt-Bornstein (2010) 176, arXiv:0903.0415[nucl-ex] .[5] CERES
Collaboration, G. Agakichiev et al. , “Enhanced production of low mass electron pairs in200-GeV/u S - Au collisions at the CERN SPS”,
Phys. Rev. Lett. (1995) 1272–1275.[6] CERES
Collaboration, D. Adamova et al. , “Modification of the ρ -meson detected by low-masselectron-positron pairs in central Pb-Au collisions at 158-A-GeV/c”, Phys. Lett.
B666 (2008)425–429.[7]
NA60
Collaboration, R. Arnaldi et al. , “First Measurement of the ρ Spectral Function inHigh-Energy Nuclear Collisions”,
Phys. Rev. Lett. (2006) 162302, arXiv:nucl-ex/0605007 .[8] NA60
Collaboration, R. Arnaldi et al. , “Evidence for Radial Flow of thermal dileptons inhigh-energy nuclear collisions”,
Phys. Rev. Lett. (2008) 022302, arXiv:0711.1816[nucl-ex] .[9]
PHENIX
Collaboration, A. Adare et al. , “Dielectron production in Au + Au collisions at √ s NN =
200 GeV”,
Phys. Rev.
C93 (2016) 014904, arXiv:1509.04667 [nucl-ex] .[10]
STAR Collaboration
Collaboration, L. Adamczyk et al. , “Dielectron Mass Spectra fromAu + Au Collisions at √ s NN =
200 GeV”,
Phys. Rev. Lett. (Jul, 2014) 022301, arXiv:1312.7397 .[11]
ALICE
Collaboration, S. Acharya et al. , “Measurement of dielectron production in centralPb-Pb collisions at √ s NN = .
76 TeV”,
Phys. Rev.
C99 (2019) 024002.[12]
PHENIX
Collaboration, A. Adare et al. , “Cross section for bb production via dielectrons in d +Au collisions at √ s NN =
200 GeV”,
Phys. Rev
C91 (2015) 014907, arXiv:1405.4004 .19ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration[13] PHENIX
Collaboration, A. Adare et al. , “Measurements of e + e − pairs from open heavy flavor in p + p and d + A collisions at √ s NN =
200 GeV”,
Phys. Rev.
C96 (2017) 024907, arXiv:1702.01084 [nucl-ex] .[14]
ALICE
Collaboration, S. Acharya et al. , “Dielectron production in proton-proton collisions at √ s = JHEP (2018) 064.[15] ALICE
Collaboration, S. Acharya et al. , “Dielectron and heavy-quark production in inelasticand high-multiplicity protonâ ˘A ¸Sproton collisions at √ s =
13 TeV”,
Phys. Lett.
B788 (2019)505–518.[16] M. Cacciari, M. Greco, and P. Nason, “The p T spectrum in heavy flavor hadroproduction”, JHEP (1998) 007, arXiv:hep-ph/9803400 [hep-ph] .[17] M. Hirai, S. Kumano, and T. H. Nagai, “Determination of nuclear parton distribution functionsand their uncertainties in next-to-leading order”, Phys. Rev.
C76 (2007) 065207.[18] K. J. Eskola, H. Paukkunen, and C. A. Salgado, “EPS09: A New Generation of NLO and LONuclear Parton Distribution Functions”,
JHEP (2009) 065.[19] K. J. Eskola, P. Paakkinen, H. Paukkunen, and C. A. Salgado, “EPPS16: Nuclear partondistributions with LHC data”, Eur. Phys. J.
C77 (2017) 163.[20] F. Gelis, E. Iancu, J. Jalilian-Marian, and R. Venugopalan, “The Color Glass Condensate”,
Ann.Rev. Nucl. Part. Sci. (2010) 463–489.[21] P. Tribedy and R. Venugopalan, “QCD saturation at the LHC: Comparisons of models to p + pand A + A data and predictions for p + Pb collisions”, Phys. Lett.
B710 (2012) 125–133.[Erratum: Phys. Lett.B718,1154(2013)].[22] J. L. Albacete, A. Dumitru, H. Fujii, and Y. Nara, “CGC predictions for p + Pb collisions at theLHC”,
Nucl. Phys.
A897 (2013) 1–27, arXiv:1209.2001 [hep-ph] .[23] A. H. Rezaeian, “CGC predictions for p+A collisions at the LHC and signature of QCDsaturation”,
Phys. Lett.
B718 (2013) 1058–1069, arXiv:1210.2385 [hep-ph] .[24] N. Armesto, “Nuclear shadowing”,
J. Phys.
G32 (2006) R367–R394, arXiv:hep-ph/0604108[hep-ph] .[25] I. Vitev, “Non-Abelian energy loss in cold nuclear matter”,
Phys. Rev.
C75 (2007) 064906, arXiv:hep-ph/0703002 [hep-ph] .[26] B. Z. Kopeliovich, J. Nemchik, A. Schafer, and A. V. Tarasov, “Cronin effect in hadronproduction off nuclei”,
Phys. Rev. Lett. (2002) 232303, arXiv:hep-ph/0201010 [hep-ph] .[27] ALICE
Collaboration, J. Adam et al. , “ D -meson production in p -Pb collisions at √ s NN = √ s = Phys. Rev.
C94 (2016) 054908.[28]
ALICE
Collaboration, S. Acharya et al. , “Measurement of prompt D , D + , D ∗ + , and D + S production in p–Pb collisions at √ s NN = 5.02 TeV”, JHEP (2019) 092.[29] ALICE
Collaboration, J. Adam et al. , “Measurement of electrons from heavy-flavour hadrondecays in p-Pb collisions at √ s NN = Phys. Lett.
B754 (2016) 81–93.[30]
ALICE
Collaboration, S. Acharya et al. , “Measurement of electrons from semileptonicheavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at √ s NN = 5.02 TeV”, Physics Letters
B804 (2020) 135377. 20ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration[31] ALICE
Collaboration, J. Adam et al. , “Measurement of azimuthal correlations of D mesons andcharged particles in pp collisions at √ s = √ s NN = .
02 TeV”,
Eur.Phys. J.
C77 (2017) 245.[32]
ALICE
Collaboration, S. Acharya et al. , “Prompt and non-prompt J / ψ production and nuclearmodification at mid-rapidity in pâ ˘A ¸SPb collisions at √ s NN = . TeV”,
Eur. Phys. J.
C78 (2018) 466.[33]
LHCb
Collaboration, R. Aaij et al. , “Study of prompt D meson production in p–Pb collisions at √ s NN = JHEP (2017) 090.[34] LHCb
Collaboration, R. Aaij et al. , “Prompt and nonprompt J/ ψ production and nuclearmodification in p Pb collisions at √ s NN = .
16 TeV”,
Phys. Lett. B (2017) 159–178.[35]
ALICE
Collaboration, S. Acharya et al. , “Production of muons from heavy-flavour hadrondecays in p-Pb collisions at √ s NN = 5.02 TeV”, Phys. Lett. B (2017) 459–472.[36]
CMS
Collaboration, S. Chatrchyan et al. , “Observation of Long-Range Near-Side AngularCorrelations in Proton-Lead Collisions at the LHC”,
Phys. Lett.
B718 (2013) 795–814.[37]
ALICE
Collaboration, B. Abelev et al. , “Long-range angular correlations on the near and awayside in p -Pb collisions at √ s NN = .
02 TeV”,
Phys. Lett.
B719 (2013) 29–41.[38]
ALICE
Collaboration, B. Abelev et al. , “Long-range angular correlations of π , K and p in p-Pbcollisions at √ s NN = 5.02 TeV”, Phys. Lett.
B726 (2013) 164–177.[39]
ATLAS
Collaboration, G. Aad et al. , “Observation of Associated Near-Side and Away-SideLong-Range Correlations in √ s NN =5.02 TeV Proton-Lead Collisions with the ATLAS Detector”, Phys. Rev. Lett. (2013) 182302.[40]
ALICE
Collaboration, J. Adam et al. , “Forward-central two-particle correlations in p-Pbcollisions at √ s NN = 5.02 TeV”, Phys. Lett.
B753 (2016) 126–139.[41]
CMS
Collaboration, A. M. Sirunyan et al. , “Elliptic flow of charm and strange hadrons inhigh-multiplicity pPb collisions at √ s NN = Phys. Rev. Lett. (2018) 082301.[42]
ALICE
Collaboration, S. Acharya et al. , “Azimuthal Anisotropy of Heavy-Flavor DecayElectrons in p -Pb Collisions at √ s NN = 5.02 TeV”, Phys. Rev. Lett. (2019) 072301.[43]
CMS
Collaboration, V. Khachatryan et al. , “Evidence for Collective Multiparticle Correlationsin p-Pb Collisions”,
Phys. Rev. Lett. (2015) 012301.[44]
ATLAS
Collaboration, M. Aaboud et al. , “Measurement of long-range multiparticle azimuthalcorrelations with the subevent cumulant method in pp and p + Pb collisions with the ATLASdetector at the CERN Large Hadron Collider”, Phys. Rev.
C97 (2018) 024904.[45]
ALICE
Collaboration, B. Abelev et al. , “Multiplicity Dependence of π , K, p and Λ Productionin p-Pb Collisions at √ s NN = 5.02 TeV”, Phys. Lett.
B728 (2014) 25–38.[46]
CMS
Collaboration, S. Chatrchyan et al. , “Study of the Production of π ± , K, and p in pPbCollisions at √ s NN = Eur. Phys. J.
C74 (2014) 2847.[47]
ALICE
Collaboration, J. Adam et al. , “Enhanced production of multi-strange hadrons inhigh-multiplicity proton-proton collisions”,
Nature Phys. (2017) 535–539.[48] ALICE
Collaboration, B. Abelev et al. , “Suppression of ψ (2S) production in p-Pb collisions at √ s NN = 5.02 TeV”, JHEP (2014) 073. 21ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration[49] LHCb
Collaboration, R. Aaij et al. , “Study of ψ ( S ) production and cold nuclear matter effectsin pPb collisions at √ s NN = JHEP (2016) 133.[50] ALICE
Collaboration, J. Adam et al. , “Centrality dependence of ψ (2S) suppression in p-Pbcollisions at √ s NN = 5.02 TeV”, JHEP (2016) 050.[51] R. Rapp, “Signatures of thermal dilepton radiation at RHIC”, Phys. Rev.
C63 (2001) 054907, arXiv:hep-ph/0010101 [hep-ph] .[52] R. Rapp, “Dilepton Spectroscopy of QCD Matter at Collider Energies”,
Adv. High Energy Phys. (2013) 148253.[53] C. Shen, J.-F. Paquet, G. S. Denicol, S. Jeon, and C. Gale, “Collectivity and electromagneticradiation in small systems”,
Phys. Rev.
C95 (2017) 014906, arXiv:1609.02590 [nucl-th] .[54]
ALICE
Collaboration, B. Abelev et al. , “Performance of the ALICE Experiment at the CERNLHC”,
Int. J. Mod. Phys.
A29 (2014) 1430044.[55]
ALICE
Collaboration, K. Aamodt et al. , “Alignment of the ALICE Inner Tracking System withcosmic-ray tracks”,
JINST (2010) P03003.[56] J. Alme et al. , “The ALICE TPC, a large 3-dimensional tracking device with fast readout forultra-high multiplicity events”, Nucl. Instrum. Methods Phys. Res.
A622 (2010) 316 – 367.[57] A. Akindinov et al. , “Performance of the ALICE Time-Of-Flight detector at the LHC”,
Eur.Phys. J. Plus (2013) 44.[58]
ALICE
Collaboration, E. Abbas et al. , “Performance of the ALICE VZERO system”,
JINST (2013) P10016.[59] ALICE
Collaboration, “ALICE luminosity determination for pp collisions at √ s = https://cds.cern.ch/record/2202638 .[60] ALICE
Collaboration, B. Abelev et al. , “Measurement of visible cross sections in proton-leadcollisions at √ s NN = 5.02 TeV in van der Meer scans with the ALICE detector”, JINST (2014)P11003.[61] R. Brun, R. Hagelberg, M. Hansroul, and J. C. Lassalle, Simulation program for particle physicsexperiments, GEANT: user guide and reference manual . CERN, Geneva, 1978. https://cds.cern.ch/record/118715 .[62] R. Brun, F. Bruyant, F. Carminati, S. Giani, M. Maire, A. McPherson, G. Patrick, and L. Urban,
GEANT: Detector Description and Simulation Tool . CERN Program Library. CERN, Geneva,1993. https://cds.cern.ch/record/1082634 . Long Writeup W5013.[63] P. Skands, S. Carrazza, and J. Rojo, “Tuning PYTHIA 8.1: the Monash 2013 Tune”,
Eur. Phys. J.
C74 (2014) 3024.[64] T. Sjostrand, S. Mrenna, and P. Z. Skands, “A Brief Introduction to PYTHIA 8.1”,
Comput. Phys.Commun. (2008) 852–867, arXiv:0710.3820 [hep-ph] .[65] S. Roesler, R. Engel, and J. Ranft, “The Monte Carlo event generator DPMJET-III”, in
AdvancedMonte Carlo for radiation physics, particle transport simulation and applications. Proceedings,Conference, MC2000, Lisbon, Portugal, October 23-26, 2000 , pp. 1033–1038. 2000. arXiv:hep-ph/0012252 [hep-ph] . 22ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration[66] T. Sjostrand, S. Mrenna, and P. Z. Skands, “PYTHIA 6.4 Physics and Manual”, JHEP (2006)026.[67] T. Pierog, I. Karpenko, J. M. Katzy, E. Yatsenko, and K. Werner, “EPOS LHC: Test of collectivehadronization with data measured at the CERN Large Hadron Collider”, Phys. Rev.
C92 (2015)034906, arXiv:1306.0121 [hep-ph] .[68] R. Barlow and C. Beeston, “Fitting using finite Monte Carlo samples”,
Computer PhysicsCommunications (1993) 219–228.[69] ALICE
Collaboration, “Momentum transformation matrix for dielectron simulations in Pb-Pbcollisions at √ s NN = .
76 TeV”, tech. rep., 2017. https://cds.cern.ch/record/2289779 .[70]
PHENIX
Collaboration, A. Adare et al. , “Detailed measurement of the e + e − pair continuum in p + p and Au+Au collisions at √ s NN =
200 GeV and implications for direct photon production”,
Phys. Rev.
C81 (2010) 034911, arXiv:0912.0244 [nucl-ex] .[71]
ALICE
Collaboration, S. Acharya et al. , “Production of π ± , K and (anti-)p in Pb-Pb andinelastic pp collisions at √ s NN = 5.02 TeV”, arXiv:1910.07678 [nucl-ex] .[72] ALICE
Collaboration, J. Adam et al. , “Multiplicity dependence of π ± , K and (anti-)p productionat large transverse momentum in p-Pb collisions at √ s NN = 5.02 TeV”, Phys. Lett.
B760 (2016)720–735.[73] M. Biyajima, T. Mizoguchi, N. Nakajima, N. Suzuki, and G. Wilk, “Modified Hagedorn formulaincluding temperature fluctuation: Estimation of temperatures at RHIC experiments”,
Eur. Phys.J.
C48 (2006) 597, arXiv:hep-ph/0602120 [hep-ph] .[74]
ALICE
Collaboration, S. Acharya et al. , “Evidence of rescattering effect in Pb-Pb collisions atthe LHC through production of K ∗ ( ) and φ ( ) mesons”, Phys. Lett.
B802 (2020)135225.[75]
ALICE
Collaboration, J. Adam et al. , “Production of K ∗ (892) and φ (1020) in p–Pb collisionsat √ s NN = 5.02 TeV”, Eur. Phys. J.
C76 (2016) 245.[76]
ALICE
Collaboration, B. Abelev et al. , “ π and η meson production in proton-proton collisionsat √ s = . √ s = Phys. Lett.
B717 (2012) 162–172.[77]
ALICE
Collaboration, S. Acharya et al. , “ π and η meson production in proton-protoncollisions at √ s = Eur. Phys. J.
C78 (2018) 263.[78]
ALICE
Collaboration, S. Acharya et al. , “ π and η meson production in p-Pb collisions at √ s NN = .
02 TeV”,
Eur. Phys. J.
C78 (2018) 624.[79]
CERES
Collaboration, R. Baur et al. , “First results of the CERES electron pair spectrometerfrom p + Be, p + Au and S + Au collisions”,
Nuclear Physics
A566 (1994) 87 – 94.[80]
WA80
Collaboration, R. Albrecht et al. , “Production of eta mesons in 200-A/GeV S + S and S +Au reactions”,
Phys. Lett.
B361 (1995) 14–20, arXiv:hep-ex/9507009 [hep-ex] .[81] P. K. Khandai, P. Shukla, and V. Singh, “Meson spectra and m T scaling in p + p , d + Au, and Au+ Au collisions at √ s NN =
200 GeV”,
Phys. Rev. C (2011) 054904, arXiv:1110.3929 .[82] L. Altenkämper, F. Bock, C. Loizides, and N. Schmidt, “Applicability of transverse mass scalingin hadronic collisions at energies available at the CERN Large Hadron Collider”, Phys. Rev.
C96 (2017) 064907. 23ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration[83] ALICE
Collaboration, S. Acharya et al. , “Inclusive J/ ψ production at mid-rapidity in ppcollisions at √ s = 5.02 TeV”, JHEP (2019) 084.[84] ALICE
Collaboration, D. Adamova et al. , “J/ ψ production as a function of charged-particlepseudorapidity density in p-Pb collisions at √ s NN = .
02 TeV”,
Phys. Lett.
B776 (2018) 91–104.[85] P. Golonka and Z. Was, “PHOTOS Monte Carlo: A Precision tool for QED corrections in Z and W decays”, Eur. Phys. J.
C45 (2006) 97–107, arXiv:hep-ph/0506026 [hep-ph] .[86] P. Z. Skands, “Tuning Monte Carlo Generators: The Perugia Tunes”,
Phys. Rev.
D82 (2010)074018, arXiv:1005.3457 [hep-ph] .[87] P. Nason, “A New method for combining NLO QCD with shower Monte Carlo algorithms”,
JHEP (2004) 040, arXiv:hep-ph/0409146 [hep-ph] .[88] S. Frixione, P. Nason, and G. Ridolfi, “A Positive-weight next-to-leading-order Monte Carlo forheavy flavour hadroproduction”, JHEP (2007) 126.[89] S. Frixione, P. Nason, and C. Oleari, “Matching NLO QCD computations with Parton Showersimulations: the POWHEG method”, JHEP (2007) 070.[90] S. Alioli, P. Nason, C. Oleari, and E. Re, “A general framework for implementing NLOcalculations in shower Monte Carlo programs: the POWHEG BOX”, JHEP (2010) 043, arXiv:1002.2581 [hep-ph] .[91] ALICE
Collaboration, “Production of ω ( ) in pp collisions at √ s = 7 TeV”, tech. rep., 2018. https://cds.cern.ch/record/2316785 .[92] ALICE
Collaboration, S. Acharya et al. , “Production of the ρ (770) meson in pp and Pb-Pbcollisions at √ s NN = 2.76 TeV”, Phys. Rev. C no. 6, (2019) 064901.[93] L. Gladilin, “Fragmentation fractions of c and b quarks into charmed hadrons at LEP”, Eur. Phys.J.
C75 (2015) 19.[94]
ALICE
Collaboration, B. Abelev et al. , “Measurement of electrons from beauty hadron decaysin pp collisions at √ s = Phys. Lett.
B721 (2013) 13–23, arXiv:1208.1902 [hep-ex] .[Erratum: Phys. Lett.B763,507(2016)].[95]
ALICE
Collaboration, S. Acharya et al. , “Measurement of D-meson production at mid-rapidityin pp collisions at √ s = Eur. Phys. J.
C77 (2017) 550.[96]
ALICE
Collaboration, S. Acharya et al. , “ Λ + c production in pp collisions at √ s = √ s NN = .
02 TeV”,
JHEP (2018) 108.[97] ALICE
Collaboration, S. Acharya et al. , “Transverse momentum spectra and nuclearmodification factors of charged particles in pp, p-Pb and Pb-Pb collisions at the LHC”,
JHEP (2018) 013.[98] R. Rapp and E. Shuryak, “Thermal dilepton radiation at intermediate masses at the cern-sps”, Physics Letters B no. 1, (2000) 13 – 19.[99]
ALICE
Collaboration, “Upgrade of the ALICE Time Projection Chamber”, Tech. Rep.CERN-LHCC-2013-020. ALICE-TDR-016, 2013. https://cds.cern.ch/record/1622286 .[100]
ALICE
Collaboration, “Addendum to the Technical Design Report for the Upgrade of theALICE Time Projection Chamber”, Tech. Rep. CERN-LHCC-2015-002.ALICE-TDR-016-ADD-1, 2015. https://cds.cern.ch/record/1984329 .24ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration[101] ALICE
Collaboration, L. Musa, “Upgrade of the Inner Tracking System Conceptual DesignReport. Conceptual Design Report for the Upgrade of the ALICE ITS”, Tech. Rep.CERN-LHCC-2012-013. LHCC-P-005, CERN, Geneva, 2012. https://cds.cern.ch/record/1475244 .[102]
ALICE
Collaboration, P. Antonioli, A. Kluge, and W. Riegler, “Upgrade of the ALICE Readoutand Trigger System”, Tech. Rep. CERN-LHCC-2013-019. ALICE-TDR-015, 2013. https://cds.cern.ch/record/1603472 .[103]
ALICE
Collaboration, P. Buncic, M. Krzewicki, and P. Vande Vyvre, “Technical Design Reportfor the Upgrade of the Online-Offline Computing System”, Tech. Rep. CERN-LHCC-2015-006.ALICE-TDR-019, 2015. https://cds.cern.ch/record/2011297 .25ielectron production in pp and p–Pb collisions at √ s NN = 5.02 TeV ALICE Collaboration A The ALICE Collaboration
S. Acharya , D. Adamová , A. Adler , J. Adolfsson , M.M. Aggarwal , G. Aglieri Rinella ,M. Agnello , N. Agrawal
10 ,54 , Z. Ahammed , S. Ahmad , S.U. Ahn , Z. Akbar , A. Akindinov ,M. Al-Turany , S.N. Alam
40 ,141 , D.S.D. Albuquerque , D. Aleksandrov , B. Alessandro ,H.M. Alfanda , R. Alfaro Molina , B. Ali , Y. Ali , A. Alici
10 ,26 ,54 , N. Alizadehvandchali ,A. Alkin , J. Alme , T. Alt , L. Altenkamper , I. Altsybeev , M.N. Anaam , C. Andrei ,D. Andreou , A. Andronic , M. Angeletti , V. Anguelov , C. Anson , T. Antiˇci´c , F. Antinori ,P. Antonioli , N. Apadula , L. Aphecetche , H. Appelshäuser , S. Arcelli , R. Arnaldi , M. Arratia ,I.C. Arsene , M. Arslandok , A. Augustinus , R. Averbeck , S. Aziz , M.D. Azmi , A. Badalà ,Y.W. Baek , S. Bagnasco , X. Bai , R. Bailhache , R. Bala , A. Balbino , A. Baldisseri , M. Ball ,S. Balouza , D. Banerjee , R. Barbera , L. Barioglio , G.G. Barnaföldi , L.S. Barnby , V. Barret ,P. Bartalini , C. Bartels , K. Barth , E. Bartsch , F. Baruffaldi , N. Bastid , S. Basu , G. Batigne ,B. Batyunya , D. Bauri , J.L. Bazo Alba , I.G. Bearden , C. Beattie , C. Bedda , N.K. Behera ,I. Belikov , A.D.C. Bell Hechavarria , F. Bellini , R. Bellwied , V. Belyaev , G. Bencedi ,S. Beole , A. Bercuci , Y. Berdnikov , D. Berenyi , R.A. Bertens , D. Berzano , M.G. Besoiu ,L. Betev , A. Bhasin , I.R. Bhat , M.A. Bhat , H. Bhatt , B. Bhattacharjee , A. Bianchi ,L. Bianchi , N. Bianchi , J. Bielˇcík , J. Bielˇcíková , A. Bilandzic , G. Biro , R. Biswas , S. Biswas ,J.T. Blair , D. Blau , C. Blume , G. Boca , F. Bock , A. Bogdanov , S. Boi , J. Bok ,L. Boldizsár , A. Bolozdynya , M. Bombara , G. Bonomi , H. Borel , A. Borissov , H. Bossi ,E. Botta , L. Bratrud , P. Braun-Munzinger , M. Bregant , M. Broz , E. Bruna , G.E. Bruno
33 ,106 ,M.D. Buckland , D. Budnikov , H. Buesching , S. Bufalino , O. Bugnon , P. Buhler , P. Buncic ,Z. Buthelezi
72 ,131 , J.B. Butt , S.A. Bysiak , D. Caffarri , A. Caliva , E. Calvo Villar ,J.M.M. Camacho , R.S. Camacho , P. Camerini , F.D.M. Canedo , A.A. Capon , F. Carnesecchi ,R. Caron , J. Castillo Castellanos , A.J. Castro , E.A.R. Casula , F. Catalano , C. Ceballos Sanchez ,P. Chakraborty , S. Chandra , W. Chang , S. Chapeland , M. Chartier , S. Chattopadhyay ,S. Chattopadhyay , A. Chauvin , C. Cheshkov , B. Cheynis , V. Chibante Barroso ,D.D. Chinellato , S. Cho , P. Chochula , T. Chowdhury , P. Christakoglou , C.H. Christensen ,P. Christiansen , T. Chujo , C. Cicalo , L. Cifarelli
10 ,26 , L.D. Cilladi , F. Cindolo , M.R. Ciupek ,G. Clai
54 ,ii , J. Cleymans , F. Colamaria , D. Colella , A. Collu , M. Colocci , M. Concas
59 ,iii , G. ConesaBalbastre , Z. Conesa del Valle , G. Contin
24 ,60 , J.G. Contreras , T.M. Cormier , Y. Corrales Morales ,P. Cortese , M.R. Cosentino , F. Costa , S. Costanza , P. Crochet , E. Cuautle , P. Cui ,L. Cunqueiro , D. Dabrowski , T. Dahms , A. Dainese , F.P.A. Damas
115 ,137 , M.C. Danisch ,A. Danu , D. Das , I. Das , P. Das , P. Das , S. Das , A. Dash , S. Dash , S. De , A. De Caro ,G. de Cataldo , J. de Cuveland , A. De Falco , D. De Gruttola , N. De Marco , S. De Pasquale ,S. Deb , H.F. Degenhardt , K.R. Deja , A. Deloff , S. Delsanto
25 ,131 , W. Deng , P. Dhankher , D. DiBari , A. Di Mauro , R.A. Diaz , T. Dietel , P. Dillenseger , Y. Ding , R. Divià , D.U. Dixit ,Ø. Djuvsland , U. Dmitrieva , A. Dobrin , B. Dönigus , O. Dordic , A.K. Dubey , A. Dubla
90 ,107 ,S. Dudi , M. Dukhishyam , P. Dupieux , R.J. Ehlers , V.N. Eikeland , D. Elia , B. Erazmus ,F. Erhardt , A. Erokhin , M.R. Ersdal , B. Espagnon , G. Eulisse , D. Evans , S. Evdokimov ,L. Fabbietti , M. Faggin , J. Faivre , F. Fan , A. Fantoni , M. Fasel , P. Fecchio , A. Feliciello ,G. Feofilov , A. Fernández Téllez , A. Ferrero , A. Ferretti , A. Festanti , V.J.G. Feuillard ,J. Figiel , S. Filchagin , D. Finogeev , F.M. Fionda , G. Fiorenza , F. Flor , A.N. Flores ,S. Foertsch , P. Foka , S. Fokin , E. Fragiacomo , U. Frankenfeld , U. Fuchs , C. Furget , A. Furs ,M. Fusco Girard , J.J. Gaardhøje , M. Gagliardi , A.M. Gago , A. Gal , C.D. Galvan , P. Ganoti ,C. Garabatos , J.R.A. Garcia , E. Garcia-Solis , K. Garg , C. Gargiulo , A. Garibli , K. Garner ,P. Gasik
105 ,107 , E.F. Gauger , M.B. Gay Ducati , M. Germain , J. Ghosh , P. Ghosh , S.K. Ghosh ,M. Giacalone , P. Gianotti , P. Giubellino
59 ,107 , P. Giubilato , A.M.C. Glaenzer , P. Glässel , A. GomezRamirez , V. Gonzalez
107 ,143 , L.H. González-Trueba , S. Gorbunov , L. Görlich , A. Goswami ,S. Gotovac , V. Grabski , L.K. Graczykowski , K.L. Graham , L. Greiner , A. Grelli , C. Grigoras ,V. Grigoriev , A. Grigoryan , S. Grigoryan , O.S. Groettvik , F. Grosa
30 ,59 , J.F. Grosse-Oetringhaus ,R. Grosso , R. Guernane , M. Guittiere , K. Gulbrandsen , T. Gunji , A. Gupta , R. Gupta ,I.B. Guzman , R. Haake , M.K. Habib , C. Hadjidakis , H. Hamagaki , G. Hamar , M. Hamid ,R. Hannigan , M.R. Haque
63 ,86 , A. Harlenderova , J.W. Harris , A. Harton , J.A. Hasenbichler ,H. Hassan , Q.U. Hassan , D. Hatzifotiadou
10 ,54 , P. Hauer , L.B. Havener , S. Hayashi ,S.T. Heckel , E. Hellbär , H. Helstrup , A. Herghelegiu , T. Herman , E.G. Hernandez , G. HerreraCorral , F. Herrmann , K.F. Hetland , H. Hillemanns , C. Hills , B. Hippolyte , B. Hohlweger , √ s NN = 5.02 TeV ALICE Collaboration J. Honermann , D. Horak , A. Hornung , S. Hornung , R. Hosokawa
15 ,133 , P. Hristov , C. Huang ,C. Hughes , P. Huhn , T.J. Humanic , H. Hushnud , L.A. Husova , N. Hussain , S.A. Hussain ,D. Hutter , J.P. Iddon
34 ,127 , R. Ilkaev , H. Ilyas , M. Inaba , G.M. Innocenti , M. Ippolitov ,A. Isakov , M.S. Islam , M. Ivanov , V. Ivanov , V. Izucheev , B. Jacak , N. Jacazio
34 ,54 ,P.M. Jacobs , S. Jadlovska , J. Jadlovsky , S. Jaelani , C. Jahnke , M.J. Jakubowska ,M.A. Janik , T. Janson , M. Jercic , O. Jevons , M. Jin , F. Jonas
96 ,144 , P.G. Jones , J. Jung ,M. Jung , A. Jusko , P. Kalinak , A. Kalweit , V. Kaplin , S. Kar , A. Karasu Uysal , D. Karatovic ,O. Karavichev , T. Karavicheva , P. Karczmarczyk , E. Karpechev , A. Kazantsev , U. Kebschull ,R. Keidel , M. Keil , B. Ketzer , Z. Khabanova , A.M. Khan , S. Khan , A. Khanzadeev ,Y. Kharlov , A. Khatun , A. Khuntia , B. Kileng , B. Kim , B. Kim , D. Kim , D.J. Kim ,E.J. Kim , H. Kim , J. Kim , J.S. Kim , J. Kim , J. Kim , J. Kim , M. Kim , S. Kim ,T. Kim , T. Kim , S. Kirsch , I. Kisel , S. Kiselev , A. Kisiel , J.L. Klay , C. Klein , J. Klein
34 ,59 ,S. Klein , C. Klein-Bösing , M. Kleiner , A. Kluge , M.L. Knichel , A.G. Knospe , C. Kobdaj ,M.K. Köhler , T. Kollegger , A. Kondratyev , N. Kondratyeva , E. Kondratyuk , J. Konig ,S.A. Konigstorfer , P.J. Konopka , G. Kornakov , L. Koska , O. Kovalenko , V. Kovalenko ,M. Kowalski , I. Králik , A. Kravˇcáková , L. Kreis , M. Krivda
64 ,111 , F. Krizek ,K. Krizkova Gajdosova , M. Krüger , E. Kryshen , M. Krzewicki , A.M. Kubera , V. Kuˇcera
34 ,61 ,C. Kuhn , P.G. Kuijer , L. Kumar , S. Kundu , P. Kurashvili , A. Kurepin , A.B. Kurepin ,A. Kuryakin , S. Kushpil , J. Kvapil , M.J. Kweon , J.Y. Kwon , Y. Kwon , S.L. La Pointe , P. LaRocca , Y.S. Lai , M. Lamanna , R. Langoy , K. Lapidus , A. Lardeux , P. Larionov , E. Laudi ,R. Lavicka , T. Lazareva , R. Lea , L. Leardini , J. Lee , S. Lee , S. Lehner , J. Lehrbach ,R.C. Lemmon , I. León Monzón , E.D. Lesser , M. Lettrich , P. Lévai , X. Li , X.L. Li , J. Lien ,R. Lietava , B. Lim , V. Lindenstruth , A. Lindner , C. Lippmann , M.A. Lisa , A. Liu , J. Liu ,S. Liu , W.J. Llope , I.M. Lofnes , V. Loginov , C. Loizides , P. Loncar , J.A. Lopez , X. Lopez ,E. López Torres , J.R. Luhder , M. Lunardon , G. Luparello , Y.G. Ma , A. Maevskaya , M. Mager ,S.M. Mahmood , T. Mahmoud , A. Maire , R.D. Majka
146 ,i , M. Malaev , Q.W. Malik , L. Malinina
75 ,iv ,D. Mal’Kevich , P. Malzacher , G. Mandaglio
32 ,56 , V. Manko , F. Manso , V. Manzari , Y. Mao ,M. Marchisone , J. Mareš , G.V. Margagliotti , A. Margotti , A. Marín , C. Markert ,M. Marquard , C.D. Martin , N.A. Martin , P. Martinengo , J.L. Martinez , M.I. Martínez ,G. Martínez García , S. Masciocchi , M. Masera , A. Masoni , L. Massacrier , E. Masson ,A. Mastroserio
53 ,138 , A.M. Mathis , O. Matonoha , P.F.T. Matuoka , A. Matyja , C. Mayer ,F. Mazzaschi , M. Mazzilli , M.A. Mazzoni , A.F. Mechler , F. Meddi , Y. Melikyan
62 ,93 ,A. Menchaca-Rocha , C. Mengke , E. Meninno
29 ,114 , A.S. Menon , M. Meres , S. Mhlanga ,Y. Miake , L. Micheletti , L.C. Migliorin , D.L. Mihaylov , K. Mikhaylov
75 ,92 , A.N. Mishra ,D. Mi´skowiec , A. Modak , N. Mohammadi , A.P. Mohanty , B. Mohanty , M. Mohisin Khan
16 ,v ,Z. Moravcova , C. Mordasini , D.A. Moreira De Godoy , L.A.P. Moreno , I. Morozov , A. Morsch ,T. Mrnjavac , V. Muccifora , E. Mudnic , D. Mühlheim , S. Muhuri , J.D. Mulligan , A. Mulliri
23 ,55 ,M.G. Munhoz , R.H. Munzer , H. Murakami , S. Murray , L. Musa , J. Musinsky , C.J. Myers ,J.W. Myrcha , B. Naik , R. Nair , B.K. Nandi , R. Nania
10 ,54 , E. Nappi , M.U. Naru ,A.F. Nassirpour , C. Nattrass , R. Nayak , T.K. Nayak , S. Nazarenko , A. Neagu , R.A. Negrao DeOliveira , L. Nellen , S.V. Nesbo , G. Neskovic , D. Nesterov , L.T. Neumann , B.S. Nielsen ,S. Nikolaev , S. Nikulin , V. Nikulin , F. Noferini
10 ,54 , P. Nomokonov , J. Norman
79 ,127 , N. Novitzky ,P. Nowakowski , A. Nyanin , J. Nystrand , M. Ogino , A. Ohlson
81 ,104 , J. Oleniacz , A.C. Oliveira DaSilva , M.H. Oliver , C. Oppedisano , A. Ortiz Velasquez , A. Oskarsson , J. Otwinowski ,K. Oyama , Y. Pachmayer , V. Pacik , S. Padhan , D. Pagano , G. Pai´c , J. Pan , S. Panebianco ,P. Pareek
50 ,141 , J. Park , J.E. Parkkila , S. Parmar , S.P. Pathak , B. Paul , J. Pazzini , H. Pei ,T. Peitzmann , X. Peng , L.G. Pereira , H. Pereira Da Costa , D. Peresunko , G.M. Perez , S. Perrin ,Y. Pestov , V. Petráˇcek , M. Petrovici , R.P. Pezzi , S. Piano , M. Pikna , P. Pillot , O. Pinazza
34 ,54 ,L. Pinsky , C. Pinto , S. Pisano
10 ,52 , D. Pistone , M. Płosko´n , M. Planinic , F. Pliquett ,M.G. Poghosyan , B. Polichtchouk , N. Poljak , A. Pop , S. Porteboeuf-Houssais , V. Pozdniakov ,S.K. Prasad , R. Preghenella , F. Prino , C.A. Pruneau , I. Pshenichnov , M. Puccio , J. Putschke ,S. Qiu , L. Quaglia , R.E. Quishpe , S. Ragoni , S. Raha , S. Rajput , J. Rak ,A. Rakotozafindrabe , L. Ramello , F. Rami , S.A.R. Ramirez , R. Raniwala , S. Raniwala ,S.S. Räsänen , R. Rath , V. Ratza , I. Ravasenga , K.F. Read
96 ,130 , A.R. Redelbach , K. Redlich
85 ,vi ,A. Rehman , P. Reichelt , F. Reidt , X. Ren , R. Renfordt , Z. Rescakova , K. Reygers , A. Riabov ,V. Riabov , T. Richert
81 ,89 , M. Richter , P. Riedler , W. Riegler , F. Riggi , C. Ristea , S.P. Rode , √ s NN = 5.02 TeV ALICE Collaboration M. Rodríguez Cahuantzi , K. Røed , R. Rogalev , E. Rogochaya , D. Rohr , D. Röhrich , P.F. Rojas ,P.S. Rokita , F. Ronchetti , A. Rosano , E.D. Rosas , K. Roslon , A. Rossi
28 ,57 , A. Rotondi ,A. Roy , P. Roy , O.V. Rueda , R. Rui , B. Rumyantsev , A. Rustamov , E. Ryabinkin , Y. Ryabov ,A. Rybicki , H. Rytkonen , O.A.M. Saarimaki , R. Sadek , S. Sadhu , S. Sadovsky , K. Šafaˇrík ,S.K. Saha , B. Sahoo , P. Sahoo , R. Sahoo , S. Sahoo , P.K. Sahu , J. Saini , S. Sakai ,S. Sambyal , V. Samsonov
93 ,98 , D. Sarkar , N. Sarkar , P. Sarma , V.M. Sarti , M.H.P. Sas ,E. Scapparone , J. Schambach , H.S. Scheid , C. Schiaua , R. Schicker , A. Schmah , C. Schmidt ,H.R. Schmidt , M.O. Schmidt , M. Schmidt , N.V. Schmidt
68 ,96 , A.R. Schmier , J. Schukraft ,Y. Schutz , K. Schwarz , K. Schweda , G. Scioli , E. Scomparin , J.E. Seger , Y. Sekiguchi ,D. Sekihata , I. Selyuzhenkov
93 ,107 , S. Senyukov , D. Serebryakov , A. Sevcenco , A. Shabanov ,A. Shabetai , R. Shahoyan , W. Shaikh , A. Shangaraev , A. Sharma , A. Sharma , H. Sharma ,M. Sharma , N. Sharma , S. Sharma , O. Sheibani , K. Shigaki , M. Shimomura , S. Shirinkin ,Q. Shou , Y. Sibiriak , S. Siddhanta , T. Siemiarczuk , D. Silvermyr , G. Simatovic , G. Simonetti ,B. Singh , R. Singh , R. Singh , R. Singh , V.K. Singh , V. Singhal , T. Sinha , B. Sitar ,M. Sitta , T.B. Skaali , M. Slupecki , N. Smirnov , R.J.M. Snellings , C. Soncco , J. Song ,A. Songmoolnak , F. Soramel , S. Sorensen , I. Sputowska , J. Stachel , I. Stan , P.J. Steffanic ,E. Stenlund , S.F. Stiefelmaier , D. Stocco , M.M. Storetvedt , L.D. Stritto , A.A.P. Suaide ,T. Sugitate , C. Suire , M. Suleymanov , M. Suljic , R. Sultanov , M. Šumbera , V. Sumberia ,S. Sumowidagdo , S. Swain , A. Szabo , I. Szarka , U. Tabassam , S.F. Taghavi , G. Taillepied ,J. Takahashi , G.J. Tambave , S. Tang , M. Tarhini , M.G. Tarzila , A. Tauro , G. Tejeda Muñoz ,A. Telesca , L. Terlizzi , C. Terrevoli , D. Thakur , S. Thakur , D. Thomas , F. Thoresen ,R. Tieulent , A. Tikhonov , A.R. Timmins , A. Toia , N. Topilskaya , M. Toppi , F. Torales-Acosta ,S.R. Torres , A. Trifiró
32 ,56 , S. Tripathy
50 ,69 , T. Tripathy , S. Trogolo , G. Trombetta , L. Tropp ,V. Trubnikov , W.H. Trzaska , T.P. Trzcinski , B.A. Trzeciak
37 ,63 , A. Tumkin , R. Turrisi ,T.S. Tveter , K. Ullaland , E.N. Umaka , A. Uras , G.L. Usai , M. Vala , N. Valle , S. Vallero ,N. van der Kolk , L.V.R. van Doremalen , M. van Leeuwen , P. Vande Vyvre , D. Varga , Z. Varga ,M. Varga-Kofarago , A. Vargas , M. Vasileiou , A. Vasiliev , O. Vázquez Doce , V. Vechernin ,E. Vercellin , S. Vergara Limón , L. Vermunt , R. Vernet , R. Vértesi , L. Vickovic , Z. Vilakazi ,O. Villalobos Baillie , G. Vino , A. Vinogradov , T. Virgili , V. Vislavicius , A. Vodopyanov ,B. Volkel , M.A. Völkl , K. Voloshin , S.A. Voloshin , G. Volpe , B. von Haller , I. Vorobyev ,D. Voscek , J. Vrláková , B. Wagner , M. Weber , S.G. Weber , A. Wegrzynek , S.C. Wenzel ,J.P. Wessels , J. Wiechula , J. Wikne , G. Wilk , J. Wilkinson
10 ,54 , G.A. Willems , E. Willsher ,B. Windelband , M. Winn , W.E. Witt , J.R. Wright , Y. Wu , R. Xu , S. Yalcin , Y. Yamaguchi ,K. Yamakawa , S. Yang , S. Yano , Z. Yin , H. Yokoyama , I.-K. Yoo , J.H. Yoon , S. Yuan ,A. Yuncu , V. Yurchenko , V. Zaccolo , A. Zaman , C. Zampolli , H.J.C. Zanoli , N. Zardoshti ,A. Zarochentsev , P. Závada , N. Zaviyalov , H. Zbroszczyk , M. Zhalov , S. Zhang , X. Zhang ,Z. Zhang , V. Zherebchevskii , Y. Zhi , D. Zhou , Y. Zhou , Z. Zhou , J. Zhu , Y. Zhu ,A. Zichichi
10 ,26 , G. Zinovjev , N. Zurlo , Affiliation notes i Deceased ii Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA),Bologna, Italy iii
Dipartimento DET del Politecnico di Torino, Turin, Italy iv M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute of Nuclear, Physics, Moscow, Russia v Department of Applied Physics, Aligarh Muslim University, Aligarh, India vi Institute of Theoretical Physics, University of Wroclaw, Poland
Collaboration Institutes A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, Yerevan, Armenia Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine Bose Institute, Department of Physics and Centre for Astroparticle Physics and Space Science (CAPSS),Kolkata, India Budker Institute for Nuclear Physics, Novosibirsk, Russia California Polytechnic State University, San Luis Obispo, California, United States √ s NN = 5.02 TeV ALICE Collaboration Central China Normal University, Wuhan, China Centre de Calcul de l’IN2P3, Villeurbanne, Lyon, France Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi’, Rome, Italy Chicago State University, Chicago, Illinois, United States China Institute of Atomic Energy, Beijing, China Comenius University Bratislava, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia COMSATS University Islamabad, Islamabad, Pakistan Creighton University, Omaha, Nebraska, United States Department of Physics, Aligarh Muslim University, Aligarh, India Department of Physics, Pusan National University, Pusan, Republic of Korea Department of Physics, Sejong University, Seoul, Republic of Korea Department of Physics, University of California, Berkeley, California, United States Department of Physics, University of Oslo, Oslo, Norway Department of Physics and Technology, University of Bergen, Bergen, Norway Dipartimento di Fisica dell’Università ’La Sapienza’ and Sezione INFN, Rome, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Bologna, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Catania, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Padova, Italy Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo Collegato INFN, Salerno, Italy Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy Dipartimento di Scienze e Innovazione Tecnologica dell’Università del Piemonte Orientale and INFNSezione di Torino, Alessandria, Italy Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy European Organization for Nuclear Research (CERN), Geneva, Switzerland Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split,Split, Croatia Faculty of Engineering and Science, Western Norway University of Applied Sciences, Bergen, Norway Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague,Czech Republic Faculty of Science, P.J. Šafárik University, Košice, Slovakia Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt,Germany Fudan University, Shanghai, China Gangneung-Wonju National University, Gangneung, Republic of Korea Gauhati University, Department of Physics, Guwahati, India Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn,Germany Helsinki Institute of Physics (HIP), Helsinki, Finland High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico Hiroshima University, Hiroshima, Japan Hochschule Worms, Zentrum für Technologietransfer und Telekommunikation (ZTT), Worms, Germany Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania Indian Institute of Technology Bombay (IIT), Mumbai, India Indian Institute of Technology Indore, Indore, India Indonesian Institute of Sciences, Jakarta, Indonesia INFN, Laboratori Nazionali di Frascati, Frascati, Italy INFN, Sezione di Bari, Bari, Italy INFN, Sezione di Bologna, Bologna, Italy INFN, Sezione di Cagliari, Cagliari, Italy INFN, Sezione di Catania, Catania, Italy √ s NN = 5.02 TeV ALICE Collaboration INFN, Sezione di Padova, Padova, Italy INFN, Sezione di Roma, Rome, Italy INFN, Sezione di Torino, Turin, Italy INFN, Sezione di Trieste, Trieste, Italy Inha University, Incheon, Republic of Korea Institute for Nuclear Research, Academy of Sciences, Moscow, Russia Institute for Subatomic Physics, Utrecht University/Nikhef, Utrecht, Netherlands Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic Institute of Space Science (ISS), Bucharest, Romania Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City, Mexico Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil Instituto de Física, Universidad Nacional Autónoma de México, Mexico City, Mexico iThemba LABS, National Research Foundation, Somerset West, South Africa Jeonbuk National University, Jeonju, Republic of Korea Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik, Fachbereich Informatik undMathematik, Frankfurt, Germany Joint Institute for Nuclear Research (JINR), Dubna, Russia Korea Institute of Science and Technology Information, Daejeon, Republic of Korea KTO Karatay University, Konya, Turkey Laboratoire de Physique des 2 Infinis, Irène Joliot-Curie, Orsay, France Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes, CNRS-IN2P3,Grenoble, France Lawrence Berkeley National Laboratory, Berkeley, California, United States Lund University Department of Physics, Division of Particle Physics, Lund, Sweden Nagasaki Institute of Applied Science, Nagasaki, Japan Nara Women’s University (NWU), Nara, Japan National and Kapodistrian University of Athens, School of Science, Department of Physics , Athens,Greece National Centre for Nuclear Research, Warsaw, Poland National Institute of Science Education and Research, Homi Bhabha National Institute, Jatni, India National Nuclear Research Center, Baku, Azerbaijan National Research Centre Kurchatov Institute, Moscow, Russia Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark Nikhef, National institute for subatomic physics, Amsterdam, Netherlands NRC Kurchatov Institute IHEP, Protvino, Russia NRC «Kurchatov» Institute - ITEP, Moscow, Russia NRNU Moscow Engineering Physics Institute, Moscow, Russia Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom Nuclear Physics Institute of the Czech Academy of Sciences, ˇRež u Prahy, Czech Republic Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States Ohio State University, Columbus, Ohio, United States Petersburg Nuclear Physics Institute, Gatchina, Russia Physics department, Faculty of science, University of Zagreb, Zagreb, Croatia
Physics Department, Panjab University, Chandigarh, India
Physics Department, University of Jammu, Jammu, India
Physics Department, University of Rajasthan, Jaipur, India
Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen, Germany
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
Physik Department, Technische Universität München, Munich, Germany
Politecnico di Bari, Bari, Italy
Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum fürSchwerionenforschung GmbH, Darmstadt, Germany
Rudjer Boškovi´c Institute, Zagreb, Croatia √ s NN = 5.02 TeV ALICE Collaboration Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom
Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú, Lima, Peru
St. Petersburg State University, St. Petersburg, Russia
Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
SUBATECH, IMT Atlantique, Université de Nantes, CNRS-IN2P3, Nantes, France
Suranaree University of Technology, Nakhon Ratchasima, Thailand
Technical University of Košice, Košice, Slovakia
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
The University of Texas at Austin, Austin, Texas, United States
Universidad Autónoma de Sinaloa, Culiacán, Mexico
Universidade de São Paulo (USP), São Paulo, Brazil
Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
Universidade Federal do ABC, Santo Andre, Brazil
University of Cape Town, Cape Town, South Africa
University of Houston, Houston, Texas, United States
University of Jyväskylä, Jyväskylä, Finland
University of Liverpool, Liverpool, United Kingdom
University of Science and Technology of China, Hefei, China
University of South-Eastern Norway, Tonsberg, Norway
University of Tennessee, Knoxville, Tennessee, United States
University of the Witwatersrand, Johannesburg, South Africa
University of Tokyo, Tokyo, Japan
University of Tsukuba, Tsukuba, Japan
Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
Université de Lyon, Université Lyon 1, CNRS/IN2P3, IPN-Lyon, Villeurbanne, Lyon, France
Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France, Strasbourg, France
Université Paris-Saclay Centre d’Etudes de Saclay (CEA), IRFU, Départment de Physique Nucléaire(DPhN), Saclay, France
Università degli Studi di Foggia, Foggia, Italy
Università degli Studi di Pavia, Pavia, Italy
Università di Brescia, Brescia, Italy
Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata, India
Warsaw University of Technology, Warsaw, Poland
Wayne State University, Detroit, Michigan, United States
Westfälische Wilhelms-Universität Münster, Institut für Kernphysik, Münster, Germany
Wigner Research Centre for Physics, Budapest, Hungary
Yale University, New Haven, Connecticut, United States