2022 076 30 March

$\rm{W}^{\pm}$ bosons in p–Pb at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV and
Pb–Pb at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV

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

The production of the $\rm{W}^{\pm}$ bosons measured in p–Pb collisions at a
centre-of-mass energy per nucleon–nucleon collision
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV and Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV with ALICE at the LHC is presented.
The $\rm{W}^{\pm}$ bosons are measured via their muonic decay channel, with
the muon reconstructed in the pseudorapidity region $-4<\eta^{\mu}_{\rm
lab}<-2.5$ with transverse momentum $p_{\rm T}^{\mu}~{}>$ 10 GeV$/c$. While in
Pb–Pb collisions the measurements are performed in the forward
($2.5<y^{\mu}_{\rm cms}<4$) rapidity region, in p–Pb collisions, where the
centre-of-mass frame is boosted with respect to the laboratory frame, the
measurements are performed in the backward ($-4.46<y^{\mu}_{\rm cms}<-2.96$)
and forward ($2.03<y^{\mu}_{\rm cms}<3.53$) rapidity regions. The $\rm{W}^{-}$
and $\rm{W}^{+}$ production cross sections, lepton-charge asymmetry, and
nuclear modification factors are evaluated as a function of the muon rapidity.
In order to study the production as a function of the p–Pb collision
centrality, the production cross sections of the $\rm{W}^{-}$ and $\rm{W}^{+}$
bosons are combined and normalised to the average number of binary
nucleon–nucleon collision $\langle N_{\mathrm{coll}}\rangle$. In Pb–Pb
collisions, the same measurements are presented as a function of the collision
centrality. Study of the binary scaling of the $\rm{W}^{\pm}$-boson cross
sections in p–Pb and Pb–Pb collisions is also reported. The results are
compared with perturbative QCD calculations, with and without nuclear
modifications of the Parton Distribution Functions (PDFs), as well as with
available data at the LHC. Significant deviations from the theory expectations
are found in the two collision systems, indicating that the measurements can
provide additional constraints for the determination of nuclear PDFs and in
particular of the light-quark distributions.

##  1 Introduction

The production of the $\rm{W}^{\pm}$\- and $\rm{Z}^{0}$-vector bosons is
extensively studied at hadron colliders. The $\rm{W}^{\pm}$ and $\rm{Z}^{0}$
bosons are weakly interacting particles, produced early in hadronic collisions
(with a formation time $t_{\rm f}\sim 1/M\sim 10^{-3}$ fm$/c$), predominantly
via the Drell-Yan process in which a quark–antiquark pair annihilates into a
lepton pair [1, 2]. Due to their large masses, $M_{\rm{W}^{\pm}}=80.379\pm
0.012$ GeV$/c^{2}$ and $M_{\rm{Z}^{0}}=91.1876\pm 0.0021$ GeV$/c^{2}$ [3],
their production is well described within the perturbative quantum
chromodynamics (pQCD) framework, up to Next-to-Next-to-Leading Order (NNLO) by
means of the QCD factorisation theorem for hard processes [4, 5].
Factorisation allows us to separate the short distance part of the cross
section, corresponding to the partonic cross section that can be expanded
perturbatively, from the long distance part containing the Parton Distribution
Functions (PDFs), parameterising the partonic content of the nucleon and
determined from experimental data. The input parameters for theoretical
calculations, such as the boson masses or the weak couplings, are known with
high accuracy, enabling the usage of measurements of the electroweak-boson
production to determine the up (u), down (d) and to a lesser extent strange
(s) PDFs (see Refs. [6, 7] for recent reviews). In nuclear collisions, the
presence of a nuclear environment affects the inner structure of the nucleon,
requiring the determination of nuclear PDFs (nPDFs). As for the free-nucleon
case, the nPDFs are obtained from a global analysis of the available data, but
in this case the results are mostly constrained by Deep-Inelastic Scatterings
(DIS) and Drell-Yan data in a limited region of the four-momentum transfer
squared $Q^{2}$ and parton longitudinal momentum fraction $x$ (Bjorken-$x$).
The resulting nPDF uncertainties drastically limit the precision of
theoretical calculations and their ability to describe and predict processes
in nuclear collisions. In order to further constrain the nPDFs and reduce
their uncertainties, the production of the $\rm{W}^{\pm}$ and $\rm{Z}^{0}$
bosons has been measured in proton–lead (p–Pb) and lead–lead (Pb–Pb)
collisions at the CERN Large Hadron Collider (LHC) by the four main
experiments, at midrapidity by ATLAS and CMS [8, 9, 10, 11, 12, 13, 14, 15,
16, 17, 18, 19] and at large rapidities by ALICE and LHCb [20, 21, 22, 23].

Four main intervals of Bjorken-$x$ featuring different nuclear modifications
can be distinguished at high $Q^{2}$ values. The nPDFs show a suppression at
low Bjorken-$x$, for $x\lesssim 0.05$, and an enhancement within the range
$x\sim 0.05-0.3$111All the Bjorken-$x$ ranges are indicative, as the precise
values of the region boundaries depend on the parton flavour, the nPDF
parametrisation, and the $Q^{2}$ scale.. Both these effects, referred to as
shadowing and anti-shadowing, respectively, originate from destructive or
constructive interferences of amplitudes arising from multiple scatterings
between partons in the nucleus [24]. Another depletion region is seen for $x$
within 0.3 – 0.9 in the so-called EMC-effect region which is not yet fully
understood [25]. Finally, for $x$ larger than 0.9 the Fermi motion of the
nucleons inside the nucleus yields an enhancement of the PDF [26]. These
effects will naturally affect the production of electroweak bosons [27], and
their measurement provides a unique opportunity to constrain the nPDFs at high
$Q^{2}\sim M^{2}_{\rm W,Z}$. Moreover, with the large luminosities and centre-
of-mass energies delivered by the LHC, combined with the wide acceptance
covered by the LHC experiments, the study of electroweak bosons has become
accessible in p–Pb and Pb–Pb collisions over a large Bjorken-$x$ range, from
almost unity down to $x\sim 10^{-4}$ where the experimental constraints are
scarce. Measurements in p–Pb collisions at large negative and positive
rapidities are of high interest as they allow the disentanglement of the high
($\sim 10^{-1}$) and low ($\sim 10^{-4}-10^{-3}$) Bjorken-$x$ intervals,
respectively. The yields of the $\rm{W}^{-}$ and $\rm{W}^{+}$ bosons, mainly
produced by interactions between u and d quarks via the
$\mathrm{d}\overline{\mathrm{u}}\rightarrow\rm{W}^{-}$ and
$\mathrm{u}\overline{\mathrm{d}}\rightarrow\rm{W}^{+}$ processes, offer a
probe of the light quark PDFs, while their asymmetry is sensitive to the down-
to-up ratio in the nucleus [28]. The leptonic decay of these bosons is of
particular interest, as the decay products do not interact strongly, therefore
being blind to the quark–gluon plasma (QGP), the hot and dense medium created
in heavy-ion collisions. In addition, the in-medium energy loss of the decay
leptons by bremsstrahlung is negligible [29]. Combined with the colourless
nature of the $\rm{W}^{\pm}$ boson itself, this physics channel provides a
medium-blind process and consequently, a direct probe of the initial state of
the collision even in the presence of a QGP. The production of electroweak
bosons, therefore, enables the study of the nPDFs of the colliding nuclei.

The measurements of the $\rm{W}^{\pm}$-boson production presented in this
publication are compared with predictions obtained from calculations at Next-
to-Leading Order (NLO), implementing the nuclear modifications of the PDFs
using the EPPS16 [30], nCTEQ15 [31] and nNNPDF2.0 [32] sets, in which the
parametrisation and determination of the nPDF follow different approaches. The
approach of the EPPS (formerly EPS) group introduces, for a given parton $i$
in a nucleus with atomic number $A$, the nuclear correction factor
$R_{i}(x,A)$ at the input parametrisation scale $Q^{2}_{0}$. In such a model,
the nPDF set is composed of nuclear modification functions to be applied to a
free-nucleon PDF set which serves as a baseline. The approach of the nCTEQ
collaboration does not utilise the nuclear correction factors, instead, it is
a full nPDF parametrisation. It starts from the functional form used for the
free-proton PDF (in the nCTEQ case the form is similar to the CTEQ6
parametrisation [33]), with the addition of $A$-dependent free parameters. The
lack of experimental data that can be used for the nPDF determination induces
a strong dependence of the models on the phenomenological and methodological
assumptions. The EPPS16 and nCTEQ15 sets show large differences in the
predicted nuclear modifications and associated uncertainties [34], originating
from the functional form, the number of free parameters, and the data points
included in the global analysis. In order to reduce the parametrisation bias,
the nNNPDF collaboration adopted the methodology described in Ref. [35], and
used artificial neural networks as universal, unbiased interpolants to
parametrise the $x$ and $A$ dependence of the nPDFs. Recently, the LHC
experiments contributed to the evolution of the models, and $\rm{W}^{\pm}$ and
$\rm{Z}^{0}$ measurements in p–Pb collisions are now included into the input
datasets, in EPPS starting with EPPS16 [30], in nCTEQ after the nCTEQ15WZ
update [36], and in nNNPDF from their 2.0 release [32]. It should be noted
that the EPPS model has recently been updated with the release of the EPPS21
set [37]. The production of electroweak bosons calculated from this set is in
fair agreement with the ones obtained with the EPPS16 model, with a
significant reduction of the associated uncertainties.

In this article, the ALICE results on the measurement of the
$\rm{W}^{\pm}$-boson production via the muonic decay channel in p–Pb
collisions at a centre-of-mass energy per nucleon–nucleon collision
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV and Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV are reported. These results constitute
the first measurements of the $\rm{W}^{\pm}$-boson production at large
rapidities for these collision systems and energies, with the p–Pb results
complementing the CMS measurements at midrapidity [15] and extending the ALICE
measurements in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV
[20]. The paper is structured as discussed in the following. Section 2
introduces the ALICE apparatus, focusing on the detectors relevant for the
analyses, followed by a description of the event and track selections. The
analysis strategy, including the procedure for the signal extraction and the
simulation of the apparatus, is presented in Section 3, together with a
discussion of the systematic uncertainties. The results are reported in
Section 4 where they are compared with theoretical predictions and other
published measurements. A summary of the results and their interpretation is
given in Section 5.

##  2 ALICE apparatus and data samples

###  2.1 The ALICE detector

The $\rm{W}^{\pm}$ bosons are detected through their muonic decay channel via
the $\rm{W}^{-}\rightarrow\mu^{-}\overline{\nu}_{\mu}$ process and its charge
conjugate, with a branching ratio BR$~{}=~{}(10.63\pm 0.15)$% [3], from data
recorded with the ALICE muon spectrometer [38, 39]. The spectrometer covers in
full azimuth the $-4<\eta_{\rm lab}<-2.5$ pseudorapidity interval222In the
ALICE reference frame, the muon spectrometer covers negative $\eta$. In
symmetric collisions such as Pb–Pb, positive values of rapidity are
conventionally used for the muon coverage. In p–Pb collisions, by convention,
the proton beam moves towards positive rapidities.. Its tracking system is
composed of five stations, each made of two planes of cathode pad chambers.
The third station sits inside a dipole magnet providing an invertible magnetic
field with integrated intensity of 3 Tm, which bends the trajectory of charged
particles thus enabling the measurement of the track momentum. The muon system
also includes a muon trigger, consisting of four planes of resistive plate
chambers arranged in two stations. The whole spectrometer is shielded by a set
of absorbers. A conical absorber of 10 interaction lengths ($\lambda_{i}$)
made of carbon, concrete, and steel is located in front of the muon
spectrometer, filtering out hadrons and low-momentum muons from the decays of
light particles such as pions and kaons. The trigger stations are located
behind a 1.2 m thick (about 7.2 $\lambda_{i}$) iron wall, absorbing hadrons
punching through the front absorber as well as low-momentum secondary muons.
Finally, a high-density cylinder made of tungsten and lead, the so-called
small-angle absorber, surrounds the beam pipe throughout the muon spectrometer
in its entirety and shields it against secondary particles produced by the
interaction of primary particles at large $\eta$ with the beam pipe.

Other detectors are needed for primary vertex reconstruction, triggering on
Minimum Bias (MB) collisions, multiplicity determination, and centrality
evaluation. The primary interaction vertex reconstruction is performed using
the Silicon Pixel Detector (SPD), the two innermost layers of the Inner
Tracking System (ITS) [40], covering the pseudorapidity intervals $|\eta_{\rm
lab}|<2.0$ and $|\eta_{\rm lab}|<1.4$. The V0 detector [41] is made of two
arrays of scintillator tiles, located asymmetrically around the collision
point, along the beam direction, at $z=3.4$ m (V0A) and $z=-0.9$ m (V0C), and
covering the pseudorapidity intervals $2.8<\eta_{\rm lab}<5.1$ and
$-3.7<\eta_{\rm lab}<-1.7$, respectively. The V0 provides an online MB trigger
through the logical coincidence of a signal in the two arrays, and
participates in the determination of the luminosity by providing a reference
process for van der Meer scans [42]. It is also used for the evaluation of the
centrality in Pb–Pb collisions by means of a Glauber model fit [43, 44] to the
sum of the signal amplitudes in the two arrays (the V0M estimator). This
allows one to classify the events in centrality classes corresponding to a
percentile of the total hadronic cross section. The centrality evaluated in
this way relies on the event charged-particle multiplicity, a method which has
been shown to be strongly biased in p–Pb collisions [45]. Instead, the
centrality estimation for this system uses the Zero Degree Calorimeter (ZDC)
[46], a set of two hadronic calorimeters located along the beam pipe, on both
sides of the collision point, 112.5 m away from it. The timing information
delivered by the V0 and ZDC detectors also helps to reduce the beam-induced
background. A complete description of the ALICE detector can be found in Ref.
[47] and its performance is reported in Ref. [48], where standard detection,
reconstruction, and analysis procedures are described.

###  2.2 Event and track selections

The analysis in p–Pb collisions uses the data samples collected in 2016 at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV. These data were taken in two
colliding beam configurations, with either the protons or lead ions moving
towards the spectrometer, hereafter referred to as the p-going and Pb-going
configurations, respectively. By convention, the protons move towards positive
rapidities. Because of the single magnet design of the LHC, the proton and Pb
beams have the same magnetic rigidity, leading to different energies per
nucleon, amounting to 6.5 TeV for the protons and 2.56 TeV for the Pb ions.
The resulting nucleon–nucleon centre-of-mass system is thus boosted with
respect to the laboratory frame, resulting in a rapidity shift of $\Delta
y_{\rm cms/lab}=0.465$ in the direction of the proton beam. The rapidity
acceptance of the spectrometer in the centre-of-mass system is then
$2.03<y_{\rm cms}<3.53$ in the p-going direction and $-4.46<y_{\rm cms}<-2.96$
in the Pb-going one. The analysis in Pb–Pb collisions uses the data samples
collected in 2015 and 2018 at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV in the
rapidity range $2.5<y^{\mu}_{\rm cms}<4$. For each sample, two sub-periods can
be distinguished according to the sign of the magnetic field delivered by the
dipole magnet.

The analysed data samples consist of events with at least one muon track
candidate selected by the muon trigger system, with an online selection on the
transverse momentum ($p_{\rm T}^{\mu}$) requiring it to be above $\simeq$ 4.2
GeV$/c$ (at the threshold, the track produces a trigger signal with a 50%
probability), in coincidence with a MB signal in the V0 detector. The Pb–Pb
analysis is limited to the most central 90% of the total hadronic cross
section, where the MB trigger is fully efficient and electromagnetic
interactions are negligible. The events were further required to have a
reconstructed vertex position along the beam direction within $\pm 10$ cm from
the nominal interaction point in order to keep the full efficiency of the SPD
for vertex reconstruction. Events in which two or more interactions occur in
the same colliding bunch (in-bunch pile-up) or during the readout time of the
SPD (out-of-bunch pile-up), amounting to about 20% of the sample, are removed
using the information from the SPD and V0 detectors. The integrated luminosity
was evaluated by estimating the equivalent number of MB events corresponding
to the muon-triggered data sample and then dividing by $\sigma_{\rm V0M}$, the
V0 visible cross section measured by means of van der Meer scans [42, 49, 50].
The number of MB events corresponding to the muon-triggered sample was
evaluated as $N_{\rm MB}=F_{\mu\text{-trig}/\text{MB}}\times
N_{\mu\text{-trig}}$, where $N_{\mu\text{-trig}}$ is the number of muon-
triggered events and $F_{\mu\text{-trig}/\text{MB}}$ is the inverse of the
probability to have a muon trigger in a MB event. The value of the
normalisation factor $F_{\mu\text{-trig}/\text{MB}}$ was evaluated with two
different methods, either by applying the muon trigger condition in the
analysis of MB events, or by comparing the counting rate of the two triggers,
both corrected for pile-up effects. The nominal value was obtained from the
method using the trigger rates, while the difference between the two methods
was taken as the systematic uncertainty on the normalisation factor. This
uncertainty amounts to 1.4% (1.1%) in p–Pb collisions for the p-going (Pb-
going) configuration, and to 1% in Pb–Pb collisions. The integrated
luminosities of the considered p–Pb data samples amount to $6.73\pm 0.16$ nb-1
and $10.0\pm 0.22$ nb-1 in the p-going and Pb-going directions, respectively,
and to $663\pm 15$ $\mu$b-1 for Pb–Pb collisions after merging the 2015 and
2018 data samples. The quoted uncertainties are the systematic uncertainties,
while the statistical ones are negligible.

The classification of the events in p–Pb collisions into centrality intervals
is performed based on the energy deposited in the neutron calorimeters (ZN) of
the ZDC in the direction of the Pb fragments. For each of these intervals, the
average number of binary nucleon–nucleon collisions $\langle
N_{\mathrm{coll}}\rangle$ is obtained from the hybrid method described in Ref.
[45]. The method relies on the assumption that the charged-particle
multiplicity measured at midrapidity is proportional to the average number of
nucleons participating in the interaction $\langle N_{\mathrm{part}}\rangle$.
The values of $\langle N_{\mathrm{part}}\rangle$ for a given ZN-centrality
class are calculated by scaling the average number of participants in MB
collisions $\langle N^{\rm MB}_{\rm part}\rangle$, estimated by means of
Glauber Monte Carlo (MC) [51, 52], with the ratio of the average charged-
particle multiplicity measured at midrapidity for the ZN-centrality class to
that in MB collisions. In the following, these values are denoted $\langle
N^{\mathrm{mult}}_{\mathrm{part}}\rangle$ to indicate this assumption. The
corresponding number of binary collisions is then obtained as $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle=\langle N^{\rm mult}_{\rm
part}\rangle-1$. The associated uncertainty is evaluated using different
approaches as described in Ref. [52]. The resulting values of $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ and their uncertainties are
summarised in Table 1. In Pb–Pb collisions, the centrality is determined from
the distribution of the signal amplitude in the V0 arrays and is expressed in
percentages of the total hadronic cross section. The collisional geometrical
properties $\langle N_{\mathrm{part}}\rangle$, $\langle
N_{\mathrm{coll}}\rangle$, and the nuclear overlap function $\langle T_{\rm
AA}\rangle$ of the different centrality intervals are obtained via a Glauber
model fit to the V0 signal amplitude distribution. The Glauber model is also
used to determine the so-called anchor point below which the centrality
determination is not reliable. The values of $\langle T_{\rm AA}\rangle$ in
Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV are given in Table
2 for the centrality classes considered in this work.

Table 1: Average number of binary nucleon–nucleon collisions $\langle N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ estimated with the hybrid method for the ZN centrality classes in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV [52]. Centrality class | 0–100% | 0–20% | 20–40% | 40–60% | 60–100%
---|---|---|---|---|---
$\langle N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ | $7.09\pm 0.28$ | $12.2\pm 0.52$ | $9.81\pm 0.17$ | $7.09\pm 0.29$ | $3.17\pm 0.09$
Table 2: Average nuclear overlap function $\langle T_{\rm AA}\rangle$ evaluated with a Glauber MC fit to the sum of the V0 amplitudes in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV [52]. Centrality class | 0–90% | 0–10% | 10–20% | 20–40% | 40–90%
---|---|---|---|---|---
$\langle T_{\rm AA}\rangle$ (mb-1) | $6.28\pm 0.06$ | $23.26\pm 0.17$ | $14.40\pm 0.13$ | $6.93\pm 0.09$ | $1.00\pm 0.02$

The muon track candidates reconstructed in the events passing the requirements
described above are selected according to the following criteria. A fiducial
selection is applied on the track pseudorapidity, requiring it to be in the
interval $-4<\eta^{\mu}_{\rm lab}<-2.5$ to remove the particles at the edge of
the spectrometer acceptance. An additional selection on the polar angle
measured at the end of the front absorber, of $170^{\circ}<\theta_{\rm
abs}<178^{\circ}$, rejects the tracks crossing the high-density region of the
front absorber, where they experience significant multiple scatterings. The
contamination by tracks not pointing to the nominal interaction vertex, mostly
originating from beam–gas interactions and secondary particles produced in the
front absorber, is efficiently removed by exploiting the correlation between
the track momentum $p$ and its distance of closest approach (DCA) to the
vertex (i.e., the distance to the primary vertex of the track trajectory
projected on the plane transverse to the beam axis). Being subject to multiple
scatterings in the front absorber, the DCA of particles produced in the
collision follows a Gaussian distribution, with a sigma depending on the
material crossed and being proportional to the inverse of the momentum $p$.
Background tracks, on the other hand, have on average a DCA larger than about
40 cm, independently of their momentum. A selection on the product of the
track momentum with its DCA ($p\times$DCA) allows the suppression of this
background source down to a negligible level. Finally, the muon identification
is performed by matching the track reconstructed in the tracking system with a
track segment in the trigger stations. The track in the tracking system is
extrapolated to the trigger stations, and a $\chi^{2}$-based criterion
determines the quality of the matching.

##  3 Analysis strategy

###  3.1 Overview

The $\rm{W}^{\pm}$ bosons are detected through their muonic decay channel via
the $\rm{W}^{-}\rightarrow\mu^{-}\overline{\nu}_{\mu}$ and
$\rm{W}^{+}\rightarrow\mu^{+}\nu_{\mu}$ processes following the method
described in Ref. [20]. Since ALICE is not a hermetic detector, one cannot
reconstruct the missing transverse energy due to the presence of a neutrino in
the final state. The signal extraction is therefore performed from the single
muon $p_{\rm T}$ distribution, excluding the $p_{\rm T}^{\mu}~{}<$ 10 GeV$/c$
interval where the signal-to-background ratio is very small. One can
distinguish three main contributions to the inclusive spectrum, namely muons
originating from the decay of $\rm{W}^{\pm}$, $\rm{Z}^{0}$/$\gamma^{*}$, and
heavy-flavour (charm and beauty) hadrons. The signal extraction procedure
relies on templates, which are generated by means of MC simulations, and are
used to fit the measured muon $p_{\rm T}$ distributions according to

$f(p_{\rm T})=N^{\rm raw}_{\rm HF}f_{\rm HF}(p_{\rm T})+N^{\rm
raw}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}\left(f_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}(p_{\rm
T})+R\times f_{\mu^{\pm}\leftarrow\rm{Z}^{0}/\gamma^{*}}(p_{\rm T})\right),$
(1)

where $f_{\rm HF}$, $f_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$, and
$f_{\mu^{\pm}\leftarrow\rm{Z}^{0}/\gamma^{*}}$ are the templates accounting
for muons from heavy-flavour hadrons, $\rm{W}^{\pm}$-boson, and
$\rm{Z}^{0}$/$\gamma^{*}$ decays, respectively. The number of muons from
heavy-flavour hadrons and $\rm{W}^{\pm}$-boson decays ($N^{\rm raw}_{\rm HF}$
and $N^{\rm raw}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$) are free parameters of
the fit, while the number of muons from $\rm{Z}^{0}$/$\gamma^{*}$ decays is
forced to be proportional to that of $\rm{W}^{\pm}$ decays according to the
ratio $R$ of their production cross sections as predicted by MC simulations
using the POWHEG event generator [53].

###  3.2 MC simulations

The production of muons from $\rm{W}^{\pm}$ and $\rm{Z}^{0}$/$\gamma^{*}$
decays was simulated by means of MC simulations at NLO using the POWHEG event
generator [53]. Since POWHEG is only intended for the simulation of hard
partonic scattering processes, it was matched to PYTHIA 6 [54] for parton
shower description. In the simulations, the CT10 PDF set [55] was used along
with the EPS09NLO [56] parametrisation of the nuclear modifications. In order
to account for the isospin effect, which is of particular importance for the
$\rm{W}^{\pm}$-boson production yields, simulations of proton–proton (pp),
proton–neutron (pn), neutron–proton (np), and also neutron–neutron (nn) binary
collisions for Pb–Pb, were performed. The total cross sections were obtained
from the single pp, pn, np, and nn cross sections combined with weights
proportional to the density of protons and neutrons in a Pb nucleus:

$\frac{\mathrm{d}^{2}\sigma^{\rm pPb}_{\rm NN}}{\mathrm{d}p_{\rm
T}\mathrm{d}y}=\frac{Z}{A}\times\frac{\mathrm{d}^{2}\sigma^{\rm pPb}_{\rm
pp}}{\mathrm{d}p_{\rm
T}\mathrm{d}y}+\frac{A-Z}{A}\times\frac{\mathrm{d}^{2}\sigma^{\rm pPb}_{\rm
pn}}{\mathrm{d}p_{\rm T}\mathrm{d}y},$ (2) $\frac{\mathrm{d}^{2}\sigma^{\rm
PbPb}_{\rm NN}}{\mathrm{d}p_{\rm
T}\mathrm{d}y}=\frac{Z^{2}}{A^{2}}\times\frac{\mathrm{d}^{2}\sigma^{\rm
PbPb}_{\rm pp}}{\mathrm{d}p_{\rm
T}\mathrm{d}y}+\frac{(A-Z)^{2}}{A^{2}}\times\frac{\mathrm{d}^{2}\sigma^{\rm
PbPb}_{\rm nn}}{\mathrm{d}p_{\rm
T}\mathrm{d}y}+\frac{Z(A-Z)}{A^{2}}\times\left(\frac{\mathrm{d}^{2}\sigma^{\rm
PbPb}_{\rm pn}}{\mathrm{d}p_{\rm
T}\mathrm{d}y}+\frac{\mathrm{d}^{2}\sigma^{\rm PbPb}_{\rm
np}}{\mathrm{d}p_{\rm T}\mathrm{d}y}\right),$ (3)

where Eq. 2 indicates the combination in p–Pb collisions and Eq. 3 the
combination for the Pb–Pb system.

The contribution of muons from heavy-flavour hadron decays was simulated using
the Fixed-Order Next-to-Leading-Log (FONLL) approach [57]. The FONLL
calculations were performed with the NNPDF3.1 PDF set [35], without accounting
for nuclear modifications. In p–Pb collisions, the nuclear effects mainly
affect the production of heavy-flavour hadrons at low $p_{\rm T}$, typically
below 5 GeV$/c$ [58], and are expected to be negligible in the $p_{\rm T}$
interval studied in this paper. In the analysis of the Pb–Pb data sample, the
FONLL predictions were multiplied by the nuclear modification factor $R_{\rm
AA}$ of muons from heavy-flavour hadron decays, taken from simulations
performed within the EPOS framework [59] in the interval $10<p_{\rm
T}^{\mu}<50$ GeV$/c$, fitted with a first-order polynomial function and
further extrapolated to high $p_{\rm T}$. The FONLL predictions were then used
as inputs for the MC generation of muons from heavy-flavour hadron decays.

The MC simulations were performed by using the GEANT3 transport code [60]
combined with a detailed simulation of the detector response and taking into
account the time evolution of the detector configuration and alignment
effects. In the high-$p_{\rm T}^{\mu}$ region studied in this analysis
($p_{\rm T}^{\mu}>10$ GeV$/c$), the tracks are weakly bent, the alignment of
the tracking chambers is therefore of utmost importance for the track
reconstruction. The absolute positions of the chambers were first measured
with photogrammetry before the data taking. The relative positions of the
detection elements were then refined with a combination of reconstructed
tracks in data samples recorded with and without magnetic field using a
modified version of the MILLEPEDE package [61], up to a precision of about 100
$\mu$m. The estimated residual misalignment is then taken into account in the
MC simulations. In addition, one may expect a misalignment of the spectrometer
in its entirety, which is addressed by studying the track-to-cluster residual
distribution in the data and the simulation. The simulation of the tracking
chamber response relies on a data-driven parametrisation of the measured
resolution of the clusters associated to a track. The distribution of the
difference between the cluster and the track positions in each chamber is
described using extended Crystal Ball (CB) [62] functions, with parameters
tuned on data. The CB parametrisation is then used to reproduce the smearing
of the track parameters in the simulations. A global misalignment of the
detector is mimicked by shifting the distribution of the track deviations in
the magnetic field. The sign of the shift is reverted for positive and
negative tracks, and according to the magnetic field polarity. Its magnitude
was tuned in order to reproduce the observed difference in the $p_{\rm
T}^{\mu}$ distribution of positive and negative tracks.

###  3.3 Signal extraction and efficiency correction

Examples of the $\rm{W}^{-}$ and $\rm{W}^{+}$ signal extraction are shown in
Fig. 1 and 2 for p–Pb and Pb–Pb collisions, respectively. In p–Pb collisions,
an example is given for each combination of the colliding beam configuration
and the charge of the muon. In Pb–Pb collisions, examples are given for the
two charges of the muon, in the full centrality interval or for the 10% most
central collisions. For both collision systems, the decay of $\rm{W}^{\pm}$
bosons becomes the dominant contribution for $p_{\rm T}^{\mu}$ above 25 or 30
GeV$/c$. The fits to Eq. 1 are found to describe well the data, although at
high $p_{\rm T}^{\mu}$ they tend to underestimate the muon yield in some
configurations. This difference between the data and the fit occurs in a
$p_{\rm T}^{\mu}$ interval where the number of muons is small, and has a
negligible impact on the signal extraction.

Figure 1: Inclusive transverse momentum distribution of negative (top) and
positive (bottom) muons at backward (left) and forward (right) rapidity in
p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV. The results of the
fit to the inclusive spectrum using a combination of MC templates is shown as
a continuous line, the green, pink and blue dashed lines representing the
contributions of the $\rm{W}^{\pm}$-, $\rm{Z}^{0}$/$\gamma^{*}$\- and heavy-
flavour hadron decay muons, respectively. The bottom panels show the ratio of
the data to the fit result.

Figure 2: Inclusive transverse momentum distribution of negative (top) and
positive (bottom) muons for the 0–90% (left) and 0–10% (right) centrality
intervals in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV. The
results of the fit to the inclusive spectrum using a combination of MC
templates is shown as a continuous line, the green, pink and blue dashed lines
representing the contributions of the $\rm{W}^{\pm}$-,
$\rm{Z}^{0}$/$\gamma^{*}$\- and heavy-flavour hadron decay muons,
respectively. The bottom panels show the ratio of the data to the fit result.

The signal extraction procedure is affected by different sources of systematic
uncertainties, which are related to the knowledge of the shape of the
templates. The effect of this uncertainty on the extracted
$\rm{W}^{\pm}$-boson yield was estimated by studying the fit stability with
reasonable variations of these shapes. The $\rm{W}^{\pm}$-boson and
$\rm{Z}^{0}$/$\gamma^{*}$ templates were generated using the CT10 [55] and
CTEQ6 [33] PDF sets paired with either EPS09 [56] or EKS98 [63] nPDF, both at
either LO or NLO. Varying the inputs of the simulations leads to different
values of the $R$ factor of Eq. 1, estimated from the same simulations. The
template accounting for muons from heavy-flavour hadron decays was computed by
varying the FONLL calculations used as input within their uncertainties,
originating from the choice of quark masses, factorisation and renormalisation
scales, and from the uncertainty on the PDFs. In Pb–Pb collisions the
uncertainty due to the $p_{\rm T}^{\mu}$ extrapolation of the $R_{\rm AA}$ of
muons from heavy-flavour hadron decays was estimated using different
functional forms, as well as fitting the ALICE measurement of the $R_{\rm AA}$
between $7<p_{\rm T}^{\mu}<20$ GeV$/c$ and extrapolating the fit result to
high $p_{\rm T}$. The difference between the various extrapolations is taken
as systematic uncertainty on the FONLL weighting procedure. For the simulation
of the detector response, the tuning parameter of the global shift was varied
within the uncertainty on its determination. The CB parameters for the cluster
resolution, obtained from the data-driven method, were replaced by a set of
parameters evaluated from simulations. The fit range was varied by moving the
lower limit of the $p_{\rm T}^{\mu}$ interval between 10 and 20 GeV$/c$ and
the higher limit between 50 and 80 GeV$/c$. All the possible combinations of
the variations were considered, each configuration yielding a value for
$N^{\rm raw}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$. The combined $\chi^{2}/$ndf
of the fits to the $\mu^{-}$ and $\mu^{+}$ distributions was required to be
smaller than 2 to ensure that only the configurations able to satisfactorily
reproduce the data were kept. The final number of muons from $\rm{W}^{\pm}$
decays, and the associated statistical uncertainty, were obtained by averaging
over the $N^{\rm raw}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$ distribution obtained
from all considered variations.

The extracted raw yield is corrected for the detection and reconstruction
efficiency $\epsilon$ obtained from the simulations described in the previous
section. The efficiency is estimated as the ratio of the number of
reconstructed muons from $\rm{W}^{\pm}$-boson decays, with the same selections
as applied to the data, to the number of generated $\rm{W}^{\pm}$-decay muons
in the region of interest, that is the fiducial region defined by the
selection on the muon $p_{\rm T}^{\mu}>$ 10 GeV$/c$, and the detector angular
acceptance, $2.5<y^{\mu}_{\rm cms}<4$. The efficiency in p–Pb collisions
amounts to 90% (91%) in the p-going configuration and 88% (89%) in the Pb-
going one for $\mu^{-}$ ($\mu^{+}$). In Pb–Pb collisions, the efficiency is
additionally affected by the detector occupancy. This effect was taken into
account by embedding the simulated signal into Pb–Pb data. The efficiency for
the most central collisions is found to be 94% of the efficiency of the most
peripheral collisions. The centrality-integrated efficiency for the 2015
period amounts to 83% and 81% for $\mu^{-}$ and $\mu^{+}$, respectively, while
for the 2018 period the efficiency is 80% and 79% for $\mu^{-}$ and $\mu^{+}$,
respectively. The efficiency has no significant dependence on $p_{\rm
T}^{\mu}$, and decreases by about 9% from the most central to the largest
rapidities.

###  3.4 Systematic uncertainties

The systematic uncertainties are summarised in Table 3. The signal extraction
procedure described in the previous section yields a distribution of $N^{\rm
raw}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$ after the variation of the fit
configuration and the simulation parameters. The dispersion (RMS) of the
distribution was used as systematic uncertainty on the signal extraction. The
uncertainty originating from the signal extraction procedure ranges from about
4% to 9% in the rapidity- and centrality-integrated studies. In the rapidity-
differential measurements, for the largest rapidity intervals, the lower
amount of signal reduces the stability of the fit such that the systematic
uncertainty rises up to 22%.

Table 3: Summary of systematic uncertainties affecting the $\rm{W}^{\pm}$-boson measurements in p–Pb and Pb–Pb collisions. The values given for Pb–Pb collisions are for the combined 2015 and 2018 data samples. The ranges correspond to the largest variations found in differential analyses. Source | Relative systematic uncertainty
---|---
p–Pb analysis |  Pb–p analysis |  Pb–Pb analysis
Signal extraction | 5.9 – 8.8 % | 3.8 – 7.3 % | 2.9 – 3.3 %
\- as a function of rapidity | 3.9 – 14.3 % | 2.5 – 22 % | —
\- as a function of centrality | 5.1 – 9.7 % | 3.6 – 9.0 % | 3.0 – 7.4 %
Tracking efficiency | 0.5 % | 1.0 % | 1.5 %
Trigger efficiency | 0.5 % | 0.75 %
Trigger–tracker matching | 0.5 % | 0.5 %
Alignment | 0.1 – 1.2 % | 1.8 %
Normalisation factor | 1.4 % | 1.1 % | 1.0 %
$\sigma_{\rm V0M}$ | 1.9 % | 2.0 %
$\langle N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ | 2.8 – 4.3 % | —
$\langle T_{\rm AA}\rangle$ | — | 0.7 – 2.0 %

The uncertainty of the efficiency computation is evaluated by varying the
simulation environment. It was observed that, in the simulations, only the
ability to properly reproduce the alignment conditions provides a significant
source of uncertainty through the estimation of the CB tails parameters and
the tuning of the parameter accounting for the global shift. The systematic
uncertainty is taken as the largest difference between the efficiencies
computed with all the possible configurations. The uncertainty on the tracking
efficiency is obtained by considering the difference between the efficiencies
obtained from data and MC simulations, using the redundancy of the tracking
chamber information [48]. The uncertainty on the muon trigger efficiency is
determined by propagating the uncertainty on the intrinsic efficiency of the
individual trigger chambers, which is evaluated using a data-driven method
based on the redundancy of the trigger chamber information [48]. The choice
for the $\chi^{2}$ value in defining the matching between the tracks in the
tracking and trigger systems introduces an additional 0.5% uncertainty. The
difference between the two methods for the computation of the normalisation,
detailed in Section 2.2, is taken as its systematic uncertainty. The
uncertainties on the $\sigma_{\rm V0M}$ values are taken from Refs. [49, 50]
where their evaluation is detailed. Finally, the uncertainty on $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ in p–Pb collisions is evaluated as
the difference with respect to the average number of binary collisions
estimated using an alternative method based on the multiplicity measured in
the Pb-going direction [52]. In Pb–Pb collisions, the uncertainty on $\langle
T_{\rm AA}\rangle$ is estimated by varying the parameters of the Glauber model
within their own uncertainties, adding in quadrature the maximum-to-average
ratio of the upward and downward variations from all sources [52]. The total
systematic uncertainty is obtained by summing all the considered sources in
quadrature.

##  4 Results

###  4.1 p–Pb collisions

####  4.1.1 Production cross sections

The $\mu^{\pm}\leftarrow\rm{W}^{\pm}$ rapidity-differential production cross
section, uncorrected for the W-to-muon branching ratio BR, is evaluated as

$\frac{\mathrm{d}\sigma_{\rm{W}^{\pm}\rightarrow\mu^{\pm}\nu_{\mu}}}{\mathrm{d}y}=\frac{N_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}}{\Delta
y\times\epsilon\times\mathcal{L}_{\rm int}},$ (4)

where $N_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$ is the measured yield of muons
from $\rm{W}^{\pm}$ decays, $\Delta y$ is the width of the rapidity interval,
$\epsilon$ is the efficiency correction factor, and $\mathcal{L}_{\rm int}$
the integrated luminosity. In p–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV, the values of the corresponding
production cross sections are reported in Table 4, where the Pb-going
denomination refers to the backward rapidity interval $-4.46<y^{\mu}_{\rm
cms}<-2.96$ and the p-going denomination to the forward interval
$2.03<y^{\mu}_{\rm cms}<3.53$.

Table 4: Rapidity-differential production cross sections of $\rm{W}^{-}$ and $\rm{W}^{+}$ bosons measured from their muonic decays in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV, for muons with $p_{\rm T}^{\mu}>10$ GeV$/c$. |  $-4.46<y^{\mu}_{\rm cms}<-2.96$ (Pb-going) |  $2.03<y^{\mu}_{\rm cms}<3.53$ (p-going)
---|---|---
$\rm{W}^{-}\rightarrow\mu^{-}\overline{\nu}_{\mu}$ | $105.4\pm 3.7\text{ (stat)}\pm 5.2\text{ (syst)}\text{ nb}$ | $90.2\pm 4.8\text{ (stat)}\pm 8.2\text{ (syst)}\text{ nb}$
$\rm{W}^{+}\rightarrow\mu^{+}\nu_{\mu}$ | $37.1\pm 2.1\text{ (stat)}\pm 2.9\text{ (syst)}\text{ nb}$ | $120.8\pm 5.2\text{ (stat)}\pm 7.7\text{ (syst)}\text{ nb}$

The production cross section is shown as a function of rapidity, in the Pb-
going and p-going directions and for both charges of the W boson, in Fig. 3.
The measurements are compared with several pQCD calculations, based on Monte
Carlo for FeMtobarn processes (MCFM) [64] or Fully Exclusive W and Z
production (FEWZ) [65] simulations. The MCFM and FEWZ codes enable the
calculation of hard processes in hadronic collisions, involving heavy flavour
and top quarks, electroweak bosons and the Higgs boson. The two codes were
shown to produce similar predictions of the electroweak-boson production at
NLO [66]. The nuclear modifications are computed using the CT14+EPPS16 [30],
nCTEQ15WZ [36] and nNNPDF2.0 [32] parametrisations, as discussed in Section 1.
To illustrate the effect of using the LHC data in the determination of nPDFs,
predictions were also obtained from the nCTEQ15 set [31] in which no LHC data
were included. In order to disentangle the effect of the nuclear modifications
of the PDFs from other effects affecting the $\rm{W}^{\pm}$-boson production,
such as the isospin, predictions are shown for the CT14 PDF [67] without
nuclear modifications. All calculations are performed at NLO, the proton and
neutron contributions are weighted following the nucleon content of the Pb ion
to reproduce the isospin dependence of the $\rm{W}^{\pm}$-boson production.

Figure 3: Production cross section of muons from $\rm{W}^{-}$ (top) and
$\rm{W}^{+}$ (bottom) decays as a function of rapidity for muons with $p_{\rm
T}^{\mu}>10$ GeV$/c$ in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$
TeV. The measurements are compared with predictions from several nPDF sets, as
well as with calculations based on the CT14 PDF set [67] without nuclear
modifications of the PDF. All the calculations include the isospin effect. The
bottom panels show the ratio of the calculations to the measured production
cross section. The horizontal bars correspond to the width of the rapidity
intervals. The vertical bars and boxes indicate the statistical and systematic
uncertainties, respectively. The data points are placed at the centres of the
rapidity intervals, while the theory predictions are horizontally shifted for
better visibility.

Several effects affect the production of the $\rm{W}^{-}$ and $\rm{W}^{+}$
bosons in p–Pb collisions. The isospin effect, originating from the difference
in the quark content of the Pb nucleus to that of the proton, increases the
production of $\rm{W}^{-}$ and decreases that of $\rm{W}^{+}$. The rapidity
shift due to the asymmetric system pushes the forward rapidity range covered
by the muon spectrometer, corresponding to the p-going configuration, towards
midrapidity, where the production cross section is higher, and moves the
backward rapidity range, in the Pb-going configuration, towards even larger
rapidities where the production rate is reduced. Moreover, the production is
affected by the helicity conservation. The weak interaction only couples left-
handed fermions and right-handed antifermions. For angular momentum
conservation, the outgoing fermion $\mu^{-}$ (antifermion $\mu^{+}$) follows
the direction of the incoming quark q (antiquark $\overline{\mathrm{q}}$). The
production cross section is then maximum when the outgoing lepton (antilepton)
goes in the direction of the incoming quark (antiquark). As a result,
$\rm{W}^{-}$ bosons produced at large absolute rapidities will preferably emit
$\mu^{-}$ in their momentum direction and $\rm{W}^{+}$ will preferably emit
$\mu^{+}$ in the opposite direction. In the latter case, the muon reaches the
large rapidity covered by the spectrometer only if the boson is produced in
the opposite direction, at even larger rapidities where the production quickly
drops. Finally, the nuclear modifications of the PDFs affect the production at
backward and forward rapidities differently. At backward rapidity, the
Bjorken-$x$ interval accessible with the ALICE measurements is influenced by
the anti-shadowing and EMC effects, yielding an enhancement and a reduction of
the production, respectively. On the other hand, the forward rapidity interval
is fully contained within the Bjorken-$x$ region dominated by shadowing,
resulting in a suppression of the parton densities. Although in most cases the
effects just discussed tend to cancel each other, at least to some extent,
they globally act towards a suppression of the $\rm{W}^{+}$ production at
backward rapidities.

The measured $\rm{W}^{+}$ production cross section is in fair agreement with
the model predictions, whereas some tension appears in the description of the
rapidity dependence of the $\rm{W}^{-}$ production cross section, for small
values of the absolute rapidity. For $\rm{W}^{+}$ bosons measured at forward
rapidities, corresponding to the shadowing region at low Bjorken-$x$, the
measurement favours predictions including the nuclear modifications of the
PDFs. The discrepancy with the free-nucleon PDF calculation is especially
visible at large positive rapidities where the deviation from the CT14-only
prediction reaches 3.5$\sigma$, with the statistical and systematic
uncertainties combined quadratically. The precision of the measurement is
better than that of the theory, highlighting its ability to provide further
constraints for nPDF sets. The comparison between the nCTEQ15 and nCTEQ15WZ
predictions shows the impact of the LHC data on the determination of the
nPDFs, whose uncertainties are substantially reduced despite the addition of
three new free parameters in nCTEQ15WZ, corresponding to the parametrisation
of the strange-quark nPDF. The nNNPDF group, which has adopted a methodology
based on machine learning for the determination of the nPDF, yields
predictions with the smallest uncertainties in the forward rapidity region,
corresponding to very low Bjorken-$x$ values. The four models including
nuclear modifications are in good agreement with each other, although some
discrepancies are present between nCTEQ15WZ and nNNPDF2.0 calculations at
backward rapidities.

The CMS Collaboration also measured the production of the $\rm{W}^{\pm}$
bosons via the muonic decay channel in p–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV from a data sample with an integrated
luminosity of $173.4~{}\pm~{}6.1$ nb-1 [15]. The production was measured at
midrapidity, in the interval $|\eta^{\mu}_{\rm lab}|<2.4$, complementary to
the ALICE measurement at large rapidities. A stronger selection was applied on
the muon transverse momentum at $p_{\rm T}^{\mu}>25$ GeV$/c$, a direct
comparison is therefore not possible. However, the two measurements can be
compared through their agreement with theoretical calculations. Figure 4 shows
the ratio of the measurements to pQCD calculations performed including the
isospin effect and using either the CT14 PDF set (without nuclear
modifications) or the CT14 set with the EPPS16 nPDFs.

Figure 4: Ratio to CT14 [67] predictions of the production of muons from
$\rm{W}^{-}$ (top) and $\rm{W}^{+}$ (bottom) decays measured in p–Pb
collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV by the ALICE and CMS
[15] Collaborations. The measured ratio is compared to the one obtained from
pQCD calculations with CT14+EPPS16 [30]. All the calculations include the
isospin effect. The grey band around the line at unity indicates the
uncertainty on the calculations with CT14 PDFs.

The measurements of ALICE extend to large rapidities the measurements of the
CMS Collaboration in the central region, and support the trend observed at the
edge of the CMS rapidity acceptance. The calculations including the EPPS16
nPDFs provide a better description of the data over the whole rapidity
interval as compared to the predictions with the CT14 PDFs without nuclear
effects, especially for the $\rm{W}^{+}$ boson.

####  4.1.2 Lepton charge asymmetry

The production of $\rm{W}^{-}$ and $\rm{W}^{+}$ bosons is significantly
dependent on the light-quark content of the nucleus. The study of the
asymmetry in their production therefore provides a sensitive probe of the up
and down nPDF as well as the down-to-up ratio in the nucleus. In this regard,
the lepton charge asymmetry $A_{\rm ch}$ can be defined as

$A_{\rm ch}=\frac{N^{\rm corr}_{\mu^{+}\leftarrow\rm{W}^{+}}-N^{\rm
corr}_{\mu^{-}\leftarrow\rm{W}^{-}}}{N^{\rm
corr}_{\mu^{+}\leftarrow\rm{W}^{+}}+N^{\rm
corr}_{\mu^{-}\leftarrow\rm{W}^{-}}},$ (5)

where $N^{\rm corr}_{\mu^{-}\leftarrow\rm{W}^{-}}$ and $N^{\rm
corr}_{\mu^{+}\leftarrow\rm{W}^{+}}$ are the number of muons from $\rm{W}^{-}$
and $\rm{W}^{+}$ decays, respectively, extracted from the data and corrected
for the detection and reconstruction efficiency. Part of the experimental
uncertainties, such as the trigger and tracking efficiencies, cancels in the
calculation of the asymmetry. The theoretical precision is also increased,
e.g. through the cancellation of the uncertainties due to the pQCD scales. It
should be noted that the lepton charge asymmetry might be much more sensitive
to the baseline PDF than to its nuclear modifications [28], possibly enabling
the study of the free-nucleon PDF in heavy-ion collisions.

The measured lepton charge asymmetries integrated over $p_{\rm T}^{\mu}>$ 10
GeV$/c$ in the rapidity intervals covered by the muon spectrometer for the two
colliding beam configurations are:

$A^{\text{Pb-going}}_{\rm ch}=-0.479\pm 0.046\text{ (stat)}\pm 0.056\text{
(syst)},\qquad A^{\text{p-going}}_{\rm ch}=0.145\pm 0.014\text{ (stat)}\pm
0.021\text{ (syst)}.$

The measured $A_{\rm ch}$ as a function of rapidity is shown in Fig. 5.
Consistently with the up and down quark compositions of the proton and Pb ion,
the $A_{\rm ch}$ shows a predominance of $\rm{W}^{-}$ bosons at backward
rapidities, in the Pb-going direction, and of $\rm{W}^{+}$ at forward
rapidities. At very large positive rapidities, the lepton charge asymmetry
becomes negative, which indicates a suppression of the $\rm{W}^{+}$
production. This suppression could be a consequence of the helicity
conservation affecting the muonic decay of the boson, or a sharper slope of
the up quark PDF in the shadowing region towards low Bjorken-$x$. The $A_{\rm
ch}$ is compared with predictions from pQCD calculations with the CT14+EPPS16,
nCTEQ15WZ, and nNNPDF2.0 PDFs sets, as well as with the CT14 PDF set for free
nucleons. The calculations are performed at NLO and the same treatment of the
isospin as for the production cross section is applied. The models reproduce
the data well at backward rapidity, although a small tension is seen for the
most central rapidity interval in which the theory predicts an increase of the
charge asymmetry, while the measurement is independent of centrality within
uncertainties. At forward rapidities, the model predictions and the
measurements are in qualitative agreement, both showing a reduction of the
charge asymmetry towards higher rapidities. However, the decrease seen in the
data is notably larger than that in calculations, and it is interesting to
note the sign inversion of the measured charge asymmetry, while the
calculations stay positive over the whole forward rapidity interval. In the
largest rapidity interval, the models are all lying more than 5$\sigma$ above
the measurement.

Figure 5: Lepton charge asymmetry for muons from $\rm{W}^{\pm}$-boson decays
with $p_{\rm T}^{\mu}>10$ GeV$/c$ in p–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV. The measurements are compared with
predictions from pQCD calculations with several nPDF sets as well as with
calculations based on the CT14 PDF [67] without nuclear modifications. All the
calculations include the isospin effect. The bottom panels show the ratio of
the calculated to the measured asymmetry. The horizontal bars correspond to
the width of the rapidity intervals. The vertical bars and boxes indicate the
statistical and systematic uncertainties, respectively. The data points are
placed at the centres of the rapidity intervals while the theory points are
horizontally shifted for better visibility.

####  4.1.3 Nuclear modification factor

In p–Pb collisions, the nuclear modification factor $R_{\rm pPb}$, integrated
over centrality, is calculated as

$R_{\rm pPb}=\frac{1}{A}\times\frac{\mathrm{d}\sigma^{\rm
pPb}_{\rm{W}^{\pm}\rightarrow\mu^{\pm}\nu_{\mu}}/\mathrm{d}y^{\mu}_{\rm
cms}}{\mathrm{d}\sigma^{\rm
pp}_{\rm{W}^{\pm}\rightarrow\mu^{\pm}\nu_{\mu}}/\mathrm{d}y^{\mu}_{\rm cms}}.$
(6)

It evaluates the deviation between the measured production cross section in
p–Pb collisions and the one expected from a superposition of uncorrelated pp
collisions. It should be noted that for electroweak bosons, the $R_{\rm pPb}$
is a peculiar quantity. It is affected by the isospin effect, and as a
consequence, expectation values for $R_{\rm pPb}$ can deviate from unity even
in the absence of nuclear effects, such as the nuclear modification of the
PDFs. Since no measurement of the $\rm{W}^{\pm}$-boson production in pp
collisions at $\sqrt{s}~{}=~{}8.16$ TeV is available, the $R_{\rm pPb}$
presented here relies on theoretical calculations for the pp production cross
section $\sigma^{\rm pp}_{\rm{W}^{\pm}\rightarrow\mu^{\pm}\nu_{\mu}}$. The
simulations are performed with the procedure discussed in Section 3, using
POWHEG [53] interfaced with PYTHIA 6 [54] for the event generation and CT10
[55] for the proton PDF. It should be mentioned that the LHCb Collaboration
has shown that the available models, including CT10, are able to describe well
the production of $\rm{W}^{\pm}$ bosons in pp collisions at similar rapidities
and energies [68]. The associated uncertainty was evaluated by varying the
strong coupling constant $\alpha_{s}$ within its uncertainties and using
CTEQ6.6 [69] as an alternative PDF set, summing the sources in quadrature. The
values of the $R_{\rm pPb}$ obtained for the $\rm{W}^{-}$\- and
$\rm{W}^{+}$-boson production integrated over $p_{\rm T}^{\mu}>$ 10 GeV$/c$
and the rapidity intervals covered by the muon spectrometer for the two
colliding beam configurations are reported in Table 5.

Table 5: Nuclear modification factors of the production of $\rm{W}^{-}$ and $\rm{W}^{+}$ bosons measured in their muonic decays in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV, for muons with $p_{\rm T}^{\mu}>10$ GeV$/c$. The pp reference cross sections are taken from simulations using the POWHEG [53] generator and CT10 PDF [55]. The quoted uncertainties correspond to the statistical and systematic uncertainties on the p–Pb measurement, and to the asymmetric systematic uncertainty on the pp reference, respectively. | Pb-going ($-4.46<y^{\mu}_{\rm cms}<-2.96$) | p-going ($2.03<y^{\mu}_{\rm cms}<3.53$)
---|---|---
$R_{\rm pPb}$ ($\rm{W}^{-}\rightarrow\mu^{-}\overline{\nu}_{\mu}$) | $1.620\pm 0.057\pm 0.079^{+0.092}_{-0.062}$ | $0.888\pm 0.047\pm 0.080^{+0.060}_{-0.039}$
$R_{\rm pPb}$ ($\rm{W}^{+}\rightarrow\mu^{+}\nu_{\mu}$) | $0.643\pm 0.036\pm 0.051^{+0.046}_{-0.031}$ | $0.793\pm 0.034\pm 0.051^{+0.048}_{-0.037}$

The measured $R_{\rm pPb}$ is shown in Fig. 6 as a function of rapidity,

Figure 6: Nuclear modification factor $R_{\rm pPb}$ for muons from
$\rm{W}^{-}$ (top) and $\rm{W}^{+}$ (bottom) decays with $p_{\rm T}^{\mu}~{}>$
10 GeV$/c$ in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV. The
measurements are compared with predictions from pQCD calculations with several
nPDF sets. The horizontal bars correspond to the width of the rapidity bins.
The vertical bars and boxes indicate the statistical and systematic
uncertainties respectively. The grey bands indicate the uncertainty on the pp
production cross section. The data points are placed at the centres of the
rapidity intervals while the theory points are horizontally shifted for better
visibility.

where it is compared with predictions from the same models, and obtained using
the same framework, as for the asymmetry $A_{\rm ch}$. It should be noted that
the nNNPDF2.0 predictions rely on a different baseline PDF, employing NNPDF3.1
[35] instead of the CT14 model used in the calculations with EPPS16 nPDFs. For
both charges of the boson, the measured $R_{\rm pPb}$ is independent of $y$ at
backward rapidities, within the uncertainties. This trend is satisfactorily
reproduced by the models for the $\rm{W}^{+}$ boson. For the $\rm{W}^{-}$
boson however, a significant rapidity dependence is seen in the two
calculations, which underestimate the measured value in the most central
interval. At forward rapidities, the measured $R_{\rm pPb}$ decreases for the
two charges while the calculations show a flat behaviour. This creates a
tension with the calculations in the intervals closest to midrapidity for the
$\rm{W}^{-}$ boson, where the models underestimate the measurement, and in the
largest rapidity interval for the $\rm{W}^{+}$ boson where the nNNPDF2.0 model
overestimates the data.

####  4.1.4 Production as a function of the collision centrality

The production of muons from $\rm{W}^{\pm}$-boson decays is studied as a
function of the collision centrality. Electroweak-boson production occurs in
hard scattering processes, during the initial stages of the collision, and is
expected to scale with the number of binary nucleon–nucleon collisions,
provided that the evaluation of the centrality is unbiased. As mentioned in
Section 2, and in order to avoid the bias in multiplicity-based centrality
estimators, the classification in centrality intervals is performed based on
the energy deposited by the spectator (non-interacting) nucleons in the
neutron zero-degree calorimeters (ZN) in the Pb-going side. The study of the
centrality dependence of the $\rm{W}^{\pm}$-boson yield can therefore also
serve as a test bench for the centrality estimation.

In order to maximise the amount of signal in each centrality class, the
$\rm{W}^{-}$ and $\rm{W}^{+}$ yields are combined. The cross section
normalised to the average number of nucleon–nucleon collisions, $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$, is then calculated as

$\frac{1}{\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle}\times\frac{N^{i}_{\rm{W}^{\pm}}}{\mathcal{L}_{\rm
int}\times f^{i}_{\rm MB}\times\epsilon},$ (7)

where $\langle N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ is the average number
of binary nucleon–nucleon collisions, $N^{i}_{\rm{W}^{\pm}}$ is the number of
muons from $\rm{W}^{\pm}$ decays in a given centrality class $i$, and
$f^{i}_{\rm MB}$ is the fraction of MB-triggered events in the centrality
class $i$ to those in the full centrality range (0–100%). The cross sections
for the two colliding beam configurations, normalised to $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ and averaged over centrality, amount
to:

$\begin{split}-4.46<y^{\mu}_{\rm
cms}<-2.96:&\qquad\sigma_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}/\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle=30.2\pm 2.0\text{ (stat)}\pm
2.8\text{ (syst)}\text{ nb},\\\ 2.03<y^{\mu}_{\rm
cms}<3.53:&\qquad\sigma_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}/\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle=44.6\pm 3.3\text{ (stat)}\pm
5.1\text{ (syst)}\text{ nb}.\\\ \end{split}$

The normalised cross sections are shown as a function of $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ in Fig. 7. The horizontal dashed
line in the figure indicates the central value of the centrality-averaged
measurement. The measured yield divided by $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ is found to be independent of
centrality within uncertainties.

Figure 7: Combined yield of muons from $\rm{W}^{-}$ and $\rm{W}^{+}$ decays
with $p_{\rm T}^{\mu}>$ 10 GeV$/c$, normalised by the average number of binary
nucleon–nucleon collisions $\langle N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$
in p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV in the Pb-going
(left) and p-going (right) configurations. The bars and boxes correspond to
statistical and systematic uncertainties respectively. The horizontal dashed
line indicates the central value of the yield normalised to $\langle
N^{\mathrm{mult}}_{\mathrm{coll}}\rangle$ measured for the 0–100% centrality
interval.

###  4.2 Pb–Pb collisions

####  4.2.1 Production cross sections and lepton charge asymmetry

In Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV, the production
cross section and lepton charge asymmetry of muons from $\rm{W}^{\pm}$-boson
decays are evaluated as in p–Pb collisions, from Eqs. 4 and 5. The V0M
amplitude is used to estimate the centrality of the collision. The production
cross sections for $\rm{W}^{-}$ and $\rm{W}^{+}$ bosons in the 0–90%
centrality class are

$\sigma_{\rm{W}^{-}\rightarrow\mu^{-}\overline{\nu}_{\mu}}=18.7\pm 0.7\text{
(stat)}\pm 0.6\text{
(syst)}\;\mu\text{b},\qquad\sigma_{\rm{W}^{+}\rightarrow\mu^{+}\nu_{\mu}}=7.0\pm
0.4\text{ (stat)}\pm 0.2\text{ (syst)}\;\mu\text{b}.$

In the left panel of Fig. 8, these values are compared with pQCD calculations
using the CT14 [67], the CT14+EPPS16 combination [67, 30], and nNNPDF2.0 [32]
PDF sets, all accounting for the isospin of the Pb–Pb system. In the Pb–Pb
collision system, one cannot disentangle the high and low Bjorken-$x$ ranges,
as it was possible in p–Pb collisions. The comparison of the production for
positively and negatively charged bosons shows the effect of the isospin,
since the up- and down-quark densities in the Pb nucleus favour the production
of $\rm{W}^{-}$ and suppress that of $\rm{W}^{+}$. The measured cross sections
are lower than the predictions with the CT14 PDFs for free nucleons,
suggesting a significant effect due to nuclear modifications of the PDFs on
the $\rm{W}^{\pm}$-boson production in Pb–Pb collisions. The calculations
including the EPPS16 and nNNPDF2.0 nuclear modifications are consistent with
the data within uncertainties. As it was observed in the predictions in p–Pb
collisions, the nNNPDF2.0 calculations have significantly smaller
uncertainties.

Figure 8: Production cross section (left panel) and lepton charge asymmetry
(right panel) of the $\rm{W}^{\pm}\rightarrow\mu^{\pm}\nu_{\mu}$ processes for
the 0–90% centrality class, for muons with $p_{\rm T}^{\mu}>10$ GeV$/c$ and
$2.5<y^{\mu}_{\rm cms}<4.0$, in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV. The measured cross sections and the
asymmetry are compared with predictions using the CT14+EPPS16 [67, 30]
combination, nNNPDF2.0 [32] nPDF model, as well as calculations with the CT14
[67] PDF without nuclear corrections. All the calculations include the isospin
effect. The vertical bars and boxes around the data points indicate the
statistical and systematic uncertainties, respectively.

The lepton charge asymmetry in the 0–90% centrality interval is measured to be

$A_{\rm ch}=-0.453\pm 0.026\text{ (stat)}\pm 0.030\text{ (syst)}.$

In the right panel of Fig. 8, this observable is compared with pQCD
calculations using the CT14+ EPPS16 [30] and nNNPDF2.0 [32] nPDFs. Both models
describe well the measured value. The partial cancellation of uncertainty in
the $A_{\rm ch}$ has a remarkable effect on the EPPS16 prediction, as the
theoretical uncertainties are now similar to that in the data and nNNPDF2.0
calculation.

####  4.2.2 Normalised yield as a function of the collision centrality

The normalised yield is obtained by dividing the yield of muons from
$\rm{W}^{\pm}$ decays, $N_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$, by the
equivalent number of MB events $N^{\rm MB}_{\rm events}$, and then normalising
to the average nuclear overlap function $\langle T_{\rm AA}\rangle$ [52]:

$\frac{1}{\langle T_{\rm
AA}\rangle}\times\frac{N_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}}{N^{\rm MB}_{\rm
events}}.$ (8)

In the 0–90% centrality class, the binary-scaled yield amounts to

$\begin{split}N_{\mu^{-}\leftarrow\rm{W}^{-}}/\left(N^{\rm MB}_{\rm
events}\times\langle T_{\rm AA}\rangle\right)&=420.5\pm 16.4\text{ (stat)}\pm
18.0\text{ (syst)}\text{ pb},\\\ N_{\mu^{+}\leftarrow\rm{W}^{+}}/\left(N^{\rm
MB}_{\rm events}\times\langle T_{\rm AA}\rangle\right)&=158.5\pm 8.2\text{
(stat)}\pm 6.9\text{ (syst)}\text{ pb}.\end{split}$

The $\rm{W}^{\pm}$-boson yield normalised to $\langle T_{\rm AA}\rangle$ as a
function of the collision centrality is shown in Fig. 9 for both charges of
the boson. The $\langle T_{\rm AA}\rangle$-scaled yields are independent of
centrality, as expected from the binary scaling of $\rm{W}^{\pm}$-boson
production in nuclear collisions assuming negligible centrality dependence of
the shadowing. The measurents are compared with pQCD calculations using the
CT14 [67] PDF combined with the EPPS16 [30] nuclear modifications. A good
agreement with the theory is found for both charges of the boson.

Figure 9: $\langle T_{\rm AA}\rangle$-scaled yield of muons from $\rm{W}^{-}$
(left) and $\rm{W}^{+}$ (right) decays in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV for muons with $p_{\rm T}^{\mu}>10$
GeV$/c$ and $2.5<y^{\mu}_{\rm cms}<4.0$. In the top panels the yield is
compared with pQCD calculations using the CT14 PDF [67] as baseline and
implementing the EPPS16 [30] nuclear modifications. The ratio to theory of the
measured yield normalised with $\langle T_{\rm AA}\rangle$ evaluated with
$\sigma^{\rm inel}_{\rm NN}$ = 67.6 mb and 47.5 mb is shown in the middle and
bottom panels, respectively (see the text for details). The horizontal bars
indicate the width of the centrality intervals, the vertical bars and boxes
correspond to the statistical and systematic uncertainties, respectively. The
band indicate the uncertainty on the theoretical computations.

The centrality dependence of the PDF modifications has been explored through
impact-parameter dependent nPDFs [70, 71], but calculations of electroweak-
boson production within this approach show a very limited dependence on the
centrality, as reported in Ref. [22]. A possible centrality dependence of the
production in terms of shadowing of the inelastic nucleon–nucleon cross
section $\sigma^{\rm inel}_{\rm NN}$ was proposed in Ref. [72]. In that study,
the standard paradigm of extracting $\sigma^{\rm inel}_{\rm NN}$ from pp data,
is questioned as a potential source of bias. The re-evaluation of the
inelastic cross section from ATLAS measurements of electroweak-boson
production in Pb–Pb collisions [11, 12] yields $\sigma^{\rm inel}_{\rm
NN}=41.5^{+16.2}_{-12.0}\text{ mb}$, a value significantly lower than the one
used for centrality determination in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV with ALICE, taken as $\sigma^{\rm
inel}_{\rm NN}=67.6\pm 0.6$ mb [52]. This alternative value of the inelastic
cross section is found to improve the agreement between the ATLAS data and the
pQCD calculations.

The bottom panels of Fig. 9 show the centrality-dependent measurements
obtained by normalising the yield with $\langle T_{\rm AA}\rangle$ evaluated
using the nuclear-suppressed inelastic cross section from Ref. [72]. The
distributions show a significant centrality dependence, with the $\rm{W}^{-}$
distribution deviating from the binary scaling. This alternative value of the
inelastic cross section, which provides a better agreement between pQCD
calculations and the ATLAS measurement in peripheral collisions, has the
opposite effect here. The yield normalised to $\langle T_{\rm AA}\rangle$ with
$\sigma^{\rm inel}_{\rm NN}=41.5$ mb shows a worse agreement with the theory
than that with $\sigma^{\rm inel}_{\rm NN}=67.5$ mb in the 40–90% centrality
interval. The authors of Ref. [72] expect other effects to be possibly
relevant in peripheral collisions, such as a possible centrality dependence of
$\sigma^{\rm inel}_{\rm NN}$ and the neutron-skin effect, which could explain
the tension with the data for peripheral collisions. It should be noted that
the neutron skin effect would affect the production of $\rm{W}^{-}$ and
$\rm{W}^{+}$ bosons in opposite directions, enhancing the former and
suppressing the latter, thus not substantially improving the description of
the measurements.

Recent measurements of the $\langle T_{\rm AA}\rangle$-normalised yield of the
$\rm{Z}^{0}$ boson [10, 12, 18, 19] have shown a decreasing trend for the most
peripheral events, contradicting the binary-scaling assumption. This
phenomenon has also been observed and studied by the ALICE Collaboration [73]
for charged particle production. A possible explanation for this observation
has been formulated in terms of event selection and geometry biases affecting
peripheral events in the HG-PYTHIA model [74]. In order to compare it with the
Pb–Pb measurements presented in this article, the $R_{\rm AA}$ for hard
scatterings calculated with this model was scaled by the centrality-averaged,
$\langle T_{\rm AA}\rangle$-normalised yields of $\rm{W}^{-}$ and $\rm{W}^{+}$
bosons measured in the 0–90% centrality class. The resulting distributions are
compared with the centrality-dependent measurements in Fig. 10. The scaled
calculations are in good agreement with the data, although the small
$\rm{W}^{\pm}$ yield in peripheral collisions does not allow for a granularity
fine enough in the 40–90% centrality interval to show, if any, a statistically
significant decrease of the production in this region.

Figure 10: $\langle T_{\rm AA}\rangle$-scaled yield of muons from $\rm{W}^{-}$
and $\rm{W}^{+}$ decays in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV for muons with $p_{\rm T}^{\mu}>10$
GeV$/c$ and $2.5<y^{\mu}_{\rm cms}<4.0$. The measured production is compared
with HG-PYTHIA [74] calculations of the $R_{\rm AA}$ of hard scatterings
scaled with the centrality-averaged production in 0–90% centrality, indicated
as dashed lines. The horizontal bars correspond to the width of the centrality
intervals, the vertical bars and boxes indicate the statistical and systematic
uncertainties, respectively.

The ATLAS Collaboration measured the production of $\rm{W}^{\pm}$ bosons in
the electronic and muonic decay channels in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV [11]. Their results are reported for
the 0–80% centrality class and are extracted from a data sample corresponding
to a total integrated luminosity of 0.49 nb-1. The decay leptons are detected
in the rapidity interval $|y|<2.5$, allowing for a complete continuity with
the ALICE measurement in $2.5<y<4.0$. Similarly to the CMS measurements
presented in Section 4.1, the ATLAS Collaboration also applied a tighter
selection on the lepton $p_{\rm T}$, at 25 GeV$/c$, the comparison is thus
performed by means of the ratio between the measured $\rm{W}^{\pm}$-boson
yields and the predictions from two pQCD calculations, the first using the
EPPS16 [30] nPDF set and the second using the CT14 [67] PDFs. The comparison
as a function of rapidity is shown in the two panels of Fig. 11 for the two
charges of the boson.

Figure 11: Ratio to pQCD calculations with CT14 PDFs [67] of the production of
muons from $\rm{W}^{-}$ (top) and $\rm{W}^{+}$ (bottom) decays measured as a
function of rapidity in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV by the ALICE and ATLAS [11]
Collaborations. The ratio of EPPS16+CT14 [30] calculations to that of
CT14-only calculations is also shown. The grey band around the line at unity
indicates the uncertainty on the calculations with CT14 PDFs.

The ALICE measurements are lower by 2$\sigma$ than the CT14 predictions and
are described by EPPS16. The ATLAS data, instead, are better described by
calculations without nPDF effects. This comparison motivated the study in Ref.
[72] with a shadowing-induced reduction of the inelastic cross section, but
other possible origins of the effect have also been proposed [75].

####  4.2.3 Nuclear modification factor

In the Pb–Pb analysis, the nuclear modification factor of muons from
$\rm{W}^{\pm}$-boson decays is evaluated by dividing the $\langle T_{\rm
AA}\rangle$-scaled yield by the $\rm{W}^{\pm}$-boson production cross section
in pp collisions:

$R_{\rm AA}=\frac{1}{\langle T_{\rm AA}\rangle}\times\frac{N^{\rm
MB}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}}{\sigma^{\mu^{\pm}\leftarrow\rm{W}^{\pm}}_{\rm
pp}},$ (9)

where $N^{\rm MB}_{\mu^{\pm}\leftarrow\rm{W}^{\pm}}$ is the number of muons
from $\rm{W}^{\pm}$ decays per MB event,
$\sigma^{\mu^{\pm}\leftarrow\rm{W}^{\pm}}_{\rm pp}$ is the
$\mu^{\pm}\leftarrow\rm{W}^{\pm}$ cross section in pp collisions, and $\langle
T_{\rm AA}\rangle$ is the average nuclear overlap function for the considered
centrality class. As in p–Pb collisions, the pp production cross section and
the associated uncertainty were obtained from POWHEG and PYTHIA 6 [53, 54]
simulations using CT10 [55] for the proton PDF. For the 0–90% centrality
interval, the $R_{\rm AA}$ of muons from $\rm{W}^{-}$\- and $\rm{W}^{+}$-boson
decays are:

$\begin{split}R^{\mu^{-}\leftarrow\rm{W}^{-}}_{\rm AA}=1.32\pm 0.05\text{
(stat)}\pm 0.06\text{ (syst)}\pm 0.14\text{ (pp ref.)},\\\
R^{\mu^{+}\leftarrow\rm{W}^{+}}_{\rm AA}=0.57\pm 0.03\text{ (stat)}\pm
0.02\text{ (syst)}\pm 0.07\text{ (pp ref.)}.\end{split}$

The production of $\rm{W}^{-}$ is enhanced, and that of $\rm{W}^{+}$ is
suppressed relative to pp collisions, as expected following the content in u
and d quarks of the Pb nucleus.

The measured $R_{\rm AA}$ is shown in Fig. 12 as a function of centrality and
for the 0–90% centrality class. The centrality-dependent measurement is
compared with HG-PYTHIA [74] calculations of the $R_{\rm AA}$ of hard
scatterings scaled with the measured value in 0–90% centrality. The
centrality-averaged $R_{\rm AA}$ is compared with pQCD calculations, using the
CT14 [67] PDFs for the proton and the nCTEQ15WZ [36] PDF set, or the
NNPDF3.1+nNNPDF2.0 combination [35, 32] for the Pb nucleus. The calculations
within the nCTEQ and NNPDF frameworks are only shown for the centrality-
averaged value as they have no centrality dependence. Both models provide a
good description of the measurement within uncertainties. It should be noted
that this agreement is realised while the measurement and models use different
PDF sets for the pp reference, and different codes for the pQCD calculations
(POWHEG [53] for the experimental results, MCFM [64] and FEWZ [65] for the
theoretical ones).

Figure 12: Nuclear modification factor of muons from $\rm{W}^{-}$ (top) and
$\rm{W}^{+}$ (bottom) decays in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV, for muons with $p_{\rm T}^{\mu}>10$
GeV$/c$ and $2.5<y^{\mu}_{\rm cms}<4.0$, in different centrality intervals
(left panels) and for the 0–90% range (right panels). The centrality-dependent
distributions are compared with the dashed curve, corresponding to the HG-
PYTHIA [74] model scaled with the measured $R_{\rm AA}$ in the 0–90%
centrality interval. The centrality-averaged measurement is compared with
CT14+nCTEQ15WZ [67, 36] and NNPDF3.1+nNNPDF2.0 [35, 32] calculations. The
horizontal bars indicate the width of the centrality bins, the vertical bars
and boxes correspond the statistical and systematic uncertainties on the Pb–Pb
measurement, respectively. The grey boxes indicate the uncertainty on the pp
reference cross section.

##  5 Summary

The measurements of the $\rm{W}^{\pm}$-boson production cross section, lepton
charge asymmetry, nuclear modification factor, and yield normalised to the
number of nucleon–nucleon collisions in p–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}8.16$ TeV were reported, constituting the first
results on the production of $\rm{W}^{\pm}$ bosons at large rapidity at this
energy, extending the measurement in p–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV with a significant improvement of the
precision. They were performed for muons with $p_{\rm T}^{\mu}>$ 10 GeV$/c$
and in the rapidity intervals $-4.46<y^{\mu}_{\rm cms}<-2.96$ and
$2.03<y^{\mu}_{\rm cms}<3.53$, where the negative rapidity interval indicates
the Pb-going side, and the positive one the p-going side. The results were
compared with pQCD calculations, using the CT14 PDF set [67], and the EPPS16
[30], nNNPDF2.0 [32] and nCTEQ15 [31, 36] nPDF models. Some tensions are
observed in the ability of the models to reproduce the data, notably in the
rapidity dependence of the observables. Significant deviations from the free-
nucleon PDF predictions, up to 3.5$\sigma$, are found at forward rapidity,
corresponding to the shadowing region of the nuclear modifications at low
Bjorken-$x$. The measurements in p–Pb collisions reported here can therefore
provide significant constraints to the nPDF models and help reducing their
uncertainties. They complement the measurements of the $\rm{Z}^{0}$-boson
production performed at large rapidities by the ALICE Collaboration [22],
where the statistical precision was too limited to draw any conclusion on the
nuclear modifications. The comparison with the CMS measurements at midrapidity
illustrates the complementarity of the LHC experiments in providing such
results. The binary scaling of hard processes is observed, as the production
cross sections in different centrality classes normalised to the average
number of binary nucleon–nucleon collisions were found to be constant within
uncertainties.

Similar measurements performed in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV were also presented, for muons from
$\rm{W}^{\pm}$-boson decays at large rapidity ($2.5<y^{\mu}_{\rm cms}<4.0$)
with $p_{\rm T}^{\mu}>$ 10 GeV$/c$, and for various centrality classes. The
normalised yield as a function of centrality follows the binary scaling
expected for a hard process in the absence of significant centrality
dependence of the shadowing. Comparisons with pQCD calculations show the
ability of the EPPS16, nCTEQ15WZ and nNNPDF2.0 nPDFs to reproduce the
production cross section, lepton charge asymmetry and nuclear modification
factor. The evaluation of the $\langle T_{\rm AA}\rangle$-normalised yield
with the nuclear-suppressed inelastic nucleon–nucleon cross section
$\sigma^{\rm inel}_{\rm NN}$ obtained from Ref. [72], which was found to
improve the agreement between the ATLAS data and the EPPS16 model, yields a
tension between the ALICE measurements and EPPS16 calculations for peripheral
events which is not seen with the standard value of $\sigma^{\rm inel}_{\rm
NN}$. The $\langle T_{\rm AA}\rangle$-scaled yield and the nuclear
modification factor are found to be in good agreement with HG-PYTHIA [74]
calculations of the $R_{\rm AA}$ of hard scatterings scaled with the value
measured in 0–90% centrality, but the statistical limitation of the
measurement does not allow to conclude on the decrease in peripheral events
expected from this model. The measured $\langle T_{\rm AA}\rangle$-scaled
yields are described by pQCD calculations with the EPPS16 nPDFs. These
measurements support the conclusion derived from the measurement of the
$\rm{Z}^{0}$-boson production in Pb–Pb collisions at
$\sqrt{s_{\mathrm{NN}}}~{}=~{}5.02$ TeV [22], showing a suppression of the
production of electroweak bosons due to the nuclear modifications of the PDF
and the resulting deviations from calculations based on free-nucleon PDFs.
Being the first measurement of the $\rm{W}^{\pm}$ production in Pb–Pb
collisions at large rapidity, this study provides important insights for
further investigation of the centrality dependence of the nPDFs.

## Acknowledgements

The authors would like to thank Hannu Paukkunen, Rabah Abdul Khalek and
Aleksander Kusina for providing the various model calculations.

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; Bulgarian Ministry of Education and
Science, within the National Roadmap for Research Infrastructures 2020¿2027
(object CERN), Bulgaria; 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; 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; National Research and Innovation Agency -
BRIN, Indonesia; Istituto Nazionale di Fisica Nucleare (INFN), Italy; 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 Education and Science, 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, Ministry of Research and
Innovation and Institute of Atomic Physics and University Politehnica of
Bucharest, Romania; 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 (NSTDA), Thailand Science Research and Innovation (TSRI)
and National Science, Research and Innovation Fund (NSRF), Thailand; Turkish
Energy, Nuclear and Mineral Research Agency (TENMAK), 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. In addition, individual groups or
members have received support from: Marie Skłodowska Curie, Strong 2020 -
Horizon 2020, European Research Council (grant nos. 824093, 896850, 950692),
European Union; Academy of Finland (Center of Excellence in Quark Matter)
(grant nos. 346327, 346328), Finland; Programa de Apoyos para la Superación
del Personal Académico, UNAM, Mexico.

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##  Appendix A The ALICE Collaboration

S. Acharya 124,131, D. Adamová 86, A. Adler69, G. Aglieri Rinella 32, M.
Agnello 29, N. Agrawal 50, Z. Ahammed 131, S. Ahmad 15, S.U. Ahn 70, I. Ahuja
37, A. Akindinov 139, M. Al-Turany 98, D. Aleksandrov 139, B. Alessandro 55,
H.M. Alfanda 6, R. Alfaro Molina 66, B. Ali 15, Y. Ali13, A. Alici 25, N.
Alizadehvandchali 113, A. Alkin 32, J. Alme 20, G. Alocco 51, T. Alt 63, I.
Altsybeev 139, M.N. Anaam 6, C. Andrei 45, A. Andronic 134, V. Anguelov 95, F.
Antinori 53, P. Antonioli 50, C. Anuj 15, N. Apadula 74, L. Aphecetche 103, H.
Appelshäuser 63, S. Arcelli 25, R. Arnaldi 55, I.C. Arsene 19, M. Arslandok
136, A. Augustinus 32, R. Averbeck 98, S. Aziz 72, M.D. Azmi 15, A. Badalà 52,
Y.W. Baek 40, X. Bai 98, R. Bailhache 63, Y. Bailung 47, R. Bala 91, A.
Balbino 29, A. Baldisseri 127, B. Balis 2, D. Banerjee 4, Z. Banoo 91, R.
Barbera 26, L. Barioglio 96, M. Barlou78, G.G. Barnaföldi 135, L.S. Barnby 85,
V. Barret 124, L. Barreto 109, C. Bartels 116, K. Barth 32, E. Bartsch 63, F.
Baruffaldi 27, N. Bastid 124, S. Basu 75, G. Batigne 103, D. Battistini 96, B.
Batyunya 140, D. Bauri46, J.L. Bazo Alba 101, I.G. Bearden 83, C. Beattie 136,
P. Becht 98, D. Behera 47, I. Belikov 126, A.D.C. Bell Hechavarria 134, F.
Bellini 25, R. Bellwied 113, S. Belokurova 139, V. Belyaev 139, G. Bencedi
135,64, S. Beole 24, A. Bercuci 45, Y. Berdnikov 139, A. Berdnikova 95, L.
Bergmann 95, M.G. Besoiu 62, L. Betev 32, P.P. Bhaduri 131, A. Bhasin 91, I.R.
Bhat91, M.A. Bhat 4, B. Bhattacharjee 41, L. Bianchi 24, N. Bianchi 48, J.
Bielčík 35, J. Bielčíková 86, J. Biernat 106, A. Bilandzic 96, G. Biro 135, S.
Biswas 4, J.T. Blair 107, D. Blau 139, M.B. Blidaru 98, N. Bluhme38, C. Blume
63, G. Boca 21,54, F. Bock 87, T. Bodova 20, A. Bogdanov139, S. Boi 22, J. Bok
57, L. Boldizsár 135, A. Bolozdynya 139, M. Bombara 37, P.M. Bond 32, G.
Bonomi 130,54, H. Borel 127, A. Borissov 139, H. Bossi 136, E. Botta 24, L.
Bratrud 63, P. Braun-Munzinger 98, M. Bregant 109, M. Broz 35, G.E. Bruno
97,31, M.D. Buckland 116, D. Budnikov 139, H. Buesching 63, S. Bufalino 29, O.
Bugnon103, P. Buhler 102, Z. Buthelezi 67,120, J.B. Butt13, A. Bylinkin 115,
S.A. Bysiak106, M. Cai 27,6, H. Caines 136, A. Caliva 98, E. Calvo Villar 101,
J.M.M. Camacho 108, R.S. Camacho44, P. Camerini 23, F.D.M. Canedo 109, M.
Carabas 123, F. Carnesecchi 32, R. Caron 125,127, J. Castillo Castellanos 127,
F. Catalano 29, C. Ceballos Sanchez 140, I. Chakaberia 74, P. Chakraborty 46,
S. Chandra 131, S. Chapeland 32, M. Chartier 116, S. Chattopadhyay 131, S.
Chattopadhyay 99, T.G. Chavez 44, T. Cheng 6, C. Cheshkov 125, B. Cheynis 125,
V. Chibante Barroso 32, D.D. Chinellato 110, E.S. Chizzali II,96, J. Cho 57,
S. Cho 57, P. Chochula 32, P. Christakoglou 84, C.H. Christensen 83, P.
Christiansen 75, T. Chujo 122, M. Ciacco 29, C. Cicalo 51, L. Cifarelli 25, F.
Cindolo 50, M.R. Ciupek98, G. ClaiIII,50, F. Colamaria 49, J.S. Colburn100, D.
Colella 97,31, A. Collu74, M. Colocci 32, M. Concas IV,55, G. Conesa Balbastre
73, Z. Conesa del Valle 72, G. Contin 23, J.G. Contreras 35, M.L. Coquet 127,
T.M. CormierI,87, P. Cortese 129,55, M.R. Cosentino 111, F. Costa 32, S.
Costanza 21,54, P. Crochet 124, R. Cruz-Torres 74, E. Cuautle64, P. Cui 6, L.
Cunqueiro87, A. Dainese 53, M.C. Danisch 95, A. Danu 62, P. Das 80, P. Das 4,
S. Das 4, S. Dash 46, A. De Caro 28, G. de Cataldo 49, L. De Cilladi 24, J. de
Cuveland38, A. De Falco 22, D. De Gruttola 28, N. De Marco 55, C. De Martin
23, S. De Pasquale 28, S. Deb 47, H.F. Degenhardt109, K.R. Deja132, R. Del
Grande 96, L. Dello Stritto 28, W. Deng 6, P. Dhankher 18, D. Di Bari 31, A.
Di Mauro 32, R.A. Diaz 140,7, T. Dietel 112, Y. Ding 125,6, R. Divià 32, D.U.
Dixit 18, Ø. Djuvsland20, U. Dmitrieva 139, A. Dobrin 62, B. Dönigus 63, A.K.
Dubey 131, J.M. Dubinski132, A. Dubla 98, S. Dudi 90, P. Dupieux 124, M.
Durkac105, N. Dzalaiova12, T.M. Eder 134, R.J. Ehlers 87, V.N. Eikeland20, F.
Eisenhut 63, D. Elia 49, B. Erazmus 103, F. Ercolessi 25, F. Erhardt 89, M.R.
Ersdal20, B. Espagnon 72, G. Eulisse 32, D. Evans 100, S. Evdokimov 139, L.
Fabbietti 96, M. Faggin 27, J. Faivre 73, F. Fan 6, W. Fan 74, A. Fantoni 48,
M. Fasel 87, P. Fecchio29, A. Feliciello 55, G. Feofilov 139, A. Fernández
Téllez 44, M.B. Ferrer 32, A. Ferrero 127, A. Ferretti 24, V.J.G. Feuillard
95, J. Figiel 106, V. Filova35, D. Finogeev 139, F.M. Fionda 51, G.
Fiorenza97, F. Flor 113, A.N. Flores 107, S. Foertsch 67, I. Fokin 95, S.
Fokin 139, E. Fragiacomo 56, E. Frajna 135, U. Fuchs 32, N. Funicello 28, C.
Furget 73, A. Furs 139, J.J. Gaardhøje 83, M. Gagliardi 24, A.M. Gago 101, A.
Gal126, C.D. Galvan 108, P. Ganoti 78, C. Garabatos 98, J.R.A. Garcia 44, E.
Garcia-Solis 9, K. Garg 103, C. Gargiulo 32, A. Garibli81, K. Garner134, E.F.
Gauger 107, A. Gautam 115, M.B. Gay Ducati 65, M. Germain 103, S.K. Ghosh4, M.
Giacalone 25, P. Gianotti 48, P. Giubellino 98,55, P. Giubilato 27, A.M.C.
Glaenzer 127, P. Glässel 95, E. Glimos119, D.J.Q. Goh76, V. Gonzalez 133, L.H.
González-Trueba 66, S. Gorbunov38, M. Gorgon 2, L. Görlich 106, S. Gotovac33,
V. Grabski 66, L.K. Graczykowski 132, E. Grecka 86, L. Greiner 74, A. Grelli
58, C. Grigoras 32, V. Grigoriev 139, S. Grigoryan 140,1, F. Grosa 32, J.F.
Grosse-Oetringhaus 32, R. Grosso 98, D. Grund 35, G.G. Guardiano 110, R.
Guernane 73, M. Guilbaud 103, K. Gulbrandsen 83, T. Gunji 121, W. Guo 6, A.
Gupta 91, R. Gupta 91, S.P. Guzman 44, L. Gyulai 135, M.K. Habib98, C.
Hadjidakis 72, H. Hamagaki 76, M. Hamid6, Y. Han 137, R. Hannigan 107, M.R.
Haque 132, A. Harlenderova98, J.W. Harris 136, A. Harton 9, J.A.
Hasenbichler32, H. Hassan 87, D. Hatzifotiadou 50, P. Hauer 42, L.B. Havener
136, S.T. Heckel 96, E. Hellbär 98, H. Helstrup 34, T. Herman 35, G. Herrera
Corral 8, F. Herrmann134, K.F. Hetland 34, B. Heybeck 63, H. Hillemanns 32, C.
Hills 116, B. Hippolyte 126, B. Hofman 58, B. Hohlweger 84, J. Honermann 134,
G.H. Hong 137, D. Horak 35, A. Horzyk 2, R. Hosokawa14, Y. Hou 6, P. Hristov
32, C. Hughes 119, P. Huhn63, L.M. Huhta 114, C.V. Hulse 72, T.J. Humanic 88,
H. Hushnud99, A. Hutson 113, D. Hutter 38, J.P. Iddon 116, R. Ilkaev139, H.
Ilyas 13, M. Inaba 122, G.M. Innocenti 32, M. Ippolitov 139, A. Isakov 86, T.
Isidori 115, M.S. Islam 99, M. Ivanov 98, V. Ivanov 139, V. Izucheev139, M.
Jablonski 2, B. Jacak 74, N. Jacazio 32, P.M. Jacobs 74, S. Jadlovska105, J.
Jadlovsky105, L. Jaffe38, C. Jahnke110, M.A. Janik 132, T. Janson69, M.
Jercic89, O. Jevons100, A.A.P. Jimenez 64, F. Jonas 87,134, P.G. Jones100,
J.M. Jowett 32,98, J. Jung 63, M. Jung 63, A. Junique 32, A. Jusko 100, M.J.
Kabus 32,132, J. Kaewjai104, P. Kalinak 59, A.S. Kalteyer 98, A. Kalweit 32,
V. Kaplin 139, A. Karasu Uysal 71, D. Karatovic 89, O. Karavichev 139, T.
Karavicheva 139, P. Karczmarczyk 132, E. Karpechev 139, V. Kashyap80, A.
Kazantsev139, U. Kebschull 69, R. Keidel 138, D.L.D. Keijdener58, M. Keil 32,
B. Ketzer 42, A.M. Khan 6, S. Khan 15, A. Khanzadeev 139, Y. Kharlov 139, A.
Khatun 15, A. Khuntia 106, B. Kileng 34, B. Kim 16, C. Kim 16, D.J. Kim 114,
E.J. Kim 68, J. Kim 137, J.S. Kim 40, J. Kim 95, J. Kim 68, M. Kim 95, S. Kim
17, T. Kim 137, S. Kirsch 63, I. Kisel 38, S. Kiselev 139, A. Kisiel 132, J.P.
Kitowski 2, J.L. Klay 5, J. Klein 32, S. Klein 74, C. Klein-Bösing 134, M.
Kleiner 63, T. Klemenz 96, A. Kluge 32, A.G. Knospe 113, C. Kobdaj 104, T.
Kollegger98, A. Kondratyev 140, N. Kondratyeva 139, E. Kondratyuk 139, J.
Konig 63, S.A. Konigstorfer 96, P.J. Konopka 32, G. Kornakov 132, S.D.
Koryciak 2, A. Kotliarov 86, O. Kovalenko 79, V. Kovalenko 139, M. Kowalski
106, I. Králik 59, A. Kravčáková 37, L. Kreis98, M. Krivda 100,59, F. Krizek
86, K. Krizkova Gajdosova 35, M. Kroesen 95, M. Krüger 63, D.M. Krupova 35, E.
Kryshen 139, M. Krzewicki38, V. Kučera 32, C. Kuhn 126, P.G. Kuijer 84, T.
Kumaoka122, D. Kumar131, L. Kumar 90, N. Kumar90, S. Kundu 32, P. Kurashvili
79, A. Kurepin 139, A.B. Kurepin 139, S. Kushpil 86, J. Kvapil 100, M.J. Kweon
57, J.Y. Kwon 57, Y. Kwon 137, S.L. La Pointe 38, P. La Rocca 26, Y.S. Lai74,
A. Lakrathok104, M. Lamanna 32, R. Langoy 118, P. Larionov 48, E. Laudi 32, L.
Lautner 32,96, R. Lavicka 102, T. Lazareva 139, R. Lea 130,54, J. Lehrbach 38,
R.C. Lemmon 85, I. León Monzón 108, M.M. Lesch 96, E.D. Lesser 18, M.
Lettrich96, P. Lévai 135, X. Li10, X.L. Li6, J. Lien 118, R. Lietava 100, B.
Lim 16, S.H. Lim 16, V. Lindenstruth 38, A. Lindner45, C. Lippmann 98, A. Liu
18, D.H. Liu 6, J. Liu 116, I.M. Lofnes 20, V. Loginov139, C. Loizides 87, P.
Loncar 33, J.A. Lopez 95, X. Lopez 124, E. López Torres 7, P. Lu 98,117, J.R.
Luhder 134, M. Lunardon 27, G. Luparello 56, Y.G. Ma 39, A. Maevskaya139, M.
Mager 32, T. Mahmoud42, A. Maire 126, M. Malaev 139, N.M. Malik 91, Q.W.
Malik19, S.K. Malik 91, L. Malinina VII,140, D. Mal’Kevich 139, D. Mallick 80,
N. Mallick 47, G. Mandaglio 30,52, V. Manko 139, F. Manso 124, V. Manzari 49,
Y. Mao 6, G.V. Margagliotti 23, A. Margotti 50, A. Marín 98, C. Markert 107,
M. Marquard63, N.A. Martin95, P. Martinengo 32, J.L. Martinez113, M.I.
Martínez 44, G. Martínez García 103, S. Masciocchi 98, M. Masera 24, A. Masoni
51, L. Massacrier 72, A. Mastroserio 128,49, A.M. Mathis 96, O. Matonoha 75,
P.F.T. Matuoka109, A. Matyja 106, C. Mayer 106, A.L. Mazuecos 32, F. Mazzaschi
24, M. Mazzilli 32, J.E. Mdhluli 120, A.F. Mechler63, Y. Melikyan 139, A.
Menchaca-Rocha 66, E. Meninno 102,28, A.S. Menon 113, M. Meres 12, S.
Mhlanga112,67, Y. Miake122, L. Micheletti 55, L.C. Migliorin125, D.L. Mihaylov
96, K. Mikhaylov 140,139, A.N. Mishra 135, D. Miśkowiec 98, A. Modak 4, A.P.
Mohanty 58, B. Mohanty 80, M. Mohisin Khan V,15, M.A. Molander 43, Z.
Moravcova 83, C. Mordasini 96, D.A. Moreira De Godoy 134, I. Morozov 139, A.
Morsch 32, T. Mrnjavac 32, V. Muccifora 48, E. Mudnic33, S. Muhuri 131, J.D.
Mulligan 74, A. Mulliri22, M.G. Munhoz 109, R.H. Munzer 63, H. Murakami 121,
S. Murray 112, L. Musa 32, J. Musinsky 59, J.W. Myrcha 132, B. Naik 120, R.
Nair 79, B.K. Nandi46, R. Nania 50, E. Nappi 49, A.F. Nassirpour 75, A. Nath
95, C. Nattrass 119, A. Neagu19, A. Negru123, L. Nellen 64, S.V. Nesbo34, G.
Neskovic 38, D. Nesterov 139, B.S. Nielsen 83, E.G. Nielsen 83, S. Nikolaev
139, S. Nikulin 139, V. Nikulin 139, F. Noferini 50, S. Noh 11, P. Nomokonov
140, J. Norman 116, N. Novitzky 122, P. Nowakowski 132, A. Nyanin 139, J.
Nystrand 20, M. Ogino 76, A. Ohlson 75, V.A. Okorokov 139, J. Oleniacz 132,
A.C. Oliveira Da Silva 119, M.H. Oliver 136, A. Onnerstad 114, C. Oppedisano
55, A. Ortiz Velasquez 64, A. Oskarsson75, J. Otwinowski 106, M. Oya93, K.
Oyama 76, Y. Pachmayer 95, S. Padhan 46, D. Pagano 130,54, G. Paić 64, A.
Palasciano 49, S. Panebianco 127, J. Park 57, J.E. Parkkila 32,114, S.P.
Pathak113, R.N. Patra91, B. Paul 22, H. Pei 6, T. Peitzmann 58, X. Peng 6,
L.G. Pereira 65, H. Pereira Da Costa 127, D. Peresunko 139, G.M. Perez 7, S.
Perrin 127, Y. Pestov139, V. Petráček 35, V. Petrov 139, M. Petrovici 45, R.P.
Pezzi 103,65, S. Piano 56, M. Pikna 12, P. Pillot 103, O. Pinazza 50,32, L.
Pinsky113, C. Pinto 96,26, S. Pisano 48, M. Płoskoń 74, M. Planinic89, F.
Pliquett63, M.G. Poghosyan 87, S. Politano 29, N. Poljak 89, A. Pop 45, S.
Porteboeuf-Houssais 124, J. Porter 74, V. Pozdniakov 140, S.K. Prasad 4, S.
Prasad 47, R. Preghenella 50, F. Prino 55, C.A. Pruneau 133, I. Pshenichnov
139, M. Puccio 32, S. Qiu 84, L. Quaglia 24, R.E. Quishpe113, S. Ragoni 100,
A. Rakotozafindrabe 127, L. Ramello 129,55, F. Rami 126, S.A.R. Ramirez 44,
T.A. Rancien73, R. Raniwala 92, S. Raniwala92, S.S. Räsänen 43, R. Rath 47, I.
Ravasenga 84, K.F. Read 87,119, A.R. Redelbach 38, K. Redlich VI,79, A.
Rehman20, P. Reichelt63, F. Reidt 32, H.A. Reme-Ness 34, Z. Rescakova37, K.
Reygers 95, A. Riabov 139, V. Riabov 139, R. Ricci 28, T. Richert75, M.
Richter 19, W. Riegler 32, F. Riggi 26, C. Ristea 62, M. Rodríguez Cahuantzi
44, K. Røed 19, R. Rogalev 139, E. Rogochaya 140, T.S. Rogoschinski 63, D.
Rohr 32, D. Röhrich 20, P.F. Rojas44, S. Rojas Torres 35, P.S. Rokita 132, F.
Ronchetti 48, A. Rosano 30,52, E.D. Rosas64, A. Rossi 53, A. Roy 47, P. Roy99,
S. Roy46, N. Rubini 25, O.V. Rueda 75, D. Ruggiano 132, R. Rui 23, B.
Rumyantsev140, P.G. Russek 2, R. Russo 84, A. Rustamov 81, E. Ryabinkin 139,
Y. Ryabov 139, A. Rybicki 106, H. Rytkonen 114, W. Rzesa 132, O.A.M. Saarimaki
43, R. Sadek 103, S. Sadovsky 139, J. Saetre 20, K. Šafařík 35, S.K. Saha 131,
S. Saha 80, B. Sahoo 46, P. Sahoo46, R. Sahoo 47, S. Sahoo60, D. Sahu 47, P.K.
Sahu 60, J. Saini 131, K. Sajdakova37, S. Sakai 122, M.P. Salvan 98, S.
Sambyal 91, T.B. Saramela109, D. Sarkar 133, N. Sarkar131, P. Sarma41, V.
Sarritzu 22, V.M. Sarti 96, M.H.P. Sas 136, J. Schambach 87, H.S. Scheid 63,
C. Schiaua 45, R. Schicker 95, A. Schmah95, C. Schmidt 98, H.R. Schmidt94,
M.O. Schmidt 32, M. Schmidt94, N.V. Schmidt 87,63, A.R. Schmier 119, R.
Schotter 126, J. Schukraft 32, K. Schwarz98, K. Schweda 98, G. Scioli 25, E.
Scomparin 55, J.E. Seger 14, Y. Sekiguchi121, D. Sekihata 121, I. Selyuzhenkov
98,139, S. Senyukov 126, J.J. Seo 57, D. Serebryakov 139, L. Šerkšnytė 96, A.
Sevcenco 62, T.J. Shaba 67, A. Shabanov139, A. Shabetai 103, R. Shahoyan32, W.
Shaikh99, A. Shangaraev 139, A. Sharma90, D. Sharma 46, H. Sharma 106, M.
Sharma 91, N. Sharma90, S. Sharma 91, U. Sharma 91, A. Shatat 72, O.
Sheibani113, K. Shigaki 93, M. Shimomura77, S. Shirinkin 139, Q. Shou 39, Y.
Sibiriak 139, S. Siddhanta 51, T. Siemiarczuk 79, T.F. Silva 109, D. Silvermyr
75, T. Simantathammakul104, R. Simeonov 36, G. Simonetti32, B. Singh91, B.
Singh 96, R. Singh 80, R. Singh 91, R. Singh 47, V.K. Singh 131, V. Singhal
131, T. Sinha 99, B. Sitar 12, M. Sitta 129,55, T.B. Skaali19, G. Skorodumovs
95, M. Slupecki 43, N. Smirnov 136, R.J.M. Snellings 58, E.H. Solheim 19, C.
Soncco101, J. Song 113, A. Songmoolnak104, F. Soramel 27, S. Sorensen 119, R.
Spijkers 84, I. Sputowska 106, J. Staa 75, J. Stachel 95, I. Stan 62, P.J.
Steffanic 119, S.F. Stiefelmaier 95, D. Stocco 103, I. Storehaug 19, M.M.
Storetvedt 34, P. Stratmann 134, S. Strazzi 25, C.P. Stylianidis84, A.A.P.
Suaide 109, C. Suire 72, M. Sukhanov 139, M. Suljic 32, V. Sumberia 91, S.
Sumowidagdo 82, S. Swain60, A. Szabo12, I. Szarka 12, U. Tabassam13, S.F.
Taghavi 96, G. Taillepied 98,124, J. Takahashi 110, G.J. Tambave 20, S. Tang
124,6, Z. Tang 117, J.D. Tapia Takaki 115, N. Tapus123, L.A. Tarasovicova 134,
M.G. Tarzila 45, A. Tauro 32, A. Telesca 32, L. Terlizzi 24, C. Terrevoli 113,
G. Tersimonov3, S. Thakur 131, D. Thomas 107, R. Tieulent 125, A. Tikhonov
139, A.R. Timmins 113, M. Tkacik105, T. Tkacik 105, A. Toia 63, N. Topilskaya
139, M. Toppi 48, F. Torales-Acosta18, T. Tork 72, A.G. Torres Ramos 31, A.
Trifiró 30,52, A.S. Triolo 30,52, S. Tripathy 50, T. Tripathy 46, S. Trogolo
32, V. Trubnikov 3, W.H. Trzaska 114, T.P. Trzcinski 132, R. Turrisi 53, T.S.
Tveter 19, K. Ullaland 20, B. Ulukutlu 96, A. Uras 125, M. Urioni 54,130, G.L.
Usai 22, M. Vala37, N. Valle 21, S. Vallero 55, L.V.R. van Doremalen58, M. van
Leeuwen 84, C.A. van Veen 95, R.J.G. van Weelden 84, P. Vande Vyvre 32, D.
Varga 135, Z. Varga 135, M. Varga-Kofarago 135, M. Vasileiou 78, A. Vasiliev
139, O. Vázquez Doce 96, V. Vechernin 139, E. Vercellin 24, S. Vergara
Limón44, L. Vermunt 58, R. Vértesi 135, M. Verweij 58, L. Vickovic33, Z.
Vilakazi120, O. Villalobos Baillie 100, G. Vino 49, A. Vinogradov 139, T.
Virgili 28, V. Vislavicius83, A. Vodopyanov 140, B. Volkel 32, M.A. Völkl 95,
K. Voloshin139, S.A. Voloshin 133, G. Volpe 31, B. von Haller 32, I. Vorobyev
96, N. Vozniuk 139, J. Vrláková 37, B. Wagner20, C. Wang 39, D. Wang39, M.
Weber 102, A. Wegrzynek 32, F.T. Weiglhofer38, S.C. Wenzel 32, J.P. Wessels
134, S.L. Weyhmiller 136, J. Wiechula 63, J. Wikne 19, G. Wilk 79, J.
Wilkinson 98, G.A. Willems 134, B. Windelband95, M. Winn 127, J.R. Wright 107,
W. Wu39, Y. Wu 117, R. Xu 6, A.K. Yadav 131, S. Yalcin 71, Y. Yamaguchi93, K.
Yamakawa93, S. Yang20, S. Yano 93, Z. Yin 6, I.-K. Yoo 16, J.H. Yoon 57, S.
Yuan20, A. Yuncu 95, V. Zaccolo 23, C. Zampolli 32, H.J.C. Zanoli58, F. Zanone
95, N. Zardoshti 32,100, A. Zarochentsev 139, P. Závada 61, N. Zaviyalov139,
M. Zhalov 139, B. Zhang 6, S. Zhang 39, X. Zhang 6, Y. Zhang117, M. Zhao 10,
V. Zherebchevskii 139, Y. Zhi10, N. Zhigareva139, D. Zhou 6, Y. Zhou 83, J.
Zhu 98,6, Y. Zhu6, G. ZinovjevI,3, N. Zurlo 130,54

## Affiliation Notes

I Deceased
II Also at: Max-Planck-Institut für Physik, Munich, Germany
III Also at: Italian National Agency for New Technologies, Energy and
Sustainable Economic Development (ENEA), Bologna, Italy
IV Also at: Dipartimento DET del Politecnico di Torino, Turin, Italy
V Also at: Department of Applied Physics, Aligarh Muslim University, Aligarh,
India
VI Also at: Institute of Theoretical Physics, University of Wroclaw, Poland
VII Also at: An institution covered by a cooperation agreement with CERN

## 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 California Polytechnic State University, San Luis Obispo, California, United
States
6 Central China Normal University, Wuhan, China
7 Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana,
Cuba
8 Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and
Mérida, Mexico
9 Chicago State University, Chicago, Illinois, United States
10 China Institute of Atomic Energy, Beijing, China
11 Chungbuk National University, Cheongju, Republic of Korea
12 Comenius University Bratislava, Faculty of Mathematics, Physics and
Informatics, Bratislava, Slovak Republic
13 COMSATS University Islamabad, Islamabad, Pakistan
14 Creighton University, Omaha, Nebraska, United States
15 Department of Physics, Aligarh Muslim University, Aligarh, India
16 Department of Physics, Pusan National University, Pusan, Republic of Korea
17 Department of Physics, Sejong University, Seoul, Republic of Korea
18 Department of Physics, University of California, Berkeley, California,
United States
19 Department of Physics, University of Oslo, Oslo, Norway
20 Department of Physics and Technology, University of Bergen, Bergen, Norway
21 Dipartimento di Fisica, Università di Pavia, Pavia, Italy
22 Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
23 Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
24 Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy
25 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Bologna, Italy
26 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Catania, Italy
27 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Padova, Italy
28 Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo
Collegato INFN, Salerno, Italy
29 Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy
30 Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy
31 Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari,
Italy
32 European Organization for Nuclear Research (CERN), Geneva, Switzerland
33 Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, Split, Croatia
34 Faculty of Engineering and Science, Western Norway University of Applied
Sciences, Bergen, Norway
35 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University in Prague, Prague, Czech Republic
36 Faculty of Physics, Sofia University, Sofia, Bulgaria
37 Faculty of Science, P.J. Šafárik University, Košice, Slovak Republic
38 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-
Universität Frankfurt, Frankfurt, Germany
39 Fudan University, Shanghai, China
40 Gangneung-Wonju National University, Gangneung, Republic of Korea
41 Gauhati University, Department of Physics, Guwahati, India
42 Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-
Wilhelms-Universität Bonn, Bonn, Germany
43 Helsinki Institute of Physics (HIP), Helsinki, Finland
44 High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico
45 Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest, Romania
46 Indian Institute of Technology Bombay (IIT), Mumbai, India
47 Indian Institute of Technology Indore, Indore, India
48 INFN, Laboratori Nazionali di Frascati, Frascati, Italy
49 INFN, Sezione di Bari, Bari, Italy
50 INFN, Sezione di Bologna, Bologna, Italy
51 INFN, Sezione di Cagliari, Cagliari, Italy
52 INFN, Sezione di Catania, Catania, Italy
53 INFN, Sezione di Padova, Padova, Italy
54 INFN, Sezione di Pavia, Pavia, Italy
55 INFN, Sezione di Torino, Turin, Italy
56 INFN, Sezione di Trieste, Trieste, Italy
57 Inha University, Incheon, Republic of Korea
58 Institute for Gravitational and Subatomic Physics (GRASP), Utrecht
University/Nikhef, Utrecht, Netherlands
59 Institute of Experimental Physics, Slovak Academy of Sciences, Košice,
Slovak Republic
60 Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India
61 Institute of Physics of the Czech Academy of Sciences, Prague, Czech
Republic
62 Institute of Space Science (ISS), Bucharest, Romania
63 Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany
64 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México,
Mexico City, Mexico
65 Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS),
Porto Alegre, Brazil
66 Instituto de Física, Universidad Nacional Autónoma de México, Mexico City,
Mexico
67 iThemba LABS, National Research Foundation, Somerset West, South Africa
68 Jeonbuk National University, Jeonju, Republic of Korea
69 Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik,
Fachbereich Informatik und Mathematik, Frankfurt, Germany
70 Korea Institute of Science and Technology Information, Daejeon, Republic of
Korea
71 KTO Karatay University, Konya, Turkey
72 Laboratoire de Physique des 2 Infinis, Irène Joliot-Curie, Orsay, France
73 Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-
Alpes, CNRS-IN2P3, Grenoble, France
74 Lawrence Berkeley National Laboratory, Berkeley, California, United States
75 Lund University Department of Physics, Division of Particle Physics, Lund,
Sweden
76 Nagasaki Institute of Applied Science, Nagasaki, Japan
77 Nara Women’s University (NWU), Nara, Japan
78 National and Kapodistrian University of Athens, School of Science,
Department of Physics , Athens, Greece
79 National Centre for Nuclear Research, Warsaw, Poland
80 National Institute of Science Education and Research, Homi Bhabha National
Institute, Jatni, India
81 National Nuclear Research Center, Baku, Azerbaijan
82 National Research and Innovation Agency - BRIN, Jakarta, Indonesia
83 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
84 Nikhef, National institute for subatomic physics, Amsterdam, Netherlands
85 Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom
86 Nuclear Physics Institute of the Czech Academy of Sciences, Husinec-Řež,
Czech Republic
87 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
88 Ohio State University, Columbus, Ohio, United States
89 Physics department, Faculty of science, University of Zagreb, Zagreb,
Croatia
90 Physics Department, Panjab University, Chandigarh, India
91 Physics Department, University of Jammu, Jammu, India
92 Physics Department, University of Rajasthan, Jaipur, India
93 Physics Program and International Institute for Sustainability with Knotted
Chiral Meta Matter (SKCM2), Hiroshima University, Hiroshima, Japan
94 Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen,
Germany
95 Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
96 Physik Department, Technische Universität München, Munich, Germany
97 Politecnico di Bari and Sezione INFN, Bari, Italy
98 Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum
für Schwerionenforschung GmbH, Darmstadt, Germany
99 Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata,
India
100 School of Physics and Astronomy, University of Birmingham, Birmingham,
United Kingdom
101 Sección Física, Departamento de Ciencias, Pontificia Universidad Católica
del Perú, Lima, Peru
102 Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
103 SUBATECH, IMT Atlantique, Nantes Université, CNRS-IN2P3, Nantes, France
104 Suranaree University of Technology, Nakhon Ratchasima, Thailand
105 Technical University of Košice, Košice, Slovak Republic
106 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of
Sciences, Cracow, Poland
107 The University of Texas at Austin, Austin, Texas, United States
108 Universidad Autónoma de Sinaloa, Culiacán, Mexico
109 Universidade de São Paulo (USP), São Paulo, Brazil
110 Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
111 Universidade Federal do ABC, Santo Andre, Brazil
112 University of Cape Town, Cape Town, South Africa
113 University of Houston, Houston, Texas, United States
114 University of Jyväskylä, Jyväskylä, Finland
115 University of Kansas, Lawrence, Kansas, United States
116 University of Liverpool, Liverpool, United Kingdom
117 University of Science and Technology of China, Hefei, China
118 University of South-Eastern Norway, Kongsberg, Norway
119 University of Tennessee, Knoxville, Tennessee, United States
120 University of the Witwatersrand, Johannesburg, South Africa
121 University of Tokyo, Tokyo, Japan
122 University of Tsukuba, Tsukuba, Japan
123 University Politehnica of Bucharest, Bucharest, Romania
124 Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
125 Université de Lyon, CNRS/IN2P3, Institut de Physique des 2 Infinis de