Multiplicity dependence of J/ ψ production at midrapidity in pp collisions at s √ = 13 TeV
EEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN-EP-2020-08819 May 2020c (cid:13)
Multiplicity dependence of J/ ψ production at midrapidity in pp collisionsat √ s = 13 TeV ALICE Collaboration ∗ Abstract
Measurements of the inclusive J/ ψ yield as a function of charged-particle pseudorapidity densityd N ch / d η in pp collisions at √ s =
13 TeV with ALICE at the LHC are reported. The J/ ψ mesonyield is measured at midrapidity ( | y | < .
9) in the dielectron channel, for events selected based onthe charged-particle multiplicity at midrapidity ( | η | <
1) and at forward rapidity ( − . < η < − . . < η < . ψ yield with normalized d N ch / d η is significantlystronger than linear and dependent on the transverse momentum. The data are compared to theoreticalpredictions, which describe the observed trends well, albeit not always quantitatively. ∗ See Appendix A for the list of collaboration members a r X i v : . [ nu c l - e x ] M a y ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration Hadronic charmonium production at collider energies is a complex and not yet fully understood process,involving hard-scale processes, i.e. the initial heavy-quark pair production, which can be described bymeans of perturbative quantum chromodynamics (pQCD), as well as soft-scale processes, i.e. the sub-sequent binding into a color-neutral charmonium state. The latter stage is addressed via models whichassume that it factorizes with respect to the perturbative early stage. The widely used non-relativisticQCD (NRQCD) effective theory incorporates contributions from several hadronization mechanisms, likecolor-singlet or color-octet models (see Ref. [1] for a recent review on models and Ref.[2] for a compar-ison with data of Run 1 at the LHC). The NRQCD formalism combined with a Color Glass Condensate(CGC) description of the incoming protons [3] is a recent example of a comprehensive treatment ofthe transverse momentum p T and rapidity dependent production, in particular extended down to zerotransverse momentum.The event-multiplicity dependent production of charmonium and open charm hadrons in pp and p–Pbcollisions are observables having the potential to give new insights on processes at the parton level andon the interplay between the hard and soft mechanisms in particle production and is widely studied at theLHC. ALICE has studied the multiplicity dependence in pp collisions at √ s = ψ production at mid- and forward rapidity [4], and prompt J/ ψ (including feed down from ψ ( S ) and χ c ),non-prompt J/ ψ (originating from bottom-meson decays) and D-meson production at midrapidity [5].The general observation is an increase of open and hidden charm production with charged-particle mul-tiplicity measured at midrapidity. For the J/ ψ production, multiplicities of about 4 times the mean valuewere reached. The results are consistent with an approximately linear increase of the normalized yieldas a function of the normalized multiplicity (both observables are normalized to their corresponding av-erages in minimum bias events). For the D-meson production, normalized event multiplicities of about6 were reached; a stronger than linear increase of D-meson production was observed at the highestmultiplicities. Observations made by the CMS Collaboration for ϒ ( nS ) production at midrapidity at √ s = .
76 TeV indicate a linear increase with the event activity, when measuring it at forward rapid-ity, and a stronger than linear increase with the event activity measured at midrapidity [6]. At RHIC,a measurement of J/ ψ production as a function of multiplicity was recently performed by the STARCollaboration [7] for √ s = . ψ production as a function of charged-particle multiplicity was studied also in p–Pb collisions, exhibitingsignificant differences for different ranges of rapidity of the J/ ψ meson [8, 9]. A clear correlation withthe event multiplicity (and event shape) was experimentally established for the inclusive charged-particleproduction [10] as well as for identified particles, including multi-strange hyperons [11].Several theoretical models, described briefly in Section 4, predict a correlation of the normalized J/ ψ production with the normalized event multiplicity which is stronger than linear. These include a coherentparticle production model [12], the percolation model [13], the EPOS3 event generator [14], a CGC-complemented NRQCD model [15], the PYTHIA 8.2 event generator [16, 17], and the 3-Pomeron CGCmodel [18]. While for instance multiparton interactions (as implemented in PYTHIA) play an importantrole in charm(onium) production, it is important to notice that the predicted correlation is, in all themodels to first order, the result of a ( N ch -dependent) reduction of the charged-particle multiplicity. Wellknown is the color string reconnection mechanism implemented in PYTHIA, but initial-state effects asin CGC models lead, with very different physics, similarly to a reduction in particle multiplicity.In this Letter, the measurements of the inclusive J/ ψ yield as a function of charged-particle pseudora-pidity density in pp collisions at √ s =
13 TeV are presented. The measurements are performed in thedielectron channel at midrapidity with the ALICE detector at the LHC. The p T -integrated and differen-tial results are presented for minimum bias events as well as for events triggered on high multiplicity,which extend the multiplicity range up to 7 times the average multiplicity, and on the electromagneticcalorimeter signals, which allow to access p T values up to 15-40 GeV/ c . Section 2 outlines the experi-2ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaborationmental setup and the data sample; Section 3 describes the analysis, while Section 4 presents the results;a brief summary and outlook are given in Section 5. The reconstruction of J/ ψ in the e + e − decay channel at midrapidity is performed using the ALICEcentral barrel detectors, described in detail in Refs. [19, 20]. The setup is located in a solenoidal magnetproviding a field of 0.5 T oriented along the beam direction.For this analysis, a minimum bias (MB) trigger, a high multiplicity (HM) trigger, and two triggers basedon the deposited energy in the combined Electromagnetic Calorimeter (EMCal) and the Di-jet Calorime-ter (DCal) [21–23] are employed. Both the MB and HM triggers are provided by the V0 detector, thatconsists of two forward scintillator arrays [24] covering the pseudorapidity ranges − . < η < − . . < η < .
1. The MB trigger signal consists of a coincident signal in both arrays, while theHM trigger requires a signal amplitude in the V0 arrays above a threshold which corresponds to the0.1% highest multiplicity events. The EMCal and DCal are located back-to-back in azimuth and forma two-arm electromagnetic calorimeter. While the EMCal detector covers | η | < . ◦ < ϕ < ◦ , the DCal covers 0 . < | η | < . ◦ < ϕ < ◦ and | η | < . ◦ < ϕ < ◦ . As a consequence of identical construction, both have identical granularity and intrin-sic energy resolution. In this paper, EMCal and DCal will be referred to together as EMCal. The EMCaltrigger consists of the sum of energy in a sliding window of 4 × | η | < . E / d x . The first two layers of the ITS (covering | η | < . | η | < . √ s =
13 TeV. The number of selected events and the correspond-ing integrated luminosities [27] are listed in Table 1 for the different triggers used in this analysis. Forthe analyzed data set, the maximum interaction rate was 260 kHz, and the maximum pileup probabilitywas about 5 × − . Table 1:
Number of selected events and corresponding integrated luminosities for the different triggers used inthis analysis.
MB and HM triggers EMCal triggersMB HM EG1 EG2Number of events 1 . × . × . × × Integrated luminosity 21 . ± . − . ± . − . ± . − . ± .
02 pb − In this work the inclusive production of J/ ψ mesons is studied as a function of the pseudorapidity densityof charged particles at midrapidity, d N ch / d η . The J/ ψ yield in a given multiplicity interval and in a givenrapidity ( y ) range d N J/ ψ / d y is normalized to the J/ ψ yield in the INEL > (cid:104) d N J/ ψ / d y (cid:105) . The3ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE CollaborationINEL > | η | <
1. In this ratio, most ofthe systematic uncertainties related to tracking and particle identification cancel.
All events selected in this analysis are required to have a reconstructed collision vertex within the longi-tudinal interval | z vtx | <
10 cm in order to ensure uniform detector performance and one SPD tracklet in | η | <
1. Beam-gas events are rejected using timing cuts with the V0 detector. Pileup events are rejectedusing a vertex finding algorithm based on SPD tracklets [20], allowing the removal of events with 2vertices. Because of the relatively small in-bunch pileup probability and the further event selection per-formed in the analysis, the fraction of remaining pileup is negligible in the minimum bias events sampleand at most 2% in the high multiplicity triggered sample. corrtrk N C oun t s
10 MB triggered eventsHM triggered eventsEMCal triggered events = 13 TeV s ALICE pp
V0 amplitude (a.u.) C oun t s
10 MB triggered eventsHM triggered eventsEMCal triggered eventsExample data taking period = 13 TeV s ALICE pp
Fig. 1:
Distribution of the corrected SPD tracklets N corrtrk (left) and V0 amplitude (right) for the MB events as wellas the HM- and EMCal-triggered events used in the analysis. The vertical lines indicate the used multiplicityintervals (see Table 2; the first bin spans from 0 to the position of the first line). For the HM-triggered events, theV0 amplitude distribution for a single data taking period is included for illustration (open squares). Events are binned in multiplicity classes based on either the SPD or the V0 detector signals, as shownin Fig. 1. Events corresponding to the onset of the V0 HM trigger are excluded; that onset is rathersharp. The smearing seen in the distribution in the right panel of Fig. 1 is due to the different thresholdsused during operation. To illustrate this, the V0-amplitude distribution for a single data taking period isincluded in Fig. 1 (right panel, open squares).For the measurement of the charged-particle pseudorapidity density d N ch / d η at midrapidity, | η | <
1, theSPD tracklets are used [28]. Given the close proximity of the SPD detector to the interaction point (thetwo layers are at radial distances of 3.9 and 7.6 cm), its geometrical acceptance changes by up to 50% inthe z vtx interval selected for analysis. In addition, the mean number of SPD tracklets also varied duringthe 3-year Run 2 data taking period due to changes in the number of active SPD detector elements. Inorder to compensate for these detector effects, a z vtx and time-dependent correction factor is applied suchthat the measured average multiplicity is equalized to a reference value. This reference was chosen tobe the largest mean SPD tracklet multiplicity observed over time and z vtx . This procedure is similar towhat was done previously in Ref. [4]. The correction factor for each event is randomly smeared usinga Poisson distribution to take into account event-by-event fluctuations. In the case of the event selectionbased on the forward multiplicity measurement with the V0 detector, the signal amplitudes are equalizedto compensate for detector ageing and for the small acceptance variation with the event vertex position.The overall inefficiency, the production of secondary particles due to interactions with the detector ma-terial and particle decays lead to a difference between the number of reconstructed tracklets and thetrue primary charged-particle multiplicity N ch (see details in Ref. [28]). Using events simulated with the4ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE CollaborationPYTHIA 8.2 event generator [29] (Monash 2013 tune, Ref. [30]), the correlation between the trackletmultiplicity (after the z vtx -correction), N corrtrk , and the generated primary charged particles N ch is deter-mined. The propagation of the simulated particles is done by GEANT 3 [31] with a full simulation of thedetector response, followed by the same reconstruction procedure as for real data. The correction factor β ( N corrtrk ) = N ch / N corrtrk to obtain the average d N ch / d η value corresponding to a given N corrtrk bin is com-puted from the N corrtrk – N ch correlation, shown in Fig. 2 for events simulated with PYTHIA 8.2 and particletransport through GEANT 3. As the generated charged-particle multiplicity in Monte Carlo differs fromdata, a corrected N ch distribution is constructed from the measured N corrtrk distribution using Bayesian un-folding. From it, the corrected β factors are obtained. A Monte Carlo closure test in PYTHIA 8.2 withunfolding based on EPOS-LHC events is used to validate the procedure. corrtrk N c h N
10 = 13 TeV s ALICE simulation pp
Fig. 2:
Correlation between the number of generated primary charged particles, N ch , and the number of recon-structed SPD tracklets, N corrtrk , in | η | <
1, from PYTHIA 8.2 simulated collisions with detector transport throughGEANT 3. The black points represent the mean values of N ch . The normalized charged-particle pseudorapidity density in each event class is calculated as:d N ch / d η (cid:104) d N ch / d η (cid:105) INEL > = β × (cid:104) N corrtrk (cid:105) ∆ η × (cid:104) d N ch / d η (cid:105) INEL > , (1)where (cid:104) N corrtrk (cid:105) is the averaged value of N corrtrk in each multiplicity class, corrected for the trigger and vertexfinding efficiencies. The former is estimated from Monte Carlo simulations and the latter with a datadriven approach. They are below unity only for the low-multiplicity events. The value corresponding toINEL > (cid:104) d N ch / d η (cid:105) INEL > , was cross-checked with the published ALICE measurement [28], andis found to be in very good agreement. A similar procedure is also used for the event selection based onthe V0 amplitude, measured as a sum of signals from charged particles in the intervals − . < η < − . . < η < .
1. The resulting values of the normalized multiplicity for the event classes consideredin the analysis are summarised in Table 2 alongside the respective fractions of the INEL > ψ signal extraction The J/ ψ meson is measured in the dielectron decay channel at midrapidity. Electrons and positrons arereconstructed in the central barrel detectors by requiring a minimum of 70 out of maximally 159 trackpoints in the TPC and a value of the track fit χ over the number of track points smaller than 4 [26].Only tracks with at least two associated hits in the ITS, and one of them in the two innermost layers,5ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration Table 2:
Average normalized charged-particle pseudorapidity density in | η | < N corrtrk measured in SPD ( | η | <
1; left part) and in V0 amplitude ( − . < η < − . . < η < .
1; right part).The values correspond to the data sample used for the p T -integrated analysis. Only systematic uncertainties areshown since the statistical ones are negligible. The corresponding fraction of the INEL > SPD selection V0 selection d N ch / d η (cid:104) d N ch / d η (cid:105) INEL > σ / σ INEL > N ch / d η (cid:104) d N ch / d η (cid:105) INEL > σ / σ INEL > . ± .
01 32% 0 . ± .
01 37%0 . ± .
01 25% 0 . ± .
01 26%1 . ± .
02 25% 1 . ± .
02 25%2 . ± .
03 11% 2 . ± .
03 9.0%2 . ± .
05 4.7% 3 . ± .
04 2.5%3 . ± .
06 1.8% 3 . ± .
06 0.5%4 . ± .
08 0.6% 4 . ± .
07 0.08%5 . ± .
09 0.2% 4 . ± .
08 0.01%6 . ± .
11 0.05%7 . ± .
12 0.02%are accepted. This requirement ensures both a good tracking resolution and the rejection of electronsand positrons produced from photons converting in the detector material. In the MB and HM triggeranalysis, a further veto on the tracks belonging to identified photon conversion topologies is applied.The electron identification is achieved by the measurement of the specific energy loss of the track in theTPC, which is required to be compatible with that expected for electrons within 3 standard deviations.Tracks with a specific energy loss being consistent with that of the pion or proton hypothesis within 3.5standard deviations are rejected. For the analysis of the EMCal-triggered events, the energy depositionof the track in the TPC is required to be in a range between − + ψ decay electrons is required tobe matched to a cluster in the EMCal, with a cluster energy above the trigger threshold and an energy-to-momentum ratio in the range 0 . < E / p < .
3. Electrons and positrons are selected in the pseudorapidityrange | η | < . p T > c .The number of reconstructed J/ ψ is obtained from the invariant mass distribution of all the opposite-sign (OS) pairs, which contains e + e − pairs from J/ ψ decays as well as combinatorics and other sources.In the MB and HM trigger analysis, the combinatorial background is estimated using a track rotationprocedure in which one of the tracks is rotated by a random azimuthal angle multiple times to obtain ahigh statistics invariant mass distribution. This distribution is then normalized such that its integral overa range of the invariant mass well above the J/ ψ mass peak matches the one of real OS pairs, and issubtracted from the latter distribution. The remaining residual background, which can be attributed tophysical sources, e.g. correlated semileptonic decays of heavy-quark pairs, is estimated using a second-order polynomial function. For the analysis of the EMCal-triggered events, a fit to the OS invariantmass distribution is performed using a MC shape for the signal added to a polynomial to describe thebackground. A second- or third-order polynomial function is used, depending on the p T range. Thenumber of J/ ψ is extracted by summing the dielectron yield in the background-subtracted invariant massdistribution in the mass interval 2 . < m ee < .
16 GeV/ c , which contains approximately 2/3 of thetotal reconstructed yield. The yield falling outside of the counting window at low invariant mass is dueto the electron bremsstrahlung in the detector material and to the radiative J/ ψ decay, and is corrected forusing Monte Carlo simulations. Also, a correction for the yield loss due to the limited trigger and vertexfinding efficiencies at low multiplicities is applied. 6ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE CollaborationDue to the trigger enhancement, the yields obtained using the EMCal-triggered events were correctedby the trigger scaling factor, which is observed to be identical for all event classes. This correction isnecessary to convert the yield per EMCal-triggered events into a yield per MB-triggered event and isaccomplished by a data-driven method using the ratio of the cluster energy distribution in triggered datadivided by the cluster energy distribution in minimum bias data. The ratio flattens above the triggerthreshold and the scaling factor is then obtained by fitting a constant to the flat interval.In the top panels of Fig. 3 are shown the OS invariant mass distribution for MB events (left), a high mul-tiplicity interval from the HM- (middle) and EMCal-triggered events (right), together with the estimatedbackground distribution. The combinatorial background distribution from the track rotation method isshown in the left and middle panels with the blue lines, while the total background is shown as blacksquares in all the panels. The signal obtained after background subtraction is described well by the signalshape obtained from Monte Carlo simulations (discussed below); these MC templates have been scaledand overlaid on the data points in the bottom panels of Fig. 3. ) m (GeV/c c C oun t s pe r M e V / | < 0.9 y = 13 TeV | s ALICE pp integrated T p MB triggers DataBackgroundComb. bg. ) c (GeV/ - e + e m – : 2479 y J/ N – : 1.11 S/B – Signif.: 36.1 SignalMC template ) m (GeV/c c C oun t s pe r M e V / | < 0.9 y = 13 TeV | s ALICE pp integrated T p MB and HM triggers < 100 corrtrk N £
80 DataBackgroundComb. bg. ) c (GeV/ - e + e m - – : 605 y J/ N – : 0.28 S/B – Signif.: 11.5 SignalMC template ) (GeV/c ee M c C oun t s pe r M e V / y = 13 TeV | s ALICE pp c < 15 GeV/ T p corrtrk N £
40 DataBackground ) c (GeV/ - e + e m - – : 280 y J/ N – : 0.85 S/B – Signif.: 11.3 SignalMC template
Fig. 3:
Top: Invariant mass distribution of electron-positron pairs for MB (left), HM (middle) and EMCal (right)triggers, together with combinatorial background estimation from the track-rotation method (blue lines in theleft and middle panels) and the full background estimation (black squares). In the lower panels, the J/ ψ signalobtained after background subtraction is shown together with the J/ ψ signal shape from Monte Carlo simulations.The entries contain a correction for the relative efficiency (see text). The J/ ψ measurement is performed integrated in transverse momentum and in the p T intervals 0 < p T < c and 4 < p T < c , using the MB and HM triggers. At higher p T , the J/ ψ mesons arereconstructed using the EMCal triggered events in the transverse momentum intervals 8 < p T < c and 15 < p T <
40 GeV/ c . It was checked that the acceptance and efficiency for J/ ψ reconstructionare not dependent on the event multiplicity. This was performed using pp collisions simulated with thePYTHIA 8.2 event generator with an injected J/ ψ signal. The dielectron decay is simulated with theEvtGen package [32] using PHOTOS [33] to describe the final-state radiation. The J/ ψ mesons areassumed to be unpolarised consistent with measurements in pp collisions at the LHC [34].To account for the multiplicity dependence of the p T spectrum of the J/ ψ mesons, a correction for therelative efficiency, namely the efficiency for a given p T value relative to the p T -integrated value, is appliedto each dielectron pair. This is contained in the invariant mass distributions shown in Fig. 3. The systematic uncertainty on the normalized multiplicity contains contri-butions from the trigger, vertex finding, and SPD efficiencies. The first two contributions are estimated7ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaborationusing alternative approaches: the trigger efficiency is calculated in a data-driven way, and for the vertexfinding efficiency Monte Carlo simulations are used. The differences to the values obtained with thedefault methods are taken as the systematic uncertainties. The contribution from the vertex finding effi-ciency is below 1% (relative uncertainty) in all event classes, the one from the trigger efficiency reachesa maximum value of 1.3% for the lowest multiplicity class.In order to estimate uncertainties due to the SPD tracklet reconstruction efficiency, the number of cor-rected tracklets is scaled up and down by 3%, which is the maximum observed discrepancy of the averagenumber of SPD tracklets between data and Monte Carlo simulations. This uncertainty amounts to 3.6%in the lowest multiplicity class, and to less than 1.5% in all other classes. The uncertainty from the un-folding of the charged-particle multiplicity distribution is estimated by varying the number of iterationsused in the Bayesian unfolding, as well as by using an alternative unfolding method [35]. The uncertaintyis found to be negligible. All the aforementioned uncertainty sources are added in quadrature, leadingto a total uncertainty on the normalized multiplicity of 3.7% for the lowest multiplicity class, and to lessthan 2% for all other classes. Normalized J/ ψ yield: The systematic uncertainties of the normalized J/ ψ yield are due to the signalextraction, bin-flow caused by the Poissonian smearing applied for the z vtx -dependent correction of theSPD acceptance and vertex finding, trigger and SPD efficiencies. For the analysis of the EMCal-triggeredevents, there is an additional component due to the matching of tracks to EMCal clusters and the electronidentification via the E / p measurement, which has a non-negligible multiplicity dependence. The E / p interval and the value of E used to select only electrons above the EMCal trigger threshold are variedto determine the systematic uncertainty of the electron identification with the EMCal, leading to valuesfrom 1% to 12%, depending on the multiplicity bin.The uncertainty of the J/ ψ signal extraction is determined by varying the functions used to fit the back-ground (first- or second-degree polynomials or exponential) and the fitting ranges, with the RMS of thedistribution of normalized yields obtained from these variations being taken as a systematic uncertainty(the normalized yield corresponds to the default selection). The bin-flow effect is estimated from theRMS of the results obtained by repeating the analysis several times with different seeds for the randomnumber generator. The uncertainties from the signal extraction and the bin-flow effect are the dominantones. They are of comparable size, with values between 1% and 8% depending on the multiplicity and p T interval. The uncertainties of the vertex finding, trigger and SPD tracklet efficiencies affect the esti-mated number of INEL > ψ yield (cid:104) d N J/ ψ / d y (cid:105) ,as well as the J/ ψ yield in the low multiplicity classes. The uncertainties of the vertex finding and SPDefficiencies are below 1% in most classes, while the uncertainty due to the trigger efficiency reaches upto 4%, depending on the multiplicity class.All the mentioned sources are added in quadrature to obtain the total systematic uncertainty, which, forthe p T -integrated results, varies between 3% and 7% with the multiplicity class. For the selected p T intervals, the uncertainties are larger, varying between 3% and 10% with multiplicity and p T interval,mainly due to the signal extraction, which is affected by statistical fluctuations of the background. Theresults at high p T , employing the EMCal, have uncertainties up to 13%, which are larger because of theadditional selection requirements on the track-cluster matching and the EMCal electron identificationselections. The top panel of Fig. 4 shows the normalized J/ ψ yield as a function of the normalized charged-particlepseudorapidity density at midrapidity, d N ch / d η / (cid:104) d N ch / d η (cid:105) . The dashed line also shown in the figure isa linear function with the slope of unity. 8ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d y = x = 13 TeV s ALICE pp integrated T p | < 0.9, y , | y Inclusive J/SPD event selectionV0 event selection |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d æ h / d c h N d Æ h / d c h N d / æ y / d y J / N d Æ y / d y J / N d Fig. 4:
Normalized inclusive p T -integrated J/ ψ yield at midrapidity as a function of normalized charged-particlepseudorapidity density at midrapidity ( | η | <
1) with the event selection based on SPD tracklets at midrapidity andon V0 amplitude at forward rapidity in pp collisions at √ s =
13 TeV. Top: normalized J/ ψ yield (diagonal drawnfor reference). Bottom: double ratio of the normalized J/ ψ yield and multiplicity. The error bars show statisticaluncertainties and the boxes systematic uncertainties. These results include both the MB and HM triggered events, which allow for a coverage of up to 7times the average charged-particle multiplicity, when events are selected based on the measured midra-pidity multiplicity. This is a significant extension with respect to our previous results in pp collisions at √ s = (cid:104) d N ch / d η (cid:105) . The results for thetwo event selection methods are in very good agreement. In both cases, the normalized J/ ψ yield growssignificantly faster than linear with the normalized multiplicity.Included in Fig. 4 is also the double ratio of the normalized J/ ψ yield to the normalized multiplicity(bottom panel). Two regimes could be identified, with a stronger increase of the double ratio for eventswith small multiplicity and a weaker increase for high-multiplicity events. It is noted that the “energycost” for the production of a J/ ψ meson, characterized by a transverse mass m T = (cid:113) m / ψ + p / c (cid:39) c , is similar to the one for particle production per unit rapidity of the underlying MB event,estimated as (cid:104) d N ch / d η (cid:105) ·(cid:104) p T (cid:105) . A linear (diagonal) correlation with multiplicity is then expected to firstorder and observed in PYTHIA 8.2 simulations [17]. As seen in Fig. 4, the data exhibit richer featuresthan this baseline expectation.The data in intervals of p T of the J/ ψ meson are shown in Fig. 5. The data exhibit a significant increaseof the normalized J/ ψ yield with the normalized multiplicity between the J/ ψ p T intervals 0–4 and 4–8 GeV/ c . This effect could be attributed to various contributions [17], like associated J/ ψ productionwith other hadrons in jet fragmentation or from beauty-quark fragmentation, as the fraction of J/ ψ fromb-hadron decays increases with p T [36]. 9ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d y = x = 13 TeV s ALICE pp | < 0.9 y , | y Inclusive J/SPD event selection c < 40 GeV/ T p
15 < c < 15 GeV/ T p c < 8 GeV/ T p c < 4 GeV/ T p |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d æ h / d c h N d Æ h / d c h N d / æ y / d y J / N d Æ y / d y J / N d |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d y = x = 13 TeV s ALICE pp | < 0.9 y , | y Inclusive J/V0 event selection c < 40 GeV/ T p
15 < c < 15 GeV/ T p c < 8 GeV/ T p c < 4 GeV/ T p |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d æ h / d c h N d Æ h / d c h N d / æ y / d y J / N d Æ y / d y J / N d Fig. 5:
Normalized inclusive J/ ψ yield at midrapidity as a function of normalized charged-particle multiplicityin pp collisions at √ s =
13 TeV, for different ranges of p T of the J/ ψ meson. Left: event selection based onmultiplicity at midrapidity. Right: event selection based on multiplicity at forward rapidity. The error bars showstatistical uncertainties and the boxes systematic uncertainties. Measurements of the correlation with the event multiplicity for inclusive charged-particle productionhave identified similar trends [10] as for the J/ ψ p T dependence. The strength of this correlation is similarfor J/ ψ and for inclusive charged particles (dominated by pions) for p T values giving a comparable m T value. The production of strange hyperons at midrapidity was also observed to exhibit a correlationwith event multiplicity in proportion to their mass [37]; a strong correlation was also measured for the ϒ mesons [6].The theoretical models currently available attribute the observed behavior to different underlying pro-cesses. In the PYTHIA 8.2 event generator [16], multiparton interactions (MPI) are an important factorin charm-quark production. Indeed, from MPIs alone a stronger than linear scaling is expected for open-charm production, as was demonstrated in Ref. [5] with PYTHIA 8.157. Taking into account all sourcesof heavy-quark production, however, a close to linear increase is predicted [17]. PYTHIA 8.2 reproduceswell the observation in data with a very similar correlation with multiplicity for the two different rapidityintervals used for multiplicity measurement, as seen in the left panel of Fig. 6, although the overall slopeof the trend is underestimated. To illustrate the effect of non-prompt J/ ψ in the inclusive production,in Fig. 6 the case of prompt J/ ψ meson production as predicted by PYTHIA 8.2 is shown in addition.A significant reduction of the correlation is observed, which appears to be stronger for the SPD eventselection case.In the EPOS3 event generator [14, 38], initial conditions are generated according to the parton-basedGribov-Regge formalism [39]. Sources of particle production in this framework are parton ladders,each composed of a pQCD hard process with initial- and final-state radiation. This model already pre-dicted the stronger than linear increase with multiplicity observed for open-charm mesons [5], origi-nating from a collective (hydrodynamical) evolution of the system. The predictions from EPOS3, herewithout the hydrodynamic component, are similar in magnitude to those from PYTHIA 8. In the perco-lation model [13], spatially extended color strings are the sources of particle production in high-energyhadronic collisions. In a high-density environment they overlap; such a decrease in the effective number10ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d y = x = 13 TeV s ALICE pp integrated T p | < 0.9, y , | y Inclusive J/SPD V0 DataPYTHIAPYTHIA, prompt 0 1 2 3 4 5 6 7 8 |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d y = x = 13 TeV s ALICE pp integrated T p | < 0.9, y , | y Inclusive J/SPD event selectionDataCPPEPOS3 (no hydro)3-Pomeron CGCPYTHIA 8.2PercolationCGC
Fig. 6:
Left: Comparison of data and PYTHIA 8.2 predictions for the two methods of event selection. ForPYTHIA 8.2, the case of prompt J/ ψ meson production is included for illustration. Right: comparison of data (withSPD event selection) with model predictions from the coherent particle production model [12], the percolationmodel [13], the EPOS3 event generator [14], the CGC model [15], the 3-Pomeron CGC model [18], and PYTHIA8.2 predictions. of strings leads to a reduction in particle production. Since the transverse size of a string is determinedby its transverse mass, lighter particles are affected in a stronger way than heavier ones. This resultsin a linear increase of heavy-particle production at low multiplicities, gradually changing to a quadraticone at high multiplicities. The coherent particle production (CPP) model [12, 40] employs phenomeno-logical parametrizations for light hadrons and J/ ψ derived from p–Pb collisions, and predicts a strongerthan linear relative increase of J/ ψ production with the normalized event multiplicity. In the Color GlassCondensate (CGC) approach, the NRQCD framework is employed for J/ ψ production. This effectivefield theory predicts, both for J/ ψ and D mesons, a relative increase with the normalized multiplicity thatis faster than linear, both for pp and p–Pb collisions [15]. In a CGC saturation model, a faster than lineartrend generically arises from the Bjorken- x dependent saturation scale which would suppress more thesoft-particle multiplicity, produced at low- x , compared to J/ ψ production which is sensitive to larger val-ues of x . In the 3-Pomeron fusion model [18], the correlation arises as J/ ψ production via 3-gluon fusionprocesses from various Pomeron configurations are considered. The larger configuration space for theparticular case of the overlapping rapidity interval for J/ ψ and charged particles leads to a significantlystronger correlation. Gluon saturation is implemented in this model; its effect, interestingly a reducedcorrelation, becomes significant for normalized multiplicities above 7.All models predict an increase which is faster than linear, as shown in the right panel of Fig.6. In all mod-els this is effectively the result of a ( N ch -dependent) reduction of the charged-particle multiplicity, real-ized through rather different physics mechanisms in the various approaches (color string reconnection orpercolation, gluon saturation, coherent particle production, 3-gluon fusion in gluon ladders/Pomerons).The PYTHIA 8.2 and EPOS3 models underpredict the data, while the percolation model slightly over-predicts them at high multiplicity; good agreement is seen for the CGC, the coherent particle production,and the 3-Pomeron models.The trend of stronger increase in the p T intervals above 4 GeV/ c seen in the data is qualitatively repro-duced by PYTHIA 8.2, EPOS3 and the coherent particle production model, as shown in Fig. 7. TheEPOS3 model, without the hydrodynamic component, underestimates the data, as does PYTHIA 8.2.It is worth noting that in all models except PYTHIA 8.2 only the prompt J/ ψ production is included,while the data contain the contribution from decays of beauty hadrons, which is p T -dependent and might11ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d s ALICE pp | < 0.9 y , | y Inclusive J/SPD event selection
Data PYTHIA ) c (GeV/ T p
15 .. 408 .. 154 .. 80 .. 4 |<1 h |INEL>0 æh /d ch N d Æ h /d ch N d I N E L > æ y / d y J / N d Æ y / d y J / N d s ALICE pp | < 0.9 y , | y Inclusive J/SPD event selection
Data EPOS CPP ) c (GeV/ T p
15 .. 408 .. 154 .. 80 .. 4
Fig. 7:
Normalized inclusive J/ ψ yield at midrapidity as a function of normalized charged-particle pseudorapiditydensity at midrapidity for different p T intervals; the data are compared to theoretical model predictions fromPYTHIA 8.2, EPOS3, and the coherent particle production model (CPP). also have a different dependency on multiplicity; the existing measurement of charm and beauty pro-duction [5] is not precise enough to be conclusive, but a study in PYTHIA 8.2 [17] showed that thefeed-down from beauty hadrons significantly influences the result. This is illustrated in Fig. 6, where forPYTHIA 8.2, the case of prompt J/ ψ meson production is included. We have presented a comprehensive measurement of inclusive production of J/ ψ mesons as a functionof the event multiplicity in pp collisions at √ s =
13 TeV performed with the ALICE apparatus. The J/ ψ production at midrapidity is studied using a data sample including minimum bias, high event activity, andEMCal triggered events. The event selection is performed based on the charged-particle measurementat midrapidity and in the forward region. The J/ ψ yield in a given multiplicity interval normalizedto the J/ ψ yield in INEL > ψ as a function of multiplicity is observedfor p T -integrated yields; this increase is stronger for high- p T J/ ψ mesons. The trends are qualitatively,and for some of the models quantitatively, reproduced by theoretical models, but a critical appraisal of thesimilarity or difference between the physics mechanisms at play in various models is yet to be performed.More stringent tests of the models are needed too. Disentangling the feed-down from beauty hadrons,not included in most of the current theoretical predictions, will be an important step towards sheddinglight on the mechanism of hadronization of charm (and beauty) quarks, in particular in the environmentof a high density of color strings created in high-multiplicity pp collisions. Data which will be collectedin Run 3 at the LHC will be a significant addition for such studies. Acknowledgements
We are grateful to E. Ferreiro, B. Kopeliovich, E. Levin, M. Siddikov, R. Venugopalan, K. Watanabe,and K. Werner for sending us the predictions of and clarifications about their models.12ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE CollaborationThe ALICE Collaboration would like to thank all its engineers and technicians for their invaluable con-tributions to the construction of the experiment and the CERN accelerator teams for the outstandingperformance of the LHC complex. The ALICE Collaboration gratefully acknowledges the resources andsupport provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG) collaboration.The ALICE Collaboration acknowledges the following funding agencies for their support in buildingand running the ALICE detector: A. I. Alikhanyan National Science Laboratory (Yerevan Physics In-stitute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS),Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M 2467-N36] and National-stiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and HighTechnologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de DesenvolvimentoCientífico e Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo àPesquisa do Estado de São Paulo (FAPESP) and Universidade Federal do Rio Grande do Sul (UFRGS),Brazil; Ministry of Education of China (MOEC) , Ministry of Science & Technology of China (MSTC)and National Natural Science Foundation of China (NSFC), China; Ministry of Science and Educationand Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear(CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, CzechRepublic; The Danish Council for Independent Research | Natural Sciences, the VILLUM FONDEN andDanish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland;Commissariat à l’Energie Atomique (CEA) and Institut National de Physique Nucléaire et de Physiquedes Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesmin-isterium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für SchwerionenforschungGmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Researchand Religions, Greece; National Research, Development and Innovation Office, Hungary; Departmentof Atomic Energy Government of India (DAE), Department of Science and Technology, Governmentof India (DST), University Grants Commission, Government of India (UGC) and Council of Scientificand Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; Centro Fermi - MuseoStorico della Fisica e Centro Studi e Ricerche Enrico Fermi and Istituto Nazionale di Fisica Nucleare(INFN), Italy; Institute for Innovative Science and Technology , Nagasaki Institute of Applied Science(IIST), Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Japan So-ciety for the Promotion of Science (JSPS) KAKENHI, Japan; Consejo Nacional de Ciencia (CONACYT)y Tecnología, through Fondo de Cooperación Internacional en Ciencia y Tecnología (FONCICYT) andDirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatievoor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway;Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pak-istan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education, NationalScience Centre and WUT ID-UB, Poland; Korea Institute of Science and Technology Information andNational Research Foundation of Korea (NRF), Republic of Korea; Ministry of Education and ScientificResearch, Institute of Atomic Physics and Ministry of Research and Innovation and Institute of AtomicPhysics, Romania; Joint Institute for Nuclear Research (JINR), Ministry of Education and Science ofthe Russian Federation, National Research Centre Kurchatov Institute, Russian Science Foundation andRussian Foundation for Basic Research, Russia; Ministry of Education, Science, Research and Sport ofthe Slovak Republic, Slovakia; National Research Foundation of South Africa, South Africa; SwedishResearch Council (VR) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organi-zation for Nuclear Research, Switzerland; Suranaree University of Technology (SUT), National Scienceand Technology Development Agency (NSDTA) and Office of the Higher Education Commission underNRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; National Academyof Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom;National Science Foundation of the United States of America (NSF) and United States Department ofEnergy, Office of Nuclear Physics (DOE NP), United States of America.13ultiplicity dependence of J/ ψ production at √ s = 13 TeV ALICE Collaboration References [1] J.-P. 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115 ,137 , M.C. Danisch ,A. Danu , D. Das , I. Das , P. Das , P. Das , S. Das , A. Dash , S. Dash , S. De , A. De Caro ,G. de Cataldo , J. de Cuveland , A. De Falco , D. De Gruttola , N. De Marco , S. De Pasquale ,S. Deb , H.F. Degenhardt , K.R. Deja , A. Deloff , S. Delsanto
25 ,131 , W. Deng , P. Dhankher , D. DiBari , A. Di Mauro , R.A. Diaz , T. Dietel , P. Dillenseger , Y. Ding , R. Divià , D.U. Dixit ,Ø. Djuvsland , U. Dmitrieva , A. Dobrin , B. Dönigus , O. Dordic , A.K. Dubey , A. Dubla
90 ,107 ,S. Dudi , M. Dukhishyam , P. Dupieux , R.J. Ehlers , V.N. Eikeland , D. Elia , B. Erazmus ,F. Erhardt , A. Erokhin , M.R. Ersdal , B. Espagnon , G. Eulisse , D. Evans , S. Evdokimov ,L. Fabbietti , M. Faggin , J. Faivre , F. Fan , A. Fantoni , M. Fasel , P. Fecchio , A. Feliciello ,G. Feofilov , A. Fernández Téllez , A. Ferrero , A. Ferretti , A. Festanti , V.J.G. Feuillard ,J. Figiel , S. Filchagin , D. Finogeev , F.M. Fionda , G. Fiorenza , F. Flor , A.N. Flores ,S. Foertsch , P. Foka , S. Fokin , E. Fragiacomo , U. Frankenfeld , U. Fuchs , C. Furget , A. Furs ,M. Fusco Girard , J.J. Gaardhøje , M. Gagliardi , A.M. Gago , A. Gal , C.D. Galvan , P. Ganoti ,C. Garabatos , J.R.A. Garcia , E. Garcia-Solis , K. Garg , C. Gargiulo , A. Garibli , K. Garner ,P. Gasik
105 ,107 , E.F. Gauger , M.B. Gay Ducati , M. Germain , J. Ghosh , P. Ghosh , S.K. Ghosh ,M. Giacalone , P. Gianotti , P. Giubellino
59 ,107 , P. Giubilato , A.M.C. Glaenzer , P. Glässel , A. GomezRamirez , V. Gonzalez
107 ,143 , L.H. González-Trueba , S. Gorbunov , L. Görlich , A. Goswami ,S. Gotovac , V. Grabski , L.K. Graczykowski , K.L. Graham , L. Greiner , A. Grelli , C. Grigoras ,V. Grigoriev , A. Grigoryan , S. Grigoryan , O.S. Groettvik , F. Grosa
30 ,59 , J.F. Grosse-Oetringhaus ,R. Grosso , R. Guernane , M. Guittiere , K. Gulbrandsen , T. Gunji , A. Gupta , R. Gupta ,I.B. Guzman , R. Haake , M.K. Habib , C. Hadjidakis , H. Hamagaki , G. Hamar , M. Hamid ,R. Hannigan , M.R. Haque
63 ,86 , A. Harlenderova , J.W. Harris , A. Harton , J.A. Hasenbichler ,H. Hassan , Q.U. Hassan , D. Hatzifotiadou
10 ,54 , P. Hauer , L.B. Havener , S. Hayashi ,S.T. Heckel , E. Hellbär , H. Helstrup , A. Herghelegiu , T. Herman , E.G. Hernandez , G. HerreraCorral , F. Herrmann , K.F. Hetland , H. Hillemanns , C. Hills , B. Hippolyte , B. Hohlweger , ψ production at √ s = 13 TeV ALICE Collaboration J. Honermann , D. Horak , A. Hornung , S. Hornung , R. Hosokawa
15 ,133 , P. Hristov , C. Huang ,C. Hughes , P. Huhn , T.J. Humanic , H. Hushnud , L.A. Husova , N. Hussain , S.A. Hussain ,D. Hutter , J.P. Iddon
34 ,127 , R. Ilkaev , H. Ilyas , M. Inaba , G.M. Innocenti , M. Ippolitov ,A. Isakov , M.S. Islam , M. Ivanov , V. Ivanov , V. Izucheev , B. Jacak , N. Jacazio
34 ,54 ,P.M. Jacobs , S. Jadlovska , J. Jadlovsky , S. Jaelani , C. Jahnke , M.J. Jakubowska ,M.A. Janik , T. Janson , M. Jercic , O. Jevons , M. Jin , F. Jonas
96 ,144 , P.G. Jones , J. Jung ,M. Jung , A. Jusko , P. Kalinak , A. Kalweit , V. Kaplin , S. Kar , A. Karasu Uysal , D. Karatovic ,O. Karavichev , T. Karavicheva , P. Karczmarczyk , E. Karpechev , A. Kazantsev , U. Kebschull ,R. Keidel , M. Keil , B. Ketzer , Z. Khabanova , A.M. Khan , S. Khan , A. Khanzadeev ,Y. Kharlov , A. Khatun , A. Khuntia , B. Kileng , B. Kim , B. Kim , D. Kim , D.J. Kim ,E.J. Kim , H. Kim , J. Kim , J.S. Kim , J. Kim , J. Kim , J. Kim , M. Kim , S. Kim ,T. Kim , T. Kim , S. Kirsch , I. Kisel , S. Kiselev , A. Kisiel , J.L. Klay , C. Klein , J. Klein
34 ,59 ,S. Klein , C. Klein-Bösing , M. Kleiner , A. Kluge , M.L. Knichel , A.G. Knospe , C. Kobdaj ,M.K. Köhler , T. Kollegger , A. Kondratyev , N. Kondratyeva , E. Kondratyuk , J. Konig ,S.A. Konigstorfer , P.J. Konopka , G. Kornakov , L. Koska , O. Kovalenko , V. Kovalenko ,M. Kowalski , I. Králik , A. Kravˇcáková , L. Kreis , M. Krivda
64 ,111 , F. Krizek ,K. Krizkova Gajdosova , M. Krüger , E. Kryshen , M. Krzewicki , A.M. Kubera , V. Kuˇcera
34 ,61 ,C. Kuhn , P.G. Kuijer , L. Kumar , S. Kundu , P. Kurashvili , A. Kurepin , A.B. Kurepin ,A. Kuryakin , S. Kushpil , J. Kvapil , M.J. Kweon , J.Y. Kwon , Y. Kwon , S.L. La Pointe , P. LaRocca , Y.S. Lai , M. Lamanna , R. Langoy , K. Lapidus , A. Lardeux , P. Larionov , E. Laudi ,R. Lavicka , T. Lazareva , R. Lea , L. Leardini , J. Lee , S. Lee , S. Lehner , J. Lehrbach ,R.C. Lemmon , I. León Monzón , E.D. Lesser , M. Lettrich , P. Lévai , X. Li , X.L. Li , J. Lien ,R. Lietava , B. Lim , V. Lindenstruth , A. Lindner , C. Lippmann , M.A. Lisa , A. Liu , J. Liu ,S. Liu , W.J. Llope , I.M. Lofnes , V. Loginov , C. Loizides , P. Loncar , J.A. Lopez , X. Lopez ,E. López Torres , J.R. Luhder , M. Lunardon , G. Luparello , Y.G. Ma , A. Maevskaya , M. Mager ,S.M. Mahmood , T. Mahmoud , A. Maire , R.D. Majka
146 ,i , M. Malaev , Q.W. Malik , L. Malinina
75 ,iv ,D. Mal’Kevich , P. Malzacher , G. Mandaglio
32 ,56 , V. Manko , F. Manso , V. Manzari , Y. Mao ,M. Marchisone , J. Mareš , G.V. Margagliotti , A. Margotti , A. Marín , C. Markert ,M. Marquard , C.D. Martin , N.A. Martin , P. Martinengo , J.L. Martinez , M.I. Martínez ,G. Martínez García , S. Masciocchi , M. Masera , A. Masoni , L. Massacrier , E. Masson ,A. Mastroserio
53 ,138 , A.M. Mathis , O. Matonoha , P.F.T. Matuoka , A. Matyja , C. Mayer ,F. Mazzaschi , M. Mazzilli , M.A. Mazzoni , A.F. Mechler , F. Meddi , Y. Melikyan
62 ,93 ,A. Menchaca-Rocha , C. Mengke , E. Meninno
29 ,114 , A.S. Menon , M. Meres , S. Mhlanga ,Y. Miake , L. Micheletti , L.C. Migliorin , D.L. Mihaylov , K. Mikhaylov
75 ,92 , A.N. Mishra ,D. Mi´skowiec , A. Modak , N. Mohammadi , A.P. Mohanty , B. Mohanty , M. Mohisin Khan
16 ,v ,Z. Moravcova , C. Mordasini , D.A. Moreira De Godoy , L.A.P. Moreno , I. Morozov , A. Morsch ,T. Mrnjavac , V. Muccifora , E. Mudnic , D. Mühlheim , S. Muhuri , J.D. Mulligan , A. Mulliri
23 ,55 ,M.G. Munhoz , R.H. Munzer , H. Murakami , S. Murray , L. Musa , J. Musinsky , C.J. Myers ,J.W. Myrcha , B. Naik , R. Nair , B.K. Nandi , R. Nania
10 ,54 , E. Nappi , M.U. Naru ,A.F. Nassirpour , C. Nattrass , R. Nayak , T.K. Nayak , S. Nazarenko , A. Neagu , R.A. Negrao DeOliveira , L. Nellen , S.V. Nesbo , G. Neskovic , D. Nesterov , L.T. Neumann , B.S. Nielsen ,S. Nikolaev , S. Nikulin , V. Nikulin , F. Noferini
10 ,54 , P. Nomokonov , J. Norman
79 ,127 , N. Novitzky ,P. Nowakowski , A. Nyanin , J. Nystrand , M. Ogino , A. Ohlson
81 ,104 , J. Oleniacz , A.C. Oliveira DaSilva , M.H. Oliver , C. Oppedisano , A. Ortiz Velasquez , A. Oskarsson , J. Otwinowski ,K. Oyama , Y. Pachmayer , V. Pacik , S. Padhan , D. Pagano , G. Pai´c , J. Pan , S. Panebianco ,P. Pareek
50 ,141 , J. Park , J.E. Parkkila , S. Parmar , S.P. Pathak , B. Paul , J. Pazzini , H. Pei ,T. Peitzmann , X. Peng , L.G. Pereira , H. Pereira Da Costa , D. Peresunko , G.M. Perez , S. Perrin ,Y. Pestov , V. Petráˇcek , M. Petrovici , R.P. Pezzi , S. Piano , M. Pikna , P. Pillot , O. Pinazza
34 ,54 ,L. Pinsky , C. Pinto , S. Pisano
10 ,52 , D. Pistone , M. Płosko´n , M. Planinic , F. Pliquett ,M.G. Poghosyan , B. Polichtchouk , N. Poljak , A. Pop , S. Porteboeuf-Houssais , V. Pozdniakov ,S.K. Prasad , R. Preghenella , F. Prino , C.A. Pruneau , I. Pshenichnov , M. Puccio , J. Putschke ,S. Qiu , L. Quaglia , R.E. Quishpe , S. Ragoni , S. Raha , S. Rajput , J. Rak ,A. Rakotozafindrabe , L. Ramello , F. Rami , S.A.R. Ramirez , R. Raniwala , S. Raniwala ,S.S. Räsänen , R. Rath , V. Ratza , I. Ravasenga , K.F. Read
96 ,130 , A.R. Redelbach , K. Redlich
85 ,vi ,A. Rehman , P. Reichelt , F. Reidt , X. Ren , R. Renfordt , Z. Rescakova , K. Reygers , A. Riabov ,V. Riabov , T. Richert
81 ,89 , M. Richter , P. Riedler , W. Riegler , F. Riggi , C. Ristea , S.P. Rode , ψ production at √ s = 13 TeV ALICE Collaboration M. Rodríguez Cahuantzi , K. Røed , R. Rogalev , E. Rogochaya , D. Rohr , D. Röhrich , P.F. Rojas ,P.S. Rokita , F. Ronchetti , A. Rosano , E.D. Rosas , K. Roslon , A. Rossi
28 ,57 , A. Rotondi ,A. Roy , P. Roy , O.V. Rueda , R. Rui , B. Rumyantsev , A. Rustamov , E. Ryabinkin , Y. Ryabov ,A. Rybicki , H. Rytkonen , O.A.M. Saarimaki , R. Sadek , S. Sadhu , S. Sadovsky , K. Šafaˇrík ,S.K. Saha , B. Sahoo , P. Sahoo , R. Sahoo , S. Sahoo , P.K. Sahu , J. Saini , S. Sakai ,S. Sambyal , V. Samsonov
93 ,98 , D. Sarkar , N. Sarkar , P. Sarma , V.M. Sarti , M.H.P. Sas ,E. Scapparone , J. Schambach , H.S. Scheid , C. Schiaua , R. Schicker , A. Schmah , C. Schmidt ,H.R. Schmidt , M.O. Schmidt , M. Schmidt , N.V. Schmidt
68 ,96 , A.R. Schmier , J. Schukraft ,Y. Schutz , K. Schwarz , K. Schweda , G. Scioli , E. Scomparin , J.E. Seger , Y. Sekiguchi ,D. Sekihata , I. Selyuzhenkov
93 ,107 , S. Senyukov , D. Serebryakov , A. Sevcenco , A. Shabanov ,A. Shabetai , R. Shahoyan , W. Shaikh , A. Shangaraev , A. Sharma , A. Sharma , H. Sharma ,M. Sharma , N. Sharma , S. Sharma , O. Sheibani , K. Shigaki , M. Shimomura , S. Shirinkin ,Q. Shou , Y. Sibiriak , S. Siddhanta , T. Siemiarczuk , D. Silvermyr , G. Simatovic , G. Simonetti ,B. Singh , R. Singh , R. Singh , R. Singh , V.K. Singh , V. Singhal , T. Sinha , B. Sitar ,M. Sitta , T.B. Skaali , M. Slupecki , N. Smirnov , R.J.M. Snellings , C. Soncco , J. Song ,A. Songmoolnak , F. Soramel , S. Sorensen , I. Sputowska , J. Stachel , I. Stan , P.J. Steffanic ,E. Stenlund , S.F. Stiefelmaier , D. Stocco , M.M. Storetvedt , L.D. Stritto , A.A.P. Suaide ,T. Sugitate , C. Suire , M. Suleymanov , M. Suljic , R. Sultanov , M. Šumbera , V. Sumberia ,S. Sumowidagdo , S. Swain , A. Szabo , I. Szarka , U. Tabassam , S.F. Taghavi , G. Taillepied ,J. Takahashi , G.J. Tambave , S. Tang , M. Tarhini , M.G. Tarzila , A. Tauro , G. Tejeda Muñoz ,A. Telesca , L. Terlizzi , C. Terrevoli , D. Thakur , S. Thakur , D. Thomas , F. Thoresen ,R. Tieulent , A. Tikhonov , A.R. Timmins , A. Toia , N. Topilskaya , M. Toppi , F. Torales-Acosta ,S.R. Torres , A. Trifiró
32 ,56 , S. Tripathy
50 ,69 , T. Tripathy , S. Trogolo , G. Trombetta , L. Tropp ,V. Trubnikov , W.H. Trzaska , T.P. Trzcinski , B.A. Trzeciak
37 ,63 , A. Tumkin , R. Turrisi ,T.S. Tveter , K. Ullaland , E.N. Umaka , A. Uras , G.L. Usai , M. Vala , N. Valle , S. Vallero ,N. van der Kolk , L.V.R. van Doremalen , M. van Leeuwen , P. Vande Vyvre , D. Varga , Z. Varga ,M. Varga-Kofarago , A. Vargas , M. Vasileiou , A. Vasiliev , O. Vázquez Doce , V. Vechernin ,E. Vercellin , S. Vergara Limón , L. Vermunt , R. Vernet , R. Vértesi , L. Vickovic , Z. Vilakazi ,O. Villalobos Baillie , G. Vino , A. Vinogradov , T. Virgili , V. Vislavicius , A. Vodopyanov ,B. Volkel , M.A. Völkl , K. Voloshin , S.A. Voloshin , G. Volpe , B. von Haller , I. Vorobyev ,D. Voscek , J. Vrláková , B. Wagner , M. Weber , S.G. Weber , A. Wegrzynek , S.C. Wenzel ,J.P. Wessels , J. Wiechula , J. Wikne , G. Wilk , J. Wilkinson
10 ,54 , G.A. Willems , E. Willsher ,B. Windelband , M. Winn , W.E. Witt , J.R. Wright , Y. Wu , R. Xu , S. Yalcin , Y. Yamaguchi ,K. Yamakawa , S. Yang , S. Yano , Z. Yin , H. Yokoyama , I.-K. Yoo , J.H. Yoon , S. Yuan ,A. Yuncu , V. Yurchenko , V. Zaccolo , A. Zaman , C. Zampolli , H.J.C. Zanoli , N. Zardoshti ,A. Zarochentsev , P. Závada , N. Zaviyalov , H. Zbroszczyk , M. Zhalov , S. Zhang , X. Zhang ,Z. Zhang , V. Zherebchevskii , Y. Zhi , D. Zhou , Y. Zhou , Z. Zhou , J. Zhu , Y. Zhu ,A. Zichichi
10 ,26 , G. Zinovjev , N. Zurlo , Affiliation notes i Deceased ii Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA),Bologna, Italy iii
Dipartimento DET del Politecnico di Torino, Turin, Italy iv M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute of Nuclear, Physics, Moscow, Russia v Department of Applied Physics, Aligarh Muslim University, Aligarh, India vi Institute of Theoretical Physics, University of Wroclaw, Poland
Collaboration Institutes A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, Yerevan, Armenia Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine Bose Institute, Department of Physics and Centre for Astroparticle Physics and Space Science (CAPSS),Kolkata, India Budker Institute for Nuclear Physics, Novosibirsk, Russia California Polytechnic State University, San Luis Obispo, California, United States ψ production at √ s = 13 TeV ALICE Collaboration Central China Normal University, Wuhan, China Centre de Calcul de l’IN2P3, Villeurbanne, Lyon, France Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi’, Rome, Italy Chicago State University, Chicago, Illinois, United States China Institute of Atomic Energy, Beijing, China Comenius University Bratislava, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia COMSATS University Islamabad, Islamabad, Pakistan Creighton University, Omaha, Nebraska, United States Department of Physics, Aligarh Muslim University, Aligarh, India Department of Physics, Pusan National University, Pusan, Republic of Korea Department of Physics, Sejong University, Seoul, Republic of Korea Department of Physics, University of California, Berkeley, California, United States Department of Physics, University of Oslo, Oslo, Norway Department of Physics and Technology, University of Bergen, Bergen, Norway Dipartimento di Fisica dell’Università ’La Sapienza’ and Sezione INFN, Rome, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Bologna, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Catania, Italy Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Padova, Italy Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo Collegato INFN, Salerno, Italy Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy Dipartimento di Scienze e Innovazione Tecnologica dell’Università del Piemonte Orientale and INFNSezione di Torino, Alessandria, Italy Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy European Organization for Nuclear Research (CERN), Geneva, Switzerland Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split,Split, Croatia Faculty of Engineering and Science, Western Norway University of Applied Sciences, Bergen, Norway Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague,Czech Republic Faculty of Science, P.J. Šafárik University, Košice, Slovakia Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt,Germany Fudan University, Shanghai, China Gangneung-Wonju National University, Gangneung, Republic of Korea Gauhati University, Department of Physics, Guwahati, India Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn,Germany Helsinki Institute of Physics (HIP), Helsinki, Finland High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico Hiroshima University, Hiroshima, Japan Hochschule Worms, Zentrum für Technologietransfer und Telekommunikation (ZTT), Worms, Germany Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania Indian Institute of Technology Bombay (IIT), Mumbai, India Indian Institute of Technology Indore, Indore, India Indonesian Institute of Sciences, Jakarta, Indonesia INFN, Laboratori Nazionali di Frascati, Frascati, Italy INFN, Sezione di Bari, Bari, Italy INFN, Sezione di Bologna, Bologna, Italy INFN, Sezione di Cagliari, Cagliari, Italy INFN, Sezione di Catania, Catania, Italy ψ production at √ s = 13 TeV ALICE Collaboration INFN, Sezione di Padova, Padova, Italy INFN, Sezione di Roma, Rome, Italy INFN, Sezione di Torino, Turin, Italy INFN, Sezione di Trieste, Trieste, Italy Inha University, Incheon, Republic of Korea Institute for Nuclear Research, Academy of Sciences, Moscow, Russia Institute for Subatomic Physics, Utrecht University/Nikhef, Utrecht, Netherlands Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovakia Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic Institute of Space Science (ISS), Bucharest, Romania Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City, Mexico Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil Instituto de Física, Universidad Nacional Autónoma de México, Mexico City, Mexico iThemba LABS, National Research Foundation, Somerset West, South Africa Jeonbuk National University, Jeonju, Republic of Korea Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik, Fachbereich Informatik undMathematik, Frankfurt, Germany Joint Institute for Nuclear Research (JINR), Dubna, Russia Korea Institute of Science and Technology Information, Daejeon, Republic of Korea KTO Karatay University, Konya, Turkey Laboratoire de Physique des 2 Infinis, Irène Joliot-Curie, Orsay, France Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes, CNRS-IN2P3,Grenoble, France Lawrence Berkeley National Laboratory, Berkeley, California, United States Lund University Department of Physics, Division of Particle Physics, Lund, Sweden Nagasaki Institute of Applied Science, Nagasaki, Japan Nara Women’s University (NWU), Nara, Japan National and Kapodistrian University of Athens, School of Science, Department of Physics , Athens,Greece National Centre for Nuclear Research, Warsaw, Poland National Institute of Science Education and Research, Homi Bhabha National Institute, Jatni, India National Nuclear Research Center, Baku, Azerbaijan National Research Centre Kurchatov Institute, Moscow, Russia Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark Nikhef, National institute for subatomic physics, Amsterdam, Netherlands NRC Kurchatov Institute IHEP, Protvino, Russia NRC «Kurchatov» Institute - ITEP, Moscow, Russia NRNU Moscow Engineering Physics Institute, Moscow, Russia Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom Nuclear Physics Institute of the Czech Academy of Sciences, ˇRež u Prahy, Czech Republic Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States Ohio State University, Columbus, Ohio, United States Petersburg Nuclear Physics Institute, Gatchina, Russia Physics department, Faculty of science, University of Zagreb, Zagreb, Croatia
Physics Department, Panjab University, Chandigarh, India
Physics Department, University of Jammu, Jammu, India
Physics Department, University of Rajasthan, Jaipur, India
Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen, Germany
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
Physik Department, Technische Universität München, Munich, Germany
Politecnico di Bari, Bari, Italy
Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum fürSchwerionenforschung GmbH, Darmstadt, Germany
Rudjer Boškovi´c Institute, Zagreb, Croatia ψ production at √ s = 13 TeV ALICE Collaboration Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom
Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú, Lima, Peru
St. Petersburg State University, St. Petersburg, Russia
Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
SUBATECH, IMT Atlantique, Université de Nantes, CNRS-IN2P3, Nantes, France
Suranaree University of Technology, Nakhon Ratchasima, Thailand
Technical University of Košice, Košice, Slovakia
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
The University of Texas at Austin, Austin, Texas, United States
Universidad Autónoma de Sinaloa, Culiacán, Mexico
Universidade de São Paulo (USP), São Paulo, Brazil
Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
Universidade Federal do ABC, Santo Andre, Brazil
University of Cape Town, Cape Town, South Africa
University of Houston, Houston, Texas, United States
University of Jyväskylä, Jyväskylä, Finland
University of Liverpool, Liverpool, United Kingdom
University of Science and Technology of China, Hefei, China
University of South-Eastern Norway, Tonsberg, Norway
University of Tennessee, Knoxville, Tennessee, United States
University of the Witwatersrand, Johannesburg, South Africa
University of Tokyo, Tokyo, Japan
University of Tsukuba, Tsukuba, Japan
Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
Université de Lyon, Université Lyon 1, CNRS/IN2P3, IPN-Lyon, Villeurbanne, Lyon, France
Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France, Strasbourg, France
Université Paris-Saclay Centre d’Etudes de Saclay (CEA), IRFU, Départment de Physique Nucléaire(DPhN), Saclay, France
Università degli Studi di Foggia, Foggia, Italy
Università degli Studi di Pavia, Pavia, Italy
Università di Brescia, Brescia, Italy
Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata, India
Warsaw University of Technology, Warsaw, Poland
Wayne State University, Detroit, Michigan, United States
Westfälische Wilhelms-Universität Münster, Institut für Kernphysik, Münster, Germany
Wigner Research Centre for Physics, Budapest, Hungary
Yale University, New Haven, Connecticut, United States