2016 046 29 February

Centrality dependence of $\mathbf{\psi}$(2S) suppression in p-Pb collisions
ALICE Collaboration††thanks: See Appendix A for the list of collaboration
members ALICE Collaboration

The inclusive production of the $\psi(\rm 2S)$ charmonium state was studied as
a function of centrality in p-Pb collisions at the nucleon-nucleon center of
mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV at the CERN LHC. The measurement
was performed with the ALICE detector in the center of mass rapidity ranges
$-4.46<y_{\rm cms}<-2.96$ and $2.03<y_{\rm cms}<3.53$, down to zero transverse
momentum, by reconstructing the $\psi(\rm 2S)$ decay to a muon pair. The
$\psi(\rm 2S)$ production cross section $\sigma_{\psi(\rm 2S)}$ is presented
as a function of the collision centrality, which is estimated through the
energy deposited in forward rapidity calorimeters. The relative strength of
nuclear effects on the $\psi(\rm 2S)$ and on the corresponding 1S charmonium
state J/$\psi$ is then studied by means of the double ratio of cross sections
$[\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]_{\rm pPb}/[\sigma_{\psi(\rm
2S)}/\sigma_{\rm J/\psi}]_{\rm pp}$ between p-Pb and pp collisions, and by the
values of the nuclear modification factors for the two charmonium states. The
results show a large suppression of $\psi(\rm 2S)$ production relative to the
J/$\psi$ at backward (negative) rapidity, corresponding to the flight
direction of the Pb-nucleus, while at forward (positive) rapidity the
suppressions of the two states are comparable. Finally, comparisons to results
from lower energy experiments and to available theoretical models are
presented.

##  1 Introduction

Charmonia are bound states of a charm and an anticharm quark
($c\overline{c}$), and represent an important testing ground for the
properties of the strong interaction. In high-energy proton-proton collisions,
the charmonium production process is usually factorized in two steps: the
creation of a $c\overline{c}$ pair followed, on a longer time scale, by the
binding and emission of one or more gluons that brings the pair to a colour
singlet state. This process is described reasonably by theoretical models
inspired by Quantum Chromodynamics (QCD) [1], although a quantitative
evaluation of the production cross sections and polarization of the charmonium
states still meets difficulties [1, 2].

If a charmonium state is produced within the nuclear medium, as can happen in
proton-nucleus collisions, several effects become important and might
influence the charmonium formation. In particular, the modification in the
nucleus of the parton distribution functions (shadowing/anti-shadowing) [3, 4,
5], can lead to a suppression or an enhancement of the charmonium production.
Furthermore, the incoming partons, as well as the outgoing $c\overline{c}$
pair, may lose energy in the nuclear medium, altering the differential
distributions of the produced charmonium state [6]. Finally, once the bound
state is formed, it may be dissociated via collisions within nuclear matter
[7, 8, 9]. However, the formation of the final-state resonance occurs in a
finite time $\tau_{\rm f}$ which, depending on the kinematics of the
$c\overline{c}$ pair and on the collision energy, may be longer than its
crossing time, $\tau_{\rm c}$, in the nucleus.

Among the narrow charmonium states, i.e. those with a mass smaller than twice
the mass of the lightest D mesons, we address in this paper the vector states
(JPC = 1–) J/$\psi$, characterized by a binding energy $\Delta E\sim 650$ MeV
(corresponding to the mass gap to the open charm threshold), and the weakly
bound $\psi(\rm 2S)$, with $\Delta E\sim 50$ MeV [10]. A comparison of the
production cross section of the two states in proton-nucleus collisions offers
interesting insights into the size of the various cold nuclear matter (CNM)
effects outlined above. In particular, shadowing acts on the initial state
partons and has a nearly identical size for the two resonances [11, 12].
Therefore, its effect largely cancels out when studying the ratio of their
production cross sections. Also coherent energy loss mechanisms [6], have a
similar effect on the two resonances, due to the fact that they act on a
compact ${c\overline{c}}$ pair not yet evolved into a final color singlet
state. On the contrary, the break-up probability of the final resonance inside
the nucleus should be much larger for the weakly bound $\psi(\rm 2S)$ [13].

Early results on J/$\psi$ and $\psi(\rm 2S)$ production in proton-nucleus
collisions were obtained at fixed target experiments by E866 [14] at FNAL
($\sqrt{s_{\rm NN}}=63$ GeV), by HERA-B [15] at HERA ($\sqrt{s_{\rm NN}}=39$
GeV) and by NA38, NA50, NA60 [16, 17, 18] at the CERN SPS ($\sqrt{s_{\rm
NN}}=17-29$ GeV). At mid-rapidity, i.e., close to $y_{\rm cms}=0$, the
relative production cross section $\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}$
was found to decrease rather strongly for increasing mass number of the
nuclear target. Since part of the kinematic domain accessed at fixed target
energies is characterized by $\tau_{\rm f}<\tau_{\rm c}$ [9], such an
observation can indeed be related to a stronger break-up effect on the weakly
bound $\psi(\rm 2S)$.

At collider energies, it becomes technically more difficult to have data
samples corresponding to various nuclear colliding species. Therefore, in
order to vary the thickness of CNM crossed by the $c\overline{c}$ pair, one
can rather select classes of events based on estimators of the geometry
(centrality) of the collision, corresponding to various ranges in the number
of nucleon-nucleon collisions $N_{\rm coll}$. This procedure was followed by
the PHENIX experiment at RHIC, which studied the nuclear modification factors,
defined as the ratio between the measured yields in d-Au and proton-proton
collisions, normalized to $N_{\rm coll}$, for the J/$\psi$ and $\psi(\rm 2S)$
resonances at mid-rapidity [19]. At $\sqrt{s_{\rm NN}}=200$ GeV, the nuclear
modification factors were smaller by a factor $\sim 3$ for $\psi(\rm 2S)$
relative to J/$\psi$ for central events, indicating a stronger suppression for
$\psi(\rm 2S)$. However, such an observation is surprising since for mid-
rapidity production at RHIC energies the time spent by the $c\overline{c}$
pair in the nucleus ($\tau_{\rm c}<0.05$ fm/$c$) is below the formation time
of the final-state resonance (most theory estimates [9, 20, 21] give
$\tau_{\rm f}>0.15$ fm/$c$). In such a situation, one would rather expect a
similar suppression for the J/$\psi$ and $\psi(\rm 2S)$ states.

At the LHC, centrality-integrated results on the $\psi(\rm 2S)$ and J/$\psi$
resonances for p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV were obtained
by ALICE [22, 23] and LHCb [24, 25]. At both forward (positive) and backward
(negative) rapidities, corresponding to the p-going and Pb-going directions
respectively, a significantly larger suppression of $\psi(\rm 2S)$ compared to
J/$\psi$ was observed, relative to proton-proton collisions. Again, this
result was unexpected, as the $\tau_{\rm c}$ values are either at most the
same order of magnitude (at negative $y_{\rm cms}$) or more than two orders of
magnitude smaller (at positive $y_{\rm cms}$) than $\tau_{\rm f}$ [22].
Therefore, additional effects, as the interaction of the loosely bound
$\psi(\rm 2S)$ with a hadronic or partonic medium produced in the collision,
might be necessary in order to explain the results [11, 26].

As outlined above, a differential measurement as a function of the collisions
centrality is equivalent to a study of the propagation of the $c\overline{c}$
pairs over various thicknesses of CNM. In this Letter, we go in that direction
by showing results obtained by the ALICE Collaboration on $\psi(\rm 2S)$
studies in p-Pb collisions as a function of centrality, estimated through the
energy deposited at very forward rapidity by the remnants of the Pb-nucleus.
The corresponding J/$\psi$ studies were published in [27]. In Sect. 2 we give
a brief overview of the experimental apparatus and run conditions. Sect. 3
presents details on the analysis procedure, while Sect. 4 is dedicated to the
results. The conclusions are presented in Sect. 5.

##  2 Experimental conditions

The analysis presented in this Letter is based on the detection of the
$\psi(2S)\rightarrow\mu^{+}\mu^{-}$ decay in the forward muon spectrometer of
ALICE, described in detail elsewhere [28, 29]. This detector covers the
pseudorapidity range $-4<\eta_{\rm lab}<-2.5$ and includes a 3 T$\cdot$ m
dipole magnet and five stations of tracking chambers, the central one being
inside the magnet gap. A main absorber (10 interaction lengths thick) is
positioned between the ALICE interaction point and the tracking system, in
order to remove hadrons. A second absorber is placed downstream of the
tracking detectors. It removes the remaining hadrons and low-momentum muons
produced predominantly from $\pi$ and $K$ decays, and is followed by two
stations of trigger chambers that select muon candidates based on their
transverse momentum ($p_{\rm T}$). In addition to the muon spectrometer, the
first two layers of the Inner Tracking System (SPD, i.e., Silicon Pixel
Detectors, the first covering $|\eta_{\rm lab}|<2.0$ and the second
$|\eta_{\rm lab}|<1.4$) [30] are used for the determination of the position of
the interaction vertex. The two V0 scintillator hodoscopes (covering
$-3.7<\eta_{\rm lab}<-1.7$ and $2.8<\eta_{\rm lab}<5.1$, respectively) are
used for triggering purposes [31]. Finally, two sets of Zero-Degree
Calorimeters (ZDC), positioned at 112.5 m on the two sides of the interaction
point, each one including a neutron calorimeter (ZN) and a proton calorimeter
(ZP), are used to clean-up the event sample from interactions occurring out of
the nominal bunches and for the centrality estimate [32, 33].

The data-taking conditions were described in [23, 34] and are briefly stated
here. Two data samples were taken, corresponding to the p-beam or the Pb-beam
going in the direction of the muon spectrometer, and labelled in the following
as p-Pb and Pb-p, respectively. The integrated luminosities were $L_{\rm
int}^{\rm pPb}=5.01\pm 0.19$ nb-1 and $L_{\rm int}^{\rm Pbp}=5.81\pm 0.20$
nb-1 [35]. The events used in this analysis were collected requiring a
coincidence between a minimum bias (MB) trigger condition, defined by the
logical AND of signals on the two V0 hodoscopes ($>$99% efficiency for non-
single diffractive events), and the detection of two candidate opposite-sign
tracks in the trigger system of the muon spectrometer. A $p^{\mu}_{\rm T}>0.5$
GeV/$c$ cut on such tracks was also imposed at the trigger level. The offline
event selection, the muon reconstruction and identification criteria and the
kinematic and quality cuts applied at the single-muon and dimuon levels have
already been described in Refs. [23, 22, 36, 27]. In particular, the covered
dimuon rapidity ranges were $2.03<y_{\rm cms}<3.53$ and $-4.46<y_{\rm
cms}<-2.96$ for the p-Pb and Pb-p configurations, respectively.

##  3 Data analysis

In this Section, the evaluation of the various elements that enter the cross
section measurements and the nuclear modification factor calculations are
described.

The centrality selection and the determination of $N_{\rm coll}$ are based on
a hybrid method described in detail in Ref. [33]. Events are selected
according to the energy deposited at very large rapidity in the ZN positioned
in the Pb-going direction, which mainly detects slow neutrons emitted by the
Pb-nucleus as the result of the interaction. Their emission, according to
results obtained in the analysis of lower energy proton-nucleus experiments,
is expected to be monotonically related to $N_{\rm coll}$ [37]. A centrality
selection based on the ZN energy is found to be less biased than other
centrality estimators, based on the charged particle multiplicity measurements
at central (SPD) or forward (V0) pseudorapidity [33]. The average number of
nucleon-nucleon collisions $\langle N_{\rm coll}\rangle$ for each ZN-selected
centrality class is then obtained by assuming that the charged particle
multiplicity measured at central rapidity is proportional to the number of
participants $N_{\rm part}=N_{\rm coll}+1$ [38]. The values of $\langle N_{\rm
coll}\rangle$, used in this analysis, are reported in Tab. 1, together with
their uncertainties.

ZN centrality class | $\langle N_{\rm coll}\rangle$
---|---
2–20% | 11.3 $\pm$ 0.6 $\pm$ 0.9
20–40% | 9.6 $\pm$ 0.2 $\pm$ 0.8
40–60% | 7.1 $\pm$ 0.3 $\pm$ 0.6
60–80% | 4.3 $\pm$ 0.3 $\pm$ 0.3
80–100% | 2.1 $\pm$ 0.1 $\pm$ 0.2
Table 1: Average numbers of binary nucleon-nucleon collisions, $N_{\rm coll}$,
evaluated in the ZN centrality classes used in this analysis. The first quoted
systematic uncertainty is uncorrelated, while the second is global.

The centrality classes used in this analysis correspond to 2–20%, 20–40%,
40–60%, 60–80% and 80–100% of the measured cross section corresponding to the
MB trigger. Very central events (0–2%) are discarded from the event sample due
to a large contamination from pile-up interactions.

The estimate of the $\psi(\rm 2S)$ signal is based on binned likelihood fits
to the dimuon invariant mass spectra $m_{\mu\mu}$ corresponding to events in
the centrality ranges defined above. Details on the procedure, on the fitting
functions and on the estimate of systematic uncertainties are discussed in
[22]. The function used in the fit is the sum of a continuum background,
mainly related to uncorrelated decays from pions and kaons and to semi-
leptonic decays of pairs of hadrons with open heavy flavor, and of resonance
shapes corresponding to the J/$\psi$ and $\psi(\rm 2S)$ mesons. The background
is parameterized by various empirical shapes, directly fitted to the data. The
resonances are described by either a Crystal Ball function or a pseudo-
gaussian with a mass-dependent width [39]. The main parameters of the J/$\psi$
line shapes, i.e. mass position and width, are left as free parameters, while
the non-gaussian tail parameters are fixed to Monte-Carlo (MC) estimates. The
$\psi(\rm 2S)$ line shape parameters, given the less favourable signal over
background, are fixed relative to those of the J/$\psi$, assuming that the
mass difference and the widths scale according to the MC result. The results
of the fits are shown in Fig. 1.

Figure 1: Opposite-sign dimuon invariant mass spectra in ZN centrality classes
at forward (top) and backward (bottom) rapidities. The fit curves shown in red
in the figure correspond to the sum of signal and background shapes, the
former being also shown separately in blue.

The quality of the fits is good, with $\chi^{2}/{\rm ndf}$ ranging from 0.7 to
1.3. The $\psi(\rm 2S)$ signal is visible in all the centrality bins, and the
signal over background ratio increases from central (0.06 for p-Pb and 0.04
for Pb-p) to peripheral events (0.15 and 0.28, respectively). The number of
reconstructed $\psi(\rm 2S)$ for the various centrality bins,
$N^{i}_{\psi(2S)\rightarrow\mu^{+}\mu^{-}}$, ranges from $265\pm 73\pm 32$
($i$= 2–20%) to $100\pm 29\pm 9$ ($i$= 80–100%) in p-Pb, where the first
uncertainty is statistical and the second one is systematic. The corresponding
values for Pb-p are $141\pm 64\pm 13$ ($i$= 2–20%) and $65\pm 20\pm 7$ ($i$=
80–100%). The systematic uncertainties on the signal extraction are given by
the root mean square of the number of $\psi(\rm 2S)$ obtained in 72 fits
corresponding to various fitting functions for background and signal, to
different fitting ranges, to variations of the non-gaussian tails of the
resonance shape, and of the $\psi(\rm 2S)$ mass resolution values. In p-Pb,
the systematic uncertainties range between 11 and 13% from peripheral to
central events (11–21% for Pb-p).

The product of acceptance times efficiency $A\times\epsilon$ for the $\psi(\rm
2S)$ resonance was calculated with the MC-based procedure described in Refs.
[23, 22]. The values are the same as quoted there for the centrality
integrated production ($0.270\pm 0.014$ for p-Pb and $0.184\pm 0.013$ for
Pb-p), since it was verified that the tracking efficiency does not depend on
the centrality of the collision [27]. The quoted errors are the quadratic sum
of the systematic uncertainties on tracking, trigger and matching efficiencies
and on the choice of the $\psi(\rm 2S)$ $p_{\rm T}$ and $y$ input shapes used
in the MC simulations.

The normalization of the $\psi(\rm 2S)$ yield was calculated according to the
procedure described in Ref. [27]. It is based on the evaluation, for each
centrality class, of the number of minimum bias events as $N^{i}_{\rm
MB}=F^{i}_{2\mu/{\rm MB}}\cdot N^{i}_{2\mu}$, where $N^{i}_{2\mu}$ is the
number of dimuon-triggered events and $F^{i}_{2\mu/{\rm MB}}$ is the inverse
of the probability of having a dimuon triggered in a MB event for that class.
The $F^{i}_{2\mu/{\rm MB}}$-values increase from central to peripheral events
and are $287\pm 3$ and $694\pm 8$ for the 2–20% centrality class in p-Pb and
Pb-p respectively. The corresponding values for the 80–100% class are $3291\pm
36$ and $3338\pm 35$. The systematic uncertainties quoted above (statistical
uncertainties are negligible) come from the comparison obtained with two
slightly different approaches in the calculation of $F^{i}_{2\mu/{\rm MB}}$,
as detailed in [27].

In the evaluation of the systematic uncertainties on $F^{i}_{2\mu/{\rm MB}}$,
the presence of interaction pile-up was considered. Pile-up can lead to a bias
in the evaluation of the centrality of the collision since, for example, the
superposition of the signals from two peripheral events in the ZN can fake a
more central event. The contribution of pile-up was calculated by detecting
events with multiple interaction vertices in the SPD, and checking via a
Monte-Carlo that the ZN energy distribution can be reproduced assuming a pile-
up probability corresponding to the observed interaction rate. Events in the
0–2% centrality interval were rejected, as the pile-up contribution becomes
significant ($\sim$30%) in that region. The effect is small but not negligible
in the 2–20% range, where it amounts to 2.1% (2.6%) for p-Pb (Pb-p), and
becomes $<1$% going towards more peripheral events.

From the quantities described above, the inclusive cross section for $\psi(\rm
2S)$ production in the centrality bin $i$, times its branching ratio to
dimuons ${\rm B.R.}_{\psi(\rm 2S)\rightarrow\mu\mu}$, was calculated with the
following expression

${\rm B.R.}_{\psi(\rm 2S)\rightarrow\mu^{+}\mu^{-}}\sigma^{i,\rm\psi(\rm
2S)}_{\rm
pPb}=\frac{N^{i}_{\psi(2S)\rightarrow\mu^{+}\mu^{-}}}{(A\times\epsilon)\cdot
N_{\rm MB}^{i}}\times\sigma_{\rm MB}$ (1)

The ratio $N_{\rm MB}/\sigma_{\rm MB}$, where $N_{\rm MB}$ is the total number
of minimum bias events and $\sigma_{\rm MB}$ is the cross section for events
satisfying the minimum bias trigger condition, gives the integrated luminosity
$L_{\rm int}$. The $\sigma_{\rm MB}$ values were evaluated through a van der
Meer scan which gives $\sigma_{\rm MB}^{\rm pPb}=2.09\pm 0.07$ b and
$\sigma_{\rm MB}^{\rm Pbp}=2.12\pm 0.07$ b [35]. A determination of the
luminosity which makes use of a different reference process, based on the
signals released in a Čerenkov counter [29], gives a result compatible within
1% [35]. Therefore, an additional 1% uncertainty is added to the $\sigma_{\rm
MB}$ values used in the $\psi(\rm 2S)$ cross section determination.

The comparison of the $\psi(\rm 2S)$ and J/$\psi$ production cross sections
can be performed by calculating the ratio ${\rm B.R.}_{\psi(\rm
2S)\rightarrow\mu^{+}\mu^{-}}\sigma_{\psi(\rm 2S)}/{\rm B.R.}_{{\rm
J}/\psi\rightarrow\mu^{+}\mu^{-}}\sigma_{{\rm J}/\psi}$. In this way, the
uncertainties related to the cross section normalization and to the
reconstruction efficiency cancel out. The J/$\psi$ cross section values that
enter this ratio are those reported in [27], with the value for the centrality
interval 2–20% obtained by summing the 2–10% and 10–20% results. This ratio
can be further normalized to the corresponding measurement in pp collisions.
This quantity, called double ratio in the following, gives direct access to
modifications in the $\psi(\rm 2S)$ production relative to that of the
J/$\psi$, going from pp to p-Pb collisions. Due to the lack of precise pp data
at $\sqrt{s}=5.02$ TeV, the results obtained at $\sqrt{s}=7$ TeV [40] were
used instead. This choice is justified from the fact that the $\sqrt{s}$\- and
$y$-dependence of the cross section ratio is known to be weak in the TeV beam
energy range. An 8% systematic uncertainty has been included, corresponding to
the maximum estimated size of the variation of the ratio between the two
energies [22].

The estimate of the nuclear modification factors $Q^{i,\psi(2S)}_{\rm pPb}$ as
a function of centrality is performed as the product of the corresponding
$Q^{i,{\rm J}/\psi}_{\rm pPb}$ for the J/$\psi$ [27] (except for the 2–20%
centrality interval where $Q^{i,{\rm J}/\psi}_{\rm pPb}$ was re-computed by
merging the 2–10% and 10–20% bins) and the double ratio between the $\psi(\rm
2S)$ and J/$\psi$ cross sections in p-Pb and pp collisions:

$Q^{i,\psi(\rm 2S)}_{\rm pPb}=Q^{i,{\rm J}/\psi}_{\rm
pPb}\cdot\frac{\sigma^{i,\psi(\rm 2S)}_{\rm pPb}}{\sigma^{i,{\rm J}/\psi}_{\rm
pPb}}\cdot\frac{\sigma^{{\rm J}/\psi}_{\rm pp}}{\sigma^{\psi(\rm 2S)}_{\rm
pp}}$ (2)

The uncertainties are obtained combining those on $Q^{i,{\rm J}/\psi}_{\rm
pPb}$ [27] with those on the double ratio, avoiding a double counting of the
J/$\psi$ related uncertainties. The notation $Q^{i,\psi(2S)}_{\rm pPb}$,
rather than the more usual $R^{i,\psi(2S)}_{\rm pPb}$, is used in this Letter,
to draw attention to possible residual biases in the centrality determination,
related to the loose correlation between the centrality estimators and the
corresponding collision geometry [33].

Table 2 summarizes the values of the systematic uncertainties on the various
ingredients that enter the cross section determination and the calculation of
the nuclear modification factor.

Source of uncertainty |  $\sigma^{\psi(\rm 2S)}_{\rm pPb}$, $Q^{\psi(\rm 2S)}_{\rm pPb}$ |  $\sigma^{\psi(\rm 2S)}_{\rm Pbp}$, $Q^{\psi(\rm 2S)}_{\rm Pbp}$
---|---|---
| 2.03$<y_{\rm cms}<$3.53 | -4.46$<y_{\rm cms}<$-2.96
Tracking efficiency (I) | 4 | 6
Trigger efficiency (I) | 3 | 3.4
Matching efficiency (I) | 1 | 1
Signal extraction | 10.8 $-$ 13.4 | 10.8 $-$ 20.9
MC input | 1.8 | 2.5
$\sigma_{\rm MB}$ (I) | 3.3 | 3.0
$\sigma_{\rm MB}$ (I,II) | 1.6 | 1.6
Table 2: Systematic uncertainties, in percentage, on the $\psi(\rm 2S)$ cross
sections and nuclear modification factors. For centrality-dependent
quantities, the range of variation is given. Type I uncertainties are
correlated over centrality, while type II are correlated between the forward
and the backward rapidity regions. When no indication is given, the
uncertainties are uncorrelated. The uncertainty on $\sigma_{\rm MB}$ is
related to the $\psi(\rm 2S)$ cross section only.

##  4 Results

The $\psi(\rm 2S)$ production cross sections as a function of the centrality
of the collision, expressed via $\langle N_{\rm coll}\rangle$, are plotted in
Fig. 2 (left).

Figure 2: Left: $\psi(\rm 2S)$ production cross sections shown as a function
of $\langle N_{\rm coll}\rangle$ for both p-Pb and Pb-p collisions. Right:
${\rm B.R.}_{\psi(\rm 2S)\rightarrow\mu^{+}\mu^{-}}\sigma_{\psi(\rm 2S)}/{\rm
B.R.}_{{\rm J}/\psi\rightarrow\mu^{+}\mu^{-}}\sigma_{{\rm J}/\psi}$ shown as a
function of $\langle N_{\rm coll}\rangle$ and compared to the pp value (line),
with a band representing its uncertainty. In both figures, vertical error bars
correspond to statistical uncertainties, while the open boxes represent the
systematic uncertainties. The Pb-p points are slightly shifted in $\langle
N_{\rm coll}\rangle$ to improve visibility.

As expected, their values increase with $\langle N_{\rm coll}\rangle$.

In Fig. 2 (right) the ratio ${\rm B.R.}_{\psi(\rm
2S)\rightarrow\mu^{+}\mu^{-}}\sigma_{\psi(\rm 2S)}/{\rm B.R.}_{{\rm
J}/\psi\rightarrow\mu^{+}\mu^{-}}\sigma_{{\rm J}/\psi}$ is shown as a function
of $\langle N_{\rm coll}\rangle$ and compared with the corresponding value for
pp collisions. Despite the large uncertainties, the data suggest a decreasing
trend from peripheral to central events, in particular at backward rapidity,
indicating a suppression of the $\psi(\rm 2S)$ production relative to the
J/$\psi$. While for peripheral collisions the cross section ratios are
consistent with the pp value, they become a factor 2–3 smaller for central
events, in both rapidity ranges. As remarked in Sect. 3, the pp cross section
ratio measured at $\sqrt{s}=7$ TeV has been used, including an 8% additional
uncertainty to account for its possible $\sqrt{s}$\- and $y$-dependence.

The degree of suppression of $\psi(\rm 2S)$ is directly quantified in Fig. 3
where the double ratio between the $\psi(\rm 2S)$ and J/$\psi$ cross sections
in p-Pb and pp collisions is shown. The result is compared with two
theoretical calculations. The first is based on a scenario where the
resonances may be dissociated via interactions with the partons or hadrons
produced in the collision in the same rapidity region (co-movers) [11]. The
model includes contributions from nuclear shadowing, based on the EPS09 LO
parameterization [3], and a co-mover interaction term, with dissociation cross
sections $\sigma^{\rm co-J/\psi}=0.65$ mb and $\sigma^{\rm co-\psi(2S)}=6$ mb,
these values being fixed from fits to low-energy experimental data [41]. The
effect of co-movers is larger at backward rapidity since their density is
larger in that region. The calculated co-mover densities are compatible with
the measured experimental charged particle multiplicities [42]. The
calculation reproduces well the measured values of the double ratio. Shadowing
effects are very similar for the two mesons and in this model they are assumed
to cancel out in the double ratio, so that only co-mover absorption plays a
role. The second model (QGP+HRG) is based on a thermal-rate equation framework
[43] which also implements the dissociation of charmonia in a hadron resonance
gas, including a total of 52 non-strange and single-strange meson species, up
to a mass of 2 GeV/$c^{2}$ [26]. The fireball evolution includes the
transition from a short QGP phase into the hadron resonance gas, through a
mixed phase. The shadowing effects, implemented through the EPS09
parametrization, cancel out in the double ratio, as in the previous model. The
result of the calculation, also shown in Fig. 3, is in fair agreement with the
measured values, in particular for central collisions. The model uncertainties
are dominated by the evaluation of the charmonium dissociation rates. The
ALICE result is also compared to mid-rapidity ($|y|<0.35$) PHENIX data [19] in
Fig. 3. Remarkably, in spite of the very different $\sqrt{s_{\rm NN}}$ and
$y_{\rm cms}$ values, the observed patterns as a function of centrality are
similar. It should also be noted that the PHENIX result can be qualitatively
described in a hadronic dissociation scenario, as discussed in [11, 26].

Figure 3: Double ratio $[\sigma_{\psi(\rm 2S)}/\sigma_{{\rm J}/\psi}]_{\rm
pPb}/[\sigma_{\psi(\rm 2S)}/\sigma_{{\rm J}/\psi}]_{\rm pp}$ for p-Pb and Pb-p
collisions, shown as a function of $\langle N_{\rm coll}\rangle$ (Pb-p points
are slightly shifted in $\langle N_{\rm coll}\rangle$ to improve visibility).
The data are compared to PHENIX mid-rapidity results [19] and to the
theoretical calculations of Ref. [11] and [26]. The boxes around unity
correspond to the global systematic uncertainties at forward (red box) and
backward (blue box) rapidities. The grey box is a global systematic
uncertainty common to both p-Pb rapidity ranges, while the green box refers to
the PHENIX results.

In Fig. 4 the nuclear modification factor for $\psi(\rm 2S)$ mesons is shown
as a function of centrality, separately for forward and backward rapidities.
In both regions, a trend towards an increasing suppression can be seen when
moving from peripheral to central collisions. The corresponding $Q^{{\rm
J}/\psi}_{\rm pPb}$ values [27] are also shown. At forward-$y$ there is an
indication for a smaller $Q^{\psi(2S)}_{\rm pPb}$ with respect to $Q^{{\rm
J}/\psi}_{\rm pPb}$. The difference between the $\psi(\rm 2S)$ and the
J/$\psi$ nuclear modification factors amounts, for central events, to
1.9$\sigma$, while, integrating over centrality, the corresponding quantity is
2.3$\sigma$. At backward-$y$ the suppression patterns for the J/$\psi$ and the
$\psi(\rm 2S)$ are different, with $Q^{{\rm J}/\psi}_{\rm pPb}\sim 1$ (or even
slightly larger), and a strong suppression for the $\psi(\rm 2S)$. In the most
central collisions, the difference between the measured $Q_{\rm pPb}$
corresponds to 4.3$\sigma$, while, integrating over centrality, suppressions
differ by 4.1$\sigma$. The results are compared to calculations including
either only shadowing (EPS09 LO [11], EPS09 NLO [44]) or only coherent energy
loss [45] and to models implementing final state interactions (co-movers [11],
QGP+HRG [26]). While the J/$\psi$ results are reproduced by shadowing/energy
loss calculations, additional final state effects, as those discussed in the
context of Fig. 3, are needed to describe the $\psi(\rm 2S)$ results, in
particular at backward rapidity.

Figure 4: J/$\psi$ [27] and $\psi(\rm 2S)$ nuclear modification factors,
$Q_{\rm pPb}$, shown as a function of $\langle N_{\rm coll}\rangle$ for the
backward (left) and forward (right) rapidity regions and compared to
theoretical models [44, 11, 26, 45]. The boxes around unity correspond to the
global $\psi(\rm 2S)$ systematic uncertainties at forward (red box) and
backward (blue box) rapidities. The grey box is a global systematic
uncertainty common to both J/$\psi$ and $\psi(\rm 2S)$.

Finally, the double ratios are shown in Fig. 5 as a function of the pair
crossing time $\tau_{\rm c}$ in nuclear matter [9]. This quantity can be
calculated as $\tau_{\rm c}=\langle L\rangle/(\beta_{\rm z}\gamma)$ where
$\langle L\rangle$ is the average thickness of nuclear matter crossed by the
pair, which was evaluated, for each centrality class, using the Glauber model
[46], $\beta_{\rm z}=\tanh y_{c\overline{c}}^{\rm rest}$ is the velocity of
the $c\overline{c}$ along the beam direction in the nucleus rest frame,
$\gamma=E_{c\overline{c}}/m_{c\overline{c}}$ and $E_{c\overline{c}}=m_{\rm
T,c\overline{c}}\cosh y_{c\overline{c}}^{\rm rest}$. The value
$m_{c\overline{c}}=3.4$ GeV/$c^{2}$ was chosen for the (average) mass of the
evolving $c{\overline{c}}$ pair [9, 47], while $m_{\rm T,c\overline{c}}$ was
calculated in each centrality bin starting from the measured J/$\psi$ $\langle
p_{\rm T}\rangle$ values [27]. We use the J/$\psi$ $\langle p_{\rm T}\rangle$
as a proxy for the average $p_{\rm T}$ of the $c{\overline{c}}$ pair, as the
$\psi(2S)$ statistics is too low to extract a corresponding $\langle p_{\rm
T}\rangle$ value. If we assume instead that $\langle p_{\rm
T}^{\psi(2S)}\rangle\sim 1.1\langle p_{\rm T}^{{\rm J}/\psi}\rangle$ as
measured by LHCb in pp collisions at $\sqrt{s}=7$ TeV [48, 49], the $\tau_{\rm
c}$ values would decrease by $\sim 4$%. Other sources of uncertainties on
$\tau_{\rm c}$ include the uncertainties on the measured J/$\psi$ $\langle
p_{\rm T}\rangle$, which contribute less than 1%, and those on $\langle
L\rangle$, which are dominant and of the order of 10%. In Fig. 5 we show the
double ratio as a function of $\tau_{\rm c}$ in the two rapidity regions.
Different $\tau_{\rm c}$ intervals can also be selected by slicing the events
in bins of $p_{\rm T}$ (see Ref. [36]), varying, in this way, the $\gamma$
values of the $c\overline{c}$. The double ratio results, obtained in [36], are
therefore also shown in Fig. 5 at their corresponding average $\tau_{\rm c}$
values. In the double ratio one effectively removes, as discussed above,
initial state effects, so that Fig. 5 shows the $\tau_{\rm c}$ dependence of
final state effects on $\psi(\rm 2S)$ compared to J/$\psi$. The two sets of
results, corresponding to a slicing of the events in centrality or in $p_{\rm
T}$, are in good agreement. At backward-$y$, where the largest $\tau_{\rm c}$
values are reached, a clearly decreasing trend can be observed. The average
resonance formation time $\tau_{\rm f}$ is, according to most theory estimates
[9, 20, 21], larger by at least a factor $\sim 2$ than the accessible
$\tau_{\rm c}$ range. On the other hand, the width of the $\tau_{\rm f}$
distribution is expected to be non-negligible [21], and it cannot be excluded
that at least a fraction of the $c\overline{c}$ pairs hadronizes inside the
nucleus. Therefore, the observed behaviour is likely due to a combination of
final state effects which take place outside the nucleus, as e.g. interaction
with a hadronic resonance gas, and dissociation effects on the fully formed
resonance, due to nuclear matter, and taking place inside the nucleus. The
relative importance of the two mechanisms is difficult to quantify in such a
simple analysis and quantitative theoretical studies, also exploring
alternative mechanisms, are needed. At forward rapidity, where $\tau_{\rm c}$
becomes smaller than $\tau_{\rm f}$ by about 2–3 orders of magnitude, the
interaction with nuclear matter is not expected to play any significant role.
The results of a similar analysis carried out on PHENIX mid-rapidity data [19]
are also shown in Fig. 5. Within uncertainties, a scaling of the ALICE and
PHENIX double ratio values with $\tau_{\rm c}$ is observed.

Figure 5: Double ratio $[\sigma_{\psi(\rm 2S)}/\sigma_{{\rm J}/\psi}]_{\rm
pPb}/[\sigma_{\psi(\rm 2S)}/\sigma_{{\rm J}/\psi}]_{\rm pp}$ shown as a
function of $\tau_{c}$ for the backward and forward rapidity regions. For each
$y$-range, the two sets of points were obtained from the centrality analysis
and from the $p_{\rm T}$-dependent analysis of Ref. [22]. Statistical
uncertainties are shown as lines, while the total systematic uncertainties are
shown as boxes around the points. The results of a corresponding analysis
carried out on the PHENIX mid-rapidity data [19] is also shown. The box around
unity represents the PHENIX global systematic uncertainty. For the ALICE
results, the global uncertainties are different for the various data sets, and
are included in the boxes around the points

##  5 Conclusions

The centrality dependence of the $\psi(\rm 2S)$ production in p-Pb collisions
at $\sqrt{s_{\rm NN}}=5.02$ TeV was measured in five intervals, using the ZN
energy as an estimator. The ratio ${\rm B.R.}_{\psi(\rm
2S)\rightarrow\mu^{+}\mu^{-}}\sigma_{\psi(\rm 2S)}/{\rm B.R.}_{{\rm
J}/\psi\rightarrow\mu^{+}\mu^{-}}\sigma_{{\rm J}/\psi}$ is compatible with pp
measurements in peripheral events, whereas a decrease is observed towards
central events, showing that the $\psi(\rm 2S)$ state is suppressed with
respect to the J/$\psi$ state. The results on the nuclear modification
factors, together with the corresponding model comparisons, show that effects
such as shadowing or energy loss are enough to explain the J/$\psi$ behaviour,
while additional mechanisms are needed to describe the $\psi(\rm 2S)$
suppression. Theoretical models that include final state interactions are able
to reproduce such a suppression. A study of the double ratio
$[\sigma_{\psi(\rm 2S)}/\sigma_{{\rm J}/\psi}]_{\rm pPb}/[\sigma_{\psi(\rm
2S)}/\sigma_{{\rm J}/\psi}]_{\rm pp}$, as a function of the crossing time
$\tau_{\rm c}$, shows that at forward-$y$ the $\tau_{\rm c}$ values are much
shorter than the resonance formation time $\tau_{\rm f}$, excluding any
significant role of final state interactions with nuclear matter. Effects
occurring at later times, such as the break-up by co-movers in the hadronic
gas, are suitable candidates for an explanation of the observed $\psi(\rm 2S)$
suppression. At backward-$y$ the $\tau_{\rm c}$ values, although significantly
larger, are still smaller than $\tau_{\rm f}$. However, the observed scaling
of the double ratios with $\tau_{\rm c}$ may be suggestive of an effect at
least partly related to a dissociation of the fully-formed resonance in
nuclear matter.

## Acknowledgements

The ALICE Collaboration would like to thank all its engineers and technicians
for their invaluable contributions to the construction of the experiment and
the CERN accelerator teams for the outstanding performance of the LHC complex.
The ALICE Collaboration gratefully acknowledges the resources and support
provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG)
collaboration. The ALICE Collaboration acknowledges the following funding
agencies for their support in building and running the ALICE detector: State
Committee of Science, World Federation of Scientists (WFS) and Swiss Fonds
Kidagan, Armenia; 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); National Natural Science
Foundation of China (NSFC), the Chinese Ministry of Education (CMOE) and the
Ministry of Science and Technology of China (MSTC); Ministry of Education and
Youth of the Czech Republic; Danish Natural Science Research Council, the
Carlsberg Foundation and the Danish National Research Foundation; The European
Research Council under the European Community’s Seventh Framework Programme;
Helsinki Institute of Physics and the Academy of Finland; French CNRS-IN2P3,
the ‘Region Pays de Loire’, ‘Region Alsace’, ‘Region Auvergne’ and CEA,
France; German Bundesministerium fur Bildung, Wissenschaft, Forschung und
Technologie (BMBF) and the Helmholtz Association; General Secretariat for
Research and Technology, Ministry of Development, Greece; National Research,
Development and Innovation Office (NKFIH), Hungary; Department of Atomic
Energy and Department of Science and Technology of the Government of India;
Istituto Nazionale di Fisica Nucleare (INFN) and Centro Fermi - Museo Storico
della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Italy; Japan Society
for the Promotion of Science (JSPS) KAKENHI and MEXT, Japan; Joint Institute
for Nuclear Research, Dubna; National Research Foundation of Korea (NRF);
Consejo Nacional de Cienca y Tecnologia (CONACYT), Direccion General de
Asuntos del Personal Academico(DGAPA), México, Amerique Latine Formation
academique - European Commission (ALFA-EC) and the EPLANET Program (European
Particle Physics Latin American Network); Stichting voor Fundamenteel
Onderzoek der Materie (FOM) and the Nederlandse Organisatie voor
Wetenschappelijk Onderzoek (NWO), Netherlands; Research Council of Norway
(NFR); National Science Centre, Poland; Ministry of National
Education/Institute for Atomic Physics and National Council of Scientific
Research in Higher Education (CNCSI-UEFISCDI), Romania; Ministry of Education
and Science of Russian Federation, Russian Academy of Sciences, Russian
Federal Agency of Atomic Energy, Russian Federal Agency for Science and
Innovations and The Russian Foundation for Basic Research; Ministry of
Education of Slovakia; Department of Science and Technology, South Africa;
Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas
(CIEMAT), E-Infrastructure shared between Europe and Latin America (EELA),
Ministerio de Economía y Competitividad (MINECO) of Spain, Xunta de Galicia
(Consellería de Educación), Centro de Aplicaciones Tecnológicas y Desarrollo
Nuclear (CEADEN), Cubaenergía, Cuba, and IAEA (International Atomic Energy
Agency); Swedish Research Council (VR) and Knut $\&$ Alice Wallenberg
Foundation (KAW); Ukraine Ministry of Education and Science; United Kingdom
Science and Technology Facilities Council (STFC); The United States Department
of Energy, the United States National Science Foundation, the State of Texas,
and the State of Ohio; Ministry of Science, Education and Sports of Croatia
and Unity through Knowledge Fund, Croatia; Council of Scientific and
Industrial Research (CSIR), New Delhi, India; Pontificia Universidad Católica
del Perú.

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##  Appendix A The ALICE Collaboration

J. Adam39, D. Adamová84, M.M. Aggarwal88, G. Aglieri Rinella35, M. Agnello110,
N. Agrawal47, Z. Ahammed133, S. Ahmad18, S.U. Ahn68, S. Aiola137, A.
Akindinov54, S.N. Alam133, D.S.D. Albuquerque121, D. Aleksandrov80, B.
Alessandro110, D. Alexandre101, R. Alfaro Molina63, A. Alici12,104, A. Alkin3,
J.R.M. Almaraz119, J. Alme22,37, T. Alt42, S. Altinpinar22, I. Altsybeev132,
C. Alves Garcia Prado120, C. Andrei78, A. Andronic97, V. Anguelov93, T.
Antičić98, F. Antinori107, P. Antonioli104, L. Aphecetche113, H.
Appelshäuser60, S. Arcelli27, R. Arnaldi110, O.W. Arnold36,94, I.C. Arsene21,
M. Arslandok60, B. Audurier113, A. Augustinus35, R. Averbeck97, M.D. Azmi18,
A. Badalà106, Y.W. Baek67, S. Bagnasco110, R. Bailhache60, R. Bala91, S.
Balasubramanian137, A. Baldisseri15, R.C. Baral57, A.M. Barbano26, R.
Barbera28, F. Barile32, G.G. Barnaföldi136, L.S. Barnby35,101, V. Barret70, P.
Bartalini7, K. Barth35, J. Bartke117, E. Bartsch60, M. Basile27, N. Bastid70,
S. Basu133, B. Bathen61, G. Batigne113, A. Batista Camejo70, B. Batyunya66,
P.C. Batzing21, I.G. Bearden81, H. Beck60,93, C. Bedda110, N.K. Behera48,50,
I. Belikov64, F. Bellini27, H. Bello Martinez2, R. Bellwied122, R. Belmont135,
E. Belmont-Moreno63, V. Belyaev75, G. Bencedi136, S. Beole26, I. Berceanu78,
A. Bercuci78, Y. Berdnikov86, D. Berenyi136, R.A. Bertens53, D. Berzano35, L.
Betev35, A. Bhasin91, I.R. Bhat91, A.K. Bhati88, B. Bhattacharjee44, J.
Bhom117,128, L. Bianchi122, N. Bianchi72, C. Bianchin135, J. Bielčík39, J.
Bielčíková84, A. Bilandzic36,81,94, G. Biro136, R. Biswas4, S. Biswas4,79, S.
Bjelogrlic53, J.T. Blair118, D. Blau80, C. Blume60, F. Bock74,93, A.
Bogdanov75, H. Bøggild81, L. Boldizsár136, M. Bombara40, J. Book60, H.
Borel15, A. Borissov96, M. Borri83,124, F. Bossú65, E. Botta26, C. Bourjau81,
P. Braun-Munzinger97, M. Bregant120, T. Breitner59, T.A. Broker60, T.A.
Browning95, M. Broz39, E.J. Brucken45, E. Bruna110, G.E. Bruno32, D.
Budnikov99, H. Buesching60, S. Bufalino26,35, P. Buncic35, O. Busch128, Z.
Buthelezi65, J.B. Butt16, J.T. Buxton19, J. Cabala115, D. Caffarri35, X. Cai7,
H. Caines137, L. Calero Diaz72, A. Caliva53, E. Calvo Villar102, P.
Camerini25, F. Carena35, W. Carena35, F. Carnesecchi27, J. Castillo
Castellanos15, A.J. Castro125, E.A.R. Casula24, C. Ceballos Sanchez9, J.
Cepila39, P. Cerello110, J. Cerkala115, B. Chang123, S. Chapeland35, M.
Chartier124, J.L. Charvet15, S. Chattopadhyay133, S. Chattopadhyay100, A.
Chauvin36,94, V. Chelnokov3, M. Cherney87, C. Cheshkov130, B. Cheynis130, V.
Chibante Barroso35, D.D. Chinellato121, S. Cho50, P. Chochula35, K. Choi96, M.
Chojnacki81, S. Choudhury133, P. Christakoglou82, C.H. Christensen81, P.
Christiansen33, T. Chujo128, S.U. Chung96, C. Cicalo105, L. Cifarelli12,27, F.
Cindolo104, J. Cleymans90, F. Colamaria32, D. Colella35,55, A. Collu74, M.
Colocci27, G. Conesa Balbastre71, Z. Conesa del Valle51, M.E. ConnorsII,137,
J.G. Contreras39, T.M. Cormier85, Y. Corrales Morales110, I. Cortés
Maldonado2, P. Cortese31, M.R. Cosentino120, F. Costa35, P. Crochet70, R. Cruz
Albino11, E. Cuautle62, L. Cunqueiro35,61, T. Dahms36,94, A. Dainese107, M.C.
Danisch93, A. Danu58, D. Das100, I. Das100, S. Das4, A. Dash79, S. Dash47, S.
De120, A. De Caro12,30, G. de Cataldo103, C. de Conti120, J. de Cuveland42, A.
De Falco24, D. De Gruttola12,30, N. De Marco110, S. De Pasquale30, A.
Deisting93,97, A. Deloff77, E. DénesI,136, C. Deplano82, P. Dhankher47, D. Di
Bari32, A. Di Mauro35, P. Di Nezza72, M.A. Diaz Corchero10, T. Dietel90, P.
Dillenseger60, R. Divià35, Ø. Djuvsland22, A. Dobrin58,82, D. Domenicis
Gimenez120, B. Dönigus60, O. Dordic21, T. Drozhzhova60, A.K. Dubey133, A.
Dubla53, L. Ducroux130, P. Dupieux70, R.J. Ehlers137, D. Elia103, E.
Endress102, H. Engel59, E. Epple36,94,137, B. Erazmus113, I. Erdemir60, F.
Erhardt129, B. Espagnon51, M. Estienne113, S. Esumi128, J. Eum96, D. Evans101,
S. Evdokimov111, G. Eyyubova39, L. Fabbietti36,94, D. Fabris107, J. Faivre71,
A. Fantoni72, M. Fasel74, L. Feldkamp61, A. Feliciello110, G. Feofilov132, J.
Ferencei84, A. Fernández Téllez2, E.G. Ferreiro17, A. Ferretti26, A.
Festanti29, V.J.G. Feuillard15,70, J. Figiel117, M.A.S. Figueredo120,124, S.
Filchagin99, D. Finogeev52, F.M. Fionda24, E.M. Fiore32, M.G. Fleck93, M.
Floris35, S. Foertsch65, P. Foka97, S. Fokin80, E. Fragiacomo109, A.
Francescon29,35, U. Frankenfeld97, G.G. Fronze26, U. Fuchs35, C. Furget71, A.
Furs52, M. Fusco Girard30, J.J. Gaardhøje81, M. Gagliardi26, A.M. Gago102, M.
Gallio26, D.R. Gangadharan74, P. Ganoti89, C. Gao7, C. Garabatos97, E. Garcia-
Solis13, C. Gargiulo35, P. Gasik36,94, E.F. Gauger118, M. Germain113, M.
Gheata35,58, P. Ghosh133, S.K. Ghosh4, P. Gianotti72, P. Giubellino35,110, P.
Giubilato29, E. Gladysz-Dziadus117, P. Glässel93, D.M. Goméz Coral63, A. Gomez
Ramirez59, A.S. Gonzalez35, V. Gonzalez10, P. González-Zamora10, S.
Gorbunov42, L. Görlich117, S. Gotovac116, V. Grabski63, O.A. Grachov137, L.K.
Graczykowski134, K.L. Graham101, A. Grelli53, A. Grigoras35, C. Grigoras35, V.
Grigoriev75, A. Grigoryan1, S. Grigoryan66, B. Grinyov3, N. Grion109, J.M.
Gronefeld97, J.F. Grosse-Oetringhaus35, R. Grosso97, F. Guber52, R.
Guernane71, B. Guerzoni27, K. Gulbrandsen81, T. Gunji127, A. Gupta91, R.
Gupta91, R. Haake35, Ø. Haaland22, C. Hadjidakis51, M. Haiduc58, H.
Hamagaki127, G. Hamar136, J.C. Hamon64, J.W. Harris137, A. Harton13, D.
Hatzifotiadou104, S. Hayashi127, S.T. Heckel60, E. Hellbär60, H. Helstrup37,
A. Herghelegiu78, G. Herrera Corral11, B.A. Hess34, K.F. Hetland37, H.
Hillemanns35, B. Hippolyte64, D. Horak39, R. Hosokawa128, P. Hristov35, T.J.
Humanic19, N. Hussain44, T. Hussain18, D. Hutter42, D.S. Hwang20, R. Ilkaev99,
M. Inaba128, E. Incani24, M. Ippolitov75,80, M. Irfan18, M. Ivanov97, V.
Ivanov86, V. Izucheev111, N. Jacazio27, P.M. Jacobs74, M.B. Jadhav47, S.
Jadlovska115, J. Jadlovsky55,115, C. Jahnke120, M.J. Jakubowska134, H.J.
Jang68, M.A. Janik134, P.H.S.Y. Jayarathna122, C. Jena29, S. Jena122, R.T.
Jimenez Bustamante97, P.G. Jones101, A. Jusko101, P. Kalinak55, A. Kalweit35,
J. Kamin60, J.H. Kang138, V. Kaplin75, S. Kar133, A. Karasu Uysal69, O.
Karavichev52, T. Karavicheva52, L. Karayan93,97, E. Karpechev52, U.
Kebschull59, R. Keidel139, D.L.D. Keijdener53, M. Keil35, M. Mohisin
KhanIII,18, P. Khan100, S.A. Khan133, A. Khanzadeev86, Y. Kharlov111, B.
Kileng37, D.W. Kim43, D.J. Kim123, D. Kim138, H. Kim138, J.S. Kim43, M.
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Kisiel134, G. Kiss136, J.L. Klay6, C. Klein60, J. Klein35, C. Klein-Bösing61,
S. Klewin93, A. Kluge35, M.L. Knichel93, A.G. Knospe118,122, C. Kobdaj114, M.
Kofarago35, T. Kollegger97, A. Kolojvari132, V. Kondratiev132, N.
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M. Kowalski117, G. Koyithatta Meethaleveedu47, I. Králik55, A. Kravčáková40,
M. Krivda55,101, F. Krizek84, E. Kryshen35,86, M. Krzewicki42, A.M. Kubera19,
V. Kučera84, C. Kuhn64, P.G. Kuijer82, A. Kumar91, J. Kumar47, L. Kumar88, S.
Kumar47, P. Kurashvili77, A. Kurepin52, A.B. Kurepin52, A. Kuryakin99, M.J.
Kweon50, Y. Kwon138, S.L. La Pointe110, P. La Rocca28, P. Ladron de Guevara11,
C. Lagana Fernandes120, I. Lakomov35, R. Langoy41, K. Lapidus36,94, C. Lara59,
A. Lardeux15, A. Lattuca26, E. Laudi35, R. Lea25, L. Leardini93, G.R. Lee101,
S. Lee138, F. Lehas82, S. Lehner112, R.C. Lemmon83, V. Lenti103, E.
Leogrande53, I. León Monzón119, H. León Vargas63, M. Leoncino26, P. Lévai136,
S. Li7,70, X. Li14, J. Lien41, R. Lietava101, S. Lindal21, V. Lindenstruth42,
C. Lippmann97, M.A. Lisa19, H.M. Ljunggren33, D.F. Lodato53, P.I. Loenne22, V.
Loginov75, C. Loizides74, X. Lopez70, E. López Torres9, A. Lowe136, P.
Luettig60, M. Lunardon29, G. Luparello25, T.H. Lutz137, A. Maevskaya52, M.
Mager35, S. Mahajan91, S.M. Mahmood21, A. Maire64, R.D. Majka137, M. Malaev86,
I. Maldonado Cervantes62, L. MalininaIV,66, D. Mal’Kevich54, P. Malzacher97,
A. Mamonov99, V. Manko80, F. Manso70, V. Manzari35,103, M.
Marchisone26,65,126, J. Mareš56, G.V. Margagliotti25, A. Margotti104, J.
Margutti53, A. Marín97, C. Markert118, M. Marquard60, N.A. Martin97, J. Martin
Blanco113, P. Martinengo35, M.I. Martínez2, G. Martínez García113, M. Martinez
Pedreira35, A. Mas120, S. Masciocchi97, M. Masera26, A. Masoni105, A.
Mastroserio32, A. Matyja117, C. Mayer117, J. Mazer125, M.A. Mazzoni108, D.
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Mercado Pérez93, M. Meres38, Y. Miake128, M.M. Mieskolainen45, K.
Mikhaylov54,66, L. Milano35,74, J. Milosevic21, A. Mischke53, A.N. Mishra48,
D. Miśkowiec97, J. Mitra133, C.M. Mitu58, N. Mohammadi53, B. Mohanty79, L.
Molnar64, L. Montaño Zetina11, E. Montes10, D.A. Moreira De Godoy61, L.A.P.
Moreno2, S. Moretto29, A. Morreale113, A. Morsch35, V. Muccifora72, E.
Mudnic116, D. Mühlheim61, S. Muhuri133, M. Mukherjee133, J.D. Mulligan137,
M.G. Munhoz120, R.H. Munzer36,60,94, H. Murakami127, S. Murray65, L. Musa35,
J. Musinsky55, B. Naik47, R. Nair77, B.K. Nandi47, R. Nania104, E. Nappi103,
M.U. Naru16, H. Natal da Luz120, C. Nattrass125, S.R. Navarro2, K. Nayak79, R.
Nayak47, T.K. Nayak133, S. Nazarenko99, A. Nedosekin54, L. Nellen62, F. Ng122,
M. Nicassio97, M. Niculescu58, J. Niedziela35, B.S. Nielsen81, S. Nikolaev80,
S. Nikulin80, V. Nikulin86, F. Noferini12,104, P. Nomokonov66, G. Nooren53,
J.C.C. Noris2, J. Norman124, A. Nyanin80, J. Nystrand22, H. Oeschler93, S.
Oh137, S.K. Oh67, A. Ohlson35, A. Okatan69, T. Okubo46, L. Olah136, J.
Oleniacz134, A.C. Oliveira Da Silva120, M.H. Oliver137, J. Onderwaater97, C.
Oppedisano110, R. Orava45, M. Oravec115, A. Ortiz Velasquez62, A. Oskarsson33,
J. Otwinowski117, K. Oyama76,93, M. Ozdemir60, Y. Pachmayer93, D. Pagano131,
P. Pagano30, G. Paić62, S.K. Pal133, J. Pan135, A.K. Pandey47, V. Papikyan1,
G.S. Pappalardo106, P. Pareek48, W.J. Park97, S. Parmar88, A. Passfeld61, V.
Paticchio103, R.N. Patra133, B. Paul100,110, H. Pei7, T. Peitzmann53, H.
Pereira Da Costa15, D. Peresunko75,80, E. Perez Lezama60, V. Peskov60, Y.
Pestov5, V. Petráček39, V. Petrov111, M. Petrovici78, C. Petta28, S. Piano109,
M. Pikna38, P. Pillot113, L.O.D.L. Pimentel81, O. Pinazza35,104, L. Pinsky122,
D.B. Piyarathna122, M. Płoskoń74, M. Planinic129, J. Pluta134, S.
Pochybova136, P.L.M. Podesta-Lerma119, M.G. Poghosyan85,87, B.
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R.J. Reed135, A. Rehman22, P. Reichelt60, F. Reidt35,93, X. Ren7, R.
Renfordt60, A.R. Reolon72, A. Reshetin52, K. Reygers93, V. Riabov86, R.A.
Ricci73, T. Richert33, M. Richter21, P. Riedler35, W. Riegler35, F. Riggi28,
C. Ristea58, E. Rocco53, M. Rodríguez Cahuantzi2,11, A. Rodriguez Manso82, K.
Røed21, E. Rogochaya66, D. Rohr42, D. Röhrich22, F. Ronchetti35,72, L.
Ronflette113, P. Rosnet70, A. Rossi29,35, F. Roukoutakis89, A. Roy48, C.
Roy64, P. Roy100, A.J. Rubio Montero10, R. Rui25, R. Russo26, B.D. Ruzza107,
E. Ryabinkin80, Y. Ryabov86, A. Rybicki117, S. Saarinen45, S. Sadhu133, S.
Sadovsky111, K. Šafařík35, B. Sahlmuller60, P. Sahoo48, R. Sahoo48, S.
Sahoo57, P.K. Sahu57, J. Saini133, S. Sakai72, M.A. Saleh135, J. Salzwedel19,
S. Sambyal91, V. Samsonov86, L. Šándor55, A. Sandoval63, M. Sano128, D.
Sarkar133, N. Sarkar133, P. Sarma44, E. Scapparone104, F. Scarlassara29, C.
Schiaua78, R. Schicker93, C. Schmidt97, H.R. Schmidt34, M. Schmidt34, S.
Schuchmann60, J. Schukraft35, M. Schulc39, Y. Schutz35,113, K. Schwarz97, K.
Schweda97, G. Scioli27, E. Scomparin110, R. Scott125, M. Šefčík40, J.E.
Seger87, Y. Sekiguchi127, D. Sekihata46, I. Selyuzhenkov97, K. Senosi65, S.
Senyukov3,35, E. Serradilla10,63, A. Sevcenco58, A. Shabanov52, A.
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Sharma91, M. Sharma91, M. Sharma91, N. Sharma125, A.I. Sheikh133, K.
Shigaki46, Q. Shou7, K. Shtejer9,26, Y. Sibiriak80, S. Siddhanta105, K.M.
Sielewicz35, T. Siemiarczuk77, D. Silvermyr33, C. Silvestre71, G.
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M. Slupecki123, N. Smirnov137, R.J.M. Snellings53, T.W. Snellman123, J.
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Zimmermann93, M.B. Zimmermann35,61, G. Zinovjev3, M. Zyzak42

Affiliation Notes

I Deceased
II Also at: Georgia State University, Atlanta, Georgia, United States
III Also at Department of Applied Physics, Aligarh Muslim University, Aligarh,
India
IV Also at: M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute
of Nuclear, Physics, Moscow, Russia

Collaboration Institutes

1 A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute)
Foundation, Yerevan, Armenia
2 Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
3 Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine
4 Bose Institute, Department of Physics and Centre for Astroparticle Physics
and Space Science (CAPSS), Kolkata, India
5 Budker Institute for Nuclear Physics, Novosibirsk, Russia
6 California Polytechnic State University, San Luis Obispo, California, United
States
7 Central China Normal University, Wuhan, China
8 Centre de Calcul de l’IN2P3, Villeurbanne, France
9 Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana,
Cuba
10 Centro de Investigaciones Energéticas Medioambientales y Tecnológicas
(CIEMAT), Madrid, Spain
11 Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City
and Mérida, Mexico
12 Centro Fermi - Museo Storico della Fisica e Centro Studi e Ricerche “Enrico
Fermi”, Rome, Italy
13 Chicago State University, Chicago, Illinois, USA
14 China Institute of Atomic Energy, Beijing, China
15 Commissariat à l’Energie Atomique, IRFU, Saclay, France
16 COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan
17 Departamento de Física de Partículas and IGFAE, Universidad de Santiago de
Compostela, Santiago de Compostela, Spain
18 Department of Physics, Aligarh Muslim University, Aligarh, India
19 Department of Physics, Ohio State University, Columbus, Ohio, United States
20 Department of Physics, Sejong University, Seoul, South Korea
21 Department of Physics, University of Oslo, Oslo, Norway
22 Department of Physics and Technology, University of Bergen, Bergen, Norway
23 Dipartimento di Fisica dell’Università ’La Sapienza’ and Sezione INFN Rome,
Italy
24 Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
25 Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
26 Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy
27 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Bologna, Italy
28 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Catania, Italy
29 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Padova, Italy
30 Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo
Collegato INFN, Salerno, Italy
31 Dipartimento di Scienze e Innovazione Tecnologica dell’Università del
Piemonte Orientale and Gruppo Collegato INFN, Alessandria, Italy
32 Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari,
Italy
33 Division of Experimental High Energy Physics, University of Lund, Lund,
Sweden
34 Eberhard Karls Universität Tübingen, Tübingen, Germany
35 European Organization for Nuclear Research (CERN), Geneva, Switzerland
36 Excellence Cluster Universe, Technische Universität München, Munich,
Germany
37 Faculty of Engineering, Bergen University College, Bergen, Norway
38 Faculty of Mathematics, Physics and Informatics, Comenius University,
Bratislava, Slovakia
39 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University in Prague, Prague, Czech Republic
40 Faculty of Science, P.J. Šafárik University, Košice, Slovakia
41 Faculty of Technology, Buskerud and Vestfold University College, Vestfold,
Norway
42 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-
Universität Frankfurt, Frankfurt, Germany
43 Gangneung-Wonju National University, Gangneung, South Korea
44 Gauhati University, Department of Physics, Guwahati, India
45 Helsinki Institute of Physics (HIP), Helsinki, Finland
46 Hiroshima University, Hiroshima, Japan
47 Indian Institute of Technology Bombay (IIT), Mumbai, India
48 Indian Institute of Technology Indore, Indore (IITI), India
49 Indonesian Institute of Sciences, Jakarta, Indonesia
50 Inha University, Incheon, South Korea
51 Institut de Physique Nucléaire d’Orsay (IPNO), Université Paris-Sud, CNRS-
IN2P3, Orsay, France
52 Institute for Nuclear Research, Academy of Sciences, Moscow, Russia
53 Institute for Subatomic Physics of Utrecht University, Utrecht, Netherlands
54 Institute for Theoretical and Experimental Physics, Moscow, Russia
55 Institute of Experimental Physics, Slovak Academy of Sciences, Košice,
Slovakia
56 Institute of Physics, Academy of Sciences of the Czech Republic, Prague,
Czech Republic
57 Institute of Physics, Bhubaneswar, India
58 Institute of Space Science (ISS), Bucharest, Romania
59 Institut für Informatik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany
60 Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany
61 Institut für Kernphysik, Westfälische Wilhelms-Universität Münster,
Münster, Germany
62 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México,
Mexico City, Mexico
63 Instituto de Física, Universidad Nacional Autónoma de México, Mexico City,
Mexico
64 Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg,
CNRS-IN2P3, Strasbourg, France
65 iThemba LABS, National Research Foundation, Somerset West, South Africa
66 Joint Institute for Nuclear Research (JINR), Dubna, Russia
67 Konkuk University, Seoul, South Korea
68 Korea Institute of Science and Technology Information, Daejeon, South Korea
69 KTO Karatay University, Konya, Turkey
70 Laboratoire de Physique Corpusculaire (LPC), Clermont Université,
Université Blaise Pascal, CNRS–IN2P3, Clermont-Ferrand, France
71 Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-
Alpes, CNRS-IN2P3, Grenoble, France
72 Laboratori Nazionali di Frascati, INFN, Frascati, Italy
73 Laboratori Nazionali di Legnaro, INFN, Legnaro, Italy
74 Lawrence Berkeley National Laboratory, Berkeley, California, United States
75 Moscow Engineering Physics Institute, Moscow, Russia
76 Nagasaki Institute of Applied Science, Nagasaki, Japan
77 National Centre for Nuclear Studies, Warsaw, Poland
78 National Institute for Physics and Nuclear Engineering, Bucharest, Romania
79 National Institute of Science Education and Research, Bhubaneswar, India
80 National Research Centre Kurchatov Institute, Moscow, Russia
81 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
82 Nikhef, Nationaal instituut voor subatomaire fysica, Amsterdam, Netherlands
83 Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom
84 Nuclear Physics Institute, Academy of Sciences of the Czech Republic, Řež u
Prahy, Czech Republic
85 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
86 Petersburg Nuclear Physics Institute, Gatchina, Russia
87 Physics Department, Creighton University, Omaha, Nebraska, United States
88 Physics Department, Panjab University, Chandigarh, India
89 Physics Department, University of Athens, Athens, Greece
90 Physics Department, University of Cape Town, Cape Town, South Africa
91 Physics Department, University of Jammu, Jammu, India
92 Physics Department, University of Rajasthan, Jaipur, India
93 Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
94 Physik Department, Technische Universität München, Munich, Germany
95 Purdue University, West Lafayette, Indiana, United States
96 Pusan National University, Pusan, South Korea
97 Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum
für Schwerionenforschung, Darmstadt, Germany
98 Rudjer Bošković Institute, Zagreb, Croatia
99 Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
100 Saha Institute of Nuclear Physics, Kolkata, India
101 School of Physics and Astronomy, University of Birmingham, Birmingham,
United Kingdom
102 Sección Física, Departamento de Ciencias, Pontificia Universidad Católica
del Perú, Lima, Peru
103 Sezione INFN, Bari, Italy
104 Sezione INFN, Bologna, Italy
105 Sezione INFN, Cagliari, Italy
106 Sezione INFN, Catania, Italy
107 Sezione INFN, Padova, Italy
108 Sezione INFN, Rome, Italy
109 Sezione INFN, Trieste, Italy
110 Sezione INFN, Turin, Italy
111 SSC IHEP of NRC Kurchatov institute, Protvino, Russia
112 Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
113 SUBATECH, Ecole des Mines de Nantes, Université de Nantes, CNRS-IN2P3,
Nantes, France
114 Suranaree University of Technology, Nakhon Ratchasima, Thailand
115 Technical University of Košice, Košice, Slovakia
116 Technical University of Split FESB, Split, Croatia
117 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of
Sciences, Cracow, Poland
118 The University of Texas at Austin, Physics Department, Austin, Texas, USA
119 Universidad Autónoma de Sinaloa, Culiacán, Mexico
120 Universidade de São Paulo (USP), São Paulo, Brazil
121 Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
122 University of Houston, Houston, Texas, United States
123 University of Jyväskylä, Jyväskylä, Finland
124 University of Liverpool, Liverpool, United Kingdom
125 University of Tennessee, Knoxville, Tennessee, United States
126 University of the Witwatersrand, Johannesburg, South Africa
127 University of Tokyo, Tokyo, Japan
128 University of Tsukuba, Tsukuba, Japan
129 University of Zagreb, Zagreb, Croatia
130 Université de Lyon, Université Lyon 1, CNRS/IN2P3, IPN-Lyon, Villeurbanne,
France
131 Università di Brescia
132 V. Fock Institute for Physics, St. Petersburg State University, St.
Petersburg, Russia
133 Variable Energy Cyclotron Centre, Kolkata, India
134 Warsaw University of Technology, Warsaw, Poland
135 Wayne State University, Detroit, Michigan, United States
136 Wigner Research Centre for Physics, Hungarian Academy of Sciences,
Budapest, Hungary
137 Yale University, New Haven, Connecticut, United States
138 Yonsei University, Seoul, South Korea
139 Zentrum für Technologietransfer und Telekommunikation (ZTT),
Fachhochschule Worms, Worms, Germany