2018 120 9 May

$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ in Xe–Xe at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV

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

In this Letter, the ALICE Collaboration presents the first measurements of the
charged-particle multiplicity density,
$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$, and total charged-particle
multiplicity, $N^{\mathrm{tot}}_{\mathrm{ch}}$, in Xe–Xe collisions at a
centre-of-mass energy per nucleon–nucleon pair of
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV. The measurements are performed as a
function of collision centrality over a wide pseudorapidity range of
$-3.5<\eta<5$. The values of $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ at
mid-rapidity and $N_{\mathrm{ch}}^{\mathrm{tot}}$ for central collisions,
normalised to the number of nucleons participating in the collision
($N_{\mathrm{part}}$) as a function of $\sqrt{\it{s}_{\mathrm{NN}}}$ follow
the trends established in previous heavy-ion measurements. The same quantities
are also found to increase as a function of $N_{\mathrm{part}}$, and up to the
5% most central collisions the trends are the same as the ones observed in
Pb–Pb at a similar energy. For more central collisions, the Xe–Xe scaled
multiplicities exceed those in Pb–Pb for a similar $N_{\mathrm{part}}$. The
results are compared to phenomenological models and theoretical calculations
based on different mechanisms for particle production in nuclear collisions.
All considered models describe the data reasonably well within 15%.

##  1 Introduction

A plasma of strongly interacting quarks and gluons is formed in the hot and
dense nuclear matter created in ultra-relativistic heavy-ion collisions [1,
2]. The multiplicity of charged particles produced in the collisions is a key
observable to characterise the properties of the matter created in these
collisions, as the overall particle production is related to the initial
energy density. Nuclei are extended objects and the degree of geometrical
overlap between them in the collision, expressed in terms of the impact
parameter ($b$), varies. Since $b$ is not directly measurable, an experimental
proxy of centrality is used to characterise the amount of nuclear overlap in
the collisions. Typical features related to the collision centrality are the
number of nucleons participating in the collision, $N_{\mathrm{part}}$, and
the number of binary nucleon-nucleon collisions, $N_{\mathrm{coll}}$, among
the participant nucleons. Collisions of nuclei of different sizes lead to
different $N_{\mathrm{part}}$ and $N_{\mathrm{coll}}$ for similar relative
nuclear overlap. The study of the production of charged particles with
different collision systems and at various collision energies can help shed
light on the role of the initial energy density and the production mechanism
of final-state particles.

Previous measurements of the system-size dependence of the charged-particle
pseudorapidity density ($\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$) were
performed at RHIC, comparing Au–Au and Cu–Cu collisions at various centre-of-
mass energies [3]. The ALICE, ATLAS and CMS Collaborations at the LHC have
previously reported on $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ in Pb–Pb
collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 2.76 TeV [4, 5, 6, 7] and 5.02
TeV [8, 9]. The dependence of the charged-particle density averaged at mid-
rapidity ($|\eta|$ $<$ 0.5)
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ over the centre-of-
mass energy shows a steeper increase in central heavy-ion collisions than in
proton–proton (pp) and proton–nucleus (pA) collisions. The values of
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$, normalised by the
number of nucleon pairs participating in the collision, increase faster than
linearly with $N_{\mathrm{part}}$. No significant differences between the
shapes of the $N_{\mathrm{part}}$ dependence for the different collision
energies were observed.

In this Letter, the ALICE Collaboration presents the first measurement of the
production of charged, primary particles in Xe–Xe collisions at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV. The size of the Xe–Xe system is
intermediate between previously studied systems at the LHC, Pb–Pb [4, 5, 8, 9]
being the largest and p–Pb and pp [10, 11] the smallest. The charged-particle
pseudorapidity density is presented over the interval $-3.5<\eta<5$ and as a
function of the collision centrality. The mid-rapidity values normalised by
the number of participating nucleon–nucleon pairs are also reported. The
results are also compared with measurements at lower collision energies and
with theoretical calculations.

##  2 Experimental setup

The data were recorded with the ALICE apparatus in 6 hours of stable data-
taking with 129Xe beams (16 bunches per beam) colliding at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV in October 2017. The data were
collected with a reduced magnetic field of 0.2 T (as compared to the nominal
value of 0.5 T) in the ALICE solenoid magnet. The performance and a detailed
description of ALICE can be found elsewhere [12]. In the following, the
detector elements relevant to this analysis are briefly described.

The innermost part of the tracking system of ALICE is the Silicon Pixel
Detector (SPD) [13] which consists of two cylindrical layers of hybrid silicon
pixel assemblies. The inner and outer SPD layers are placed at radii of 3.9
and 7.6 cm from the interaction point and cover $|\eta|<2$ and $|\eta|<1.4$,
respectively. The Forward Multiplicity Detector (FMD) [14, 15] consists of
three sets of silicon strip sensors, covering the pseudorapidities
$-3.5<\eta<-1.8$ and $1.8<\eta<5$. The FMD records the energy deposited by
charged particles impinging the detector. The V0 detector [16, 15] is used for
triggering and centrality classification. It consists of two sub-detectors,
V0-A and V0-C, covering the pseudorapidity regions $2.8<\eta<5.1$ and
$-3.7<\eta<-1.7$, respectively. The V0 has a timing resolution better than 1
ns, allowing its fast signals to be combined in a programmable logic to reject
beam-induced background events while ensuring maximum efficiency for the
selection of collision events. The Zero-Degree Calorimeters (ZDCs) [17] are
located at a distance of 112.5 m from the interaction point along the beam
line, on either side of the experiment. They measure the energy of spectator
(non–interacting) nucleons. The ZDCs are also used for triggering and provide
timing information used to select collisions occurring in the interaction
point region.

##  3 Data sample and analysis method

The hadronic interaction rate in ALICE was about 150 (80) Hz at the beginning
(end) of the data-taking. The magnetic field of 0.2 T, reduced as compared to
normal Pb–Pb settings (0.5 T) increases the acceptance for low-momentum
particles, thus enhancing the acceptance of the V0 system for electromagnetic
(EM) interactions, which constitute a background for this analysis. In order
to suppress this source of contamination, the minimum bias interaction trigger
required a signal in each of the V0 sub-detectors in coincidence with a signal
in each of the two neutron ZDCs. It was verified by means of a set of control
triggers that such a trigger is fully efficient for hadronic interactions in
the 0–90% centrality range. In addition, beam-background interactions are
removed using the V0 and the ZDC timing information. The interaction
probability per bunch-crossing was sufficiently small that the chance of two
hadronic interactions occurring within the integration time of the involved
detectors, so-called pileup events, was negligible. A total of about 1 million
hadronic collisions are used in this analysis.

The classification of collisions into centrality classes uses the sum of the
amplitudes of the signals in the V0-A and V0-C detectors. A model of particle
production, based on a Glauber description [18, 19], is fitted to the V0
amplitude distribution [20]. The number of particles in the V0 detector is
calculated with a two-component model for the number of sources given by

$N_{\mathrm{sources}}=f\times N_{\mathrm{part}}+(1-f)\times
N_{\mathrm{coll}}\quad,$ (1)

where $f$ constrains the relative contributions of $N_{\mathrm{part}}$ and
$N_{\mathrm{coll}}$, coupled to a particle production model for each source
parameterised by the negative binomial distribution (NBD). In the Glauber
calculation, the nuclear density for 129Xe is described by a Woods-Saxon
distribution for a deformed nucleus

$\rho(r,\vartheta)=\rho_{0}\frac{1}{1+\exp\left(\frac{r-R(\vartheta)}{a}\right)}\quad.$
(2)

The parameter $\rho_{0}$ is the nucleon density, which provides the overall
normalisation. The nuclear skin thickness is $a=0.59\pm 0.07\,\mathrm{fm}$
[21]. The nuclear radius $R$ is parametrised as a function of the polar angle
$\vartheta$ by $R(\vartheta)=R_{0}[1+\beta_{2}Y_{20}(\vartheta)]$, where
$R_{0}$ is the average radius and the Legendre polynomial $Y_{20}$ describes
the nucleus deformation for an axially symmetric case with no dependence on
the azimuthal angle. For the average radius we used $R_{0}=5.4\pm
0.1\,\mathrm{fm}$, scaling the results for 132Xe reported in [21] by the
atomic mass number (A) dependence of the radius, namely $(129/132)^{1/3}$
[19]. The deformation parameter $\beta_{2}=0.18\pm 0.02$ is obtained by
linearly interpolating the values measured for the Xe A-even isotopes from 124
to 136 [22]. In the Glauber model calculation, the orientation of the spheroid
symmetry axis is randomly sampled. For $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44
TeV collisions, an inelastic nucleon–nucleon cross section of $68.4\pm
0.5\,\mathrm{mb}$, obtained by logarithmic interpolation of cross section
measurements with respect to collision energies in pp collisions [23], is
used. The NBD-Glauber fit provides a good description of the observed V0
amplitude in the region corresponding to the top 90% of the hadronic cross
section, where the effects of trigger inefficiency and contamination by EM
processes are negligible. The average numbers of participants $\langle
N_{\mathrm{part}}\rangle$ reported in Tab. 1 are estimated from the Glauber
model imposing the same cuts applied to the data on the simulated V0 response.
One should note that the centrality selection based on the V0 amplitude
induces a bias on the measured
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$. This leads to a
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ in the 70–-80%
(80–-90%) centrality class about 3% (10%) lower than the value one would
obtain with a centrality selection based on the impact parameter.

For all the collisions in the 0–90% centrality range the coordinates of the
primary interaction point can be reconstructed with good accuracy by
correlating hits in the two SPD layers. The measurement of the charged-
particle multiplicity density at mid-rapidity uses information from the SPD.
The acceptance of the SPD for charged particles spans different pseudorapidity
regions depending on the position of the interaction point along the beam
line, $z$. For example, for collisions with the vertex located within
$\left|z\right|<7\,\mathrm{cm}$ a maximum acceptance of
$\left|\eta\right|<1.5$ can be reached, with approximately constant acceptance
for $\left|\eta\right|<0.5$. To extend the pseudorapidity coverage up to
$\left|\eta\right|<2$, all collisions with a primary vertex located within
$\left|z\right|<20\,\mathrm{cm}$ have been considered.

Following the method developed earlier [5, 4, 8, 9, 24], tracklets (short
track segments) are formed using the position of the primary vertex and all
possible combinations of hits between the two SPD layers. The primary charged-
particle multiplicity density $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ is
obtained from the number of tracklets that pass the quality selection
criteria, after correcting for detector acceptance, reconstruction and
selection efficiencies and contamination from combinatorial background and
secondary charged particles. This selection allows primary charged-particle
detection down to a momentum of 30 MeV/$c$. The corrections are estimated
using a detailed simulation based on events generated with the HIJING event
generator [25] with particle transport in ALICE performed by GEANT3 [26]. The
decay products of long-lived decaying particles like
$\mathrm{K}^{0}_{\mathrm{S}}$, $\Lambda$, $\bar{\Lambda}$ and other strange
hadrons are classified as secondary particles [27] and the contamination from
these particles is subtracted from data. It is known that HIJING
underestimates the relative production rate of strange particles in high-
energy heavy-ion collisions. For this reason, the simulation has been
reweighed to reproduce the relative particle abundances observed in the data
which are about 30% (50%) higher than HIJING in the most central (peripheral)
collisions. The reweighing factors have been derived from an estimate of
$\mathrm{K}^{0}_{\mathrm{S}}$, $\Lambda$ and $\bar{\Lambda}$ relative
production in the data, obtained via invariant mass reconstruction and
compared to HIJING.

The deposited energy signal in the FMD is used to measure the charged-particle
pseudorapidity density in the forward regions ($-3.5<\eta<-1.8$ and
$1.8<\eta<5$), following the method described elsewhere [5]. The energy loss
is measured in the 51,200 Si strip sensors of the detector and a statistical
approach is used to calculate the inclusive number of charged particles. A
data-driven correction derived from previous studies [24] corrects for the
background of secondary particles, which are abundant in the forward regions.

##  4 Systematic uncertainties

The systematic uncertainties on $\langle N_{\mathrm{part}}\rangle$ are
obtained by varying the parameters of the Glauber model independently within
their estimated uncertainties and repeating the NBD-Glauber fit. The
uncertainty due to the centrality determination is estimated by changing the
value of V0 amplitude that corresponds to the top $90\%$ of the hadronic cross
section by $\pm 0.5\%$. This results in an uncertainty on
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ of 0.1% to 4.8% from
central to peripheral collisions. An additional 4% uncertainty assigned to the
most peripheral class, arising from the remaining contamination from EM
processes, was estimated by studying the energy deposition in the ZDCs [28].

For the tracklet analysis at mid-rapidity the relative systematic uncertainty
on the measurement of the charged-particle multiplicity in peripheral
(central) events arises from the following sources: tracklet selection 0.1%
(0.8%), calculated by varying the tracklet quality cut up to 4 times the
nominal value; combinatorial background subtraction 0.5% (2.0%), estimated
from simulations and cross-checked using an alternative method where
artificial SPD clusters are added to the data and the number of corresponding
artificial reconstructed tracklets are used for background subtraction;
particle composition 0.2% (0.2%), estimated by changing the relative
abundances of protons, pions and kaons by $\pm$30% in the simulation;
contamination by weak decays 0.3% (0.3%), estimated by changing the
reweighting factors; extrapolation to zero transverse momentum 0.6% (0.6%),
obtained from the variation of the estimated yield of particles at low
transverse momentum by a factor of two in the simulation; variations in
detector acceptance and efficiency 1% (1%), evaluated by carrying out the
analysis for different slices of the $z$-position of the interaction vertex
and with subsamples in azimuth. At forward rapidities, the uncertainties
related to the measurement of multiplicity arise from the following sources:
the data-driven correction for secondary particles [9] 6.1%; the merging
algorithms of signals from Si strips to a single particle 1%; variation in
rejection threshold for calculation of the charged-particle multiplicity per
event ${}^{+1\%}_{-2\%}$; particle composition 2%, estimated in the same way
as in the tracklet analysis.

The systematic uncertainties from centrality selection and electromagnetic
interactions affect the overall normalisation of the results. The total
systematic uncertainty, obtained by adding in quadrature all contributions,
amounts to 6.4% (2%) for peripheral (central) in $|\eta|<2$, to 6.9% for
$\eta>3.5$ and to 6.4% elsewhere in the forward region, and is partially
correlated over $\eta$ and between different centrality classes.

##  5 Results

Centrality | $\langle N_{\mathrm{part}}\rangle$ | $\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ | $\frac{2}{\langle N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ | $N_{\mathrm{ch}}^{\mathrm{tot}}$ | $\frac{2}{\langle N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$
---|---|---|---|---|---
0–1% | 246 $\pm$ 2 | 1302 $\pm$ 17 | 10.6 $\pm$ 0.2 | 14700 $\pm$ 300 | 119.5 $\pm$ 2.6
1–2% | 241 $\pm$ 2 | 1223 $\pm$ 25 | 10.1 $\pm$ 0.2 | 13840 $\pm$ 250 | 114.9 $\pm$ 2.3
2–3% | 236 $\pm$ 3 | 1166 $\pm$ 23 | 9.88 $\pm$ 0.23 | 13250 $\pm$ 280 | 112.3 $\pm$ 2.8
3–4% | 231 $\pm$ 2 | 1113 $\pm$ 20 | 9.64 $\pm$ 0.19 | 12700 $\pm$ 290 | 110.0 $\pm$ 2.7
4–5% | 225 $\pm$ 3 | 1069 $\pm$ 20 | 9.50 $\pm$ 0.22 | 12180 $\pm$ 260 | 108.3 $\pm$ 2.7
0–2.5% | 242 $\pm$ 2 | 1238 $\pm$ 25 | 10.2 $\pm$ 0.2 | 14100 $\pm$ 320 | 116.5 $\pm$ 2.8
2.5–5.0% | 229 $\pm$ 2 | 1096 $\pm$ 27 | 9.57 $\pm$ 0.25 | 12440 $\pm$ 280 | 108.6 $\pm$ 2.6
5.0–7.5% | 214 $\pm$ 3 | 986 $\pm$ 25 | 9.21 $\pm$ 0.27 | 11230 $\pm$ 330 | 105.0 $\pm$ 3.4
7.5–10% | 199 $\pm$ 2 | 891 $\pm$ 24 | 8.95 $\pm$ 0.26 | 10300 $\pm$ 300 | 103.5 $\pm$ 3.2
0–5% | 236 $\pm$ 2 | 1167 $\pm$ 26 | 9.89 $\pm$ 0.24 | 13230 $\pm$ 280 | 112.1 $\pm$ 2.6
5–10% | 207 $\pm$ 3 | 939 $\pm$ 24 | 9.07 $\pm$ 0.27 | 10820 $\pm$ 280 | 105.0 $\pm$ 3.1
10–20% | 165 $\pm$ 3 | 706 $\pm$ 17 | 8.56 $\pm$ 0.26 | 8200 $\pm$ 310 | 99.4 $\pm$ 4.2
20–30% | 118 $\pm$ 4 | 478 $\pm$ 11 | 8.10 $\pm$ 0.33 | 5670 $\pm$ 300 | 96.1 $\pm$ 6.0
30–40% | 82.2 $\pm$ 3.9 | 315 $\pm$ 8 | 7.66 $\pm$ 0.41 | 3770 $\pm$ 270 | 91.7 $\pm$ 7.9
40–50% | 54.6 $\pm$ 3.6 | 198 $\pm$ 5 | 7.25 $\pm$ 0.51 | 2460 $\pm$ 220 | 90.1 $\pm$ 10
50–60% | 34.1 $\pm$ 3.0 | 118 $\pm$ 3 | 6.92 $\pm$ 0.63 | 1480 $\pm$ 170 | 86.8 $\pm$ 13
60–70% | 19.7 $\pm$ 2.1 | 64.7 $\pm$ 2.0 | 6.57 $\pm$ 0.73 | 828 $\pm$ 44 | 84.1 $\pm$ 10
70–80% | 10.5 $\pm$ 1.1 | 32.0 $\pm$ 1.3 | 6.10 $\pm$ 0.68 | 437 $\pm$ 16 | 83.2 $\pm$ 9.2
80–90% | 5.13 $\pm$ 0.46 | 13.3 $\pm$ 0.9 | 5.19 $\pm$ 0.58 | 181 $\pm$ 7.0 | 70.6 $\pm$ 6.9
Table 1:  The $\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ and
$N_{\mathrm{ch}}^{\mathrm{tot}}$ values for different centrality classes,
defined by V0 multiplicity. The errors are total uncertainties, the
statistical contribution being negligible. The values of $\langle
N_{\mathrm{part}}\rangle$ obtained with the Glauber model are also reported.
The errors are obtained by varying the parameters of the NBD-Glauber
calculation.

Figure 1 presents the charged-particle multiplicity density
$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ as a function of pseudorapidity for
12 centrality classes. The measurement is obtained from the SPD at mid-
rapidity, FMD in forward-rapidities, and combined in regions of overlap
($1.8<|\eta|<2$) between the two detectors by taking the weighted average
using the non-shared uncertainties as weights. The data are symmetrised around
$\eta=0$, averaging positive and negative $\eta$ results wherever possible,
and extended into the non-measured region $-5<\eta<-3.5$ by reflecting the
$3.5<\eta<5$ values around $\eta=0$. Averaged values (left and right) agree
within the uncertainties. Assuming that the charged-particle rapidity density
$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}y$ has Gaussian shape and using an
effective Jacobian, the measured $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ is
fitted with this ansatz and a width of $\sigma=4.4\pm 0.1$ is found,
consistent with the value obtained in Pb–Pb at $\sqrt{\it{s}_{\mathrm{NN}}}$ =
5.02 TeV [9].

The multiplicity density averaged over $|\eta|<0.5$ in different centrality
classes is shown in Tab. 1. The total charged-particle multiplicity
$N_{\mathrm{ch}}^{\mathrm{tot}}$ is determined from the data in the measured
region and from extrapolations, up to $\eta=\pm y_{\mathrm{beam}}$, in the
unmeasured region. Three different functions are used to extrapolate the data
points: the difference of two Gaussian distributions centred at $\eta=0$; a
Woods-Saxon-like distribution in rapidity as proposed by PHOBOS [29]; and a
trapezoidal form. The trapezoid ansatz in the forward unmeasured regions
corresponds to a linear extrapolation up to $\eta=\pm y_{\mathrm{beam}}$ with
the starting point constrained by the measurements. A Gaussian
$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}y$ in rapidity results in a distribution
in pseudorapidity which is very similar to the difference of two Gaussians
centered at $\eta$ = 0. The central value in the unmeasured regions
($-8.6<\eta<-3.5$ and $5<\eta<8.6$) is taken as the average between the
trapezoidal function (which gives the lowest $N^{\mathrm{tot}}_{\mathrm{ch}}$)
and the Gaussian $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}y$ (which gives the
highest $N^{\mathrm{tot}}_{\mathrm{ch}}$). The contribution from the
extrapolated region is less than 30% of $N^{\mathrm{tot}}_{\mathrm{ch}}$. The
systematic uncertainty of the extrapolated $N_{\mathrm{ch}}^{\mathrm{tot}}$ is
calculated as the quadratic sum of contributions from the systematic
uncertainty of the data and a conservative contribution obtained by comparing
the results from the different fit functions. It amounts to about 14% (4%) of
$N_{\mathrm{ch}}^{\mathrm{tot}}$ in peripheral (central) events. In order to
compare bulk particle production at different energies and in different
collision systems, the average charged-particle multiplicity density
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ at mid-rapidity is
divided by the average number of participating nucleon pairs, $\langle
N_{\mathrm{part}}\rangle$/2. This allows one to compare nuclear collisions to
pp and $\mathrm{p\overline{p}}$ collisions. The $\langle
N_{\mathrm{part}}\rangle$ values are calculated within the Glauber model.

Figure 1:  Charged–particle pseudorapidity density for 12 centrality classes
over a broad $\eta$ range in Xe–Xe collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$
= 5.44 TeV. Boxes around the points reflect the total systematic
uncertainties, while the filled squares on the right reflect the normalisation
uncertainty from the centrality determination. Statistical errors are
negligible. The reflection (open circles) of the $3.5<\eta<5$ values around
$\eta=0$ is also shown. The lines correspond to fits to a gaussian
distribution in rapidity multiplied by an effective Jacobian of transformation
from $\eta$ to $y$.  Figure 2: Values of $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
(top) and $\frac{2}{\langle
N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$ (bottom) for the 5%
most central Xe–Xe collisions compared to previous measurements in Pb–Pb [8,
9, 4, 6, 7, 30] and Au–Au [31, 32, 33, 3, 34] as a function of
$\sqrt{\it{s}_{\mathrm{NN}}}$, as well as for inelastic pp,
$\mathrm{p\overline{p}}$ [10, 35, 36] and non-single diffractive pA and dA
collisions [11, 37]. The lines are power law fits to the data, excluding Xe–Xe
results. The central Pb–Pb measurements from CMS and ATLAS at 2.76 TeV have
been shifted horizontally for clarity.

Figure 2 (top) shows the mid-rapidity charged-particle multiplicity normalised
by the number of nucleon pairs participating in the collision,
$\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$,
in pp, $\mathrm{p\bar{p}}$, p(d)A and in central heavy-ion collisions as a
function of the centre-of-mass energy. The lines represent fits to lower
energy results. The Xe–Xe result is in agreement within the uncertainties with
the trend established from previous heavy-ion measurements, which shows a
stronger rise as a function of $\sqrt{\it{s}_{\mathrm{NN}}}$ than for pp and
p–Pb collisions. Figure 2 (bottom) shows the total charged-particle
multiplicity per participant nucleon pair $\frac{2}{\langle
N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$ , which follows the
trend for central heavy-ion collisions.

Figure 3 shows the centrality dependence of the mid-rapidity and the total
multiplicities per participant nucleon pairs. The point-to-point centrality-
dependent uncertainties are indicated by error bars whereas the shaded bands
show the correlated uncertainties. The values of $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
and $\frac{2}{\langle N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$
decrease by a factor 2 from the most central to the most peripheral
collisions, where they agree with the values measured in minimum bias pp and
p–Pb collisions [10, 11]. The data are compared to lower energy results at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 200 GeV [3] for the RHIC experiment,
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 2.76 TeV [4, 5] and
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV [8, 9] for Pb–Pb collisions where the
latter has been re-analysed with the same analysis technique in narrower
centrality classes, scaled to match the Xe–Xe data at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV. The scaling factors are calculated
using the fit function of Fig. 2 for the top 5% central collisions. For the 5%
most central Xe–Xe and for the 2% most central Pb–Pb collisions, the
$\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
increases steeply. A similar conclusion was also reached for the RHIC data
[3]: the Cu–Cu trend resembles that of Au–Au up to the most central collisions
and rises above it for the most central collisions. The RHIC data are also
shown in Fig. 3 and a deviation from the LHC data for $N_{\mathrm{part}}<100$
is visible, although with large uncertainties. The steeper rise might be due
to multiplicity fluctuations in the tail of the Xe–Xe V0 amplitude
distribution [22]. The fluctuations occur both in the number of collisions
over participants and in the number of charged particles over participants.
The rise is quantitatively reproduced by the NBD-Glauber fit. The total number
of charged particles scaled by the number of participant pairs shows a slight
increase as a function of the number of participants in Fig. 3 (bottom),
similar to that of the midrapidity results, albeit with larger experimental
uncertainties. Figure 4 shows the Xe–Xe and Pb–Pb results as a function of a
different scaling variable $(\langle N_{\mathrm{part}}\rangle-2)/(2A)$, where
$A$ is the atomic mass number of the colliding nucleus. The figure shows that
$\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
and $\frac{2}{\langle N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$
have a similar dependence on the number of participants relative to the
possible maximum number of participants, which indicates a stronger dependence
on geometric properties of the collision zone than on the collision system
sizes.

Figure 3: The $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
(top) and $\frac{2}{\langle
N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$ (bottom) for Xe–Xe
collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV as a function of
$\langle N_{\mathrm{part}}\rangle$. The error bars indicate the point-to-point
centrality-dependent uncertainties whereas the shaded band shows the
correlated contributions. Also shown in the figure is the result from
inelastic pp at $\sqrt{s}$ = 5.02 TeV as well as non-single diffractive p–Pb
collisions [11] and Pb–Pb collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02
TeV [8, 9]. Note that Pb–Pb data at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV
were re-analysed in narrower centrality classes. Data from lower energies at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 2.76 TeV [4, 5] and 200 GeV [3] are shown for
comparison.

The study of the centrality dependence of particle multiplicity for different
collision systems provides a variable number of nucleon-nucleon collisions at
equal number of participating nucleons and therefore may provide further
information to clarify the measured deviation from $N_{\mathrm{part}}$
scaling. The scaling of the charged-particle multiplicity by the number of
participant nucleons was studied in detail and a deviation from
$N_{\mathrm{part}}$-scaling was observed at RHIC energies [30, 38, 39, 40, 3].
The deviation from $N_{\mathrm{part}}$-scaling was initially thought to be due
to a relative increase in hard processes in central collisions, but no
conclusive evidence was found to support this interpretation. Figure 5
compares $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
in Xe–Xe collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV with different
parameterisations for particle production. Specifically, we used the two-
component model in Eq. 1 and two power-law functions
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle\propto
N_{\mathrm{part}}^{\alpha}$ and
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle\propto
N_{\mathrm{coll}}^{\beta}$. The functions were fitted to the Pb–Pb data at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV [8]. For the Xe–Xe data only the
absolute normalisation was adjusted. The values of the parameters are also
consistent with those obtained at SPS and RHIC energies [41, 30]. While no
unique physics conclusion can be drawn from such fits, this suggests that
geometrical arguments may be sufficient to provide a good description of
particle production across different colliding systems and beam energies.

Figure 4: The $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
(top) and $\frac{2}{\langle
N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$ (bottom) for Xe–Xe
collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV as a function of
$(\langle N_{\mathrm{part}}\rangle-2)/(2A)$.

Describing particle production in relativistic heavy-ion collisions as a
superposition of emission from a thermal core and hard scatterings in a corona
[42], one can classify the participating nucleons into those that scatter only
once ($N_{\mathrm{part}}^{\mathrm{corona}}$) and those that scatter multiple
times ($N_{\mathrm{part}}^{\mathrm{core}}$). The multiplicity can then be
fitted with the sum of those contributions,
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle_{\mathrm{pp}}\,N_{\mathrm{part}}^{\mathrm{corona}}+\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle_{\mathrm{core}}\,N_{\mathrm{part}}^{\mathrm{core}}$,
where $\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle_{\mathrm{pp}}$
is the multiplicity measured in inelastic pp collisions [10] and
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle_{\mathrm{core}}$ is
the contribution to the charged-particle multiplicity from the core of the
fireball, which is fitted to the data.

Figure 5: The $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
for Xe–Xe collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV and Pb–Pb
collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV [8], as a function of
$\langle N_{\mathrm{part}}\rangle$. The Pb–Pb data are fitted with various
parameterisations of $N_{\mathrm{part}}$ and $N_{\mathrm{coll}}$, calculated
with the Glauber model. The same functions, with the values of the parameters
from the Pb–Pb fit, are used for the Xe–Xe data. Also shown is
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ per participant
quark, $N_{\text{q-part}}$, calculated with the effective wounded constituent
quarks model [43], as a function of $\langle N_{\mathrm{part}}\rangle$. The
number of participant quarks $N_{\text{q-part}}$ is normalised by the average
number of participant quarks in pp collisions, $\mu$.

Figure 5 also shows $\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
per participant quark $N_{\text{q-part}}$ calculated with a Glauber model
using effective wounded constituent quarks [44][43], as a function of
$N_{\mathrm{part}}$, as was done for Pb–Pb collisions at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV [45] that have been re-analysed in
narrower centrality classes. In the implementation of the quark-Glauber model
the partonic degrees of freedom (3 or 5) are located around the nucleon
centres [43]. The effective inelastic scattering cross section for collisions
of constituent quarks is set to 20.38 mb and 9.76 mb, for $N_{\text{q}}=3$ and
$N_{\text{q}}=5$, respectively, adjusted to reproduce the 68.4 mb
nucleon–nucleon inelastic cross section at 5.44 TeV. $N_{\text{q-part}}$ has
been divided by the average value in pp collisions $\mu$ = $\langle
N_{\text{q-part}}\rangle$, which is 3.5 (4.3) for $N_{\text{q}}=3$
($N_{\text{q}}=5$). Comparing the behaviour of
$\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$ in terms of the
dependence on the number of nucleon or quark participants in the collision,
one concludes that $N_{\text{q-part}}$ scaling describes the data better than
$N_{\mathrm{part}}$ scaling as previously observed [45, 40] except the 0–10%
centrality range in Xe–Xe collisions where a clear scaling violation is
observed.

Figure 6 shows a comparison of the Xe–Xe data to calculations from theoretical
models at mid-rapidity. HIJING 2.1 [46, 47] combines perturbative QCD
processes with soft interactions, and includes a strong impact parameter
dependence of parton shadowing [48].

Figure 6: The $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
for Xe–Xe collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV as a function
of $\langle N_{\mathrm{part}}\rangle$ compared to model predictions [46, 47,
49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65]. The
bottom panel shows the ratio of the models to the data. The shaded band around
the points reflects the correlated systematic uncertainties.

For Xe–Xe data at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.44 TeV it uses a large
gluon shadowing parameter of 0.28 to limit the multiplicity per participant.
With this choice, the same as in Pb–Pb collisions at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV, the multiplicities at mid-rapidity
and the centrality dependence in the most central collisions are reproduced.
AMPT [50, 51] is a model which implements hydrodynamical evolution of an
initial state produced by HIJING. It includes spatial coalescence of quarks to
hadrons, followed by hadronic scattering. AMPT describes both the shape and
the overall magnitude of the mid-rapidity data. PYTHIA/Angantyr [52] extends
the nucleon–nucleon model of PYTHIA 8.230 [53] to the case of heavy-ion
collisions, essentially performing individual nucleon–nucleon collisions at
the parton level, while the resulting Lund-strings are hadronised as an
ensemble. It is interesting to note that this model agrees reasonably well
with the data even though it was developed as an extension of a generator for
nucleon–nucleon collisions. EPOS LHC [49] is a parton model based on the
Gribov-Regge theory, designed for minimum bias hadronic interactions, which
incorporates collective effects treated via a flow parameterisation and a
separation of the initial state into core–corona parts. The shape of the
centrality dependence is reproduced fairly well at intermediate centralities,
however, the model underestimates the absolute values of the multiplicity, as
was the case in Pb–Pb collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV
[8]. The Duke global calibrated model is based on a Bayesian Statistics
analysis using TRENTo initial conditions for high-energy nuclear collisions
[66, 67]. The subsequent transport dynamics is then simulated using the iEBE-
VISHNU event-by-event simulations for relativistic heavy-ion collisions which
uses a hybrid approach based on (2 + 1)-dimensional viscous hydrodynamics
coupled to a hadronic cascade model [68]. The Duke global calibrated model can
reproduce the shape of the mid-rapidity distribution, but overestimates
slightly the overall magnitude.

Figure 7: Comparison of $\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ as a
function of $\eta$ in the 0–5% central class to model predictions. The bottom
panel shows the ratio of the models to the data. Boxes around the points
reflect the total uncorrelated systematic uncertainties.

Saturation-inspired models (rcBK-MC [54, 55], KLN [56, 57, 58, 59], ASW [60],
IP-Glasma [61, 62] and EKRT [63, 64, 65]) rely on perturbative QCD and an
energy-dependent saturation scale, which limits the number of produced
partons, and in turn the number of produced particles. This results in a
factorisation of the energy and centrality dependence of particle production
or, in other words, in the invariance of the centrality growth, as observed in
the experimental data [69]. The rcBK-MC model limits the centrality growth
using the rc-BK equation. It provides a good description of the mid-rapidity
data, both of the shape and the highest multiplicity reached in central
collisions. The ASW prediction overestimates the data, while it was very
accurate in Pb–Pb at $\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV. The KLN model
does not describe the shape well and, although it agrees with the value
measured for most central collisions, it is significantly above the centrality
dependence of the data. The IP-Glasma model naturally produces initial energy
fluctuations computed within the Color Glass Condensate framework combining an
impact parameter dependent saturation model. It uses a gluon multiplicity
scaled to describe hadron multiplicities measured in Pb–Pb collisions at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV [8]. The centrality dependence is
stronger than that observed in mid-rapidity data over(under)-predicting the
data in central (peripheral) collisions. The EKRT model for heavy-ion
collisions uses perturbative QCD with a conjecture of gluon saturation to
suppress soft parton production. The saturation scale is also dependent on the
local product of thickness functions, implying a geometrical scaling. The
space-time evolution of the system is then described with viscous fluid
dynamics event-by-event. The normalisation is fixed by exploiting the 0–5%
most central multiplicity measurement in Pb–Pb collisions at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 2.76 TeV [70]. As for Pb–Pb collisions at
$\sqrt{\it{s}_{\mathrm{NN}}}$ = 5.02 TeV, the EKRT model can describe both the
shape and the overall magnitude of multiplicity on centrality. In general,
almost all models reproduce the steep rise versus $\langle
N_{\mathrm{part}}\rangle$ while EPOS-LHC, ASW and KLN show a saturation
behaviour. The predictions show a similar trend as for the Pb–Pb case [8] and
altogether a flatter distribution with respect to data.

In Fig. 7, the models are compared to the pseudorapidity dependence of the
$\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta$ for the top 5% central collisions.
HIJING 2.1 reproduces the pseudorapidity dependence at mid-rapidity well, but
overestimates the data at forward rapidity, due to the large value of the
shadowing parameter used. AMPT and PYTHIA/Angantyr describe the data fairly
well, with a slight overestimate at forward rapidities. EPOS LHC reproduces
the shape well, but under-predicts the multiplicity overall. The rcBK-MC is
restricted to $|\eta|<2.5$ since its formalism can only be used for rapidities
far from the fragmentation regions. It shows a narrower distribution than what
is seen in data. KLN agrees with the data at mid-rapidity, but not at forward
rapidity, where it under-predicts the data. For IP-Glasma the rapidity
dependence is provided by the IP-Sat model [71] and it is converted to
pseudorapidity using an effective mass of 0.2 GeV/$\mathrm{c}^{2}$. The shape
is wider than that of the data. Regarding the case of the pseudorapidity
dependence all the models show similar trends as for Pb–Pb collisions [9]
except HIJING 2.1 which describes the Xe–Xe measurements better than the Pb–Pb
data.

##  6 Conclusions

The measurements of the charged-particle multiplicity density and its
centrality dependence in Xe–Xe collisions at $\sqrt{\it{s}_{\mathrm{NN}}}$ =
5.44 TeV have been presented over the pseudorapidity range $-3.5<\eta<5$ using
the full acceptance of the ALICE detector. For the 5% most central collisions,
the average charged-particle pseudorapidity density at mid-rapidity
($|\eta|<0.5$) is $1167\pm 26$ and the total number of charged particles is
$13230\pm 280$. Scaled by the number of participant pairs, these are found to
follow the same power-law dependence with energy established in previous
heavy-ion measurements.

The centrality dependences of $\frac{2}{\langle
N_{\mathrm{part}}\rangle}\langle\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta\rangle$
and $\frac{2}{\langle N_{\mathrm{part}}\rangle}N^{\mathrm{tot}}_{\mathrm{ch}}$
are very similar to those previously measured in Pb–Pb collisions at similar
or lower energies up to the 5% most central Xe–Xe collisions, where the Xe–Xe
results are larger than the Pb–Pb results at a similar number of participating
nucleons. Similar conclusions were drawn at RHIC from the comparison of the
data for Cu–Cu and Au–Au collisions [72]. The steeper rise might be due to
multiplicity fluctuations in the tail of the Xe–Xe V0 amplitude.

While measurements of particle production in large and medium-sized colliding
systems such as Xe–Xe are abundant and become even more precise, the
underlying mechanism to describe the increase with energy and centrality is
still not completely understood. Deeper insight of the system size dependence
of particle production may come from the study of light-nuclei collisions,
still not much explored at high energy, which could bridge the gap between the
trends observed in pp and pA collisions and those of the mid-sized Xe–Xe and
the large Pb–Pb systems.

## Acknowledgements

The ALICE Collaboration would like to thank N. Armesto, W.-T. Deng, A.
Dumitru, K. Eskola, G. Levin, L. Lonnblad, S. Moreland, H. Niemi, T. Pierog
and B. Schenke for helpful discussions on their model predictions.

The ALICE Collaboration would like to thank all its engineers and technicians
for their invaluable contributions to the construction of the experiment and
the CERN accelerator teams for the outstanding performance of the LHC complex.
The ALICE Collaboration gratefully acknowledges the resources and support
provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG)
collaboration. The ALICE Collaboration acknowledges the following funding
agencies for their support in building and running the ALICE detector: A. I.
Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation
(ANSL), State Committee of Science and World Federation of Scientists (WFS),
Armenia; Austrian Academy of Sciences and Nationalstiftung für Forschung,
Technologie und Entwicklung, Austria; Ministry of Communications and High
Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional
de Desenvolvimento Científico e Tecnológico (CNPq), Universidade Federal do
Rio Grande do Sul (UFRGS), Financiadora de Estudos e Projetos (Finep) and
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil;
Ministry of Science & Technology of China (MSTC), National Natural Science
Foundation of China (NSFC) and Ministry of Education of China (MOEC) , China;
Ministry of Science and Education, Croatia; Ministry of Education, Youth and
Sports of the Czech Republic, Czech Republic; The Danish Council for
Independent Research — Natural Sciences, the Carlsberg Foundation and Danish
National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics
(HIP), Finland; Commissariat à l’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, Wissenschaft, Forschung und Technologie (BMBF) and GSI
Helmholtzzentrum für Schwerionenforschung GmbH, Germany; General Secretariat
for Research and Technology, Ministry of Education, Research and Religions,
Greece; National Research, Development and Innovation Office, Hungary;
Department of Atomic Energy Government of India (DAE), Department of Science
and Technology, Government of India (DST), University Grants Commission,
Government of India (UGC) and Council of Scientific and Industrial Research
(CSIR), India; Indonesian Institute of Science, Indonesia; Centro Fermi -
Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi and Istituto
Nazionale di Fisica Nucleare (INFN), Italy; Institute for Innovative Science
and Technology , Nagasaki Institute of Applied Science (IIST), Japan Society
for the Promotion of Science (JSPS) KAKENHI and Japanese Ministry of
Education, Culture, Sports, Science and Technology (MEXT), Japan; Consejo
Nacional de Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación
Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de
Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor
Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway,
Norway; Commission on Science and Technology for Sustainable Development in
the South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru;
Ministry of Science and Higher Education and National Science Centre, Poland;
Korea Institute of Science and Technology Information and National Research
Foundation of Korea (NRF), Republic of Korea; Ministry of Education and
Scientific Research, Institute of Atomic Physics and Romanian National Agency
for Science, Technology and Innovation, Romania; Joint Institute for Nuclear
Research (JINR), Ministry of Education and Science of the Russian Federation
and National Research Centre Kurchatov Institute, Russia; Ministry of
Education, Science, Research and Sport of the Slovak Republic, Slovakia;
National Research Foundation of South Africa, South Africa; Centro de
Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba and
Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
(CIEMAT), Spain; Swedish Research Council (VR) and Knut & Alice Wallenberg
Foundation (KAW), Sweden; European Organization for Nuclear Research,
Switzerland; National Science and Technology Development Agency (NSDTA),
Suranaree University of Technology (SUT) and Office of the Higher Education
Commission under NRU project of Thailand, Thailand; Turkish Atomic Energy
Agency (TAEK), Turkey; National Academy of Sciences of Ukraine, Ukraine;
Science and Technology Facilities Council (STFC), United Kingdom; National
Science Foundation of the United States 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. Acharyaorg138&F.T.-. Acostaorg22&D. Adamováorg94&J. Adolfssonorg81&M.M.
Aggarwalorg98&G. Aglieri Rinellaorg36&M. Agnelloorg33&N. Agrawalorg49&Z.
Ahammedorg138&S.U. Ahnorg77&S. Aiolaorg143&A. Akindinovorg65&M. Al-
Turanyorg104&S.N. Alamorg138&D.S.D. Albuquerqueorg120&D. Aleksandrovorg88&B.
Alessandroorg59&R. Alfaro Molinaorg73&Y. Aliorg16&A. Aliciorg11,org54,org29&A.
Alkinorg3&J. Almeorg24&T. Altorg70&L. Altenkamperorg24&I. Altsybeevorg137&C.
Andreiorg48&D. Andreouorg36&H.A. Andrewsorg108&A. Andronicorg141,org104&M.
Angelettiorg36&V. Anguelovorg102&C. Ansonorg17&T. Antičićorg105&F.
Antinoriorg57&P. Antonioliorg54&R. Anwarorg124&N. Apadulaorg80&L.
Aphecetcheorg112&H. Appelshäuserorg70&S. Arcelliorg29&R. Arnaldiorg59&O.W.
Arnoldorg103,org115&I.C. Arseneorg23&M. Arslandokorg102&B. Audurierorg112&A.
Augustinusorg36&R. Averbeckorg104&M.D. Azmiorg18&A. Badalàorg56&Y.W.
Baekorg61,org42&S. Bagnascoorg59&R. Bailhacheorg70&R. Balaorg99&A.
Baldisseriorg134&M. Ballorg44&R.C. Baralorg86&A.M. Barbanoorg28&R.
Barberaorg30&F. Barileorg53&L. Barioglioorg28&G.G. Barnaföldiorg142&L.S.
Barnbyorg93&V. Barretorg131&P. Bartaliniorg7&K. Barthorg36&E. Bartschorg70&N.
Bastidorg131&S. Basuorg140&G. Batigneorg112&B. Batyunyaorg76&P.C.
Batzingorg23&J.L. Bazo Albaorg109&I.G. Beardenorg89&H. Beckorg102&C.
Beddaorg64&N.K. Beheraorg61&I. Belikovorg133&F. Belliniorg36&H. Bello
Martinezorg2&R. Bellwiedorg124&L.G.E. Beltranorg118&V. Belyaevorg92&G.
Bencediorg142&S. Beoleorg28&A. Bercuciorg48&Y. Berdnikovorg96&D.
Berenyiorg142&R.A. Bertensorg127&D. Berzanoorg36,org59&L. Betevorg36&P.P.
Bhaduriorg138&A. Bhasinorg99&I.R. Bhatorg99&H. Bhattorg49&B.
Bhattacharjeeorg43&J. Bhomorg116&A. Bianchiorg28&L. Bianchiorg124&N.
Bianchiorg52&J. Bielčíkorg39&J. Bielčíkováorg94&A. Bilandzicorg115,org103&G.
Biroorg142&R. Biswasorg4&S. Biswasorg4&J.T. Blairorg117&D. Blauorg88&C.
Blumeorg70&G. Bocaorg135&F. Bockorg36&A. Bogdanovorg92&L. Boldizsárorg142&M.
Bombaraorg40&G. Bonomiorg136&M. Bonoraorg36&H. Borelorg134&A.
Borissovorg20,org141&M. Borriorg126&E. Bottaorg28&C. Bourjauorg89&L.
Bratrudorg70&P. Braun-Munzingerorg104&M. Bregantorg119&T.A. Brokerorg70&M.
Brozorg39&E.J. Bruckenorg45&E. Brunaorg59&G.E. Brunoorg36,org35&D.
Budnikovorg106&H. Bueschingorg70&S. Bufalinoorg33&P. Buhlerorg111&P.
Buncicorg36&O. Buschorg130org*&Z. Butheleziorg74&J.B. Buttorg16&J.T.
Buxtonorg19&J. Cabalaorg114&D. Caffarriorg90&H. Cainesorg143&A.
Calivaorg104&E. Calvo Villarorg109&R.S. Camachoorg2&P. Cameriniorg27&A.A.
Caponorg111&F. Carenaorg36&W. Carenaorg36&F. Carnesecchiorg29,org11&J.
Castillo Castellanosorg134&A.J. Castroorg127&E.A.R. Casulaorg55&C. Ceballos
Sanchezorg9&S. Chandraorg138&B. Changorg125&W. Changorg7&S. Chapelandorg36&M.
Chartierorg126&S. Chattopadhyayorg138&S. Chattopadhyayorg107&A.
Chauvinorg103,org115&C. Cheshkovorg132&B. Cheynisorg132&V. Chibante
Barrosoorg36&D.D. Chinellatoorg120&S. Choorg61&P. Chochulaorg36&T.
Chowdhuryorg131&P. Christakoglouorg90&C.H. Christensenorg89&P.
Christiansenorg81&T. Chujoorg130&S.U. Chungorg20&C. Cicaloorg55&L.
Cifarelliorg11,org29&F. Cindoloorg54&J. Cleymansorg123&F. Colamariaorg53&D.
Colellaorg66,org36,org53&A. Colluorg80&M. Colocciorg29&M. Concasorg59orgI&G.
Conesa Balbastreorg79&Z. Conesa del Valleorg62&J.G. Contrerasorg39&T.M.
Cormierorg95&Y. Corrales Moralesorg59&P. Corteseorg34&M.R. Cosentinoorg121&F.
Costaorg36&S. Costanzaorg135&J. Crkovskáorg62&P. Crochetorg131&E.
Cuautleorg71&L. Cunqueiroorg141,org95&T. Dahmsorg103,org115&A. Daineseorg57&S.
Daniorg67&M.C. Danischorg102&A. Danuorg69&D. Dasorg107&I. Dasorg107&S.
Dasorg4&A. Dashorg86&S. Dashorg49&S. Deorg50&A. De Caroorg32&G. de
Cataldoorg53&C. de Contiorg119&J. de Cuvelandorg41&A. De Falcoorg26&D. De
Gruttolaorg11,org32&N. De Marcoorg59&S. De Pasqualeorg32&R.D. De
Souzaorg120&H.F. Degenhardtorg119&A. Deistingorg104,org102&A. Delofforg85&S.
Delsantoorg28&C. Deplanoorg90&P. Dhankherorg49&D. Di Bariorg35&A. Di
Mauroorg36&B. Di Ruzzaorg57&R.A. Diazorg9&T. Dietelorg123&P.
Dillensegerorg70&Y. Dingorg7&R. Diviàorg36&Ø. Djuvslandorg24&A. Dobrinorg36&D.
Domenicis Gimenezorg119&B. Dönigusorg70&O. Dordicorg23&L.V.R.
Doremalenorg64&A.K. Dubeyorg138&A. Dublaorg104&L. Ducrouxorg132&S.
Dudiorg98&A.K. Duggalorg98&M. Dukhishyamorg86&P. Dupieuxorg131&R.J.
Ehlersorg143&D. Eliaorg53&E. Endressorg109&H. Engelorg75&E. Eppleorg143&B.
Erazmusorg112&F. Erhardtorg97&M.R. Ersdalorg24&B. Espagnonorg62&G.
Eulisseorg36&J. Eumorg20&D. Evansorg108&S. Evdokimovorg91&L.
Fabbiettiorg103,org115&M. Fagginorg31&J. Faivreorg79&A. Fantoniorg52&M.
Faselorg95&L. Feldkamporg141&A. Felicielloorg59&G. Feofilovorg137&A. Fernández
Téllezorg2&A. Ferrettiorg28&A. Festantiorg31,org36&V.J.G. Feuillardorg102&J.
Figielorg116&M.A.S. Figueredoorg119&S. Filchaginorg106&D. Finogeevorg63&F.M.
Fiondaorg24&G. Fiorenzaorg53&F. Flororg124&M. Florisorg36&S. Foertschorg74&P.
Fokaorg104&S. Fokinorg88&E. Fragiacomoorg60&A. Francesconorg36&A.
Franciscoorg112&U. Frankenfeldorg104&G.G. Fronzeorg28&U. Fuchsorg36&C.
Furgetorg79&A. Fursorg63&M. Fusco Girardorg32&J.J. Gaardhøjeorg89&M.
Gagliardiorg28&A.M. Gagoorg109&K. Gajdosovaorg89&M. Gallioorg28&C.D.
Galvanorg118&P. Ganotiorg84&C. Garabatosorg104&E. Garcia-Solisorg12&K.
Gargorg30&C. Gargiuloorg36&P. Gasikorg115,org103&E.F. Gaugerorg117&M.B. Gay
Ducatiorg72&M. Germainorg112&J. Ghoshorg107&P. Ghoshorg138&S.K. Ghoshorg4&P.
Gianottiorg52&P. Giubellinoorg104,org59&P. Giubilatoorg31&P.
Glässelorg102&D.M. Goméz Coralorg73&A. Gomez Ramirezorg75&V. Gonzalezorg104&P.
González-Zamoraorg2&S. Gorbunovorg41&L. Görlichorg116&S. Gotovacorg37&V.
Grabskiorg73&L.K. Graczykowskiorg139&K.L. Grahamorg108&L. Greinerorg80&A.
Grelliorg64&C. Grigorasorg36&V. Grigorievorg92&A. Grigoryanorg1&S.
Grigoryanorg76&J.M. Gronefeldorg104&F. Grosaorg33&J.F. Grosse-
Oetringhausorg36&R. Grossoorg104&R. Guernaneorg79&B. Guerzoniorg29&M.
Guittiereorg112&K. Gulbrandsenorg89&T. Gunjiorg129&A. Guptaorg99&R.
Guptaorg99&I.B. Guzmanorg2&R. Haakeorg36&M.K. Habiborg104&C.
Hadjidakisorg62&H. Hamagakiorg82&G. Hamarorg142&M. Hamidorg7&J.C.
Hamonorg133&R. Hanniganorg117&M.R. Haqueorg64&J.W. Harrisorg143&A.
Hartonorg12&H. Hassanorg79&D. Hatzifotiadouorg54,org11&S. Hayashiorg129&S.T.
Heckelorg70&E. Hellbärorg70&H. Helstruporg38&A. Herghelegiuorg48&E.G.
Hernandezorg2&G. Herrera Corralorg10&F. Herrmannorg141&K.F. Hetlandorg38&T.E.
Hildenorg45&H. Hillemannsorg36&C. Hillsorg126&B. Hippolyteorg133&B.
Hohlwegerorg103&D. Horakorg39&S. Hornungorg104&R. Hosokawaorg130,org79&J.
Hotaorg67&P. Hristovorg36&C. Huangorg62&C. Hughesorg127&P. Huhnorg70&T.J.
Humanicorg19&H. Hushnudorg107&N. Hussainorg43&T. Hussainorg18&D.
Hutterorg41&D.S. Hwangorg21&J.P. Iddonorg126&S.A. Iga Buitronorg71&R.
Ilkaevorg106&M. Inabaorg130&M. Ippolitovorg88&M.S. Islamorg107&M.
Ivanovorg104&V. Ivanovorg96&V. Izucheevorg91&B. Jacakorg80&N.
Jacazioorg29&P.M. Jacobsorg80&M.B. Jadhavorg49&S. Jadlovskaorg114&J.
Jadlovskyorg114&S. Jaelaniorg64&C. Jahnkeorg119,org115&M.J.
Jakubowskaorg139&M.A. Janikorg139&C. Jenaorg86&M. Jercicorg97&R.T. Jimenez
Bustamanteorg104&M. Jinorg124&P.G. Jonesorg108&A. Juskoorg108&P.
Kalinakorg66&A. Kalweitorg36&J.H. Kangorg144&V. Kaplinorg92&S. Karorg7&A.
Karasu Uysalorg78&O. Karavichevorg63&T. Karavichevaorg63&P.
Karczmarczykorg36&E. Karpechevorg63&U. Kebschullorg75&R. Keidelorg47&D.L.D.
Keijdenerorg64&M. Keilorg36&B. Ketzerorg44&Z. Khabanovaorg90&A.M. Khanorg7&S.
Khanorg18&S.A. Khanorg138&A. Khanzadeevorg96&Y. Kharlovorg91&A. Khatunorg18&A.
Khuntiaorg50&M.M. Kielbowiczorg116&B. Kilengorg38&B. Kimorg61&B. Kimorg130&D.
Kimorg144&D.J. Kimorg125&E.J. Kimorg14&H. Kimorg144&J.S. Kimorg42&J.
Kimorg102&M. Kimorg61,org102&S. Kimorg21&T. Kimorg144&T. Kimorg144&S.
Kirschorg41&I. Kiselorg41&S. Kiselevorg65&A. Kisielorg139&J.L. Klayorg6&C.
Kleinorg70&J. Kleinorg36,org59&C. Klein-Bösingorg141&S. Klewinorg102&A.
Klugeorg36&M.L. Knichelorg36&A.G. Knospeorg124&C. Kobdajorg113&M.
Kofaragoorg142&M.K. Köhlerorg102&T. Kolleggerorg104&N. Kondratyevaorg92&E.
Kondratyukorg91&A. Konevskikhorg63&M. Konyushikhinorg140&O. Kovalenkoorg85&V.
Kovalenkoorg137&M. Kowalskiorg116&I. Králikorg66&A. Kravčákováorg40&L.
Kreisorg104&M. Krivdaorg66,org108&F. Krizekorg94&M. Krügerorg70&E.
Kryshenorg96&M. Krzewickiorg41&A.M. Kuberaorg19&V. Kučeraorg94,org61&C.
Kuhnorg133&P.G. Kuijerorg90&J. Kumarorg49&L. Kumarorg98&S. Kumarorg49&S.
Kunduorg86&P. Kurashviliorg85&A. Kurepinorg63&A.B. Kurepinorg63&A.
Kuryakinorg106&S. Kushpilorg94&M.J. Kweonorg61&Y. Kwonorg144&S.L. La
Pointeorg41&P. La Roccaorg30&Y.S. Laiorg80&I. Lakomovorg36&R. Langoyorg122&K.
Lapidusorg143&C. Laraorg75&A. Lardeuxorg23&P. Larionovorg52&E. Laudiorg36&R.
Lavickaorg39&R. Leaorg27&L. Leardiniorg102&S. Leeorg144&F. Lehasorg90&S.
Lehnerorg111&J. Lehrbachorg41&R.C. Lemmonorg93&I. León Monzónorg118&P.
Lévaiorg142&X. Liorg13&X.L. Liorg7&J. Lienorg122&R. Lietavaorg108&B.
Limorg20&S. Lindalorg23&V. Lindenstruthorg41&S.W. Lindsayorg126&C.
Lippmannorg104&M.A. Lisaorg19&V. Litichevskyiorg45&A. Liuorg80&H.M.
Ljunggrenorg81&W.J. Llopeorg140&D.F. Lodatoorg64&V. Loginovorg92&C.
Loizidesorg95,org80&P. Loncarorg37&X. Lopezorg131&E. López Torresorg9&A.
Loweorg142&P. Luettigorg70&J.R. Luhderorg141&M. Lunardonorg31&G.
Luparelloorg60&M. Lupiorg36&A. Maevskayaorg63&M. Magerorg36&S.M.
Mahmoodorg23&A. Maireorg133&R.D. Majkaorg143&M. Malaevorg96&Q.W. Malikorg23&L.
Malininaorg76orgII&D. Mal’Kevichorg65&P. Malzacherorg104&A. Mamonovorg106&V.
Mankoorg88&F. Mansoorg131&V. Manzariorg53&Y. Maoorg7&M.
Marchisoneorg74,org128,org132&J. Marešorg68&G.V. Margagliottiorg27&A.
Margottiorg54&J. Marguttiorg64&A. Marínorg104&C. Markertorg117&M.
Marquardorg70&N.A. Martinorg104&P. Martinengoorg36&J.L. Martinezorg124&M.I.
Martínezorg2&G. Martínez Garcíaorg112&M. Martinez Pedreiraorg36&S.
Masciocchiorg104&M. Maseraorg28&A. Masoniorg55&L. Massacrierorg62&E.
Massonorg112&A. Mastroserioorg53&A.M. Mathisorg103,org115&P.F.T.
Matuokaorg119&A. Matyjaorg127,org116&C. Mayerorg116&M. Mazzilliorg35&M.A.
Mazzoniorg58&F. Meddiorg25&Y. Melikyanorg92&A. Menchaca-Rochaorg73&E.
Meninnoorg32&J. Mercado Pérezorg102&M. Meresorg15&C.S. Mezaorg109&S.
Mhlangaorg123&Y. Miakeorg130&L. Michelettiorg28&M.M. Mieskolainenorg45&D.L.
Mihaylovorg103&K. Mikhaylovorg65,org76&A. Mischkeorg64&A.N. Mishraorg71&D.
Miśkowiecorg104&J. Mitraorg138&C.M. Mituorg69&N. Mohammadiorg36&A.P.
Mohantyorg64&B. Mohantyorg86&M. Mohisin Khanorg18orgIII&D.A. Moreira De
Godoyorg141&L.A.P. Morenoorg2&S. Morettoorg31&A. Morrealeorg112&A.
Morschorg36&V. Mucciforaorg52&E. Mudnicorg37&D. Mühlheimorg141&S.
Muhuriorg138&M. Mukherjeeorg4&J.D. Mulliganorg143&M.G. Munhozorg119&K.
Münningorg44&M.I.A. Munozorg80&R.H. Munzerorg70&H. Murakamiorg129&S.
Murrayorg74&L. Musaorg36&J. Musinskyorg66&C.J. Myersorg124&J.W.
Myrchaorg139&B. Naikorg49&R. Nairorg85&B.K. Nandiorg49&R. Naniaorg54,org11&E.
Nappiorg53&A. Narayanorg49&M.U. Naruorg16&A.F. Nassirpourorg81&H. Natal da
Luzorg119&C. Nattrassorg127&S.R. Navarroorg2&K. Nayakorg86&R. Nayakorg49&T.K.
Nayakorg138&S. Nazarenkoorg106&R.A. Negrao De Oliveiraorg70,org36&L.
Nellenorg71&S.V. Nesboorg38&G. Neskovicorg41&F. Ngorg124&M. Nicassioorg104&J.
Niedzielaorg139,org36&B.S. Nielsenorg89&S. Nikolaevorg88&S. Nikulinorg88&V.
Nikulinorg96&F. Noferiniorg11,org54&P. Nomokonovorg76&G. Noorenorg64&J.C.C.
Norisorg2&J. Normanorg79&A. Nyaninorg88&J. Nystrandorg24&H. Ohorg144&A.
Ohlsonorg102&J. Oleniaczorg139&A.C. Oliveira Da Silvaorg119&M.H.
Oliverorg143&J. Onderwaaterorg104&C. Oppedisanoorg59&R. Oravaorg45&M.
Oravecorg114&A. Ortiz Velasquezorg71&A. Oskarssonorg81&J. Otwinowskiorg116&K.
Oyamaorg82&Y. Pachmayerorg102&V. Pacikorg89&D. Paganoorg136&G. Paićorg71&P.
Palniorg7&J. Panorg140&A.K. Pandeyorg49&S. Panebiancoorg134&V. Papikyanorg1&P.
Pareekorg50&J. Parkorg61&J.E. Parkkilaorg125&S. Parmarorg98&A.
Passfeldorg141&S.P. Pathakorg124&R.N. Patraorg138&B. Paulorg59&H. Peiorg7&T.
Peitzmannorg64&X. Pengorg7&L.G. Pereiraorg72&H. Pereira Da Costaorg134&D.
Peresunkoorg88&E. Perez Lezamaorg70&V. Peskovorg70&Y. Pestovorg5&V.
Petráčekorg39&M. Petroviciorg48&C. Pettaorg30&R.P. Pezziorg72&S. Pianoorg60&M.
Piknaorg15&P. Pillotorg112&L.O.D.L. Pimentelorg89&O. Pinazzaorg54,org36&L.
Pinskyorg124&S. Pisanoorg52&D.B. Piyarathnaorg124&M. Płoskońorg80&M.
Planinicorg97&F. Pliquettorg70&J. Plutaorg139&S. Pochybovaorg142&P.L.M.
Podesta-Lermaorg118&M.G. Poghosyanorg95&B. Polichtchoukorg91&N. Poljakorg97&W.
Poonsawatorg113&A. Poporg48&H. Poppenborgorg141&S. Porteboeuf-
Houssaisorg131&V. Pozdniakovorg76&S.K. Prasadorg4&R. Preghenellaorg54&F.
Prinoorg59&C.A. Pruneauorg140&I. Pshenichnovorg63&M. Puccioorg28&V.
Puninorg106&J. Putschkeorg140&S. Rahaorg4&S. Rajputorg99&J. Rakorg125&A.
Rakotozafindrabeorg134&L. Ramelloorg34&F. Ramiorg133&R. Raniwalaorg100&S.
Raniwalaorg100&S.S. Räsänenorg45&B.T. Rascanuorg70&V. Ratzaorg44&I.
Ravasengaorg33&K.F. Readorg127,org95&K. Redlichorg85orgIV&A. Rehmanorg24&P.
Reicheltorg70&F. Reidtorg36&X. Renorg7&R. Renfordtorg70&A. Reshetinorg63&J.-P.
Revolorg11&K. Reygersorg102&V. Riabovorg96&T. Richertorg64,org81&M.
Richterorg23&P. Riedlerorg36&W. Rieglerorg36&F. Riggiorg30&C. Risteaorg69&S.P.
Rodeorg50&M. Rodríguez Cahuantziorg2&K. Røedorg23&R. Rogalevorg91&E.
Rogochayaorg76&D. Rohrorg36&D. Röhrichorg24&P.S. Rokitaorg139&F.
Ronchettiorg52&E.D. Rosasorg71&K. Roslonorg139&P. Rosnetorg131&A.
Rossiorg31&A. Rotondiorg135&F. Roukoutakisorg84&C. Royorg133&P. Royorg107&O.V.
Ruedaorg71&R. Ruiorg27&B. Rumyantsevorg76&A. Rustamovorg87&E.
Ryabinkinorg88&Y. Ryabovorg96&A. Rybickiorg116&S. Saarinenorg45&S.
Sadhuorg138&S. Sadovskyorg91&K. Šafaříkorg36&S.K. Sahaorg138&B. Sahooorg49&P.
Sahooorg50&R. Sahooorg50&S. Sahooorg67&P.K. Sahuorg67&J. Sainiorg138&S.
Sakaiorg130&M.A. Salehorg140&S. Sambyalorg99&V. Samsonovorg96,org92&A.
Sandovalorg73&A. Sarkarorg74&D. Sarkarorg138&N. Sarkarorg138&P.
Sarmaorg43&M.H.P. Sasorg64&E. Scapparoneorg54&F. Scarlassaraorg31&B.
Schaeferorg95&H.S. Scheidorg70&C. Schiauaorg48&R. Schickerorg102&C.
Schmidtorg104&H.R. Schmidtorg101&M.O. Schmidtorg102&M. Schmidtorg101&N.V.
Schmidtorg95,org70&J. Schukraftorg36&Y. Schutzorg36,org133&K. Schwarzorg104&K.
Schwedaorg104&G. Scioliorg29&E. Scomparinorg59&M. Šefčíkorg40&J.E.
Segerorg17&Y. Sekiguchiorg129&D. Sekihataorg46&I. Selyuzhenkovorg104,org92&K.
Senosiorg74&S. Senyukovorg133&E. Serradillaorg73&P. Settorg49&A.
Sevcencoorg69&A. Shabanovorg63&A. Shabetaiorg112&R. Shahoyanorg36&W.
Shaikhorg107&A. Shangaraevorg91&A. Sharmaorg98&A. Sharmaorg99&M.
Sharmaorg99&N. Sharmaorg98&A.I. Sheikhorg138&K. Shigakiorg46&M.
Shimomuraorg83&S. Shirinkinorg65&Q. Shouorg7,org110&K. Shtejerorg28&Y.
Sibiriakorg88&S. Siddhantaorg55&K.M. Sielewiczorg36&T. Siemiarczukorg85&D.
Silvermyrorg81&G. Simatovicorg90&G. Simonettiorg36,org103&R.
Singarajuorg138&R. Singhorg86&R. Singhorg99&V. Singhalorg138&T. Sinhaorg107&B.
Sitarorg15&M. Sittaorg34&T.B. Skaaliorg23&M. Slupeckiorg125&N.
Smirnovorg143&R.J.M. Snellingsorg64&T.W. Snellmanorg125&J. Songorg20&F.
Soramelorg31&S. Sorensenorg127&F. Sozziorg104&I. Sputowskaorg116&J.
Stachelorg102&I. Stanorg69&P. Stankusorg95&E. Stenlundorg81&D.
Stoccoorg112&M.M. Storetvedtorg38&P. Strmenorg15&A.A.P. Suaideorg119&T.
Sugitateorg46&C. Suireorg62&M. Suleymanovorg16&M. Suljicorg36,org27&R.
Sultanovorg65&M. Šumberaorg94&S. Sumowidagdoorg51&K. Suzukiorg111&S.
Swainorg67&A. Szaboorg15&I. Szarkaorg15&U. Tabassamorg16&J.
Takahashiorg120&G.J. Tambaveorg24&N. Tanakaorg130&M. Tarhiniorg112&M.
Tariqorg18&M.G. Tarzilaorg48&A. Tauroorg36&G. Tejeda Muñozorg2&A.
Telescaorg36&C. Terrevoliorg31&B. Teyssierorg132&D. Thakurorg50&S.
Thakurorg138&D. Thomasorg117&F. Thoresenorg89&R. Tieulentorg132&A.
Tikhonovorg63&A.R. Timminsorg124&A. Toiaorg70&N. Topilskayaorg63&M.
Toppiorg52&S.R. Torresorg118&S. Tripathyorg50&S. Trogoloorg28&G.
Trombettaorg35&L. Tropporg40&V. Trubnikovorg3&W.H. Trzaskaorg125&T.P.
Trzcinskiorg139&B.A. Trzeciakorg64&T. Tsujiorg129&A. Tumkinorg106&R.
Turrisiorg57&T.S. Tveterorg23&K. Ullalandorg24&E.N. Umakaorg124&A.
Urasorg132&G.L. Usaiorg26&A. Utrobicicorg97&M. Valaorg114&J.W. Van
Hoorneorg36&M. van Leeuwenorg64&P. Vande Vyvreorg36&D. Vargaorg142&A.
Vargasorg2&M. Vargyasorg125&R. Varmaorg49&M. Vasileiouorg84&A.
Vasilievorg88&A. Vauthierorg79&O. Vázquez Doceorg103,org115&V.
Vecherninorg137&A.M. Veenorg64&E. Vercellinorg28&S. Vergara Limónorg2&L.
Vermuntorg64&R. Vernetorg8&R. Vértesiorg142&L. Vickovicorg37&J.
Viinikainenorg125&Z. Vilakaziorg128&O. Villalobos Baillieorg108&A. Villatoro
Telloorg2&A. Vinogradovorg88&T. Virgiliorg32&V. Vislaviciusorg89,org81&A.
Vodopyanovorg76&M.A. Völklorg101&K. Voloshinorg65&S.A. Voloshinorg140&G.
Volpeorg35&B. von Hallerorg36&I. Vorobyevorg115,org103&D. Voscekorg114&D.
Vranicorg104,org36&J. Vrlákováorg40&B. Wagnerorg24&H. Wangorg64&M. Wangorg7&Y.
Watanabeorg130&M. Weberorg111&S.G. Weberorg104&A. Wegrzynekorg36&D.F.
Weiserorg102&S.C. Wenzelorg36&J.P. Wesselsorg141&U. Westerhofforg141&A.M.
Whiteheadorg123&J. Wiechulaorg70&J. Wikneorg23&G. Wilkorg85&J.
Wilkinsonorg54&G.A. Willemsorg141,org36&M.C.S. Williamsorg54&E.
Willsherorg108&B. Windelbandorg102&W.E. Wittorg127&R. Xuorg7&S. Yalcinorg78&K.
Yamakawaorg46&S. Yanoorg46&Z. Yinorg7&H. Yokoyamaorg79,org130&I.-K.
Yooorg20&J.H. Yoonorg61&V. Yurchenkoorg3&V. Zaccoloorg59&A. Zamanorg16&C.
Zampolliorg36&H.J.C. Zanoliorg119&N. Zardoshtiorg108&A. Zarochentsevorg137&P.
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Zhangorg7&Y. Zhangorg7&Z. Zhangorg7,org131&C. Zhaoorg23&V.
Zherebchevskiiorg137&N. Zhigarevaorg65&D. Zhouorg7&Y. Zhouorg89&Z.
Zhouorg24&H. Zhuorg7&J. Zhuorg7&Y. Zhuorg7&A. Zichichiorg29,org11&M.B.
Zimmermannorg36&G. Zinovjevorg3&J. Zmeskalorg111&S. Zouorg7&

## Affiliation notes

org*Deceased

orgIDipartimento DET del Politecnico di Torino, Turin, Italy

orgIIM.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute of
Nuclear, Physics, Moscow, Russia

orgIIIDepartment of Applied Physics, Aligarh Muslim University, Aligarh, India

orgIVInstitute of Theoretical Physics, University of Wroclaw, Poland

## Collaboration Institutes

org1A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute)
Foundation, Yerevan, Armenia

org2Benemérita Universidad Autónoma de Puebla, Puebla, Mexico

org3Bogolyubov Institute for Theoretical Physics, National Academy of Sciences
of Ukraine, Kiev, Ukraine

org4Bose Institute, Department of Physics and Centre for Astroparticle Physics
and Space Science (CAPSS), Kolkata, India

org5Budker Institute for Nuclear Physics, Novosibirsk, Russia

org6California Polytechnic State University, San Luis Obispo, California,
United States

org7Central China Normal University, Wuhan, China

org8Centre de Calcul de l’IN2P3, Villeurbanne, Lyon, France

org9Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana,
Cuba

org10Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City
and Mérida, Mexico

org11Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche
“Enrico Fermi’, Rome, Italy

org12Chicago State University, Chicago, Illinois, United States

org13China Institute of Atomic Energy, Beijing, China

org14Chonbuk National University, Jeonju, Republic of Korea

org15Comenius University Bratislava, Faculty of Mathematics, Physics and
Informatics, Bratislava, Slovakia

org16COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan

org17Creighton University, Omaha, Nebraska, United States

org18Department of Physics, Aligarh Muslim University, Aligarh, India

org19Department of Physics, Ohio State University, Columbus, Ohio, United
States

org20Department of Physics, Pusan National University, Pusan, Republic of
Korea

org21Department of Physics, Sejong University, Seoul, Republic of Korea

org22Department of Physics, University of California, Berkeley, California,
United States

org23Department of Physics, University of Oslo, Oslo, Norway

org24Department of Physics and Technology, University of Bergen, Bergen,
Norway

org25Dipartimento di Fisica dell’Università ’La Sapienza’ and Sezione INFN,
Rome, Italy

org26Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy

org27Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy

org28Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy

org29Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Bologna, Italy

org30Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Catania, Italy

org31Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Padova, Italy

org32Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo
Collegato INFN, Salerno, Italy

org33Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy

org34Dipartimento di Scienze e Innovazione Tecnologica dell’Università del
Piemonte Orientale and INFN Sezione di Torino, Alessandria, Italy

org35Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari,
Italy

org36European Organization for Nuclear Research (CERN), Geneva, Switzerland

org37Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, Split, Croatia

org38Faculty of Engineering and Science, Western Norway University of Applied
Sciences, Bergen, Norway

org39Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University in Prague, Prague, Czech Republic

org40Faculty of Science, P.J. Šafárik University, Košice, Slovakia

org41Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-
Universität Frankfurt, Frankfurt, Germany

org42Gangneung-Wonju National University, Gangneung, Republic of Korea

org43Gauhati University, Department of Physics, Guwahati, India

org44Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-
Wilhelms-Universität Bonn, Bonn, Germany

org45Helsinki Institute of Physics (HIP), Helsinki, Finland

org46Hiroshima University, Hiroshima, Japan

org47Hochschule Worms, Zentrum für Technologietransfer und Telekommunikation
(ZTT), Worms, Germany

org48Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest, Romania

org49Indian Institute of Technology Bombay (IIT), Mumbai, India

org50Indian Institute of Technology Indore, Indore, India

org51Indonesian Institute of Sciences, Jakarta, Indonesia

org52INFN, Laboratori Nazionali di Frascati, Frascati, Italy

org53INFN, Sezione di Bari, Bari, Italy

org54INFN, Sezione di Bologna, Bologna, Italy

org55INFN, Sezione di Cagliari, Cagliari, Italy

org56INFN, Sezione di Catania, Catania, Italy

org57INFN, Sezione di Padova, Padova, Italy

org58INFN, Sezione di Roma, Rome, Italy

org59INFN, Sezione di Torino, Turin, Italy

org60INFN, Sezione di Trieste, Trieste, Italy

org61Inha University, Incheon, Republic of Korea

org62Institut de Physique Nucléaire d’Orsay (IPNO), Institut National de
Physique Nucléaire et de Physique des Particules (IN2P3/CNRS), Université de
Paris-Sud, Université Paris-Saclay, Orsay, France

org63Institute for Nuclear Research, Academy of Sciences, Moscow, Russia

org64Institute for Subatomic Physics, Utrecht University/Nikhef, Utrecht,
Netherlands

org65Institute for Theoretical and Experimental Physics, Moscow, Russia

org66Institute of Experimental Physics, Slovak Academy of Sciences, Košice,
Slovakia

org67Institute of Physics, Bhubaneswar, India

org68Institute of Physics of the Czech Academy of Sciences, Prague, Czech
Republic

org69Institute of Space Science (ISS), Bucharest, Romania

org70Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany

org71Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México,
Mexico City, Mexico

org72Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS),
Porto Alegre, Brazil

org73Instituto de Física, Universidad Nacional Autónoma de México, Mexico
City, Mexico

org74iThemba LABS, National Research Foundation, Somerset West, South Africa

org75Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik,
Fachbereich Informatik und Mathematik, Frankfurt, Germany

org76Joint Institute for Nuclear Research (JINR), Dubna, Russia

org77Korea Institute of Science and Technology Information, Daejeon, Republic
of Korea

org78KTO Karatay University, Konya, Turkey

org79Laboratoire de Physique Subatomique et de Cosmologie, Université
Grenoble-Alpes, CNRS-IN2P3, Grenoble, France

org80Lawrence Berkeley National Laboratory, Berkeley, California, United
States

org81Lund University Department of Physics, Division of Particle Physics,
Lund, Sweden

org82Nagasaki Institute of Applied Science, Nagasaki, Japan

org83Nara Women’s University (NWU), Nara, Japan

org84National and Kapodistrian University of Athens, School of Science,
Department of Physics , Athens, Greece

org85National Centre for Nuclear Research, Warsaw, Poland

org86National Institute of Science Education and Research, HBNI, Jatni, India

org87National Nuclear Research Center, Baku, Azerbaijan

org88National Research Centre Kurchatov Institute, Moscow, Russia

org89Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

org90Nikhef, National institute for subatomic physics, Amsterdam, Netherlands

org91NRC Kurchatov Institute IHEP, Protvino, Russia

org92NRNU Moscow Engineering Physics Institute, Moscow, Russia

org93Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United
Kingdom

org94Nuclear Physics Institute of the Czech Academy of Sciences, Řež u Prahy,
Czech Republic

org95Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

org96Petersburg Nuclear Physics Institute, Gatchina, Russia

org97Physics department, Faculty of science, University of Zagreb, Zagreb,
Croatia

org98Physics Department, Panjab University, Chandigarh, India

org99Physics Department, University of Jammu, Jammu, India

org100Physics Department, University of Rajasthan, Jaipur, India

org101Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen,
Germany

org102Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg,
Heidelberg, Germany

org103Physik Department, Technische Universität München, Munich, Germany

org104Research Division and ExtreMe Matter Institute EMMI, GSI
Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany

org105Rudjer Bošković Institute, Zagreb, Croatia

org106Russian Federal Nuclear Center (VNIIEF), Sarov, Russia

org107Saha Institute of Nuclear Physics, Kolkata, India

org108School of Physics and Astronomy, University of Birmingham, Birmingham,
United Kingdom

org109Sección Física, Departamento de Ciencias, Pontificia Universidad
Católica del Perú, Lima, Peru

org110Shanghai Institute of Applied Physics, Shanghai, China

org111Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria

org112SUBATECH, IMT Atlantique, Université de Nantes, CNRS-IN2P3, Nantes,
France

org113Suranaree University of Technology, Nakhon Ratchasima, Thailand

org114Technical University of Košice, Košice, Slovakia

org115Technische Universität München, Excellence Cluster ’Universe’, Munich,
Germany

org116The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy
of Sciences, Cracow, Poland

org117The University of Texas at Austin, Austin, Texas, United States

org118Universidad Autónoma de Sinaloa, Culiacán, Mexico

org119Universidade de São Paulo (USP), São Paulo, Brazil

org120Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil

org121Universidade Federal do ABC, Santo Andre, Brazil

org122University College of Southeast Norway, Tonsberg, Norway

org123University of Cape Town, Cape Town, South Africa

org124University of Houston, Houston, Texas, United States

org125University of Jyväskylä, Jyväskylä, Finland

org126University of Liverpool, Department of Physics Oliver Lodge Laboratory ,
Liverpool, United Kingdom

org127University of Tennessee, Knoxville, Tennessee, United States

org128University of the Witwatersrand, Johannesburg, South Africa

org129University of Tokyo, Tokyo, Japan

org130University of Tsukuba, Tsukuba, Japan

org131Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France

org132Université de Lyon, Université Lyon 1, CNRS/IN2P3, IPN-Lyon,
Villeurbanne, Lyon, France

org133Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg,
France, Strasbourg, France

org134 Université Paris-Saclay Centre d¿Études de Saclay (CEA), IRFU,
Department de Physique Nucléaire (DPhN), Saclay, France

org135Università degli Studi di Pavia, Pavia, Italy

org136Università di Brescia, Brescia, Italy

org137V. Fock Institute for Physics, St. Petersburg State University, St.
Petersburg, Russia

org138Variable Energy Cyclotron Centre, Kolkata, India

org139Warsaw University of Technology, Warsaw, Poland

org140Wayne State University, Detroit, Michigan, United States

org141Westfälische Wilhelms-Universität Münster, Institut für Kernphysik,
Münster, Germany

org142Wigner Research Centre for Physics, Hungarian Academy of Sciences,
Budapest, Hungary

org143Yale University, New Haven, Connecticut, United States

org144Yonsei University, Seoul, Republic of Korea