Coherent \rm{J/ψ} and \rm{ψ'} photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at \sqrt{s_{\mathrm{NN}}}~=~5.02 TeV
EEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN-EP-2021-0025 January 2021© 2021 CERN for the benefit of the ALICE Collaboration.Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 license.
Coherent J / ψ and ψ (cid:48) photoproduction at midrapidity in ultra-peripheralPb–Pb collisions at √ s NN = . TeV
ALICE Collaboration * Abstract
The coherent photoproduction of J / ψ and ψ (cid:48) mesons was measured in ultra-peripheral Pb–Pb colli-sions at a center-of-mass energy √ s NN = .
02 TeV with the ALICE detector. Charmonia are detectedin the central rapidity region for events where the hadronic interactions are strongly suppressed. TheJ / ψ is reconstructed using the dilepton ( l + l − ) and proton-antiproton decay channels, while for the ψ (cid:48) the dilepton and the l + l − π + π − decay channels are studied. The analysis is based on an eventsample corresponding to an integrated luminosity of about 233 µ b − . The results are compared withtheoretical models for coherent J / ψ and ψ (cid:48) photoproduction. The coherent cross section is found tobe in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.65at a Bjorken- x of around 6 × − , such as the EPS09 parametrization, however none of the modelsis able to fully describe the rapidity dependence of the coherent J / ψ cross section including ALICEmeasurements at forward rapidity. The ratio of ψ (cid:48) to J / ψ coherent photoproduction cross sectionswas also measured and found to be consistent with the one for photoproduction off protons. * See Appendix A for the list of collaboration members a r X i v : . [ nu c l - e x ] J a n oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration Photonuclear reactions can be studied in ultra-peripheral collisions (UPCs) of heavy ions where the twonuclei pass by with an impact parameter larger than the sum of their radii. Hadronic interactions aresuppressed and electromagnetic interactions are mediated by photons of small virtualities. The intensityof the photon flux is growing with the squared nuclear charge of the colliding ion resulting in largecross sections for the photoproduction of vector mesons in heavy-ion collisions. The photoproductionprocess has a clear experimental signature: the decay products of vector mesons are the only signal in anotherwise empty detector.The physics of vector meson photoproduction is described in [1–4]. Photoproduction of vector mesonsin ion collisions can either be coherent, i.e. the photon interacts consistently with all nucleons in a nu-cleus, or incoherent, i.e. the photon interacts with a single nucleon. Experimentally, one can distinguishbetween these two production types through the typical transverse momentum of the produced vectormesons, which is inversely proportional to the transverse size of the target. While the coherent photopro-duction is characterized by the production of mesons with low transverse momentum ( (cid:104) p T (cid:105) ∼
60 MeV/ c ),the incoherent is dominated by mesons with higher values ( (cid:104) p T (cid:105) ∼
500 MeV/ c ). In the first case, the nu-clei usually do not dissociate, but the electromagnetic fields of ultrarelativistic heavy nuclei are strongenough to develop other independent soft electromagnetic interactions accompanying the coherent pho-toproduction process and resulting in the excitation of one or both of the nuclei. In the second case,the nucleus breaks up and usually emits neutrons close to the beam rapidities which can be measuredin zero-degree calorimeters (ZDC) placed at long distances on both sides of the detector. The incoher-ent photoproduction can also be accompanied by the excitation and dissociation of the target nucleonresulting in even higher transverse momenta of the produced vector mesons [5].Coherent heavy vector meson photoproduction is of particular interest because of its connection with thegluon distribution functions (PDFs) in protons and nuclei [6]. At low Bjorken- x values, parton distribu-tion functions are significantly suppressed in the nucleus with respect to free proton PDFs, a phenomenonknown as parton shadowing [7]. Shadowing effects are usually attributed to multiple scattering and ad-dressed in various phenomenological approaches based on elastic Glauber-like rescatterings of hadroniccomponents of the photon, Glauber-Gribov inelastic rescatterings, and high-density QCD [8–13]. Be-sides, different parameterizations of nuclear partonic distributions based on fits to existing data are avail-able [14–17], however these parameterizations are affected by large uncertainties at low Bjorken- x valuesdue to the limited kinematic coverage of the available data samples.Heavy vector meson photoproduction measurements provide a powerful tool to study poorly knowngluon shadowing effects at low x . The scale of the four-momentum transfer of the interaction is relatedto the mass m V of the vector meson as Q ∼ m V / x of the gluons as x = (cid:0) m V / √ s NN (cid:1) exp ( ± y ) , where the sign of the exponent reflects that each of theincoming lead nuclei may act as the photon source. The gluon shadowing factor R g ( x , Q ) , i.e. the ratioof the nuclear gluon density distribution to the gluon distribution in the proton, can be evaluated viathe measurement of the nuclear suppression factor defined as the square root of the ratio of the coherentvector meson photoproduction cross section on nuclei to the photoproduction cross section in the impulseapproximation that is based on the exclusive photoproduction measurements with the proton target [18,19]. The square root in this definition is motivated by the fact that the coherent photoproduction crosssection is expected to scale as the square of the gluon density in leading order pQCD.The extraction of the nuclear suppression factor in UPC measurements is complicated by the fact thatthe measured vector meson cross section in UPCs is expressed as a sum of two contributions since eitherof the colliding ions can serve as a photon source. At forward rapidities one contribution corresponds tohigher photon–nucleus energies while the other to lower energies resulting in ambiguities in the extrac-2oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaborationtion of the nuclear suppression factor. The midrapidity region has the advantage that both contributionsare the same and the suppression factor can be extracted unambiguously in this case.Charmonium photoproduction in Pb–Pb UPCs was previously studied by the ALICE Collaboration at √ s NN = .
76 TeV [20–22]. The coherent J / ψ photoproduction cross section was measured both atmidrapidity | y | < . − . < y < − .
6. In addition, the CMS Collaborationstudied the coherent J / ψ photoproduction accompanied by neutron emission at semi-forward rapidity1 . < | y | < . √ s NN = .
76 TeV [23]. The results were compared with various models and thebest description was found amongst those introducing moderate gluon shadowing in the nucleus. TheALICE measurements were used in Ref. [18] to extract the nuclear gluon shadowing factor R g yielding R g ( x ∼ − ) = . + . − . and R g ( x ∼ − ) = . + . − . at the scale of the charm quark mass. TheALICE measurement of ψ (cid:48) photoproduction at midrapidity also supports the moderate-shadowing sce-nario [22]. A complementary rapidity-differential measurement of the coherent J / ψ and ψ (cid:48) photopro-duction at forward rapidity in Pb–Pb UPCs at √ s NN = .
02 TeV by the ALICE Collaboration further un-derlines the importance of gluon shadowing effects [24]. The gluon shadowing factor R g ( x ∼ − ) ∼ . x ∼ − , can be neglected in the measured cross sections.In this publication, we present the first measurement of the coherent J / ψ and ψ (cid:48) photoproduction crosssections at the midrapidity range | y | < . √ s NN = .
02 TeV, recorded by ALICEin 2018. The J / ψ photoproduction cross section in this measurement is sensitive to x ∈ ( . , . ) × − ,a factor 2 smaller than in the previous midrapidity measurement at √ s NN = .
76 TeV [21]. This datasample is approximately 10 times larger than Pb–Pb sample at √ s NN = .
76 TeV used for the ALICEresults reported in Refs. [21, 22]. The larger data sample allows for a measurement of the J / ψ crosssection in three rapidity intervals ( | y | < .
15, 0 . < | y | < .
35, 0 . < | y | < .
8) extending the previousrapidity-differential cross section measurement in the forward range at √ s NN = .
02 TeV [24]. J / ψ decays to µ + µ − , e + e − and pp and ψ (cid:48) decays to µ + µ − π + π − , e + e − π + π − and l + l − are investigated. Thecoherent J / ψ production in the pp channel in UPCs is measured for the first time. The ratio of the ψ (cid:48) and J / ψ cross sections is also measured and compared with earlier ALICE measurements [22, 24]. Themeasured cross sections are compared to models assuming no gluon shadowing as well as to predictionsthat employ moderate gluon shadowing. Shadowing models are based on a parametrization of previouslyavailable data, the leading twist approximation and several variations of the color dipole approach. The ALICE detector and its performance are described in [25, 26]. The main components of the ALICEdetector are a central barrel placed in a large solenoid magnet ( B = . − . < η < − .
5. Threecentral barrel detectors, the Inner Tracking System (ITS), the Time Projection Chamber (TPC), and theTime-of-Flight detector (TOF), are used in this analysis.The ITS is made of six silicon layers and is used for particle tracking and interaction vertex reconstruc-tion [27]. The Silicon Pixel Detector (SPD) makes up the two innermost layers of the ITS with about10 pixels covering the pseudorapidity intervals | η | < | η | < . | z | =
250 cm, areinstrumented with Multi-Wire-Proportional-Chambers (MWPCs) with 560,000 readout pads, allowing3oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaborationhigh precision track measurements in the transverse plane. The z coordinate is given by the time of driftin the TPC electric field. The TPC acceptance covers the pseudorapidity region | η | < .
9. Ionizationmeasurements of individual track clusters are used for particle identification.The TOF detector is a large cylindrical barrel of multigap resistive plate chambers with about 150,000readout channels surrounding the TPC and providing very high precision timing measurement [29]. TheTOF pseudorapidity coverage is | η | < .
8. In combination with the tracking system, the TOF detector isused for charged particle identification up to a momentum of about 2.5 GeV / c for pions and kaons andup to 4 GeV / c for protons. The TOF readout channels are grouped into 1608 trigger channels (maxipads)arranged into 18 azimuthal regions and provide topological-trigger decisions.The measurement also makes use of the three forward detectors. The V0 counters consist of two arraysof 32 scintillator tiles each, covering the interval 2 . < η < . − . < η < − . z =
340 cm and z = −
90 cm from the interaction point [30]. The AL-ICE Diffractive (AD) detector consists of two arrays of 8 scintillator tiles each arranged in two layers,covering the range 4 . < η < . − . < η < − . z =
17 m and z = − . ± . ≈ .
94) to detectneutrons with | η | > . The data analysis in this paper is based on the event sample recorded during the Pb–Pb at √ s NN = .
02 TeVdata taking period in 2018. A dedicated central barrel UPC trigger consists of topological trigger formedby at least two and up to six TOF maxipads with at least one pair of maxipads having an opening anglein azimuth larger than 150 degrees and a topological trigger formed by at least four triggered SPD chips.The triggered SPD chips are required to form two pairs, each pair with two chips in different SPD layersfalling in compatible azimuthal regions. The two pairs of chips are required to have an opening angle inazimuth larger than 153 degrees. It is further vetoed by any activity within the time windows for nominalbeam–beam interactions on the V0 and AD detectors on both sides of the interaction point.The used data sample corresponds to an integrated luminosity of 233 µ b − , derived from the counts oftwo independent reference triggers, one based on multiplicity selection in the V0 detector and anotherone based on neutron detection in the ZDC. The reference trigger cross sections were determined fromvan der Meer scans; this procedure has an uncertainty of 2.2% [33].The determination of the live-timeof the UPC trigger has an additional uncertainty of 1.5%. The total relative systematic uncertainty of theintegrated luminosity is thus 2.7%.Additional offline vetoes are applied on the AD and V0 detector signals to ensure the exclusive pro-duction of the charmonia. The offline selection in these detectors is more precise than vetoes at thetrigger level, because it relies on larger time windows than the trigger electronics and on a more refinedalgorithm to quantify the signal.Online and offline V0 and AD veto requirements may result in significant inefficiencies (denoted asveto inefficiencies) in selecting signal events with exclusive charmonium production due to additionalactivity induced by hadronic or electromagnetic pile–up processes from independent Pb–Pb collisionsaccompanying the coherent charmonium photoproduction. The probability of hadronic pile–up in the4oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaborationcollected sample does not exceed 0.2%, however there is a significant pile–up contribution from theelectromagnetic electron-pair production process. The veto inefficiency induced by these pile–up effectsin the V0 and AD detectors is estimated using events selected with an unbiased trigger based only on thetiming of bunches crossing the interaction region. The average veto efficiency ε pileupveto = . ± .
002 isapplied to raw charmonium yields to account for hadronic and electromagnetic pile-up processes.Signal events with exclusive charmonium production, accompanied by electromagnetic nuclear dissoci-ation (EMD), can be rejected if, in addition to the forward neutrons, other particles, produced at largerapidities, leave a signal either in the AD or the V0 detectors. These extra particles may come frommultifragmentation or pion production processes, and the corresponding cross sections are expected tobe large [34]. The amount of good events with neutrons, which are lost due to AD and V0 vetoes, isestimated using control triggers. The fraction of losses for this category of events (EMD) amounts to26% ±
4% for events with a signal either in ZNA or ZNC and reach 43% ±
5% for events with a signalin both ZNA and ZNC. The average event loss is computed using fractions of events with and withoutneutrons on either side. The average veto efficiency correction ε EMDveto = . ± .
02 is applied to rawcharmonium yields to account for the EMD process.The selected events are required to have a reconstructed primary vertex determined using at least tworeconstructed tracks and having a longitudinal position within 15 cm of either side of the nominal inter-action point. The analysis is aimed at the reconstruction of J / ψ decaying to µ + µ − , e + e − , pp and of ψ (cid:48) decaying to l + l − and J / ψπ + π − followed by J / ψ → l + l − . Therefore, events with two or four tracks inthe central barrel are required.Two types of tracks are considered in the analysis: global tracks and ITS standalone tracks. Global tracksare reconstructed using combined tracking in ITS and TPC detectors. Tracks are required to cross at least70 (out of 159) TPC pad-rows and to have a cluster on each of the two layers of the SPD. Each trackmust have a distance of closest approach to the primary vertex of less than 2 cm in the direction of z -axis.ITS standalone tracks are reconstructed using ITS clusters not attached to any global track, requiring atleast four clusters in the ITS, out of which two must be in the SPD.The two-body decays are selected by looking for events with exactly two global tracks with oppositeelectric charge (unlike-sign). The probability to find extra global tracks not passing the standard trackselection criteria or being reconstructed only in ITS is found to be negligible. The four-body decays of ψ (cid:48) are selected by looking for exactly four tracks with at least two being global tracks. The kinematics of the ψ (cid:48) → l + l − π + π − decay is such that pions and leptons are well separated: leptons have high p T ≈ c while pions are much softer with p T ≈ . c . This feature is used to identify the pion pair. Tracksare sorted according to their p T and the two with lowest p T are assumed to be pions, while the other twoare assumed to be leptons. The tagged pions and lepton pairs are required to consist of opposite-signtracks.To separate the J / ψ → µ + µ − , e + e − and pp decays, the particle identification (PID) capabilities of theTPC and TOF detectors are used. The momenta of the tracks from J / ψ decays are p ∈ ( . , . ) GeV / c for the µ + µ − and e + e − channels and p ∈ ( . , . ) GeV / c for the pp channel. The PID resolutionof the TPC allows for complete separation of electrons and muons in the momentum range mentionedabove. Since the specific ionization energy loss (d E / d x ) of electron and proton become equal at momentaaround 1 GeV/ c , the TPC PID is not applicable for the identification of protons from coherently producedJ / ψ . However, the PID capabilities of the TOF detector allow for the separation of protons from otherparticle species in the momentum range relevant for this analysis. For the J / ψ → pp channel, at least onetrack is required to have valid TOF PID information. If no TOF PID is available for the second track,TPC PID is used. The d E / d x in TPC or the Lorentz Beta factor ( β = v / c ) of each reconstructed track inTOF is measured in units of the standard deviation ( σ ) with respect to expected values for µ , e , p at thegiven measured momentum. The track pair is accepted if n σ + + n σ − < / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationThe charmonium photoproduction may be accompanied by pile-up from electromagnetic electron-pairproduction or by noise in the SPD resulting in extra fired SPD trigger chips satisfying the SPD triggerselection topology. In order to exclude contamination of events not triggered by the charmonium decayproducts, the fired SPD trigger chips are required to match SPD clusters corresponding to the selectedtracks. It is found that 11% (7%) of the events with a J / ψ candidate decaying into dimuons (di-electrons)with 4 SPD clusters cannot be matched to the fired trigger chips. The matching requirement has a muchstronger effect for the 4-track decay channels of ψ (cid:48) removing 40% and 22% of the candidates in the ψ (cid:48) → µ + µ − π + π − and ψ (cid:48) → e + e − π + π − channel, respectively. The product of acceptance and efficiency of the J / ψ and ψ (cid:48) reconstruction ( ε ) is evaluated using alarge Monte Carlo (MC) sample of coherent and incoherent J / ψ and ψ (cid:48) events generated by STARlight2.2.0 [35] with decay particles tracked in a model of the experimental apparatus implemented in GEANT3.21 [36]. The model includes a realistic description of the detector status during data taking and itsvariation with time.For this analysis, the primary J / ψ and ψ (cid:48) vector mesons produced in UPCs are considered to be trans-versely polarized. This is consistent with expectations from helicity conservation in photo productionand consistent with H1 and ZEUS measurements [37–39]. As observed in previous experiments, bothJ / ψ and the two pions from ψ (cid:48) decay are in the S-wave state resulting into the full transfer of the ψ (cid:48) polarisation to the J / ψ [40]. The expected polarization states of primary J / ψ and ψ (cid:48) as well as of sec-ondary J / ψ from ψ (cid:48) decays are properly taken into account in the MC simulations used in this analysis.These MC simulations are also used in the evaluation of the feed-down contribution to the two-bodydecay channels from the ψ (cid:48) → J / ψ + π + π − and ψ (cid:48) → J / ψ + π π decays and for modeling the signalshape and different background contributions.The efficiency of the SPD trigger chips is measured with a data-driven approach using a minimum biastrigger. Tracks selected without requiring hits in both SPD layers are matched to the trigger chips theycross. The obtained efficiency maps are introduced on an event-by-event basis to the MC simulations.The overall effect corresponds to an efficiency of about 0.72 ± The extraction of coherent J / ψ and ψ (cid:48) yields in all decay channels is performed in the rapidity interval | y | < .
8. In addition, the J / ψ measurements in the dielectron and dimuon channels are performed inthree rapidity intervals: | y | < .
15, 0 . < | y | < .
35, and 0 . < | y | < . y ranges werechosen to have approximately the same number of candidates per range. An enriched sample of coherentJ / ψ and ψ (cid:48) candidates is obtained by selecting the reconstructed candidates with transverse momentum p T < . / c .The invariant mass distributions for dimuon and dielectron pairs reconstructed in the full rapidity rangeare shown in Fig. 1, left. The inclusive J / ψ yields are obtained by fitting the invariant mass distributionswith an exponential function describing the underlying continuum and two Crystal Ball functions todescribe the J / ψ and ψ (cid:48) signals. The J / ψ pole mass and width were left free, while the tail parameters( α and n ) in the Crystal Ball function were fixed to the values obtained in MC simulations in order to6oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaborationgain higher stability of the fits. In the case of the ψ (cid:48) signal, all the Crystal Ball parameters were fixed tothe values obtained in MC simulations.The raw inclusive J / ψ yields obtained from invariant mass fits contain contributions from the coherentand incoherent J / ψ photoproduction that can be separated via the analysis of the transverse momentumspectra. The inclusive p T distributions for µ + µ − and e + e − candidates around the J / ψ mass are shownin the right panels of Fig. 1. These distributions are fitted with MC templates produced using STARlight,followed by full detector simulation and reconstruction, corresponding to different production mecha-nisms: coherent and incoherent J / ψ , feed-down J / ψ from decays of coherent and incoherent ψ (cid:48) and thedilepton continuum from the γγ → l + l − process. Incoherent J / ψ production with nucleon dissociation(or dissociative J / ψ ) is also taken into account to describe the high- p T tail with the template based onthe H1 parametrization [37]. Normalization of feed-down J / ψ from coherent and incoherent ψ (cid:48) decaysis constrained to the normalization of primary J / ψ templates according to the feed-down fractions ex-tracted as described below. The normalization of the dilepton continuum from the γγ → l + l − process isfixed by the results for the background description of the invariant mass fits. The combinatorial back-ground, estimated by considering the distribution of like-sign candidates, is found to be negligible in theJ / ψ mass region.The templates are fitted to the data leaving the normalization free for coherent J / ψ , incoherent J / ψ anddissociative J / ψ production. The extracted incoherent J / ψ fraction f I = N incoh N coh for p T < . c is4 . ± . ( . ± . ) % for the µ + µ − ( e + e − ) decay channel. The quoted fractions include the contribu-tion of incoherent J / ψ with nucleon dissociation.The invariant mass and the p T distributions for the J / ψ → p¯p decay channel are shown in Fig. 2. Thedata sample obtained in this channel is too small to fit the p T distribution with MC templates. However,since the difference in resolution of p T shapes of the coherent or incoherent MC samples for the pp and µ + µ − channels is negligible, one can expect the f I fraction to be the same. This is due to the fact thatneither the µ + µ − nor the pp channels suffer from bremsstrahlung. This is not the case for dielectronswhere bremsstrahlung induces the large difference in the mass and momentum resolution which affectthe templates and consequently the f I fraction.As one can see in Fig. 1, the ψ (cid:48) yields in the µ + µ − and e + e − channels are small and lying on top of asignificant background. In order to increase the significance of the ψ (cid:48) signal and to reduce the statisticaluncertainty, the ψ (cid:48) yield is extracted from the merged l + l − sample. Fig. 3 shows the merged dileptonmass spectrum together with the p T distribution of the dilepton candidates in the invariant mass rangeunder the ψ (cid:48) mass peak. The fit to the invariant mass distribution is performed in the same way asdescribed before.Fig. 4 shows the invariant mass (left) and the p T distribution (right) for ψ (cid:48) → µ + µ − π + π − and ψ (cid:48) → e + e − π + π − quadruplets. A coherent peak is clearly visible at low p T . The signal extraction in the µ + µ − π + π − and e + e − π + π − channel is straight-forward since the signal is very clean. The number ofcandidates is extracted by summing the bin contents in the mass interval 3 . < m µµππ < . c and3 . < m ee ππ < . c . The number of candidates with wrong-sign combinations in the same massinterval, representing the level of background, is subtracted afterwards.The incoherent contamination of the ψ (cid:48) sample is estimated as follows. The incoherent-to-coherent pho-toproduction cross section ratio is expected to be similar for 1S and 2S charmonium states [35, 41]. Dueto lack of model calculations for the incoherent ψ (cid:48) cross section in UPCs at √ s NN = .
02 TeV, pre-dicted incoherent-to-coherent cross section ratios for J / ψ from Refs. [5, 13, 35] are used as an estimateof the incoherent-to-coherent cross section ratio for ψ (cid:48) . The factor f I = N incoh N coh ≈
6% is extracted fromthe predicted cross section ratios, corrected for acceptance and efficiency of coherent and incoherent ψ (cid:48) states. The difference in the predicted incoherent-to-coherent cross section ratios is used as an estimateof the systematic uncertainty. 7oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration ) c (GeV/ mm m c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - m + m fi y J/ -1 b m – = 233 int UPC, L c < 0.2 GeV/ T p | < 0.8 y | 61 – = 3120 y J/ N – = 58 ' y N = 0.86 dof / c ) c (GeV/ T p - ) c ( G e V / T p d N / d - - - = 5.02 TeV NN s Pb - ALICE, Pb -1 b m – = 233 int UPC, L c < 3.20 GeV/ mm m y | ALICE data y Coherent J/ y Incoherent J/ with nucleon dissociation y Incoherent J/ ' decay y from y Coherent J/ ' decay y from y Incoherent J/ ll fi gg Continuum =2.44 dof / c Fit: (a) J / ψ → µ + µ − ) c (GeV/ ee m c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - e + e fi y J/ -1 b m – = 233 int UPC, L c < 0.2 GeV/ T p | < 0.8 y | 65 – = 2116 y J/ N – = 30 ' y N = 1.22 dof / c ) c (GeV/ T p - ) c ( G e V / T p d N / d - - - = 5.02 TeV NN s Pb - ALICE, Pb -1 b m – = 233 int UPC, L c < 3.20 GeV/ ee m y | ALICE data y Coherent J/ y Incoherent J/ with nucleon dissociation y Incoherent J/ ' decay y from y Coherent J/ ' decay y from y Incoherent J/ ll fi gg Continuum =1.09 dof / c Fit: (b) J / ψ → e + e − Figure 1:
Left: Invariant mass distribution of l + l − pairs. The dashed green line corresponds to the background.The solid magenta and red lines correspond to Crystal Ball functions representing the J / ψ and ψ (cid:48) signal, re-spectively. The solid blue line corresponds to the sum of background and signal functions. Right: Transversemomentum distribution of J / ψ candidates in the range quoted in the figure (around the J / ψ nominal mass). / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration ) c (GeV/ pp m c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb p p fi y J/ -1 b m – = 233 int UPC, L c < 0.2 GeV/ T p | < 0.8 y | 8 – = 61 y J/ N = 0.73 dof / c ) c (GeV/ T p c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb p p fi y J/ -1 b m – = 233 int UPC, L ) < 3.2 c (GeV/ pp m y | Figure 2:
Left: Invariant mass distribution of pp pairs. The dashed green line corresponds to the backgrounddescription. The solid magenta and red lines correspond to Crystal Ball functions representing the J / ψ and ψ (cid:48) signals, respectively. The solid blue line corresponds to the sum of background and signal functions. Right:Transverse momentum distribution of J / ψ candidates in the range quoted in the figure (around the J / ψ nominalmass). ) c (GeV/ ll m c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - l + l fi ' y -1 b m – = 233 int UPC, L c < 0.2 GeV/ T p | < 0.8 y | 89 – = 5343 y J/ N – = 102 ' y N = 1.16 dof / c ) c (GeV/ T p c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - l + l fi ' y -1 b m – = 233 int UPC, L ) < 3.8 c (GeV/ ll m y | Figure 3:
Left: Invariant mass distribution of l + l − pairs. The dashed green line corresponds to the backgrounddescription. The solid magenta and red line correspond to Crystal Ball functions representing the J / ψ and ψ (cid:48) signals, respectively. The solid blue line corresponds to the sum of background and signal functions. Right:Transverse momentum distribution of ψ (cid:48) candidates in the mass range quoted in the figure (around the ψ (cid:48) mass). / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration ) c (GeV/ ppmm m c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - p + p - m + m fi ' y -1 b m – = 233 int UPC, L c < 0.2 GeV/ T p | < 0.8 y | 8 – = 53 ' y N ) c (GeV/ T p c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - p + p - m + m fi ' y -1 b m – = 233 int UPC, L ) < 3.8 c (GeV/ ppmm m y | (a) ψ (cid:48) → µ + µ − π + π − ) c (GeV/ pp ee m c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - p + p - e + e fi ' y -1 b m – = 233 int UPC, L c < 0.2 GeV/ T p | < 0.8 y | 6 – = 39 ' y N ) c (GeV/ T p c C oun t s pe r M e V / = 5.02 TeV NN s Pb - ALICE, Pb - p + p - e + e fi ' y -1 b m – = 233 int UPC, L ) < 3.8 c (GeV/ pp ee m y | (b) ψ (cid:48) → e + e − π + π − Figure 4:
Left: Invariant mass distribution for ψ (cid:48) → µ + µ − π + π − (upper panel) and ψ (cid:48) → e + e − π + π − (bottompanel). The green line shows the wrong sign four-track events. The red line shows the ψ (cid:48) signal as described inthe text. Right: Transverse momentum distribution of ψ (cid:48) candidates in the mass range quoted in the figure (aroundthe ψ (cid:48) nominal mass). / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationThe raw J / ψ yields contain a significant feed-down contribution originating from decays ψ (cid:48) → J / ψ + anything, dominated by the ψ (cid:48) → J / ψ + π + π − and ψ (cid:48) → J / ψ + π π decay channels. The feed-downfraction f D = N ( FeedDown ) N ( primary ) can be extracted from the ratio of raw J / ψ and ψ (cid:48) yields: R N = N ψ (cid:48) N J / ψ = . ± . ( . ± . ) , (1)for µ + µ − ( e + e − ). The raw ψ (cid:48) and J / ψ yields in this ratio contain contributions both from coherent andincoherent photoproduction. However, according to the p T fits, the fraction f I does not exceed 6% and,according to STARlight, the fraction of the incoherent contributions is expected to be similar in the ψ (cid:48) and J / ψ yields. The R N ratio can therefore be considered as a good estimate of the ratio of coherent J / ψ and ψ (cid:48) yields, since the incoherent fractions largely cancel in the ratio. The f D ratio can be expressed viathe measured R N ratio: (cid:18) f D + (cid:19) − = N feed − downJ / ψ N J / ψ = ( BR · ε ) ψ (cid:48) → J / ψπ + π − → l + l − π + π − + ( BR · ε ) ψ (cid:48) → J / ψπ π → l + l − π π ( BR × ε ) ψ (cid:48) → l + l − × R N , (2)where ( BR × ε ) in the corresponding channels denote products of world-average branching ratios [42]and the product of acceptance and efficiency of measuring exactly two leptons. The f D fractions of3 . ± .
5% and 4 . ± .
7% are obtained in the µ + µ − and in e + e − channel respectively, with theuncertainty being the quadratic sum of statistical and systematic uncertainties, where the statistical un-certainty dominates. The systematic uncertainty includes contributions from the J / ψ and ψ (cid:48) signal ex-traction and the branching ratios. The coherent vector meson differential cross section is given by:d σ cohVM dy = N cohVM ( Acc × ε ) VM × ε pileupveto × ε EMDveto × BR ( VM → X + Y ) × L int × ∆ y (3)where N coh J / ψ = N yield + f I + f D (4)and N coh ψ (cid:48) = N yield + f I . (5)The raw J / ψ and ψ (cid:48) yield values, efficiencies, f I and f D fractions as well as coherent cross sections withstatistical and systematic uncertainties are summarized in Table 1 and Table 2. The associated systematicuncertainties are briefly described in the following.The offline AD and V0 vetoes decreases the J / ψ ( ψ (cid:48) ) yield by 8% (16%) and also results in a lower ε pileupveto efficiency. These two effects do not cancel-out completely. A residual discrepancy of 3% (10%)in the cross section of J / ψ ( ψ (cid:48) ) is included in the systematic uncertainty.The uncertainty related to the evaluation of the incoherent contamination comes from the shape of thecontinuum template. By default the γγ → l + l − template from the STARlight MC simulation is used.Alternative way would be to use a data-driven template generated from the side bands of the invariantmass distribution of the J / ψ . These events are, in contrast to the pure MC, supposed to include the samebackground as under the J / ψ peak. By comparing the f I fraction obtained with the side bands methodand the STARlight template, a 0.8 (0.5%) uncertainty of the cross section for the µ + µ − ( e + e − ) channelis found. 11oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration Table 1:
Raw J / ψ yields, ε , f D and f I fractions and coherent J / ψ cross sections per decay channel Decay | y | N J / ψ ε f D f I d σ cohJ / ψ / dy (mb) µ + µ − (0.00, 0.80) 3120 ±
61 0.037 0.035 0 . ± .
003 4 . ± . ( stat . ) ± . ( syst . ) µ + µ − (0.00, 0.15) 1027 ±
35 0.064 0.035 0 . ± .
003 4 . ± . ( stat ) ± . ( syst ) µ + µ − (0.15, 0.35) 1083 ±
36 0.051 0.035 0 . ± .
003 4 . ± . ( stat ) ± . ( syst ) µ + µ − (0.35, 0.80) 976 ±
33 0.022 0.035 0 . ± .
003 3 . ± . ( stat ) ± . ( syst ) e + e − (0.00, 0.80) 2116 ±
65 0.025 0.043 0 . ± .
005 4 . ± . ( stat . ) ± . ( syst . ) e + e − (0.00, 0.15) 683 ±
33 0.046 0.043 0 . ± .
005 3 . ± . ( stat ) ± . ( syst ) e + e − (0.15, 0.35) 743 ±
34 0.034 0.043 0 . ± .
005 4 . ± . ( stat ) ± . ( syst ) e + e − (0.35, 0.80) 643 ±
31 0.014 0.043 0 . ± .
005 3 . ± . ( stat ) ± . ( syst ) pp (0.00, 0.80) 61 ± . ± .
003 3 . ± . ( stat . ) ± . ( syst . ) Table 2:
Raw ψ (cid:48) yields, ε , f I fractions and coherent ψ (cid:48) cross sections per decay channel Decay | y | N ψ (cid:48) ε f I d σ coh ψ (cid:48) / dy (mb) µ + µ − π + π − (0.0, 0.8) 53 ± . ± . ( stat . ) ± . ( syst . ) e + e − π + π − (0.0, 0.8) 39 ± . ± . ( stat . ) ± . ( syst . ) l + l − (0.0, 0.8) 102 ±
24 0.0324 0.063 0 . ± . ( stat . ) ± . ( syst . ) - m + m fi y J/ - e + e fi y J/ p p fi y J/ / d y ( m b ) c oh s d = 5.02 TeV NN s Pb - ALICE, Pb -1 b m – = 233 int UPC, L - p + p - m + m fi ' y - p + p - e + e fi ' y - l + l fi ' y / d y ( m b ) c oh s d = 5.02 TeV NN s Pb - ALICE, Pb -1 b m – = 233 int UPC, L
Figure 5:
Measured differential cross section of coherent J / ψ (left) and ψ (cid:48) (right) photoproduction in Pb–Pb UPCsin | y | < .
8. The points show the measurements for different decay channels. The error bars (boxes) represent thestatistical (decay channel uncorrelated systematic) uncertainty. The gray box shows the average value (dashed line)and correlated systematic uncertainty. / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationA systematic uncertainty of the tracking efficiency of 2% per track is estimated by comparing, in dataand in MC, the ITS (TPC) hit matching efficiency to the tracks reconstructed with TPC (ITS) hits only.This leads to a 2.8% (4%) systematic uncertainty for two-track (four-track) channels.For the signal extraction in the J / ψ analysis the goodness of the description of the J / ψ signal by theCrystal Ball function is checked. The yield from the fit is compared to the number of events computedby bin counting in the peak region with the γγ contribution subtracted using the exponential backgroundshape from the fit. Half differences of 0.3%, 2.4%, 0.6% were assigned as the systematic uncertainty inthe muon, electron and proton channel, respectively.Another contribution to the signal extraction uncertainties is the difference between the function usedin the fit and the true shape of the background. It is estimated by varying the fit range. A systematicuncertainty of 0.4% (0.3%) is determined for the µ + µ − ( e + e − ) decay channel of the J / ψ meson. Theuncertainty in the background subtraction rises rapidly as the signal-to-background ratio drops. A similarstudy for the l + l − decay of the ψ (cid:48) meson results in a 10% systematic uncertainty.The uncertainty associated to the determination of the trigger efficiency of the SPD chips is obtained bychanging the requirements on the probe tracks used in the data-driven method. Variations include therunning conditions, the maximum amount of activity allowed in the event, and the definition of tracksaccepted in the efficiency computation. This uncertainty amounts to 1%.The uncertainty of the TOF trigger efficiency due to the spread of the arrival times of various particlespecies to TOF is evaluated as 0.5% per track (1% in total). The uncertainty in case of four track decaysof ψ (cid:48) applies only for the lepton tracks since the low-momentum pions do not reach the TOF detector.In the J / ψ → pp analysis, at least one track is required to have proton PID from the TOF. Comparingthe efficiency of the track matching to TOF in data and MC samples, a 10% disagreement is found. Thematching efficiency from MC is used and a half-difference of 5% as an additional systematic uncertaintyfor the pp channel is assigned.Tables 3 and 4 show the uncertainties for each source and channel separately as well as quadratic sumsof the channel-correlated and uncorrelated sources.The signal extraction, incoherent contamination and branching ratio are considered as channel-uncorrelatedsources of systematic uncertainties. The other sources are fully correlated and are the same for all chan-nels. In the case of the ψ (cid:48) , the four track channels have an extra ITS-TPC matching uncertainty for thepion tracks which is not correlated with the l + l − channel, thus it is quoted separately.The J / ψ and ψ (cid:48) cross sections for various decay channels computed using Eq. 3 are shown in Fig. 5. Themean values of the J / ψ and ψ (cid:48) cross sections are obtained as a weighted average of the cross sections perdecay channel with weights corresponding to the inverse of the quadratic sum of statistical and channel-uncorrelated systematic uncertainties. The cross section value averaged over the three decay channels ofthe coherent J / ψ photoproduction measurements is:d σ coh J / ψ d y = . ± . ( stat . ) ± . ( syst . ) mb . (6)The cross section value averaged over the three channels of coherent ψ (cid:48) photoproduction measurementsis: d σ coh ψ (cid:48) d y = . ± . ( stat . ) ± . ( syst . ) mb . (7)13oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration Table 3:
Sources of systematic uncertainty for the coherent J / ψ cross section measurements per decay channel inpercent J / ψ → µ + µ − J / ψ → e + e − J / ψ → ppSignal Extraction 0.5 2.4 0.7Incoherent contamination 0.8 0.5 0.8Branching ratio 0.5 0.5 1.4TOF matching – – 5.0ITS-TPC matching 2.8 2.8 2.8AD and V0 veto 3.0 3.0 3.0SPD trigger efficiency 1.0 1.0 1.0TOF trigger efficiency 0.7 0.7 0.7Luminosity 2.7 2.7 2.7EMD correction 2.0 2.0 2.0Feed down 0.6 0.6 0.6Channel uncorrelated 1.1 2.5 5.3Channel correlated 5.5 5.5 5.5 Table 4:
Sources of systematic uncertainty for the coherent ψ (cid:48) cross section measurements per decay channel inpercent ψ (cid:48) → µ + µ − π + π − ψ (cid:48) → e + e − π + π − ψ (cid:48) → l + l − Signal Extraction 1.0 2.0 10.0Incoherent contamination 1.4 1.8 1.8Branching ratio 1.5 1.5 4.8ITS-TPC matching pions 2.8 2.8 –ITS-TPC matching leptons 2.8 2.8 2.8AD and V0 veto 10.0 10.0 10.0SPD trigger efficiency 1.0 1.0 1.0TOF trigger efficiency 0.7 0.7 0.7Luminosity 2.7 2.7 2.7EMD correction 2.0 2.0 2.0Channel uncorrelated 3.5 5.8 11.2Channel correlated 11.0 11.0 11.014oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationThe ratio of the 2S to 1S charmonium states is: σ coh ψ (cid:48) d y σ coh J / ψ d y = . ± . ( stat . ) ± . ( syst . ) ± . ( BR ) . (8)Many systematic uncertainties of the J / ψ and ψ (cid:48) cross section measurements are correlated and cancelin the cross section ratio. Since the analysis relies on the same data sample and on the same trigger,the systematic uncertainties of the luminosity evaluation, trigger efficiency, EMD correction and ITS-TPC matching of leptons were considered as fully correlated. The AD and V0 offline veto uncertaintyis partially correlated, so the difference of the uncertainties for ψ (cid:48) and J / ψ is taken into account inthe uncertainty of the ratio. The systematic uncertainties connected to the signal extraction, incoherentcontamination and the branching ratio are considered uncorrelated between the two measurements. Thedominant uncertainty comes from the uncorrelated part of the AD and V0 veto uncertainty for ψ (cid:48) . Figure 6 shows the rapidity-differential cross section of the coherent photoproduction of J / ψ and ψ (cid:48) vec-tor mesons in Pb–Pb UPCs including previous ALICE measurements of J / ψ at forward rapidity [24].At midrapidity, J / ψ measurements performed in absolute rapidity ranges are shown at positive rapiditiesand reflected into negative rapidities. The ALICE measurements are compared to several models whichare discussed in the following:The impulse approximation, taken from STARlight [43], is based on data from exclusive J / ψ photopro-duction off protons and neglects all nuclear effects except for the coherence. The square root of the ratioof experimental cross sections to the impulse approximation is 0 . ± .
03 for J / ψ and 0 . ± .
06 for ψ (cid:48) , where statistical and systematic uncertainties of the ALICE measurements and a conservative 10%uncertainty on the impulse approximation are added in quadrature. The obtained nuclear suppressionfactor reflects the magnitude of the nuclear gluon shadowing factor at typical Bjorken- x values in therange ( . , . ) × − and is in good agreement with R g ( x ∼ − ) = . + . − . obtained in Ref. [18]from the J / ψ cross section measurement in UPCs at √ s NN = .
76 TeV. y - - - - / d y ( m b ) s d NN s y Pb+Pb+J/ fi ALICE Pb+Pb y ALICE coherent J/Impulse approximationSTARLIGHTEPS09 LO (GKZ)LTA (GKZ)IIM BG (GM)IPsat (LM)BGK-I (LS)GG-HS (CCK)b-BK (BCCM) y - - - - / d y ( m b ) s d NN s ' y Pb+Pb+ fi ALICE Pb+Pb ' y ALICE coherent Impulse approximationSTARLIGHTEPS09 LO (GKZ)LTA (GKZ)GG-HS (CCK)b-BK (BCCM)
Figure 6:
Measured differential cross section of the coherent J / ψ (left) and ψ (cid:48) (right) photoproduction in Pb–PbUPC events. The error bars (boxes) show the statistical (systematic) uncertainties. The theoretical calculations arealso shown. The green band represents the uncertainties of the EPS09 LO calculation. / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationSTARlight is based on the Vector Meson Dominance model and a parametrization of the existing dataon J / ψ photoproduction off protons [35]. A Glauber-like formalism is used to calculate the J / ψ photo-production cross section in Pb–Pb UPCs accounting for multiple interactions within the nucleus but notaccounting for the gluon shadowing corrections. The STARlight model overpredicts the data indicatingthat Glauber-like rescatterings alone are not enough to explain the observed suppression of the coherentJ / ψ cross section.Guzey, Kryshen and Zhalov [44] provide two calculations (GKZ), one based on the EPS09 LO parametriza-tion of the available nuclear shadowing data [14] and the other on the leading twist approximation (LTA)of nuclear shadowing based on the combination of the Gribov-Glauber theory and the diffractive PDFsfrom HERA [8]. Both the LTA model and the EPS09 curve, corresponding to the EPS09 LO central set(uncertainties of the EPS09 calculation are represented by the green band), are found to be in a goodagreement with the J / ψ and ψ (cid:48) cross sections measured at midrapidity. However, these models are intension with the J / ψ data at semi-forward rapidity in the range 2 . < | y | < .
5, indicating that the nuclearshadowing might have a smaller effect at Bjorken x ∼ − or x ∼ × − corresponding to this rapidityrange.Calculations by Cepila, Contreras, Krelina and Tapia Takaki (CCK) are based on the colour dipole modelwith the structure of the nucleon in the transverse plane described by the so-called hot spots, regionsof high gluonic density, whose number increases with the increasing energy [13, 45]. Nuclear effectsare implemented along the ideas proposed in the energy-dependent hot-spot model with the standardGlauber-Gribov formalism (GG-HS) for the extension to the nuclear case. The GG-HS model agreeswith the J / ψ measurements at midrapidity and at most forward rapidities but underpredicts them atsemi-forward rapidities. The ψ (cid:48) measurement at midrapidity is overpredicted by this model.Calculations by Bendova, Cepila, Contreras, Matas (BCCM) are based on the color dipole approachcoupled to the solutions of the impact-parameter dependent Balitsky-Kovchegov equation with initialconditions based on the Woods-Saxon shape of the Pb nucleus [9]. The model is in a reasonable agree-ment with the J / ψ and ψ (cid:48) data at midrapidity.Several theory groups provided predictions for J / ψ within the color dipole approach coupled to theColor Glass Condensate (CGC) formalism with different assumptions on the dipole-proton scatteringamplitude. Predictions by Gonçalves, Machado et al. (GM) [10, 46] based on the IIM and b-CGCmodels for the scattering amplitude agree with the J / ψ data rather well at midrapidity but stronglyunderpredict the data at forward rapidities. Predictions by Lappi and Mäntysaari (LM) based on theIPsat model [11, 47] overpredict the ALICE measurements at midrapidity, but match them at forwardrapidities. Recent predictions by Łuszczak and Schäfer (LS BGK-I) within the color-dipole formulationof the Glauber-Gribov theory [12] are in agreement with the J / ψ data at semi-forward rapidities, 2 . < | y | <
3, slightly underpredict the data at more forward rapidities 3 < | y | < ψ (cid:48) to J / ψ cross section is compatible with the previous ALICE measurementat forward rapidities R = . ± . ( stat . ) ± . ( syst . ) ± . ( BR ) [24], with the exclusive photo-production cross section ratio R = . ± . ( stat . ) ± . ( syst . ) ± . ( BR ) measured by the H1collaboration in ep collisions [38] and with the ratio R ≈ .
19 measured by the LHCb collaboration in ppcollisions [48]. The measured ratio also agrees with the ratio R ≈ .
20 predicted in the leading twist ap-proximation [44] for Pb–Pb UPCs at midrapidity. The ψ (cid:48) to J / ψ coherent cross section ratio is expectedto have a mild dependence on the collision energy [44]. Therefore, the measured ratio can be directlycompared to the unexpectedly large ψ (cid:48) to J / ψ coherent cross section ratio R = . + . − . , measured byALICE at midrapidity in Pb–Pb UPCs at √ s NN = .
76 TeV [22]. The previous measurement is abouta factor two larger but is still compatible within 2 standard deviations with the present measurement,owing mainly to the large uncertainties of the previous result.16oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration The first rapidity-differential measurement on the coherent photoproduction of J / ψ at midrapidity | y | < . √ s NN = .
02 TeV has been presented and compared to the model calculations.This data complements the ALICE measurement of the coherent J / ψ cross section at forward rapidity − < y < − . x values x ∈ ( . , . ) × − is estimatedfrom the comparison of the measured coherent J / ψ cross section with the impulse approximation atmidrapidity. This result is in agreement with the gluon shadowing factor extracted from the previous AL-ICE measurement of the coherent J / ψ cross section at midrapidity in Pb–Pb UPCs at √ s NN = .
76 TeV.None of the models is able to fully describe the measured forward and central rapidity dependence of thecoherent J / ψ cross section. The J / ψ measurements at central and most forward rapidities are found tobe in agreement with the models based either on the leading twist approximation of nuclear shadowing,or the central value of the EPS09 parameterization as well as with the energy-dependent hot-spot modelextended to the nuclear case by the standard Glauber-Gribov formalism and the color dipole approachcoupled to the solutions of the impact-parameter dependent Balitsky-Kovchegov equation. However,these models appear to be in tension with the data at semi-forward rapidities in the range 2 . < | y | < .
5. The data might be better explained with a model where shadowing has a smaller effect at Bjorken x ∼ − or x ∼ × − corresponding to this rapidity range. On the other hand, the models based onthe color dipole approach coupled to the color glass condensate formalism describe either the forward orcentral measurements depending on the dipole scattering amplitude assumptions but they are not able todescribe the measured cross section in the full rapidity range.The ratio of the ψ (cid:48) to J / ψ cross sections at midrapidity is in a reasonable agreement with the ratioof photoproduction cross sections off protons measured by the H1 and LHCb collaborations, with theleading twist approximation predictions for Pb–Pb UPCs as well as with the ALICE measurement atforward rapidities. Acknowledgements
The ALICE Collaboration would like to thank all its engineers and technicians for their invaluable con-tributions to the construction of the experiment and the CERN accelerator teams for the outstandingperformance of the LHC complex. The ALICE Collaboration gratefully acknowledges the resources andsupport provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG) collaboration.The ALICE Collaboration acknowledges the following funding agencies for their support in building andrunning 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, Austrian Science Fund (FWF): [M 2467-N36] and Nationalstiftung fürForschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies,National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tec-nológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo à Pesquisa do Estadode São Paulo (FAPESP) and Universidade Federal do Rio Grande do Sul (UFRGS), Brazil; Ministry ofEducation of China (MOEC) , Ministry of Science & Technology of China (MSTC) and National NaturalScience Foundation of China (NSFC), China; Ministry of Science and Education and Croatian ScienceFoundation, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaen-ergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; CzechScience Foundation; The Danish Council for Independent Research | Natural Sciences, the VILLUMFONDEN and Danish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics(HIP), Finland; Commissariat à l’Energie Atomique (CEA) and Institut National de Physique Nucléaireet de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France;17oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationBundesministerium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für Schwerionen-forschung GmbH, Germany; General Secretariat for Research and Technology, Ministry of Education,Research and Religions, Greece; National Research, Development and Innovation Office, Hungary; De-partment of Atomic Energy Government of India (DAE), Department of Science and Technology, Gov-ernment of India (DST), University Grants Commission, Government of India (UGC) and Council ofScientific and Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; IstitutoNazionale di Fisica Nucleare (INFN), Italy; Institute for Innovative Science and Technology , NagasakiInstitute of Applied Science (IIST), Japanese Ministry of Education, Culture, Sports, Science and Tech-nology (MEXT) and Japan Society for the Promotion of Science (JSPS) KAKENHI, Japan; ConsejoNacional de Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación Internacional en Cien-cia y Tecnología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA),Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The ResearchCouncil of Norway, Norway; Commission on Science and Technology for Sustainable Development inthe South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Scienceand Higher Education, National Science Centre and WUT ID-UB, Poland; Korea Institute of Scienceand Technology Information and National Research Foundation of Korea (NRF), Republic of Korea;Ministry of Education and Scientific Research, Institute of Atomic Physics and Ministry of Research andInnovation and Institute of Atomic Physics, Romania; Joint Institute for Nuclear Research (JINR), Min-istry of Education and Science of the Russian Federation, National Research Centre Kurchatov Institute,Russian Science Foundation and Russian Foundation for Basic Research, Russia; Ministry of Educa-tion, Science, Research and Sport of the Slovak Republic, Slovakia; National Research Foundation ofSouth Africa, South Africa; Swedish Research Council (VR) and Knut & Alice Wallenberg Founda-tion (KAW), Sweden; European Organization for Nuclear Research, Switzerland; Suranaree Universityof Technology (SUT), National Science and Technology Development Agency (NSDTA) and Office ofthe Higher Education Commission under NRU project of Thailand, Thailand; Turkish Atomic EnergyAgency (TAEK), Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and TechnologyFacilities Council (STFC), United Kingdom; National Science Foundation of the United States of Amer-ica (NSF) and United States Department of Energy, Office of Nuclear Physics (DOE NP), United Statesof America. References [1] C. A. Bertulani, S. R. Klein, and J. Nystrand, “Physics of ultra-peripheral nuclear collisions”,
Ann.Rev. Nucl. Part. Sci. (2005) 271–310, arXiv:nucl-ex/0502005 .[2] A. Baltz, “The Physics of Ultraperipheral Collisions at the LHC”, Phys. Rept. (2008) 1–171, arXiv:0706.3356 [nucl-ex] .[3] J. G. Contreras and J. D. Tapia Takaki, “Ultra-peripheral heavy-ion collisions at the LHC”,
Int. J.Mod. Phys.
A30 (2015) 1542012.[4] S. R. Klein and H. Mäntysaari, “Imaging the nucleus with high-energy photons”,
Nature Rev.Phys. no. 11, (2019) 662–674, arXiv:1910.10858 [hep-ex] .[5] V. Guzey, M. Strikman, and M. Zhalov, “Nucleon dissociation and incoherent J / ψ photoproduction on nuclei in ion ultraperipheral collisions at the Large Hadron Collider”, Phys.Rev. C no. 1, (2019) 015201, arXiv:1808.00740 [hep-ph] .[6] M. Ryskin, “Diffractive J / ψ electroproduction in LLA QCD”, Z. Phys. C (1993) 89–92.[7] N. Armesto, “Nuclear shadowing”, J. Phys. G (2006) R367–R394, arXiv:hep-ph/0604108 .18oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration[8] L. Frankfurt, V. Guzey, and M. Strikman, “Leading Twist Nuclear Shadowing Phenomena in HardProcesses with Nuclei”, Phys. Rept. (2012) 255–393, arXiv:1106.2091 [hep-ph] .[9] D. Bendova, J. Cepila, J. G. Contreras, and M. Matas, “Photonuclear J / ψ production at the LHC:proton-based versus nuclear dipole scattering amplitudes”, arXiv:2006.12980 [hep-ph] .[10] V. P. Gonçalves, B. D. Moreira, and F. S. Navarra, “Investigation of diffractive photoproduction ofJ / ψ in hadronic collisions”, Phys. Rev. C (Jul, 2014) 015203. https://link.aps.org/doi/10.1103/PhysRevC.90.015203 .[11] T. Lappi and H. Mäntysaari, “Incoherent diffractive J / ψ production in high-energy nucleardeep-inelastic scattering”, Phys. Rev. C (Jun, 2011) 065202. https://link.aps.org/doi/10.1103/PhysRevC.83.065202 .[12] A. Łuszczak and W. Schäfer, “Coherent photoproduction of J / ψ in nucleus-nucleus collisions inthe color dipole approach”, Phys. Rev. C no. 4, (2019) 044905, arXiv:1901.07989[hep-ph] .[13] J. Cepila, J. G. Contreras, and M. Krelina, “Coherent and incoherent J / ψ photonuclear productionin an energy-dependent hot-spot model”, Phys. Rev. C no. 2, (2018) 024901, arXiv:1711.01855 [hep-ph] .[14] K. Eskola, H. Paukkunen, and C. Salgado, “EPS09: A New Generation of NLO and LO NuclearParton Distribution Functions”, JHEP (2009) 065, arXiv:0902.4154 [hep-ph] .[15] K. J. Eskola, P. Paakkinen, H. Paukkunen, and C. A. Salgado, “EPPS16: Nuclear partondistributions with LHC data”, Eur. Phys. J. C no. 3, (2017) 163, arXiv:1612.05741[hep-ph] .[16] K. Kovarik et al. , “nCTEQ15 - Global analysis of nuclear parton distributions with uncertainties inthe CTEQ framework”, Phys. Rev. D no. 8, (2016) 085037, arXiv:1509.00792 [hep-ph] .[17] R. Abdul Khalek, J. J. Ethier, J. Rojo, and G. van Weelden, “nNNPDF2.0: quark flavor separationin nuclei from LHC data”, JHEP (2020) 183, arXiv:2006.14629 [hep-ph] .[18] V. Guzey, E. Kryshen, M. Strikman, and M. Zhalov, “Evidence for nuclear gluon shadowing fromthe ALICE measurements of PbPb ultraperipheral exclusive J / ψ production”, Phys. Lett. B (2013) 290–295, arXiv:1305.1724 [hep-ph] .[19] J. G. Contreras, “Gluon shadowing at small x from coherent J / ψ photoproduction data at energiesavailable at the CERN Large Hadron Collider”, Phys. Rev. C no. 1, (2017) 015203, arXiv:1610.03350 [nucl-ex] .[20] ALICE
Collaboration, B. Abelev et al. , “Coherent J / ψ photoproduction in ultra-peripheral Pb-Pbcollisions at √ s NN = .
76 TeV”,
Phys. Lett. B (2013) 1273–1283, arXiv:1209.3715[nucl-ex] .[21]
ALICE
Collaboration, E. Abbas et al. , “Charmonium and e + e − pair photoproduction atmid-rapidity in ultra-peripheral Pb-Pb collisions at √ s NN =2.76 TeV”, Eur. Phys. J. C no. 11,(2013) 2617, arXiv:1305.1467 [nucl-ex] .[22] ALICE
Collaboration, J. Adam et al. , “Coherent ψ (2S) photo-production in ultra-peripheralPb–Pb collisions at √ s NN = 2.76 TeV”, Phys. Lett. B (2015) 358–370, arXiv:1508.05076[nucl-ex] . 19oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration[23] CMS
Collaboration, V. Khachatryan et al. , “Coherent J / ψ photoproduction in ultra-peripheralPbPb collisions at √ s NN = Phys. Lett. B (2017)489–511, arXiv:1605.06966 [nucl-ex] .[24]
ALICE
Collaboration, S. Acharya et al. , “Coherent J / ψ photoproduction at forward rapidity inultra-peripheral Pb-Pb collisions at √ s NN = .
02 TeV”,
Phys. Lett.
B798 (2019) 134926, arXiv:1904.06272 [nucl-ex] .[25]
ALICE
Collaboration, K. Aamodt et al. , “The ALICE experiment at the CERN LHC”,
JINST (2008) S08002.[26] ALICE
Collaboration, B. B. Abelev et al. , “Performance of the ALICE Experiment at the CERNLHC”,
Int. J. Mod. Phys. A (2014) 1430044, arXiv:1402.4476 [nucl-ex] .[27] ALICE
Collaboration, K. Aamodt et al. , “Alignment of the ALICE Inner Tracking System withcosmic-ray tracks”,
JINST (2010) P03003, arXiv:1001.0502 [physics.ins-det] .[28] J. Alme, Y. Andres, H. Appelshäuser, S. Bablok, N. Bialas, R. Bolgen, U. Bonnes, R. Bramm,P. Braun-Munzinger, R. Campagnolo, and et al., “The ALICE TPC, a large 3-dimensional trackingdevice with fast readout for ultra-high multiplicity events”, Nuclear Instruments and Methods inPhysics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment no. 1, (Oct, 2010) 316–367. http://dx.doi.org/10.1016/j.nima.2010.04.042 .[29] A. Akindinov et al. , “Performance of the ALICE Time-Of-Flight detector at the LHC”,
Eur. Phys.J. Plus (2013) 44.[30]
ALICE
Collaboration, E. Abbas et al. , “Performance of the ALICE VZERO system”,
JINST (2013) P10016, arXiv:1306.3130 [nucl-ex] .[31] LHC Forward Physics Working Group
Collaboration, K. Akiba et al. , “LHC Forward Physics”,
J. Phys. G (2016) 110201, arXiv:1611.05079 [hep-ph] .[32] ALICE
Collaboration, B. Abelev et al. , “Measurement of the Cross Section for ElectromagneticDissociation with Neutron Emission in Pb-Pb Collisions at √ s NN = 2.76 TeV”, Phys. Rev. Lett. (2012) 252302, arXiv:1203.2436 [nucl-ex] .[33]
ALICE
Collaboration, S. Acharya et al. , “ALICE luminosity determination for Pb–Pb collisionsat √ s NN = ALICE-PUBLIC-2021-001 .[34] I. A. Pshenichnov, “Electromagnetic excitation and fragmentation of ultrarelativistic nuclei”,
Phys. Part. Nucl. (2011) 215–250.[35] S. R. Klein, J. Nystrand, J. Seger, Y. Gorbunov, and J. Butterworth, “STARlight: A Monte Carlosimulation program for ultra-peripheral collisions of relativistic ions”, Comput. Phys. Commun. (2017) 258–268, arXiv:1607.03838 [hep-ph] .[36] R. Brun, F. Bruyant, F. Carminati, S. Giani, M. Maire, A. McPherson, G. Patrick, and L. Urban,
GEANT: Detector Description and Simulation Tool; Oct 1994 . CERN Program Library. CERN,Geneva, 1993. http://cds.cern.ch/record/1082634 . Long Writeup W5013.[37] H1 Collaboration, C. Alexa et al. , “Elastic and Proton-Dissociative Photoproduction of J / ψ Mesons at HERA”,
Eur. Phys. J.
C73 no. 6, (2013) 2466, arXiv:1304.5162 [hep-ex] .[38] H1 Collaboration, C. Adloff et al. , “Diffractive photoproduction of ψ (2S) mesons at HERA”, Phys. Lett. B (2002) 251–264, arXiv:hep-ex/0205107 .20oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration[39] ZEUS
Collaboration, S. Chekanov et al. , “Exclusive photoproduction of J / psi mesons at HERA”,
Eur. Phys. J. C (2002) 345–360, arXiv:hep-ex/0201043 .[40] BES
Collaboration, J. Z. Bai et al. , “ ψ ( ) → π + π − J / ψ decay distributions”, Phys. Rev. D (Jul, 2000) 032002. https://link.aps.org/doi/10.1103/PhysRevD.62.032002 .[41] M. B. G. Ducati, M. Griep, and M. Machado, “Diffractive photoproduction of radially excitedpsi(2S) mesons in photon-Pomeron reactions in PbPb collisions at the CERN LHC”, Phys. Rev. C (2013) 014910, arXiv:1305.2407 [hep-ph] .[42] Particle Data Group
Collaboration, P. Zyla et al. , “Review of Particle Physics”,
PTEP no. 8, (2020) 083C01.[43] S. R. Klein and J. Nystrand, “Exclusive vector meson production in relativistic heavy ioncollisions”,
Phys. Rev. C (1999) 014903. https://link.aps.org/doi/10.1103/PhysRevC.60.014903 .[44] V. Guzey, E. Kryshen, and M. Zhalov, “Coherent photoproduction of vector mesons inultraperipheral heavy ion collisions: Update for run 2 at the CERN Large Hadron Collider”, Phys.Rev. C no. 5, (2016) 055206, arXiv:1602.01456 [nucl-th] .[45] J. Cepila, J. G. Contreras, and J. D. Tapia Takaki, “Energy dependence of dissociative J / ψ photoproduction as a signature of gluon saturation at the LHC”, Phys. Lett. B (2017) 186–191, arXiv:1608.07559 [hep-ph] .[46] G. Sampaio dos Santos and M. Machado, “On theoretical uncertainty of color dipolephenomenology in the J / ψ and ϒ photoproduction in pA and AA collisions at the CERN LargeHadron Collider”, J. Phys. G no. 10, (2015) 105001, arXiv:1411.7918 [hep-ph] .[47] T. Lappi and H. Mäntysaari, “J / ψ production in ultraperipheral Pb+Pb and p +Pb collisions atenergies available at the CERN Large Hadron Collider”, Phys. Rev. C (Mar, 2013) 032201. https://link.aps.org/doi/10.1103/PhysRevC.87.032201 .[48] LHCb
Collaboration, R. Aaij et al. , “Central exclusive production of J / ψ and ψ ( S ) mesons in pp collisions at √ s =
13 TeV”,
JHEP (2018) 167, arXiv:1806.04079 [hep-ex] .21oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration A The ALICE Collaboration
S. Acharya , D. Adamová , A. Adler , J. Adolfsson , G. Aglieri Rinella , M. Agnello ,N. Agrawal , Z. Ahammed , S. Ahmad , S.U. Ahn , Z. Akbar , A. Akindinov ,M. Al-Turany , D.S.D. Albuquerque , D. Aleksandrov , B. Alessandro , H.M. Alfanda ,R. Alfaro Molina , B. Ali , Y. Ali , A. Alici , N. Alizadehvandchali , A. Alkin , J. Alme ,T. Alt , L. Altenkamper , I. Altsybeev , M.N. Anaam , C. Andrei , D. Andreou , A. Andronic ,V. Anguelov , T. Antiˇci´c , F. Antinori , P. Antonioli , C. Anuj , N. Apadula , L. Aphecetche ,H. Appelshäuser , S. Arcelli , R. Arnaldi , M. Arratia , I.C. Arsene , M. Arslandok , ,A. Augustinus , R. Averbeck , S. Aziz , M.D. Azmi , A. Badalà , Y.W. Baek , X. Bai ,R. Bailhache , R. Bala , A. Balbino , A. Baldisseri , M. Ball , D. Banerjee , R. Barbera ,L. Barioglio , M. Barlou , G.G. Barnaföldi , L.S. Barnby , V. Barret , C. Bartels , K. Barth ,E. Bartsch , F. Baruffaldi , N. Bastid , S. Basu , , G. Batigne , B. Batyunya , D. Bauri ,J.L. Bazo Alba , I.G. Bearden , C. Beattie , I. Belikov , A.D.C. Bell Hechavarria , F. Bellini ,R. Bellwied , S. Belokurova , V. Belyaev , G. Bencedi , , S. Beole , A. Bercuci ,Y. Berdnikov , A. Berdnikova , D. Berenyi , L. Bergmann , M.G. Besoiu , L. Betev ,P.P. Bhaduri , A. Bhasin , I.R. Bhat , M.A. Bhat , B. Bhattacharjee , P. Bhattacharya ,A. Bianchi , L. Bianchi , N. Bianchi , J. Bielˇcík , J. Bielˇcíková , A. Bilandzic , G. Biro ,S. Biswas , J.T. Blair , D. Blau , M.B. Blidaru , C. Blume , G. Boca , F. Bock ,A. Bogdanov , S. Boi , J. Bok , L. Boldizsár , A. Bolozdynya , M. Bombara , P.M. Bond ,G. Bonomi , H. Borel , A. Borissov , , H. Bossi , E. Botta , L. Bratrud ,P. Braun-Munzinger , M. Bregant , M. Broz , G.E. Bruno , , M.D. Buckland ,D. Budnikov , H. Buesching , S. Bufalino , O. Bugnon , P. Buhler , P. Buncic ,Z. Buthelezi , , J.B. Butt , S.A. Bysiak , D. Caffarri , A. Caliva , E. Calvo Villar ,J.M.M. Camacho , R.S. Camacho , P. Camerini , F.D.M. Canedo , A.A. Capon ,F. Carnesecchi , R. Caron , J. Castillo Castellanos , E.A.R. Casula , F. Catalano , C. CeballosSanchez , P. Chakraborty , S. Chandra , W. Chang , S. Chapeland , M. Chartier ,S. Chattopadhyay , S. Chattopadhyay , A. Chauvin , T.G. Chavez , C. Cheshkov ,B. Cheynis , V. Chibante Barroso , D.D. Chinellato , S. Cho , P. Chochula , P. Christakoglou ,C.H. Christensen , P. Christiansen , T. Chujo , C. Cicalo , L. Cifarelli , F. Cindolo ,M.R. Ciupek , G. Clai II , , J. Cleymans , F. Colamaria , J.S. Colburn , D. Colella , ,A. Collu , M. Colocci , , M. Concas III , , G. Conesa Balbastre , Z. Conesa del Valle , G. Contin ,J.G. Contreras , T.M. Cormier , P. Cortese , M.R. Cosentino , F. Costa , S. Costanza ,P. Crochet , E. Cuautle , P. Cui , L. Cunqueiro , A. Dainese , F.P.A. Damas , ,M.C. Danisch , A. Danu , I. Das , P. Das , P. Das , S. Das , S. Dash , S. De , A. De Caro ,G. de Cataldo , L. De Cilladi , J. de Cuveland , A. De Falco , D. De Gruttola , N. De Marco ,C. De Martin , S. De Pasquale , S. Deb , H.F. Degenhardt , K.R. Deja , L. Dello Stritto ,S. Delsanto , W. Deng , P. Dhankher , D. Di Bari , A. Di Mauro , R.A. Diaz , T. Dietel ,Y. Ding , R. Divià , D.U. Dixit , Ø. Djuvsland , U. Dmitrieva , J. Do , A. Dobrin , B. Dönigus ,O. Dordic , A.K. Dubey , A. Dubla , , S. Dudi , M. Dukhishyam , P. Dupieux ,T.M. Eder , R.J. Ehlers , V.N. Eikeland , D. Elia , B. Erazmus , F. Ercolessi , 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. Fuchs , N. Funicello , 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 , E.F. Gauger , M.B. Gay Ducati ,M. Germain , J. Ghosh , P. Ghosh , S.K. Ghosh , M. Giacalone , P. Gianotti ,22oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationP. Giubellino , , P. Giubilato , A.M.C. Glaenzer , P. Glässel , V. Gonzalez ,L.H. González-Trueba , S. Gorbunov , L. Görlich , S. Gotovac , V. Grabski ,L.K. Graczykowski , K.L. Graham , L. Greiner , A. Grelli , C. Grigoras , V. Grigoriev ,A. Grigoryan I , , S. Grigoryan , , O.S. Groettvik , F. Grosa , J.F. Grosse-Oetringhaus ,R. Grosso , R. Guernane , M. Guilbaud , 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 , , A. Harlenderova ,J.W. Harris , A. Harton , J.A. Hasenbichler , H. Hassan , D. Hatzifotiadou , P. Hauer ,L.B. Havener , S. Hayashi , S.T. Heckel , E. Hellbär , H. Helstrup , T. Herman ,E.G. Hernandez , G. Herrera Corral , F. Herrmann , K.F. Hetland , H. Hillemanns , C. Hills ,B. Hippolyte , B. Hohlweger , J. Honermann , G.H. Hong , D. Horak , S. Hornung ,R. Hosokawa , P. Hristov , C. Huang , C. Hughes , P. Huhn , T.J. Humanic , H. Hushnud ,L.A. Husova , N. Hussain , D. Hutter , J.P. Iddon , , 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 , , 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 , , P.G. Jones , J. Jung , M. Jung , A. Junique , 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 , 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 , S. Kirsch , I. Kisel ,S. Kiselev , A. Kisiel , J.L. Klay , J. Klein , , S. Klein , C. Klein-Bösing , M. Kleiner ,T. Klemenz , A. Kluge , 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 , S.D. Koryciak , L. Koska , O. Kovalenko , V. Kovalenko ,M. Kowalski , I. Králik , A. Kravˇcáková , L. Kreis , M. Krivda , , F. Krizek ,K. Krizkova Gajdosova , M. Kroesen , M. Krüger , E. Kryshen , M. Krzewicki , V. Kuˇcera ,C. Kuhn , P.G. Kuijer , T. Kumaoka , 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. La Rocca , Y.S. Lai , A. Lakrathok , M. Lamanna , R. Langoy ,K. Lapidus , P. Larionov , E. Laudi , L. Lautner , R. Lavicka , T. Lazareva , R. Lea , J. Lee ,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 , S.H. Lim , V. Lindenstruth , A. Lindner ,C. Lippmann , A. Liu , J. Liu , 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 I , , M. Malaev , Q.W. Malik , L. Malinina IV , , D. Mal’Kevich , N. Mallick ,P. Malzacher , G. Mandaglio , , V. Manko , F. Manso , V. Manzari , Y. Mao , J. Mareš ,G.V. Margagliotti , A. Margotti , A. Marín , C. Markert , M. Marquard , N.A. Martin ,P. Martinengo , J.L. Martinez , M.I. Martínez , G. Martínez García , S. Masciocchi ,M. Masera , A. Masoni , L. Massacrier , A. Mastroserio , , A.M. Mathis , O. Matonoha ,P.F.T. Matuoka , A. Matyja , C. Mayer , A.L. Mazuecos , F. Mazzaschi , M. Mazzilli , ,M.A. Mazzoni , A.F. Mechler , F. Meddi , Y. Melikyan , A. Menchaca-Rocha , C. Mengke , ,E. Meninno , , A.S. Menon , M. Meres , S. Mhlanga , Y. Miake , L. Micheletti ,L.C. Migliorin , D.L. Mihaylov , K. Mikhaylov , , A.N. Mishra , , D. Mi´skowiec ,A. Modak , N. Mohammadi , A.P. Mohanty , B. Mohanty , M. Mohisin Khan , 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 , M.G. Munhoz , R.H. Munzer , H. Murakami , S. Murray , L. Musa ,23oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationJ. Musinsky , C.J. Myers , J.W. Myrcha , B. Naik , R. Nair , B.K. Nandi , R. Nania ,E. Nappi , M.U. Naru , A.F. Nassirpour , C. Nattrass , S. Nazarenko , A. Neagu , L. Nellen ,S.V. Nesbo , G. Neskovic , D. Nesterov , B.S. Nielsen , S. Nikolaev , S. Nikulin , V. Nikulin ,F. Noferini , S. Noh , P. Nomokonov , J. Norman , N. Novitzky , P. Nowakowski ,A. Nyanin , J. Nystrand , M. Ogino , A. Ohlson , J. Oleniacz , A.C. Oliveira Da Silva ,M.H. Oliver , A. Onnerstad , C. Oppedisano , A. Ortiz Velasquez , T. Osako , A. Oskarsson ,J. Otwinowski , K. Oyama , Y. Pachmayer , S. Padhan , D. Pagano , G. Pai´c ,A. Palasciano , J. Pan , S. Panebianco , P. Pareek , 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 DaCosta , D. Peresunko , G.M. Perez , S. Perrin , Y. Pestov , V. Petráˇcek , M. Petrovici ,R.P. Pezzi , S. Piano , M. Pikna , P. Pillot , O. Pinazza , , L. Pinsky , C. Pinto , S. Pisano ,M. Płosko´n , M. Planinic , F. Pliquett , M.G. Poghosyan , B. Polichtchouk , N. Poljak ,A. Pop , S. Porteboeuf-Houssais , J. Porter , V. Pozdniakov , S.K. Prasad , R. Preghenella ,F. Prino , C.A. Pruneau , I. Pshenichnov , M. Puccio , S. Qiu , L. Quaglia , R.E. Quishpe ,S. Ragoni , A. Rakotozafindrabe , L. Ramello , F. Rami , S.A.R. Ramirez , A.G.T. Ramos ,R. Raniwala , S. Raniwala , S.S. Räsänen , R. Rath , I. Ravasenga , K.F. Read , ,A.R. Redelbach , K. Redlich V , , A. Rehman , P. Reichelt , F. Reidt , R. Renfordt ,Z. Rescakova , K. Reygers , A. Riabov , V. Riabov , T. Richert , , M. Richter , P. Riedler ,W. Riegler , F. Riggi , C. Ristea , S.P. Rode , M. Rodríguez Cahuantzi , K. Røed , R. Rogalev ,E. Rogochaya , T.S. Rogoschinski , D. Rohr , D. Röhrich , P.F. Rojas , P.S. Rokita ,F. Ronchetti , A. Rosano , , E.D. Rosas , A. Rossi , A. Rotondi , A. Roy , P. Roy ,N. Rubini , O.V. Rueda , R. Rui , B. Rumyantsev , A. Rustamov , E. Ryabinkin , Y. Ryabov ,A. Rybicki , H. Rytkonen , W. Rzesa , O.A.M. Saarimaki , R. Sadek , S. Sadovsky ,J. Saetre , K. Šafaˇrík , S.K. Saha , S. Saha , B. Sahoo , P. Sahoo , R. Sahoo , S. Sahoo ,D. Sahu , P.K. Sahu , J. Saini , S. Sakai , S. Sambyal , V. Samsonov I , , , D. Sarkar ,N. Sarkar , P. Sarma , V.M. Sarti , M.H.P. Sas , , J. Schambach , , H.S. Scheid ,C. Schiaua , R. Schicker , A. Schmah , C. Schmidt , H.R. Schmidt , M.O. Schmidt ,M. Schmidt , N.V. Schmidt , , A.R. Schmier , R. Schotter , J. Schukraft , Y. Schutz ,K. Schwarz , K. Schweda , G. Scioli , E. Scomparin , J.E. Seger , Y. Sekiguchi ,D. Sekihata , I. Selyuzhenkov , , S. Senyukov , J.J. Seo , D. Serebryakov , L. Šerkšnyt˙e ,A. Sevcenco , A. Shabanov , A. Shabetai , R. Shahoyan , W. Shaikh , A. Shangaraev ,A. Sharma , H. Sharma , M. Sharma , N. Sharma , S. Sharma , O. Sheibani ,A.I. Sheikh , K. Shigaki , M. Shimomura , S. Shirinkin , Q. Shou , Y. Sibiriak , S. Siddhanta ,T. Siemiarczuk , T.F.D. Silva , 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 , G. Skorodumovs , 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 , S.F. Stiefelmaier , D. Stocco , M.M. Storetvedt , C.P. Stylianidis ,A.A.P. Suaide , T. Sugitate , C. Suire , 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 , , Z. Tang , M. Tarhini ,M.G. Tarzila , A. Tauro , G. Tejeda Muñoz , A. Telesca , L. Terlizzi , C. Terrevoli ,G. Tersimonov , S. Thakur , D. Thomas , R. Tieulent , A. Tikhonov , A.R. Timmins ,M. Tkacik , A. Toia , N. Topilskaya , M. Toppi , F. Torales-Acosta , S.R. Torres ,A. Trifiró , , S. Tripathy , T. Tripathy , S. Trogolo , G. Trombetta , V. Trubnikov ,W.H. Trzaska , T.P. Trzcinski , B.A. Trzeciak , A. Tumkin , R. Turrisi , T.S. Tveter ,K. Ullaland , E.N. Umaka , A. Uras , M. Urioni , 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. VázquezDoce , V. Vechernin , E. Vercellin , S. Vergara Limón , L. Vermunt , R. Vértesi ,24oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationM. Verweij , 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 , A. Wegrzynek , S.C. Wenzel , J.P. Wessels , J. Wiechula , J. Wikne ,G. Wilk , J. Wilkinson , 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 , Y. Zhang , V. Zherebchevskii , Y. Zhi , D. Zhou , Y. Zhou , J. Zhu , , Y. Zhu ,A. Zichichi , G. Zinovjev , N. Zurlo Affiliation Notes I Deceased II Also at: Italian National Agency for New Technologies, Energy and Sustainable EconomicDevelopment (ENEA), Bologna, Italy
III
Also at: Dipartimento DET del Politecnico di Torino, Turin, Italy IV Also at: M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute of Nuclear, Physics,Moscow, Russia V Also at: Institute of Theoretical Physics, University of Wroclaw, Poland
Collaboration Institutes A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, Yerevan,Armenia AGH University of Science and Technology, Cracow, Poland 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 Central China Normal University, Wuhan, China Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico Chicago State University, Chicago, Illinois, United States China Institute of Atomic Energy, Beijing, China Chungbuk National University, Cheongju, Republic of Korea 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, Norway25oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE Collaboration 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 Nucleare e Teorica, Università di Pavia and Sezione INFN, Pavia, 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 ofSplit, 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 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 Gravitational and Subatomic Physics (GRASP), Utrecht University/Nikhef, Utrecht,26oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationNetherlands Institute for Nuclear Research, Academy of Sciences, Moscow, Russia 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 Moscow Institute for Physics and Technology, Moscow, Russia 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 and Sezione INFN, Bari, Italy
Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für27oherent J / ψ and ψ (cid:48) photoproduction at midrapidity ALICE CollaborationSchwerionenforschung GmbH, Darmstadt, Germany Rudjer Boškovi´c Institute, Zagreb, Croatia
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, CNRS/IN2P3, Institut de Physique des 2 Infinis de Lyon , 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 PhysiqueNucléaire (DPhN), Saclay, France
Università degli Studi di Foggia, Foggia, Italy
Università di Brescia and Sezione INFN, 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 States148