First measurement of Ξ 0c production in pp collisions at √s=7 TeV

Physics Letters B 781 (2018) 8–19 Contents lists available at ScienceDirect Physics Letters B www.elsevier.com/locate/physletb First measurement of 0 cproduction in pp collisions at √s=7TeV .ALICE Collaboration a r t i c l e i n f o a b s t r a c t Article history: Received 15 December 2017 Received in revised form 5 March 2018 Accepted 21 March 2018 Available online 27 March 2018 Editor: L. Rolandi The production of the charm-strange baryon 0 cis measured for the first time at the LHC via its semileptonic decay into e+−νein pp collisions at √s=7TeV with the ALICE detector. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 1 <pT<8GeV/cat mid-rapidity, |y| <0.5. The transverse momentum dependence of the 0 cbaryon production relative to the D0meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured crosssection ratio. ©2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3. Quantum Chromodynamics (QCD) as the theory of the strong interaction has been a cornerstone of the Standard Model for several decades. It has been tested through measurements in e+e−, pp, pp and ep collisions at momentum-transfer scales where perturbative techniques are applicable [1]. In particular, measurements of charm hadrons have provided important tests of the theory because perturbative techniques are applicable down to low transverse momentum (pT) thanks to the large mass of the charm quark compared to the QCD scale parameter (QCD ∼200 MeV). The production cross sections of charm hadrons can be calculated using the factorisation approach as a convolution of three factors [2]: the parton distribution functions of the incoming protons, the hard-scattering cross section at partonic level and the fragmentation functions of charm quarks into charm hadrons. There are several state-of-the-art calculations adopting different factorisation schemes. The collinear factorisation scheme is used by calculations at next-to-leading order in αs, such as the general-mass variable flavour number scheme (gm-vfns)[3–5] and the fixed order with next-to-leading-log resummation (fonll)[6,7] approaches, while the kTfactorisation scheme is employed at leading order in Refs. [8–10]. However, some of these calculations do not provide predictions for heavy-baryon production due to the lack of knowledge about the fragmentation function of charm quarks into baryonic states. Measurements of the production of charm baryons, such as + cand 0 c, are essential to develop and test models of the hadronisation process. While a variety of new charm-baryon resonances, such as 0 c[11], ++ cc [12], have recently been found, charm-hadron crosssection measurements at the Large Hadron Collider (LHC) are mainly limited to mesons [13–21], apart from a few measure- E-mail address: alice -publications @cern .ch. ments of the + ccross section in pp and p–Pb collisions [16, 22]. In the case of 0 c, the existing measurements are currently limited to e+e−collisions [23–27]. New measurements of charmbaryon production are therefore needed to provide further insights into the hadronisation processes in pp collisions. For example, interactions at the partonic level among the produced quarks and gluons, such as colour reconnection, could be stronger in pp collisions than in e+e−collisions, resulting in an enhanced production of baryons relative to mesons [28]. The measurements of charmbaryon production in pp collisions also serve as a reference for heavy-ion collisions, where a modification of the baryon-to-meson ratio is expected if a substantial fraction of charm quarks hadronises via recombination with other quarks from the deconfined medium created in the collision [29–33]. Measurements of charmstrange baryons, e.g. 0 c, could also provide additional input to better understand the hadronisation mechanism of strange quarks in pp collisions because of their valence quark composition. In this paper, we report the first measurement of the pT-differential production cross section of 0 cmultiplied by the branching ratio (BR) into the semileptonic decay mode, 0 c→e+−νe, and its ratio to the measured production cross section of D0 mesons [21]as a function of pT, up to 8GeV/c. The absolute branching ratio of this 0 cdecay is currently unknown [34]. Using a data sample of pp collisions at √s=7TeV recorded with the ALICE detector in 2010, the measurement is performed by analysing e+−pairs formed by combining positrons and −baryons reconstructed with the detectors of the ALICE central barrel, covering the pseudorapidity interval |η| <0.9. The missing momentum of the neutrino is corrected using unfolding techniques. Charge conjugate modes are implied everywhere, unless otherwise stated. Only the sub-detectors relevant for this data analysis are described below. A more complete and detailed description of the ALICE detector and its performance can be found in Refs. [35,36]. https://doi.org/10.1016/j.physletb.2018.03.061 0370-2693/©2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3. ALICE Collaboration / Physics Letters B 781 (2018) 8–19 9 The detectors used in this analysis include the Inner Tracking System (ITS), the Time Projection Chamber (TPC) and the TimeOf-Flight detector (TOF). These detectors are located in a large solenoid magnet producing a magnetic field of 0.5 T parallel to the LHC beam axis. The ITS consists of six cylindrical layers of silicon detectors, placed at radial distances ranging from 3.9 cm to 43 cm from the nominal beam axis and covering the full azimuth. The two innermost layers consist of Silicon Pixel Detectors (SPD), the two intermediate layers of Silicon Drift Detectors (SDD) and the two outermost layers of Silicon Strip Detectors (SSD). The total material budget of the ITS is on average 7.7% of a radiation length, for particles with η=0[37]. The ITS spatial resolution enables the measurement of the distance of closest approach (d0) of tracks to the primary vertex with a resolution better than 75 μm in the transverse plane for pT>1GeV/cin pp collisions [38]. The TPC is a cylindrical gaseous detector with a volume of about 90 m3. The TPC provides track reconstruction with up to 159 space points at radial distances from the beam axis ranging between 85 cm and 247 cm, within the full azimuth. The TPC cluster-position resolution is about 500 μm along the beam direction and in the transverse direction for tracks with η=0[39]. The TPC also provides particle identification capabilities via the measurement of the specific ionisation energy loss, dE/dx, with a resolution of approximately 5.2% in pp collisions [36]. The TOF detector consists of multi-gap resistive plate chambers placed at a radial distance of 3.7 m from the beam axis and also covers the full azimuth. The TOF detector, with a timing resolution of about 80 ps, measures the time-of-flight of particles relative to the time of the collision, which is determined by the arrival time of the particles at the TOF detector and by the T0 detector, an array of Cherenkov counters placed at +370 cm and −70 cm from the nominal interaction point along the beam axis [40]. The analysed data sample consists of pp collisions at √s= 7TeV recorded during the 2010 LHC data taking period with a minimum bias trigger that requires at least one hit in either the SPD or the V0 detectors. The two layers of the SPD detector cover |η| <2.0. The two V0 detectors, each comprising 32 scintillator tiles, are installed on both sides of the interaction point and cover −3.7 <η<−1.7 and 2.8 <η<5.1. The trigger condition captures 87% of the pp inelastic cross section [41]. The collision vertex is reconstructed with an efficiency of 88% and only events with a reconstructed vertex within 10 cm from the nominal interaction point along the beam direction are used in this analysis. Pile-up events are identified by searching for a second interaction vertex, reconstructed with at least three SPD tracklets (that are two-point track segments connecting hits in the two SPD layers) pointing to a common vertex, which is separated from the first vertex by at least 8 mm. After the selections, the analysed sample corresponds to an integrated luminosity Lint =5.9 ±0.2nb −1. The 0 ccandidates are defined from e+−pairs by combining a track originating from the primary vertex (denoted by “electron track” in the following) and a reconstructed −baryon. Electron tracks satisfying |η| <0.8 and pT>0.5 GeV/care required to have at least 100 associated clusters in the TPC (out of which at least 80 are used for the calculation of the dE/dxsignal), a χ2normalised to the number of TPC clusters smaller than 4 and at least 4 hits in the ITS. It is also required that the electron track has associated hits in the two innermost layers of the ITS, in order to reject electrons from photon conversions occurring in the detector material outside the innermost SPD layer [13]. Electrons are identified using the dE/dxmeasurement in the TPC and the time-of-flight measurement of the TOF detector. In both cases, the selection is applied on the nTPC σand nTOF σvariables defined as the difference between the measured dE/dxor time-of-flight values and the one expected for electrons, divided by the corresponding detector resFig. 1. Invariant-mass distribution of −→π−(and charge conjugate) candidates integrated over pT. The arrow indicates the world average −mass from Ref. [34] and the dashed lines indicate the selected interval for the −candidates. olution. The following selection criteria are applied: |nTOF σ| <3 and −3.9 +1.2pT−0.094p2 T<nTPC σ(pT) <3. The pT-dependent lower limit on nTPC σwas optimised to reject hadrons. Thus, an electron purity of 98% is achieved over the whole pTrange. The background from “photonic” electrons (originating from Dalitz decays of neutral mesons and photon conversions in the detector material) remaining in the electron sample are identified using a technique based on the invariant mass of e+e−pairs [42]. The electron tracks are paired with opposite-sign tracks from the same event passing loose selection criteria (|nTPC σ| <5without TOF requirement) and are identified as photonic electrons if there is at least one pair with an invariant mass smaller than 50 MeV/c2. Setting such loose electron identification criteria is meant to increase the efficiency of finding the partners. This improves the signal-tobackground ratio for 0 cby about 50%, while the fraction of the signal lost due to misidentifications is less than 2%. The −baryons are reconstructed from the decay chain −→ π−, followed by  →pπ−. Tracks used to define −candidates are required to have at least 80 clusters in the TPC and a dE/dx signal in the TPC consistent with the expected values for protons (pions) within 4σ. The −and baryons have long lifetimes (cτ of about 4.91 cm and 7.89 cm, respectively [34]), and thus they can be identified using their characteristic cascade-like or V-shaped decay topologies [43–45]. Pions originating directly from −decays are selected by requiring d0>0.02 cm; protons and pions originating from decays are required to have d0>0.07 cm. The d0of the trajectory to the primary vertex is required to be larger than 0.03 cm, while its cosine of the pointing angle, which is the angle between the reconstructed momentum and the line connecting the and −decay vertices, is required to be larger than 0.98. The distances of the −and decay vertices from the beam line are required to be larger than 0.4 and 2.7 cm, respectively. These selection criteria are tuned to reduce the background, while keeping a high efficiency for the signal. Fig. 1shows the −peak in the π−invariant-mass distribution integrated over pT. Only −candidates with invariant masses within 8MeV/c2from the −mass (1321.71 ±0.07 MeV/c2[34]) indicated by an arrow in Fig. 1are kept for further analysis. In this interval, the signal-to-background ratio is about 8. The e+−pairs are formed from selected positrons and − candidates. Only pairs with an opening angle smaller than 90 degrees are used for the analysis. The background in the e+−pair distribution is estimated by exploiting the fact that 0 cbaryons decay into e+−νe(right-sign, RS), but not into e−−νe(wrongsign, WS), while most of the background sources contribute equally to RS and WS pairs. The yield of WS pairs is therefore used to estimate the background and is subtracted from the yield of RS pairs to obtain the 0 craw yield. The procedure is verified with 10 ALICE Collaboration / Physics Letters B 781 (2018) 8–19 Fig. 2. (a) Invariant-mass distributions of right-sign and wrong-sign (and charge conjugate) pairs integrated over the whole pTinterval. (b) Invariant-mass distribution of 0 c candidates obtained by subtracting the wrong-sign pair yield from the right-sign one compared with the signal distribution from the simulation, which is normalised to the measured RS−WS yield. The arrow indicates the 0 cmass [34]. pythia 6.4.21 [46] simulations using the Perugia-0 tune [47]and the geant3 transport code [48], including a realistic description of the detector response and alignment during the data taking period. A similar procedure was adopted by the ARGUS and CLEO collaborations studying e+e−collisions [24,25]. Fig. 2(a) shows the invariant-mass distributions of RS and WS pairs, integrated over the whole pTinterval. The invariant-mass distribution of 0 ccandidates obtained by subtracting the WS pair yield from the RS one is shown in Fig. 2(b) together with the signal distribution from the simulation, which is normalised to the measured RS−WS yield. The shapes of the two distributions are found to be consistent with each other. Due to the missing momentum of the neutrino, the invariant-mass distribution of the e+−pair does not peak at the 0 cmass (2470.85+0.28 −0.40 MeV/c2[34]) indicated by an arrow in Fig. 2(b). The invariant mass of e+−pairs from 0 cdecays is bounded by the 0 cmass due to the missing momentum of the neutrino. Thus only e+−pairs satisfying me<2.5GeV/c2are selected for further analysis. In order to obtain the pT-differential production cross section of 0 cbaryons, the background-subtracted (WS-subtracted) yield needs to be corrected for: the signal loss due to misidentification of photonic electrons, the bcontribution in the WS pairs, the missing neutrino momentum, the detector acceptance and the track-reconstruction and the candidate-selection efficiencies. No correction is applied for possible differences in the acceptance of RS and WS pairs, which are found to be negligible for the current analysis based on a study with the mixed-event technique (i.e. by pairing electrons and −from different events). The first correction accounts for the signal loss caused by the misidentification of photonic electrons. The misidentification occurs when electrons from 0 cdecays accidentally have oppositesign partners giving rise to a very small invariant mass of the e+e− pair. The misidentification probability is estimated to be less than 2% by applying the tagging algorithm to e+e+and e−e−pairs. The correction is applied as a function of the pTof the e+− pair. The second correction accounts for the overestimation of the background caused by b→e−−νeXdecays, which produce WS pairs. Since the branching ratio of binto e−−νeXand the b cross section in pp collisions at LHC energies have not been measured yet, two assumptions are made to estimate this contribution. First, the shape of the transverse momentum distribution of the b baryon is assumed to be the same as that of 0 b, which was measured for pT>10 GeV/cand |y| <2by the CMS collaboration [49]. This measurement is extrapolated to pT=0using the Tsallis function, Fig. 3. Correlation between the generated 0 c-baryon pTand the reconstructed e+−pair pT, obtained from the simulation based on pythia 6 described in the text. (For interpretation of the colours in the figure(s), the reader is referred to the web version of this article.) CpT ⎡ ⎢ ⎣1+p2 T+m2−m nT ⎤ ⎥ ⎦(1) whose parameters were also determined by the CMS collaboration by fitting the measured distribution. The fit parameters are consistent with those determined by the LHCb collaboration for the measurement of 0 bdown to pT=0at forward rapidity (2 <y <4.5) [50]. The second hypothesis is made for the total yield of b→e−−νeX, which is determined by using the measurements of BR(b →b) ·BR(b→−l−νX)[51]and BR(b → 0 b) ·BR(0 b→l−νX)[52]in e+e−collisions and by assuming that the fraction of beauty quarks that hadronise into 0 band b baryons are the same as those in e+e−collisions. This assumption is supported by B-meson measurements, which show that the yield of B0 smesons relative to non-strange B mesons is consistent in e+e−and pp collisions [53]. The bdistribution obtained with these assumptions is further processed to take into account the detector acceptance, efficiency and the momentum carried by non-reconstructed decay particles. This is done with the pythia 6 simulation using geant3 for particle transport through the detector. The correction increases with pTand reaches 2% at the highest pTinterval. The transverse momentum distribution of e+−pairs is corrected for the missing momentum of the neutrino using unfolding techniques. The response matrix to correct for the missing neutrino momentum is generated based on the correlation between the pT of the 0 cbaryon and that of the reconstructed e+−pair, which is obtained from the simulation described above and is shown in Fig. 3. The response matrix includes both the decay kinematics and ALICE Collaboration / Physics Letters B 781 (2018) 8–19 11 Table 1 Summary of systematic uncertainties on the pT-differential cross section of 0 c→e+−νefor 5 pTintervals. The uncertainty on the missing neutrino momentum is denoted as pν Tin the table. Source Relative systematic uncertainty (%) in the measured pTintervals (GeV/c) 1–2 2–3.2 3.2–4.4 4.4–6 6–8 Raw yield 55555 (A×ε)30 22 16 13 14 pν T29 86710 Normalisation 3.5 the instrumental effects, such as energy loss and bremsstrahlung in the detector material. The response matrix needs to be determined using a realistic 0 c-baryon pTdistribution. However, the distribution is not known a priori. Therefore, the response matrix is prepared in two steps. In the first step, the response matrix is obtained with the pTdistribution generated with pythia 6. The resulting 0 cmomentum distribution is used to produce the response matrix for the second iteration. The unfolding is performed with the RooUnfold [54] implementation of the Bayesian unfolding technique [55], which is an iterative method based on Bayes’ theorem. Convergence of the Bayesian method is achieved after three iterations. The pT-differential production cross section of 0 cbaryons multiplied by the branching ratio into the considered semileptonic decay channel is calculated from the yields obtained by the unfolding approach as follows: BR ·d2σ0 c dpTdy= N0 c 2·pTy·(A×ε)·Lint ·BR− ,(2) where N0 cis the yield in a given pTinterval with width pT. The yield is divided by the integrated luminosity Lint of the analysed sample and by the product of the branching ratios of the decays −→π−(99.887 ±0.035% [34]) and  →pπ−(63.9 ± 0.5% [34]), which is indicated as BR−. The factor 1/2 is needed because the cross section is computed for the average of 0 cand 0 c, while the raw yield includes both contributions. The factor (A ×ε) is the product of the geometrical acceptance (A) and the reconstruction and selection efficiency (ε) for 0 c→e+−νedecays determined for 0 cgenerated in |y| <0.8. Finally, the yield is normalised to one unit of rapidity by dividing it by y =1.6under the assumption that the rapidity distribution of 0 cis uniform in the range |y| <0.8. This assumption is verified with an accuracy of 1% using pythia 6. Note that the flatness of the rapidity distribution in |y| <0.8is also relevant for the comparison to the D0 meson cross section, which was determined in |y| <0.5[21]. The acceptance and the efficiency are calculated from the simulations with an additional correction to take into account the fact that the elastic cross section of anti-protons is not accurate in geant3[56]. The correction is calculated using the geant4 transport code [57], which has a more accurate description of the cross section, and found to be less than 2%. Since the acceptance and the efficiency depend on the 0 c-baryon pT, the 0 cshould be generated with a realistic momentum distribution. This was obtained via a two-step procedure similar to that used for the response matrix. Fig. 4shows the product of the geometrical acceptance and the reconstruction and selection efficiency (A ×ε)of 0 cas a function of pT. The systematic uncertainty on the 0 ccross section has different contributions, which are the uncertainties on the raw yield (owing to the procedure of background estimation), on the (A ×ε) factor (due to imperfections in the simulated samples), on the correction of the missing neutrino momentum (related to the unfolding procedure) and on the normalisation. Table 1summarises Fig. 4. Product of acceptance and efficiency (A ×ε) of 0 cbaryons generated in |y| <0.8decaying into e+−νeas a function of pT, determined from simulations pythia 6 (see text). the estimated systematic uncertainties, reporting their values in all the pTintervals. The total systematic uncertainty is determined by adding the individual contributions in quadrature in each pTinterval. The systematic uncertainty on the raw yield includes the uncertainties due to the WS subtraction procedure and to the estimation of the bcontribution. In the WS subtraction procedure described above, it was assumed that all the background sources contribute equally to RS and WS pairs. This is true as long as the background comprises uncorrelated pairs of electrons and −. A systematic uncertainty of 4% on the 0 csignal yield due to possible differences between RS and WS is estimated from simulations with the pythia 6 event generator by checking the remaining contamination of background pairs in the RS yield after the subtraction of the WS pairs. The WS subtraction could also be affected by the amount of hadron contamination in the electron sample and the signal-tobackground ratio of the 0 csignal. This effect is studied by repeating the analysis with different electron identification criteria. The results obtained with these modified criteria are found to be consistent with the ones from the default selections and therefore no systematic uncertainty is assigned. The systematic uncertainty due to the bcontribution to the WS pairs is estimated by varying the bmomentum distribution within the quoted uncertainty of about 50% on the cross section of 0 bin pp collisions [49] and the quoted uncertainty of about 50% on the ratio of the fragmentation fractions of beauty quarks into 0 band bin e+e−collisions [51, 52]. The effect on the final results is found to be about 1% because the contribution from bis small. These systematic uncertainties add up to a total uncertainty of 5% for the raw yield extraction. The systematic uncertainties arising from the reconstruction and selection efficiencies are estimated by repeating the analysis with different selection criteria for electrons, −and e+−pairs and by comparing the corrected yields. Due to the statistical limitations of the 0 csample, the electron efficiencies are studied via variations of the track-quality criteria and of the nσvalues for the electron identification with TPC and TOF in the + c→e+νedecays, which are analysed with the same procedure and have higher statistical significance. The RMS of the deviations of the corrected 12 ALICE Collaboration / Physics Letters B 781 (2018) 8–19 Fig. 5. Inclusive 0 c-baryon pT-differential production cross section multiplied by the branching ratio into e+−νe, as a function of pTfor |y| <0.5, in pp collisions at √s=7TeV. The error bars and boxes represent the statistical and systematic uncertainties, respectively. The contribution from bdecays is not subtracted. yields relative to the value obtained with the standard selection criteria, which amounts to 4% and 3%, is then assigned as a systematic uncertainty on the reconstruction and selection efficiency. Similarly, a systematic uncertainty of 1% on both the −reconstruction and selection efficiency is estimated from the RMS deviation of the inclusive −corrected yield against variations of the criteria applied to select the −decay tracks and its cascade decay topology. In addition, a systematic uncertainty of 4% on the −efficiency due to possible imperfections in the description of the detector material in the simulations [44]is considered and summed in quadrature with that estimated from the variation of the selection criteria. The uncertainties on the electron and − track-quality criteria are considered as correlated and combined linearly. The uncertainty on the e+−pair selection efficiency is estimated by varying the selection criteria on the opening angle and the invariant mass of the pair and a systematic uncertainty of 3–27% is assigned depending on pT. Finally, a systematic uncertainty may also arise from an imperfect description of the acceptance of e+−pairs in the simulation. It is estimated to be 11% by comparing the azimuthal distributions of inclusive electrons and −baryons in the data and in the simulation. The uncertainty on the e+−pair acceptance is summed in quadrature with that on the electron and −selection efficiencies, resulting in a systematic uncertainty on the (A ×ε)correction factor ranging from 13% to 30% depending on pT. The systematic uncertainty on the missing neutrino momentum correction with the unfolding procedure is evaluated by varying the prior distribution to the Bayesian unfolding and by using different unfolding techniques, such as the χ2minimisation method [58, 59] and the Singular Value Decomposition (SVD) method [60]. The RMS deviation of the results, ranging between 4% and 29% depending on pT, is assigned as a systematic uncertainty. A systematic uncertainty of 3% is also assigned due to the imperfect knowledge of the 0 c-baryon pTdistributions used as input for the efficiency calculation and the unfolding procedure from the simulation. It is estimated from the difference induced in the result by adding an additional step in the iterative procedure described above to obtain the input pTdistributions. These systematic uncertainties add up to an uncertainty ranging between 6% and 29% depending on pT. Finally, the results have a 3.5% normalisation systematic uncertainty arising from the uncertainty in the determination of the minimum-bias trigger cross section in pp collisions at √s= 7TeV[41]. The pT-differential cross section of 0 cbaryons multiplied by the branching ratio into e+−νeis shown in Fig. 5for the pT interval 1 <pT<8 GeV/cat mid-rapidity, |y| <0.5. The error bars and boxes represent the statistical and systematic uncertainties, respectively. The feed down contribution from b, e.g. Fig. 6. Ratio of the pT-differential cross sections of 0 cbaryons (multiplied by the branching ratio into e+−νe) and D0mesons [21]as a function of pTfor |y| <0.5, in pp collisions at √s=7TeV. The error bars and boxes represent the statistical and systematic uncertainties, respectively. Predictions from theoretical models, (a) pythia 8 with different tunes [28,62]. (b) dipsy [63]andherwig 7[64], are shown as shaded bands representing the range of the currently available theoretical predictions for the branching ratio of the considered 0 cdecay mode. − b→0 cπ−[61], is not subtracted due to the lack of knowledge of the absolute branching ratios of b→0 c+X. The ratio of the pT-differential cross section of 0 cbaryons to that of D0mesons [21]is shown in Fig. 6. The pTintervals of the cross-section measurements are combined to have the same pTbin boundaries for 0 cand D0. The systematic uncertainty in a merged pTinterval is defined by propagating the yield extraction uncertainties of the D0measurement as uncorrelated among pTintervals and all the other uncertainties of the D0and 0 cmeasurements as correlated. The systematic uncertainty on the 0 c/D0 ratio is calculated treating all the uncertainties on the 0 cand D0 cross sections as uncorrelated, except for the normalisation uncertainty that cancels out in the ratio. The ratio integrated in the transverse momentum interval 1 <pT<8GeV/cis found to be (7.0 ±1.5(stat) ±2.6(syst)) ×10−3. In Fig. 6(a), the measured transverse momentum dependence of the 0 c/D0ratio is compared with predictions from the pythia 8.211 event generator [46,65]. pythia 8 uses 2 →2 processes followed by a leading-logarithmic pT-ordered parton shower for the charm quark pair production and the hadronisation is treated with the Lund string model [66]. The figure shows the results obtained with different tunes of hadronisation: the Monash 2013 tune [62] and the Mode 0 tune from [28]. The latter is based on a model for the hadronisation of multi-parton systems, which includes string formation beyond the leading-colour approximation and is implemented in pythia 8 with specific tuning of the colour reconnection parameters. As compared to the Monash 2013 tune, this model provides a better description of the measured baryon-to-meson ratios in the light-flavour sector. Two other tunes (Mode 2 and Mode 3) provided in Ref. [28]give similar 0 c/D0ratios as Mode 0. In Fig. 6(b), the measured ratio is also compared to other models implementing different hadronisation mechanisms: dipsy [63] ALICE Collaboration / Physics Letters B 781 (2018) 8–19 13 with the rope hadronisation [67] and herwig 7.0.4 [64]with the cluster hadronisation [68]. To compare the data with these models, theoretical calculations of the branching ratio, which range between 0.83% and 4.2% [69–71], are used. This range defines the width of the bands shown for the model calculations represented in Fig. 6. Although the predictions of the Mode 0 tune of pythia 8 are the closest to the data compared to the other models, all calculations underestimate the measured ratio significantly. Thus, this new measurement can provide an important constraint to the models of charm quark hadronisation in pp collisions, once a measurement of the absolute branching ratio of the 0 cwill become available. In summary, we reported on the first LHC measurement of the inclusive pT-differential production cross section of the charmstrange baryon 0 cmultiplied by the branching ratio into e+−νe in pp collisions at √s=7TeV. The ratio of this measurement integrated over 1 <pT<8GeV/cto the production cross section of the D0meson integrated over the same pTinterval was found to be (7.0 ±1.5(stat) ±2.6(syst)) ×10−3. Several event generators with various models and tunes for the hadronisation mechanism underestimate the measured ratio. Acknowledgements 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 Collaboration gratefully acknowledges the resources and support 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 building and running the ALICE detector: A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS), Armenia; Austrian Academy of Sciences and Nationalstiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Universidade Federal do Rio Grande do Sul (UFRGS), Financiadora de Estudos e Projetos (Finep) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil; Ministry of Science & Technology of China (MSTC), National Natural Science Foundation of China (NSFC) and Ministry of Education of China (MOEC), China; Ministry of Science, Education and Sports and Croatian Science Foundation, Croatia; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; The Danish Council for Independent Research—Natural Sciences, the Carlsberg Foundation and Danish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat à l’Énergie Atomique (CEA) and Institut National de Physique Nucléaire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Research and Religions, Greece; National Research, Development and Innovation Office, Hungary; Department of Atomic Energy, Government of India (DAE), Department of Science and Technology, Government of India (DST), University Grants Commission, Government of India (UGC) and Council of Scientific and Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; Centro Fermi – Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi and Instituto Nazionale di Fisica Nucleare (INFN), Italy; Institute for Innovative Science and Technology, Nagasaki Institute of Applied Science (IIST), Japan Society for the Promotion of Science (JSPS) KAKENHI and Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan; Consejo Nacional de Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education and National Science Centre, Poland; Korea Institute of Science and Technology Information and National Research Foundation of Korea (NRF), Republic of Korea; Ministry of Education and Scientific Research, Institute of Atomic Physics and Romanian National Agency for Science, Technology and Innovation, Romania; Joint Institute for Nuclear Research (JINR), Ministry of Education and Science of the Russian Federation and National Research Centre Kurchatov Institute, Russia; Ministry of Education, Science, Research and Sport of the Slovak Republic, Slovakia; National Research Foundation of South Africa, South Africa; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba and Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Spain; Swedish Research Council (VR) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organization for Nuclear Research, Switzerland; National Science and Technology Development Agency (NSDTA), Suranaree University of Technology (SUT) and Office of the Higher Education Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom; National Science Foundation of the United States (NSF) and United States Department of Energy, Office of Nuclear Physics (DOE NP), United States. References [1] R.K. Ellis, W.J. Stirling, B.R. Webber, QCD and Collider Physics, Cambridge University Press, 1996. [2] J.C. Collins, D.E. Soper, G.F. Sterman, Heavy particle production in high-energy hadron collisions, Nucl. Phys. B 263 (1986) 37. [3] B.A. Kniehl, G. Kramer, I. Schienbein, H. Spiesberger, Inclusive D∗± production in p anti-p collisions with massive charm quarks, Phys. Rev. D 71 (2005) 014018, arXiv:hep -ph /0410289. [4] B.A. Kniehl, G. Kramer, I. Schienbein, H. Spiesberger, Collinear subtractions in hadroproduction of heavy quarks, Eur. Phys. J. C 41 (2005) 199, arXiv:hep -ph / 0502194. [5] B.A. Kniehl, G. Kramer, I. Schienbein, H. Spiesberger, Inclusive charmed-meson production at the CERN LHC, Eur. Phys. J. C 72 (2012) 2082, arXiv:1202 .0439 [hep -ph]. [6] M. Cacciari, M. Greco, P. Nason, The pTspectrum in heavy flavor hadroproduction, J. High Energy Phys. 05 (1998) 007, arXiv:hep -ph /9803400. [7] M. Cacciari, S. Frixione, N. Houdeau, M.L. Mangano, P. Nason, G. Ridolfi, Theoretical predictions for charm and bottom production at the LHC, J. High Energy Phys. 10 (2012) 137, arXiv:1205 .6344 [hep -ph]. [8] S. Catani, M. Ciafaloni, F. Hautmann, High-energy factorization and small x heavy flavor production, Nucl. Phys. B 366 (1991) 135. [9] M. Luszczak, R. Maciula, A. Szczurek, Nonphotonic electrons at RHIC within kt-factorization approach and with experimental semileptonic decay functions, Phys. Rev. D 79 (2009) 034009, arXiv:0807.5044 [hep -ph]. [10] R. Maciula, A. Szczurek, Open charm production at the LHC – kt-factorization approach, Phys. Rev. D 87 (2013) 094022, arXiv:1301.3033 [hep -ph]. [11] LHCb Collaboration, R. Aaij, et al., Observation of five new narrow 0 cstates decaying to + cK−, Phys. Rev. Lett. 118 (18) (2017) 182001, arXiv:1703 .04639 [hep -ex]. [12] LHCb Collaboration, R. Aaij, et al., Observation of the doubly charmed baryon ++ cc , arXiv:1707.01621 [hep -ex]. [13] ALICE Collaboration, B. Abelev, et al., Measurement of electrons from semileptonic heavy-flavour hadron decays in pp collisions at √s=7TeV, Phys. Rev. D 86 (2012) 112007, arXiv:1205 .5423 [hep -ex]. 14 ALICE Collaboration / Physics Letters B 781 (2018) 8–19 [14] ALICE Collaboration, B. Abelev, et al., Production of muons from heavy flavour decays at forward rapidity in pp and Pb–Pb collisions at √sNN =2.76 TeV, Phys. Rev. Lett. 109 (2012) 112301, arXiv:1205 .6443 [hep -ex]. [15] ALICE Collaboration, B. Abelev, et al., Heavy flavour decay muon production at forward rapidity in proton–proton collisions at √s=7TeV, Phys. Lett. B 708 (2012) 265–275, arXiv:1201.3791 [hep -ex]. [16] LHCb Collaboration, R. Aaij, et al., Prompt charm production in pp collisions at √s=7TeV, Nucl. Phys. B 871 (2013) 1, arXiv:1302 .2864 [hep -ex]. [17] ALICE Collaboration, B. Abelev, et al., Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at √s=2.76 TeV, Phys. Rev. D 91 (2015) 012001, arXiv:1405 .4117 [nucl -ex]. [18] LHCb Collaboration, R. Aaij, et al., Measurements of prompt charm production cross-sections in pp collisions at √s=13 TeV, J. High Energy Phys. 03 (2016) 159, arXiv:1510 .01707 [hep -ex]; J. High Energy Phys. 05 (2017) 074 (Erratum). [19] ATLAS Collaboration, G. Aad, et al., Measurement of D∗±, D±and D± smeson production cross sections in pp collisions at √s=7TeV with the ATLAS detector, Nucl. Phys. B 907 (2016) 717, arXiv:1512 .02913 [hep -ex]. [20] LHCb Collaboration, R. Aaij, et al., Measurements of prompt charm production cross-sections in pp collisions at √s=5TeV, arXiv:1610 .02230 [hep -ex]. [21] ALICE Collaboration, S. Acharya, et al., Measurement of D-meson production at mid-rapidity in pp collisions at √s=7TeV, arXiv:1702 .00766 [hep -ex]. [22] LHCb Collaboration, Prompt + cproduction in pPb collisions at √sNN = 5.02 TeV, Tech. Rep. LHCb-CONF-2017-005. CERN-LHCb-CONF-2017-005, CERN, Geneva, Sep. 2017, http://cds .cern .ch /record /2282379. [23] ARGUS Collaboration, H. Albrecht, et al., Measurement of cproduction in e+e−annihilation at 10.5-GeV center-of-mass energy, Phys. Lett. B 247 (1990) 121. [24] ARGUS Collaboration, H. Albrecht, et al., Observation of 0 csemileptonic decay, Phys. Lett. B 303 (1993) 368. [25] CLEO Collaboration, J.P. Alexander, et al., First observation of + c→0e+νe and an estimate of the + c/0 clifetime ratio, Phys. Rev. Lett. 74 (1995) 3113; Phys. Rev. Lett. 75 (1995) 4155 (Erratum). [26] ARGUS Collaboration, H. Albrecht, et al., Evidence for W exchange in charmed baryon decays, Phys. Lett. B 342 (1995) 397. [27] BaBar Collaboration, B. Aubert, et al., Production and decay of 0 cat BABAR, Phys. Rev. Lett. 95 (2005) 142003, arXiv:hep -ex /0504014. [28] J.R. Christiansen, P.Z. Skands, String formation beyond leading colour, J. High Energy Phys. 08 (2015) 003, arXiv:1505 .01681 [hep -ph]. [29] P.R. Sorensen, X. Dong, Suppression of non-photonic electrons from enhancement of charm baryons in heavy ion collisions, Phys. Rev. C 74 (2006) 024902, arXiv:nucl -th /0512042. [30] S.H. Lee, K. Ohnishi, S. Yasui, I.-K. Yoo, C.-M. Ko, cenhancement from strongly coupled quark–gluon plasma, Phys. Rev. Lett. 100 (2008) 222301, arXiv:0709 . 3637 [nucl -th]. [31] G. Martinez-Garcia, S. Gadrat, P. Crochet, Consequences of a c/D enhancement effect on the non-photonic electron nuclear modification factor in central heavy ion collisions at RHIC energy, Phys. Lett. B 663 (2008) 55, arXiv: 0710 .2152 [hep -ph]; Phys. Lett. B 666 (2008) 533 (Erratum). [32] Y. Oh, C.M. Ko, S.H. Lee, S. Yasui, Heavy baryon/meson ratios in relativistic heavy ion collisions, Phys. Rev. C 79 (2009) 044905, arXiv:0901.1382 [nucl -th]. [33] S. Ghosh, S.K. Das, V. Greco, S. Sarkar, J.-e. Alam, Diffusion of cin hot hadronic medium and its impact on c/Dratio, Phys. Rev. D 90 (2014) 054018, arXiv:1407.5069 [nucl -th]. [34] Particle Data Group Collaboration, K.A. Olive, et al., Review of particle physics, Chin. Phys. C 40 (2016) 100001. [35] ALICE Collaboration, K. Aamodt, et al., The ALICE experiment at the CERN LHC, J. Instrum. 3 (2008) S08002. [36] ALICE Collaboration, B. Abelev, et al., Performance of the ALICE experiment at the CERN LHC, Int. J. Mod. Phys. A 29 (2014) 1430044, arXiv:1402 .4476 [nucl - ex]. [37] ALICE Collaboration, K. Aamodt, et al., Alignment of the ALICE Inner Tracking System with cosmic-ray tracks, J. Instrum. 5 (2010) P03003, arXiv:1001.0502 [physics .ins -det]. [38] ALICE Collaboration, B. Abelev, et al., Measurement of charm production at central rapidity in proton–proton collisions at √s=7TeV, J. High Energy Phys. 01 (2012) 128, arXiv:1111.1553 [hep -ex]. [39] J. Alme, et al., The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events, Nucl. Instrum. Methods Phys. Res., Sect. A 622 (2010) 316, arXiv:1001.1950 [physics .ins -det]. [40] ALICE Collaboration, J. Adam, et al., Determination of the event collision time with the ALICE detector at the LHC, Eur. Phys. J. Plus 132 (2017) 99, arXiv: 1610 .03055 [physics .ins -det]. [41] ALICE Collaboration, B. Abelev, et al., Measurement of inelastic, singleand double-diffraction cross sections in proton–proton collisions at the LHC with ALICE, Eur. Phys. J. C 73 (2013) 2456, arXiv:1208 .4968 [hep -ex]. [42] ALICE Collaboration, J. Adam, et al., Measurement of electrons from heavyflavour hadron decays in p–Pb collisions at √sNN =5.02 TeV, Phys. Lett. B 754 (2016) 81, arXiv:1509 .07491 [nucl -ex]. [43] ALICE Collaboration, K. Aamodt, et al., Strange particle production in proton– proton collisions at √s=0.9TeV with ALICE at the LHC, Eur. Phys. J. C 71 (2011) 1594, arXiv:1012 .3257 [hep -ex]. [44] ALICE Collaboration, B. Abelev, et al., Multi-strange baryon production in pp collisions at √s=7TeV with ALICE, Phys. Lett. B 712 (2012) 309, arXiv:1204 . 0282 [nucl -ex]. [45] ALICE Collaboration, B. Abelev, et al., Production of (1385)±and (1530)0 in proton–proton collisions at √s=7TeV, Eur. Phys. J. C 75 (2015) 1, arXiv: 1406 .3206 [nucl -ex]. [46] T. Sjostrand, S. Mrenna, P.Z. Skands, PYTHIA 6.4 physics and manual, J. High Energy Phys. 05 (2006) 026, arXiv:hep -ph /0603175. [47] P.Z. Skands, The Perugia tunes, in: Proceedings, 1st International Workshop on Multiple Partonic Interactions at the LHC (MPI08), Perugia, Italy, October 27–31, 2008, 2009, p. 284, arXiv:0905 .3418 [hep -ph]. [48] R. Brun, F. Bruyant, F. Carminati, S. Giani, M. Maire, A. McPherson, G. Patrick, L. Urban, GEANT detector description and simulation tool, CERN-W5013, CERNW-5013, W5013, W-5013. [49] CMS Collaboration, S. Chatrchyan, et al., Measurement of the bcross section and the ¯ bto bratio with J/decays in pp collisions at √s=7TeV, Phys. Lett. B 714 (2012) 136, arXiv:1205 .0594 [hep -ex]. [50] LHCb Collaboration, R. Aaij, et al., Study of the production of 0 band B0 hadrons in pp collisions and first measurement of the 0 b→J/ψ pK−branching fraction, Chin. Phys. C 40 (2016) 011001, arXiv:1509 .00292 [hep -ex]. [51] ALEPH Collaboration, D. Buskulic, et al., Strange b baryon production and lifetime in Z decays, Phys. Lett. B 384 (1996) 449. [52] ALEPH Collaboration, R. Barate, et al., Measurement of the Bbaryon lifetime and branching fractions in Zdecays, Eur. Phys. J. C 2 (1998) 197. [53] CDF Collaboration, T. Aaltonen, et al., Measurement of ratios of fragmentation fractions for bottom hadrons in p¯ pcollisions at √s=1.96-TeV, Phys. Rev. D 77 (2008) 072003, arXiv:0801.4375 [hep -ex]. [54] T. Adye, Unfolding algorithms and tests using RooUnfold, in: Proceedings, PHYSTAT 2011 Workshop on Statistical Issues Related to Discovery Claims in Search Experiments and Unfolding, CERN, Geneva, Switzerland 17–20 January 2011, CERN, Geneva, 2011, p. 313, arXiv:1105 .1160 [physics .data -an]. [55] G. D’Agostini, A multidimensional unfolding method based on Bayes’ theorem, Nucl. Instrum. Methods Phys. Res., Sect. A 362 (1995) 487. [56] ALICE Collaboration, E. Abbas, et al., Mid-rapidity anti-baryon to baryon ratios in pp collisions at √s=0.9, 2.76 and 7TeV measured by ALICE, Eur. Phys. J. C 73 (2013) 2496, arXiv:1305 .1562 [nucl -ex]. [57] GEANT4 Collaboration, S. Agostinelli, et al., GEANT4: a simulation toolkit, Nucl. Instrum. Methods Phys. Res., Sect. A 506 (2003) 250. [58] ALICE Collaboration, J.F. Grosse-Oetringhaus, Comments on unfolding methods in ALICE, in: Proceedings, PHYSTAT 2011 Workshop on Statistical Issues Related to Discovery Claims in Search Experiments and Unfolding, CERN, Geneva, Switzerland 17–20 January 2011, CERN, Geneva, 2011, p. 309, https:// inspirehep .net /record /1478299 /files /1087459 _309 -312 .pdf. [59] V. Blobel, in: 8th CERN School of Comp. – CSC’84, Aiguablava, Spain, 9–22 Sep. 1984, CERN-85-09, 88, 1985. [60] A. Hocker, V. Kartvelishvili, SVD approach to data unfolding, Nucl. Instrum. Methods Phys. Res., Sect. A 372 (1996) 469, arXiv:hep -ph /9509307. [61] LHCb Collaboration, R. Aaij, et al., Precision measurement of the mass and lifetime of the − bbaryon, Phys. Rev. Lett. 113 (2014) 242002, arXiv:1409 .8568 [hep -ex]. [62] P. Skands, S. Carrazza, J. Rojo, Tuning PYTHIA 8.1: the Monash 2013 tune, Eur. Phys. J. C 74 (2014) 3024, arXiv:1404 .5630 [hep -ph]. [63] C. Bierlich, J.R. Christiansen, Effects of color reconnection on hadron flavor observables, Phys. Rev. D 92 (9) (2015) 094010, arXiv:1507.02091 [hep -ph]. [64] M. Bahr, et al., Herwig++ physics and manual, Eur. Phys. J. C 58 (2008) 639–707, arXiv:0803 .0883 [hep -ph]. [65] T. Sjostrand, S. Mrenna, P.Z. Skands, Abrief introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852, arXiv:0710 .3820 [hep -ph]. [66] B. Andersson, G. Gustafson, G. Ingelman, T. Sjostrand, Parton fragmentation and string dynamics, Phys. Rep. 97 (1983) 31. [67] T.S. Biro, H.B. Nielsen, J. Knoll, Color rope model for extreme relativistic heavy ion collisions, Nucl. Phys. B 245 (1984) 449–468. [68] B.R. Webber, AQCD model for jet fragmentation including soft gluon interference, Nucl. Phys. B 238 (1984) 492–528. [69] R. Perez-Marcial, R. Huerta, A. Garcia, M. Avila-Aoki, Predictions for semileptonic decays of charm baryons. 2. Nonrelativistic and MIT bag quark models, Phys. Rev. D 40 (1989) 2955; Phys. Rev. D 44 (1991) 2203 (Erratum). [70] R.L. Singleton, Semileptonic baryon decays with a heavy quark, Phys. Rev. D 43 (1991) 2939. [71] H.-Y. Cheng, B. Tseng, 1/M corrections to baryonic form-factors in the quark model, Phys. Rev. D 53 (1996) 1457, arXiv:hep -ph /9502391; Phys. Rev. D 55 (1997) 1697 (Erratum). ALICE Collaboration / Physics Letters B 781 (2018) 8–19 15 ALICE Collaboration S. Acharya137, D. Adamová94, J. Adolfsson34, M.M. Aggarwal99, G. Aglieri Rinella35, M. Agnello 31, N. Agrawal48, Z. Ahammed 137, S.U. Ahn79, S. Aiola141, A. Akindinov64, M. Al-Turany 106, S.N. Alam137, D.S.D. Albuquerque122, D. Aleksandrov 90, B. Alessandro58, R. Alfaro Molina74, Y. Ali 15, A. Alici12,53,27, A. Alkin3, J. Alme 22, T. Alt 70, L. Altenkamper22, I. Altsybeev136, C. Alves Garcia Prado121, C. Andrei87, D. Andreou35, H.A. Andrews110, A. Andronic106, V. Anguelov104, C. Anson97, T. Antiˇ ci´ c107, F. Antinori56, P. Antonioli 53, L. Aphecetche114, H. Appelshäuser70, S. Arcelli27, R. Arnaldi 58, O.W. Arnold105,36, I.C. Arsene21, M. Arslandok104, B. Audurier114, A. Augustinus35, R. Averbeck106, M.D. Azmi17, A. Badalà55, Y.W. Baek 60,78, S. Bagnasco58, R. Bailhache70, R. Bala 101, A. Baldisseri75, M. Ball45, R.C. Baral67,88, A.M. Barbano26, R. Barbera28, F. Barile 33, L. Barioglio26, G.G. Barnaföldi140, L.S. Barnby93, V. Barret131, P. Bartalini7, K. Barth35, E. Bartsch70, N. Bastid131, S. Basu139, G. Batigne114, B. Batyunya77, P.C. Batzing21, J.L. Bazo Alba111, I.G. Bearden91, H. Beck104, C. Bedda63, N.K. Behera60, I. Belikov 133, F. Bellini 35,27, H. Bello Martinez2, R. Bellwied124, L.G.E. Beltran120, V. Belyaev83, G. Bencedi 140, S. Beole26, A. Bercuci87, Y. Berdnikov 96, D. Berenyi140, R.A. Bertens127, D. Berzano58,35, L. Betev35, P.P. Bhaduri 137, A. Bhasin101, I.R. Bhat101, B. Bhattacharjee44, J. Bhom118, A. Bianchi26, L. Bianchi124, N. Bianchi51, C. Bianchin139, J. Bielˇ cík39, J. Bielˇ cíková94, A. Bilandzic36,105, G. Biro140, R. Biswas4, S. Biswas4, J.T. Blair 119, D. Blau90, C. Blume 70, G. Boca134, F. Bock 35, A. Bogdanov83, L. Boldizsár140, M. Bombara40, G. Bonomi135, M. Bonora35, H. Borel75, A. Borissov104,19, M. Borri 126, E. Botta26, C. Bourjau91, L. Bratrud70, P. Braun-Munzinger106, M. Bregant121, T.A. Broker 70, M. Broz39, E.J. Brucken46, E. Bruna 58, G.E. Bruno35,33, D. Budnikov 108, H. Buesching70, S. Bufalino31, P. Buhler 113, P. Buncic 35, O. Busch130, Z. Buthelezi76, J.B. Butt15, J.T. Buxton18, J. Cabala116, D. Caffarri35,92, H. Caines141, A. Caliva106,63, E. Calvo Villar111, P. Camerini25, A.A. Capon113, F. Carena 35, W. Carena 35, F. Carnesecchi12,27, J. Castillo Castellanos75, A.J. Castro127, E.A.R. Casula54, C. Ceballos Sanchez9, S. Chandra137, B. Chang125, W. Chang 7, S. Chapeland35, M. Chartier126, S. Chattopadhyay137, S. Chattopadhyay109, A. Chauvin36,105, C. Cheshkov132, B. Cheynis132, V. Chibante Barroso35, D.D. Chinellato122, S. Cho60, P. Chochula 35, M. Chojnacki91, S. Choudhury137, T. Chowdhury 131, P. Christakoglou92, C.H. Christensen91, P. Christiansen34, T. Chujo 130, S.U. Chung19, C. Cicalo54, L. Cifarelli12,27, F. Cindolo 53, J. Cleymans100, F. Colamaria 52,33, D. Colella52,35,65, A. Collu82, M. Colocci27, M. Concas58,ii, G. Conesa Balbastre81, Z. Conesa del Valle 61, J.G. Contreras 39, T.M. Cormier95, Y. Corrales Morales58, I. Cortés Maldonado 2, P. Cortese 32, M.R. Cosentino123, F. Costa 35, S. Costanza134, J. Crkovská61, P. Crochet 131, E. Cuautle72, L. Cunqueiro95,71, T. Dahms 36,105, A. Dainese56, M.C. Danisch104, A. Danu68, D. Das 109, I. Das109, S. Das4, A. Dash 88, S. Dash48, S. De49, A. De Caro30, G. de Cataldo 52, C. de Conti121, J. de Cuveland42, A. De Falco24, D. De Gruttola30,12, N. De Marco58, S. De Pasquale30, R.D. De Souza122, H.F. Degenhardt121, A. Deisting106,104, A. Deloff86, C. Deplano92, P. Dhankher48, D. Di Bari33, A. Di Mauro35, P. Di Nezza51, B. Di Ruzza56, M.A. Diaz Corchero 10, T. Dietel 100, P. Dillenseger70, Y. Ding 7, R. Divià35, Ø. Djuvsland22, A. Dobrin35, D. Domenicis Gimenez121, B. Dönigus70, O. Dordic21, L.V.R. Doremalen63, A.K. Dubey137, A. Dubla106, L. Ducroux132, S. Dudi99, A.K. Duggal99, M. Dukhishyam88, P. Dupieux131, R.J. Ehlers141, D. Elia 52, E. Endress111, H. Engel69, E. Epple141, B. Erazmus114, F. Erhardt 98, B. Espagnon61, G. Eulisse35, J. Eum19, D. Evans110, S. Evdokimov112, L. Fabbietti105,36, J. Faivre81, A. Fantoni51, M. Fasel 95, L. Feldkamp71, A. Feliciello58, G. Feofilov136, A. Fernández Téllez2, E.G. Ferreiro16, A. Ferretti26, A. Festanti29,35, V.J.G. Feuillard75,131, J. Figiel118, M.A.S. Figueredo121, S. Filchagin108, D. Finogeev62, F.M. Fionda 22,24, M. Floris 35, S. Foertsch76, P. Foka 106, S. Fokin90, E. Fragiacomo59, A. Francescon35, A. Francisco114, U. Frankenfeld 106, G.G. Fronze26, U. Fuchs 35, C. Furget81, A. Furs62, M. Fusco Girard30, J.J. Gaardhøje91, M. Gagliardi26, A.M. Gago111, K. Gajdosova91, M. Gallio26, C.D. Galvan 120, P. Ganoti 85, C. Garabatos106, E. Garcia-Solis13, K. Garg28, C. Gargiulo35, P. Gasik 105,36, E.F. Gauger119, M.B. Gay Ducati73, M. Germain114, J. Ghosh109, P. Ghosh137, S.K. Ghosh4, P. Gianotti51, P. Giubellino35,106,58, P. Giubilato29, E. Gladysz-Dziadus118, P. Glässel104, D.M. Goméz Coral74, A. Gomez Ramirez69, A.S. Gonzalez35, V. Gonzalez10, P. González-Zamora10,2, S. Gorbunov42, L. Görlich118, S. Gotovac117, V. Grabski74, L.K. Graczykowski138, K.L. Graham110, L. Greiner82, A. Grelli63, C. Grigoras35, V. Grigoriev83, A. Grigoryan1, S. Grigoryan77, J.M. Gronefeld106, F. Grosa31, J.F. Grosse-Oetringhaus35, R. Grosso106, F. Guber 62, R. Guernane81, B. Guerzoni27, M. Guittiere114, 16 ALICE Collaboration / Physics Letters B 781 (2018) 8–19 K. Gulbrandsen91, T. Gunji129, A. Gupta101, R. Gupta101, I.B. Guzman2, R. Haake35, C. Hadjidakis61, H. Hamagaki84, G. Hamar140, J.C. Hamon133, M.R. Haque63, J.W. Harris 141, A. Harton13, H. Hassan 81, D. Hatzifotiadou53,12, S. Hayashi129, S.T. Heckel70, E. Hellbär70, H. Helstrup37, A. Herghelegiu87, E.G. Hernandez2, G. Herrera Corral11, F. Herrmann71, B.A. Hess 103, K.F. Hetland37, H. Hillemanns 35, C. Hills126, B. Hippolyte133, B. Hohlweger105, D. Horak39, S. Hornung106, R. Hosokawa130,81, P. Hristov35, C. Hughes127, T.J. Humanic 18, N. Hussain44, T. Hussain 17, D. Hutter42, D.S. Hwang20, J.P. Iddon126, S.A. Iga Buitron72, R. Ilkaev108, M. Inaba130, M. Ippolitov 83,90, M.S. Islam109, M. Ivanov106, V. Ivanov96, V. Izucheev112, B. Jacak82, N. Jacazio 27, P.M. Jacobs 82, M.B. Jadhav48, S. Jadlovska116, J. Jadlovsky116, S. Jaelani63, C. Jahnke36, M.J. Jakubowska138, M.A. Janik 138, P.H.S.Y. Jayarathna124, C. Jena88, M. Jercic98, R.T. Jimenez Bustamante106, P.G. Jones110, A. Jusko110, P. Kalinak 65, A. Kalweit35, J.H. Kang142, V. Kaplin83, S. Kar 137, A. Karasu Uysal80, O. Karavichev62, T. Karavicheva 62, L. Karayan106,104, P. Karczmarczyk 35, E. Karpechev62, U. Kebschull 69, R. Keidel143, D.L.D. Keijdener63, M. Keil 35, B. Ketzer45, Z. Khabanova 92, P. Khan 109, S. Khan17, S.A. Khan137, A. Khanzadeev96, Y. Kharlov 112, A. Khatun17, A. Khuntia49, M.M. Kielbowicz118, B. Kileng37, B. Kim130, D. Kim142, D.J. Kim125, H. Kim 142, J.S. Kim43, J. Kim104, M. Kim60, S. Kim 20, T. Kim 142, S. Kirsch42, I. Kisel42, S. Kiselev64, A. Kisiel138, G. Kiss140, J.L. Klay6, C. Klein 70, J. Klein35, C. Klein-Bösing71, S. Klewin104, A. Kluge35, M.L. Knichel104,35, A.G. Knospe124, C. Kobdaj 115, M. Kofarago 140, M.K. Köhler104, T. Kollegger106, V. Kondratiev136, N. Kondratyeva83, E. Kondratyuk112, A. Konevskikh62, M. Konyushikhin139, M. Kopcik116, M. Kour 101, C. Kouzinopoulos35, O. Kovalenko86, V. Kovalenko136, M. Kowalski 118, G. Koyithatta Meethaleveedu48, I. Králik65, A. Kravˇ cáková 40, L. Kreis106, M. Krivda110,65, F. Krizek 94, E. Kryshen96, M. Krzewicki42, A.M. Kubera18, V. Kuˇ cera94, C. Kuhn133, P.G. Kuijer 92, A. Kumar101, J. Kumar 48, L. Kumar 99, S. Kumar48, S. Kundu88, P. Kurashvili86, A. Kurepin62, A.B. Kurepin62, A. Kuryakin108, S. Kushpil94, M.J. Kweon60, Y. Kwon 142, S.L. La Pointe42, P. La Rocca28, C. Lagana Fernandes121, Y.S. Lai 82, I. Lakomov 35, R. Langoy 41, K. Lapidus141, C. Lara69, A. Lardeux21, A. Lattuca26, E. Laudi35, R. Lavicka39, R. Lea25, L. Leardini104, S. Lee 142, F. Lehas92, S. Lehner113, J. Lehrbach42, R.C. Lemmon93, E. Leogrande63, I. León Monzón 120, P. Lévai 140, X. Li 14, X.L. Li7, J. Lien41, R. Lietava110, B. Lim 19, S. Lindal21, V. Lindenstruth42, S.W. Lindsay126, C. Lippmann106, M.A. Lisa18, V. Litichevskyi 46, A. Liu82, W.J. Llope 139, D.F. Lodato63, P.I. Loenne22, V. Loginov83, C. Loizides82,95, P. Loncar 117, X. Lopez 131, E. López Torres9, A. Lowe140, P. Luettig70, J.R. Luhder71, M. Lunardon29, G. Luparello25,59, M. Lupi35, T.H. Lutz 141, A. Maevskaya62, M. Mager35, S.M. Mahmood21, A. Maire133, R.D. Majka 141, M. Malaev96, L. Malinina77,iii, D. Mal’Kevich64, P. Malzacher106, A. Mamonov108, V. Manko90, F. Manso131, V. Manzari52, Y. Mao7, M. Marchisone128,132,76, J. Mareš66, G.V. Margagliotti25, A. Margotti53, J. Margutti63, A. Marín 106, C. Markert119, M. Marquard70, N.A. Martin106, P. Martinengo35, J.A.L. Martinez69, M.I. Martínez2, G. Martínez García114, M. Martinez Pedreira35, S. Masciocchi106, M. Masera26, A. Masoni54, L. Massacrier61, E. Masson114, A. Mastroserio52, A.M. Mathis36,105, P.F.T. Matuoka 121, A. Matyja127, C. Mayer118, J. Mazer127, M. Mazzilli33, M.A. Mazzoni57, F. Meddi23, Y. Melikyan 83, A. Menchaca-Rocha74, E. Meninno30, J. Mercado Pérez104, M. Meres38, S. Mhlanga100, Y. Miake130, M.M. Mieskolainen46, D.L. Mihaylov105, K. Mikhaylov77,64, A. Mischke63, A.N. Mishra49, D. Mi´ skowiec 106, J. Mitra137, C.M. Mitu68, N. Mohammadi 63,35, A.P. Mohanty63, B. Mohanty88, M. Mohisin Khan17,iv, E. Montes10, D.A. Moreira De Godoy71, L.A.P. Moreno2, S. Moretto 29, A. Morreale114, A. Morsch35, V. Muccifora51, E. Mudnic117, D. Mühlheim 71, S. Muhuri137, J.D. Mulligan141, M.G. Munhoz 121, K. Münning45, R.H. Munzer70, H. Murakami129, S. Murray76, L. Musa35, J. Musinsky65, C.J. Myers124, J.W. Myrcha138, D. Nag4, B. Naik48, R. Nair86, B.K. Nandi48, R. Nania12,53, E. Nappi52, A. Narayan48, M.U. Naru15, H. Natal da Luz121, C. Nattrass127, S.R. Navarro2, K. Nayak 88, R. Nayak48, T.K. Nayak 137, S. Nazarenko108, R.A. Negrao De Oliveira70,35, L. Nellen72, S.V. Nesbo37, G. Neskovic42, F. Ng 124, M. Nicassio106, M. Niculescu68, J. Niedziela138,35, B.S. Nielsen91, S. Nikolaev90, S. Nikulin 90, V. Nikulin 96, A. Nobuhiro47, F. Noferini12,53, P. Nomokonov 77, G. Nooren63, J.C.C. Noris2, J. Norman81,126, A. Nyanin90, J. Nystrand22, H. Oeschler19,104,i, H. Oh 142, A. Ohlson104, L. Olah140, J. Oleniacz138, A.C. Oliveira Da Silva121, M.H. Oliver141, J. Onderwaater106, C. Oppedisano58, R. Orava46, M. Oravec116, A. Ortiz Velasquez72, A. Oskarsson34, J. Otwinowski118, K. Oyama84, Y. Pachmayer 104, V. Pacik91, D. Pagano135, G. Pai´ c72, P. Palni 7, J. Pan139, A.K. Pandey48,