2021 261 09 December

Neutral to charged kaon yield fluctuations

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

We present the first measurement of event-by-event fluctuations in the kaon
sector in Pb – Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 TeV with the ALICE
detector at the LHC. The robust fluctuation correlator $\nu_{\rm dyn}$ is used
to evaluate the magnitude of fluctuations of the relative yields of neutral
and charged kaons, as well as the relative yields of charged kaons, as a
function of collision centrality and selected kinematic ranges. While the
correlator $\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]$ exhibits a scaling
approximately in inverse proportion of the charged particle multiplicity,
$\nu_{\rm dyn}[\rm K_{S}^{0},\rm K^{\pm}]$ features a significant deviation
from such scaling. Within uncertainties, the value of $\nu_{\rm dyn}[\rm
K_{S}^{0},\rm K^{\pm}]$ is independent of the selected transverse momentum
interval, while it exhibits a pseudorapidity dependence. The results are
compared with HIJING, AMPT and EPOS–LHC predictions, and are further discussed
in the context of the possible production of disoriented chiral condensates in
central Pb – Pb collisions.

The primary intent of high-energy heavy-ion collisions at the Relativistic
Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) is the
production and study of the state of matter in which quarks and gluons are
deconfined. The matter formed in these collisions is characterised as a low-
viscosity fluid, which undergoes a transition to the hadronic phase, after it
expands and cools down [1]. The transition from the hadronic to the QGP phase
involves a partial restoration of chiral symmetry and color deconfinement.
Deconfinement of quarks and gluonic degrees of freedom, and the production of
QGP were brought to light by measurements of jet quenching [2, 3, 4, 5, 6],
quarkonium state suppression, and measurements of anisotropic flow [7, 8, 9,
10, 11, 12]. Anomalous fluctuations of conserved charges were predicted to
arise in the vicinity of the phase boundary and potential signals of the
production of a deconfined phase [13, 14, 15, 16, 17].

Several studies of particle yield fluctuations have already been reported [18,
19, 20, 21] but their interpretation is largely a matter of debate. More
recently, the ALICE collaboration has also investigated fluctuations of net
charge, net protons, as well as fluctuations of the relative yields of pions,
kaons, and protons [22, 23, 24]. Measurements of such fluctuations are of
interest, in particular, as they are nominally sensitive to QGP
susceptibilities [25], the proximity of the hadron gas-QGP phase boundary, as
well as, when considered at lower beam energy, the existence of a critical
point [26, 27] in the phase diagram of nuclear matter. Additionally,
measurements of fluctuations are also of interest to probe the existence (or
proximity) of the chiral phase transition, which should manifest itself by the
production of anomalous fluctuations [17]. A specific manifestation of this
transition from the chiral symmetric phase (high temperature) to a broken
phase (low temperature) involves the production of disoriented chiral
condensates (DCCs) [28], a region in isospin space where the chiral order
parameter is misaligned from its vacuum orientation. Theoretical studies of
the production and decay of DCCs are typically formulated in the context of
the SU(2) symmetry. It is predicted that the production and decay of DCCs
shall manifest through enhanced fluctuations of neutral and charged pion
multiplicities [29, 30]. The past searches in this sector have yielded no
evidence for DCC production [31, 32, 33]. However, the production of distinct
DCC domains might result in “isospin fluctuations” in the kaon sector, i.e.,
enhanced fluctuations of the relative yields of neutral and charged kaons
which can be measured by means of the $\nu_{\rm dyn}[\rm K^{0},\rm K^{c}]$
[34, 35, 36, 37, 38]. Specifically, it was predicted that the production of
DCC domains in A–A collisions might lead to an anomalous scaling of the net
charge correlator $\nu_{\rm dyn}$, defined in the following, as a function of
charged particle multiplicity [39]. A search of kaon isospin fluctuations at
LHC energies is thus of significant interest. Given that kaons from DCC are
expected to be produced at modest transverse momentum [40], the present study
is restricted to measurements of $\rm K^{\pm}$ and $\rm K_{S}^{0}$ at the
lowest possible transverse momenta ($p_{\rm T}$) aiming at checking whether
data support some basic expectations from the DCC production.

A measurement of dynamical neutral-to-charged kaon fluctuations, with
$\nu_{\rm dyn}$, is also of interest in the broader context of two-particle
correlations induced by the hadronization of the QGP, via e.g., quark
coalescence, and the transport of produced hadrons, as well as the possibility
that high mass resonances lead to the production of pairs of kaons. Examples
of such resonance decays that contribute to the $\nu_{\rm dyn}$ correlator
include $\rm\phi(1020)\rightarrow\rm K^{+}+\rm K^{-}$,
$\rm\phi_{3}(1850)\rightarrow\rm K+\overline{\rm K}^{*}$,
$f_{2}(2300)\rightarrow\rm\phi+\rm\phi$, as well as several $\rm D$-mesons
states. As they decay in-flight, these high-mass states would induce pair
correlations of charged and neutral kaons. The relative abundance of such
states might be larger in central collisions because of higher initial
temperature and density conditions. The relative yield of neutral and charged
kaons, and their fluctuations, might then exhibit a centrality dependence as a
result of feed-down contributions from such states. Additionally, given that
the relative yield of neutral kaons and charged kaons in general is determined
by the relative yields of strange, up, and down quarks (and their anti-
particles) before hadronization, and given that the production of strangeness
is both energy and collision centrality dependent, one might anticipate a
change in the size of the fluctuations from peripheral to central heavy-ion
collisions. Note, however, that the presence of kaons resulting from feed-down
contributions, which, for central Pb – Pb collisions at LHC energy, amount to
about 50 percent at the lowest momenta considered [41], reduces but does not
eliminate the sensitivity of the method to the presence of strange DCCs or
other processes inducing variations of the direct kaon production [39].

In this letter, we report measurements of event-by-event fluctuations of
inclusive multiplicities of charged and neutral kaons based on the robust
statistical observable, $\nu_{\rm dyn}$, defined as

$\nu_{\rm dyn}=R_{\rm cc}+R_{\rm 00}-2R_{\rm c0},$ (1)

where the indices $\rm c$ and $0$ stand for charged and neutral kaons,
respectively. The correlators $R_{xy}$ are normalized factorial cumulants
calculated according to

$R_{xy}=\frac{\left<N_{x}(N_{y}-\delta_{xy})\right>}{\left<N_{x}\right>\left<N_{y}\right>}-1,$
(2)

Here $\delta_{xy}=$ 1 for x = y and 0 for $x\neq y$. The correlators $R_{xy}$
and $\nu_{\rm dyn}$ vanish in the absence of pair correlations, i.e., for
Poisson fluctuations, but deviate from zero in the presence of particle
correlations. Their magnitudes are expected to approximately scale in inverse
proportion of the charged particle multiplicity, $N_{\rm ch}$, produced in
heavy-ion collisions and shall be insensitive to detection inefficiencies, and
only weakly dependent on the acceptance of the measurement [38].

In order to reduce the challenge of measuring neutral kaon multiplicities on
an event-by-event basis, the neutral kaon measurement is restricted to $\rm
K_{\rm S}^{0}$ by means of their decay into a pair of $\rm\pi^{+}$,
$\rm\pi^{-}$ (69.2$\%$ branching ratio [42]) with a displaced vertex. The wide
acceptance and high detection efficiency of charged pions enables event-by-
event reconstruction of $\rm K_{\rm S}^{0}$ with high efficiency and small
combinatorial background. It is thus possible to measure their multiplicity
event-by-event and compute the first, $\langle N_{\rm K_{\rm S}^{0}}\rangle$,
as well as second, $\langle N_{\rm K_{\rm S}^{0}}(N_{\rm K_{\rm
S}^{0}}-1)\rangle$ factorial moments. These constitute estimators to moments
of neutral kaon (and anti-kaon) yields. Indeed, given neutral kaons have a 50%
probability of being a $\rm K_{\rm S}^{0}$, with a binomial probability
distribution, a measurement of the ratio $\langle N_{\rm K_{\rm S}^{0}}(N_{\rm
K_{\rm S}^{0}}-1)\rangle/\langle N_{\rm K_{\rm S}^{0}}\rangle^{2}$ is thus
strictly equivalent to $\langle N_{\rm K^{0}}(N_{\rm K^{0}}-1)\rangle/\langle
N_{\rm K^{0}}\rangle^{2}$. Likewise, $\langle N_{\rm K_{\rm S}^{0}}N_{\rm
K^{c}})\rangle/\langle N_{\rm K_{\rm S}^{0}}\rangle\langle N_{\rm
K^{c}}\rangle$ is equivalent to $\langle N_{\rm K^{0}}N_{\rm
K^{c}})\rangle/\langle N_{\rm K^{0}}\rangle\langle N_{\rm K^{c}}\rangle$. A
measurement of $\nu_{\rm dyn}[N_{\rm K_{\rm S}^{0}},N_{\rm K^{c}}]$ thus
provides a proper and unbiased proxy to that of $\nu_{\rm dyn}[N_{\rm
K^{0}},N_{\rm K^{c}}]$ even without a measurement of $\rm K_{L}^{0}$.

The results presented in this letter are based on $1.3\times 10^{7}$ minimum
bias (MB) Pb – Pb collisions at center-of-mass energy per nucleon pair,
$\sqrt{s_{\rm NN}}$ = 2.76 TeV collected during the 2010 LHC heavy-ion run
with the ALICE detector. The reported correlation functions are measured for
charged particles reconstructed within the Inner Tracking System (ITS) [43]
and the Time Projection Chamber (TPC) [44]. The TPC consists of a 5 m long gas
volume contained in a cylindrical electric field cage oriented along the beam
axis, which is housed within a large solenoidal magnet designed and operated
to produce a uniform longitudinal magnetic field of 0.5 T. Signals from
charged particles produced in the TPC gas are readout at both end caps. The
ITS is comprised of three subsystems, each consisting of two cylindrical
layers of silicon detectors designed to match the acceptance of the TPC and
provide high position resolution. Together, the TPC and ITS provide charged
particle track reconstruction and momentum determination with full coverage in
azimuth over the pseudorapidity range $|\eta|<0.8$ and with good
reconstruction efficiency for charged particles with $p_{\rm T}>0.2$ GeV$/c$.
Two forward scintillator systems, known as V$0$A and V$0$C, covering the
pseudorapidity ranges $2.8<\eta<5.1$ and $-3.7<\eta<-1.7$, respectively, are
additionally used for triggering and event classification purposes. Detailed
descriptions of the ALICE detector components and their respective
performances are given in Refs. [45, 46]. The MB interaction trigger required
at least two out of the following three conditions: i) two pixel chips hit in
the outer layer of the silicon pixel detectors ii) a signal in V0A iii) a
signal in V0C. The hit multiplicity in the V0 detectors is additionally used
to estimate the collision centrality reported in seven classes corresponding
to 0–5% (most central), 5–10%, 10–15%, 15–20%, 20–40%, 40–60%, and 60–80%
(most peripheral) of the hadronic Pb – Pb cross section [47]. The approximate
position along the beam line of the primary vertex ($z_{\rm vtx}$) of each
collision is first determined based on hits recorded in the two inner layers
of the ITS detector. Reconstructed charged particle tracks in the ITS and TPC
are finally propagated to the primary vertex to achieve optimal position
resolution. In the context of this analysis, the vertex is required to be in
the range $|z_{\rm vtx}|\leq 10$ cm of the nominal interaction point in order
to ensure a uniform detector acceptance and minimize variations of the
efficiency across the fiducial volume of the experiment. In addition, the
standard track quality selections were used to ensure that only well-
reconstructed tracks were taken in the analysis. All selected tracks of each
event are processed to identify pions and kaons with the techniques described
below. Event-by-event combinations of two oppositely charged pions are formed
to reconstruct topological $\rm K^{0}_{\rm S}$ candidates. Standard ALICE
topological criteria, also detailed below, are then used to identify and
select $\rm K^{0}_{\rm S}$ candidates. Charged and neutral kaons are counted,
event-by-event, to calculate the moments $\langle N_{c}\rangle$, $\langle
N_{0}\rangle$, $\langle N_{c}(N_{c}-1)\rangle$, $\langle
N_{0}(N_{0}-1)\rangle$ and $\langle N_{c}N_{0}\rangle$, in each collision
centrality class. The corrections for particle losses are obtained event-by-
event by dividing single and pair yields by the detection efficiency and
products of efficiencies, respectively. Transverse momentum and pseudorapidity
dependent efficiencies were evaluated from GEANT simulations (discussed below)
of the particle detection performance with the HIJING model. The moments are
finally combined to calculate $\nu_{\rm dyn}$ values in each class according
to Eq. (1).

Charged particle identification (PID) is performed in the pseudorapidity range
$|\eta|<0.5$ using the $n\sigma$ method based on their energy loss (${\rm
d}E/{\rm d}x$) and their time of flight, measured in the TPC and TOF
detectors, respectively [45, 46]. A selection resulting in a PID with a high
purity is crucial in order to minimize biases in measurements of $\nu_{\rm
dyn}$. Kaons are selected from TPC ${\rm d}E/{\rm d}x$ with $|n\sigma|<2$ in
the ranges 0.2 $<p<$ 0.39 GeV$/c$ and 0.47 $<p<$ 0.5 GeV$/c$, and
$-0.5<n\sigma<2$ in the range 0.39 $<p<$ 0.47 GeV$/c$ to reduce contamination
from electrons. Both TPC and TOF signals, with $|n\sigma|<2$, are used in the
range 0.5 $<p<$ 1.5 GeV$/c$. Furthermore, kaon tracks are selected based on
their distance of closest approach (DCA) to the collision primary vertex in
order to select primary tracks and suppress contamination from secondary
particles and processes. Only tracks with DCAs smaller than 3.2 cm and 2.4 cm
along and transverse to the beam direction, respectively, are included in the
analysis. These selection cuts lead to charged kaon contamination ranging from
1.0% (TPC) to 1.4% (TPC+TOF) in peripheral collisions, and 2.7% (TPC) to 4.4%
(TPC+TOF) in 5% most central collisions.

Neutral kaons, $\rm K_{\rm S}^{0}$, are reconstructed and selected within 0.4
$<p_{\rm T}<$ 1.5 GeV$/c$ and $|\eta|<$ 0.5 based on their weak decay $\rm
K_{\rm S}^{0}\rightarrow\pi^{+}+\rm\pi^{-}$ topology and an invariant mass
selection criterion, 0.480 $<M_{\rm\pi^{+}\rm\pi^{-}}<$ 0.515 GeV$/c^{2}$ with
their decay-product tracks within the acceptance window $|\eta|<$ 0.8.
Standard ALICE topological cuts [48] are used towards the selection of $\rm
K_{\rm S}^{0}$ candidates formed from $\rm\pi^{+}$ and $\rm\pi^{-}$ tracks
identified with the TPC and TOF detectors with $p_{\rm T}>$ 0.2 GeV$/c$. The
maximum DCA of neutral kaons is set to 0.1 cm in all directions. The required
$n\sigma$ values for the pions were $|n\sigma|<2$ in both TPC and TOF
detectors for 0.2 $<p<$ 1.5 GeV$/c$. These selection criteria yield a
combinatorial $\rm\pi^{+}+\rm\pi^{-}$ pair contamination ranging from 1.3% in
peripheral collisions to 4.0% in 5% most central collisions, shown as a red-
brown area in Fig. 1.

Figure 1: Invariant mass distribution of $\pi^{+}+\pi^{-}$ pairs measured in
central (0–5$\%$) Pb – Pb collisions. The yellow and black solid lines show a
second order polynomial fit of the combinatorial background and a
Gaussian+second order polynomial fit to the invariant mass spectrum,
respectively. The vertical dash lines delineate the mass range used for the
determination of neutral-kaon yields. Given the red-brown area, which
corresponds to combinatorial background, cannot be properly assessed event by
event, the average of the yellow areas is used as proxy, event-by-event, to
estimate the true combinatorial yield represented by the red-brown area.

Event-by-event fluctuations of the combinatorial background artificially
increase the factorial moment $\langle{N_{0}(N_{0}-1)}\rangle$ and may bias
$\langle N_{0}N_{c}\rangle$. A correction for such contamination is
accomplished by additionally measuring correlators involving moments of the
number of background pion pairs, $N_{\rm b}$, in side band mass ranges
$0.430<M<0.460$ GeV$/c^{2}$ and $0.540<M<0.575$ GeV$/c^{2}$ used as proxies of
the number of background pairs in the nominal mass range $0.480<M<0.515$
GeV$/c^{2}$, shown in Fig. 1, as yellow and red-brown areas. The background
suppressed correlators $R_{\rm 00}$ and $R_{\rm c0}$ are thus calculated
according to

$\displaystyle R_{\rm 00}$ $\displaystyle=$
$\displaystyle(1-f_{ab})^{-2}\left[R_{\rm aa}-2f_{ab}R_{\rm
ab}+f_{ab}^{2}R_{\rm bb}\right],$ (3) $\displaystyle R_{\rm c0}$
$\displaystyle=$ $\displaystyle(1-f_{ab})^{-1}\left[R_{\rm ac}-f_{ab}R_{\rm
bc}\right],$ (4)

where the labels $\rm a$, $\rm b$, and $\rm c$ represent pairs in the nominal
mass range, pairs observed in either side bands, and pairs of charged kaons,
respectively. The fraction $f_{ab}=\langle N_{\rm b}\rangle/\langle N_{\rm
a}\rangle$ is determined for each collision centrality bin as the average
number of background pairs in the range $0.480<M<0.515$ GeV$/c^{2}$ estimated
from a polynomial fit to the background, as illustrated in Fig. 1. Corrections
for combinatorial contamination based on Eqs. (3,4) range from 4.7% in
peripheral to 2.5% in central collisions. Additionally, given the number of
charged and neutral kaons grows monotonically with collision centrality,
values of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ are corrected for
finite centrality bin widths. The bin width correction is calculated by
considering the weighted average of $\nu_{dyn}$ evaluated in 1% intervals of
collision centrality across the reported bin widths [49]. These corrections
range from 3.9% in peripheral to 2.1% in central collisions.

Statistical uncertainties are evaluated with the event subsampling method
using 10 subsamples [24, 50]. The systematic uncertainties include
contributions from secondary particles, as well as from the $p_{\rm T}$
dependence of the tracking efficiency which is not perfectly canceled in the
determination of the normalized cumulants $R_{xy}$. The event and track
selection criteria were varied, and a statistical test [51] was used to
identify significant sources of systematic uncertainties. The largest sources
of systematic uncertainties include: (i) the effect of varying the minimum or
maximum decay length ($<4$%), (ii) variations of the K± purity when changing
the sigma selection criteria ($<4$%), (iii) variations during the data taking
period of the $\rm K^{\pm}$ and $\rm K_{\rm S}^{0}$ yields ($<3$%), and (iv)
variations of $R_{00}$ when correcting for combinatorial background using
different fiducial invariant mass ranges and side bands ($<2$%). Additional
uncertainties arise when varying the range of accepted primary vertices
($<4$%). Adding all sources in quadrature, systematic uncertainties are
estimated to be smaller than 13%, independently of collision centrality.

Figure 2:  (a) Measured values of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm
K^{\pm}]$ (top) and $\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]$ (bottom) compared
with HIJING and AMPT model calculations of these observables at generator
level. (b) Values of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ (top) and
$\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]$ (bottom) scaled by
$\alpha\equiv(\langle\rm K_{\rm S}^{0}\rangle^{-1}+\langle\rm
K^{\pm}\rangle^{-1})$. Statistical and systematic uncertainties are
represented as vertical bar and boxes, respectively.

Heavy-ion collisions simulated with the HIJING v2.0 [52] and AMPT v2.21 [53]
Monte Carlo (MC) event generators, including the propagation of the produced
particles through the detectors using GEANT3 [54], are used to validate the
correction method. To that end, the reconstructed values of $\nu_{\rm dyn}$
obtained from full MC simulations are processed as data, then the fully
corrected $\nu_{\rm dyn}$ values are compared to those obtained at generator
level, i.e., from simulations without detector effects. The agreement between
the reconstructed and generator level values of $\nu_{\rm dyn}$ are found to
be within 1%. Generator level MC simulations performed with the AMPT and
EPOS–LHC [55] models are additionally used to obtain basic theoretical
expectations for the magnitude of charged to neutral kaon yield fluctuations.
AMPT events produced with the options of string melting on (SON) and
rescattering off (ROFF), string melting off (SOFF) and rescattering on (RON),
and SON and RON are considered. Furthermore, EPOS–LHC events are analyzed at
generator level for Pb – Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. All
sets of simulated data are analyzed with selection parameters and conditions
identical to those used in the analysis of the experimental data.
Additionally, the robustness of the analysis was tested by performing a
closure test. To that end, values of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm
K^{\pm}]$ obtained with HIJING simulated events at both the detector and
generator levels are compared, and verified that values of $\nu_{\rm dyn}$
obtained with full simulations of the detector performance and data
reconstruction (detector level) are in excellent agreement with those obtained
with generator level data sets.

The top panel of Fig. 2 (a) presents $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm
K^{\pm}]$ (red solid circles) as a function of the Pb–Pb collision centrality.
The largest $\nu_{\rm dyn}$ is observed in the most peripheral collisions and
monotonically decreases for more central collisions. Such a behavior is
qualitatively well described by HIJING, AMPT and EPOS–LHC calculations, but
these models underestimate the magnitude of $\nu_{\rm dyn}[\rm K_{\rm
S}^{0},\rm K^{\pm}]$ by an approximate factor of two in peripheral collisions
and by an order of magnitude in most central collisions. The magnitude of
$\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ is expected to approximately
scale in inverse proportion to the number of sources of correlated particles,
$N_{\rm s}$, for a collision system involving independent nucleon–nucleon
collisions and no scattering of produced particles. This scaling is explored
in the top panel of Fig. 2(b) which displays the centrality dependence of
$\nu_{\rm dyn}$ scaled by the factor $\alpha\equiv(\langle\rm K_{\rm
S}^{0}\rangle^{-1}+\langle\rm K^{\pm}\rangle^{-1})$. This factor is known to
be approximately proportional to $N_{\rm s}$ [56]. Scaled values predicted by
the models are found to be essentially invariant with collision centrality.
HIJING, in particular, exhibits nearly constant values of $\nu_{\rm dyn}[\rm
K_{\rm S}^{0},\rm K^{\pm}]/\alpha$ as a function of collision centrality,
whereas AMPT calculations with SON and ROFF options display a very modest
collision centrality dependence, hardly visible in Fig. 2(b). The measured
data, by contrast, feature a strong variation with decreasing centrality. In
particular, $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]/\alpha$ rises from
$\approx 0.053\pm 0.005(\rm stat)\pm 0.007(\rm sys)$ in the 60–80% collision
centrality range to $0.213\pm 0.021(\rm stat)\pm 0.025(\rm sys)$ in 5% most
central collisions and thus one then concludes the expected $1/N_{\rm s}$
scaling of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ is strongly
violated.

In order to interpret the dependence of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm
K^{\pm}]$ on collision centrality and identify the origin of the $1/N_{\rm s}$
scaling violation, we study the collision centrality dependence of the
components $R_{\rm cc}$, $R_{\rm c0}$, and $R_{\rm 00}$ relative to those
obtained with HIJING. Correlators computed with HIJING have a nearly perfect
$1/N_{\rm s}$ scaling as a function of collision centrality. This means they
can be used as “no-scaling-violation” baselines to investigate the collision
centrality dependence of the evolution of the measured $R_{\rm cc}$, $R_{\rm
c0}$, and $R_{\rm 00}$ correlators with collision centrality. Figure 3
presents ratios of measured correlators to those obtained with HIJING as a
function of collision centrality. The ratio $R_{\rm 00}/R_{\rm 00}^{\rm
HIJING}$ exhibits the largest deviation from unity but is otherwise
independent, within uncertainties, of collision centrality. This term thus
essentially features the $1/N_{\rm s}$ scaling expected from a system
consisting of a number of independent sources, albeit with a magnitude larger
by about 15% than that expected from HIJING. By contrast, the ratio $R_{\rm
cc}/R_{\rm cc}^{\rm HIJING}$ is closest to unity but features a modest
collision centrality dependence. This modest dependence, discussed further
below, is not the main cause of the observed scaling violation of $\nu_{\rm
dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ with collision centrality. Indeed, it is
found that the ratio $R_{\rm c0}/R_{\rm c0}^{\rm HIJING}$ manifests a more
significant collision centrality dependence. The ratio is of the order of
unity in the 60–80% collision centrality range with a deviation from unity
consistent, more or less, with that observed for the ratio $R_{\rm cc}/R_{\rm
cc}^{\rm HIJING}$ across all centralities. HIJING thus appears to provide a
reasonable approximation of the measured correlation strength of neutral to
charged kaons in peripheral collisions. However, the deviation of the measured
$R_{\rm c0}$ from HIJING predictions increases monotonically from peripheral
to central Pb–Pb collisions, with the largest deviation observed for the 0–5%
Pb–Pb collisions. We then conclude that it is the $R_{\rm c0}$ term that most
affect the collision centrality dependence and scaling violation of $\nu_{\rm
dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$. Interestingly, it happens to be the term
most sensitive to variations in the make up of kaons: combining a strange
quark ($s$) with anti-up ($\bar{u}$) and anti-down quark ($\bar{d}$), one
obtains $\rm K^{-}$ and $\rm K^{0}$, respectively (similarly, combining
$\bar{s}$ to $u$ and $d$ quarks, one obtains $\rm K^{+}$ and $\rm K^{0}$).
Fluctuations in the relative number of neutral and charged kaons, measured by
the $R_{\rm c0}$ term, are thus sensitive to fluctuations in the relative
local abundances of $u$ ($\bar{u}$) and $d$ ($\bar{d}$) quarks. The observed
scaling violation of $R_{\rm c0}$ with collision centrality thus suggests the
relative abundances of $\bar{u}$ and $\bar{d}$ (as well as $u$ and $d$)
available for the makeup of kaons might be evolving with collision centrality.

Figure 3: Ratio (Data/HIJING) of individual terms of $\nu_{\rm dyn}[\rm K_{\rm
S}^{0},\rm K^{\pm}]$ as a function of collision centrality. Statistical and
systematic uncertainties are represented as vertical bar and boxes,
respectively.

The strength of charged kaon correlations is examined in closer detail by
plotting measured values of $\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]$ and
predictions by AMPT, HIJING and EPOS–LHC for this observable as a function of
collision centrality in the bottom panel of Fig. 2 (a), and values scaled by
$\alpha$ in Fig. 2 (b). The deviations of measured $\nu_{\rm dyn}[\rm
K^{+},\rm K^{-}]$ from model predictions are smaller than those for $\nu_{\rm
dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ but measured $\nu_{\rm dyn}[\rm K^{+},\rm
K^{-}]$ values lie systematically above those obtained from the models.
Although HIJING, AMPT and EPOS–LHC do not perfectly capture the magnitude and
collision dependence of $\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]$, they nonetheless
provide a relatively accurate description of the role of charge conservation,
for charged kaons, in Pb – Pb collisions. Additionally note that scaled values
$\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]/\alpha$ are invariant, within
uncertainties, with collision centrality, much like values obtained with the
three models. Scaling violations of $\nu_{\rm dyn}[\rm K^{+},\rm K^{-}]$ with
collision centrality, if any, are not observable within the uncertainties of
this measurement and stand in sharp contrast to the large scaling violation of
$\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ shown in the top panel of Fig.
2(b). One can then conclude that the large centrality dependence of $\nu_{\rm
dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ does not originate from anomalous charge
correlations.

The observed strong decrease of $R_{\rm c0}/R_{\rm c0}^{\rm HIJING}$ in
central collisions indicates that the level of correlations between neutral
and charged kaons is weakening in this range relative to that predicted by
HIJING. A weaker correlation is expected from the production of large strange
DCCs, as shown in Fig. 5 of Ref. [39] presenting a simple phenomenological
model of kaon DCC production. The observed dependence of $\nu_{\rm dyn}[\rm
K_{\rm S}^{0},\rm K^{\pm}]$ on collision centrality is consistent with
expectations based on a simple DCC model. However, significant contributions
from other final state effects in central collisions might also dilute the
correlation developed in initial stages.

Nominally, the production of strange DCCs should manifest itself by the
emission of relatively low-$p_{\rm T}$ kaons in the rest frame of the DCC
[37]. Even though there is no quantitative prediction in the literature, the
radial acceleration [57, 58] known to occur in relativistic A–A collisions may
affect the DCCs and the particles they produce. Therefore, the strength of the
$\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ correlator is studied in
different ranges of transverse momentum.

Figure 4: (a) top: measured and HIJING (generator level) predicted values of
$\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ scaled by $\alpha$ as a
function of collision centrality for various transverse momentum interval of
charged kaons. HIJING predicted scaled values are multiplied by a factor of 5
to approximately match the measured values in most peripheral collisions;
middle: ratio of data for various transverse momentum interval as a function
of centrality; bottom: ratio of HIJING for various transverse momentum
interval as a function of centrality.

The collision centrality evolution of the scaled values of $\nu_{\rm dyn}[\rm
K_{\rm S}^{0},\rm K^{\pm}]$ is shown in Fig. 4 for selected $p_{\rm T}$
ranges. The $\nu_{\rm dyn}/\alpha$ scaling violation is observed in both the
higher and lower selected $p_{\rm T}$ ranges. Contrary to what one expects
from DCC production, within uncertainties, the scaled correlation strength
does not show a significant enhancement at low $p_{\rm T}$. As shown in the
bottom panel of Fig. 4, HIJING also predicts larger correlation strengths in
the lower $p_{\rm T}$ range. Additionally, Fig. 5 presents the dependence of
$\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$, in panel (a), and $\nu_{\rm
dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]/\alpha$, in panel (b), on the width of the
pseudorapidity acceptance, $\Delta\eta$, for 0–5% and 5–10% Pb – Pb collision
centrality ranges. In panel (a), the data exhibit a monotonic decrease of
$\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm K^{\pm}]$ with increasing $\Delta\eta$,
which reflects the finite correlation width of all three integral correlator
terms $R_{xy}$, whereas in panel (b), scaled values of $\nu_{\rm dyn}[\rm
K_{\rm S}^{0},\rm K^{\pm}]$ exhibit a monotonically decreasing trend with
decreasing $\Delta\eta$ acceptance that stems largely from the decrease of the
integrated yield of kaons with shrinking $\Delta\eta$ acceptance. DCCs are
expected to produce relatively low $p_{\rm T}$ particles [29, 36] and should
thus be characterized by relatively narrow correlation functions in momentum
space. Radial acceleration associated with the collision system expansion
shall further narrow the correlation dependence on $\Delta\eta$. We note,
however, that the peak widths, $\sigma_{\Delta\eta}$, observed in data are not
significantly smaller than those obtained with the HIJING calculations.
Qualitatively, one would expect radial flow to further reduce the
$\sigma_{\Delta\eta}$ difference among low-$p_{\rm T}$ kaons produced by the
decay of strange DCCs. Unfortunately, the absence of a prediction of the
effect of radial flow on DCCs and given that the observed widths are only
slightly smaller than those estimated with HIJING, the measured data thus do
not make a compelling case for the production of strange DCCs in Pb – Pb
collisions at the TeV scale.

Figure 5: (a) Measured values of $\nu_{\rm dyn}[\rm K_{\rm S}^{0},\rm
K^{\pm}]$ plotted as a function of the width of the acceptance $\Delta\eta$ in
the 0–5% and 5–10% collision centrality ranges are compared HIJING (generator
level) calculations scaled by a factor of 18. (b) Values of $\nu_{\rm dyn}[\rm
K_{\rm S}^{0},\rm K^{\pm}]$ shown in panel (a) are scaled by $\alpha$ . HIJING
values are scaled by a factor of 15 for easier comparison with the data. The
statistical and systematic uncertainties are represented as bar and boxes,
respectively.

In this letter, we presented measurements of event-by-event fluctuations of
the relative yield of the neutral and charged kaons in Pb – Pb collisions at
$\sqrt{s_{\rm NN}}$ = 2.76 TeV based on the $\nu_{\rm dyn}$ observable. The
centrality dependence of $\nu_{\rm dyn}$ is observed to violate the $1/N_{\rm
s}$ multiplicity scaling expected from a system of $N$ independent sources,
but this effect is not reproduced by HIJING, AMPT, and EPOS–LHC models. Close
examination of the three terms of $\nu_{\rm dyn}$ reveals that the strength of
correlations among charged kaons features a collision centrality dependence
close to that expected with these three models. The $R_{\rm c0}$ cross-term,
however, is found to weaken considerably, in most central collisions, relative
to a naive $1/N_{\rm s}$ expectation. This indicates correlations between
charged and neutral kaons are significantly suppressed in central collisions.
Given the fact that at this time it is unknown if other processes could mimic
the signature of kaon production via DCCs and that the expected momentum
dependence is not observed in the data, the reported measurement does not
support the case for strange DCC production in heavy-ion collisions at LHC
energies. Further measurements of differential correlations in $\Delta\eta$
vs. $\Delta\phi$ and higher factorial moments are of interest, as they could
provide information on the momentum correlation length and the typical size of
correlated kaon sources.

The ALICE Collaboration would like to thank all its engineers and technicians
for their invaluable contributions to the construction of the experiment and
the CERN accelerator teams for the outstanding performance of the LHC complex.
The ALICE Collaboration gratefully acknowledges the resources and support
provided by all Grid centres and the Worldwide LHC Computing Grid (WLCG)
collaboration. The ALICE Collaboration acknowledges the following funding
agencies for their support in building and running the ALICE detector: A. I.
Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation
(ANSL), State Committee of Science and World Federation of Scientists (WFS),
Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M
2467-N36] and Nationalstiftung für Forschung, Technologie und Entwicklung,
Austria; Ministry of Communications and High Technologies, National Nuclear
Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e
Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de
Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Universidade Federal do
Rio Grande do Sul (UFRGS), Brazil; Ministry of Education of China (MOEC) ,
Ministry of Science & Technology of China (MSTC) and National Natural Science
Foundation of China (NSFC), China; Ministry of Science and Education and
Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnológicas y
Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth
and Sports of the Czech Republic, Czech Republic; The Danish Council for
Independent Research — Natural Sciences, the VILLUM FONDEN and Danish National
Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP),
Finland; Commissariat à l’Energie Atomique (CEA) and Institut National de
Physique Nucléaire et de Physique des Particules (IN2P3) and Centre National
de la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung und
Forschung (BMBF) and GSI Helmholtzzentrum für Schwerionenforschung GmbH,
Germany; General Secretariat for Research and Technology, Ministry of
Education, Research and Religions, Greece; National Research, Development and
Innovation Office, Hungary; Department of Atomic Energy Government of India
(DAE), Department of Science and Technology, Government of India (DST),
University Grants Commission, Government of India (UGC) and Council of
Scientific and Industrial Research (CSIR), India; Indonesian Institute of
Science, Indonesia; Istituto Nazionale di Fisica Nucleare (INFN), Italy;
Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT)
and Japan Society for the Promotion of Science (JSPS) KAKENHI, Japan; Consejo
Nacional de Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación
Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de
Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor
Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway,
Norway; Commission on Science and Technology for Sustainable Development in
the South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru;
Ministry of Education and Science, National Science Centre and WUT ID-UB,
Poland; Korea Institute of Science and Technology Information and National
Research Foundation of Korea (NRF), Republic of Korea; Ministry of Education
and Scientific Research, Institute of Atomic Physics, Ministry of Research and
Innovation and Institute of Atomic Physics and University Politehnica of
Bucharest, Romania; Joint Institute for Nuclear Research (JINR), Ministry of
Education and Science of the Russian Federation, National Research Centre
Kurchatov Institute, Russian Science Foundation and Russian Foundation for
Basic Research, Russia; Ministry of Education, Science, Research and Sport of
the Slovak Republic, Slovakia; National Research Foundation of South Africa,
South Africa; Swedish Research Council (VR) and Knut & Alice Wallenberg
Foundation (KAW), Sweden; European Organization for Nuclear Research,
Switzerland; Suranaree University of Technology (SUT), National Science and
Technology Development Agency (NSDTA) and Office of the Higher Education
Commission under NRU project of Thailand, Thailand; Turkish Energy, Nuclear
and Mineral Research Agency (TENMAK), Turkey; National Academy of Sciences of
Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United
Kingdom; National Science Foundation of the United States of America (NSF) and
United States Department of Energy, Office of Nuclear Physics (DOE NP), United
States of America.

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##  Appendix A The ALICE Collaboration

S. Acharya142, D. Adamová96, A. Adler74, J. Adolfsson81, G. Aglieri Rinella34,
M. Agnello30, N. Agrawal54, Z. Ahammed142, S. Ahmad16, S.U. Ahn76, I. Ahuja38,
Z. Akbar51, A. Akindinov93, M. Al-Turany108, S.N. Alam16, D. Aleksandrov89, B.
Alessandro59, H.M. Alfanda7, R. Alfaro Molina71, B. Ali16, Y. Ali14, A.
Alici25, N. Alizadehvandchali125, A. Alkin34, J. Alme21, G. Alocco55, T.
Alt68, I. Altsybeev113, M.N. Anaam7, C. Andrei48, D. Andreou91, A.
Andronic145, V. Anguelov105, F. Antinori57, P. Antonioli54, C. Anuj16, N.
Apadula80, L. Aphecetche115, H. Appelshäuser68, S. Arcelli25, R. Arnaldi59,
I.C. Arsene20, M. Arslandok147, A. Augustinus34, R. Averbeck108, S. Aziz78,
M.D. Azmi16, A. Badalà56, Y.W. Baek41, X. Bai129,108, R. Bailhache68, Y.
Bailung50, R. Bala102, A. Balbino30, A. Baldisseri139, B. Balis2, D.
Banerjee4, Z. Banoo102, R. Barbera26, L. Barioglio106, M. Barlou85, G.G.
Barnaföldi146, L.S. Barnby95, V. Barret136, C. Bartels128, K. Barth34, E.
Bartsch68, F. Baruffaldi27, N. Bastid136, S. Basu81, G. Batigne115, D.
Battistini106, B. Batyunya75, D. Bauri49, J.L. Bazo Alba112, I.G. Bearden90,
C. Beattie147, P. Becht108, I. Belikov138, A.D.C. Bell Hechavarria145, F.
Bellini25, R. Bellwied125, S. Belokurova113, V. Belyaev94, G. Bencedi146,69,
S. Beole24, A. Bercuci48, Y. Berdnikov99, A. Berdnikova105, L. Bergmann105,
M.G. Besoiu67, L. Betev34, P.P. Bhaduri142, A. Bhasin102, I.R. Bhat102, M.A.
Bhat4, B. Bhattacharjee42, P. Bhattacharya22, L. Bianchi24, N. Bianchi52, J.
Bielčík37, J. Bielčíková96, J. Biernat118, A. Bilandzic106, G. Biro146, S.
Biswas4, J.T. Blair119, D. Blau89,82, M.B. Blidaru108, C. Blume68, G.
Boca28,58, F. Bock97, A. Bogdanov94, S. Boi22, J. Bok61, L. Boldizsár146, A.
Bolozdynya94, M. Bombara38, P.M. Bond34, G. Bonomi141,58, H. Borel139, A.
Borissov82, H. Bossi147, E. Botta24, L. Bratrud68, P. Braun-Munzinger108, M.
Bregant121, M. Broz37, G.E. Bruno107,33, M.D. Buckland23,128, D. Budnikov109,
H. Buesching68, S. Bufalino30, O. Bugnon115, P. Buhler114, Z. Buthelezi72,132,
J.B. Butt14, A. Bylinkin127, S.A. Bysiak118, M. Cai27,7, H. Caines147, A.
Caliva108, E. Calvo Villar112, J.M.M. Camacho120, R.S. Camacho45, P.
Camerini23, F.D.M. Canedo121, M. Carabas135, F. Carnesecchi34,25, R.
Caron137,139, J. Castillo Castellanos139, E.A.R. Casula22, F. Catalano30, C.
Ceballos Sanchez75, I. Chakaberia80, P. Chakraborty49, S. Chandra142, S.
Chapeland34, M. Chartier128, S. Chattopadhyay142, S. Chattopadhyay110, T.G.
Chavez45, T. Cheng7, C. Cheshkov137, B. Cheynis137, V. Chibante Barroso34,
D.D. Chinellato122, S. Cho61, P. Chochula34, P. Christakoglou91, C.H.
Christensen90, P. Christiansen81, T. Chujo134, C. Cicalo55, L. Cifarelli25, F.
Cindolo54, M.R. Ciupek108, G. ClaiII,54, J. CleymansI,124, F. Colamaria53,
J.S. Colburn111, D. Colella53,107,33, A. Collu80, M. Colocci25,34, M.
ConcasIII,59, G. Conesa Balbastre79, Z. Conesa del Valle78, G. Contin23, J.G.
Contreras37, M.L. Coquet139, T.M. Cormier97, P. Cortese31, M.R. Cosentino123,
F. Costa34, S. Costanza28,58, P. Crochet136, R. Cruz-Torres80, E. Cuautle69,
P. Cui7, L. Cunqueiro97, A. Dainese57, M.C. Danisch105, A. Danu67, P. Das87,
P. Das4, S. Das4, S. Dash49, A. De Caro29, G. de Cataldo53, L. De Cilladi24,
J. de Cuveland39, A. De Falco22, D. De Gruttola29, N. De Marco59, C. De
Martin23, S. De Pasquale29, S. Deb50, H.F. Degenhardt121, K.R. Deja143, R. Del
Grande106, L. Dello Stritto29, W. Deng7, P. Dhankher19, D. Di Bari33, A. Di
Mauro34, R.A. Diaz8, T. Dietel124, Y. Ding137,7, R. Divià34, D.U. Dixit19, Ø.
Djuvsland21, U. Dmitrieva63, J. Do61, A. Dobrin67, B. Dönigus68, A.K.
Dubey142, A. Dubla108,91, S. Dudi101, P. Dupieux136, M. Durkac117, N.
Dzalaiova13, T.M. Eder145, R.J. Ehlers97, V.N. Eikeland21, F. Eisenhut68, D.
Elia53, B. Erazmus115, F. Ercolessi25, F. Erhardt100, A. Erokhin113, M.R.
Ersdal21, B. Espagnon78, G. Eulisse34, D. Evans111, S. Evdokimov92, L.
Fabbietti106, M. Faggin27, J. Faivre79, F. Fan7, W. Fan80, A. Fantoni52, M.
Fasel97, P. Fecchio30, A. Feliciello59, G. Feofilov113, A. Fernández Téllez45,
A. Ferrero139, A. Ferretti24, V.J.G. Feuillard105, J. Figiel118, V. Filova37,
D. Finogeev63, F.M. Fionda55, G. Fiorenza34, F. Flor125, A.N. Flores119, S.
Foertsch72, S. Fokin89, E. Fragiacomo60, E. Frajna146, A. Francisco136, U.
Fuchs34, N. Funicello29, C. Furget79, A. Furs63, J.J. Gaardhøje90, M.
Gagliardi24, A.M. Gago112, A. Gal138, C.D. Galvan120, P. Ganoti85, C.
Garabatos108, J.R.A. Garcia45, E. Garcia-Solis10, K. Garg115, C. Gargiulo34,
A. Garibli88, K. Garner145, P. Gasik108, E.F. Gauger119, A. Gautam127, M.B.
Gay Ducati70, M. Germain115, S.K. Ghosh4, M. Giacalone25, P. Gianotti52, P.
Giubellino108,59, P. Giubilato27, A.M.C. Glaenzer139, P. Glässel105, E.
Glimos131, D.J.Q. Goh83, V. Gonzalez144, L.H. González-Trueba71, S.
Gorbunov39, M. Gorgon2, L. Görlich118, S. Gotovac35, V. Grabski71, L.K.
Graczykowski143, L. Greiner80, A. Grelli62, C. Grigoras34, V. Grigoriev94, S.
Grigoryan75,1, F. Grosa34,59, J.F. Grosse-Oetringhaus34, R. Grosso108, D.
Grund37, G.G. Guardiano122, R. Guernane79, M. Guilbaud115, K. Gulbrandsen90,
T. Gunji133, W. Guo7, A. Gupta102, R. Gupta102, S.P. Guzman45, L. Gyulai146,
M.K. Habib108, C. Hadjidakis78, H. Hamagaki83, M. Hamid7, R. Hannigan119, M.R.
Haque143, A. Harlenderova108, J.W. Harris147, A. Harton10, J.A.
Hasenbichler34, H. Hassan97, D. Hatzifotiadou54, P. Hauer43, L.B. Havener147,
S.T. Heckel106, E. Hellbär108, H. Helstrup36, T. Herman37, G. Herrera Corral9,
F. Herrmann145, K.F. Hetland36, H. Hillemanns34, C. Hills128, B. Hippolyte138,
B. Hofman62, B. Hohlweger91, J. Honermann145, G.H. Hong148, D. Horak37, S.
Hornung108, A. Horzyk2, R. Hosokawa15, Y. Hou7, P. Hristov34, C. Hughes131, P.
Huhn68, L.M. Huhta126, C.V. Hulse78, T.J. Humanic98, H. Hushnud110, L.A.
Husova145, A. Hutson125, J.P. Iddon34,128, R. Ilkaev109, H. Ilyas14, M.
Inaba134, G.M. Innocenti34, M. Ippolitov89, A. Isakov96, T. Isidori127, M.S.
Islam110, M. Ivanov108, V. Ivanov99, V. Izucheev92, M. Jablonski2, B. Jacak80,
N. Jacazio34, P.M. Jacobs80, S. Jadlovska117, J. Jadlovsky117, S. Jaelani62,
C. Jahnke122,121, M.J. Jakubowska143, A. Jalotra102, M.A. Janik143, T.
Janson74, M. Jercic100, O. Jevons111, A.A.P. Jimenez69, F. Jonas97,145, P.G.
Jones111, J.M. Jowett 34,108, J. Jung68, M. Jung68, A. Junique34, A. Jusko111,
M.J. Kabus143, J. Kaewjai116, P. Kalinak64, A.S. Kalteyer108, A. Kalweit34, V.
Kaplin94, A. Karasu Uysal77, D. Karatovic100, O. Karavichev63, T.
Karavicheva63, P. Karczmarczyk143, E. Karpechev63, V. Kashyap87, A.
Kazantsev89, U. Kebschull74, R. Keidel47, D.L.D. Keijdener62, M. Keil34, B.
Ketzer43, A.M. Khan7, S. Khan16, A. Khanzadeev99, Y. Kharlov92,82, A.
Khatun16, A. Khuntia118, B. Kileng36, B. Kim17,61, C. Kim17, D.J. Kim126, E.J.
Kim73, J. Kim148, J.S. Kim41, J. Kim105, J. Kim73, M. Kim105, S. Kim18, T.
Kim148, S. Kirsch68, I. Kisel39, S. Kiselev93, A. Kisiel143, J.P. Kitowski2,
J.L. Klay6, J. Klein34, S. Klein80, C. Klein-Bösing145, M. Kleiner68, T.
Klemenz106, A. Kluge34, A.G. Knospe125, C. Kobdaj116, T. Kollegger108, A.
Kondratyev75, N. Kondratyeva94, E. Kondratyuk92, J. Konig68, S.A.
Konigstorfer106, P.J. Konopka34, G. Kornakov143, S.D. Koryciak2, A.
Kotliarov96, O. Kovalenko86, V. Kovalenko113, M. Kowalski118, I. Králik64, A.
Kravčáková38, L. Kreis108, M. Krivda111,64, F. Krizek96, K. Krizkova
Gajdosova37, M. Kroesen105, M. Krüger68, D.M. Krupova37, E. Kryshen99, M.
Krzewicki39, V. Kučera34, C. Kuhn138, P.G. Kuijer91, T. Kumaoka134, D.
Kumar142, L. Kumar101, N. Kumar101, S. Kundu34, P. Kurashvili86, A. Kurepin63,
A.B. Kurepin63, A. Kuryakin109, S. Kushpil96, J. Kvapil111, M.J. Kweon61, J.Y.
Kwon61, Y. Kwon148, S.L. La Pointe39, P. La Rocca26, Y.S. Lai80, A.
Lakrathok116, M. Lamanna34, R. Langoy130, P. Larionov34,52, E. Laudi34, L.
Lautner34,106, R. Lavicka114,37, T. Lazareva113, R. Lea141,23,58, J.
Lehrbach39, R.C. Lemmon95, I. León Monzón120, M.M. Lesch106, E.D. Lesser19, M.
Lettrich34,106, P. Lévai146, X. Li11, X.L. Li7, J. Lien130, R. Lietava111, B.
Lim17, S.H. Lim17, V. Lindenstruth39, A. Lindner48, C. Lippmann108, A. Liu19,
D.H. Liu7, J. Liu128, I.M. Lofnes21, V. Loginov94, C. Loizides97, P. Loncar35,
J.A. Lopez105, X. Lopez136, E. López Torres8, J.R. Luhder145, M. Lunardon27,
G. Luparello60, Y.G. Ma40, A. Maevskaya63, M. Mager34, T. Mahmoud43, A.
Maire138, M. Malaev99, N.M. Malik102, Q.W. Malik20, S.K. Malik102, L.
MalininaIV,75, D. Mal’Kevich93, D. Mallick87, N. Mallick50, G. Mandaglio32,56,
V. Manko89, F. Manso136, V. Manzari53, Y. Mao7, G.V. Margagliotti23, A.
Margotti54, A. Marín108, C. Markert119, M. Marquard68, N.A. Martin105, P.
Martinengo34, J.L. Martinez125, M.I. Martínez45, G. Martínez García115, S.
Masciocchi108, M. Masera24, A. Masoni55, L. Massacrier78, A.
Mastroserio140,53, A.M. Mathis106, O. Matonoha81, P.F.T. Matuoka121, A.
Matyja118, C. Mayer118, A.L. Mazuecos34, F. Mazzaschi24, M. Mazzilli34, J.E.
Mdhluli132, A.F. Mechler68, Y. Melikyan63, A. Menchaca-Rocha71, E.
Meninno114,29, A.S. Menon125, M. Meres13, S. Mhlanga124,72, Y. Miake134, L.
Micheletti59, L.C. Migliorin137, D.L. Mihaylov106, K. Mikhaylov75,93, A.N.
Mishra146, D. Miśkowiec108, A. Modak4, A.P. Mohanty62, B. Mohanty87, M.
Mohisin KhanV,16, M.A. Molander44, Z. Moravcova90, C. Mordasini106, D.A.
Moreira De Godoy145, I. Morozov63, A. Morsch34, T. Mrnjavac34, V. Muccifora52,
E. Mudnic35, D. Mühlheim145, S. Muhuri142, J.D. Mulligan80, A. Mulliri22, M.G.
Munhoz121, R.H. Munzer68, H. Murakami133, S. Murray124, L. Musa34, J.
Musinsky64, J.W. Myrcha143, B. Naik132, R. Nair86, B.K. Nandi49, R. Nania54,
E. Nappi53, A.F. Nassirpour81, A. Nath105, C. Nattrass131, R. Nayak49, T.K.
Nayak87, A. Neagu20, A. Negru135, L. Nellen69, S.V. Nesbo36, G. Neskovic39, D.
Nesterov113, B.S. Nielsen90, E.G. Nielsen90, S. Nikolaev89, S. Nikulin89, V.
Nikulin99, F. Noferini54, S. Noh12, P. Nomokonov75, J. Norman128, N.
Novitzky134, P. Nowakowski143, A. Nyanin89, J. Nystrand21, M. Ogino83, A.
Ohlson81, V.A. Okorokov94, J. Oleniacz143, A.C. Oliveira Da Silva131, M.H.
Oliver147, A. Onnerstad126, C. Oppedisano59, A. Ortiz Velasquez69, T. Osako46,
A. Oskarsson81, J. Otwinowski118, M. Oya46, K. Oyama83, Y. Pachmayer105, S.
Padhan49, D. Pagano141,58, G. Paić69, A. Palasciano53, S. Panebianco139, J.
Park61, J.E. Parkkila126, S.P. Pathak125, R.N. Patra102,34, B. Paul22, H.
Pei7, T. Peitzmann62, X. Peng7, L.G. Pereira70, H. Pereira Da Costa139, D.
Peresunko89,82, G.M. Perez8, S. Perrin139, Y. Pestov5, V. Petráček37, V.
Petrov113, M. Petrovici48, R.P. Pezzi115,70, S. Piano60, M. Pikna13, P.
Pillot115, O. Pinazza54,34, L. Pinsky125, C. Pinto26, S. Pisano52, M.
Płoskoń80, M. Planinic100, F. Pliquett68, M.G. Poghosyan97, B. Polichtchouk92,
S. Politano30, N. Poljak100, A. Pop48, S. Porteboeuf-Houssais136, J. Porter80,
V. Pozdniakov75, S.K. Prasad4, R. Preghenella54, F. Prino59, C.A. Pruneau144,
I. Pshenichnov63, M. Puccio34, S. Qiu91, L. Quaglia24, R.E. Quishpe125, S.
Ragoni111, A. Rakotozafindrabe139, L. Ramello31, F. Rami138, S.A.R. Ramirez45,
T.A. Rancien79, R. Raniwala103, S. Raniwala103, S.S. Räsänen44, R. Rath50, I.
Ravasenga91, K.F. Read97,131, A.R. Redelbach39, K. RedlichVI,86, A. Rehman21,
P. Reichelt68, F. Reidt34, H.A. Reme-ness36, Z. Rescakova38, K. Reygers105, A.
Riabov99, V. Riabov99, T. Richert81, M. Richter20, W. Riegler34, F. Riggi26,
C. Ristea67, M. Rodríguez Cahuantzi45, K. Røed20, R. Rogalev92, E.
Rogochaya75, T.S. Rogoschinski68, D. Rohr34, D. Röhrich21, P.F. Rojas45, S.
Rojas Torres37, P.S. Rokita143, F. Ronchetti52, A. Rosano32,56, E.D. Rosas69,
A. Rossi57, A. Roy50, P. Roy110, S. Roy49, N. Rubini25, O.V. Rueda81, D.
Ruggiano143, R. Rui23, B. Rumyantsev75, P.G. Russek2, R. Russo91, A.
Rustamov88, E. Ryabinkin89, Y. Ryabov99, A. Rybicki118, H. Rytkonen126, W.
Rzesa143, O.A.M. Saarimaki44, R. Sadek115, S. Sadovsky92, J. Saetre21, K.
Šafařík37, S.K. Saha142, S. Saha87, B. Sahoo49, P. Sahoo49, R. Sahoo50, S.
Sahoo65, D. Sahu50, P.K. Sahu65, J. Saini142, S. Sakai134, M.P. Salvan108, S.
Sambyal102, T.B. Saramela121, D. Sarkar144, N. Sarkar142, P. Sarma42, V.M.
Sarti106, M.H.P. Sas147, J. Schambach97, H.S. Scheid68, C. Schiaua48, R.
Schicker105, A. Schmah105, C. Schmidt108, H.R. Schmidt104, M.O. Schmidt34,105,
M. Schmidt104, N.V. Schmidt97,68, A.R. Schmier131, R. Schotter138, J.
Schukraft34, K. Schwarz108, K. Schweda108, G. Scioli25, E. Scomparin59, J.E.
Seger15, Y. Sekiguchi133, D. Sekihata133, I. Selyuzhenkov108,94, S.
Senyukov138, J.J. Seo61, D. Serebryakov63, L. Šerkšnytė106, A. Sevcenco67,
T.J. Shaba72, A. Shabanov63, A. Shabetai115, R. Shahoyan34, W. Shaikh110, A.
Shangaraev92, A. Sharma101, H. Sharma118, M. Sharma102, N. Sharma101, S.
Sharma102, U. Sharma102, A. Shatat78, O. Sheibani125, K. Shigaki46, M.
Shimomura84, S. Shirinkin93, Q. Shou40, Y. Sibiriak89, S. Siddhanta55, T.
Siemiarczuk86, T.F. Silva121, D. Silvermyr81, T. Simantathammakul116, G.
Simonetti34, B. Singh106, R. Singh87, R. Singh102, R. Singh50, V.K. Singh142,
V. Singhal142, T. Sinha110, B. Sitar13, M. Sitta31, T.B. Skaali20, G.
Skorodumovs105, M. Slupecki44, N. Smirnov147, R.J.M. Snellings62, C.
Soncco112, J. Song125, A. Songmoolnak116, F. Soramel27, S. Sorensen131, I.
Sputowska118, J. Stachel105, I. Stan67, P.J. Steffanic131, S.F.
Stiefelmaier105, D. Stocco115, I. Storehaug20, M.M. Storetvedt36, P.
Stratmann145, S. Strazzi25, C.P. Stylianidis91, A.A.P. Suaide121, C. Suire78,
M. Sukhanov63, M. Suljic34, R. Sultanov93, V. Sumberia102, S. Sumowidagdo51,
S. Swain65, A. Szabo13, I. Szarka13, U. Tabassam14, S.F. Taghavi106, G.
Taillepied108,136, J. Takahashi122, G.J. Tambave21, S. Tang136,7, Z. Tang129,
J.D. Tapia TakakiVII,127, N. Tapus135, M.G. Tarzila48, A. Tauro34, G. Tejeda
Muñoz45, A. Telesca34, L. Terlizzi24, C. Terrevoli125, G. Tersimonov3, S.
Thakur142, D. Thomas119, R. Tieulent137, A. Tikhonov63, A.R. Timmins125, M.
Tkacik117, A. Toia68, N. Topilskaya63, M. Toppi52, F. Torales-Acosta19, T.
Tork78, A.G. Torres Ramos33, A. Trifiró32,56, A.S. Triolo32, S. Tripathy54,69,
T. Tripathy49, S. Trogolo34,27, V. Trubnikov3, W.H. Trzaska126, T.P.
Trzcinski143, A. Tumkin109, R. Turrisi57, T.S. Tveter20, K. Ullaland21, A.
Uras137, M. Urioni58,141, G.L. Usai22, M. Vala38, N. Valle28, S. Vallero59,
L.V.R. van Doremalen62, M. van Leeuwen91, R.J.G. van Weelden91, P. Vande
Vyvre34, D. Varga146, Z. Varga146, M. Varga-Kofarago146, M. Vasileiou85, A.
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Yamaguchi46, K. Yamakawa46, S. Yang21, S. Yano46, Z. Yin7, I.-K. Yoo17, J.H.
Yoon61, S. Yuan21, A. Yuncu105, V. Zaccolo23, C. Zampolli34, H.J.C. Zanoli62,
F. Zanone105, N. Zardoshti34, A. Zarochentsev113, P. Závada66, N.
Zaviyalov109, M. Zhalov99, B. Zhang7, S. Zhang40, X. Zhang7, Y. Zhang129, V.
Zherebchevskii113, Y. Zhi11, N. Zhigareva93, D. Zhou7, Y. Zhou90, J. Zhu108,7,
Y. Zhu7, G. ZinovjevI,3, N. Zurlo141,58

## Affiliation Notes

I Deceased
II Also at: Italian National Agency for New Technologies, Energy and
Sustainable Economic Development (ENEA), Bologna, Italy
III Also at: Dipartimento DET del Politecnico di Torino, Turin, Italy
IV Also at: M.V. Lomonosov Moscow State University, D.V. Skobeltsyn Institute
of Nuclear, Physics, Moscow, Russia
V Also at: Department of Applied Physics, Aligarh Muslim University, Aligarh,
India
VI Also at: Institute of Theoretical Physics, University of Wroclaw, Poland
VII Also at: University of Kansas, Lawrence, Kansas, United States

## Collaboration Institutes

1 A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute)
Foundation, Yerevan, Armenia
2 AGH University of Science and Technology, Cracow, Poland
3 Bogolyubov Institute for Theoretical Physics, National Academy of Sciences
of Ukraine, Kiev, Ukraine
4 Bose Institute, Department of Physics and Centre for Astroparticle Physics
and Space Science (CAPSS), Kolkata, India
5 Budker Institute for Nuclear Physics, Novosibirsk, Russia
6 California Polytechnic State University, San Luis Obispo, California, United
States
7 Central China Normal University, Wuhan, China
8 Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana,
Cuba
9 Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and
Mérida, Mexico
10 Chicago State University, Chicago, Illinois, United States
11 China Institute of Atomic Energy, Beijing, China
12 Chungbuk National University, Cheongju, Republic of Korea
13 Comenius University Bratislava, Faculty of Mathematics, Physics and
Informatics, Bratislava, Slovakia
14 COMSATS University Islamabad, Islamabad, Pakistan
15 Creighton University, Omaha, Nebraska, United States
16 Department of Physics, Aligarh Muslim University, Aligarh, India
17 Department of Physics, Pusan National University, Pusan, Republic of Korea
18 Department of Physics, Sejong University, Seoul, Republic of Korea
19 Department of Physics, University of California, Berkeley, California,
United States
20 Department of Physics, University of Oslo, Oslo, Norway
21 Department of Physics and Technology, University of Bergen, Bergen, Norway
22 Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
23 Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
24 Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy
25 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Bologna, Italy
26 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Catania, Italy
27 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Padova, Italy
28 Dipartimento di Fisica e Nucleare e Teorica, Università di Pavia, Pavia,
Italy
29 Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo
Collegato INFN, Salerno, Italy
30 Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy
31 Dipartimento di Scienze e Innovazione Tecnologica dell’Università del
Piemonte Orientale and INFN Sezione di Torino, Alessandria, Italy
32 Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy
33 Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari,
Italy
34 European Organization for Nuclear Research (CERN), Geneva, Switzerland
35 Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, Split, Croatia
36 Faculty of Engineering and Science, Western Norway University of Applied
Sciences, Bergen, Norway
37 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University in Prague, Prague, Czech Republic
38 Faculty of Science, P.J. Šafárik University, Košice, Slovakia
39 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-
Universität Frankfurt, Frankfurt, Germany
40 Fudan University, Shanghai, China
41 Gangneung-Wonju National University, Gangneung, Republic of Korea
42 Gauhati University, Department of Physics, Guwahati, India
43 Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-
Wilhelms-Universität Bonn, Bonn, Germany
44 Helsinki Institute of Physics (HIP), Helsinki, Finland
45 High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico
46 Hiroshima University, Hiroshima, Japan
47 Hochschule Worms, Zentrum für Technologietransfer und Telekommunikation
(ZTT), Worms, Germany
48 Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest, Romania
49 Indian Institute of Technology Bombay (IIT), Mumbai, India
50 Indian Institute of Technology Indore, Indore, India
51 Indonesian Institute of Sciences, Jakarta, Indonesia
52 INFN, Laboratori Nazionali di Frascati, Frascati, Italy
53 INFN, Sezione di Bari, Bari, Italy
54 INFN, Sezione di Bologna, Bologna, Italy
55 INFN, Sezione di Cagliari, Cagliari, Italy
56 INFN, Sezione di Catania, Catania, Italy
57 INFN, Sezione di Padova, Padova, Italy
58 INFN, Sezione di Pavia, Pavia, Italy
59 INFN, Sezione di Torino, Turin, Italy
60 INFN, Sezione di Trieste, Trieste, Italy
61 Inha University, Incheon, Republic of Korea
62 Institute for Gravitational and Subatomic Physics (GRASP), Utrecht
University/Nikhef, Utrecht, Netherlands
63 Institute for Nuclear Research, Academy of Sciences, Moscow, Russia
64 Institute of Experimental Physics, Slovak Academy of Sciences, Košice,
Slovakia
65 Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India
66 Institute of Physics of the Czech Academy of Sciences, Prague, Czech
Republic
67 Institute of Space Science (ISS), Bucharest, Romania
68 Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany
69 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México,
Mexico City, Mexico
70 Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS),
Porto Alegre, Brazil
71 Instituto de Física, Universidad Nacional Autónoma de México, Mexico City,
Mexico
72 iThemba LABS, National Research Foundation, Somerset West, South Africa
73 Jeonbuk National University, Jeonju, Republic of Korea
74 Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik,
Fachbereich Informatik und Mathematik, Frankfurt, Germany
75 Joint Institute for Nuclear Research (JINR), Dubna, Russia
76 Korea Institute of Science and Technology Information, Daejeon, Republic of
Korea
77 KTO Karatay University, Konya, Turkey
78 Laboratoire de Physique des 2 Infinis, Irène Joliot-Curie, Orsay, France
79 Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-
Alpes, CNRS-IN2P3, Grenoble, France
80 Lawrence Berkeley National Laboratory, Berkeley, California, United States
81 Lund University Department of Physics, Division of Particle Physics, Lund,
Sweden
82 Moscow Institute for Physics and Technology, Moscow, Russia
83 Nagasaki Institute of Applied Science, Nagasaki, Japan
84 Nara Women’s University (NWU), Nara, Japan
85 National and Kapodistrian University of Athens, School of Science,
Department of Physics , Athens, Greece
86 National Centre for Nuclear Research, Warsaw, Poland
87 National Institute of Science Education and Research, Homi Bhabha National
Institute, Jatni, India
88 National Nuclear Research Center, Baku, Azerbaijan
89 National Research Centre Kurchatov Institute, Moscow, Russia
90 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
91 Nikhef, National institute for subatomic physics, Amsterdam, Netherlands
92 NRC Kurchatov Institute IHEP, Protvino, Russia
93 NRC KurchatovInstitute - ITEP, Moscow, Russia
94 NRNU Moscow Engineering Physics Institute, Moscow, Russia
95 Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom
96 Nuclear Physics Institute of the Czech Academy of Sciences, Řež u Prahy,
Czech Republic
97 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
98 Ohio State University, Columbus, Ohio, United States
99 Petersburg Nuclear Physics Institute, Gatchina, Russia
100 Physics department, Faculty of science, University of Zagreb, Zagreb,
Croatia
101 Physics Department, Panjab University, Chandigarh, India
102 Physics Department, University of Jammu, Jammu, India
103 Physics Department, University of Rajasthan, Jaipur, India
104 Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen,
Germany
105 Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg,
Heidelberg, Germany
106 Physik Department, Technische Universität München, Munich, Germany
107 Politecnico di Bari and Sezione INFN, Bari, Italy
108 Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum
für Schwerionenforschung GmbH, Darmstadt, Germany
109 Russian Federal Nuclear Center (VNIIEF), Sarov, Russia
110 Saha Institute of Nuclear Physics, Homi Bhabha National Institute,
Kolkata, India
111 School of Physics and Astronomy, University of Birmingham, Birmingham,
United Kingdom
112 Sección Física, Departamento de Ciencias, Pontificia Universidad Católica
del Perú, Lima, Peru
113 St. Petersburg State University, St. Petersburg, Russia
114 Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
115 SUBATECH, IMT Atlantique, Université de Nantes, CNRS-IN2P3, Nantes, France
116 Suranaree University of Technology, Nakhon Ratchasima, Thailand
117 Technical University of Košice, Košice, Slovakia
118 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of
Sciences, Cracow, Poland
119 The University of Texas at Austin, Austin, Texas, United States
120 Universidad Autónoma de Sinaloa, Culiacán, Mexico
121 Universidade de São Paulo (USP), São Paulo, Brazil
122 Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
123 Universidade Federal do ABC, Santo Andre, Brazil
124 University of Cape Town, Cape Town, South Africa
125 University of Houston, Houston, Texas, United States
126 University of Jyväskylä, Jyväskylä, Finland
127 University of Kansas, Lawrence, Kansas, United States
128 University of Liverpool, Liverpool, United Kingdom
129 University of Science and Technology of China, Hefei, China
130 University of South-Eastern Norway, Tonsberg, Norway
131 University of Tennessee, Knoxville, Tennessee, United States
132 University of the Witwatersrand, Johannesburg, South Africa
133 University of Tokyo, Tokyo, Japan
134 University of Tsukuba, Tsukuba, Japan
135 University Politehnica of Bucharest, Bucharest, Romania
136 Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
137 Université de Lyon, CNRS/IN2P3, Institut de Physique des 2 Infinis de
Lyon, Lyon, France
138 Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France,
Strasbourg, France
139 Université Paris-Saclay Centre d’Etudes de Saclay (CEA), IRFU, Départment
de Physique Nucléaire (DPhN), Saclay, France
140 Università degli Studi di Foggia, Foggia, Italy
141 Università di Brescia, Brescia, Italy
142 Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata,
India
143 Warsaw University of Technology, Warsaw, Poland
144 Wayne State University, Detroit, Michigan, United States
145 Westfälische Wilhelms-Universität Münster, Institut für Kernphysik,
Münster, Germany
146 Wigner Research Centre for Physics, Budapest, Hungary
147 Yale University, New Haven, Connecticut, United States
148 Yonsei University, Seoul, Republic of Korea