EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-EP-2017-135 LHCb-PAPER-2017-015 10th July 2017

Study of prompt ${{D}^{0}}$ meson production in $p\mathrm{Pb}$ collisions at
${\sqrt{s_{\mathrm{NN}}}}=5\,\mathrm{\,Te\kern-2.07413ptV}$

The LHCb collaboration†††Authors are listed at the end of this paper.

Production of prompt ${{D}^{0}}$ mesons is studied in proton-lead and lead-
proton collisions recorded at the LHCb detector at the LHC. The data sample
corresponds to an integrated luminosity of $1.58\pm 0.02\mbox{\,nb}^{-1}$
recorded at a nucleon-nucleon centre-of-mass energy of
${\sqrt{s_{\mathrm{NN}}}}=5\mathrm{\,Te\kern-1.00006ptV}$. Measurements of the
differential cross-section, the forward-backward production ratio and the
nuclear modification factor are reported using ${{D}^{0}}$ candidates with
transverse momenta less than $10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and
rapidities in the ranges $1.5<y^{*}<4.0$ and $-5.0<y^{*}<-2.5$ in the nucleon-
nucleon centre-of-mass system.

Submitted to JHEP

© CERN on behalf of the LHCb collaboration, licence CC-BY-4.0.

##  1 Introduction

Charm hadrons produced in hadronic and nuclear collisions are excellent probes
to study nuclear matter in extreme conditions. The differential cross-sections
of $c$-quark production in $pp$ or $p\bar{p}$ collisions have been calculated
based on perturbative quantum chromodynamics (QCD) and collinear or
$k_{\mathrm{T}}$ factorisation [1, 2, 3, 4, 5, 6]. These phenomenological
models [7] are also able to predict the differential cross-section of
$c$-quark production including most of the commonly assumed “cold nuclear
matter” (CNM) effects in nuclear collisions, where CNM effects related to the
parton flux differences and other effects come into play. Since heavy quarks
are produced at a time scale of approximately 0.1 fm/$c$ after the collision,
they are ideal to examine hot nuclear matter, the so-called “quark-gluon
plasma” (QGP), by studying how they traverse this medium and interact with it
right after their formation. These studies require a thorough understanding of
the CNM effects, which can be investigated in systems where the formation of
QGP is not expected. In addition, a precise quantification of CNM effects
would significantly improve the understanding of charmonium and open-charm
production by confirming or discarding the possibility that the suppression
pattern in the production of quarkonium states, like
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$, at the SPS, RHIC and LHC is
due to QGP formation [7].

The study of CNM effects is best performed in collisions of protons with heavy
nuclei like lead, where the most studied CNM effects, such as gluon saturation
[8, 9] and in-medium energy loss [10] in initial- and final-state radiation
[11, 12], are more evident. Phenomenologically, collinear parton distributions
are often used to describe the nuclear modification of the parton flux in the
nucleus. The modification with respect to the free nucleon depends on the
parton fractional longitudinal momentum, $x$, and the atomic mass number of
the nucleus $A$ [13, 14]. In the low-$x$ region, down to $x\approx
10^{-5}-10^{-6}$, which is accessible at LHC energies, stronger onset of gluon
saturation [15, 16, 17, 18] is expected to play a major role. Its effect can
be quantified by studying production of ${{D}^{0}}$ mesons at low transverse
momentum $p_{\mathrm{T}}$ [19], ideally down to zero $p_{\mathrm{T}}$. The in-
medium energy loss occurs when the partons lose energy in the cold medium
through both initial- and final-state radiation.

CNM effects have been investigated in detail at the RHIC collider in $pp$ and
$d$Au collisions [7, 20] at a nucleon-nucleon centre-of-mass energy of
${\sqrt{s_{\mathrm{NN}}}}=200$$\mathrm{\,Ge\kern-1.00006ptV}$. Most recently,
CNM effects were measured in $p$Pb collisions at the LHC for quarkonium and
heavy flavour production [21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,
34, 35, 36]. The ALICE experiment [28] studied $D$ meson production in $p$Pb
collisions at ${\sqrt{s_{\mathrm{NN}}}}=5$$\mathrm{\,Te\kern-1.00006ptV}$ in
the region $−0.96<y^{*}<0.04$ for
$\mbox{$p_{\mathrm{T}}$}>2{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, where $y^{*}$
is the rapidity of the $D$ meson defined in the centre-of-mass system of the
colliding nucleons. Their results suggest that the suppression observed in
PbPb collisions is due to hot nuclear matter effects, i.e. QGP formation.
Results on leptons from semileptonic heavy-flavour decays at various
rapidities are also available [37, 38, 39].

In this paper the measurement of the cross-section and of the nuclear
modification factors of “prompt” $D^{0}$ mesons, i.e. those directly produced
in proton-lead collisions and not coming from decays of $b$-hadrons, is
presented. The measurement is performed at ${\sqrt{s_{\mathrm{NN}}}}=5$ TeV
with the LHCb [40] detector at the LHC. Depending on the direction of the
proton and 208Pb beams and due to the different energies per nucleon in the
two beams, the LHCb detector covers two different acceptance regions in the
nucleon-nucleon rest frame,

  * •

$1.5<y^{\ast}<4.0$, denoted as “forward” beam configuration,

  * •

$-5.0<y^{\ast}<-2.5$, denoted as “backward” beam configuration,

where the rapidity $y^{\ast}$ is defined with respect to the direction of the
proton beam, The measurement is performed in the range of ${D}^{0}$ transverse
momentum $\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, in
both backward and forward collisions.

##  2 Detector and data samples

The LHCb detector [40, 41] is a single-arm forward spectrometer covering the
pseudorapidity range $2<\eta<5$, designed for the study of particles
containing $b$ or $c$ quarks. The detector includes a high-precision tracking
system consisting of a silicon-strip vertex detector surrounding the $pp$
interaction region (VELO), a large-area silicon-strip detector (TT) located
upstream of a dipole magnet with a bending power of about $4{\mathrm{\,Tm}}$,
and three stations of silicon-strip detectors and straw drift tubes (OT)
placed downstream of the magnet. The tracking system provides a measurement of
momentum, $p$, of charged particles with a relative uncertainty that varies
from 0.5% at low momentum to 1.0% at
200${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The minimum distance of a track to
a primary vertex (PV), the impact parameter, is measured with a resolution of
$(15+29/\mbox{$p_{\mathrm{T}}$}){\,\upmu\mathrm{m}}$, where $p_{\mathrm{T}}$
is the component of the momentum transverse to the beam, in
${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. Different types of charged hadrons are
distinguished using information from two ring-imaging Cherenkov detectors.
Photons, electrons and hadrons are identified by a calorimeter system
consisting of scintillating-pad and preshower detectors, an electromagnetic
calorimeter and a hadronic calorimeter. Muons are identified by a system
composed of alternating layers of iron and multiwire proportional chambers.
The online event selection is performed by a trigger [42], which consists of a
hardware stage, based on information from the calorimeter and muon systems,
followed by a software stage, which applies a full event reconstruction.

The data sample used in this analysis consists of $p$Pb collisions collected
in early 2013, corresponding to integrated luminosities of ($1.06\pm
0.02$)$\mbox{\,nb}^{-1}$ and ($0.52\pm 0.01$)$\mbox{\,nb}^{-1}$ for the
forward and backward colliding beam configurations, respectively. The
luminosity has been determined using the same method as in the LHCb
measurement of ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ production in
$p$Pb collisions [43], with a precision of about 2%. The instantaneous
luminosity during the period of data taking was around 5$\times 10^{27}$ cm-2
s-1, which led to an event rate that was three orders of magnitude lower than
in nominal LHCb $pp$ operation. Therefore, the hardware trigger simply
rejected empty events, while the next level software trigger accepted all
events with at least one track in the VELO.

For the analyses presented below, simulated samples of $pp$ collisions at 8
TeV are used to determine geometrical acceptance and reconstruction
efficiencies. Effects due to the different track multiplicity distributions in
the $pp$ and $p$Pb collision data and the effects of the asymmetric beam
energies in $p$Pb collisions are taken into account as described later. In the
simulation, $pp$ collisions are generated using Pythia [44, *Sjostrand:2007gs]
with a specific LHCb configuration [46]. Decays of hadronic particles are
described by EvtGen [47], in which final-state radiation is generated using
Photos [48]. The interaction of the generated particles with the detector, and
its response, are implemented using the Geant4 toolkit [49,
*Agostinelli:2002hh, 51].

##  3 Cross-section determination

The double-differential cross-section for prompt ${{D}^{0}}$ production in a
given $(\mbox{$p_{\mathrm{T}}$},y^{*})$ kinematic bin is defined as

$\frac{\mathrm{d}^{2}\sigma}{\mathrm{d}\mbox{$p_{\mathrm{T}}$}\mathrm{d}y^{*}}=\frac{N({{{D}^{0}}\rightarrow
K^{\mp}\pi^{\pm}})}{\mathcal{L}\times{\varepsilon_{\mathrm{tot}}}\times{\mathcal{B}}({{{D}^{0}}\rightarrow
K^{\mp}\pi^{\pm}})\times\Delta\mbox{$p_{\mathrm{T}}$}\times\Delta y^{*}},$ (1)

where $N({{{D}^{0}}\rightarrow K^{\mp}\pi^{\pm}})$ is the number of prompt
${D}^{0}$ signal candidates reconstructed through the ${{{D}^{0}}\rightarrow
K^{\mp}\pi^{\pm}}$ decay channels111Charge conjugation is implied throughout
this document if not otherwise specified., ${\varepsilon_{\mathrm{tot}}}$ is
the total ${D}^{0}$ detection efficiency, $\mathcal{L}$ is the integrated
luminosity, ${\mathcal{B}}({{{D}^{0}}\rightarrow K^{\mp}\pi^{\pm}})=(3.94\pm
0.04)\%$ is the sum of the branching fractions of the decays
${{{D}^{0}}\rightarrow K^{-}\pi^{+}}$ and ${{{D}^{0}}\rightarrow
K^{+}\pi^{-}}$ [52],
$\Delta\mbox{$p_{\mathrm{T}}$}=1{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ is the
bin width of the ${D}^{0}$ transverse momentum, and $\Delta y^{*}=0.5$ is the
bin width of the ${D}^{0}$ rapidity. The rapidity $y^{*}$ is defined in the
nucleon-nucleon centre-of-mass frame, where the positive direction is that of
the proton beam. The measurement is performed in the ${D}^{0}$ kinematic
region defined by
$\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and
rapidities $1.5<y^{*}<4.0$ for the forward sample and $-5.0<y^{*}<-2.5$ for
the backward sample.

The total cross-section over a specific kinematic range is determined by
integration of the double-differential cross-section. The nuclear modification
factor, $R_{p{\rm Pb}}$, is the ratio of the ${D}^{0}$ production cross-
section in forward or backward collisions to that in $pp$ at the same nucleon-
nucleon centre-of-mass energy ${\sqrt{s_{\mathrm{NN}}}}$

$R_{p{\rm Pb}}(\mbox{$p_{\mathrm{T}}$},y^{*})\equiv\frac{1}{A}\frac{{\rm
d}^{2}\sigma_{p{\rm Pb}}(\mbox{$p_{\mathrm{T}}$},y^{*})/{\rm
d}\mbox{$p_{\mathrm{T}}$}{\rm d}y^{*}}{{\rm
d}^{2}\sigma_{pp}(\mbox{$p_{\mathrm{T}}$},y^{*})/{\rm
d}\mbox{$p_{\mathrm{T}}$}{\rm d}y^{*}},$ (2)

where $A$=208 is the atomic mass number of the lead nucleus. The forward-
backward production ratio, $R_{\rm FB}$, is defined as

$R_{\rm FB}(\mbox{$p_{\mathrm{T}}$},y^{*})\equiv\frac{{\rm d}^{2}\sigma_{p{\rm
Pb}}(\mbox{$p_{\mathrm{T}}$},+|y^{*}|)/{\rm d}\mbox{$p_{\mathrm{T}}$}{\rm
d}y^{*}}{{\rm d}^{2}\sigma_{{\rm Pb}p}(\mbox{$p_{\mathrm{T}}$},-|y^{*}|)/{\rm
d}\mbox{$p_{\mathrm{T}}$}{\rm d}y^{*}},$ (3)

where $\sigma_{p{\rm Pb}}$ and $\sigma_{{\rm Pb}p}$ indicate the cross-
sections in the forward and backward configurations respectively, measured in
a common rapidity range. The ${D}^{0}$ candidates are selected according to
the same requirements as used in the ${{D}^{0}}$ production cross-section
measurements in $pp$ collisions at $\sqrt{s}=7\mathrm{\,Te\kern-1.00006ptV}$
[53] and $\sqrt{s}=13\mathrm{\,Te\kern-1.00006ptV}$[54]. The kaon and pion
tracks from the ${D}^{0}$ candidate and the vertex they form are both required
to be of good quality. The requirements set on particle identification (PID)
criteria are tighter than in $pp$ collisions to increase the signal-over-
background ratio given the high detector occupancy observed in $p$Pb
collisions.

|
---|---
Figure 1: The (left) $M(K^{\mp}\pi^{\pm})$ and (right) ${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ distributions and the fit result for the inclusive ${{D}^{0}}$ mesons in the forward data sample in the kinematic range of $2<\mbox{$p_{\mathrm{T}}$}<3{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and $2.5<y^{*}<3.0$. |
---|---
Figure 2: The (left) $M(K^{\mp}\pi^{\pm})$ and (right)
${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ distributions and the fit
result for the inclusive ${{D}^{0}}$ mesons in the backward data sample in the
kinematic range of
$2<\mbox{$p_{\mathrm{T}}$}<3{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and
$-4.0<y^{*}<-3.5$.

The signal yield is determined from an extended unbinned maximum likelihood
fit to the distribution of the invariant mass $M(K^{\mp}\pi^{\pm})$. The
fraction of nonprompt ${{D}^{0}}$ mesons originating from $b$-hadron decays,
called ${{D}^{0}}$-from-$b$ in the following, is determined from the
${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ distribution, where
$\chi^{2}_{\text{$\rm IP$}}(D^{0})$ is defined as the difference in vertex-fit
$\chi^{2}$ of a given PV computed with and without the ${D}^{0}$ meson
candidate[53, 54]. On average, prompt ${D}^{0}$ mesons have much smaller
$\chi^{2}_{\text{$\rm IP$}}(D^{0})$ values than ${{D}^{0}}$-from-$b$. The fit
is performed in two steps. First, the invariant mass distributions are fitted
to determine the ${{D}^{0}}$ meson inclusive yield and the number of
background candidates, then the ${\log_{10}(\chi^{2}_{\text{$\rm
IP$}}({{D}^{0}}))}$ fit is performed for candidates with mass within $\pm
20{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ around the fitted value of the
${D}^{0}$ mass. In the ${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$
fit, the number of background candidates is constrained to the value obtained
from the invariant mass fit, scaled to the selected mass range.

The distribution of ${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ is
shown in the right-hand plots of Figs. 1 and 2 for the forward and backward
samples, respectively. The signal shape in the $M(K^{\mp}\pi^{\pm})$
distributions is described by a Crystal Ball (CB) function [55] plus a
Gaussian. The mean is the same for both functions, and the ratios of widths
and tail parameters are fixed following simulation studies, as in previous
LHCb analyses [53, 54]. The width, mean, and signal yields are left free to
vary. The background is described by a linear function. The candidates are
fitted in the range 1792–1942${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. The
invariant mass distributions in the inclusive forward and backward samples are
shown in the left-hand plots of Figs. 1 and 2 respectively.

The fits to the invariant mass and ${\log_{10}(\chi^{2}_{\text{$\rm
IP$}}({{D}^{0}}))}$ distributions are performed independently in each bin of
$(\mbox{$p_{\mathrm{T}}$},y^{*})$ of the ${{D}^{0}}$ meson. The contribution
of the ${{D}^{0}}$-from-$b$ component increases with transverse momentum up to
10%. The ${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ shapes for the
prompt ${D}^{0}$ meson signal candidates are estimated using the simulation
and modelled with a modified Gaussian function

$f_{\mathrm{}}(x;\mu,\sigma,\epsilon,\rho_{\mathrm{L}},\rho_{\mathrm{R}})=\begin{cases}e^{\frac{\rho_{\mathrm{L}}^{2}}{2}+\rho_{\mathrm{L}}\frac{x-\mu}{(1-\epsilon)\sigma}}&x<\mu-(\rho_{\mathrm{L}}\sigma(1-\epsilon)),\\\
e^{-\left(\frac{x-\mu}{\sqrt{2}\sigma(1-\epsilon)}\right)^{2}}&\mu-(\rho_{\mathrm{L}}\sigma(1-\epsilon))\leq
x<\mu,\\\
e^{-\left(\frac{x-\mu}{\sqrt{2}\sigma(1+\epsilon)}\right)^{2}}&\mu\leq
x<\mu+(\rho_{\mathrm{R}}\sigma(1+\epsilon)),\\\
e^{\frac{\rho_{\mathrm{R}}^{2}}{2}-\rho_{\mathrm{R}}\frac{x-\mu}{(1+\epsilon)\sigma}}&x\geq\mu+(\rho_{\mathrm{R}}\sigma(1+\epsilon)),\end{cases}$
(4)

where the values of $\epsilon$, $\rho_{\mathrm{L}}$ and $\rho_{\mathrm{R}}$
are fixed to the values obtained in the simulation and $\mu$ and $\sigma$ are
free parameters. The ${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$
distribution for the ${{D}^{0}}$-from-$b$ component is described by a Gaussian
function. The shape of the combinatorial background is estimated using the
distribution of candidates with mass in the ranges
1797–1827${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ and
1907–1937${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$, i.e. between 40 and 70
${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ away from the observed ${{D}^{0}}$
meson mass.

The total efficiency ${\varepsilon_{\mathrm{tot}}}$ in Eq. 1 includes the
effects of geometrical acceptance and the efficiencies of the trigger, of the
reconstruction and of the PID criteria used in the analysis. The analysis uses
a minimum activity trigger, whose efficiency for events containing a ${D}^{0}$
meson is found to be 100%. The geometrical acceptance and reconstruction
efficiencies are estimated using $pp$ simulated samples, validated with data.
The difference between the distributions of the track multiplicity in the
$p$Pb and $pp$ collisions is accounted for by studying the efficiency in bins
of the track multiplicity, and weighting the efficiency according to the
multiplicity distributions seen in $p$Pb and Pb$p$ data. The related
systematic uncertainties are discussed in Sec. 4. The PID efficiency is
estimated using a calibration sample of ${D}^{0}$ meson decays selected in
data without PID requirements [41], and collected in the same period as the
$p\mathrm{Pb}$ sample used for the analysis. The PID selection efficiency is
calculated by using the $K^{\mp}$ and $\pi^{\pm}$ single-track efficiencies
from calibration data, and averaging them according to the kinematic
distributions observed in the simulation in each ${{D}^{0}}$
$(\mbox{$p_{\mathrm{T}}$},y^{*})$ bin.

##  4 Systematic Uncertainties

The systematic uncertainties affecting the cross-sections are listed in Table
1.

Table 1: Summary of systematic and statistical uncertainties on the cross-section. The ranges indicate the variations between bins, with the uncertainty on average increasing with rapidity and momentum. Source | Relative uncertainty (%)
---|---
| Forward | Backward
Correlated between bins |  |
Invariant mass fits | 0.0 $-$05.0 | 0.0 $-$05.0
$\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))$ fits | 0.0 $-$05.0 | 0.0 $-$05.0
Tracking efficiency | 3.0 | 5.0
PID efficiency |  0.6 $-$ 17.0 |  0.6 $-$ 30.0
Luminosity | 1.9 | 2.1
$\mathcal{B}({{{D}^{0}}\rightarrow K^{\mp}\pi^{\pm}})$ | 1.0 | 1.0
Uncorrelated between bins |  |
Simulation sample size | 1.0 $-$04.0 | 1.0 $-$05.0
Statistical uncertainty |  0.5 $-$ 20.0 |  1.0 $-$ 20.0

They are evaluated separately for the backward and forward samples unless
otherwise specified. The systematic uncertainty associated to the
determination of the signal yield has contributions from the signal and
background models. The uncertainty associated to the modelling of the signal
is studied by using alternative models of single or sum of two Gaussian
functions to fit the invariant mass in the forward and backward samples. A
variation of the parameters which are fixed in the default model, within the
ranges indicated by the simulation, is also explored. The largest difference
between the nominal and the alternative fits is taken as the uncertainty on
the method, which results in a bin-dependent uncertainty, not exceeding 5%.
The effect due to background modelling in the invariant mass fit is studied by
using an exponential as an alternative to the linear function. This
uncertainty is found to be negligible. For the fit to the
${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ distribution, the
$\rho_{\mathrm{L}}$ and $\rho_{\mathrm{R}}$ parameters of the prompt signal
component are varied within the ranges studied in simulation. The distribution
of combinatorial backgrounds is studied with candidates in different
background mass regions. The shape of the distribution for the
${{D}^{0}}$-from-$b$ component is fixed when studying the variation of its
fraction. The same procedure is followed to estimate the uncertainty on the
${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ fits. The systematic
uncertainty on the prompt signal yields, determined by the
${\log_{10}(\chi^{2}_{\text{$\rm IP$}}({{D}^{0}}))}$ fit, depends on the
kinematic bin and is estimated to be less than 5% in all cases.

The systematic uncertainty associated with the tracking efficiency has the
components described in the following. The efficiency measurement is affected
by the imperfect modelling of the tracking efficiency by simulation, which is
corrected using a data-driven method [56], and the uncertainty of the
correction is propagated into an uncertainty on the ${D}^{0}$ yield. The
limited sizes of the simulated samples affect the precision of the efficiency,
especially in the high multiplicity region. Another source of uncertainty is
introduced by the choice of variable representing the detector occupancy, used
to weight the distributions. The number of tracks and the number of hits in
the VELO and in the TT and OT are all considered separately. The largest
difference between the efficiencies when weighted by each of these variables
and their average, which is the default, is taken as systematic uncertainty.
An additional uncertainty comes from the detector occupancy distribution
estimated in backward and forward data. The effects are summed in quadrature,
yielding a total uncertainty on the tracking efficiency of $3\%$ and $5\%$ for
the forward and backward collision sample respectively.

The limited size of the calibration sample, the binning scheme and the signal
fit model used to determine the $\pi$ and $K$ PID efficiency from the
calibration sample, all contribute to the systematic uncertainty. The first is
evaluated by estimating new sets of efficiencies through the variation of the
$\pi$ and $K$ PID efficiencies in the calibration sample within the
statistical uncertainties, the second by using alternative binning schemes and
the third by varying the signal function used to determine the signal. The
uncertainty is taken to be the quadratic sum of the three components. The
total PID systematic uncertainty ranges between 1% and 30% depending on the
kinematic region and the collision sample.

The relative uncertainty associated with the luminosity measurement is
approximately $2\%$ for both forward and backward samples. The relative
uncertainty of the branching fraction ${\mathcal{B}}({{{D}^{0}}\rightarrow
K^{\mp}\pi^{\pm}})$ is $1\%$ [52]. The limited size of the simulation sample
introduces uncertainties on the efficiencies which are then propagated to the
cross-section measurements; this effect is negligible for the central rapidity
region but increases in the regions close to the boundaries of
$p_{\mathrm{T}}$ and $y$, ranging between 1% and 5%.

##  5 Results

###  5.1 Production cross-sections

The measured values of the double-differential cross-section of prompt
${{D}^{0}}$ mesons in proton-lead collisions in the forward and backward
regions as a function of $p_{\mathrm{T}}$ and $y^{*}$ are given in Table 5.1
and shown in Fig. 3.

Table 2: Double-differential cross-section
$\frac{\mathrm{d}^{2}\sigma}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y^{*}}$
(mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$)) for prompt ${{D}^{0}}$ meson
production as functions of $p_{\mathrm{T}}$ and $y^{*}$ in ${p\mathrm{Pb}}$
forward and backward data, respectively. The first uncertainty is statistical,
the second is the component of the systematic uncertainty that is uncorrelated
between bins and the third is the correlated component. In the regions with no
entries the signal is not statistically significant.

| Forward (mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$))
---|---
$\mbox{$p_{\mathrm{T}}$}[{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}]$ | $1.5<y^{*}<2.0$ | $2.0<y^{*}<2.5$ | $2.5<y^{*}<3.0$ | $3.0<y^{*}<3.5$ | $3.5<y^{*}<4.0$
$[0,1]$ | $24.67\pm 0.32\pm 0.50\pm 3.45$ | $23.48\pm 0.17\pm 0.25\pm 1.70$ | $22.01\pm 0.16\pm 0.20\pm 1.16$ | $20.19\pm 0.21\pm 0.23\pm 1.02$ | $18.41\pm 0.36\pm 0.33\pm 1.09$
$[1,2]$ | $40.79\pm 0.34\pm 0.61\pm 3.83$ | $38.45\pm 0.19\pm 0.35\pm 2.19$ | $33.79\pm 0.18\pm 0.26\pm 1.50$ | $29.89\pm 0.22\pm 0.28\pm 1.31$ | $24.17\pm 0.34\pm 0.40\pm 1.63$
$[2,3]$ | $25.50\pm 0.20\pm 0.39\pm 1.76$ | $23.73\pm 0.11\pm 0.20\pm 1.08$ | $20.34\pm 0.10\pm 0.16\pm 0.82$ | $16.84\pm 0.11\pm 0.17\pm 0.69$ | $13.03\pm 0.17\pm 0.23\pm 0.78$
$[3,4]$ | $12.46\pm 0.11\pm 0.21\pm 0.63$ | $11.09\pm 0.06\pm 0.10\pm 0.47$ | $\phantom{0}9.31\pm 0.05\pm 0.09\pm 0.38$ | $\phantom{0}7.73\pm 0.06\pm 0.09\pm 0.36$ | $\phantom{0}5.22\pm 0.09\pm 0.11\pm 0.46$
$[4,5]$ | $\phantom{0}5.79\pm 0.06\pm 0.11\pm 0.27$ | $\phantom{0}5.23\pm 0.04\pm 0.06\pm 0.21$ | $\phantom{0}4.36\pm 0.03\pm 0.05\pm 0.17$ | $\phantom{0}3.32\pm 0.04\pm 0.05\pm 0.14$ | $\phantom{0}2.17\pm 0.07\pm 0.07\pm 0.45$
$[5,6]$ | $\phantom{0}2.94\pm 0.04\pm 0.07\pm 0.14$ | $\phantom{0}2.53\pm 0.03\pm 0.04\pm 0.11$ | $\phantom{0}2.04\pm 0.02\pm 0.03\pm 0.09$ | $\phantom{0}1.47\pm 0.02\pm 0.03\pm 0.10$ | $\phantom{0}0.93\pm 0.07\pm 0.07\pm 0.37$
$[6,7]$ | $\phantom{0}1.42\pm 0.02\pm 0.04\pm 0.08$ | $\phantom{0}1.26\pm 0.02\pm 0.02\pm 0.05$ | $\phantom{0}1.04\pm 0.02\pm 0.02\pm 0.06$ | $\phantom{0}0.72\pm 0.02\pm 0.02\pm 0.10$ | $\phantom{0}0.31\pm 0.08\pm 0.06\pm 0.20$
$[7,8]$ | $\phantom{0}0.84\pm 0.02\pm 0.03\pm 0.04$ | $\phantom{0}0.66\pm 0.01\pm 0.02\pm 0.04$ | $\phantom{0}0.53\pm 0.01\pm 0.01\pm 0.03$ | $\phantom{0}0.36\pm 0.02\pm 0.02\pm 0.09$ | $-$
$[8,9]$ | $\phantom{0}0.47\pm 0.01\pm 0.02\pm 0.02$ | $\phantom{0}0.38\pm 0.01\pm 0.01\pm 0.03$ | $\phantom{0}0.32\pm 0.01\pm 0.01\pm 0.03$ | $\phantom{0}0.17\pm 0.02\pm 0.02\pm 0.06$ | $-$
$[9,10]$ | $\phantom{0}0.31\pm 0.01\pm 0.02\pm 0.02$ | $\phantom{0}0.24\pm 0.01\pm 0.01\pm 0.02$ | $\phantom{0}0.17\pm 0.01\pm 0.01\pm 0.02$ | $\phantom{0}0.07\pm 0.01\pm 0.01\pm 0.03$ | $-$
| Backward (mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$))
$\mbox{$p_{\mathrm{T}}$}[{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}]$ | $-3.0<y^{*}<-2.5$ | $-3.5<y^{*}<-3.0$ | $-4.0<y^{*}<-3.5$ | $-4.5<y^{*}<-4.0$ | $-5.0<y^{*}<-4.5$
$[0,1]$ | $27.75\pm 0.48\pm 0.47\pm 5.78$ | $29.56\pm 0.33\pm 0.29\pm 2.98$ | $28.47\pm 0.38\pm 0.28\pm 1.98$ | $25.03\pm 0.58\pm 0.28\pm 1.78$ | $20.85\pm 1.08\pm 0.43\pm 2.21$
$[1,2]$ | $46.66\pm 0.51\pm 0.69\pm 6.13$ | $46.10\pm 0.35\pm 0.38\pm 3.40$ | $40.35\pm 0.38\pm 0.33\pm 2.61$ | $35.82\pm 0.56\pm 0.38\pm 2.54$ | $27.00\pm 1.01\pm 0.45\pm 2.81$
$[2,3]$ | $28.55\pm 0.29\pm 0.41\pm 2.41$ | $25.90\pm 0.19\pm 0.22\pm 1.62$ | $21.47\pm 0.18\pm 0.17\pm 1.26$ | $17.13\pm 0.23\pm 0.19\pm 1.09$ | $11.82\pm 0.45\pm 0.23\pm 0.97$
$[3,4]$ | $12.73\pm 0.15\pm 0.18\pm 0.93$ | $10.98\pm 0.10\pm 0.10\pm 0.64$ | $\phantom{0}8.75\pm 0.09\pm 0.08\pm 0.50$ | $\phantom{0}6.33\pm 0.10\pm 0.08\pm 0.45$ | $\phantom{0}3.61\pm 0.17\pm 0.09\pm 0.55$
$[4,5]$ | $\phantom{0}5.60\pm 0.08\pm 0.09\pm 0.38$ | $\phantom{0}4.59\pm 0.05\pm 0.05\pm 0.26$ | $\phantom{0}3.36\pm 0.05\pm 0.04\pm 0.19$ | $\phantom{0}2.21\pm 0.05\pm 0.03\pm 0.14$ | $\phantom{0}1.47\pm 0.13\pm 0.06\pm 0.43$
$[5,6]$ | $\phantom{0}2.53\pm 0.05\pm 0.05\pm 0.16$ | $\phantom{0}1.93\pm 0.03\pm 0.03\pm 0.11$ | $\phantom{0}1.38\pm 0.03\pm 0.02\pm 0.08$ | $\phantom{0}0.82\pm 0.03\pm 0.02\pm 0.10$ | $\phantom{0}0.57\pm 0.14\pm 0.06\pm 0.30$
$[6,7]$ | $\phantom{0}1.32\pm 0.03\pm 0.03\pm 0.08$ | $\phantom{0}0.92\pm 0.02\pm 0.02\pm 0.06$ | $\phantom{0}0.62\pm 0.02\pm 0.01\pm 0.04$ | $\phantom{0}0.28\pm 0.02\pm 0.01\pm 0.07$ | $-$
$[7,8]$ | $\phantom{0}0.65\pm 0.02\pm 0.02\pm 0.04$ | $\phantom{0}0.48\pm 0.02\pm 0.01\pm 0.04$ | $\phantom{0}0.31\pm 0.01\pm 0.01\pm 0.04$ | $\phantom{0}0.19\pm 0.03\pm 0.01\pm 0.08$ | $-$
$[8,9]$ | $\phantom{0}0.33\pm 0.02\pm 0.01\pm 0.02$ | $\phantom{0}0.24\pm 0.01\pm 0.01\pm 0.02$ | $\phantom{0}0.14\pm 0.01\pm 0.01\pm 0.03$ | $\phantom{0}0.11\pm 0.03\pm 0.01\pm 0.08$ | $-$
$[9,10]$ | $\phantom{0}0.22\pm 0.01\pm 0.01\pm 0.02$ | $\phantom{0}0.13\pm 0.01\pm 0.01\pm 0.01$ | $\phantom{0}0.08\pm 0.01\pm 0.00\pm 0.02$ | $-$ | $-$

The one-dimensional differential prompt ${{D}^{0}}$ meson cross-sections as a
function of $p_{\mathrm{T}}$ or $y^{*}$ are reported in Tables 5.1 and 4, and
are displayed in Fig. 4. The measurements are also shown as a function of
$p_{\mathrm{T}}$ integrated222 The integration over $y^{\ast}$ is performed up
to $|y^{\ast}|$=3.5 for
$\mbox{$p_{\mathrm{T}}$}>6{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, neglecting
the bin $3.5<|y^{*}|<4.0$ since it is not populated in the forward sample.
This applies for the integrated cross-sections presented in this subsection,
in Tables 5.1, 5.1 and 5.3 and in Figs. 4, 5, 8 and 9. over $y^{*}$ in the
common rapidity range $2.5<|y^{*}|<4.0$.

Figure 3: Double-differential cross-section
$\frac{\mathrm{d}^{2}\sigma}{\mathrm{d}p_{\mathrm{T}}\mathrm{d}y^{*}}$
(mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$)) of prompt ${{D}^{0}}$ meson
production in ${p\mathrm{Pb}}$ collisions in the (left) forward and (right)
backward collision samples. The uncertainty is the quadratic sum of the
statistical and systematic components.

Figure 4: Differential cross-section of prompt ${{D}^{0}}$ meson production in
${p\mathrm{Pb}}$ collisions as a function of (left) $p_{\mathrm{T}}$
($\frac{\mathrm{d}\sigma}{\mathrm{d}p_{\rm T}}$) and (right) $y^{*}$
($\frac{\mathrm{d}\sigma}{\mathrm{d}y^{*}}$) in the forward and backward
collision samples. The uncertainty is the quadratic sum of the statistical and
systematic components. The measurements are compared with theoretical
predictions including different nuclear parton distribution functions as
explained in the text.

Table 3: Measured differential cross-section
$\frac{\mathrm{d}\sigma}{\mathrm{d}p_{\mathrm{T}}}$
(mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$)) for prompt ${{D}^{0}}$ meson
production as a function of $p_{\mathrm{T}}$ in ${p\mathrm{Pb}}$ forward and
backward data, respectively. The first uncertainty is statistical, the second
is the component of the systematic uncertainty that is uncorrelated between
bins and the third is the correlated component. The results in the last two
columns are integrated over the common rapidity range $2.5<|y^{*}|<4.0$ for
$\mbox{$p_{\mathrm{T}}$}<6{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and over
$2.5<|y^{*}|<3.5$ for
$6<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$.

| Forward (mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$))
---|---
$\mbox{$p_{\mathrm{T}}$}[{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}]$ | $1.5<y^{*}<4.0$ | $2.5<y^{*}<4.0$ | $2.5<y^{*}<3.5$
$[0,1]$ | $54.38\pm 0.29\pm 0.36\pm 3.96$ | $30.31\pm 0.22\pm 0.22\pm 1.59$ | $-$
$[1,2]$ | $83.54\pm 0.30\pm 0.45\pm 5.01$ | $43.92\pm 0.22\pm 0.28\pm 2.17$ | $-$
$[2,3]$ | $49.72\pm 0.16\pm 0.27\pm 2.45$ | $25.11\pm 0.11\pm 0.16\pm 1.11$ | $-$
$[3,4]$ | $22.91\pm 0.09\pm 0.14\pm 1.10$ | $11.13\pm 0.06\pm 0.08\pm 0.55$ | $-$
$[4,5]$ | $10.43\pm 0.06\pm 0.08\pm 0.54$ | $\phantom{0}4.92\pm 0.04\pm 0.05\pm 0.32$ | $-$
$[5,6]$ | $\phantom{0}4.95\pm 0.05\pm 0.06\pm 0.35$ | $\phantom{0}2.21\pm 0.04\pm 0.04\pm 0.26$ | $-$
$[6,7]$ | $\phantom{0}2.37\pm 0.05\pm 0.04\pm 0.21$ | $-$ | $\phantom{0}0.88\pm 0.01\pm 0.01\pm 0.07$
$[7,8]$ | $\phantom{0}1.20\pm 0.02\pm 0.02\pm 0.09$ | $-$ | $\phantom{0}0.45\pm 0.01\pm 0.01\pm 0.06$
$[8,9]$ | $\phantom{0}0.67\pm 0.01\pm 0.01\pm 0.06$ | $-$ | $\phantom{0}0.24\pm 0.01\pm 0.01\pm 0.04$
$[9,10]$ | $\phantom{0}0.39\pm 0.01\pm 0.01\pm 0.04$ | $-$ | $\phantom{0}0.08\pm 0.00\pm 0.00\pm 0.01$
| Backward (mb/(${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$))
$\mbox{$p_{\mathrm{T}}$}[{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}]$ | $-5.0<y^{*}<-2.5$ | $-4.0<y^{*}<-2.5$ | $-3.5<y^{*}<-2.5$
$[0,1]$ | $65.83\pm 0.70\pm 0.40\pm 6.85$ | $42.89\pm 0.35\pm 0.31\pm 5.15$ | $-$
$[1,2]$ | $97.97\pm 0.68\pm 0.52\pm 8.30$ | $66.56\pm 0.36\pm 0.43\pm 5.80$ | $-$
$[2,3]$ | $52.43\pm 0.32\pm 0.29\pm 3.57$ | $37.96\pm 0.20\pm 0.25\pm 2.56$ | $-$
$[3,4]$ | $21.21\pm 0.14\pm 0.13\pm 1.45$ | $16.23\pm 0.10\pm 0.11\pm 1.01$ | $-$
$[4,5]$ | $\phantom{0}8.62\pm 0.09\pm 0.06\pm 0.62$ | $\phantom{0}6.78\pm 0.05\pm 0.05\pm 0.41$ | $-$
$[5,6]$ | $\phantom{0}3.61\pm 0.08\pm 0.04\pm 0.33$ | $\phantom{0}2.92\pm 0.03\pm 0.03\pm 0.18$ | $-$
$[6,7]$ | $\phantom{0}1.57\pm 0.03\pm 0.02\pm 0.12$ | $-$ | $\phantom{0}1.12\pm 0.02\pm 0.02\pm 0.07$
$[7,8]$ | $\phantom{0}0.81\pm 0.02\pm 0.01\pm 0.09$ | $-$ | $\phantom{0}0.57\pm 0.01\pm 0.01\pm 0.04$
$[8,9]$ | $\phantom{0}0.41\pm 0.02\pm 0.01\pm 0.07$ | $-$ | $\phantom{0}0.29\pm 0.01\pm 0.01\pm 0.02$
$[9,10]$ | $\phantom{0}0.22\pm 0.01\pm 0.01\pm 0.02$ | $-$ | $\phantom{0}0.11\pm 0.01\pm 0.01\pm 0.01$

Table 4: Differential cross-section $\frac{\mathrm{d}\sigma}{\mathrm{d}y^{*}}$
(mb) for prompt ${{D}^{0}}$ meson production as a function of $|y^{*}|$ in
${p\mathrm{Pb}}$ forward and backward data, respectively. The first
uncertainty is statistical, the second is the component of the systematic
uncertainty that is uncorrelated between bins and the third is the correlated
component. Forward (mb)
---
$y^{*}$ | $0<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$
$[1.5,2.0]$ | $115.19\pm 0.53\pm 0.91\pm 9.99$
$[2.0,2.5]$ | $107.05\pm 0.29\pm 0.50\pm 5.73$
$[2.5,3.0]$ | $\phantom{0}93.90\pm 0.27\pm 0.38\pm 4.14$
$[3.0,3.5]$ | $\phantom{0}80.76\pm 0.33\pm 0.42\pm 3.71$
$[3.5,4.0]$ | $\phantom{0}64.24\pm 0.55\pm 0.58\pm 4.79$
Backward (mb)
$y^{*}$ | $0<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$
$[-3.0,-2.5]$ | $126.35\pm 0.78\pm 0.95\pm 15.54$
$[-3.5,-3.0]$ | $120.84\pm 0.53\pm 0.53\pm\phantom{0}8.89$
$[-4.0,-3.5]$ | $104.93\pm 0.58\pm 0.47\pm\phantom{0}6.66$
$[-4.5,-4.0]$ | $\phantom{0}87.92\pm 0.85\pm 0.52\pm\phantom{0}6.13$
$[-5.0,-4.5]$ | $\phantom{0}65.32\pm 1.57\pm 0.68\pm\phantom{0}7.07$

The integrated cross-sections of prompt ${{D}^{0}}$ meson production in
${p\mathrm{Pb}}$ forward data in the full and common fiducial regions are

$\sigma_{\mathrm{forward}}(\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c},1.5<y^{*}<4.0)=230.6\pm
0.5\pm 13.0\mathrm{\,mb},$

$\sigma_{\mathrm{forward}}(\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c},2.5<y^{*}<4.0)=119.1\pm
0.3\pm\phantom{0}5.6\mathrm{\,mb}.$

The integrated cross-sections of prompt ${{D}^{0}}$ meson production in Pb$p$
backward data in the two fiducial regions are

$\sigma_{\mathrm{backward}}(\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c},-2.5<y^{*}<-5.0)=252.7\pm
1.0\pm 20.0\mathrm{\,mb},$

$\sigma_{\mathrm{backward}}(\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c},-2.5<y^{*}<-4.0)=175.5\pm
0.6\pm 14.4\mathrm{\,mb},$

where the first uncertainties are statistical and the second systematic.

The cross-sections as a function of $p_{\mathrm{T}}$ and $y^{*}$, shown in
Fig. 4, are compared with calculations [57, 58, 59] validated with results of
heavy-flavour production cross-section in $pp$ collisions. The nuclear effects
are considered by using three different sets of nuclear parton distribution
functions (nPDFs), the leading-order EPS09 (EPS09LO) [60], the next-to-leading
order EPS09 (EPS09NLO) [60] and nCTEQ15 [61]. The free nucleon PDF CT10NLO
[62] is also used as a reference for the cross-section predictions in $pp$
collisions. Within large theoretical uncertainties, all three sets of nPDFs
can give descriptions consistent with the LHCb data, although a discrepancy is
observed in the low $p_{\mathrm{T}}$ region between the measurements and the
nCTEQ15 predictions.

###  5.2 Nuclear modification factors

The value of the ${{D}^{0}}$ meson production cross-section in $pp$ collisions
at $5\mathrm{\,Te\kern-1.00006ptV}$, needed for the measurement of the nuclear
modification factor $R_{{p\mathrm{Pb}}}$, is taken from the LHCb measurement
[63]. Correlations between the uncertainties of quantities that are common to
both measurements are taken into account. The nuclear modification factor for
prompt ${{D}^{0}}$ meson production is shown in Fig. 5 in bins of
$p_{\mathrm{T}}$ and Fig. 6 in bins of $y^{*}$. The nuclear modification
factors are calculated as a function of $p_{\mathrm{T}}$ integrated over
$y^{*}$ in the ranges described in Fig. 5 for both forward and backward
samples. The values of $R_{{p\mathrm{Pb}}}$, summarised in Tables 5.1 and 5.1,
show a slight increase as a function of $p_{\mathrm{T}}$, suggesting that the
suppression may decrease with increasing transverse momentum.

Figure 5: Nuclear modification factor $R_{{p\mathrm{Pb}}}$ as a function of
$p_{\mathrm{T}}$ for prompt ${{D}^{0}}$ meson production in the (left)
backward data and (right) forward data, integrated over the common rapidity
range $2.5<|y^{*}|<4.0$ for
$\mbox{$p_{\mathrm{T}}$}<6{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and over
$2.5<|y^{*}|<3.5$ for
$6<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The
uncertainty is the quadratic sum of the statistical and systematic components.
The CGC predictions are only available for the forward region.

Figure 6: Nuclear modification factor $R_{{p\mathrm{Pb}}}$ as a function of
$y^{*}$ for prompt ${{D}^{0}}$ meson production, integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The
uncertainty is the quadratic sum of the statistical and systematic components.

The measurements are compared with calculations using EPS09LO, EPSNLO and
nCTEQ15 nPDFs [58, 57, 59]. For the results in the backward configuration, all
three predictions show reasonable agreement with each other and with LHCb
data. In the forward configuration, nCTEQ15 and EPS09LO show better agreement
with the data than EPS09NLO. Calculations [64] using CTEQ6M [65] nucleon PDF
and EPS09NLO nPDF give results for $R_{{p\mathrm{Pb}}}$ that are similar to a
combination of CT10NLO and EPS09NLO.

The nuclear modification factors for prompt $D^{0}$ are also compared with
those for prompt ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ [43] in Fig.
6 as a function of $p_{\mathrm{T}}$ integrated over rapidity, and they are
found to be consistent. This is the first measurement of $R_{{p\mathrm{Pb}}}$
in this kinematic range. The ratios of the nuclear modification factors of
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ and ${\psi{(2S)}}$ mesons to
${{D}^{0}}$ mesons as a function of rapidity are shown in Fig. 7 where a
different suppression between the two charmonium states can be observed. In
Figs. 5 and 6 the measurements are also compared with calculations in the
colour glass condensate framework (CGC) [66], which includes the effect of the
saturation of partons at small $x$. The CGC model is found to be able to
describe the trend of prompt ${{D}^{0}}$ meson nuclear modifications as a
function of $p_{\mathrm{T}}$ and of rapidity. The uncertainty band for this
model is much smaller than for the nuclear PDF calculations, since it only
contains the variation of charm quark masses and factorisation scale which
largely cancel in this ratio of cross-sections. Another CGC framework
calculation gives similar results for nuclear modifications of charm
production [67]. In the context of $p$Pb collisions, recent measurements have
shown that long-range collective effects, which have previously been observed
in relatively large nucleus-nucleus collision systems, may also be present in
smaller collision systems at large charged particle multiplicities [68, 69,
70, 71]. If these effects are due to the creation of a hydrodynamic system,
momentum anisotropies at the quark level can arise, which may modify the final
distribution of observed heavy-quark hadrons [72]. Since the measurements in
this analysis do not consider a classification in charged particle
multiplicity, potential modifications in high-multiplicity events are weakened
as the presented observables are integrated over charged particle
multiplicity.

Table 6: Nuclear modification factor $R_{{p\mathrm{Pb}}}$ for prompt
${{D}^{0}}$ meson production in different $y^{*}$ ranges, integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The first
uncertainty is statistical and the second systematic.

###  5.3 Forward-backward ratio

In the forward-backward production ratio $R_{\mathrm{FB}}$ the common
uncertainty between the forward and backward measurements largely cancels. The
uncertainties of branching fraction, signal yield and tracking are considered
fully correlated, while the PID uncertainty is considered 90% correlated since
it is a mixture of statistical uncertainty (uncorrelated) and the
uncertainties due to the binning scheme and yield determination (correlated).
All other uncertainties are uncorrelated. The measured $R_{\mathrm{FB}}$
values are shown in Fig. 8, as a function of $p_{\mathrm{T}}$ integrated over
the range $2.5<|y^{*}|<4.0$, and as a function of $y^{*}$ integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The
$R_{\mathrm{FB}}$ values in different kinematic bins are also summarised in
Table 5.3. Good agreement is found between measurements and theoretical
predictions using EPS09LO and nCTEQ15 nPDFs.

Table 7: Forward-backward ratio $R_{\mathrm{FB}}$ for prompt ${{D}^{0}}$ meson
production in different $p_{\mathrm{T}}$ ranges, integrated over the common
rapidity range $2.5<|y^{*}|<4.0$ for
$\mbox{$p_{\mathrm{T}}$}<6{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and over
$2.5<|y^{*}|<3.5$ for
$6<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, and in
different $y^{*}$ ranges integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The first
uncertainty is the statistical and the second is the systematic component.

In the common kinematic range
$\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$,
$2.5<|y^{*}|<4.0$, the forward-backward ratio $R_{\mathrm{FB}}$ is $0.71\pm
0.01(\mathrm{stat})\pm 0.04(\mathrm{syst})$, indicating a significant
asymmetry. The predictions for $R_{\mathrm{FB}}$ integrated over the same
kinematic range are $0.71^{+0.21}_{-0.24}$ for EPS09 at leading order,
$0.81^{+0.10}_{-0.09}$ for EPS09 at next-to-leading order and
$0.69^{+0.07}_{-0.07}$ for the nCTEQ15 nPDF set, which are all in good
agreement with the measured value. The forward-backward production ratio
increases slightly with increasing $p_{\mathrm{T}}$, and decreases strongly
with increasing rapidity $|y^{*}|$. This behaviour is consistent with the
expectations from the QCD calculations.

In order to compare the production of open charm and charmonium, the ratio of
$R_{\mathrm{FB}}$ for prompt ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$
mesons divided by $R_{\mathrm{FB}}$ for prompt ${{D}^{0}}$ mesons is shown in
Fig. 9. The measurement shows that $R_{\mathrm{FB}}$ has the same size for
prompt ${{D}^{0}}$ and prompt ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$
mesons within the uncertainties in the LHCb kinematic range.

Figure 7: Ratio of nuclear modification factors $R_{{p\mathrm{Pb}}}$ of
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ and ${\psi{(2S)}}$ to
${{D}^{0}}$ mesons in bins of rapidity integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ in the common
rapidity range $2.5<|y^{*}|<4.0$. The uncertainty is the quadratic sum of the
statistical and systematic components.

Figure 8: Forward-backward ratio $R_{\mathrm{FB}}$ for prompt ${{D}^{0}}$
meson production (left) as a function of $p_{\mathrm{T}}$ integrated over the
common rapidity range $2.5<|y^{*}|<4.0$ for
$\mbox{$p_{\mathrm{T}}$}<6{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and over
$2.5<|y^{*}|<3.5$ for
$6<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$; (right) as
a function of $y^{*}$ integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The
uncertainty is the quadratic sum of the statistical and systematic components.

Figure 9:  Relative forward-backward production ratio $R_{\mathrm{FB}}$ for
prompt ${{D}^{0}}$ mesons over that for prompt
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ mesons (left) as a function
of $p_{\mathrm{T}}$ integrated over the common rapidity range
$2.5<|y^{*}|<4.0$ for
$\mbox{$p_{\mathrm{T}}$}<6{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and over
$2.5<|y^{*}|<3.5$ for
$6<\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$; (right) as
a function of $y^{*}$ integrated up to
$\mbox{$p_{\mathrm{T}}$}=10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The red
inner bars in the uncertainty represent the statistical uncertainty and the
black outer bars the quadratic sum of the statistical and systematic
components.

##  6 Conclusion

The prompt ${{D}^{0}}$ production cross-section has been measured with LHCb
proton-lead collision data at
${\sqrt{s_{\mathrm{NN}}}}=5\mathrm{\,Te\kern-1.00006ptV}$. The measurement is
performed in the range of ${D}^{0}$ transverse momentum
$\mbox{$p_{\mathrm{T}}$}<10{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, in both
backward and forward collisions covering the ranges $1.5<y^{\ast}<4.0$ and
$-5.0<y^{\ast}<-2.5$. This is the first measurement of this kind down to zero
transverse momentum of the ${D}^{0}$ meson. Nuclear modification factors and
forward-backward production ratios are also measured in the same kinematic
range. Both observables are excellent probes to constrain the PDF
uncertainties, which are currently significantly larger than the uncertainties
on the experimental results. A large asymmetry in the forward-backward
production is observed, which is consistent with the expectations from nuclear
parton distribution functions, and colour glass condensate calculations for
the forward rapidity part. The results are found to be consistent with the
theoretical predictions considered.

## Acknowledgements

We would like to thank Andrea Dainese, Bertrand Ducloué, Jean-Philippe
Lansberg and Huasheng Shao for providing the theoretical predictions for our
measurements. We express our gratitude to our colleagues in the CERN
accelerator departments for the excellent performance of the LHC. We thank the
technical and administrative staff at the LHCb institutes. We acknowledge
support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and
FINEP (Brazil); MOST and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG
(Germany); INFN (Italy); NWO (The Netherlands); MNiSW and NCN (Poland);
MEN/IFA (Romania); MinES and FASO (Russia); MinECo (Spain); SNSF and SER
(Switzerland); NASU (Ukraine); STFC (United Kingdom); NSF (USA). We
acknowledge the computing resources that are provided by CERN, IN2P3 (France),
KIT and DESY (Germany), INFN (Italy), SURF (The Netherlands), PIC (Spain),
GridPP (United Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland),
IFIN-HH (Romania), CBPF (Brazil), PL-GRID (Poland) and OSC (USA). We are
indebted to the communities behind the multiple open source software packages
on which we depend. Individual groups or members have received support from
AvH Foundation (Germany), EPLANET, Marie Skłodowska-Curie Actions and ERC
(European Union), Conseil Général de Haute-Savoie, Labex ENIGMASS and OCEVU,
Région Auvergne (France), RFBR and Yandex LLC (Russia), GVA, XuntaGal and
GENCAT (Spain), Herchel Smith Fund, The Royal Society, Royal Commission for
the Exhibition of 1851 and the Leverhulme Trust (United Kingdom).

## References

  * [1] B. A. Kniehl, G. Kramer, I. Schienbein, and H. Spiesberger, _Reconciling open charm production at the Fermilab Tevatron with QCD_ , Phys. Rev. Lett. 96 (2006) 012001, arXiv:hep-ph/0508129
  * [2] B. A. Kniehl, G. Kramer, I. Schienbein, and H. Spiesberger, _Inclusive charmed-meson production at the CERN LHC_ , Eur. Phys. J. C72 (2012) 2082, arXiv:1202.0439
  * [3] M. Cacciari, M. Greco, and P. Nason, _The $p_{T}$ spectrum in heavy flavor hadroproduction_, JHEP 05 (1998) 007, arXiv:hep-ph/9803400
  * [4] M. Cacciari and P. Nason, _Charm cross-sections for the Tevatron Run II_ , JHEP 09 (2003) 006, arXiv:hep-ph/0306212
  * [5] M. Cacciari et al., _Theoretical predictions for charm and bottom production at the LHC_ , JHEP 10 (2012) 137, arXiv:1205.6344
  * [6] R. Maciula and A. Szczurek, _Open charm production at the LHC: $k_{t}$-factorization approach_, Phys. Rev. D87 (2013) 094022, arXiv:1301.3033
  * [7] A. Andronic et al., _Heavy-flavour and quarkonium production in the LHC era: from proton-proton to heavy-ion collisions_ , Eur. Phys. J. C76 (2016) 107, arXiv:1506.03981
  * [8] D. Kharzeev and K. Tuchin, _Signatures of the color glass condensate in $J/\psi$ production off nuclear targets_, Nucl. Phys. A770 (2006) 40, arXiv:hep-ph/0510358
  * [9] H. Fujii, F. Gelis, and R. Venugopalan, _Quark pair production in high energy pA collisions: General features_ , Nucl. Phys. A780 (2006) 146, arXiv:hep-ph/0603099
  * [10] F. Arleo and S. Peigné, _Heavy-quarkonium suppression in p-A collisions from parton energy loss in cold QCD matter_ , JHEP 03 (2013) 122, arXiv:1212.0434
  * [11] S. Gavin and J. Milana, _Energy loss at large $x_{F}$ in nuclear collisions_, Phys. Rev. Lett. 68 (1992) 1834
  * [12] R. Vogt, _The $x_{F}$ dependence of $\psi$ and Drell-Yan production_, Phys. Rev. C61 (2000) 035203, arXiv:hep-ph/9907317
  * [13] N. Armesto, _Nuclear shadowing_ , J. Phys. G32 (2006) R367, arXiv:hep-ph/0604108
  * [14] S. Malace, D. Gaskell, D. W. Higinbotham, and I. Cloet, _The challenge of the EMC effect: Existing data and future directions_ , Int. J. Mod. Phys. E23 (2014) 1430013, arXiv:1405.1270
  * [15] H. Fujii and K. Watanabe, _Heavy quark pair production in high energy pA collisions: Open heavy flavors_ , Nucl. Phys. A920 (2013) 78, arXiv:1308.1258
  * [16] P. Tribedy and R. Venugopalan, _QCD saturation at the LHC: Comparisons of models to p + p and A + A data and predictions for p + Pb collisions_ , Phys. Lett. B710 (2012) 125, arXiv:1112.2445, [Erratum: Phys. Lett.B718 (2013) 1154]
  * [17] J. L. Albacete, A. Dumitru, H. Fujii, and Y. Nara, _CGC predictions for p + Pb collisions at the LHC_ , Nucl. Phys. A897 (2013) 1, arXiv:1209.2001
  * [18] A. H. Rezaeian, _CGC predictions for p+A collisions at the LHC and signature of QCD saturation_ , Phys. Lett. B718 (2013) 1058, arXiv:1210.2385
  * [19] ALICE collaboration, B. Abelev et al., _Suppression of high transverse momentum D mesons in central Pb-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=2.76\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 09 (2012) 112, arXiv:1203.2160
  * [20] R. Averbeck, _Heavy-flavor production in heavy-ion collisions and implications for the properties of hot QCD matter_ , Prog. Part. Nucl. Phys. 70 (2013) 159, arXiv:1505.03828
  * [21] ALICE collaboration, D. Adamova et al., _$J/\psi$ production as a function of charged-particle pseudorapidity density in pPb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, arXiv:1704.00274
  * [22] ALICE collaboration, J. Adam et al., _$D$ -meson production in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$ and in pp collisions at $\sqrt{s}=7\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Rev. C94 (2016) 054908, arXiv:1605.07569
  * [23] ALICE collaboration, J. Adam et al., _Centrality dependence of $\mathbf{\psi}$(2S) suppression in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 06 (2016) 050, arXiv:1603.02816
  * [24] ALICE collaboration, J. Adam et al., _Measurement of D-meson production versus multiplicity in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 08 (2016) 078, arXiv:1602.07240
  * [25] ALICE collaboration, J. Adam et al., _Centrality dependence of inclusive $J/\psi$ production in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 11 (2015) 127, arXiv:1506.08808
  * [26] ALICE collaboration, J. Adam et al., _Rapidity and transverse-momentum dependence of the inclusive J/ $\psi$ nuclear modification factor in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\,\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 06 (2015) 055, arXiv:1503.07179
  * [27] ALICE collaboration, B. B. Abelev et al., _Production of inclusive $\Upsilon$(1S) and $\Upsilon$(2S) in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Lett. B740 (2015) 105, arXiv:1410.2234
  * [28] ALICE collaboration, B. B. Abelev et al., _Measurement of prompt $D$-meson production in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Rev. Lett. 113 (2014) 232301, arXiv:1405.3452
  * [29] ALICE collaboration, B. B. Abelev et al., _$J/\psi$ production and nuclear effects in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 02 (2014) 073, arXiv:1308.6726
  * [30] ALICE collaboration, B. B. Abelev et al., _Suppression of $\psi$(2S) production in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\,\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 12 (2014) 073, arXiv:1405.3796
  * [31] ATLAS collaboration, G. Aad et al., _Measurement of differential $J/\psi$ production cross sections and forward-backward ratios in p Pb collisions with the ATLAS detector_, Phys. Rev. C92 (2015) 034904, arXiv:1505.08141
  * [32] CMS collaboration, S. Chatrchyan et al., _Event activity dependence of Y(nS) production in ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$ $p$Pb and $\sqrt{s}=2.76\mathrm{\,Te\kern-1.00006ptV}$ $pp$ collisions_, JHEP 04 (2014) 103, arXiv:1312.6300
  * [33] CMS collaboration, A. M. Sirunyan et al., _Measurement of prompt and nonprompt $\mathrm{J}/{\psi}$ production in $\mathrm{p}\mathrm{p}$ and $\mathrm{p}\mathrm{Pb}$ collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Eur. Phys. J. C77 (2017) 269, arXiv:1702.01462
  * [34] CMS collaboration, A. M. Sirunyan et al., _Measurements of the charm jet cross section and nuclear modification factor in pPb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, arXiv:1612.08972
  * [35] CMS collaboration, V. Khachatryan et al., _Transverse momentum spectra of inclusive b jets in pPb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Lett. B754 (2016) 59, arXiv:1510.03373
  * [36] CMS collaboration, V. Khachatryan et al., _Study of B meson production in pPb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02 \mathrm{\,Te\kern-1.00006ptV}$ using exclusive hadronic decays_, Phys. Rev. Lett. 116 (2016) 032301, arXiv:1508.06678
  * [37] ALICE collaboration, J. Adam et al., _Measurement of electrons from heavy-flavour hadron decays in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Lett. B754 (2016) 81, arXiv:1509.07491
  * [38] ALICE collaboration, J. Adam et al., _Measurement of electrons from beauty-hadron decays in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$ and Pb-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=2.76$ $\mathrm{\,Te\kern-1.00006ptV}$_, arXiv:1609.03898
  * [39] ALICE collaboration, S. Acharya et al., _Production of muons from heavy-flavour hadron decays in p-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Lett. B770 (2017) 459, arXiv:1702.01479
  * [40] LHCb collaboration, A. A. Alves Jr. et al., _The LHCb detector at the LHC_, JINST 3 (2008) S08005
  * [41] LHCb collaboration, R. Aaij et al., _LHCb detector performance_ , Int. J. Mod. Phys. A30 (2015) 1530022, arXiv:1412.6352
  * [42] R. Aaij et al., _The LHCb trigger and its performance in 2011_, JINST 8 (2013) P04022, arXiv:1211.3055
  * [43] LHCb collaboration, R. Aaij et al., _Study of ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ production and cold nuclear matter effects in ${p}$Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5\,\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 02 (2014) 072, arXiv:1308.6729
  * [44] T. Sjöstrand, S. Mrenna, and P. Skands, _PYTHIA 6.4 physics and manual_ , JHEP 05 (2006) 026, arXiv:hep-ph/0603175
  * [45] T. Sjöstrand, S. Mrenna, and P. Skands, _A brief introduction to PYTHIA 8.1_ , Comput. Phys. Commun. 178 (2008) 852, arXiv:0710.3820
  * [46] I. Belyaev et al., _Handling of the generation of primary events in Gauss, the LHCb simulation framework_ , J. Phys. Conf. Ser. 331 (2011) 032047
  * [47] D. J. Lange, _The EvtGen particle decay simulation package_ , Nucl. Instrum. Meth. A462 (2001) 152
  * [48] P. Golonka and Z. Was, _PHOTOS Monte Carlo: A precision tool for QED corrections in $Z$ and $W$ decays_, Eur. Phys. J. C45 (2006) 97, arXiv:hep-ph/0506026
  * [49] Geant4 collaboration, J. Allison et al., _Geant4 developments and applications_ , IEEE Trans. Nucl. Sci. 53 (2006) 270
  * [50] Geant4 collaboration, S. Agostinelli et al., _Geant4: A simulation toolkit_ , Nucl. Instrum. Meth. A506 (2003) 250
  * [51] M. Clemencic et al., _The LHCb simulation application, Gauss: Design, evolution and experience_, J. Phys. Conf. Ser. 331 (2011) 032023
  * [52] Particle Data Group, C. Patrignani et al., _Review of particle physics_ , Chin. Phys. C40 (2016) 100001
  * [53] LHCb collaboration, R. Aaij et al., _Prompt charm production in ${p}{p}$ collisions at $\sqrt{s}=7$$\mathrm{\,Te\kern-1.00006ptV}$_, Nucl. Phys. B871 (2013) 1, arXiv:1302.2864
  * [54] LHCb collaboration, R. Aaij et al., _Measurements of prompt charm production cross-sections in ${p}{p}$ collisions at $\sqrt{s}=13\,$$\mathrm{\,Te\kern-1.00006ptV}$_, JHEP 03 (2016) 159, arXiv:1510.01707
  * [55] T. Skwarnicki, A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, DESY-F31-86-02
  * [56] LHCb collaboration, R. Aaij et al., _Measurement of the track reconstruction efficiency at LHCb_ , JINST 10 (2015) P02007, arXiv:1408.1251
  * [57] J.-P. Lansberg and H.-S. Shao, _Towards an automated tool to evaluate the impact of the nuclear modification of the gluon density on quarkonium, D and B meson production in proton-nucleus collisions_ , Eur. Phys. J. C77 (2017) 1, arXiv:1610.05382
  * [58] H.-S. Shao, _HELAC-Onia: An automatic matrix element generator for heavy quarkonium physics_ , Comput. Phys. Commun. 184 (2013) 2562, arXiv:1212.5293
  * [59] H.-S. Shao, _HELAC-Onia 2.0: an upgraded matrix-element and event generator for heavy quarkonium physics_ , Comput. Phys. Commun. 198 (2016) 238, arXiv:1507.03435
  * [60] K. J. Eskola, H. Paukkunen, and C. A. Salgado, _EPS09: a new generation of NLO and LO nuclear parton distribution functions_ , JHEP 04 (2009) 065, arXiv:0902.4154
  * [61] K. Kovarik et al., _nCTEQ15 - Global analysis of nuclear parton distributions with uncertainties in the CTEQ framework_ , Phys. Rev. D93 (2016) 085037, arXiv:1509.00792
  * [62] H.-L. Lai et al., _New parton distributions for collider physics_ , Phys. Rev. D82 (2010) 074024, arXiv:1007.2241
  * [63] LHCb collaboration, R. Aaij et al., _Measurements of prompt charm production cross-sections in ${p}{p}$ collisions at $\sqrt{s}=5$ $\mathrm{\,Te\kern-1.00006ptV}$_, arXiv:1610.02230, submitted to JHEP
  * [64] M. L. Mangano, P. Nason, and G. Ridolfi, _Heavy quark correlations in hadron collisions at next-to-leading order_ , Nucl. Phys. B373 (1992) 295
  * [65] D. Stump et al., _Inclusive jet production, parton distributions, and the search for new physics_ , JHEP 10 (2003) 046, arXiv:hep-ph/0303013
  * [66] B. Ducloué, T. Lappi, and H. Mäntysaari, _Forward $J/\psi$ production in proton-nucleus collisions at high energy_, Phys. Rev. D91 (2015) 114005, arXiv:1503.02789
  * [67] H. Fujii and K. Watanabe, _Nuclear modification of forward $D$ production in pPb collisions at the LHC_, arXiv:1706.06728
  * [68] CMS collaboration, S. Chatrchyan et al., _Observation of long-range near-side angular correlations in proton-lead collisions at the LHC_ , Phys. Lett. B718 (2013) 795, arXiv:1210.5482
  * [69] ALICE collaboration, B. Abelev et al., _Long-range angular correlations on the near and away side in $p$-Pb collisions at ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$_, Phys. Lett. B719 (2013) 29, arXiv:1212.2001
  * [70] ATLAS collaboration, G. Aad et al., _Observation of associated near-side and away-side long-range correlations in ${\sqrt{s_{\mathrm{NN}}}}=5.02\mathrm{\,Te\kern-1.00006ptV}$ proton-lead collisions with the ATLAS detector_, Phys. Rev. Lett. 110 (2013) 182302, arXiv:1212.5198
  * [71] PHENIX collaboration, A. Adare et al., _Quadrupole anisotropy in dihadron azimuthal correlations in central $d$$+$Au collisions at ${\sqrt{s_{\mathrm{NN}}}}$=200 GeV_, Phys. Rev. Lett. 111 (2013) 212301, arXiv:1303.1794
  * [72] A. Beraudo et al., _Heavy-flavour production in high-energy d-Au and p-Pb collisions_ , JHEP 03 (2016) 123, arXiv:1512.05186

LHCb collaboration

R. Aaij40, B. Adeva39, M. Adinolfi48, Z. Ajaltouni5, S. Akar59, J. Albrecht10,
F. Alessio40, M. Alexander53, A. Alfonso Albero38, S. Ali43, G. Alkhazov31, P.
Alvarez Cartelle55, A.A. Alves Jr59, S. Amato2, S. Amerio23, Y. Amhis7, L.
An3, L. Anderlini18, G. Andreassi41, M. Andreotti17,g, J.E. Andrews60, R.B.
Appleby56, F. Archilli43, P. d’Argent12, J. Arnau Romeu6, A. Artamonov37, M.
Artuso61, E. Aslanides6, G. Auriemma26, M. Baalouch5, I. Babuschkin56, S.
Bachmann12, J.J. Back50, A. Badalov38, C. Baesso62, S. Baker55, V.
Balagura7,c, W. Baldini17, A. Baranov35, R.J. Barlow56, C. Barschel40, S.
Barsuk7, W. Barter56, F. Baryshnikov32, M. Baszczyk27,l, V. Batozskaya29, V.
Battista41, A. Bay41, L. Beaucourt4, J. Beddow53, F. Bedeschi24, I. Bediaga1,
A. Beiter61, L.J. Bel43, N. Beliy63, V. Bellee41, N. Belloli21,i, K. Belous37,
I. Belyaev32, E. Ben-Haim8, G. Bencivenni19, S. Benson43, S. Beranek9, A.
Berezhnoy33, R. Bernet42, D. Berninghoff12, E. Bertholet8, A. Bertolin23, C.
Betancourt42, F. Betti15, M.-O. Bettler40, M. van Beuzekom43, Ia. Bezshyiko42,
S. Bifani47, P. Billoir8, A. Birnkraut10, A. Bitadze56, A. Bizzeti18,u, M.B.
Bjoern57, T. Blake50, F. Blanc41, J. Blouw11,†, S. Blusk61, V. Bocci26, T.
Boettcher58, A. Bondar36,w, N. Bondar31, W. Bonivento16, I. Bordyuzhin32, A.
Borgheresi21,i, S. Borghi56, M. Borisyak35, M. Borsato39, M. Borysova46, F.
Bossu7, M. Boubdir9, T.J.V. Bowcock54, E. Bowen42, C. Bozzi17,40, S. Braun12,
T. Britton61, J. Brodzicka56, D. Brundu16, E. Buchanan48, C. Burr56, A.
Bursche16,f, J. Buytaert40, W. Byczynski40, S. Cadeddu16, H. Cai64, R.
Calabrese17,g, R. Calladine47, M. Calvi21,i, M. Calvo Gomez38,m, A. Camboni38,
P. Campana19, D.H. Campora Perez40, L. Capriotti56, A. Carbone15,e, G.
Carboni25,j, R. Cardinale20,h, A. Cardini16, P. Carniti21,i, L. Carson52, K.
Carvalho Akiba2, G. Casse54, L. Cassina21,i, L. Castillo Garcia41, M.
Cattaneo40, G. Cavallero20,40,h, R. Cenci24,t, D. Chamont7, M. Charles8, Ph.
Charpentier40, G. Chatzikonstantinidis47, M. Chefdeville4, S. Chen56, S.F.
Cheung57, S.-G. Chitic40, V. Chobanova39, M. Chrzaszcz42,27, A. Chubykin31, X.
Cid Vidal39, G. Ciezarek43, P.E.L. Clarke52, M. Clemencic40, H.V. Cliff49, J.
Closier40, V. Coco59, J. Cogan6, E. Cogneras5, V. Cogoni16,f, L. Cojocariu30,
P. Collins40, T. Colombo40, A. Comerma-Montells12, A. Contu40, A. Cook48, G.
Coombs40, S. Coquereau38, G. Corti40, M. Corvo17,g, C.M. Costa Sobral50, B.
Couturier40, G.A. Cowan52, D.C. Craik52, A. Crocombe50, M. Cruz Torres62, R.
Currie52, C. D’Ambrosio40, F. Da Cunha Marinho2, E. Dall’Occo43, J. Dalseno48,
A. Davis3, O. De Aguiar Francisco54, K. De Bruyn6, S. De Capua56, M. De
Cian12, J.M. De Miranda1, L. De Paula2, M. De Serio14,d, P. De Simone19, C.T.
Dean53, D. Decamp4, L. Del Buono8, H.-P. Dembinski11, M. Demmer10, A.
Dendek28, D. Derkach35, O. Deschamps5, F. Dettori54, B. Dey65, A. Di Canto40,
P. Di Nezza19, H. Dijkstra40, F. Dordei40, M. Dorigo41, A. Dosil Suárez39, L.
Douglas53, A. Dovbnya45, K. Dreimanis54, L. Dufour43, G. Dujany8, K. Dungs40,
P. Durante40, R. Dzhelyadin37, M. Dziewiecki12, A. Dziurda40, A. Dzyuba31, N.
Déléage4, S. Easo51, M. Ebert52, U. Egede55, V. Egorychev32, S. Eidelman36,w,
S. Eisenhardt52, U. Eitschberger10, R. Ekelhof10, L. Eklund53, S. Ely61, S.
Esen12, H.M. Evans49, T. Evans57, A. Falabella15, N. Farley47, S. Farry54, R.
Fay54, D. Fazzini21,i, L. Federici25, D. Ferguson52, G. Fernandez38, P.
Fernandez Declara40, A. Fernandez Prieto39, F. Ferrari15, F. Ferreira
Rodrigues2, M. Ferro-Luzzi40, S. Filippov34, R.A. Fini14, M. Fiore17,g, M.
Fiorini17,g, M. Firlej28, C. Fitzpatrick41, T. Fiutowski28, F. Fleuret7,b, K.
Fohl40, M. Fontana16,40, F. Fontanelli20,h, D.C. Forshaw61, R. Forty40, V.
Franco Lima54, M. Frank40, C. Frei40, J. Fu22,q, W. Funk40, E. Furfaro25,j, C.
Färber40, E. Gabriel52, A. Gallas Torreira39, D. Galli15,e, S. Gallorini23, S.
Gambetta52, M. Gandelman2, P. Gandini57, Y. Gao3, L.M. Garcia Martin70, J.
García Pardiñas39, J. Garra Tico49, L. Garrido38, P.J. Garsed49, D. Gascon38,
C. Gaspar40, L. Gavardi10, G. Gazzoni5, D. Gerick12, E. Gersabeck12, M.
Gersabeck56, T. Gershon50, Ph. Ghez4, S. Gianì41, V. Gibson49, O.G. Girard41,
L. Giubega30, K. Gizdov52, V.V. Gligorov8, D. Golubkov32, A. Golutvin55,40, A.
Gomes1,a, I.V. Gorelov33, C. Gotti21,i, E. Govorkova43, J.P. Grabowski12, R.
Graciani Diaz38, L.A. Granado Cardoso40, E. Graugés38, E. Graverini42, G.
Graziani18, A. Grecu30, R. Greim9, P. Griffith16, L. Grillo21,40,i, L.
Gruber40, B.R. Gruberg Cazon57, O. Grünberg67, E. Gushchin34, Yu. Guz37, T.
Gys40, C. Göbel62, T. Hadavizadeh57, C. Hadjivasiliou5, G. Haefeli41, C.
Haen40, S.C. Haines49, B. Hamilton60, X. Han12, T. Hancock57, S. Hansmann-
Menzemer12, N. Harnew57, S.T. Harnew48, J. Harrison56, C. Hasse40, M. Hatch40,
J. He63, M. Hecker55, K. Heinicke10, A. Heister9, K. Hennessy54, P. Henrard5,
L. Henry70, E. van Herwijnen40, M. Heß67, A. Hicheur2, D. Hill57, C.
Hombach56, P.H. Hopchev41, Z.-C. Huard59, W. Hulsbergen43, T. Humair55, M.
Hushchyn35, D. Hutchcroft54, P. Ibis10, M. Idzik28, P. Ilten58, R.
Jacobsson40, J. Jalocha57, E. Jans43, A. Jawahery60, F. Jiang3, M. John57, D.
Johnson40, C.R. Jones49, C. Joram40, B. Jost40, N. Jurik57, S. Kandybei45, M.
Karacson40, J.M. Kariuki48, S. Karodia53, M. Kecke12, M. Kelsey61, M.
Kenzie49, T. Ketel44, E. Khairullin35, B. Khanji12, C. Khurewathanakul41, T.
Kirn9, S. Klaver56, K. Klimaszewski29, T. Klimkovich11, S. Koliiev46, M.
Kolpin12, I. Komarov41, R. Kopecna12, P. Koppenburg43, A. Kosmyntseva32, S.
Kotriakhova31, M. Kozeiha5, L. Kravchuk34, M. Kreps50, P. Krokovny36,w, F.
Kruse10, W. Krzemien29, W. Kucewicz27,l, M. Kucharczyk27, V. Kudryavtsev36,w,
A.K. Kuonen41, K. Kurek29, T. Kvaratskheliya32,40, D. Lacarrere40, G.
Lafferty56, A. Lai16, G. Lanfranchi19, C. Langenbruch9, T. Latham50, C.
Lazzeroni47, R. Le Gac6, J. van Leerdam43, A. Leflat33,40, J. Lefrançois7, R.
Lefèvre5, F. Lemaitre40, E. Lemos Cid39, O. Leroy6, T. Lesiak27, B.
Leverington12, T. Li3, Y. Li7, Z. Li61, T. Likhomanenko35,68, R. Lindner40, F.
Lionetto42, X. Liu3, D. Loh50, A. Loi16, I. Longstaff53, J.H. Lopes2, D.
Lucchesi23,o, M. Lucio Martinez39, H. Luo52, A. Lupato23, E. Luppi17,g, O.
Lupton40, A. Lusiani24, X. Lyu63, F. Machefert7, F. Maciuc30, V. Macko41, P.
Mackowiak10, B. Maddock59, S. Maddrell-Mander48, O. Maev31, K. Maguire56, D.
Maisuzenko31, M.W. Majewski28, S. Malde57, A. Malinin68, T. Maltsev36, G.
Manca16,f, G. Mancinelli6, P. Manning61, D. Marangotto22,q, J. Maratas5,v,
J.F. Marchand4, U. Marconi15, C. Marin Benito38, M. Marinangeli41, P.
Marino24,t, J. Marks12, G. Martellotti26, M. Martin6, M. Martinelli41, D.
Martinez Santos39, F. Martinez Vidal70, D. Martins Tostes2, L.M. Massacrier7,
A. Massafferri1, R. Matev40, A. Mathad50, Z. Mathe40, C. Matteuzzi21, A.
Mauri42, E. Maurice7,b, B. Maurin41, A. Mazurov47, M. McCann55,40, A. McNab56,
R. McNulty13, J.V. Mead54, B. Meadows59, C. Meaux6, F. Meier10, N. Meinert67,
D. Melnychuk29, M. Merk43, A. Merli22,40,q, E. Michielin23, D.A. Milanes66, E.
Millard50, M.-N. Minard4, L. Minzoni17, D.S. Mitzel12, A. Mogini8, J. Molina
Rodriguez1, T. Mombacher10, I.A. Monroy66, S. Monteil5, M. Morandin23, M.J.
Morello24,t, O. Morgunova68, J. Moron28, A.B. Morris52, R. Mountain61, F.
Muheim52, M. Mulder43, M. Mussini15, D. Müller56, J. Müller10, K. Müller42, V.
Müller10, P. Naik48, T. Nakada41, R. Nandakumar51, A. Nandi57, I. Nasteva2, M.
Needham52, N. Neri22,40, S. Neubert12, N. Neufeld40, M. Neuner12, T.D.
Nguyen41, C. Nguyen-Mau41,n, S. Nieswand9, R. Niet10, N. Nikitin33, T.
Nikodem12, A. Nogay68, D.P. O’Hanlon50, A. Oblakowska-Mucha28, V. Obraztsov37,
S. Ogilvy19, R. Oldeman16,f, C.J.G. Onderwater71, A. Ossowska27, J.M. Otalora
Goicochea2, P. Owen42, A. Oyanguren70, P.R. Pais41, A. Palano14,d, M.
Palutan19,40, A. Papanestis51, M. Pappagallo14,d, L.L. Pappalardo17,g, C.
Pappenheimer59, W. Parker60, C. Parkes56, G. Passaleva18, A. Pastore14,d, M.
Patel55, C. Patrignani15,e, A. Pearce40, A. Pellegrino43, G. Penso26, M. Pepe
Altarelli40, S. Perazzini40, P. Perret5, L. Pescatore41, K. Petridis48, A.
Petrolini20,h, A. Petrov68, M. Petruzzo22,q, E. Picatoste Olloqui38, B.
Pietrzyk4, M. Pikies27, D. Pinci26, A. Pistone20,h, A. Piucci12, V.
Placinta30, S. Playfer52, M. Plo Casasus39, T. Poikela40, F. Polci8, M. Poli
Lener19, A. Poluektov50,36, I. Polyakov61, E. Polycarpo2, G.J. Pomery48, S.
Ponce40, A. Popov37, D. Popov11,40, S. Poslavskii37, C. Potterat2, E. Price48,
J. Prisciandaro39, C. Prouve48, V. Pugatch46, A. Puig Navarro42, H. Pullen57,
G. Punzi24,p, W. Qian50, R. Quagliani7,48, B. Quintana5, B. Rachwal28, J.H.
Rademacker48, M. Rama24, M. Ramos Pernas39, M.S. Rangel2, I. Raniuk45,†, F.
Ratnikov35, G. Raven44, M. Ravonel Salzgeber40, M. Reboud4, F. Redi55, S.
Reichert10, A.C. dos Reis1, C. Remon Alepuz70, V. Renaudin7, S. Ricciardi51,
S. Richards48, M. Rihl40, K. Rinnert54, V. Rives Molina38, P. Robbe7, A.B.
Rodrigues1, E. Rodrigues59, J.A. Rodriguez Lopez66, P. Rodriguez Perez56,†, A.
Rogozhnikov35, S. Roiser40, A. Rollings57, V. Romanovskiy37, A. Romero
Vidal39, J.W. Ronayne13, M. Rotondo19, M.S. Rudolph61, T. Ruf40, P. Ruiz
Valls70, J. Ruiz Vidal70, J.J. Saborido Silva39, E. Sadykhov32, N. Sagidova31,
B. Saitta16,f, V. Salustino Guimaraes1, D. Sanchez Gonzalo38, C. Sanchez
Mayordomo70, B. Sanmartin Sedes39, R. Santacesaria26, C. Santamarina Rios39,
M. Santimaria19, E. Santovetti25,j, G. Sarpis56, A. Sarti26, C. Satriano26,s,
A. Satta25, D.M. Saunders48, D. Savrina32,33, S. Schael9, M. Schellenberg10,
M. Schiller53, H. Schindler40, M. Schlupp10, M. Schmelling11, T. Schmelzer10,
B. Schmidt40, O. Schneider41, A. Schopper40, H.F. Schreiner59, K. Schubert10,
M. Schubiger41, M.-H. Schune7, R. Schwemmer40, B. Sciascia19, A. Sciubba26,k,
A. Semennikov32, A. Sergi47, N. Serra42, J. Serrano6, L. Sestini23, P.
Seyfert40, M. Shapkin37, I. Shapoval45, Y. Shcheglov31, T. Shears54, L.
Shekhtman36,w, V. Shevchenko68, B.G. Siddi17,40, R. Silva Coutinho42, L. Silva
de Oliveira2, G. Simi23,o, S. Simone14,d, M. Sirendi49, N. Skidmore48, T.
Skwarnicki61, E. Smith55, I.T. Smith52, J. Smith49, M. Smith55, l. Soares
Lavra1, M.D. Sokoloff59, F.J.P. Soler53, B. Souza De Paula2, B. Spaan10, P.
Spradlin53, S. Sridharan40, F. Stagni40, M. Stahl12, S. Stahl40, P. Stefko41,
S. Stefkova55, O. Steinkamp42, S. Stemmle12, O. Stenyakin37, H. Stevens10, S.
Stone61, B. Storaci42, S. Stracka24,p, M.E. Stramaglia41, M. Straticiuc30, U.
Straumann42, L. Sun64, W. Sutcliffe55, K. Swientek28, V. Syropoulos44, M.
Szczekowski29, T. Szumlak28, M. Szymanski63, S. T’Jampens4, A. Tayduganov6, T.
Tekampe10, G. Tellarini17,g, F. Teubert40, E. Thomas40, J. van Tilburg43, M.J.
Tilley55, V. Tisserand4, M. Tobin41, S. Tolk49, L. Tomassetti17,g, D.
Tonelli24, S. Topp-Joergensen57, F. Toriello61, R. Tourinho Jadallah Aoude1,
E. Tournefier4, M. Traill53, M.T. Tran41, M. Tresch42, A. Trisovic40, A.
Tsaregorodtsev6, P. Tsopelas43, A. Tully49, N. Tuning43, A. Ukleja29, A.
Ustyuzhanin35, U. Uwer12, C. Vacca16,f, A. Vagner69, V. Vagnoni15,40, A.
Valassi40, S. Valat40, G. Valenti15, R. Vazquez Gomez19, P. Vazquez
Regueiro39, S. Vecchi17, M. van Veghel43, J.J. Velthuis48, M. Veltri18,r, G.
Veneziano57, A. Venkateswaran61, T.A. Verlage9, M. Vernet5, M. Vesterinen57,
J.V. Viana Barbosa40, B. Viaud7, D. Vieira63, M. Vieites Diaz39, H. Viemann67,
X. Vilasis-Cardona38,m, M. Vitti49, V. Volkov33, A. Vollhardt42, B. Voneki40,
A. Vorobyev31, V. Vorobyev36,w, C. Voß9, J.A. de Vries43, C. Vázquez Sierra39,
R. Waldi67, C. Wallace50, R. Wallace13, J. Walsh24, J. Wang61, D.R. Ward49,
H.M. Wark54, N.K. Watson47, D. Websdale55, A. Weiden42, M. Whitehead40, J.
Wicht50, G. Wilkinson57,40, M. Wilkinson61, M. Williams56, M.P. Williams47, M.
Williams58, T. Williams47, F.F. Wilson51, J. Wimberley60, M.A. Winn7, J.
Wishahi10, W. Wislicki29, M. Witek27, G. Wormser7, S.A. Wotton49, K.
Wraight53, K. Wyllie40, Y. Xie65, Z. Xu4, Z. Yang3, Z. Yang60, Y. Yao61, H.
Yin65, J. Yu65, X. Yuan61, O. Yushchenko37, K.A. Zarebski47, M.
Zavertyaev11,c, L. Zhang3, Y. Zhang7, A. Zhelezov12, Y. Zheng63, X. Zhu3, V.
Zhukov33, J.B. Zonneveld52, S. Zucchelli15.

2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 3Center
for High Energy Physics, Tsinghua University, Beijing, China 4LAPP, Université
Savoie Mont-Blanc, CNRS/IN2P3, Annecy-Le-Vieux, France 5Clermont Université,
Université Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM,
Aix-Marseille Université, CNRS/IN2P3, Marseille, France 7LAL, Université
Paris-Sud, CNRS/IN2P3, Orsay, France 8LPNHE, Université Pierre et Marie Curie,
Université Paris Diderot, CNRS/IN2P3, Paris, France 9I. Physikalisches
Institut, RWTH Aachen University, Aachen, Germany 10Fakultät Physik,
Technische Universität Dortmund, Dortmund, Germany 11Max-Planck-Institut für
Kernphysik (MPIK), Heidelberg, Germany 12Physikalisches Institut, Ruprecht-
Karls-Universität Heidelberg, Heidelberg, Germany 13School of Physics,
University College Dublin, Dublin, Ireland 14Sezione INFN di Bari, Bari, Italy
15Sezione INFN di Bologna, Bologna, Italy 16Sezione INFN di Cagliari,
Cagliari, Italy 17Universita e INFN, Ferrara, Ferrara, Italy 18Sezione INFN di
Firenze, Firenze, Italy 19Laboratori Nazionali dell’INFN di Frascati,
Frascati, Italy 20Sezione INFN di Genova, Genova, Italy 21Universita & INFN,
Milano-Bicocca, Milano, Italy 22Sezione di Milano, Milano, Italy 23Sezione
INFN di Padova, Padova, Italy 24Sezione INFN di Pisa, Pisa, Italy 25Sezione
INFN di Roma Tor Vergata, Roma, Italy 26Sezione INFN di Roma La Sapienza,
Roma, Italy 27Henryk Niewodniczanski Institute of Nuclear Physics Polish
Academy of Sciences, Kraków, Poland 28AGH - University of Science and
Technology, Faculty of Physics and Applied Computer Science, Kraków, Poland
29National Center for Nuclear Research (NCBJ), Warsaw, Poland 30Horia Hulubei
National Institute of Physics and Nuclear Engineering, Bucharest-Magurele,
Romania 31Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
32Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
33Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow,
Russia 34Institute for Nuclear Research of the Russian Academy of Sciences
(INR RAN), Moscow, Russia 35Yandex School of Data Analysis, Moscow, Russia
36Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia
37Institute for High Energy Physics (IHEP), Protvino, Russia 38ICCUB,
Universitat de Barcelona, Barcelona, Spain 39Universidad de Santiago de
Compostela, Santiago de Compostela, Spain 40European Organization for Nuclear
Research (CERN), Geneva, Switzerland 41Institute of Physics, Ecole
Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland 42Physik-
Institut, Universität Zürich, Zürich, Switzerland 43Nikhef National Institute
for Subatomic Physics, Amsterdam, The Netherlands 44Nikhef National Institute
for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands
45NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
46Institute for Nuclear Research of the National Academy of Sciences (KINR),
Kyiv, Ukraine 47University of Birmingham, Birmingham, United Kingdom 48H.H.
Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom
49Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
50Department of Physics, University of Warwick, Coventry, United Kingdom
51STFC Rutherford Appleton Laboratory, Didcot, United Kingdom 52School of
Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
53School of Physics and Astronomy, University of Glasgow, Glasgow, United
Kingdom 54Oliver Lodge Laboratory, University of Liverpool, Liverpool, United
Kingdom 55Imperial College London, London, United Kingdom 56School of Physics
and Astronomy, University of Manchester, Manchester, United Kingdom
57Department of Physics, University of Oxford, Oxford, United Kingdom
58Massachusetts Institute of Technology, Cambridge, MA, United States
59University of Cincinnati, Cincinnati, OH, United States 60University of
Maryland, College Park, MD, United States 61Syracuse University, Syracuse, NY,
United States 62Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio),
Rio de Janeiro, Brazil, associated to 2 63University of Chinese Academy of
Sciences, Beijing, China, associated to 3 64School of Physics and Technology,
Wuhan University, Wuhan, China, associated to 3 65Institute of Particle
Physics, Central China Normal University, Wuhan, Hubei, China, associated to 3
66Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia,
associated to 8 67Institut für Physik, Universität Rostock, Rostock, Germany,
associated to 12 68National Research Centre Kurchatov Institute, Moscow,
Russia, associated to 32 69National Research Tomsk Polytechnic University,
Tomsk, Russia, associated to 32 70Instituto de Fisica Corpuscular, Centro
Mixto Universidad de Valencia - CSIC, Valencia, Spain, associated to 38 71Van
Swinderen Institute, University of Groningen, Groningen, The Netherlands,
associated to 43

aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil
bLaboratoire Leprince-Ringuet, Palaiseau, France cP.N. Lebedev Physical
Institute, Russian Academy of Science (LPI RAS), Moscow, Russia dUniversità di
Bari, Bari, Italy eUniversità di Bologna, Bologna, Italy fUniversità di
Cagliari, Cagliari, Italy gUniversità di Ferrara, Ferrara, Italy hUniversità
di Genova, Genova, Italy iUniversità di Milano Bicocca, Milano, Italy
jUniversità di Roma Tor Vergata, Roma, Italy kUniversità di Roma La Sapienza,
Roma, Italy lAGH - University of Science and Technology, Faculty of Computer
Science, Electronics and Telecommunications, Kraków, Poland mLIFAELS, La
Salle, Universitat Ramon Llull, Barcelona, Spain nHanoi University of Science,
Hanoi, Viet Nam oUniversità di Padova, Padova, Italy pUniversità di Pisa,
Pisa, Italy qUniversità degli Studi di Milano, Milano, Italy rUniversità di
Urbino, Urbino, Italy sUniversità della Basilicata, Potenza, Italy tScuola
Normale Superiore, Pisa, Italy uUniversità di Modena e Reggio Emilia, Modena,
Italy vIligan Institute of Technology (IIT), Iligan, Philippines wNovosibirsk
State University, Novosibirsk, Russia †Deceased