2021 002 5 January

Coherent $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ photoproduction at midrapidity

ALICE Collaboration††thanks: See Appendix A for the list of collaboration
members ALICE Collaboration

The coherent photoproduction of $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ mesons
was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV with the ALICE detector. Charmonia are
detected in the central rapidity region for events where the hadronic
interactions are strongly suppressed. The $\rm{J/\psi}$ is reconstructed using
the dilepton ($l^{+}l^{-}$) and proton-antiproton decay channels, while for
the $\rm{\psi^{\prime}}$ the dilepton and the $l^{+}l^{-}\pi^{+}\pi^{-}$ decay
channels are studied. The analysis is based on an event sample corresponding
to an integrated luminosity of about 233 ${\rm\mu b}^{-1}$. The results are
compared with theoretical models for coherent $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ photoproduction. The coherent cross section is found to
be in a good agreement with models incorporating moderate nuclear gluon
shadowing of about 0.64 at a Bjorken-$x$ of around $6\times 10^{-4}$, such as
the EPS09 parametrization, however none of the models is able to fully
describe the rapidity dependence of the coherent $\rm{J/\psi}$ cross section
including ALICE measurements at forward rapidity. The ratio of
$\rm{\psi^{\prime}}$ to $\rm{J/\psi}$ coherent photoproduction cross sections
was also measured and found to be consistent with the one for photoproduction
off protons.

##  1 Introduction

Photonuclear reactions can be studied in ultra-peripheral collisions (UPCs) of
heavy ions where the two nuclei pass by with an impact parameter larger than
the sum of their radii. Hadronic interactions are suppressed and the dominant
electromagnetic interactions are mediated by photons of small virtualities.
The intensity of the photon flux is growing with the squared nuclear charge of
the colliding ion resulting in large cross sections for the photoproduction of
vector mesons in heavy-ion collisions. The photoproduction process has a clear
experimental signature: the decay products of vector mesons are the only
signal in an otherwise empty detector.

The physics of vector meson photoproduction is described in [1, 2, 3, 4].
Photoproduction of vector mesons in ion collisions can either be coherent,
i.e. the photon interacts consistently with all nucleons in a nucleus, or
incoherent, i.e. the photon interacts with a single nucleon. Experimentally,
one can distinguish between these two production types through the typical
transverse momentum of the produced vector mesons, which is inversely
proportional to the transverse size of the target. While the coherent
photoproduction is characterized by the production of mesons with low
transverse momentum ($\langle p_{\rm T}\rangle\sim$ 60 MeV/$c$), the
incoherent is dominated by mesons with higher values ($\langle p_{\rm
T}\rangle\sim$ 500 MeV/$c$). In the first case, the nuclei usually do not
dissociate, but the electromagnetic fields of ultrarelativistic heavy nuclei
are strong enough to develop other independent soft electromagnetic
interactions accompanying the coherent photoproduction 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 measured in zero-degree calorimeters (ZDC) placed at long
distances on both sides of the detector[5]. The incoherent photoproduction can
also be accompanied by the excitation and dissociation of the target nucleon
resulting in even higher transverse momenta of the produced vector mesons [6].

Coherent heavy vector meson photoproduction is of particular interest because
of its connection with the gluon distribution functions (PDFs) in protons and
nuclei [7]. At low Bjorken-$x$ values, nuclear parton distribution functions
are significantly suppressed in the nucleus with respect to free proton PDFs,
a phenomenon known as parton shadowing [8]. Shadowing effects are usually
attributed to multiple scattering and addressed in various phenomenological
approaches based on elastic Glauber-like rescatterings of hadronic components
of the photon, Glauber-Gribov inelastic rescatterings, and high-density QCD
[9, 10, 11, 12, 13, 14]. Besides, different parameterizations of nuclear
partonic distributions based on fits to existing data are available [15, 16,
17, 18], however these parameterizations are affected by large uncertainties
at low Bjorken-$x$ values due to the limited kinematic coverage of the
available data samples.

Heavy vector meson photoproduction measurements provide a powerful tool to
study poorly known gluon shadowing effects at low $x$. The scale of the four-
momentum transfer of the interaction is related to the mass $m_{V}$ of the
vector meson as $Q^{2}~{}\sim~{}m^{2}_{V}/4$ corresponding to the perturbative
regime in the case of heavy charmonium states. The rapidity of the coherently
produced $\rm c\bar{c}$ states is related to the Bjorken-$x$ of the gluons as
$x~{}=~{}\left(m_{V}/\sqrt{s_{NN}}\right)\exp\left(\pm~{}y\right)$, where the
sign of the exponent reflects that each of the incoming lead nuclei may act as
the photon source. The gluon shadowing factor $R_{g}(x,Q^{2})$, i.e. the ratio
of the nuclear gluon density distribution to the gluon distribution in the
proton, can be evaluated via the measurement of the nuclear suppression factor
defined as the square root of the ratio of the coherent vector meson
photoproduction cross section on nuclei to the photoproduction cross section
in the impulse approximation that is based on the exclusive photoproduction
measurements with the proton target [19, 20]. The square root in this
definition is motivated by the fact that the coherent photoproduction cross
section 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 that the measured vector meson cross section in UPCs
is expressed as a sum of two contributions since either of the colliding ions
can serve as a photon source. At forward rapidities one contribution
corresponds to higher photon–nucleus energies while the other to lower
energies resulting in ambiguities in the extraction of the nuclear suppression
factor. The midrapidity region has the advantage that both contributions are
the same and the suppression factor can be extracted unambiguously in this
case. Since the contribution of the high and low energies as the rapidity
changes varies across models, the measurement of the rapidity dependence of
the cross section for coherent charmonium production may provide a new tool to
constrain the evolution of the parton distribution in the different models.

Photoproduction cross section measurements for different quarkonium species
provide an opportunity to probe gluon shadowing effects at different $Q^{2}$
scales. On the other hand, the comparison of excited and ground states of
charmonia can shed light on the modelling of the charmonium wave functions and
help to disentangle perturbative from non-perturbative effects in the model
calculations [21, 22].

Charmonium photoproduction in Pb–Pb UPCs was previously studied by the ALICE
Collaboration at $\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV [23, 24, 25]. The
coherent $\rm{J/\psi}$ photoproduction cross section was measured both at
midrapidity $|y|<0.9$ and at forward rapidity $-3.6<y<-2.6$. In addition, the
CMS Collaboration studied the coherent $\rm{J/\psi}$ photoproduction
accompanied by neutron emission at semi-forward rapidity $1.8<|y|<2.3$ at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV [26]. The results were compared with
various models and the best description was found amongst those introducing
moderate gluon shadowing in the nucleus. The ALICE measurements were used in
Ref. [19] to extract the nuclear gluon shadowing factor $R_{g}$ yielding
$R_{g}(x\sim 10^{-3})=0.61^{+0.05}_{-0.04}$ and $R_{g}(x\sim
10^{-2})=0.74^{+0.11}_{-0.12}$ at the scale of the charm quark mass. The ALICE
measurement of $\rm{\psi^{\prime}}$ photoproduction at midrapidity also
supports the moderate-shadowing scenario [25]. A complementary rapidity-
differential measurement of the coherent $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ photoproduction at forward rapidity in Pb–Pb UPCs at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV by the ALICE Collaboration further
underlines the importance of gluon shadowing effects [27]. The gluon shadowing
factor $R_{g}(x\sim 10^{-2})\sim 0.8$ was obtained under assumption that the
contribution from high photon-nucleus energies, i.e. low Bjorken $x\sim
10^{-5}$, can be neglected in the measured cross sections.

In this publication, we present the first measurement of the coherent
$\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ photoproduction cross sections at the
midrapidity range $|y|<0.8$ in the Pb–Pb UPCs at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV, recorded by ALICE in 2018. The
$\rm{J/\psi}$ photoproduction cross section in this measurement is sensitive
to $x\in(0.3,1.4)\times 10^{-3}$, a factor 2 smaller than in the previous
midrapidity measurement at $\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV [24]. This
data sample is approximately 10 times larger than Pb–Pb sample at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV used for the ALICE results reported in
Refs. [24, 25]. The larger data sample allows for a measurement of the
$\rm{J/\psi}$ cross section in three rapidity intervals ($|y|<0.15$,
$0.15<|y|<0.35$, $0.35<|y|<0.8$) extending the previous rapidity-differential
cross section measurement in the forward range at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV [27]. $\rm{J/\psi}$ decays to
$\mu^{+}\mu^{-}$, $e^{+}e^{-}$ and $\rm{p}\overline{p}$ and
$\rm{\psi^{\prime}}$ decays to $\mu^{+}\mu^{-}\pi^{+}\pi^{-}$,
$e^{+}e^{-}\pi^{+}\pi^{-}$ and $l^{+}l^{-}$ are investigated. The coherent
$\rm{J/\psi}$ production in the $\rm{p}\overline{p}$ channel in UPCs is
measured for the first time. The ratio of the $\rm{\psi^{\prime}}$ and
$\rm{J/\psi}$ cross sections is also measured and compared with earlier ALICE
measurements [25, 27]. The measured cross sections are compared to models
assuming no gluon shadowing as well as to predictions that employ moderate
gluon shadowing. Shadowing models are based on a parametrization of previously
available data, the leading twist approximation and several variations of the
color dipole approach.

##  2 Detector description

The ALICE detector and its performance are described in [28, 29]. The main
components of the ALICE detector are a central barrel placed in a large
solenoid magnet ($B=0.5$ T), covering the central pseudorapidity region, and a
muon spectrometer at forward rapidity, covering the range $-4.0<\eta<-2.5$.
Three central barrel detectors, the Inner Tracking System (ITS), the Time
Projection Chamber (TPC), and the Time-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 reconstruction [30]. The Silicon Pixel Detector (SPD) makes
up the two innermost layers of the ITS with about $10^{7}$ pixels covering the
pseudorapidity intervals $|\eta|<2$ and $|\eta|<1.4$ for the inner (radius 3.9
cm) and outer (radius 7.6 cm) layers, respectively. The SPD is read out by 400
(800) chips in the inner (outer) layer with each of the readout chips also
providing a trigger signal if at least one of its pixels is fired. When
projected into the transverse plane, the chips are arranged in 20 (40)
azimuthal regions in the inner (outer) layer allowing for a topological
selection of events at the trigger level.

The TPC is used for tracking and for particle identification [31]. A 100 kV
central electrode separates the two drift volumes, providing an electric field
for electron drift. The two end-plates, at $|z|=250$ cm, are instrumented with
Multi-Wire-Proportional-Chambers (MWPCs) with 560,000 readout pads, allowing
high precision track measurements in the transverse plane. The $z$ coordinate
is given by the time of drift in the TPC electric field. The TPC acceptance
covers the pseudorapidity region $|\eta|<0.9$. Ionization measurements of
individual track clusters are used for particle identification.

The TOF detector is a large cylindrical barrel of multigap resistive plate
chambers with about 150,000 readout channels surrounding the TPC and providing
very high precision timing measurement [32]. The TOF pseudorapidity coverage
is $|\eta|<0.8$. In combination with the tracking system, the TOF detector is
used for charged particle identification up to a momentum of about 2.5 GeV$/c$
for pions and kaons and up 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 arrays of 32 scintillator tiles each, covering the interval
$2.8\rm<\eta<5.1$ (V0A) and $-3.7\rm<\eta<-1.7$ (V0C) and positioned
respectively at $z=340$ cm and $z=-90$ cm from the interaction point [33]. The
ALICE Diffractive (AD) detector consists of two arrays of 8 scintillator tiles
each arranged in two layers, covering the range $4.9\rm<\eta<6.3$ (ADA) and
$-7.0\rm<\eta<-4.8$ (ADC) and positioned at $z=17$ m and $z=-19.5$ m from the
interaction point, respectively [34]. Both V0 and AD can be used to veto
hadronic interactions at the trigger level.

Finally, two zero-degree calorimeters ZNA and ZNC, located at $\pm 112.5$ m
from the interaction point, are used for the measurement of neutrons at beam
rapidity. They have good efficiency ($\approx 0.94$) to detect neutrons with
$|\eta|>8.8$ and have a relative energy resolution of about 20% for single
neutrons, which allows for a clear separation of events with either zero or a
few neutrons at beam rapidity [5].

##  3 Data analysis

###  3.1 Event selection

The data analysis in this paper is based on the event sample recorded during
the Pb–Pb at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV data taking period in
2018. A dedicated central barrel UPC trigger consists of topological trigger
formed by at least two and up to six TOF maxipads with at least one pair of
maxipads having an opening angle in 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 layers falling in compatible azimuthal regions. The two pairs of
chips are required to have an opening angle in azimuth larger than 153
degrees. It is further vetoed by any activity within the time windows for
nominal beam–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 $233\,\mu{\rm
b}^{-1}$, derived from the counts of two independent reference triggers, one
was based on multiplicity selection in the V0 detector and another one based
on neutron detection in the ZDC. The reference trigger cross sections were
determined from van der Meer scans; this procedure has an uncertainty of 2.2%
[35].The determination of the live-time of the UPC trigger has an additional
uncertainty of 1.5%. The total relative systematic uncertainty of the
integrated luminosity is thus 2.7%. Alternatively the reference cross section
can be calibrated using Glauber calculation [27]. The difference between the
two methods is smaller than the quoted systematic uncertainty. Alternatively
the reference cross section can be calibrated using Glauber calculation [27].
The difference between the two methods is smaller than the quoted systematic
uncertainty.

Additional offline vetoes are applied on the AD and V0 detector signals to
ensure the exclusive production of the charmonia. The offline selection in
these detectors is more precise than vetoes at the trigger level, because it
relies on larger time windows than the trigger electronics and on a more
refined algorithm to quantify the signal.

Online and offline V0 and AD veto requirements may result in significant
inefficiencies (denoted as veto inefficiencies) in selecting signal events
with exclusive charmonium production due to additional activity induced by
hadronic or electromagnetic pile–up processes from independent Pb–Pb
collisions accompanying the coherent charmonium photoproduction. The
probability of hadronic pile–up in the collected sample does not exceed 0.2%,
however there is a significant pile–up contribution from the electromagnetic
electron-pair production process. The veto inefficiency induced by these
pile–up effects in the V0 and AD detectors is estimated using events selected
with an unbiased trigger based only on the timing of bunches crossing the
interaction region. The average veto efficiency $\epsilon_{\rm veto}^{\rm
pileup}=0.920\pm 0.002$ is applied to raw charmonium yields to account for
hadronic and electromagnetic pile-up processes. In the forward rapidity
analysis a higher veto efficiency was obtained due to missing veto on V0C
detector.

Signal events with exclusive charmonium production, accompanied by
electromagnetic nuclear dissociation (EMD), can be rejected if, in addition to
the forward neutrons, other particles, produced at large rapidities, leave a
signal either in the AD or the V0 detectors. These extra particles may come
from multifragmentation or pion production processes, and the corresponding
cross sections are expected to be large [36]. The amount of good events with
neutrons, which are lost due to AD and V0 vetoes, is estimated using control
triggers without veto on AD and/or VZERO detectors. The fraction of losses for
this category of events (EMD) amounts to $26\%\pm 4\%$ for events with a
signal either in ZNA or ZNC and reach $43\%\pm 5\%$ for events with a signal
in both ZNA and ZNC. The average event loss is computed using fractions of
events with and without neutrons on either side. The average veto efficiency
correction $\epsilon_{\rm veto}^{\rm EMD}=0.92\pm 0.02$ is applied to raw
charmonium yields to account for the EMD process.

The selected events are required to have a reconstructed primary vertex
determined using at least two reconstructed tracks and having a longitudinal
position within 15 cm of either side of the nominal interaction point. The
analysis is aimed at the reconstruction of $\rm{J/\psi}$ decaying to
$\mu^{+}\mu^{-}$, $e^{+}e^{-}$, $\rm{p}\overline{p}$ and of
$\rm{\psi^{\prime}}$ decaying to $l^{+}l^{-}$and $\rm{J/\psi}$$\pi^{+}\pi^{-}$
followed by $\rm{J/\psi}$$\rightarrow l^{+}l^{-}$. Therefore, events with two
or four tracks in the central barrel are required.

Two types of tracks are considered in the analysis: global tracks and ITS
standalone tracks. Global tracks are reconstructed using combined tracking in
ITS and TPC detectors. Tracks are required to cross at least 70 (out of 159)
TPC pad-rows and to have a cluster on each of the two layers of the SPD. Each
track must 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
at least 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 opposite electric charge (unlike-sign). The probability to find
extra global tracks not passing the standard track selection criteria or being
reconstructed only in ITS is found to be negligible. The four-body decays of
$\rm{\psi^{\prime}}$ are selected by looking for exactly four tracks with at
least two being global tracks. The kinematics of the $\psi^{\prime}\rightarrow
l^{+}l^{-}\pi^{+}\pi^{-}$ decay is such that pions and leptons are well
separated: leptons have high $p_{\rm T}\approx 1$ GeV/$c$ while pions are much
softer with $p_{\rm T}\approx 0.3$ GeV/$c$. This feature is used to identify
the pion pair. Tracks are sorted according to their $p_{\rm T}$ and the two
with lowest $p_{\rm T}$ are assumed to be pions, while the other two are
assumed to be leptons. The tagged pions and lepton pairs are required to
consist of opposite-sign tracks.

To separate the $\rm{J/\psi}$$\rightarrow$ $\mu^{+}\mu^{-}$, $e^{+}e^{-}$ and
$\rm{p}\overline{p}$ decays, the particle identification (PID) capabilities of
the TPC and TOF detectors are used. The momenta of the tracks from
$\rm{J/\psi}$ decays are $p\in(1.0,2.0)$ GeV$/c$ for the $\mu^{+}\mu^{-}$ and
$e^{+}e^{-}$ channels and $p\in(0.75,1.75)$ GeV$/c$ for the
$\rm{p}\overline{p}$ channel. The PID resolution of the TPC allows for
complete separation of electrons and muons in the momentum range mentioned
above. Since the specific ionization energy loss (${\rm d}E/{\rm d}x$) of
electron and proton become equal at momenta around 1 GeV/$c$, the TPC PID is
not applicable for the identification of protons from coherently produced
$\rm{J/\psi}$. However, the PID capabilities of the TOF detector allow for the
separation of protons from other particle species in the momentum range
relevant for this analysis. For the $\rm{J/\psi}$$\rightarrow$
$\rm{p}\overline{p}$ channel, at least one track is required to have valid TOF
PID information. If no TOF PID is available for the second track, TPC PID is
used. The ${\rm d}E/{\rm d}x$ in TPC or the Lorentz Beta factor ($\beta=v/c$)
of each reconstructed track in TOF is measured in units of the standard
deviation ($\sigma$) with respect to expected values for $\mu,e,\rm p$ at the
given measured momentum. The track pair is accepted if
$n^{2}_{\sigma+}+n^{2}_{\sigma-}<16$.

The charmonium photoproduction may be accompanied by pile-up from
electromagnetic electron-pair production or by noise in the SPD resulting in
extra fired SPD trigger chips satisfying the SPD trigger selection topology.
In order to exclude contamination of events not triggered by the charmonium
decay products, the fired SPD trigger chips are required to match SPD clusters
corresponding to the selected tracks. It is found that 11% (7%) of the events
with a $\rm{J/\psi}$ candidate decaying into dimuons (di-electrons) with 4 SPD
clusters cannot be matched to the fired trigger chips. The matching
requirement has a much stronger effect for the 4-track decay channels of
$\rm{\psi^{\prime}}$ removing 40% and 22% of the candidates in the
$\rm{\psi^{\prime}}$$\rightarrow$ $\mu^{+}\mu^{-}\pi^{+}\pi^{-}$ and
$\rm{\psi^{\prime}}$$\rightarrow$ $e^{+}e^{-}\pi^{+}\pi^{-}$channel,
respectively.

###  3.2 Acceptance and efficiency correction

The product of acceptance and efficiency of the $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ reconstruction ($\epsilon$) is evaluated using a large
Monte Carlo (MC) sample of coherent and incoherent $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ events generated by STARlight 2.2.0 [37] with decay
particles tracked in a model of the experimental apparatus implemented in
GEANT 3.21 [38]. The model includes a realistic description of the detector
status during data taking and its variation with time.

For this analysis, the primary $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ vector
mesons produced in UPCs are considered to be transversely polarized. This is
consistent with expectations from helicity conservation in photo production
and consistent with H1 and ZEUS measurements [39, 40, 41]. As observed in
previous experiments, both $\rm{J/\psi}$ and the two pions from
$\rm{\psi^{\prime}}$ decay are in the S-wave state resulting into the full
transfer of the $\rm{\psi^{\prime}}$ polarisation to the $\rm{J/\psi}$ [42].
The expected polarization states of primary $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ as well as of secondary $\rm{J/\psi}$ from
$\rm{\psi^{\prime}}$ 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-body decay channels from
the $\psi^{\prime}\rightarrow\rm J/\psi+\pi^{+}\pi^{-}$ and
$\rm\psi^{\prime}\rightarrow\rm J/\psi+\pi^{0}\pi^{0}$ decays and for modeling
the signal shape and different background contributions.

The efficiency of the SPD trigger chips is measured with a data-driven
approach using a minimum bias trigger. Tracks selected without requiring hits
in both SPD layers are matched to the trigger chips they cross. The obtained
efficiency maps are introduced on an event-by-event basis to the MC
simulations. The single chip efficiency is about 92%. As the trigger requires
4 chips, the overall effect corresponds to an efficiency of about 0.72 $\pm$
0.01.

The TOF trigger efficiency is also estimated with a data-driven approach and
is taken into account in the MC simulations. The average coverage of the
active TOF trigger channels is approximately 90%. The average trigger
efficiency of the active channels is defined as the probability to find
signals in maxipads crossed by extrapolated TPC tracks from minimum bias
events and is found to be 97–98%, depending on track arrival times. More than
93% of the active channels are almost 100% efficient. The low efficiency in
some channels is caused by timing alignment issues and partially disconnected
or broken equipment.

###  3.3 Signal extraction

The extraction of coherent $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ yields in
all decay channels is performed in the rapidity interval $|y|<0.8$. In
addition, the $\rm{J/\psi}$ measurements in the dielectron and dimuon channels
are performed in three rapidity intervals: $|y|<0.15$, $0.15<|y|<0.35$, and
$0.35<|y|<0.8$ where the $y$ ranges were chosen to have approximately the same
number of candidates per range. An enriched sample of coherent $\rm{J/\psi}$
and $\rm{\psi^{\prime}}$ candidates is obtained by selecting the reconstructed
candidates with transverse momentum $p_{\rm T}<0.2$ GeV$/c$.

The invariant mass distributions for dimuon and dielectron pairs reconstructed
in the full rapidity range are shown in Fig. 1, left. The inclusive
$\rm{J/\psi}$ yields are obtained by fitting the invariant mass distributions
with an exponential function describing the underlying continuum and two
Crystal Ball functions to describe the $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$
signals. The $\rm{J/\psi}$ pole mass and width were left free, while the tail
parameters ($\alpha$ and $n$) in the Crystal Ball function were fixed to the
values obtained in MC simulations in order to gain higher stability of the
fits. In the case of the $\rm{\psi^{\prime}}$ signal, all the Crystal Ball
parameters were fixed to the values obtained in MC simulations.

The raw inclusive $\rm{J/\psi}$ yields obtained from invariant mass fits
contain contributions from the coherent and incoherent $\rm{J/\psi}$
photoproduction that can be separated via the analysis of the transverse
momentum spectra. The inclusive $p_{\rm T}$ distributions for $\mu^{+}\mu^{-}$
and $e^{+}e^{-}$ candidates around the $\rm{J/\psi}$ mass are shown in 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 mechanisms: coherent and
incoherent $\rm{J/\psi}$, feed-down $\rm{J/\psi}$ from decays of coherent and
incoherent $\rm{\psi^{\prime}}$ and the dilepton continuum from the
$\gamma\gamma\rightarrow l^{+}l^{-}$ process. Incoherent $\rm{J/\psi}$
production with nucleon dissociation (or dissociative $\rm{J/\psi}$) is also
taken into account to describe the high-$p_{\rm T}$ tail with the template
based on the H1 parametrization [39]. Normalization of feed-down $\rm{J/\psi}$
from coherent and incoherent $\rm{\psi^{\prime}}$ decays is constrained to the
normalization of primary $\rm{J/\psi}$ templates according to the feed-down
fractions extracted as described below. The normalization of the dilepton
continuum from the $\gamma\gamma\rightarrow l^{+}l^{-}$ process is fixed by
the results for the background description of the invariant mass fits. The
combinatorial background, estimated by considering the distribution of like-
sign candidates, is found to be negligible in the $\rm{J/\psi}$ mass region.

The templates are fitted to the data leaving the normalization free for
coherent $\rm{J/\psi}$, incoherent $\rm{J/\psi}$ and dissociative
$\rm{J/\psi}$ production. The extracted incoherent $\rm{J/\psi}$ fraction
$f_{\rm I}=\frac{N^{\rm incoh}}{N^{\rm coh}}$ for $p_{\rm T}<0.2$ GeV/$c$ is
$4.7\pm 0.3\%$ $(5.0\pm 0.5)\%$ for the $\mu^{+}\mu^{-}$($e^{+}e^{-}$) decay
channel. The quoted fractions include the contribution of incoherent
$\rm{J/\psi}$ with nucleon dissociation.

The invariant mass and the $p_{\rm T}$ distributions for the
$\rm{J}/\psi\rightarrow{\rm p\bar{p}}$ decay channel are shown in Fig. 2. The
data sample obtained in this channel is too small to fit the $p_{\rm T}$
distribution with MC templates. However, since the difference in resolution of
$p_{\rm T}$ shapes of the coherent or incoherent MC samples for the
$\rm{p}\overline{p}$ and $\mu^{+}\mu^{-}$ channels is negligible, one can
expect the $f_{\rm I}$ fraction to be the same. This is due to the fact that
neither the $\mu^{+}\mu^{-}$ nor the $\rm{p}\overline{p}$ channels suffer from
bremsstrahlung. This is not the case for dielectrons where bremsstrahlung
induces the large difference in the mass and momentum resolution which affect
the templates and consequently the $f_{\rm I}$ fraction.

(a) $\rm{J/\psi}$$\rightarrow$ $\mu^{+}\mu^{-}$

(b) $\rm{J/\psi}$$\rightarrow$ $e^{+}e^{-}$

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 $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ signal, respectively. The solid blue line corresponds to
the sum of background and signal functions. Right: Transverse momentum
distribution of $\rm{J/\psi}$ candidates in the range quoted in the figure
(around the $\rm{J/\psi}$ nominal mass).

Figure 2: Left: Invariant mass distribution of $\rm{p}\overline{p}$ pairs. The
dashed green line corresponds to the background description. The solid magenta
and red lines correspond to Crystal Ball functions representing the
$\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ signals, respectively. The solid blue
line corresponds to the sum of background and signal functions. Right:
Transverse momentum distribution of $\rm{J/\psi}$ candidates in the range
quoted in the figure (around the $\rm{J/\psi}$ nominal mass).

As one can see in Fig. 1, the $\rm{\psi^{\prime}}$ yields in the
$\mu^{+}\mu^{-}$ and $e^{+}e^{-}$ channels are small and lying on top of a
significant background. In order to increase the significance of the
$\rm{\psi^{\prime}}$ signal and to reduce the statistical uncertainty, the
$\rm{\psi^{\prime}}$ yield is extracted from the merged $l^{+}l^{-}$ sample
with significance $\approx 3$. Fig. 3 shows the merged dilepton mass spectrum
together with the $p_{\rm T}$ distribution of the dilepton candidates in the
invariant mass range under the $\rm{\psi^{\prime}}$ mass peak. The fit to the
invariant mass distribution is performed in the same way as described before.

Fig. 4 shows the invariant mass (left) and the $p_{\rm T}$ distribution
(right) for $\rm{\psi^{\prime}}$ $\rightarrow$ $\mu^{+}\mu^{-}\pi^{+}\pi^{-}$
and $\rm{\psi^{\prime}}$ $\rightarrow$ $e^{+}e^{-}\pi^{+}\pi^{-}$ quadruplets.
Distributions include combinatorial background. A coherent peak is clearly
visible at low $p_{\rm T}$. The signal extraction in the
$\mu^{+}\mu^{-}\pi^{+}\pi^{-}$ and $e^{+}e^{-}\pi^{+}\pi^{-}$ channel is
straight-forward since the signal is very clean. The number of candidates is
extracted by summing the bin contents in the mass interval $\rm
3.6<m_{\mu\mu\pi\pi}<3.8$ GeV/$c^{2}$ and $\rm 3.4<m_{ee\pi\pi}<3.8$
GeV/$c^{2}$. The number of candidates with wrong-sign combinations in the same
mass interval, representing the level of background, is subtracted afterwards.

The incoherent contamination of the $\rm{\psi^{\prime}}$ sample is estimated
as follows. The incoherent-to-coherent photoproduction cross section ratio is
expected to be similar for 1S and 2S charmonium states [43, 37]. Due to lack
of model calculations for the incoherent $\rm{\psi^{\prime}}$ cross section in
UPCs at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV, predicted incoherent-to-
coherent cross section ratios for $\rm{J/\psi}$ from Refs. [37, 14, 6] are
used as an estimate of the incoherent-to-coherent cross section ratio for
$\rm{\psi^{\prime}}$. The factor $f_{\rm I}=\frac{N^{\rm incoh}}{N^{\rm
coh}}\approx 6\%$ is extracted from the predicted cross section ratios,
corrected for acceptance and efficiency of coherent and incoherent
$\rm{\psi^{\prime}}$ states. The difference in the predicted incoherent-to-
coherent cross section ratios is used as an estimate of the systematic
uncertainty.

Figure 3: Left: Invariant mass distribution of $l^{+}l^{-}$ pairs. The dashed
green line corresponds to the background description. The solid magenta and
red line correspond to Crystal Ball functions representing the $\rm{J/\psi}$
and $\rm{\psi^{\prime}}$ signals, respectively. The solid blue line
corresponds to the sum of background and signal functions. Right: Transverse
momentum distribution of $\rm{\psi^{\prime}}$ candidates in the mass range
quoted in the figure (around the $\rm{\psi^{\prime}}$ mass).

(a) $\rm{\psi^{\prime}}$$\rightarrow$ $\mu^{+}\mu^{-}\pi^{+}\pi^{-}$

(b) $\rm{\psi^{\prime}}$$\rightarrow$ $e^{+}e^{-}\pi^{+}\pi^{-}$

Figure 4: Left: Invariant mass distribution for $\rm{\psi^{\prime}}$
$\rightarrow$ $\mu^{+}\mu^{-}\pi^{+}\pi^{-}$ (upper panel) and
$\rm{\psi^{\prime}}$ $\rightarrow$ $e^{+}e^{-}\pi^{+}\pi^{-}$ (bottom panel).
The green line shows the wrong sign four-track events. The red line shows the
$\rm{\psi^{\prime}}$ signal as described in the text. Right: Transverse
momentum distribution of $\rm{\psi^{\prime}}$ candidates in the mass range
quoted in the figure (around the $\rm{\psi^{\prime}}$ nominal mass).

The raw $\rm{J/\psi}$ yields contain a significant feed-down contribution
originating from decays $\psi^{\prime}\ \rightarrow{\rm J}/\psi+{\rm
anything}$, dominated by the $\rm{\psi^{\prime}}$ $\rightarrow$ $\rm{J/\psi}$
\+ $\pi^{+}\pi^{-}$ and $\rm{\psi^{\prime}}$ $\rightarrow$ $\rm{J/\psi}$\+
$\pi^{0}\pi^{0}$ decay channels. The feed-down fraction $f_{\rm
D}=\frac{N({\rm FeedDown})}{N({\rm primary})}$ can be extracted from the ratio
of raw $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ yields:

$R_{N}=\frac{N_{\psi^{\prime}}}{N_{J/\psi}}=0.0170\pm 0.0024(0.0184\pm
0.0030),$ (1)

for $\mu^{+}\mu^{-}$($e^{+}e^{-}$). The raw $\rm{\psi^{\prime}}$ and
$\rm{J/\psi}$ yields in this ratio contain contributions both from coherent
and incoherent photoproduction. However, according to the $p_{\rm T}$ fits,
the fraction $f_{\rm I}$ does not exceed 6% and, according to STARlight, the
fraction of the incoherent contributions is expected to be similar in the
$\rm{\psi^{\prime}}$ and $\rm{J/\psi}$ yields. The $R_{N}$ ratio can therefore
be considered as a good estimate of the ratio of coherent $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ yields, since the incoherent fractions largely cancel in
the ratio. The $f_{\rm D}$ ratio can be expressed via the measured $R_{N}$
ratio:

$\left(\frac{1}{f_{\rm D}}+1\right)^{-1}=\frac{N_{{\rm J}/\psi}^{\rm feed-
down}}{N_{{\rm J}/\psi}}=\frac{({\rm
BR}\times\epsilon)_{\psi^{\prime}\rightarrow{\rm
J}/\psi\pi^{+}\pi^{-}\rightarrow l^{+}l^{-}\pi^{+}\pi^{-}}+({\rm
BR}\times\epsilon)_{\psi^{\prime}\rightarrow{\rm
J}/\psi\pi^{0}\pi^{0}\rightarrow l^{+}l^{-}\pi^{0}\pi^{0}}}{({\rm
BR}\times\epsilon)_{\psi^{\prime}\to l^{+}l^{-}}}\times R_{N},$ (2)

where $({\rm BR}\times\epsilon)$ in the corresponding channels denote products
of world-average branching ratios [44] and the product of acceptance and
efficiency of measuring exactly two leptons. The $f_{\rm D}$ fractions of
$3.5\%\pm 0.5\%$ and $4.3\%\pm 0.7\%$ are obtained in the $\mu^{+}\mu^{-}$and
in $e^{+}e^{-}$ channel respectively, with the uncertainty being the quadratic
sum of statistical and systematic uncertainties, where the statistical
uncertainty dominates. The systematic uncertainty includes contributions from
the $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ signal extraction and the branching
ratios.

##  4 Results

The coherent vector meson differential cross section is given by:

$\frac{\rm{d}\sigma^{coh}_{\rm VM}}{\rm{d}y}=\frac{N^{\rm coh}_{\rm
VM}}{\epsilon_{\rm VM}~{}\times~{}\epsilon_{\rm veto}^{\rm
pileup}~{}\times~{}\epsilon_{\rm veto}^{\rm
EMD}~{}\times~{}\rm{BR}~{}\times~{}\mathcal{L}_{\rm int}~{}\times~{}\Delta y}$
(3)

where

$N^{\rm coh}_{J/\psi}=\frac{N_{\rm yield}}{1+f_{\rm I}+f_{\rm D}}$ (4)

and

$N^{\rm coh}_{\psi^{\prime}}=\frac{N_{\rm yield}}{1+f_{\rm I}}.$ (5)

The raw $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ yield values, reconstruction
efficiencies $\epsilon$, fractions corresponding to incoherent $f_{\rm I}$ and
feed-down $f_{\rm D}$ contamination as well as coherent cross sections with
statistical and systematic uncertainties are summarized in Table 1 and Table
2. Further components in the formula include integrated luminosity
$\mathcal{L}_{\rm int}$, branching ratio of the decay BR, veto efficiencies
corresponding to the pile-up $\epsilon_{\rm veto}^{\rm pileup}$ and
electromagnetic dissociation $\epsilon_{\rm veto}^{\rm EMD}$ and the rapidity
interval $\Delta\rm y$. The associated systematic uncertainties are briefly
described in the following.

Table 1: Raw $\rm{J/\psi}$ yields, $\epsilon$, $f_{\rm D}$ and $f_{\rm I}$ fractions and coherent $\rm{J/\psi}$ cross sections per decay channel Decay | $|y|$ | $N_{J/\psi}$ | $\epsilon$ | $f_{\rm D}$ | $f_{\rm I}$ |  $\rm{d}\sigma^{coh}_{J/\psi}/\ \rm{d}y$ (mb)
---|---|---|---|---|---|---
$\mu^{+}\mu^{-}$ | (0.00, 0.80) | $3120\pm 61$ | 0.037 | 0.035 | $0.047\pm 0.003$ | $4.12\pm 0.08\rm(stat.)\pm 0.23(syst.)$
$\mu^{+}\mu^{-}$ | (0.00, 0.15) | $1027\pm 35$ | 0.064 | 0.035 | $0.047\pm 0.003$ | $4.23\pm 0.15\rm(stat)\pm 0.24(syst)$
$\mu^{+}\mu^{-}$ | (0.15, 0.35) | $1083\pm 36$ | 0.051 | 0.035 | $0.047\pm 0.003$ | $4.22\pm 0.14\rm(stat)\pm 0.23(syst)$
$\mu^{+}\mu^{-}$ | (0.35, 0.80) | $976\pm 33$ | 0.022 | 0.035 | $0.047\pm 0.003$ | $3.85\pm 0.13\rm(stat)\pm 0.21(syst)$
$e^{+}e^{-}$ | (0.00, 0.80) | $2116\pm 65$ | 0.025 | 0.043 | $0.050\pm 0.005$ | $4.05\pm 0.13\rm(stat.)\pm 0.24(syst.)$
$e^{+}e^{-}$ | (0.00, 0.15) | $683\pm 33$ | 0.046 | 0.043 | $0.050\pm 0.005$ | $3.83\pm 0.19\rm(stat)\pm 0.23(syst)$
$e^{+}e^{-}$ | (0.15, 0.35) | $743\pm 34$ | 0.034 | 0.043 | $0.050\pm 0.005$ | $4.20\pm 0.19\rm(stat)\pm 0.25(syst)$
$e^{+}e^{-}$ | (0.35, 0.80) | $643\pm 31$ | 0.014 | 0.043 | $0.050\pm 0.005$ | $3.90\pm 0.19\rm(stat)\pm 0.23(syst)$
$\rm{p}\overline{p}$ | (0.00, 0.80) | $61\pm 8$ | 0.023 | 0.035 | $0.047\pm 0.003$ | $3.73\pm 0.51\rm(stat.)\pm 0.28(syst.)$
Table 2: Raw $\rm{\psi^{\prime}}$ yields, $\epsilon$, $f_{\rm I}$ fractions and coherent $\rm{\psi^{\prime}}$ cross sections per decay channel Decay | $|y|$ | $N_{\psi^{\prime}}$ | $\epsilon$ | $f_{\rm I}$ |  $\rm{d}\sigma^{coh}_{\psi^{\prime}}/\rm{d}y$ (mb)
---|---|---|---|---|---
$\mu^{+}\mu^{-}\pi^{+}\pi^{-}$ | (0.0, 0.8) | $53\pm 8$ | 0.0103 | 0.057 | $0.77\pm 0.11\rm(stat.)\pm 0.09(syst.)$
$e^{+}e^{-}\pi^{+}\pi^{-}$ | (0.0, 0.8) | $39\pm 6$ | 0.0068 | 0.064 | $0.86\pm 0.15\rm(stat.)\pm 0.11(syst.)$
$l^{+}l^{-}$ | (0.0, 0.8) | $102\pm 24$ | 0.0324 | 0.063 | $0.61\pm 0.15\rm(stat.)\pm 0.10(syst.)$

Figure 5: Measured differential cross section of coherent $\rm{J/\psi}$ (left)
and $\rm{\psi^{\prime}}$ (right) photoproduction in Pb–Pb UPCs in $|y|<0.8$.
The points show the measurements for different decay channels. The error bars
(boxes) represent the statistical (decay channel uncorrelated systematic)
uncertainty. The gray box shows the average value (dashed line) and correlated
systematic uncertainty.

The offline AD and V0 vetoes decreases the $\rm{J/\psi}$
($\rm{\psi^{\prime}}$) yield by 8% (16%) and also results in a lower
$\epsilon_{{\rm veto}}^{{\rm pileup}}$ efficiency. These two effects do not
cancel-out completely. A residual discrepancy of 3% (10%) in the cross section
of $\rm{J/\psi}$ ($\rm{\psi^{\prime}}$) is included in the systematic
uncertainty.

The uncertainty related to the evaluation of the incoherent contamination
comes from the shape of the continuum template. By default the
$\gamma\gamma\to l^{+}l^{-}$ 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 invariant mass distribution of the $\rm{J/\psi}$. These
events are, in contrast to the pure MC, supposed to include the same
background as under the $\rm{J/\psi}$ peak. By comparing the $f_{\rm I}$
fraction obtained with the side bands method and the STARlight template, a 0.8
(0.5%) uncertainty of the cross section for the $\mu^{+}\mu^{-}$
($e^{+}e^{-}$) channel is found.

A systematic uncertainty of the tracking efficiency of 2% per track is
estimated by comparing, in data and 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 $\rm{J/\psi}$ analysis the goodness of the
description of the $\rm{J/\psi}$ signal by the Crystal Ball function is
checked. The yield from the fit is compared to the number of events computed
by bin counting in the peak region with the background contribution subtracted
using the exponential background shape from the fit. Half differences of 0.3%,
2.4%, 0.6% were assigned as the systematic uncertainty in the muon, electron
and proton channel, respectively.

Another contribution to the signal extraction uncertainties is the difference
between the function used in the fit and the true shape of the background. It
is estimated by varying the fit range. A systematic uncertainty of 0.4% (0.3%)
is determined for the $\mu^{+}\mu^{-}$ ($e^{+}e^{-}$) decay channel of the
$\rm{J/\psi}$meson. The uncertainty in the background subtraction rises
rapidly as the signal-to-background ratio drops. A similar study for the
$l^{+}l^{-}$ decay of the $\rm{\psi^{\prime}}$ meson results in a 10%
systematic uncertainty.

The uncertainty associated to the determination of the trigger efficiency of
the SPD chips is obtained by changing the requirements on the probe tracks
used in the data-driven method. Variations include the running conditions, the
maximum amount of activity allowed in the event, and the definition of tracks
accepted 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 particle species to TOF is evaluated as 0.5% per track (1% in
total). The uncertainty in case of four track decays of $\rm{\psi^{\prime}}$
applies only for the lepton tracks since the low-momentum pions do not reach
the TOF detector.

In the ${\rm J}/\psi\rightarrow\rm p\overline{p}$ analysis, at least one track
is required to have proton PID from the TOF. Comparing the efficiency of the
track matching to TOF in data and MC samples, a $10\%$ disagreement is found.
The matching efficiency from MC is used and a half-difference of 5% as an
additional systematic uncertainty for the $\rm p\overline{p}$ channel is
assigned.

Tables 3 and 4 show the uncertainties for each source and channel separately
as well as quadratic sums of the channel-correlated and uncorrelated sources.

The signal extraction, incoherent contamination and branching ratio are
considered as channel-uncorrelated sources of systematic uncertainties. The
other sources are fully correlated and are the same for all channels. In the
case of the $\rm{\psi^{\prime}}$, the four track channels have an extra ITS-
TPC matching uncertainty for the pion tracks which is not correlated with the
$l^{+}l^{-}$ channel, thus it is quoted separately.

Table 3: Sources of systematic uncertainty for the coherent $\rm{J/\psi}$ cross section measurements per decay channel in percent | $\rm J/\psi\rightarrow\mu^{+}\mu^{-}$ | ${\rm J}/\psi\rightarrow e^{+}e^{-}$ | $\rm J/\psi\rightarrow p\overline{p}$
---|---|---|---
Signal Extraction | 0.5 | 2.4 | 0.7
Incoherent contamination | 0.8 | 0.5 | 0.8
Branching ratio | 0.5 | 0.5 | 1.4
TOF matching | – | – | 5.0
ITS-TPC matching | 2.8 | 2.8 | 2.8
AD and V0 veto | 3.0 | 3.0 | 3.0
SPD trigger efficiency | 1.0 | 1.0 | 1.0
TOF trigger efficiency | 0.7 | 0.7 | 0.7
Luminosity | 2.7 | 2.7 | 2.7
EMD correction | 2.0 | 2.0 | 2.0
Feed down | 0.6 | 0.6 | 0.6
Channel uncorrelated | 1.1 | 2.5 | 5.3
Channel correlated | 5.5 | 5.5 | 5.5
Table 4: Sources of systematic uncertainty for the coherent $\rm{\psi^{\prime}}$ cross section measurements per decay channel in percent | $\psi^{\prime}\rightarrow\mu^{+}\mu^{-}\pi^{+}\pi^{-}$ | $\psi^{\prime}\rightarrow e^{+}e^{-}\pi^{+}\pi^{-}$ | $\psi^{\prime}\rightarrow l^{+}l^{-}$
---|---|---|---
Signal Extraction | 1.0 | 2.0 | 10.0
Incoherent contamination | 1.4 | 1.8 | 1.8
Branching ratio | 1.5 | 1.5 | 4.8
ITS-TPC matching pions | 2.8 | 2.8 | –
ITS-TPC matching leptons | 2.8 | 2.8 | 2.8
AD and V0 veto | 10.0 | 10.0 | 10.0
SPD trigger efficiency | 1.0 | 1.0 | 1.0
TOF trigger efficiency | 0.7 | 0.7 | 0.7
Luminosity | 2.7 | 2.7 | 2.7
EMD correction | 2.0 | 2.0 | 2.0
Channel uncorrelated | 3.5 | 5.8 | 11.2
Channel correlated | 11.0 | 11.0 | 11.0

The $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ cross sections for various decay
channels computed using Eq. 3 are shown in Fig. 5. The mean values of the
$\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ cross sections are obtained as a
weighted average of the cross sections per decay 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 of the coherent $\rm{J/\psi}$ photoproduction
measurements is:

$\frac{{\rm d}\sigma^{\rm coh}_{J/\psi}}{{\rm d}y}=4.10~{}\pm
0.07\rm(stat.)\pm 0.23\rm(syst.)mb.$ (6)

The cross section value averaged over the three channels of coherent
$\rm{\psi^{\prime}}$ photoproduction measurements is:

$\frac{{\rm d}\sigma^{\rm coh}_{\psi^{\prime}}}{{\rm d}y}=0.76~{}\pm
0.08\rm(stat.)\pm 0.09\rm(syst.)mb.$ (7)

The ratio of the 2S to 1S charmonium states is:

$\frac{\frac{\sigma^{\rm coh}_{\psi^{\prime}}}{{\rm d}y}}{\frac{\sigma^{\rm
coh}_{J/\psi}}{{\rm d}y}}=0.18~{}\pm 0.0185\rm(stat.)\pm 0.028\rm(syst.)\pm
0.005\rm(BR).$ (8)

Many systematic uncertainties of the $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$
cross section measurements are correlated and cancel in 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 uncertainty is partially
correlated, so the difference of the uncertainties for $\rm{\psi^{\prime}}$
and $\rm{J/\psi}$ is taken into account in the uncertainty of the ratio. The
systematic uncertainties connected to the signal extraction, incoherent
contamination and the branching ratio are considered uncorrelated between the
two measurements. The dominant uncertainty comes from the uncorrelated part of
the AD and V0 veto uncertainty for $\rm{\psi^{\prime}}$.

##  5 Discussion

Figure 6 shows the rapidity-differential cross section of the coherent
photoproduction of $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ vector mesons in
Pb–Pb UPCs including previous ALICE measurements of $\rm{J/\psi}$ at forward
rapidity [27]. At midrapidity, $\rm{J/\psi}$ measurements performed in
absolute rapidity ranges are shown at positive rapidities and reflected into
negative rapidities. The ALICE measurements are compared to several models
which are discussed in the following:

Figure 6: Measured differential cross section of the coherent $\rm{J/\psi}$
(left) and $\rm{\psi^{\prime}}$ (right) photoproduction in Pb–Pb UPC events.
The error bars (boxes) show the statistical (systematic) uncertainties. The
theoretical calculations are also shown. The green band represents the
uncertainties of the EPS09 LO calculation.

The impulse approximation, taken from STARlight [45], is based on data from
exclusive $\rm{J/\psi}$ photoproduction off protons and neglects all nuclear
effects except for the coherence. The square root of the ratio of experimental
cross sections to the impulse approximation is $0.64\pm 0.04$ for
$\rm{J/\psi}$ and $0.66\pm 0.06$ for $\rm{\psi^{\prime}}$, 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 suppression factor reflects the magnitude of the nuclear gluon
shadowing factor at typical Bjorken-$x$ values in the range $(0.3,1.4)\times
10^{-3}$ and is in good agreement with $R_{g}(x\sim
10^{-3})=0.61^{+0.05}_{-0.04}$ obtained in Ref. [19] from the $\rm{J/\psi}$
cross section measurement in UPCs at $\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV.

STARlight is based on the Vector Meson Dominance model and a parametrization
of the existing data on $\rm{J/\psi}$ photoproduction off protons [37]. A
Glauber-like formalism is used to calculate the $\rm{J/\psi}$ photoproduction
cross section in Pb–Pb UPCs accounting for multiple interactions within the
nucleus but not accounting for the gluon shadowing corrections. The STARlight
model overpredicts the data indicating that Glauber-like rescatterings alone
are not enough to explain the observed suppression of the coherent
$\rm{J/\psi}$ cross section.

Guzey, Kryshen and Zhalov [46] provide two calculations (GKZ), one based on
the EPS09 LO parametrization of the available nuclear shadowing data [15] and
the other on the leading twist approximation (LTA) of nuclear shadowing based
on the combination of the Gribov-Glauber theory and the diffractive PDFs from
HERA [9]. 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 good agreement with the $\rm{J/\psi}$ and
$\rm{\psi^{\prime}}$ cross sections measured at midrapidity. However, these
models are in tension with the $\rm{J/\psi}$ data at semi-forward rapidity in
the range $2.5<|y|<3.5$, indicating that the nuclear shadowing might have a
smaller effect at Bjorken $x\sim 10^{-2}$ or $x\sim 5\times 10^{-5}$
corresponding to this rapidity range. It is worth noting that the GKZ
predictions are based on gluon shadowing effects at a scale $Q^{2}=3\,{\rm
GeV^{2}}$ in contrast to the default value of $2.4\,{\rm GeV^{2}}$ which is
used in other models and also in LTA predictions at lower energies [47]. The
modified $Q^{2}$ value was found to provide better description of the coherent
$\rm{J/\psi}$ production cross section in Pb–Pb UPC measured by ALICE in Run 1
as well as exclusive $\rm{J/\psi}$ photoproduction off protons [48].

Calculations by Cepila, Contreras, Krelina and Tapia Takaki (CCK) are based on
the colour dipole model with the structure of the nucleon in the transverse
plane described by the so-called hot spots, regions of high gluonic density,
whose number increases with the increasing energy [49, 14]. Nuclear effects
are implemented along the ideas proposed in the energy-dependent hot-spot
model with the standard Glauber-Gribov formalism (GG-HS) for the extension to
the nuclear case. The GG-HS model agrees with the $\rm{J/\psi}$ measurements
at midrapidity and at most forward rapidities but underpredicts them at semi-
forward rapidities. The $\rm{\psi^{\prime}}$ measurement at midrapidity is
overpredicted by this model.

Calculations by Bendova, Cepila, Contreras, Matas (BCCM) are based on the
color dipole approach coupled to the solutions of the impact-parameter
dependent Balitsky-Kovchegov equation with initial conditions based on the
Woods-Saxon shape of the Pb nucleus [10]. The model is in a reasonable
agreement with the $\rm{J/\psi}$ and $\rm{\psi^{\prime}}$ data at midrapidity.

Several theory groups provided predictions for $\rm{J/\psi}$ within the color
dipole approach coupled to the Color Glass Condensate (CGC) formalism with
different assumptions on the dipole-proton scattering amplitude. Predictions
by Gonçalves, Machado et al. (GM) [11, 50] based on the IIM and b-CGC models
for the scattering amplitude agree with the $\rm{J/\psi}$ data rather well at
midrapidity but strongly underpredict the data at forward rapidities.
Predictions by Lappi and Mäntysaari (LM) based on the IPsat model [12, 51]
overpredict the ALICE measurements at midrapidity, but match them at forward
rapidities. Recent predictions by Łuszczak and Schäfer (LS BGK-I) within the
color-dipole formulation of the Glauber-Gribov theory [13] are in agreement
with the $\rm{J/\psi}$ data at semi-forward rapidities, $2.5<|y|<3$, slightly
underpredict the data at more forward rapidities $3<|y|<4$ and overpredict the
data at midrapidity.

The comparison of the current results and those at lower energies of Run 1 may
provide interesting insights for model builders and further constraints on
gluon shadowing effects. In particular, the ratio of the coherent
$\rm{J/\psi}$ production cross sections at central and forward rapidities at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV:

$r(5.02\,{\rm TeV})=\frac{{\rm d}\sigma^{\rm coh}_{J/\psi}/{\rm
d}y(|y|<0.8,5.02\,{\rm TeV})}{{\rm d}\sigma^{\rm coh}_{J/\psi}/{\rm
d}y(-3.25<y<-3.0,5.02\,{\rm TeV})}=1.45^{+0.13}_{-0.12}$ (9)

is significantly smaller compared to a similar ratio at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV [24]:

$r(2.76\,{\rm TeV})=\frac{{\rm d}\sigma^{\rm coh}_{J/\psi}/{\rm
d}y(|y|<0.9,2.76\,{\rm TeV})}{{\rm d}\sigma^{\rm coh}_{J/\psi}/{\rm
d}y(-3.6<y<-2.6,2.76\,{\rm TeV})}=2.38^{+0.46}_{-0.38}$ (10)

where statistical and systematic uncertainties were added in quadrature. The
observed flattening of the shape of the rapidity-differential cross section is
qualitatively reproduced in the impulse approximation from STARlight where the
central-to-forward ratio decreases from 2.66 at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV to 2.22 at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV mainly due to increased contribution
of higher photon-nucleus energies to the measured cross section at forward
rapidity. However, the magnitude and the energy dependence of the central-to-
forward ratio are significantly modified compared to the impulse approximation
due to gluon shadowing effects.

The measured ratio of the $\rm{\psi^{\prime}}$ to $\rm{J/\psi}$ cross section
is compatible with the previous ALICE measurement at forward rapidities
$R=0.150\pm 0.018\rm(stat.)\pm 0.021\rm(syst.)\pm 0.007\rm(BR)$ [27], with the
exclusive photoproduction cross section ratio $R=0.166\pm 0.007\rm(stat.)\pm
0.008\rm(syst.)\pm 0.007\rm(BR)$ measured by the H1 collaboration in ep
collisions [40] and with the ratio $R\approx 0.19$ measured by the LHCb
collaboration in pp collisions [52]. The measured ratio also agrees with the
ratio $R\approx 0.20$ predicted in the leading twist approximation [46] for
Pb–Pb UPCs at midrapidity. The $\rm{\psi^{\prime}}$ to $\rm{J/\psi}$ coherent
cross section ratio is expected to have a mild dependence on the collision
energy [46]. Therefore, the measured ratio can be directly compared to the
unexpectedly large $\rm{\psi^{\prime}}$ to $\rm{J/\psi}$ coherent cross
section ratio $R=0.34^{+0.08}_{-0.07}$, measured by ALICE at midrapidity in
Pb–Pb UPCs at $\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV [25]. The previous
measurement is about a 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.

##  6 Conclusions

The first rapidity-differential measurement on the coherent photoproduction of
$\rm{J/\psi}$ at midrapidity $|y|<0.8$ in Pb–Pb UPCs at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV has been presented and compared to the
model calculations. This data complements the ALICE measurement of the
coherent $\rm{J/\psi}$ cross section at forward rapidity $-4<y<-2.5$ allowing
us to provide stringent constraints on nuclear gluon shadowing models.

The nuclear gluon shadowing factor of about 0.64 at Bjorken-$x$ values
$x\in(0.3,1.4)\times 10^{-3}$ is estimated from the comparison of the measured
coherent $\rm{J/\psi}$ cross section with the impulse approximation at
midrapidity. This result is in agreement with the gluon shadowing factor
extracted from the previous ALICE measurement of the coherent $\rm{J/\psi}$
cross section at midrapidity in Pb–Pb UPCs at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}2.76$ TeV.

None of the models is able to fully describe the measured forward and central
rapidity dependence of the coherent $\rm{J/\psi}$ cross section. The
$\rm{J/\psi}$ measurements at central and most forward rapidities are found to
be 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 model extended
to the nuclear case by the standard Glauber-Gribov formalism and the color
dipole approach coupled 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 $2.5<|y|<3.5$. The data
might be better explained with a model where shadowing has a smaller effect at
Bjorken $x\sim 10^{-2}$ or $x\sim 5\times 10^{-5}$ corresponding to this
rapidity range. On the other hand, the models based on the color dipole
approach coupled to the color glass condensate formalism describe either the
forward or central measurements depending on the dipole scattering amplitude
assumptions but they are not able to describe the measured cross section in
the full rapidity range.

The ratio of the $\rm{\psi^{\prime}}$ to $\rm{J/\psi}$ cross sections at
midrapidity is in a reasonable agreement with the ratio of photoproduction
cross sections off protons measured by the H1 and LHCb collaborations, with
the leading twist approximation predictions for Pb–Pb UPCs as well as with the
ALICE measurement at forward rapidities.

## Acknowledgements

The ALICE Collaboration would like to thank all its engineers and technicians for their invaluable contributions to the construction of the experiment and the CERN accelerator teams for the outstanding performance of the LHC complex. The ALICE Collaboration gratefully acknowledges the resources and support provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG) collaboration. The ALICE Collaboration acknowledges the following funding agencies for their support in building and running the ALICE detector: A. I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS), Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M 2467-N36] and Nationalstiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo à Pesquisa 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 Education and Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; Czech Science Foundation; The Danish Council for Independent Research | Natural Sciences, the VILLUM FONDEN and Danish 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 Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Research and Religions, Greece; National Research, Development and Innovation Office, Hungary; Department of Atomic Energy Government of India (DAE), Department of Science and Technology, Government of India (DST), University Grants Commission, Government of India (UGC) and Council of Scientific and Industrial Research (CSIR), India; Indonesian Institute of Science, Indonesia; 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 Society 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) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Science and Higher Education, National Science Centre and WUT ID-UB, Poland; Korea Institute of Science and Technology Information and National Research Foundation of Korea (NRF), Republic of Korea; Ministry of Education and Scientific Research, Institute of Atomic Physics and Ministry of Research and Innovation and Institute of Atomic Physics, Romania; Joint Institute for Nuclear Research (JINR), Ministry 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 Education, Science, Research and Sport of the Slovak Republic, Slovakia; National Research Foundation of South Africa, South Africa; Swedish Research Council (VR) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organization for Nuclear Research, Switzerland; Suranaree University of Technology (SUT), National Science and Technology Development Agency (NSDTA) and Office of the Higher Education Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy Agency (TAEK), Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom; National Science Foundation of the United States of America (NSF) and United States Department of Energy, Office of Nuclear Physics (DOE NP), United States of America.

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##  Appendix A The ALICE Collaboration

S. Acharya142, D. Adamová97, A. Adler75, J. Adolfsson82, G. Aglieri Rinella35,
M. Agnello31, N. Agrawal55, Z. Ahammed142, S. Ahmad16, S.U. Ahn77, Z. Akbar52,
A. Akindinov94, M. Al-Turany109, D.S.D. Albuquerque124, D. Aleksandrov90, B.
Alessandro60, H.M. Alfanda7, R. Alfaro Molina72, B. Ali16, Y. Ali14, A.
Alici26, N. Alizadehvandchali127, A. Alkin35, J. Alme21, T. Alt69, L.
Altenkamper21, I. Altsybeev115, M.N. Anaam7, C. Andrei49, D. Andreou92, A.
Andronic145, V. Anguelov106, T. Antičić110, F. Antinori58, P. Antonioli55, C.
Anuj16, N. Apadula81, L. Aphecetche117, H. Appelshäuser69, S. Arcelli26, R.
Arnaldi60, M. Arratia81, I.C. Arsene20, M. Arslandok147,106, A. Augustinus35,
R. Averbeck109, S. Aziz79, M.D. Azmi16, A. Badalà57, Y.W. Baek42, X. Bai109,
R. Bailhache69, R. Bala103, A. Balbino31, A. Baldisseri139, M. Ball44, D.
Banerjee4, R. Barbera27, L. Barioglio25, M. Barlou86, G.G. Barnaföldi146, L.S.
Barnby96, V. Barret136, C. Bartels129, K. Barth35, E. Bartsch69, F.
Baruffaldi28, N. Bastid136, S. Basu82,144, G. Batigne117, B. Batyunya76, D.
Bauri50, J.L. Bazo Alba114, I.G. Bearden91, C. Beattie147, I. Belikov138,
A.D.C. Bell Hechavarria145, F. Bellini35, R. Bellwied127, S. Belokurova115, V.
Belyaev95, G. Bencedi70,146, S. Beole25, A. Bercuci49, Y. Berdnikov100, A.
Berdnikova106, D. Berenyi146, L. Bergmann106, M.G. Besoiu68, L. Betev35, P.P.
Bhaduri142, A. Bhasin103, I.R. Bhat103, M.A. Bhat4, B. Bhattacharjee43, P.
Bhattacharya23, A. Bianchi25, L. Bianchi25, N. Bianchi53, J. Bielčík38, J.
Bielčíková97, A. Bilandzic107, G. Biro146, S. Biswas4, J.T. Blair121, D.
Blau90, M.B. Blidaru109, C. Blume69, G. Boca29, F. Bock98, A. Bogdanov95, S.
Boi23, J. Bok62, L. Boldizsár146, A. Bolozdynya95, M. Bombara39, P.M. Bond35,
G. Bonomi141, H. Borel139, A. Borissov83,95, H. Bossi147, E. Botta25, L.
Bratrud69, P. Braun-Munzinger109, M. Bregant123, M. Broz38, G.E. Bruno108,34,
M.D. Buckland129, D. Budnikov111, H. Buesching69, S. Bufalino31, O. Bugnon117,
P. Buhler116, P. Buncic35, Z. Buthelezi73,133, J.B. Butt14, S.A. Bysiak120, D.
Caffarri92, M. Cai28,7, A. Caliva109, E. Calvo Villar114, J.M.M. Camacho122,
R.S. Camacho46, P. Camerini24, F.D.M. Canedo123, A.A. Capon116, F.
Carnesecchi26, R. Caron139, J. Castillo Castellanos139, E.A.R. Casula23, F.
Catalano31, C. Ceballos Sanchez76, P. Chakraborty50, S. Chandra142, W. Chang7,
S. Chapeland35, M. Chartier129, S. Chattopadhyay142, S. Chattopadhyay112, A.
Chauvin23, T.G. Chavez46, C. Cheshkov137, B. Cheynis137, V. Chibante
Barroso35, D.D. Chinellato124, S. Cho62, P. Chochula35, P. Christakoglou92,
C.H. Christensen91, P. Christiansen82, T. Chujo135, C. Cicalo56, L.
Cifarelli26, F. Cindolo55, M.R. Ciupek109, G. ClaiII,55, J. Cleymans126, F.
Colamaria54, J.S. Colburn113, D. Colella54,146, A. Collu81, M. Colocci35,26,
M. ConcasIII,60, G. Conesa Balbastre80, Z. Conesa del Valle79, G. Contin24,
J.G. Contreras38, T.M. Cormier98, P. Cortese32, M.R. Cosentino125, F. Costa35,
S. Costanza29, P. Crochet136, E. Cuautle70, P. Cui7, L. Cunqueiro98, A.
Dainese58, F.P.A. Damas117,139, M.C. Danisch106, A. Danu68, I. Das112, P.
Das88, P. Das4, S. Das4, S. Dash50, S. De88, A. De Caro30, G. de Cataldo54, L.
De Cilladi25, J. de Cuveland40, A. De Falco23, D. De Gruttola30, N. De
Marco60, C. De Martin24, S. De Pasquale30, S. Deb51, H.F. Degenhardt123, K.R.
Deja143, L. Dello Stritto30, S. Delsanto25, W. Deng7, P. Dhankher19, D. Di
Bari34, A. Di Mauro35, R.A. Diaz8, T. Dietel126, Y. Ding7, R. Divià35, D.U.
Dixit19, Ø. Djuvsland21, U. Dmitrieva64, J. Do62, A. Dobrin68, B. Dönigus69,
O. Dordic20, A.K. Dubey142, A. Dubla109,92, S. Dudi102, M. Dukhishyam88, P.
Dupieux136, T.M. Eder145, R.J. Ehlers98, V.N. Eikeland21, D. Elia54, B.
Erazmus117, F. Ercolessi26, F. Erhardt101, A. Erokhin115, M.R. Ersdal21, B.
Espagnon79, G. Eulisse35, D. Evans113, S. Evdokimov93, L. Fabbietti107, M.
Faggin28, J. Faivre80, F. Fan7, A. Fantoni53, M. Fasel98, P. Fecchio31, A.
Feliciello60, G. Feofilov115, A. Fernández Téllez46, A. Ferrero139, A.
Ferretti25, A. Festanti35, V.J.G. Feuillard106, J. Figiel120, S. Filchagin111,
D. Finogeev64, F.M. Fionda21, G. Fiorenza54, F. Flor127, A.N. Flores121, S.
Foertsch73, P. Foka109, S. Fokin90, E. Fragiacomo61, U. Fuchs35, N.
Funicello30, C. Furget80, A. Furs64, M. Fusco Girard30, J.J. Gaardhøje91, M.
Gagliardi25, A.M. Gago114, A. Gal138, C.D. Galvan122, P. Ganoti86, C.
Garabatos109, J.R.A. Garcia46, E. Garcia-Solis10, K. Garg117, C. Gargiulo35,
A. Garibli89, K. Garner145, P. Gasik107, E.F. Gauger121, M.B. Gay Ducati71, M.
Germain117, J. Ghosh112, P. Ghosh142, S.K. Ghosh4, M. Giacalone26, P.
Gianotti53, P. Giubellino109,60, P. Giubilato28, A.M.C. Glaenzer139, P.
Glässel106, V. Gonzalez144, L.H. González-Trueba72, S. Gorbunov40, L.
Görlich120, S. Gotovac36, V. Grabski72, L.K. Graczykowski143, K.L. Graham113,
L. Greiner81, A. Grelli63, C. Grigoras35, V. Grigoriev95, A. GrigoryanI,1, S.
Grigoryan76,1, O.S. Groettvik21, F. Grosa60, J.F. Grosse-Oetringhaus35, R.
Grosso109, R. Guernane80, M. Guilbaud117, M. Guittiere117, K. Gulbrandsen91,
T. Gunji134, A. Gupta103, R. Gupta103, I.B. Guzman46, R. Haake147, M.K.
Habib109, C. Hadjidakis79, H. Hamagaki84, G. Hamar146, M. Hamid7, R.
Hannigan121, M.R. Haque143,88, A. Harlenderova109, J.W. Harris147, A.
Harton10, J.A. Hasenbichler35, H. Hassan98, D. Hatzifotiadou55, P. Hauer44,
L.B. Havener147, S. Hayashi134, S.T. Heckel107, E. Hellbär69, H. Helstrup37,
T. Herman38, E.G. Hernandez46, G. Herrera Corral9, F. Herrmann145, K.F.
Hetland37, H. Hillemanns35, C. Hills129, B. Hippolyte138, B. Hohlweger107, J.
Honermann145, G.H. Hong148, D. Horak38, S. Hornung109, R. Hosokawa15, P.
Hristov35, C. Huang79, C. Hughes132, P. Huhn69, T.J. Humanic99, H. Hushnud112,
L.A. Husova145, N. Hussain43, D. Hutter40, J.P. Iddon35,129, R. Ilkaev111, H.
Ilyas14, M. Inaba135, G.M. Innocenti35, M. Ippolitov90, A. Isakov38,97, M.S.
Islam112, M. Ivanov109, V. Ivanov100, V. Izucheev93, B. Jacak81, N.
Jacazio35,55, P.M. Jacobs81, S. Jadlovska119, J. Jadlovsky119, S. Jaelani63,
C. Jahnke123, M.J. Jakubowska143, M.A. Janik143, T. Janson75, M. Jercic101, O.
Jevons113, M. Jin127, F. Jonas98,145, P.G. Jones113, J. Jung69, M. Jung69, A.
Junique35, A. Jusko113, P. Kalinak65, A. Kalweit35, V. Kaplin95, S. Kar7, A.
Karasu Uysal78, D. Karatovic101, O. Karavichev64, T. Karavicheva64, P.
Karczmarczyk143, E. Karpechev64, A. Kazantsev90, U. Kebschull75, R. Keidel48,
M. Keil35, B. Ketzer44, Z. Khabanova92, A.M. Khan7, S. Khan16, A.
Khanzadeev100, Y. Kharlov93, A. Khatun16, A. Khuntia120, B. Kileng37, B.
Kim62, D. Kim148, D.J. Kim128, E.J. Kim74, H. Kim17, J. Kim148, J.S. Kim42, J.
Kim106, J. Kim148, J. Kim74, M. Kim106, S. Kim18, T. Kim148, S. Kirsch69, I.
Kisel40, S. Kiselev94, A. Kisiel143, J.L. Klay6, J. Klein35,60, S. Klein81, C.
Klein-Bösing145, M. Kleiner69, T. Klemenz107, A. Kluge35, A.G. Knospe127, C.
Kobdaj118, M.K. Köhler106, T. Kollegger109, A. Kondratyev76, N. Kondratyeva95,
E. Kondratyuk93, J. Konig69, S.A. Konigstorfer107, P.J. Konopka2,35, G.
Kornakov143, S.D. Koryciak2, L. Koska119, O. Kovalenko87, V. Kovalenko115, M.
Kowalski120, I. Králik65, A. Kravčáková39, L. Kreis109, M. Krivda113,65, F.
Krizek97, K. Krizkova Gajdosova38, M. Kroesen106, M. Krüger69, E. Kryshen100,
M. Krzewicki40, V. Kučera35, C. Kuhn138, P.G. Kuijer92, T. Kumaoka135, L.
Kumar102, S. Kundu88, P. Kurashvili87, A. Kurepin64, A.B. Kurepin64, A.
Kuryakin111, S. Kushpil97, J. Kvapil113, M.J. Kweon62, J.Y. Kwon62, Y.
Kwon148, S.L. La Pointe40, P. La Rocca27, Y.S. Lai81, A. Lakrathok118, M.
Lamanna35, R. Langoy131, K. Lapidus35, P. Larionov53, E. Laudi35, L.
Lautner35, R. Lavicka38, T. Lazareva115, R. Lea24, J. Lee135, J. Lehrbach40,
R.C. Lemmon96, I. León Monzón122, E.D. Lesser19, M. Lettrich35, P. Lévai146,
X. Li11, X.L. Li7, J. Lien131, R. Lietava113, B. Lim17, S.H. Lim17, V.
Lindenstruth40, A. Lindner49, C. Lippmann109, A. Liu19, J. Liu129, I.M.
Lofnes21, V. Loginov95, C. Loizides98, P. Loncar36, J.A. Lopez106, X.
Lopez136, E. López Torres8, J.R. Luhder145, M. Lunardon28, G. Luparello61,
Y.G. Ma41, A. Maevskaya64, M. Mager35, S.M. Mahmood20, T. Mahmoud44, A.
Maire138, R.D. MajkaI,147, M. Malaev100, Q.W. Malik20, L. MalininaIV,76, D.
Mal’Kevich94, N. Mallick51, P. Malzacher109, G. Mandaglio33,57, V. Manko90, F.
Manso136, V. Manzari54, Y. Mao7, J. Mareš67, G.V. Margagliotti24, A.
Margotti55, A. Marín109, C. Markert121, M. Marquard69, N.A. Martin106, P.
Martinengo35, J.L. Martinez127, M.I. Martínez46, G. Martínez García117, S.
Masciocchi109, M. Masera25, A. Masoni56, L. Massacrier79, A.
Mastroserio140,54, A.M. Mathis107, O. Matonoha82, P.F.T. Matuoka123, A.
Matyja120, C. Mayer120, A.L. Mazuecos35, F. Mazzaschi25, M. Mazzilli35,54,
M.A. Mazzoni59, A.F. Mechler69, F. Meddi22, Y. Melikyan64, A. Menchaca-
Rocha72, E. Meninno116,30, A.S. Menon127, M. Meres13, S. Mhlanga126, Y.
Miake135, L. Micheletti25, L.C. Migliorin137, D.L. Mihaylov107, K.
Mikhaylov76,94, A.N. Mishra146,70, D. Miśkowiec109, A. Modak4, N. Mohammadi35,
A.P. Mohanty63, B. Mohanty88, M. Mohisin Khan16, Z. Moravcova91, C.
Mordasini107, D.A. Moreira De Godoy145, L.A.P. Moreno46, I. Morozov64, A.
Morsch35, T. Mrnjavac35, V. Muccifora53, E. Mudnic36, D. Mühlheim145, S.
Muhuri142, J.D. Mulligan81, A. Mulliri23, M.G. Munhoz123, R.H. Munzer69, H.
Murakami134, S. Murray126, L. Musa35, J. Musinsky65, C.J. Myers127, J.W.
Myrcha143, B. Naik50, R. Nair87, B.K. Nandi50, R. Nania55, E. Nappi54, M.U.
Naru14, A.F. Nassirpour82, C. Nattrass132, S. Nazarenko111, A. Neagu20, L.
Nellen70, S.V. Nesbo37, G. Neskovic40, D. Nesterov115, B.S. Nielsen91, S.
Nikolaev90, S. Nikulin90, V. Nikulin100, F. Noferini55, S. Noh12, P.
Nomokonov76, J. Norman129, N. Novitzky135, P. Nowakowski143, A. Nyanin90, J.
Nystrand21, M. Ogino84, A. Ohlson82, J. Oleniacz143, A.C. Oliveira Da
Silva132, M.H. Oliver147, A. Onnerstad128, C. Oppedisano60, A. Ortiz
Velasquez70, T. Osako47, A. Oskarsson82, J. Otwinowski120, K. Oyama84, Y.
Pachmayer106, S. Padhan50, D. Pagano141, G. Paić70, A. Palasciano54, J.
Pan144, S. Panebianco139, P. Pareek142, J. Park62, J.E. Parkkila128, S.
Parmar102, S.P. Pathak127, B. Paul23, J. Pazzini141, H. Pei7, T. Peitzmann63,
X. Peng7, L.G. Pereira71, H. Pereira Da Costa139, D. Peresunko90, G.M. Perez8,
S. Perrin139, Y. Pestov5, V. Petráček38, M. Petrovici49, R.P. Pezzi71, S.
Piano61, M. Pikna13, P. Pillot117, O. Pinazza55,35, L. Pinsky127, C. Pinto27,
S. Pisano53, M. Płoskoń81, M. Planinic101, F. Pliquett69, M.G. Poghosyan98, B.
Polichtchouk93, N. Poljak101, A. Pop49, S. Porteboeuf-Houssais136, J.
Porter81, V. Pozdniakov76, S.K. Prasad4, R. Preghenella55, F. Prino60, C.A.
Pruneau144, I. Pshenichnov64, M. Puccio35, S. Qiu92, L. Quaglia25, R.E.
Quishpe127, S. Ragoni113, A. Rakotozafindrabe139, L. Ramello32, F. Rami138,
S.A.R. Ramirez46, A.G.T. Ramos34, R. Raniwala104, S. Raniwala104, S.S.
Räsänen45, R. Rath51, I. Ravasenga92, K.F. Read98,132, A.R. Redelbach40, K.
RedlichV,87, A. Rehman21, P. Reichelt69, F. Reidt35, R. Renfordt69, Z.
Rescakova39, K. Reygers106, A. Riabov100, V. Riabov100, T. Richert82,91, M.
Richter20, P. Riedler35, W. Riegler35, F. Riggi27, C. Ristea68, S.P. Rode51,
M. Rodríguez Cahuantzi46, K. Røed20, R. Rogalev93, E. Rogochaya76, T.S.
Rogoschinski69, D. Rohr35, D. Röhrich21, P.F. Rojas46, P.S. Rokita143, F.
Ronchetti53, A. Rosano33,57, E.D. Rosas70, A. Rossi58, A. Rotondi29, A. Roy51,
P. Roy112, N. Rubini26, O.V. Rueda82, R. Rui24, B. Rumyantsev76, A.
Rustamov89, E. Ryabinkin90, Y. Ryabov100, A. Rybicki120, H. Rytkonen128, W.
Rzesa143, O.A.M. Saarimaki45, R. Sadek117, S. Sadovsky93, J. Saetre21, K.
Šafařík38, S.K. Saha142, S. Saha88, B. Sahoo50, P. Sahoo50, R. Sahoo51, S.
Sahoo66, D. Sahu51, P.K. Sahu66, J. Saini142, S. Sakai135, S. Sambyal103, V.
SamsonovI,100,95, D. Sarkar144, N. Sarkar142, P. Sarma43, V.M. Sarti107,
M.H.P. Sas147,63, J. Schambach98,121, H.S. Scheid69, C. Schiaua49, R.
Schicker106, A. Schmah106, C. Schmidt109, H.R. Schmidt105, M.O. Schmidt106, M.
Schmidt105, N.V. Schmidt98,69, A.R. Schmier132, R. Schotter138, J.
Schukraft35, Y. Schutz138, K. Schwarz109, K. Schweda109, G. Scioli26, E.
Scomparin60, J.E. Seger15, Y. Sekiguchi134, D. Sekihata134, I.
Selyuzhenkov109,95, S. Senyukov138, J.J. Seo62, D. Serebryakov64, L.
Šerkšnytė107, A. Sevcenco68, A. Shabanov64, A. Shabetai117, R. Shahoyan35, W.
Shaikh112, A. Shangaraev93, A. Sharma102, H. Sharma120, M. Sharma103, N.
Sharma102, S. Sharma103, O. Sheibani127, A.I. Sheikh142, K. Shigaki47, M.
Shimomura85, S. Shirinkin94, Q. Shou41, Y. Sibiriak90, S. Siddhanta56, T.
Siemiarczuk87, T.F.D. Silva123, D. Silvermyr82, G. Simatovic92, G.
Simonetti35, B. Singh107, R. Singh88, R. Singh103, R. Singh51, V.K. Singh142,
V. Singhal142, T. Sinha112, B. Sitar13, M. Sitta32, T.B. Skaali20, G.
Skorodumovs106, M. Slupecki45, N. Smirnov147, R.J.M. Snellings63, C.
Soncco114, J. Song127, A. Songmoolnak118, F. Soramel28, S. Sorensen132, I.
Sputowska120, J. Stachel106, I. Stan68, P.J. Steffanic132, S.F.
Stiefelmaier106, D. Stocco117, M.M. Storetvedt37, C.P. Stylianidis92, A.A.P.
Suaide123, T. Sugitate47, C. Suire79, M. Suljic35, R. Sultanov94, M.
Šumbera97, V. Sumberia103, S. Sumowidagdo52, S. Swain66, A. Szabo13, I.
Szarka13, U. Tabassam14, S.F. Taghavi107, G. Taillepied136, J. Takahashi124,
G.J. Tambave21, S. Tang136,7, Z. Tang130, M. Tarhini117, M.G. Tarzila49, A.
Tauro35, G. Tejeda Muñoz46, A. Telesca35, L. Terlizzi25, C. Terrevoli127, G.
Tersimonov3, S. Thakur142, D. Thomas121, R. Tieulent137, A. Tikhonov64, A.R.
Timmins127, M. Tkacik119, A. Toia69, N. Topilskaya64, M. Toppi53, F. Torales-
Acosta19, S.R. Torres38, A. Trifiró33,57, S. Tripathy70, T. Tripathy50, S.
Trogolo28, G. Trombetta34, V. Trubnikov3, W.H. Trzaska128, T.P. Trzcinski143,
B.A. Trzeciak38, A. Tumkin111, R. Turrisi58, T.S. Tveter20, K. Ullaland21,
E.N. Umaka127, A. Uras137, M. Urioni141, G.L. Usai23, M. Vala39, N. Valle29,
S. Vallero60, N. van der Kolk63, L.V.R. van Doremalen63, M. van Leeuwen92, P.
Vande Vyvre35, D. Varga146, Z. Varga146, M. Varga-Kofarago146, A. Vargas46, M.
Vasileiou86, A. Vasiliev90, O. Vázquez Doce107, V. Vechernin115, E.
Vercellin25, S. Vergara Limón46, L. Vermunt63, R. Vértesi146, M. Verweij63, L.
Vickovic36, Z. Vilakazi133, O. Villalobos Baillie113, G. Vino54, A.
Vinogradov90, T. Virgili30, V. Vislavicius91, A. Vodopyanov76, B. Volkel35,
M.A. Völkl105, K. Voloshin94, S.A. Voloshin144, G. Volpe34, B. von Haller35,
I. Vorobyev107, D. Voscek119, J. Vrláková39, B. Wagner21, M. Weber116, A.
Wegrzynek35, S.C. Wenzel35, J.P. Wessels145, J. Wiechula69, J. Wikne20, G.
Wilk87, J. Wilkinson109, G.A. Willems145, E. Willsher113, B. Windelband106, M.
Winn139, W.E. Witt132, J.R. Wright121, Y. Wu130, R. Xu7, S. Yalcin78, Y.
Yamaguchi47, K. Yamakawa47, S. Yang21, S. Yano47,139, Z. Yin7, H. Yokoyama63,
I.-K. Yoo17, J.H. Yoon62, S. Yuan21, A. Yuncu106, V. Yurchenko3, V. Zaccolo24,
A. Zaman14, C. Zampolli35, H.J.C. Zanoli63, N. Zardoshti35, A.
Zarochentsev115, P. Závada67, N. Zaviyalov111, H. Zbroszczyk143, M. Zhalov100,
S. Zhang41, X. Zhang7, Y. Zhang130, V. Zherebchevskii115, Y. Zhi11, D. Zhou7,
Y. Zhou91, J. Zhu7,109, Y. Zhu7, A. Zichichi26, G. Zinovjev3, N. Zurlo141

Affiliation Notes

I Deceased

II Also at: Italian National Agency for New Technologies, Energy and
Sustainable Economic Development (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

1 A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute)
Foundation, Yerevan, Armenia

2 AGH University of Science and Technology, Cracow, Poland

3 Bogolyubov Institute for Theoretical Physics, National Academy of Sciences
of Ukraine, Kiev, Ukraine

4 Bose Institute, Department of Physics and Centre for Astroparticle Physics
and Space Science (CAPSS), Kolkata, India

5 Budker Institute for Nuclear Physics, Novosibirsk, Russia

6 California Polytechnic State University, San Luis Obispo, California, United
States

7 Central China Normal University, Wuhan, China

8 Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana,
Cuba

9 Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and
Mérida, Mexico

10 Chicago State University, Chicago, Illinois, United States

11 China Institute of Atomic Energy, Beijing, China

12 Chungbuk National University, Cheongju, Republic of Korea

13 Comenius University Bratislava, Faculty of Mathematics, Physics and
Informatics, Bratislava, Slovakia

14 COMSATS University Islamabad, Islamabad, Pakistan

15 Creighton University, Omaha, Nebraska, United States

16 Department of Physics, Aligarh Muslim University, Aligarh, India

17 Department of Physics, Pusan National University, Pusan, Republic of Korea

18 Department of Physics, Sejong University, Seoul, Republic of Korea

19 Department of Physics, University of California, Berkeley, California,
United States

20 Department of Physics, University of Oslo, Oslo, Norway

21 Department of Physics and Technology, University of Bergen, Bergen, Norway

22 Dipartimento di Fisica dell’Università ’La Sapienza’ and Sezione INFN,
Rome, Italy

23 Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy

24 Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy

25 Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy

26 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Bologna, Italy

27 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Catania, Italy

28 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Padova, Italy

29 Dipartimento di Fisica e Nucleare e Teorica, Università di Pavia and
Sezione INFN, Pavia, Italy

30 Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo
Collegato INFN, Salerno, Italy

31 Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy

32 Dipartimento di Scienze e Innovazione Tecnologica dell’Università del
Piemonte Orientale and INFN Sezione di Torino, Alessandria, Italy

33 Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy

34 Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari,
Italy

35 European Organization for Nuclear Research (CERN), Geneva, Switzerland

36 Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, Split, Croatia

37 Faculty of Engineering and Science, Western Norway University of Applied
Sciences, Bergen, Norway

38 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University in Prague, Prague, Czech Republic

39 Faculty of Science, P.J. Šafárik University, Košice, Slovakia

40 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-
Universität Frankfurt, Frankfurt, Germany

41 Fudan University, Shanghai, China

42 Gangneung-Wonju National University, Gangneung, Republic of Korea

43 Gauhati University, Department of Physics, Guwahati, India

44 Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-
Wilhelms-Universität Bonn, Bonn, Germany

45 Helsinki Institute of Physics (HIP), Helsinki, Finland

46 High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico

47 Hiroshima University, Hiroshima, Japan

48 Hochschule Worms, Zentrum für Technologietransfer und Telekommunikation
(ZTT), Worms, Germany

49 Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest, Romania

50 Indian Institute of Technology Bombay (IIT), Mumbai, India

51 Indian Institute of Technology Indore, Indore, India

52 Indonesian Institute of Sciences, Jakarta, Indonesia

53 INFN, Laboratori Nazionali di Frascati, Frascati, Italy

54 INFN, Sezione di Bari, Bari, Italy

55 INFN, Sezione di Bologna, Bologna, Italy

56 INFN, Sezione di Cagliari, Cagliari, Italy

57 INFN, Sezione di Catania, Catania, Italy

58 INFN, Sezione di Padova, Padova, Italy

59 INFN, Sezione di Roma, Rome, Italy

60 INFN, Sezione di Torino, Turin, Italy

61 INFN, Sezione di Trieste, Trieste, Italy

62 Inha University, Incheon, Republic of Korea

63 Institute for Gravitational and Subatomic Physics (GRASP), Utrecht
University/Nikhef, Utrecht, Netherlands

64 Institute for Nuclear Research, Academy of Sciences, Moscow, Russia

65 Institute of Experimental Physics, Slovak Academy of Sciences, Košice,
Slovakia

66 Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India

67 Institute of Physics of the Czech Academy of Sciences, Prague, Czech
Republic

68 Institute of Space Science (ISS), Bucharest, Romania

69 Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany

70 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México,
Mexico City, Mexico

71 Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS),
Porto Alegre, Brazil

72 Instituto de Física, Universidad Nacional Autónoma de México, Mexico City,
Mexico

73 iThemba LABS, National Research Foundation, Somerset West, South Africa

74 Jeonbuk National University, Jeonju, Republic of Korea

75 Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik,
Fachbereich Informatik und Mathematik, Frankfurt, Germany

76 Joint Institute for Nuclear Research (JINR), Dubna, Russia

77 Korea Institute of Science and Technology Information, Daejeon, Republic of
Korea

78 KTO Karatay University, Konya, Turkey

79 Laboratoire de Physique des 2 Infinis, Irène Joliot-Curie, Orsay, France

80 Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-
Alpes, CNRS-IN2P3, Grenoble, France

81 Lawrence Berkeley National Laboratory, Berkeley, California, United States

82 Lund University Department of Physics, Division of Particle Physics, Lund,
Sweden

83 Moscow Institute for Physics and Technology, Moscow, Russia

84 Nagasaki Institute of Applied Science, Nagasaki, Japan

85 Nara Women’s University (NWU), Nara, Japan

86 National and Kapodistrian University of Athens, School of Science,
Department of Physics , Athens, Greece

87 National Centre for Nuclear Research, Warsaw, Poland

88 National Institute of Science Education and Research, Homi Bhabha National
Institute, Jatni, India

89 National Nuclear Research Center, Baku, Azerbaijan

90 National Research Centre Kurchatov Institute, Moscow, Russia

91 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

92 Nikhef, National institute for subatomic physics, Amsterdam, Netherlands

93 NRC Kurchatov Institute IHEP, Protvino, Russia

94 NRC «Kurchatov»Institute - ITEP, Moscow, Russia

95 NRNU Moscow Engineering Physics Institute, Moscow, Russia

96 Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom

97 Nuclear Physics Institute of the Czech Academy of Sciences, Řež u Prahy,
Czech Republic

98 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

99 Ohio State University, Columbus, Ohio, United States

100 Petersburg Nuclear Physics Institute, Gatchina, Russia

101 Physics department, Faculty of science, University of Zagreb, Zagreb,
Croatia

102 Physics Department, Panjab University, Chandigarh, India

103 Physics Department, University of Jammu, Jammu, India

104 Physics Department, University of Rajasthan, Jaipur, India

105 Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen,
Germany

106 Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg,
Heidelberg, Germany

107 Physik Department, Technische Universität München, Munich, Germany

108 Politecnico di Bari and Sezione INFN, Bari, Italy

109 Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum
für Schwerionenforschung GmbH, Darmstadt, Germany

110 Rudjer Bošković Institute, Zagreb, Croatia

111 Russian Federal Nuclear Center (VNIIEF), Sarov, Russia

112 Saha Institute of Nuclear Physics, Homi Bhabha National Institute,
Kolkata, India

113 School of Physics and Astronomy, University of Birmingham, Birmingham,
United Kingdom

114 Sección Física, Departamento de Ciencias, Pontificia Universidad Católica
del Perú, Lima, Peru

115 St. Petersburg State University, St. Petersburg, Russia

116 Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria

117 SUBATECH, IMT Atlantique, Université de Nantes, CNRS-IN2P3, Nantes, France

118 Suranaree University of Technology, Nakhon Ratchasima, Thailand

119 Technical University of Košice, Košice, Slovakia

120 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of
Sciences, Cracow, Poland

121 The University of Texas at Austin, Austin, Texas, United States

122 Universidad Autónoma de Sinaloa, Culiacán, Mexico

123 Universidade de São Paulo (USP), São Paulo, Brazil

124 Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil

125 Universidade Federal do ABC, Santo Andre, Brazil

126 University of Cape Town, Cape Town, South Africa

127 University of Houston, Houston, Texas, United States

128 University of Jyväskylä, Jyväskylä, Finland

129 University of Liverpool, Liverpool, United Kingdom

130 University of Science and Technology of China, Hefei, China

131 University of South-Eastern Norway, Tonsberg, Norway

132 University of Tennessee, Knoxville, Tennessee, United States

133 University of the Witwatersrand, Johannesburg, South Africa

134 University of Tokyo, Tokyo, Japan

135 University of Tsukuba, Tsukuba, Japan

136 Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France

137 Université de Lyon, CNRS/IN2P3, Institut de Physique des 2 Infinis de Lyon
, Lyon, France

138 Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France,
Strasbourg, France

139 Université Paris-Saclay Centre d’Etudes de Saclay (CEA), IRFU, Départment
de Physique Nucléaire (DPhN), Saclay, France

140 Università degli Studi di Foggia, Foggia, Italy

141 Università di Brescia and Sezione INFN, Brescia, Italy

142 Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata,
India

143 Warsaw University of Technology, Warsaw, Poland

144 Wayne State University, Detroit, Michigan, United States

145 Westfälische Wilhelms-Universität Münster, Institut für Kernphysik,
Münster, Germany

146 Wigner Research Centre for Physics, Budapest, Hungary

147 Yale University, New Haven, Connecticut, United States

148 Yonsei University, Seoul, Republic of Korea