Measurement of electrons from beauty-hadron decays in p-Pb collisions at √sNN=5.02 TeV and Pb-Pb collisions at √sNN=2.76 TeV

JHEP07(2017)052 Published for SISSA by Springer Received:September 27, 2016 Revised:May 8, 2017 Accepted:June 17, 2017 Published:July 11, 2017 Measurement of electrons from beauty-hadron decays in p-Pb collisions at √sNN = 5.02 TeV and Pb-Pb collisions at √sNN = 2.76 TeV The ALICE collaboration E-mail: [email protected] Abstract: The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1< pT<8 GeV/cin minimum-bias p-Pb collisions at √sNN = 5.02 TeV and in 1.3< pT< 8 GeV/cin the 20% most central Pb-Pb collisions at √sNN = 2.76 TeV. The pp reference spectra at √s= 5.02 TeV and √s= 2.76 TeV, needed for the calculation of the nuclear modification factors RpPb and RPbPb, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at √s= 7 TeV. In the pTinterval 3< pT<8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower pT, the RPbPb values increase with large systematic uncertainties. The RpPb is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured RpPb and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of RPbPb below unity at high pTmay be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions. Keywords: Heavy Ion Experiments ArXiv ePrint: 1609.03898 Open Access, Copyright CERN, for the benefit of the ALICE Collaboration. Article funded by SCOAP3. https://doi.org/10.1007/JHEP07(2017)052 JHEP07(2017)052 Contents 1 Introduction 1 2 Experimental apparatus and data samples 3 3 Analysis overview and electrons from background sources 5 4 Data analysis in p-Pb collisions 8 4.1 Extraction of electrons from beauty-hadron decays 8 4.2 Systematic uncertainties estimation 11 5 Data analysis in Pb-Pb collisions 12 5.1 Extraction of electrons from beauty-hadron decays 13 5.2 Systematic uncertainties estimation 15 6 Reference pp cross sections at √s = 2.76 TeV and √s = 5.02 TeV 18 7 Results 20 8 Summary 24 The ALICE collaboration 33 1 Introduction In collisions of heavy nuclei at ultra-relativistic energies, a high-density colour-deconfined state of strongly-interacting matter, called Quark-Gluon Plasma (QGP), is expected to be produced [1,2]. Due to their large masses (mQΛQCD), heavy quarks (charm and beauty) are almost exclusively produced in the early stage of the collision via hard parton scatterings characterised by production-time scales of less than 0.1 and 0.01 fm/cfor charm and beauty quarks, respectively [3]. They can, therefore, serve as probes to test the mechanisms of medium-induced parton energy loss, because the formation time of the QGP medium is expected to be about 0.3 fm/c[4] and its decoupling time is about 10 fm/cfor collisions at LHC energies [5]. Due to their stronger colour coupling to the medium gluons are argued to lose more energy than quarks [6–8]. Furthermore, the radiative energy loss of heavy quarks is predicted to be reduced with respect to light quarks due to the massdependent restriction of the phase space into which medium-induced gluon radiation can take place (dead-cone effect) [9–12]. The effect of the charm-quark mass on energy loss becomes negligible at high transverse momentum, pT&10 GeV/c, where the ratio mc/pT approaches zero [13]. Therefore, due to the larger mass, beauty quarks can be sensitive – 1 – JHEP07(2017)052 probes for testing the mass dependence of the parton energy loss up to transverse momenta well above 10 GeV/c [13]. Final-state effects, such as colour-charge and mass dependence of parton energy loss, can be studied experimentally through the spectra of hadrons containing heavy quarks in comparison with light-flavour hadrons in heavy-ion (AA) collisions. The understanding of final-state effects requires measurements of initial-state effects in Cold Nuclear Matter (CNM), which are inherent to nuclei in the collision system and thus present in AA collisions. Measurements in proton-nucleus (p-A) collisions are used to investigate cold nuclear matter effects such as the modification of the Parton Distribution Functions (PDF) inside the nucleus with respect to those in the proton, kTbroadening via parton collisions inside the nucleus prior to the hard scattering and energy loss in cold nuclear matter [14–18]. The effects of hot (cold) nuclear matter can be studied using the nuclear modification factor, RAA (RpA), defined as the ratio of the pTdistributions measured in AA (p-A) collisions with respect to the one in pp collisions: RAA =1 hTAAi dNAA/dpT dσpp/dpT ,(1.1) where dNAA/dpTand dσpp/dpTare the pT-differential yield and production cross section of a given particle species in AA and pp collisions, respectively, and hTAAiis the average of the nuclear overlap function for the centrality range under study [19]. Previous beauty-hadron production measurements in pp collisions at various energies at RHIC [20,21], the Tevatron [22] and the LHC [3,23–28] are described by Fixed Order plus Next-to-Leading-Log perturbative Quantum Chromodynamics (FONLL pQCD) calculations [29–31] within uncertainties. At both RHIC and the LHC, a suppression of the yield of D mesons and high-pT electrons and muons from heavy-flavour hadron decays was observed in AA collisions. The suppression is nearly as large as that of light-flavour hadrons at high pT[32–36]. The D meson and pion RPbPb were found to be consistent within uncertainties and described by model calculations that include a colour-charge dependent energy loss [34,37,38]. However, in addition to energy loss, the nuclear modification factor is also influenced by e.g. the parton pTspectrum and the fragmentation into hadrons [13,39]. Furthermore, the nuclear modification factors RPbPb of prompt D mesons and of J/ψfrom B meson decays were compared in the pTinterval 8 < pT<16 GeV/c for D mesons and 6.5< pT<30 GeV/c for J/ψmesons in order to have a similar average pT(≈10 GeV/c) for the heavy hadrons [34,40,41]. This comparison with models indicates that charm quarks lose more energy than beauty quarks in this pTinterval in central Pb-Pb collisions. The b-jet yield as measured in Pb-Pb collisions also shows a suppression compared with the yield expected from pp collisions in the jet-pTinterval 70 < pT<250 GeV/c [42]. Recently, the relative contributions of electrons from charmand beauty-hadron decays were measured as a function of transverse momentum in Au-Au collisions at RHIC [43]. There is a hint that in the momentum interval 3 < pT<4 GeV/c the RAuAu of electrons from beauty-hadron decays is larger than that of electrons from charm-hadron decays. In p-Pb collisions at the LHC, the nuclear modification factors of B mesons [44], bjets [45], J/ψfrom beauty-hadron decays [46,47], leptons from heavy-flavour hadron decays – 2 – JHEP07(2017)052 and D mesons [48,49] were investigated extensively. The results are consistent with unity within uncertainties and compatible with theoretical calculations including cold nuclear matter effects [45–48]. Therefore, the observed suppression of charm and beauty yields at high pTin Pb-Pb collisions is not explained in terms of initial-state effects but is due to strong final-state effects induced by hot partonic matter. In central d-Au collisions at √sNN = 200 GeV at RHIC, an enhancement was measured at backward rapidity by means of RdAu of muons from heavy-flavour hadron decays [50]. Theoretical calculations including modified PDFs cannot describe the data, implying that models incorporating only initial-state effects are not sufficient and suggesting the possible importance of final-state effects in the d-Au collision system. Recently, a potential signature of collective behaviour in small systems was observed via the anisotropic flow parameter v2of charged hadrons in p-Pb collisions [51–54] and in d-Au collisions [55,56], suggesting radial flow as a possible explanation of the enhancement of the RdAu [57]. In this paper, the invariant cross section in p-Pb and yield in Pb-Pb collisions are presented together with the nuclear modification factors, RpPb and RPbPb, of electrons from beauty-hadron decays in p-Pb and Pb-Pb collisions at √sNN = 5.02 TeV and √sNN = 2.76 TeV, respectively. The identification of electrons from beauty-hadron decays is based on their separation from the interaction vertex, induced by the sizable lifetime of beauty hadrons. The p-Pb (Pb-Pb) measurement covers the rapidity range |ylab| ≤ 0.6 (|ylab| ≤ 0.8) and the pTinterval 1.0< pT<8.0 GeV/c (1.3< pT<8.0 GeV/c). In the p-Pb collisions, due to the different energy per nucleon of the proton and lead beam, the centre-of-mass system (cms) is shifted by ∆y= 0.465 in the proton beam direction, resulting in the rapidity coverage −1.06 < ycms <0.14 for electrons. Given the cms energies and the rapidity coverages in the p-Pb and Pb-Pb collisions, both measurements probe, at the lowest pT, similar values of Bjorken-xof about 10−3for electrons from beauty-hadron decays [58]. The Pb-Pb measurement is restricted to the 20% most central Pb-Pb collisions, where the largest effect of energy loss on heavy-flavour production is expected. The paper is organised as follows: section 2describes the experimental apparatus and the data samples used in both analyses, which are outlined in section 3. Details of the analysis in p-Pb and Pb-Pb collisions are given in sections 4and 5, respectively. The determination of the pp reference spectra for the calculations of the RpPb and RPbPb is reported in section 6. The results are presented and discussed in section 7. Section 8 summarises the results. 2 Experimental apparatus and data samples A comprehensive description of the ALICE apparatus and its performance can be found in [59] and [60], respectively. Electron tracks were reconstructed and identified using detectors located inside the solenoid magnet that generates a field of 0.5 T parallel to the beam direction. Forward and backward detectors inside and outside the magnet were employed for triggering, background rejection and event characterisation. Charged particles are tracked with the Inner Tracking System (ITS) [59,61] and the Time Projection Chamber (TPC) [62] in the pseudorapidity range |η|<0.9. The ITS – 3 – JHEP07(2017)052 consists of six cylindrical layers of silicon detectors. The two innermost layers are made of Silicon Pixel Detectors (SPD), the two middle layers of Silicon Drift Detectors (SDD) and the two outermost layers of Silicon Strip Detectors (SSD). In the direction perpendicular to the detector surface, the total material budget of the ITS corresponds on average to 7.7% of a radiation length [61]. In this analysis, the ITS was also used to reconstruct the primary (interaction) vertex and the track impact parameter d0, defined as the distance of closest approach of the track to the interaction vertex in the plane transverse to the beam direction. The resolution on d0is better than 65 µm and 70 µm for charged particles with momenta larger than 1 GeV/c in Pb-Pb and p-Pb collisions [60], respectively, including the resolution of the primary vertex determination. The particle identification capability of the four outer layers of the ITS via the measurement of the ionisation energy loss dE/dx was used at low transverse momentum in the p-Pb analysis. The TPC, which provides up to 159 space points per track, is used for particle identification via the measurement of the specific energy loss dE/dxin the detector gas. The tracks reconstructed in the ITS and the TPC are matched to hits in the other detectors inside the magnet located at larger radii. The Transition Radiation Detector (TRD) [63] surrounding the TPC provides hadron and electron identification via the measurement of the specific energy loss dE/dxand transition radiation. During the Pb-Pb (p-Pb) data taking period it covered 7/18 (13/18) of the full azimuth. Therefore, only in the Pb-Pb analysis it was used to verify the amount of hadron contamination within the electron identification strategy at low transverse momentum (see section 5). The Time-Of-Flight array (TOF) [64], based on Multi-gap Resistive Plate Chambers (MRPCs), provides hadron rejection at low transverse momentum via the timeof-flight measurement, within the electron identification strategy applied in both analyses. The T0 detectors, arrays of Cherenkov counters, located at +350 cm and −70 cm from the interaction point along the beam direction [65] provided, together with the TOF detector, the precise start time for the time-of-flight measurement in the p-Pb analysis. For central Pb-Pb events the start time was estimated only using the particle arrival times at the TOF detector. The SPD, the T0 detectors as well as the V0 scintillator arrays, placed on both sides of the interaction point at 2.8 < η < 5.1 (V0-A) and −3.7 < η < −1.7 (V0-C), respectively, can be employed to define a minimum-bias trigger. The two Zero Degree Calorimeters (ZDC), that are symmetrically located 112.5 m from the interaction point on either side, were used in the offline event selection to reject beam-gas interactions by correlating the time information with the one from the V0 detectors. The Pb-Pb and p-Pb data presented here were recorded in 2010 and 2013, respectively. Minimum-bias p-Pb collisions were selected by requiring coincident signals in V0-A and V0-C (V0AND condition). Beam-gas interactions were rejected offline by the aforementioned correlation of the ZDC and V0 time information. The Pb-Pb collisions were collected with two different minimum-bias interaction triggers. The first trigger condition required signals in two of the following three detectors: SPD (two hits in the outer SPD layer), V0-A and V0-C. The second trigger condition required a coincidence between V0-A and V0-C. Both minimum-bias trigger conditions had efficiencies larger than 95% for hadronic interactions, whereas the second rejected electromagnetic processes to a large – 4 – JHEP07(2017)052 extent [66]. Only events with a primary vertex within ±10 cm from the centre of the detector along the beam direction were considered in the p-Pb and Pb-Pb analyses. The Pb-Pb events were categorised into centrality classes by fitting the sum of the two V0 signal amplitudes with a geometrical Glauber-model simulation [19], as described in [66]. The Glauber-model simulation yields a value of 18.93 ±0.74 mb−1for the average nuclear overlap function hTAAifor the 20% most central Pb-Pb collisions considered in the analysis. About 100 and 3 million p-Pb and 20% most central Pb-Pb events passed the offline selection criteria corresponding to an integrated luminosity of LpPb int = 47.8±1.6µb−1and LPbPb int = 2.2±0.2µb−1, respectively. 3 Analysis overview and electrons from background sources The identification of electrons from beauty-hadron decays is divided into the following steps: •selection of tracks with good quality, •electron identification (eID), •determination of the electron yield from beauty-hadron decays. The signal contains both electrons from direct decays (b →e, branching ratio: ≈11%) as well as cascade decays (b →c→e, branching ratio: ≈10%) of hadrons that contain a beauty (or anti-beauty) quark [67]. Throughout the paper the term ‘electron’ denotes both electron and positron. The track selection procedure is identical to previous analyses on the production of electrons from beauty-hadron decays [23,24]. The selection criteria are the same in the p-Pb and Pb-Pb analyses, except for the restriction of the geometrical acceptance in rapidity, which was adjusted in each collision system to the region where the TPC could provide optimal electron identification, taking into account the detector and running conditions during each data-taking period. In Pb-Pb collisions this corresponds to the rapidity range |ylab| ≤ 0.8 and in p-Pb to |ylab| ≤ 0.6. The tracks were required to have associated hits in both SPD layers, in order to minimise the contribution of electrons from photon conversions in the ITS detector material and the fraction of tracks with misassociated hits (see below). The electrons were identified with the TPC and the TOF detectors via the measurement of their respective signal, specific energy loss in the gas (dE/dx) and the time-offlight. The selection variable (hereafter nTPC σor nTOF σ) is defined as the deviation of the measured signal of a track with respect to the expected signal for an electron in units of the corresponding detector resolution (σTPC or σTOF). The expected signal and the resolution originate from parametrisations of the TPC and TOF detector signals, described in detail in [60]. For both analyses, particles were accepted with the TPC as electron candidates if they satisfied the condition −0.5< nTPC σ<3. This asymmetric selection was chosen to remove hadrons, that are mainly found at negative nTPC σvalues. However, at low and high transverse momentum, the eID strategy based on TPC is subject to contamination from pions, kaons, protons and deuterons. To resolve these ambiguities, a selection cut of |nTOF σ| ≤ 3 was applied for the whole pTrange in the Pb-Pb analysis and for pT – 5 – JHEP07(2017)052 ≤2.5 GeV/c in the p-Pb analysis. The remaining hadron contamination was determined via data-driven methods in the p-Pb analysis and subtracted statistically (see section 4). The technique used for the Pb-Pb analysis is described in section 5. The electrons passing the track and eID selection criteria originate, besides from beauty-hadron decays, from the following background sources. In what follows, prompt and non-prompt contributions are marked in parentheses as ‘P’ and ‘NP’, respectively: •(P) Dalitz and di-electron decays of prompt light neutral mesons (π0, η, ρ, ω, η0, φ), •(P) di-electron decays of prompt heavy quarkonia (J/ψ, etc.). •(NP) decay chains of hadrons carrying a strange (or anti-strange) quark, •(NP) photon conversions in the detector material, •(NP) semi-leptonic decays of prompt hadrons carrying a charm (or anti-charm) quark. The measurement of the production of electrons from beauty-hadron decays exploits their larger mean proper decay length (cτ ≈500 µm [67]) compared to that of charm hadrons and most other background sources, resulting in a larger average impact parameter. The sign of the impact parameter value is attributed based on the relative position of the track and the primary vertex, i.e. if the primary vertex lies on the leftor right-hand side of the track with respect to the particle momentum direction in the transverse plane. For the presented analyses, the impact parameter was multiplied with the sign of the particle charge and of the magnetic field component along the beam axis (plus or minus for the two field orientations). With this definition, the sign of the impact parameter depends on whether the primary vertex lies inside or outside of the circle defined by the track projection in the transverse plane. Electrons from the conversion of photons in the detector material have an initial momentum with a very small angle to the direction of the photon. The magnetic field bends the track away from the primary vertex. Thus, they typically have an impact parameter d0<0. The asymmetric shape helps to differentiate this background source. It is important to include the field configuration, because the magnetic field direction was reversed during the Pb-Pb data taking period, which motivated this redefinition. Figure 1shows for two pTintervals the resulting distribution of the measured impact parameter value multiplied by the sign of the charge of each track and the sign of the magnetic field in the 20% most central Pb-Pb collisions. The impact parameter distributions for electrons from beautyand charm-hadron decays, from Dalitz decays of light mesons, and from photon conversions are also drawn for comparison. The distributions were obtained from Monte Carlo simulations and normalised to the data using the fit values described in section 5. The distribution for electrons from photon conversions is, as explained before, visible as an asymmetric and shifted distribution. The impact parameter distribution of electrons from prompt sources, such as Dalitz and quarkonium decays, is determined by the impact parameter resolution. The electrons from these sources are thus categorised as Dalitz decays within both analyses. – 6 – JHEP07(2017)052 -0.1 -0.05 0 0.05 0.1 Entries 10 2 10 3 10 4 10 Data e→c Conversion electrons e→ c) →b ( Dalitz electrons Sum = 2.76 TeV NN sPb, −20% Pb−ALICE, 0 c < 2.0 GeV/ T p1.5 < = 2.76 TeV NN sPb, −20% Pb−ALICE, 0 c < 2.0 GeV/ T p1.5 < field) (cm)× sign(charge × 0 d -0.1 -0.05 0 0.05 0.1 Ratio 1 2 -0.1 -0.05 0 0.05 0.1 Entries 1 10 2 10 3 10 Data e→c Conversion electrons e→ c) →b ( Dalitz electrons Sum = 2.76 TeV NN sPb, −20% Pb−ALICE, 0 c < 6.0 GeV/ T p5.0 < = 2.76 TeV NN sPb, −20% Pb−ALICE, 0 c < 6.0 GeV/ T p5.0 < field) (cm)× sign(charge × 0 d -0.1 -0.05 0 0.05 0.1 Ratio 1 2 Figure 1. Impact parameter distribution for the interval (left) 1.5< pT<2.0 GeV/c and (right) 5< pT<6 GeV/c in the 20% most central Pb-Pb collisions. The impact parameter value of each track was multiplied by the sign of the charge of each track and the sign of the magnetic field. The individual distributions for electrons from beauty-hadron and charm-hadron decays, from Dalitz-decays of light mesons, and from photon conversions were obtained by HIJING and PYTHIA simulations. The bottom panel shows the ratio of the data and ‘Sum’. The Monte Carlo simulations were produced as follows. A sample of minimum-bias Pb-Pb collisions at √sNN = 2.76 TeV was generated with HIJING v1.36 [68] for efficiency and acceptance corrections as well as to obtain the impact parameter distributions for photon conversions and Dalitz decays. To increase the statistics of electrons from charmand beauty-hadron decays, a signal enhanced sample was generated using pp events produced by the generator PYTHIA v6.4.21 [69] with Perugia-0 tune [70]. Each added pp event contains one cc or bb pair. For the p-Pb analysis, the same procedure was used. The generated particles were propagated through the ALICE apparatus using GEANT3 [71] and a realistic detector response was applied to reproduce the performance of the detector system during data taking. The inclusive yield of electrons originating from strange-hadron decays is small compared to the other background sources. However, as these electrons originate from secondary π0from strange-hadron decays (K0 S, K0 L, K±, Λ) and three prong decays of strange hadrons (K0 L,K±), the impact parameter distribution is broader than that of electrons from Dalitz and di-electron decays of other light neutral mesons. Sections 4and 5describe how the analyses handle this background contribution. Although requiring hits in both SPD layers, electrons from photon conversions in detector material with production radii outside the SPD layers were observed to have passed the track selection. These electron tracks are wrongly associated with signals of other particles in the inner detector layers. Within this paper these electrons are called – 7 – JHEP07(2017)052 ‘mismatched conversions’. The amount of mismatched conversions depends on the track multiplicity within the event and thus has a larger impact for the Pb-Pb analysis. Sections 4 and 5outline how the analyses deal with the mismatched conversions. The impact parameter distributions of electrons from most background sources are narrow compared to the one of electrons from beauty-hadron decays. By applying a minimum cut on the absolute value of the impact parameter |d0|, the fraction of electrons from beauty-hadron decays can thus be enhanced. The remaining background can be described using a cocktail method and subtracted statistically to obtain electrons from beauty-hadron decays [23,24]. This method was applied in the p-Pb analysis and is described in detail in section 4. Another technique, used in the Pb-Pb analysis (see section 5), is to make use of the whole impact parameter distribution, i.e. to compare the impact parameter distributions of the various electron sources from simulation (templates) with the impact parameter distribution of all measured electron candidates to estimate the individual contributions. 4 Data analysis in p-Pb collisions The identification of electrons from beauty-hadron decays in the p-Pb analysis is based on the selection of electrons with large impact parameters. This method was already applied in pp collisions at √s= 2.76 TeV and √s= 7 TeV [23,24]. Since the impact parameter distribution of electrons from beauty-hadron decays is broader compared to the one of electrons from most background sources (see section 3), the requirement of a minimum absolute impact parameter enhances the signal-to-background (S/B) ratio of electrons from beauty-hadron decays. The remaining background due to hadron contamination and electrons from background sources was obtained via a data-driven method and from Monte Carlo simulations re-weighted to match the pTdistributions of the background sources in data, respectively, and then subtracted. 4.1 Extraction of electrons from beauty-hadron decays Electron candidates with an impact parameter |d0|>0.0054 + 0.078 ×exp(−0.56 ×pT) (with d0in cm and pTin GeV/c) were selected. This selection criterion was determined from Monte Carlo simulations to maximise the significance for electrons from beautyhadron decays. The selection of the minimum impact parameter is pTdependent, because the width of the impact parameter distribution, the S/B ratio as well as the true impact parameter distribution of the various electron sources [23] are pTdependent. The number of hadrons passing the track selection, eID, and the minimum impact parameter requirement was estimated at high transverse momentum (pT≥4 GeV/c) by parametrising the TPC nTPC σdistribution in momentum slices, and it was subtracted [72]. Above a pTof 4 GeV/c, the hadron contamination increases with transverse momentum and reaches 10% at 8 GeV/c, see figure 2(left). At low transverse momentum (pT ≤4 GeV/c), the hadron contamination is negligible except in the transverse momentum interval 1 < pT<1.2 GeV/c, see figure 2(left), where electrons cannot be distinguished from protons via the measurement of specific energy loss in the TPC gas. In addition, the requirement of a minimum impact parameter increases the relative contribution of secondary – 8 – JHEP07(2017)052 The off-diagonal elements of the response matrix are small. For this reason no regularisation was used in the unfolding procedure to avoid additional systematic uncertainties. The unfolding was done using a matrix inversion of the response matrix [76]. Due to the restricted pTrange of the measurement there is some dependence of the unfolded values on bins that have not been measured, mainly the adjacent bins. To solve this, the yield was measured in two further bins (1.1< pT<1.3 GeV/c and 8 < pT<12 GeV/c) and used only in the unfolding calculations. The statistical uncertainties were propagated accordingly. To validate this signal extraction method, the template fit method was also applied to the p-Pb data, where results were found to be consistent with the cut method described in section 4. 5.2 Systematic uncertainties estimation The systematic uncertainties are summarized in table 2. They were estimated using datadriven methods where possible. An overview of the efficiencies of the different track selection steps may be found in figure 3. The efficiency due to the ITS track selection criteria (hits in both SPD layers) does not depend strongly on the particle species. Thus, charged tracks could be used as a representative sample with respect to the geometric effects, such as inactive areas of the detector. The normalisation for the efficiency was performed by making use of phase space (pseudorapidity and azimuthal angle) regions where the efficiency was close to unity. Averaging over the phase space yields a proxy for the total efficiency which was compared between data and Monte Carlo simulations and yielded a difference of 2%. The uncertainty for non-geometric effects was estimated to be smaller than 3%. The efficiencies of the requirements on charged tracks with good quality, the TOF matching and TOF eID depend more strongly on the particle type. Therefore, only an electron sample could be representative. It was obtained by selecting electrons from photon conversions. Due to the large particle multiplicity in central Pb-Pb collisions (resulting in a sizeable hadron contamination), the comparison was done using weak additional particle identification (−1.5< nTPC σ<4), in more peripheral collisions (20−40%,40−80%), and with different ITS track selection criteria (excluding signals in the innermost layer). To account for biases due to these additional criteria, they were varied and the results were checked for consistency. The estimated systematic uncertainties are about 3% for the requirement of charged tracks with good quality and about 10% for the TOF matching and eID. The systematic uncertainty of the TPC eID includes differences in the eID efficiency for electrons from beauty-hadron decays and for electrons from photon conversion (due to the different pseudorapidity distributions) in the sample as well as the uncertainty of the extrapolation towards lower nTPC σ. The uncertainty due to the modelling of the nTPC σdistribution was checked by comparing different model descriptions with the standard one and by comparing with a sample of pions selected with the TRD and TOF. The total uncertainty of 5% for the TPC eID is the quadratic sum of the following contributions: 2% from the extrapolation, 2% from the pseudorapidity dependence, 3% from a possible pTdependence and 2% from the tail of the nTPC σdistribution. – 15 – JHEP07(2017)052 To estimate the statistical and systematic uncertainty on the extracted signal yield due to the maximum-likelihood fit, a Monte Carlo closure test was used. For this purpose, the templates were slightly smoothed and the result sampled with the statistics present in the measurement. The pseudo-data was created by using the measured contributions as input. The application of the template fit allowed for a comparison of the measured and true value. Repetitions of this process gave an estimation of the statistical and systematic contribution to the uncertainty. The charm yield of the test was varied to avoid underestimating the uncertainty in pTintervals with downward fluctuations of the measured charm yield. The systematic uncertainty varies between 19% and 6% between the different pTintervals. There is an uncertainty in how well the impact parameter distributions of the different electron sources are described by the Monte Carlo simulations. Where possible, any differences were corrected for. The remaining uncertainty was propagated to the measured spectrum of electrons from beauty-hadron decays by changing the fit templates within their uncertainties. The different resolution of the impact parameter (d0) with the given track and event selection criteria in Monte Carlo simulations and data was corrected for. The size of the correction was estimated by comparing the impact parameter distributions of primary pions, yielding a 10–12% worse resolution in data compared to the Monte Carlo simulations in the pTrange of the measurement. To correct for this effect, a Gaussian distributed random number was added to each impact parameter value such that the resolution in the Monte Carlo simulations matched that of the data. The central values of the yield of electrons from beauty-hadron decays were estimated using a resolution correction of 10%. The yield using a correction of 12% instead, differs by about 10% at pT= 1.3 GeV/c with the difference decreasing quickly towards higher pT. The effect of the correction was found to be negligible for the p-Pb analysis. Despite the strong eID requirements, there is a significant contamination of the electron sample by hadrons (mostly charged pions). The contribution was estimated using a clean TPC energy loss signal of pions identified with the TRD, which was fitted to the nTPC σ distribution, suggesting a contamination of the electron candidate sample of about 15% even for low transverse momentum. The contamination was not explicitly subtracted. The impact parameter distribution of charged hadrons is similar to that of the Dalitz template. This means that the contribution of the hadron contamination to the impact parameter distribution was absorbed into the Dalitz template by the fit method. To account for slight differences between the distributions, the result was compared with a fit using the hadron impact parameter template instead. A hypothetical template with the same mixture of Dalitz electrons and hadrons as in data would yield a result between these two extreme cases. For pT≥5 GeV/c, the fit using the hadron template was used for the central points as the contribution from hadrons dominates compared to that of the Dalitz electrons. The difference in the measured yield of electrons from beauty-hadron decays after exchanging the Dalitz template for the hadron template is 7% at pT= 1.3 GeV/c decreasing towards higher transverse momentum. The proton contamination is significant only below pT= 1.3 GeV/c. Like for the p-Pb analysis, the influence of the difference in yield of mismatched conversions in data and Monte Carlo simulations had to be considered, especially as it increases – 16 – JHEP07(2017)052 with the multiplicity of the event. By making use of the multiplicity dependence, it was possible to create templates that either overor underestimate this effect. This was crosschecked using charged pions from K0 Sdecays as done in the p-Pb analysis (see section 4.2). The change of the resulting measured spectra of electrons from beauty-hadron decays was used as an estimate for the systematic uncertainty, which is 14% at pT= 1.3 GeV/c and decreases quickly towards higher transverse momentum. As for the p-Pb analysis, electrons from secondary pion and three-body decays of hadrons carrying a strange (or anti-strange) quark had to be considered, especially as these have broader impact parameter distributions than Dalitz electrons (see section 3). Due to the different final states, both the template for electrons from photon conversions and the template for Dalitz electrons are affected. These were split into a contribution from the decay of strange particles and the rest. For the fit they were considered as separate templates, but the amplitude parameters were coupled to have a fixed ratio. This was necessary because the contribution from strangeness is very small and could not be constrained by the information from the impact parameter distribution alone. The relative strength of the strangeness content was varied by a factor of two which includes the variation expected from the measured kaon/pion ratio [37]. The resulting difference in the yield of electrons from beauty-hadron decays was used as the estimate for the systematic uncertainty. It is 1.3% for low pT, decreasing towards higher transverse momentum. Electrons at a fixed transverse momentum have mother particles in a range of pTvalues. The impact parameter distributions of electrons depend on the momentum distributions of the mother particles. For the charm case this can be disentangled by making use of the measured charm pTdistribution [83]. For the beauty case this means that the result of the measurement depends on the input beauty-hadron spectrum in the Monte Carlo simulation. The effect was estimated by varying the beauty-hadron pTdistribution of the templates and observing the resulting change in the measured electron pTdistribution. The beauty-hadron pTdistribution was obtained according to PYTHIA simulations with a Perugia-0 tune which describes the measured p-Pb data well. Therefore, an effect of the variation of the pTdistribution was studied by introducing a momentum-dependent nuclear modification factor RAA. An RAA based on a theoretical calculation was used for the central points [84]. It has values near unity for low transverse momenta and drops to about 0.5 from a hadron pTof 5 to 10 GeV/c. This was varied to half its effect (RAA →(1+RAA)/2) in order to estimate the associated uncertainty. For the charm case, the variation was done according to the measurement uncertainties [83]. The difference in the resulting measured yield of electrons from beauty-hadron decays is about 8%, with no visible pTdependence. For the template fit, all species of charmed hadrons were combined into one template. The same holds for the beauty case. The baryon fraction of heavy hadrons is currently not known for Pb-Pb collisions and might be different than for pp collisions. Because of the different masses and decay channels, the various heavy-flavour hadron decays produce electrons with different impact parameter distributions. The templates were split into their contributions from only mesons or only baryons, with fixed ratios of the fit amplitudes. To estimate the uncertainty, the baryon fraction was increased by a factor of three for both charm and beauty simultaneously, motivated by the results of thermal model calcu- – 17 – JHEP07(2017)052 Source Associated uncertainty Tracking and matching 4.7% TOF matching and eID 10% TPC eID 5% Signal extraction 17% to 12% d0resolution correction 10% to 0.4% Hadron contamination 7% to 1.4% Mismatched conversions 14% to 0.02% Strangeness 1.3% to 0.3% Mother particle pTdistribution 8% Baryon/meson ratio 5% Total 26% to 17% Table 2. Systematic uncertainties in the Pb-Pb analysis. Individual sources of systematic uncertainties are pTdependent, which is reported using intervals. The lower and upper value of the interval, respectively, lists the uncertainty at pT= 1.3 GeV/c and pT= 8.0 GeV/c. The second group of entries in the table is related to the method used to extract the electrons from beautyhadron decays. lations [85]. This led to a change in the measured yield of electrons from beauty-hadron decays of about 5% with no clear momentum dependence. Decreasing the baryon ratio even to 0 has a smaller effect. 6 Reference pp cross sections at √s = 2.76 TeV and √s = 5.02 TeV For the calculations of the nuclear modification factors RpPb and RPbPb, corresponding pp reference spectra at √s= 5.02 TeV and √s= 2.76 TeV are needed. To obtain these, the same method is used in both analyses. It is described in more detail in the following for the p-Pb analysis. At present no pp measurement at √s= 5.02 TeV exists. Therefore, the cross section of electrons from beauty-hadron decays measured in the momentum interval 1 < pT< 8 GeV/c at √s= 7 TeV [23] was scaled to √s= 5.02 TeV by applying a pQCD-driven √sscaling [86]. The pT-dependent scaling function was obtained by calculating the ratio of the production cross sections of electrons from beauty-hadron decays from FONLL pQCD calculations [29–31] at √s= 5.02 TeV and √s= 7 TeV. Both the direct (b → e) and the cascade decay (b →c→e) were considered. For the calculations at both energies the same parameters were used for the beauty-quark mass (mb= 4.75 GeV/c2), the PDFs (CTEQ6.6 [87]) as well as the factorisation µFand renormalisation µRscales with µR=µF=µ0=qm2 b+p2 T,b, where pT,bdenotes the transverse momentum of the beauty quark. The uncertainties of the pT-dependent scaling function were estimated by varying the parameters. The beauty-quark mass was set to mb= 4.5 and 5 GeV/c2. The uncertainties for the PDFs were obtained by using the CTEQ6.6 PDF uncertainties [87]. The contribution from the scale uncertainties was estimated by using six different sets: (µR/µ0, µF/µ0) = (0.5,0.5),(1,0.5),(0.5,1),(2,1),(1,2),(2,2). The uncertainties originating – 18 – JHEP07(2017)052 )c (GeV/ T p 0 1 2 3 4 5 6 7 8 9 10 ) 2 )c) (mb/(GeV/yd T p/(dσ 2 ) d T pπ 1/(2 -7 10 -6 10 -5 10 -4 10 -3 10 ALICE e→ c) →b ( = 2.76 TeV measureds pp, = 7 TeV scaled to 2.76 TeVspp Figure 4. Invariant cross section of electrons from beauty-hadron decays at √s= 2.76 TeV obtained by a pQCD-driven scaling of the cross section measured in pp collisions at √s= 7 TeV in comparison with the measured spectrum in pp collisions at √s= 2.76 TeV [88]. from the mass and PDF variations are negligible. The uncertainty stemming from the variation of the scales was defined as the largest deviation from the scaling factor obtained with µR=µF=µ0. The resulting √s-scaling uncertainty is almost independent of pT. It ranges from +4 −2% at 1 GeV/c to about +2 −2% at 8 GeV/c. The total systematic uncertainty of the pp reference spectrum at √s= 5.02 TeV is then given as the bin-by-bin quadratic sum of the √s-scaling uncertainty and the relative systematic uncertainty of the measured spectrum at √s= 7 TeV. For the statistical uncertainties the relative uncertainties of the spectrum measured at √s= 7 TeV were taken. For the RPbPb analysis, the measured spectrum at √s= 7 TeV was scaled to √s= 2.76 TeV using FONLL pQCD calculations at the respective energies. The systematic scaling uncertainty is about +11 −7% at 1 GeV/c and about +7 −5% at 8 GeV/c. The resulting pp reference spectrum was found to be consistent with the measurement of electrons from beauty-hadron decays in pp collisions at √s= 2.76 TeV [88], shown in figure 4. The measured spectrum at √s= 2.76 TeV was not taken as a reference for the RPbPb, because of larger statistical and systematic uncertainties than the reference obtained via the √s-scaling. The systematic uncertainty of the normalisation related to the determination of the cross section of the minimum-bias trigger used for the measurement at √s= 7 TeV is 3.5% and also holds for the obtained pp reference spectra at √s= 5.02 TeV and √s= 2.76 TeV. The systematic uncertainties of the input pT-differential cross section of electrons from beauty-hadron decays measured at √s= 7 TeV, the normalisation uncertainty, as well as the scaling uncertainties for the reference spectra are summarised in table 3. – 19 – JHEP07(2017)052 pp spectrum 7 TeV 45% to 35% for 1 < pT<1.5 GeV/c 35% to 20% for 1.5< pT<2.5 GeV/c ≤20% for pT≥2.5 GeV/c Normalisation uncertainty 3.5% scaling uncertainty for p-Pb (√s= 5.02 TeV) Pb-Pb (√s= 2.76 TeV) at pT= 1 GeV/c +4 −2%+11 −7% at pT= 8 GeV/c +2 −2%+7 −5% Table 3. Systematic uncertainties of the pT-differential cross section of electrons from beautyhadron decays measured at √s= 7 TeV [23], the normalisation uncertainty, as well as the scaling uncertainties for the reference spectra at √s= 5.02 TeV and √s= 2.76 TeV. The scaling uncertainties for the reference spectra are slightly pTdependent; the uncertainties are given for the two extreme pTintervals. Details are described in the text. )c (GeV/ T p 0 1 2 3 4 5 6 7 8 9 10 ) 2 )c) (mb/(GeV/yd T p/(dσ 2 ) d T pπ 1/(2 -4 10 -3 10 -2 10 -1 10 1 < 0.14 cms y1.06 < − = 5.02 TeV NN sPb, −p 208× = 5.02 TeV s pp scaled to ALICE e→ c) →b ( Pb not shown− 3.7% norm. unc. on p± 3.5% norm. unc. on pp ref. not shown± )c (GeV/ T p 0 1 2 3 4 5 6 7 8 9 10 ) 2 )c) (1/(GeV/yd T p/(dN 2 ) d T pπ 1/(2 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 | < 0.8 cms y| = 2.76 TeV NN s Pb, −20% Pb−0 〉 AA T〈 × = 2.76 TeV s pp scaled to ALICE e→ c) →b ( not shown〉 AA T〈 3.9% unc. on ± 3.5% norm. unc. on pp ref. not shown± Figure 5. Invariant cross section (left) and yield (right) of electrons from beauty-hadron decays as a function of transverse momentum in minimum-bias p-Pb collisions at √sNN = 5.02 TeV and in the 20% most central Pb-Pb collisions at √sNN = 2.76 TeV. The pp reference spectra scaled by the number of nucleons in the Pb nucleus (A = 208) and by hTAAi, respectively, are shown as well. The vertical bars represent the statistical uncertainties, the boxes indicate the systematic uncertainties. The pp and p-Pb normalisation uncertainties of 3.5% and 3.7% as well as the one of the nuclear overlap function hTAAiof 3.9% are not shown. 7 Results The pT-differential cross section and invariant yield of electrons from beauty-hadron decays at mid-rapidity in minimum-bias p-Pb collisions at √sNN = 5.02 TeV and in the 20% most central Pb-Pb collisions at √sNN = 2.76 TeV, respectively, are shown in figure 5. The markers are plotted at the centre of the pTbin. The vertical bars indicate the statistical uncertainties, the boxes represent the systematic uncertainties. The pp reference spectra, obtained via the pQCD-driven √s-scaling from the measurement in pp collisions – 20 – JHEP07(2017)052 )c (GeV/ T p 0 1 2 3 4 5 6 7 8 9 10 Nuclear modification factor 0.5 1 1.5 2 2.5 3 | < 0.8 cms y| = 2.76 TeV NN sPb, −20% Pb−0 < 0.14 cms y1.06 < − = 5.02 TeV NN sPb, −p ALICE e→ c) →b ( )c (GeV/ T p 0 2 4 6 8 10 12 14 16 18 20 Nuclear modification factor 0.5 1 1.5 2 2.5 3 | < 0.8 cms y e, | → c) →b ( | < 0.6 cms y e, | →b, c ALICE = 2.76 TeV NN sPb, −20% Pb−0 Figure 6. (Left) Nuclear modification factors RpPb and RPbPb of electrons from beauty-hadron decays at mid-rapidity as a function of transverse momentum for minimum-bias p-Pb collisions at √sNN = 5.02 TeV and 20% most central Pb-Pb collisions at √sNN = 2.76 TeV. The data points of the p-Pb analysis were shifted by 0.05 GeV/c to the left along the pTaxis for better visibility. (Right) RPbPb of electrons from beauty-hadron decays together with the corresponding result for beautyand charm-hadron decays [89] for the 20% most central Pb-Pb collisions. The vertical bars represent the statistical uncertainties, while the boxes indicate the systematic uncertainties. The normalisation uncertainties, common to all points, are shown as filled boxes at high pTfor all nuclear modification factors. at √s= 7 TeV as described in section 6, are shown for comparison. The pp reference spectra were multiplied by the number of nucleons in the Pb nucleus (A = 208) for the p-Pb and with the nuclear overlap function (hTAAi) for the Pb-Pb comparison. The Pb-Pb result shows a suppression of electrons from beauty-hadron decays at high pTcompared to the yield in pp collisions. Such a suppression is not seen in the comparison of the p-Pb spectrum with the corresponding pp reference. The nuclear modification factors RPbPb and RpPb are shown in figure 6(left). The RPbPb was obtained using equation (1.1). The RpPb was calculated as the ratio of the cross section of electrons from beauty-hadron decays in p-Pb and pp collisions scaled by the number of nucleons in the Pb nucleus (A = 208). The statistical and systematic uncertainties of the Pb-Pb or p-Pb and the pp spectra were propagated as independent uncertainties. The systematic uncertainties of the nuclear modification factors are partially correlated between the pTbins. The normalisation uncertainty of the pp spectrum and the uncertainty of the nuclear overlap function hTAAior the normalisation uncertainties of the p-Pb spectrum, respectively, were added in quadrature. The normalisation uncertainties are shown as filled boxes at high transverse momentum in figure 6. The RpPb is consistent with unity within uncertainties (of about 20% for pT>2 GeV/c) for all shown transverse momenta. The production of electrons from beauty-hadron decays is thus consistent with binary-collision scaling of the corresponding measurement in pp collisions at the same centre-of-mass energy. The values of the RPbPb for the 20% most – 21 – JHEP07(2017)052 )c (GeV/ T p 0 1 2 3 4 5 6 7 8 9 10 pPb R 0.5 1 1.5 2 2.5 3ALICE e→ c) →b ( < 0.14 cms y1.06 < − = 5.02 TeV, NN sPb, −p FONLL + EPS09NLO shad. Blast wave calculation : Coherent scattering + CNM energy losset al.Sharma : Incoherent multiple scatteringet al.Kang )c (GeV/ T p 0 1 2 3 4 5 6 7 8 9 10 PbPb R 0.5 1 1.5 2 2.5 3 | < 0.8 ALICE cms y e | → c) →b ( = 2.76 TeV NN sPb, −20% Pb−0 FONLL + EPS09NLO shad. MC@sHQ+EPOS2, Coll+Rad(LPM) =1.0κBAMPS, =0.2κBAMPS, WHDG TAMU =155 MeV) dec TPOWLANG-lQCD ( =155 MeV) dec TPOWLANG-HTL ( AdS/CFT Figure 7. Nuclear modification factors RpPb (left) and RPbPb (right) of electrons from beautyhadron decays in comparison with different theoretical predictions [17,18,29–31,57,84,90–97], see text for details. The vertical bars represent the statistical uncertainties, while the boxes indicate the systematic uncertainties. The normalisation uncertainty, common to all points, is shown as a filled box at high pTfor both collision systems. central Pb-Pb collisions increase, for pT≤3 GeV/c, with sizeable uncertainties of 30–45%. In the interval 3 < pT<6 GeV/c, the RPbPb is about 0.7 with a systematic uncertainty of about 30%; in 6 < pT<8 GeV/c the ratio is 0.48 with an uncertainty of about 25%. In the latter transverse momentum range the suppression with respect to RPbPb =1isa 3.3σeffect taking into account the statistical and systematic uncertainties. A comparison of the RPbPb of electrons from beauty-hadron decays with the one from charmand beauty-hadron decays is shown in figure 6(right) for the 20% most central Pb-Pb collisions. For the latter RPbPb, the pT-differential invariant yields of electrons from charmand beauty-hadron decays published in [89] for the centrality classes 0–10% and 10–20% were combined. For the pp reference in the momentum range up to pT≤12 GeV/c, the corresponding invariant cross section measurement at √s= 2.76 TeV [24], which has uncertainties of about 20%, was used. For pT≥12 GeV/c, the ATLAS measurement [72] at √s= 7 TeV was extrapolated to √s= 2.76 TeV applying a FONLL pQCD-driven √sscaling analogous to the method described in section 6. The uncertainty of the pp reference in this momentum range is about 15%. As expected, the results agree within uncertainties at high pT, where the beauty contribution is larger than the charm contribution [24]. In the pTinterval 3 < pT<6 GeV/c, the suppression of the RPbPb for electrons from beauty-hadron decays is about 1.2σless. This difference is consistent with the ordering of charm and beauty suppression seen in the prompt D meson and J/ψfrom B meson comparison [34,40,41]. Within uncertainties, the RpPb is described by pQCD calculations including modifications of the parton distribution functions (FONLL [29–31] + EPS09NLO [90] nuclear PDFs) as shown in figure 7(left). The data and the calculation suggest that cold nuclear matter effects are small at high transverse momentum. Recent measurements of long-range – 22 – JHEP07(2017)052 correlations for charged hadrons [51,53,54] and studies of the mean transverse momentum as a function of the charged-particle multiplicity in the event [73] suggest that there might be collective effects in p-Pb collisions. The figure also reports the result of a calculation based on the idea proposed in ref. [57], in which the pTdistribution of beauty hadrons from a hydrodynamically expanding medium is obtained from a blast-wave model. The blast-wave parameters were extracted from fits to the pT-spectra of light hadrons [73] in p-Pb collisions. The uncertainties of the measurement do not allow for a conclusion on possible flow effects. The data are also described by calculations which include CNM energy loss, nuclear shadowing and coherent multiple scattering at the partonic level [17]. An enhancement at intermediate pTis predicted by the calculations based on incoherent multiple scattering [18]. Presently, the large systematic uncertainties of the measurement do not allow one to discriminate between the aforementioned theoretical approaches. Perturbative QCD calculations including initial-state effects for Pb-Pb collisions at √s= 2.76 TeV (FONLL [29–31] + EPS09NLO [90] nuclear PDFs) cannot describe the RPbPb at high transverse momentum (see figure 7, right), indicating that the suppression, particularly evident in the interval 6 < pT<8 GeV/c, is induced by the presence of a hot and dense medium in the final state. At lower transverse momentum, the large uncertainties do not allow one to conclude whether the measured RPbPb is larger than that obtained from this calculation. In order to gain further insight into the energy loss mechanisms, particularly the relative importance of radiative and collisional energy loss, the data are compared with several models of heavy-quark transport and energy loss in the QGP. Both radiative and collisional energy loss are included in the pQCD model MC@sHQ+EPOS2 [91], the partonic transport description BAMPS [96,97], and in WHDG [93–95]. The non-perturbative transport model TAMU [84] includes only collisional processes, while the POWLANG [92] transport calculation simulates the production of heavy quarks using POWHEG and their propagation in the plasma via a relativistic Langevin equation. Heavy-quark energy loss can also be calculated using the AdS/CFT heavy-quark drag model [95]. The right-hand side of figure 7shows the comparison of the various models with the measured RPbPb. The MC@sHQ+EPOS2 calculation with EPOS initial conditions [98,99], including the Landau-Pomeranchuk-Migdal (LPM) effect [100], is consistent with the data at high pT. The BAMPS [96,97] model is based on pQCD cross sections including the running of the coupling and scaled by a constant factor κ. The two shown values of κ cannot be distinguished given the uncertainties in the data. In the WHDG calculation, the medium density is assumed to be proportional to the charged particle multiplicity and a 1-D Bjorken-expansion is included. The WHDG model describes the measurement well within the restricted pTrange shown. The TAMU model includes collisional processes and incorporates resonance formation close to the critical temperature as well as diffusion of heavy-flavour mesons in the hadronic phase. The hydrodynamic expansion is constrained by pTspectra and elliptic flow measurements of light hadrons. The calculations are consistent with the data at high pT, indicating a limited sensitivity of the current data to radiative energy loss effects. The POWLANG [92] transport calculation takes into account initial-state nuclear effects via – 23 – JHEP07(2017)052 EPS09 modifications of the PDFs and describes the medium using an underlying hydrodynamical model. The transport coefficients used for the evolution of the heavy quark in the medium are either extracted from lattice-QCD calculations or Hard-Thermal-Loop (HTL) resummation [101] of medium effects. The hadronisation via in-vacuum fragmentation functions or via in-medium string-fragmentation routines occurs once the decoupling temperature is reached. The calculations are shown for different transport coefficients with a decoupling temperature Tdec = 155 MeV; the results with a temperature of Tdec = 170 MeV look similar. No scenario is clearly favoured by the current data set. The AdS/CFT model, which includes energy loss fluctuations in a realistic strong-coupling energy loss mode, clearly shows a stronger suppression than the measured RPbPb. The MC@sHQ+EPOS2, the BAMPS as well as the TAMU calculation describe the suppression seen in data at high transverse momentum. They also show an increase towards lower momentum reaching RPbPb values around unity or slightly above. The data show a larger increase with decreasing transverse momentum, however exhibit large systematic and statistical uncertainties. 8 Summary The pT-differential cross section and invariant yield of electrons from beauty-hadron decays in minimum-bias p-Pb collisions and in the 20% most central Pb-Pb collisions, respectively, were measured at mid-rapidity. The measurements are compared via the nuclear modification factors with pp reference spectra, obtained by a pQCD-driven √s-scaling of the cross section of electrons from beauty-hadron decays measured at √s= 7 TeV. The RpPb is consistent with unity within uncertainties of about 20% at high transverse momentum pT, which increase towards low pT. The RpPb is described by pQCD calculations including initial-state effects, energy loss approaches as well as by a blast wave model calculation that parametrises possible hydrodynamic effects. The RPbPb is about 0.7 with an uncertainty of about 30% in the interval 3 < pT<6 GeV/c and 0.48 with an uncertainty of about 25% for 6< pT<8 GeV/c. The suppression seen in the higher transverse momentum interval is not described by pQCD calculations including only initial-state effects, indicating a final-state effect as the origin. The values of the RPbPb increase for pT≤3 GeV/c with uncertainties of about 30–45%. The measured RPbPb is described within uncertainties by pQCD-inspired models of beauty-quark energy loss in the QGP. In the interval 3 < pT<6 GeV/c, we observe that the suppression of the RPbPb for electrons from beauty-hadron decays is about 1.2σless than that from charmand beauty-hadron decays. This difference is consistent with the ordering of charm and beauty suppression seen in the prompt D meson and J/ψ from B meson comparison. Acknowledgments The ALICE Collaboration would like to thank all its engineers and technicians for their invaluable contributions to the construction of the experiment and the CERN accelerator teams for the outstanding performance of the LHC complex. The ALICE Collab- – 24 – JHEP07(2017)052 [82] ALICE collaboration, Neutral pion production at midrapidity in pp and Pb-Pb collisions at √sNN = 2.76 TeV,Eur. Phys. J. C 74 (2014) 3108 [arXiv:1405.3794] [INSPIRE]. 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Buitron63 , P. Buncic35 , O. Busch131 , Z. Buthelezi66 , J.B. Butt16 , J.T. Buxton19 , J. Cabala117 , D. Caffarri35 , X. Cai7, H. Caines140 , A. Caliva54 , E. Calvo Villar104 , P. Camerini25 , F. Carena35 , W. Carena35 , F. Carnesecchi12 ,27 , J. Castillo Castellanos15 , A.J. Castro128 , E.A.R. Casula24 , C. Ceballos Sanchez9, J. Cepila39 , P. Cerello112 , J. Cerkala117 , B. Chang126 , S. Chapeland35 , M. Chartier127 , J.L. Charvet15 , S. Chattopadhyay136 , S. Chattopadhyay102 , A. Chauvin96 ,36 , V. Chelnokov3, M. Cherney88 , C. Cheshkov133 , B. Cheynis133 , V. Chibante Barroso35 , D.D. Chinellato123 , S. Cho51 , P. Chochula35 , K. Choi98 , M. Chojnacki82 , S. Choudhury136 , P. Christakoglou83 , C.H. Christensen82 , P. Christiansen34 , T. Chujo131 , S.U. Chung98 , C. Cicalo107 , L. Cifarelli12 ,27 , F. Cindolo106 , J. Cleymans91 , F. Colamaria33 , D. Colella56 ,35 , A. Collu75 , M. Colocci27 , G. Conesa Balbastre72 , Z. Conesa del Valle52 , M.E. Connors140 ,ii, J.G. Contreras39 , T.M. Cormier86 , Y. Corrales Morales112 , I. Cort´es Maldonado2, P. Cortese32 , M.R. Cosentino122 ,124 , F. Costa35 , J. Crkovsk´a52 , P. Crochet71 , R. Cruz Albino11 , E. Cuautle63 , L. Cunqueiro35 ,62 , T. Dahms36 ,96 , A. Dainese109 , M.C. Danisch95 , A. Danu59 , D. Das102 , I. Das102 , S. Das4, A. Dash80 , S. Dash48 , S. De122 , A. De Caro30 , G. de Cataldo105 , C. de Conti122 , J. de Cuveland42 , A. De Falco24 , D. De Gruttola30 ,12 , N. De Marco112 , S. De Pasquale30 , R.D. De Souza123 , A. Deisting95 ,99 , A. Deloff78 , C. Deplano83 , P. Dhankher48 , D. Di Bari33 , A. Di Mauro35 , P. Di Nezza73 , B. Di Ruzza109 , M.A. Diaz Corchero10 , T. Dietel91 , P. Dillenseger61 , R. Divi`a35 , Ø. Djuvsland22 , A. Dobrin83 ,35 , D. Domenicis Gimenez122 , B. D¨onigus61 , O. Dordic21 , T. Drozhzhova61 , A.K. Dubey136 , A. Dubla99 , L. Ducroux133 , A.K. Duggal89 , P. Dupieux71 , R.J. Ehlers140 , D. Elia105 , E. Endress104 , H. Engel60 , E. Epple140 , B. Erazmus115 , F. Erhardt132 , B. Espagnon52 , M. Estienne115 , S. Esumi131 , G. Eulisse35 , J. Eum98 , D. Evans103 , S. Evdokimov113 , – 33 – JHEP07(2017)052 G. Eyyubova39 , L. Fabbietti36 ,96 , D. Fabris109 , J. Faivre72 , A. Fantoni73 , M. Fasel75 , L. Feldkamp62 , A. Feliciello112 , G. Feofilov135 , J. Ferencei85 , A. Fern´andez T´ellez2, E.G. Ferreiro17 , A. Ferretti26 , A. Festanti29 , V.J.G. Feuillard71 ,15 , J. Figiel119 , M.A.S. Figueredo122 , S. Filchagin101 , D. Finogeev53 , F.M. Fionda24 , E.M. Fiore33 , M. Floris35 , S. Foertsch66 , P. Foka99 , S. Fokin81 , E. Fragiacomo111 , A. Francescon35 , A. Francisco115 , U. Frankenfeld99 , G.G. Fronze26 , U. Fuchs35 , C. Furget72 , A. Furs53 , M. Fusco Girard30 , J.J. Gaardhøje82 , M. Gagliardi26 , A.M. Gago104 , K. Gajdosova82 , M. Gallio26 , C.D. Galvan121 , D.R. Gangadharan75 , P. Ganoti35 ,90 , C. Gao7, C. Garabatos99 , E. Garcia-Solis13 , K. Garg28 , P. Garg49 , C. Gargiulo35 , P. Gasik96 ,36 , E.F. Gauger120 , M. Germain115 , M. Gheata59 ,35 , P. Ghosh136 , S.K. Ghosh4, P. Gianotti73 , P. Giubellino35 ,112 , P. Giubilato29 , E. Gladysz-Dziadus119 , P. Gl¨assel95 , D.M. Gom´ez Coral64 , A. Gomez Ramirez60 , A.S. Gonzalez35 , V. Gonzalez10 , P. Gonz´alez-Zamora10 , S. Gorbunov42 , L. G¨orlich119 , S. Gotovac118 , V. Grabski64 , O.A. Grachov140 , L.K. Graczykowski137 , K.L. Graham103 , A. Grelli54 , C. Grigoras35 , V. Grigoriev76 , A. Grigoryan1, S. Grigoryan67 , B. Grinyov3, N. Grion111 , J.M. Gronefeld99 , J.F. Grosse-Oetringhaus35 , R. Grosso99 , L. Gruber114 , F. Guber53 , R. Guernane72 ,35 , B. Guerzoni27 , K. Gulbrandsen82 , T. Gunji130 , A. Gupta92 , R. Gupta92 , I.B. Guzman2, R. Haake62 ,35 , C. Hadjidakis52 , M. Haiduc59 , H. Hamagaki130 ,77 , G. Hamar139 , J.C. Hamon65 , J.W. Harris140 , A. Harton13 , D. Hatzifotiadou106 , S. Hayashi130 , S.T. Heckel61 , E. Hellb¨ar61 , H. Helstrup37 , A. Herghelegiu79 , G. Herrera Corral11 , F. Herrmann62 , B.A. Hess94 , K.F. Hetland37 , H. Hillemanns35 , B. Hippolyte65 , D. Horak39 , R. Hosokawa131 , P. Hristov35 , C. Hughes128 , T.J. Humanic19 , N. Hussain44 , T. Hussain18 , D. Hutter42 , D.S. Hwang20 , R. Ilkaev101 , M. Inaba131 , E. Incani24 , M. Ippolitov81 ,76 , M. Irfan18 , V. Isakov53 , M. Ivanov35 ,99 , V. Ivanov87 , V. Izucheev113 , B. Jacak75 , N. Jacazio27 , P.M. Jacobs75 , M.B. Jadhav48 , S. Jadlovska117 , J. Jadlovsky56 ,117 , C. Jahnke122 ,36 , M.J. Jakubowska137 , M.A. Janik137 , P.H.S.Y. Jayarathna125 , C. Jena80 , S. Jena125 , R.T. Jimenez Bustamante99 , P.G. Jones103 , H. Jung43 , A. Jusko103 , P. Kalinak56 , A. Kalweit35 , J.H. Kang141 , V. Kaplin76 , S. Kar136 , A. Karasu Uysal70 , O. Karavichev53 , T. Karavicheva53 , L. Karayan99 ,95 , E. Karpechev53 , U. Kebschull60 , R. Keidel142 , D.L.D. Keijdener54 , M. Keil35 , M. Mohisin Khan18 ,iii, P. Khan102 , S.A. Khan136 , A. Khanzadeev87 , Y. Kharlov113 , A. Khatun18 , A. Khuntia49 , B. Kileng37 , D.W. Kim43 , D.J. Kim126 , D. Kim141 , H. Kim141 , J.S. Kim43 , J. Kim95 , M. Kim51 , M. Kim141 , S. Kim20 , T. Kim141 , S. Kirsch42 , I. Kisel42 , S. Kiselev55 , A. Kisiel137 ,35 , G. Kiss139 , J.L. Klay6, C. Klein61 , J. Klein35 , C. Klein-B¨osing62 , S. Klewin95 , A. Kluge35 , M.L. Knichel95 , A.G. Knospe120 ,125 , C. Kobdaj116 , M. Kofarago35 , T. Kollegger99 , A. Kolojvari135 , V. Kondratiev135 , N. Kondratyeva76 , E. Kondratyuk113 , A. Konevskikh53 , M. Kopcik117 , M. Kour92 , C. Kouzinopoulos35 , O. Kovalenko78 , V. Kovalenko135 , M. Kowalski119 , G. Koyithatta Meethaleveedu48 , I. Kr´alik56 , A. Kravˇc´akov´a40 , M. Krivda103 ,56 , F. Krizek85 , E. Kryshen87 ,35 , M. Krzewicki42 , A.M. Kubera19 , V. Kuˇcera85 , C. Kuhn65 , P.G. Kuijer83 , A. Kumar92 , J. Kumar48 , L. Kumar89 , S. Kumar48 , S. Kundu80 , P. Kurashvili78 , A. Kurepin53 , A.B. Kurepin53 , A. Kuryakin101 , M.J. Kweon51 , Y. Kwon141 , S.L. La Pointe42 , P. La Rocca28 , C. Lagana Fernandes122 , I. Lakomov35 , R. Langoy41 , K. Lapidus36 ,140 , C. Lara60 , A. Lardeux15 , A. Lattuca26 , E. Laudi35 , L. Lazaridis35 , R. Lea25 , L. Leardini95 , S. Lee141 , F. Lehas83 , S. Lehner114 , J. Lehrbach42 , R.C. Lemmon84 , V. Lenti105 , E. Leogrande54 , I. Le´on Monz´on121 , H. Le´on Vargas64 , M. Leoncino26 , P. L´evai139 , S. Li7, X. Li14 , J. Lien41 , R. Lietava103 , S. Lindal21 , V. Lindenstruth42 , C. Lippmann99 , M.A. Lisa19 , H.M. Ljunggren34 , D.F. Lodato54 , P.I. Loenne22 , V. Loginov76 , C. Loizides75 , X. Lopez71 , E. L´opez Torres9, A. Lowe139 , P. Luettig61 , M. Lunardon29 , G. Luparello25 , M. Lupi35 , T.H. Lutz140 , A. Maevskaya53 , M. Mager35 , S. Mahajan92 , S.M. Mahmood21 , A. Maire65 , – 34 – JHEP07(2017)052 R.D. Majka140 , M. Malaev87 , I. Maldonado Cervantes63 , L. Malinina67 ,iv, D. Mal’Kevich55 , P. Malzacher99 , A. Mamonov101 , V. Manko81 , F. Manso71 , V. Manzari105 , Y. Mao7, M. Marchisone129 ,66 , J. Mareˇs57 , G.V. Margagliotti25 , A. Margotti106 , J. Margutti54 , A. Mar´ın99 , C. Markert120 , M. Marquard61 , N.A. Martin99 , P. Martinengo35 , M.I. Mart´ınez2, G. Mart´ınez Garc´ıa115 , M. Martinez Pedreira35 , A. Mas122 , S. Masciocchi99 , M. Masera26 , A. Masoni107 , A. Mastroserio33 , A. Matyja119 ,128 , C. Mayer119 , J. Mazer128 , M. Mazzilli33 , M.A. Mazzoni110 , F. Meddi23 , Y. Melikyan76 , A. Menchaca-Rocha64 , E. Meninno30 , J. Mercado P´erez95 , M. Meres38 , S. Mhlanga91 , Y. Miake131 , M.M. Mieskolainen46 , K. Mikhaylov55 ,67 , J. Milosevic21 , A. Mischke54 , A.N. Mishra49 , T. Mishra58 , D. Mi´skowiec99 , J. Mitra136 , C.M. Mitu59 , N. Mohammadi54 , B. Mohanty80 , L. Molnar65 , E. Montes10 , D.A. Moreira De Godoy62 , L.A.P. Moreno2, S. Moretto29 , A. Morreale115 , A. Morsch35 , V. Muccifora73 , E. Mudnic118 , D. M¨uhlheim62 , S. Muhuri136 , M. Mukherjee136 , J.D. Mulligan140 , M.G. Munhoz122 , K. M¨unning45 , R.H. Munzer61 ,96 ,36 , H. Murakami130 , S. Murray66 , L. Musa35 , J. Musinsky56 , B. Naik48 , R. Nair78 , B.K. Nandi48 , R. Nania106 , E. Nappi105 , M.U. Naru16 , H. Natal da Luz122 , C. 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Pereira Da Costa15 , D. Peresunko76 ,81 , E. Perez Lezama61 , V. Peskov61 , Y. Pestov5, V. Petr´aˇcek39 , V. Petrov113 , M. Petrovici79 , C. Petta28 , S. Piano111 , M. Pikna38 , P. Pillot115 , L.O.D.L. Pimentel82 , O. Pinazza35 ,106 , L. Pinsky125 , D.B. Piyarathna125 , M. P losko´n75 , M. Planinic132 , J. Pluta137 , S. Pochybova139 , P.L.M. Podesta-Lerma121 , M.G. Poghosyan86 , B. Polichtchouk113 , N. Poljak132 , W. Poonsawat116 , A. Pop79 , H. Poppenborg62 , S. Porteboeuf-Houssais71 , J. Porter75 , J. Pospisil85 , S.K. Prasad4, R. Preghenella106 ,35 , F. Prino112 , C.A. Pruneau138 , I. Pshenichnov53 , M. Puccio26 , G. Puddu24 , P. Pujahari138 , V. Punin101 , J. Putschke138 , H. Qvigstad21 , A. Rachevski111 , S. Raha4, S. Rajput92 , J. Rak126 , A. Rakotozafindrabe15 , L. Ramello32 , F. Rami65 , R. Raniwala93 , S. Raniwala93 , S.S. R¨as¨anen46 , B.T. Rascanu61 , D. Rathee89 , V. Ratza45 , I. Ravasenga26 , K.F. Read86 ,128 , K. Redlich78 , A. Rehman22 , P. Reichelt61 , F. 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Schweda99 , G. Scioli27 , E. Scomparin112 , R. Scott128 , M. ˇ Sefˇc´ık40 , J.E. Seger88 , Y. Sekiguchi130 , – 35 – JHEP07(2017)052 D. Sekihata47 , I. Selyuzhenkov99 , K. Senosi66 , S. Senyukov35 ,3, E. Serradilla10 ,64 , A. Sevcenco59 , A. Shabanov53 , A. Shabetai115 , O. Shadura3, R. Shahoyan35 , A. Shangaraev113 , A. Sharma92 , A. Sharma89 , M. Sharma92 , M. Sharma92 , N. Sharma128 , A.I. Sheikh136 , K. Shigaki47 , Q. Shou7, K. Shtejer26 ,9, Y. Sibiriak81 , S. Siddhanta107 , K.M. Sielewicz35 , T. Siemiarczuk78 , D. Silvermyr34 , C. Silvestre72 , G. Simatovic132 , G. Simonetti35 , R. Singaraju136 , R. Singh80 , V. Singhal136 , T. Sinha102 , B. Sitar38 , M. Sitta32 , T.B. Skaali21 , M. Slupecki126 , N. Smirnov140 , R.J.M. Snellings54 , T.W. Snellman126 , J. Song98 , M. Song141 , Z. Song7, F. Soramel29 , S. Sorensen128 , F. Sozzi99 , E. Spiriti73 , I. Sputowska119 , M. Spyropoulou-Stassinaki90 , J. Stachel95 , I. Stan59 , P. Stankus86 , E. Stenlund34 , G. Steyn66 , J.H. Stiller95 , D. 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V´azquez Doce96 ,36 , V. Vechernin135 , A.M. Veen54 , A. Velure22 , E. Vercellin26 , S. Vergara Lim´on2, R. Vernet8, R. V´ertesi139 , L. Vickovic118 , S. Vigolo54 , J. Viinikainen126 , Z. Vilakazi129 , O. Villalobos Baillie103 , A. Villatoro Tello2, A. Vinogradov81 , L. Vinogradov135 , T. Virgili30 , V. Vislavicius34 , A. Vodopyanov67 , M.A. V¨olkl95 , K. Voloshin55 , S.A. Voloshin138 , G. Volpe139 ,33 , B. von Haller35 , I. Vorobyev36 ,96 , D. Voscek117 , D. Vranic35 ,99 , J. Vrl´akov´a40 , B. Vulpescu71 , B. Wagner22 , J. Wagner99 , H. Wang54 , M. Wang7, D. Watanabe131 , Y. Watanabe130 , M. Weber114 , S.G. Weber99 , D.F. Weiser95 , J.P. Wessels62 , U. Westerhoff62 , A.M. Whitehead91 , J. Wiechula61 ,94 , J. Wikne21 , G. Wilk78 , J. Wilkinson95 , G.A. Willems62 , M.C.S. Williams106 , B. Windelband95 , M. Winn95 , S. Yalcin70 , P. Yang7, S. Yano47 , Z. Yin7, H. Yokoyama131 ,72 , I.-K. Yoo35 ,98 , J.H. Yoon51 , V. Yurchenko3, V. Zaccolo82 , A. Zaman16 , C. Zampolli35 ,106 , H.J.C. Zanoli122 , S. Zaporozhets67 , N. Zardoshti103 , A. Zarochentsev135 , P. Z´avada57 , N. Zaviyalov101 , H. Zbroszczyk137 , I.S. Zgura59 , M. Zhalov87 , H. Zhang22 ,7, X. Zhang7,75 , Y. Zhang7, C. Zhang54 , Z. Zhang7, C. Zhao21 , N. Zhigareva55 , D. Zhou7, Y. Zhou82 , Z. Zhou22 , H. Zhu22 ,7, J. Zhu115 ,7, A. Zichichi27 ,12 , A. Zimmermann95 , M.B. Zimmermann62 ,35 , G. Zinovjev3, J. Zmeskal114 iDeceased ii Also at: Georgia State University, Atlanta, Georgia, United States iii Also at: Also at Department of Applied Physics, Aligarh Muslim University, Aligarh, India iv Also at: M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute of Nuclear, Physics, Moscow, Russia 1A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, Yerevan, Armenia 2Benem´erita Universidad Aut´onoma de Puebla, Puebla, Mexico 3Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine 4Bose Institute, Department of Physics and Centre for Astroparticle Physics and Space Science (CAPSS), Kolkata, India 5Budker Institute for Nuclear Physics, Novosibirsk, Russia – 36 – JHEP07(2017)052 6California Polytechnic State University, San Luis Obispo, California, United States 7Central China Normal University, Wuhan, China 8Centre de Calcul de l’IN2P3, Villeurbanne, Lyon, France 9Centro de Aplicaciones Tecnol´ogicas y Desarrollo Nuclear (CEADEN), Havana, Cuba 10 Centro de Investigaciones Energ´eticas Medioambientales y Tecnol´ogicas (CIEMAT), Madrid, Spain 11 Centro de Investigaci´on y de Estudios Avanzados (CINVESTAV), Mexico City and M´erida, Mexico 12 Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi’, Rome, Italy 13 Chicago State University, Chicago, Illinois, United States 14 China Institute of Atomic Energy, Beijing, China 15 Commissariat `a l’Energie Atomique, IRFU, Saclay, France 16 COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan 17 Departamento de F´ısica de Part´ıculas and IGFAE, Universidad de Santiago de Compostela, Santiago de Compostela, Spain 18 Department of Physics, Aligarh Muslim University, Aligarh, India 19 Department of Physics, Ohio State University, Columbus, Ohio, United States 20 Department of Physics, Sejong University, Seoul, South Korea 21 Department of Physics, University of Oslo, Oslo, Norway 22 Department of Physics and Technology, University of Bergen, Bergen, Norway 23 Dipartimento di Fisica dell’Universit`a ’La Sapienza’ and Sezione INFN, Rome, Italy 24 Dipartimento di Fisica dell’Universit`a and Sezione INFN, Cagliari, Italy 25 Dipartimento di Fisica dell’Universit`a and Sezione INFN, Trieste, Italy 26 Dipartimento di Fisica dell’Universit`a and Sezione INFN, Turin, Italy 27 Dipartimento di Fisica e Astronomia dell’Universit`a and Sezione INFN, Bologna, Italy 28 Dipartimento di Fisica e Astronomia dell’Universit`a and Sezione INFN, Catania, Italy 29 Dipartimento di Fisica e Astronomia dell’Universit`a and Sezione INFN, Padova, Italy 30 Dipartimento di Fisica ‘E.R. Caianiello’ dell’Universit`a and Gruppo Collegato INFN, Salerno, Italy 31 Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy 32 Dipartimento di Scienze e Innovazione Tecnologica dell’Universit`a del Piemonte Orientale and INFN Sezione di Torino, Alessandria, Italy 33 Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy 34 Division of Experimental High Energy Physics, University of Lund, Lund, Sweden 35 European Organization for Nuclear Research (CERN), Geneva, Switzerland 36 Excellence Cluster Universe, Technische Universit¨at M¨unchen, Munich, Germany 37 Faculty of Engineering, Bergen University College, Bergen, Norway 38 Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia 39 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic 40 Faculty of Science, P.J. ˇ Saf´arik University, Koˇsice, Slovakia 41 Faculty of Technology, Buskerud and Vestfold University College, Tonsberg, Norway 42 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universit¨at Frankfurt, Frankfurt, Germany 43 Gangneung-Wonju National University, Gangneung, South Korea 44 Gauhati University, Department of Physics, Guwahati, India 45 Helmholtz-Institut f¨ur Strahlenund Kernphysik, Rheinische Friedrich-Wilhelms-Universit¨at Bonn, Bonn, Germany 46 Helsinki Institute of Physics (HIP), Helsinki, Finland 47 Hiroshima University, Hiroshima, Japan 48 Indian Institute of Technology Bombay (IIT), Mumbai, India 49 Indian Institute of Technology Indore, Indore, India 50 Indonesian Institute of Sciences, Jakarta, Indonesia 51 Inha University, Incheon, South Korea 52 Institut de Physique Nucl´eaire d’Orsay (IPNO), Universit´e Paris-Sud, CNRS-IN2P3, Orsay, France – 37 – JHEP07(2017)052 53 Institute for Nuclear Research, Academy of Sciences, Moscow, Russia 54 Institute for Subatomic Physics of Utrecht University, Utrecht, Netherlands 55 Institute for Theoretical and Experimental Physics, Moscow, Russia 56 Institute of Experimental Physics, Slovak Academy of Sciences, Koˇsice, Slovakia 57 Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic 58 Institute of Physics, Bhubaneswar, India 59 Institute of Space Science (ISS), Bucharest, Romania 60 Institut f¨ur Informatik, Johann Wolfgang Goethe-Universit¨at Frankfurt, Frankfurt, Germany 61 Institut f¨ur Kernphysik, Johann Wolfgang Goethe-Universit¨at Frankfurt, Frankfurt, Germany 62 Institut f¨ur Kernphysik, Westf¨alische Wilhelms-Universit¨at M¨unster, M¨unster, Germany 63 Instituto de Ciencias Nucleares, Universidad Nacional Aut´onoma de M´exico, Mexico City, Mexico 64 Instituto de F´ısica, Universidad Nacional Aut´onoma de M´exico, Mexico City, Mexico 65 Institut Pluridisciplinaire Hubert Curien (IPHC), Universit´e de Strasbourg, CNRS-IN2P3, Strasbourg, France 66 iThemba LABS, National Research Foundation, Somerset West, South Africa 67 Joint Institute for Nuclear Research (JINR), Dubna, Russia 68 Konkuk University, Seoul, South Korea 69 Korea Institute of Science and Technology Information, Daejeon, South Korea 70 KTO Karatay University, Konya, Turkey 71 Laboratoire de Physique Corpusculaire (LPC), Clermont Universit´e, Universit´e Blaise Pascal, CNRS–IN2P3, Clermont-Ferrand, France 72 Laboratoire de Physique Subatomique et de Cosmologie, Universit´e Grenoble-Alpes, CNRS-IN2P3, Grenoble, France 73 Laboratori Nazionali di Frascati, INFN, Frascati, Italy 74 Laboratori Nazionali di Legnaro, INFN, Legnaro, Italy 75 Lawrence Berkeley National Laboratory, Berkeley, California, United States 76 Moscow Engineering Physics Institute, Moscow, Russia 77 Nagasaki Institute of Applied Science, Nagasaki, Japan 78 National Centre for Nuclear Studies, Warsaw, Poland 79 National Institute for Physics and Nuclear Engineering, Bucharest, Romania 80 National Institute of Science Education and Research, Bhubaneswar, India 81 National Research Centre Kurchatov Institute, Moscow, Russia 82 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark 83 Nikhef, Nationaal instituut voor subatomaire fysica, Amsterdam, Netherlands 84 Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom 85 Nuclear Physics Institute, Academy of Sciences of the Czech Republic, ˇ Reˇz u Prahy, Czech Republic 86 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States 87 Petersburg Nuclear Physics Institute, Gatchina, Russia 88 Physics Department, Creighton University, Omaha, Nebraska, United States 89 Physics Department, Panjab University, Chandigarh, India 90 Physics Department, University of Athens, Athens, Greece 91 Physics Department, University of Cape Town, Cape Town, South Africa 92 Physics Department, University of Jammu, Jammu, India 93 Physics Department, University of Rajasthan, Jaipur, India 94 Physikalisches Institut, Eberhard Karls Universit¨at T¨ubingen, T¨ubingen, Germany 95 Physikalisches Institut, Ruprecht-Karls-Universit¨at Heidelberg, Heidelberg, Germany 96 Physik Department, Technische Universit¨at M¨unchen, Munich, Germany 97 Purdue University, West Lafayette, Indiana, United States 98 Pusan National University, Pusan, South Korea 99 Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum f¨ur Schwerionenforschung, Darmstadt, Germany 100 Rudjer Boˇskovi´c Institute, Zagreb, Croatia – 38 – JHEP07(2017)052 101 Russian Federal Nuclear Center (VNIIEF), Sarov, Russia 102 Saha Institute of Nuclear Physics, Kolkata, India 103 School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom 104 Secci´on F´ısica, Departamento de Ciencias, Pontificia Universidad Cat´olica del Per´u, Lima, Peru 105 Sezione INFN, Bari, Italy 106 Sezione INFN, Bologna, Italy 107 Sezione INFN, Cagliari, Italy 108 Sezione INFN, Catania, Italy 109 Sezione INFN, Padova, Italy 110 Sezione INFN, Rome, Italy 111 Sezione INFN, Trieste, Italy 112 Sezione INFN, Turin, Italy 113 SSC IHEP of NRC Kurchatov institute, Protvino, Russia 114 Stefan Meyer Institut f¨ur Subatomare Physik (SMI), Vienna, Austria 115 SUBATECH, Ecole des Mines de Nantes, Universit´e de Nantes, CNRS-IN2P3, Nantes, France 116 Suranaree University of Technology, Nakhon Ratchasima, Thailand 117 Technical University of Koˇsice, Koˇsice, Slovakia 118 Technical University of Split FESB, Split, Croatia 119 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland 120 The University of Texas at Austin, Physics Department, Austin, Texas, United States 121 Universidad Aut´onoma de Sinaloa, Culiac´an, Mexico 122 Universidade de S˜ao Paulo (USP), S˜ao Paulo, Brazil 123 Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil 124 Universidade Federal do ABC, Santo Andre, Brazil 125 University of Houston, Houston, Texas, United States 126 University of Jyv¨askyl¨a, Jyv¨askyl¨a, Finland 127 University of Liverpool, Liverpool, United Kingdom 128 University of Tennessee, Knoxville, Tennessee, United States 129 University of the Witwatersrand, Johannesburg, South Africa 130 University of Tokyo, Tokyo, Japan 131 University of Tsukuba, Tsukuba, Japan 132 University of Zagreb, Zagreb, Croatia 133 Universit´e de Lyon, Universit´e Lyon 1, CNRS/IN2P3, IPN-Lyon, Villeurbanne, Lyon, France 134 Universit`a di Brescia, Brescia, Italy 135 V. Fock Institute for Physics, St. Petersburg State University, St. Petersburg, Russia 136 Variable Energy Cyclotron Centre, Kolkata, India 137 Warsaw University of Technology, Warsaw, Poland 138 Wayne State University, Detroit, Michigan, United States 139 Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary 140 Yale University, New Haven, Connecticut, United States 141 Yonsei University, Seoul, South Korea 142 Zentrum f¨ur Technologietransfer und Telekommunikation (ZTT), Fachhochschule Worms, Worms, Germany – 39 –