2022 283 12 December

Spin alignment of $\mathrm{D^{*+}}$ vector mesons in pp collisions at
$\sqrt{s}=13$ TeV ALICE Collaboration††thanks: See Appendix A for the list of
Collaboration members ALICE Collaboration

This letter reports the first measurement of spin alignment, with respect to
the helicity axis, for $\mathrm{D^{*+}}$ vector mesons and their charge
conjugates from charm-quark hadronisation (prompt) and from beauty-meson
decays (non-prompt) in hadron collisions. The measurements were performed at
midrapidity ($|y|<0.8$) as a function of transverse momentum
($p_{\mathrm{T}}$) in proton–proton (pp) collisions collected by ALICE at the
centre-of-mass energy $\sqrt{s}=13~{}\mathrm{TeV}$. The diagonal spin density
matrix element $\rho_{00}$ of $\mathrm{D^{*+}}$ mesons was measured from the
angular distribution of the
$\mathrm{D}^{*+}\to\mathrm{D}^{0}(\to\mathrm{K}^{-}\uppi^{+})\uppi^{+}$ decay
products, in the $\mathrm{D^{*+}}$ rest frame, with respect to the
$\mathrm{D^{*+}}$ momentum direction in the pp centre of mass frame. The
$\rho_{00}$ value for prompt $\mathrm{D^{*+}}$ mesons is consistent with
$1/3$, which implies no spin alignment. However, for non-prompt
$\mathrm{D^{*+}}$ mesons an evidence of $\rho_{00}$ larger than $1/3$ is
found. The measured value of the spin density element is $\rho_{00}=0.455\pm
0.022(\text{stat.})\pm 0.035(\text{syst.})$ in the
$5<p_{\mathrm{T}}<20~{}\mathrm{GeV}/c$ interval, which is consistent with a
Pythia 8 Monte Carlo simulation coupled with the EvtGen package, which
implements the helicity conservation in the decay of $\mathrm{D^{*+}}$ meson
from beauty mesons. In non-central heavy-ion collisions, the spin of the
$\mathrm{D^{*+}}$ mesons may be globally aligned with the direction of the
initial angular momentum and magnetic field. Based on the results for pp
collisions reported in this letter it is shown that alignment of non-prompt
$\mathrm{D^{*+}}$ mesons due to the helicity conservation coupled to the
collective anisotropic expansion may mimic the signal of global spin alignment
in heavy-ion collisions.

##  1 Introduction

The production of hadrons containing heavy quarks, i.e. charm and beauty, has
been extensively studied in both lepton and hadron collisions, improving
significantly the understanding of the hadronisation mechanism [1, 2, 3, 4, 5,
6, 7, 8]. However, several aspects of the transition of the heavy quark to the
final-state hadron are not yet settled. One of them regards the spin
properties of produced particles in the quark hadronisation. In the limit of
very large heavy-quark mass ($m_{\mathrm{Q}}\rightarrow\infty$), the
polarisation of heavy-flavour baryons is assumed to be that carried by the
heavy valence quark [9]. This assumption was studied at LEP in
$\mathrm{e^{+}e^{-}}$ collisions where the polarisation of
$\mathrm{{\Lambda_{b}^{0}}}$ baryons was used to probe the electroweak
structure of the $\mathrm{Z}^{0}$ boson production and decays [10, 11, 12, 13,
14]. In hadronic collisions, the polarisation of $\mathrm{{\Lambda_{b}^{0}}}$
baryons can arise during the hadronisation process if beauty quarks are
produced with a transverse polarisation, as predicted by the heavy-quark
effective theory [11, 9]. At this time, one measurement, performed by the LHCb
Collaboration, found no significant polarisation [15]. For vector mesons with
quantum numbers $J^{P}=1^{-}$, both in lepton and hadron collisions, at least
part of the polarisation should arise from the hadronisation process [9].
Models based on statistical quantum mechanics considerations [16, 17], heavy-
quark effective theory [9], or inspired by quantum chromodynamics (QCD) [18]
provide very different predictions, from no polarisation, to very large
longitudinal or transverse polarisation. This aspect of the hadronisation is
typically not accounted for in QCD-inspired Monte Carlo (MC) generators based
on the Lund string model [19], such as Pythia 8 [20, 21], or the clustering
model [22], as implemented in Herwig 7 [23]. Measurements of excited B vector
meson states in $\mathrm{Z}^{0}$ decays at LEP did not show any significant
polarisation [24, 25]. For charm vector mesons ($\mathrm{D^{*+}}$) a
longitudinal polarisation was observed by OPAL [26]. However, previous
measurements in $\mathrm{e^{+}e^{-}}$ collisions indicated no significant
polarisation for $\mathrm{D^{*+}}$ mesons [27, 28, 29].

The polarisation of vector mesons containing heavy quarks in heavy-ion
collisions is of special interest. The initial stages of such collisions, with
non-zero impact parameter, are expected to be characterised by a large orbital
angular momentum [30] and a strong magnetic field [31, 32, 33]. These initial
conditions could influence the produced colour-deconfined matter (called
quark–gluon plasma [34, 35]). The directions of the angular momentum and the
magnetic field in such collisions are perpendicular to the reaction plane
(subtended by the beam axis and impact parameter) [36]. Theoretical
calculations at LHC energies predict the values of the angular momentum to be
of the order of $10^{7}$ $\hslash$ [30] and the magnetic field to be about
$10^{16}$ T [37, 32, 38, 33, 31]. While the angular momentum, a conserved
quantity in strong interactions, is expected to affect the whole evolution of
the collision, the magnetic field is transient in nature and its strength
falls steeply with time. Heavy quarks are produced at the initial stages of
heavy-ion collisions, in a time scale shorter than the quark–gluon plasma
formation time [39] and are sensitive to the large initial magnetic field as
well as the angular momentum. In the presence of these initial conditions,
charm quarks can be polarised. The quark polarisation is expected to be
further transferred to the final-state hadrons during hadronisation and it is
predicted to be different in the case of hadronisation in vacuum, or
recombination with light quarks from the deconfined medium [36, 40, 41, 42].
Measurements in heavy-ion collisions indicate that the recombination mechanism
is important to describe the production and angular anisotropies of charm
hadrons [43, 44, 45, 46, 47, 48, 49, 50, 51]. If observed, a non-zero
polarisation of $\mathrm{D^{*+}}$ mesons will be a manifestation of the
angular momentum and the magnetic field created in heavy-ion collisions. The
study of $\mathrm{D^{*+}}$ mesons would provide additional information,
crucial for the interpretation of the recently measured $\mathrm{J}/\uppsi$
polarisation in Pb–Pb collisions by the ALICE Collaboration [52, 53]. In fact,
the polarisation of $\mathrm{D^{*+}}$ and $\mathrm{J}/\uppsi$ mesons have
different contributions from the angular momentum and the magnetic field,
given the valence light quark present in the $\mathrm{D^{*+}}$ meson, which is
expected to be less sensitive than the charm quark to the magnetic field.
However, the interpretation of experimental data for heavy-ion collisions
requires a baseline study in elementary proton–proton (pp) collisions, where
such initial conditions are not expected to form. Moreover, in this study, one
of the major sources of background is the feed-down contribution of
$\mathrm{D^{*+}}$ mesons originating from decays of scalar mesons containing a
beauty quark, which are observed to be longitudinally polarised by the Belle
and LHCb Collaborations in $\mathrm{e^{+}e^{-}}$ and pp collisions,
respectively [54, 55]. This is a direct consequence of the helicity
conservation and the Vector–Axial (V$-$A) nature of the weak interaction
involved in the $\mathrm{b}\to\mathrm{c}$ decay, which leads to left-handed
fermion couplings in interactions with W bosons [56, 57]. It is therefore
important to separate contributions to the polarisation from promptly produced
mesons and from those originating in beauty-hadron decays. This was not
possible in the case of the $\mathrm{J}/\uppsi$ meson in Pb–Pb collisions with
LHC Run 2 data, for which only the inclusive polarisation was used as baseline
[53].

The polarisation of $\mathrm{D^{*+}}$ vector mesons cannot be probed directly
as $\mathrm{D^{*+}}$ mesons are measured through the parity conserving strong
decay $\mathrm{D}^{*+}\to\mathrm{D}^{0}(\to\mathrm{K}^{-}\uppi^{+})\uppi^{+}$.
However, experimentally, the spin alignment along the quantisation direction
can be studied by measuring the diagonal spin density matrix element
($\rho_{00}$) of the vector meson. The $\rho_{00}$ reflects the probability of
finding a vector meson in the state with spin zero out of possible states with
spin projection $-1$, 0, and 1 [58]. If the spin of particles is homogeneously
distributed, all spin states are expected to be equally probable, thereby
yielding $\rho_{00}=1/3$. The spin alignment is studied by measuring the
angular distribution of the decay products of vector mesons. Their decay
products are measured with respect to a quantisation axis, which is the vector
meson momentum direction (helicity axis) in pp collisions and the
perpendicular direction of the reaction plane in heavy-ion collisions. In the
latter, these two axes are further correlated through the anisotropic
collective expansion which is quantified by coefficients in a Fourier
decomposition of the azimuthal-angle distribution of final-state particle
momenta, with the second-harmonic coefficient $v_{2}$, called elliptic flow
[59], being the dominant one [50]. The angular distribution of the
$\mathrm{D^{*+}}$ decay products is expressed as

$\frac{\mathrm{d}N}{\mathrm{d}\cos{\theta^{*}}}\propto[1-\rho_{00}+(3\rho_{00}-1)\cos^{2}{\theta^{*}}],$
(1)

where $\theta^{*}$ is the angle between the momentum of either the
$\mathrm{D^{0}}$ meson or the pion in the rest frame of the vector meson with
respect to the quantisation axis [60].

In this letter, the first measurement of the spin alignment of
$\mathrm{D^{*+}}$ mesons from charm-quark hadronisation (prompt) and from
beauty-hadron decays (non-prompt) at midrapidity is presented as a function of
transverse momentum ($p_{\mathrm{T}}$) in pp collisions at a centre-of-mass
energy of $\sqrt{s}=13~{}\mathrm{TeV}$. Based on these measurements,
quantitative predictions for the spin distributions of non-prompt
$\mathrm{D^{*+}}$ meson for a future measurement of the
$\mathrm{D^{*+}}$-meson spin alignment in heavy-ion collisions are provided.

##  2 Experimental apparatus and data analysis

The analysis was performed using about $1.8\times 10^{9}$ minimum-bias and
about $10^{9}$ high-multiplicity triggered pp collisions at
$\sqrt{s}=13~{}\mathrm{TeV}$ recorded with the ALICE apparatus [61, 62],
corresponding to an integrated luminosity of
$\mathcal{L}_{\mathrm{int}}\approx 32$ $\mathrm{nb}^{-1}$ and
$\mathcal{L}_{\mathrm{int}}\approx 7.7~{}\mathrm{pb}^{-1}$, respectively. The
minimum-bias trigger required coincident signals in the two V0 detectors,
which are two scintillator arrays covering the pseudorapidity intervals
$-3.7<\eta<-1.7$ and $2.8<\eta<5.1$ [63]. The high-multiplicity trigger
selected the 0.17% highest-multiplicity events out of all inelastic collisions
with at least one charged particle in the pseudorapidity range $|\eta|<1$,
relying on the signal amplitudes of the V0 detectors. Events were further
selected offline to remove machine-induced backgrounds [61]. They were
required to have a reconstructed collision vertex located within $\pm
10~{}\mathrm{cm}$ from the centre of the detector along the beam-line
direction to maintain a uniform acceptance. Events with multiple reconstructed
primary vertices (pileup) were rejected. Primary vertices were reconstructed
from track segments measured with the two innermost layers of the Inner
Tracking System (ITS), which consists of six cylindrical layers of silicon
detectors [64]. The remaining undetected pileup was studied and found to be
negligible for this analysis.

The $\mathrm{D^{*+}}$ mesons and their charge conjugates were measured at
midrapidity ($|y|<0.8$) via the
$\mathrm{D}^{*+}\to\mathrm{D}^{0}(\to\mathrm{K}^{-}\uppi^{+})\uppi^{+}$ decay
channel, with branching ratio $\mathrm{BR}=(2.67\pm 0.03)\%$ [65]. The
measurement of $\mathrm{D^{*+}}$ mesons was based on charged-particle tracks
reconstructed with the Time Projection Chamber (TPC) [66] and ITS detectors.
The $\mathrm{D^{0}}$ decay candidates were defined combining pairs of tracks
with the expected charge combinations. Each track from the decay was required
to have $|\eta|<0.8$, $p_{\mathrm{T}}>0.3~{}\mathrm{GeV}/c$, at least 70 (out
of 159) associated space points in the TPC, and a minimum of two hits in the
ITS, with at least one in either of the two innermost layers to ensure a good
pointing resolution. The $\mathrm{D^{*+}}$-meson candidates were reconstructed
by combining $\mathrm{D^{0}}$ candidates with low-$p_{\mathrm{T}}$ tracks
(referred to as soft pions) having $|\eta|<0.8$,
$p_{\mathrm{T}}>50~{}\mathrm{MeV}/c$, and at least two hits in the ITS. The
analysis was based on the reconstruction of decay-vertex topologies of
$\mathrm{D^{0}}$ mesons displaced from the interaction vertex. In particular,
the proper decay length of $\mathrm{D^{0}}$ mesons of $c\tau\approx
123~{}\mathrm{\mu m}$ and that of beauty hadrons of $c\tau\approx
500~{}\mathrm{\mu m}$ were exploited to resolve the $\mathrm{D^{0}}$-meson
decay vertices. In order to reduce the large combinatorial background and to
separate the contribution of prompt and non-prompt $\mathrm{D^{*+}}$ mesons, a
multiclass classification algorithm based on Boosted Decision Trees (BDTs) was
used [67, 68]. The candidate information used by the BDT algorithm to
distinguish among prompt and non-prompt $\mathrm{D^{*+}}$ mesons and
background candidates was based on i) the distance between the reconstructed
$\mathrm{D^{0}}$-meson decay vertex and the primary vertex, ii) the
$\mathrm{D^{0}}$-meson and soft-pion distance of closest approach to the
interaction vertex, iii) the cosine of the pointing angle between the
$\mathrm{D^{0}}$-meson candidate line of flight and its reconstructed momentum
vector, and iv) the particle identification (PID) information of the decay
tracks. The PID information was provided by the specific energy loss and the
flight time of particles measured with the TPC and Time Of Flight (TOF) [69]
detectors, respectively. Signal samples of prompt and non-prompt
$\mathrm{D^{*+}}$ mesons for the BDT training were obtained from MC
simulations based on the Pythia 8.243 event generator [20, 21] with the Monash
tune [70] and Geant 3 package [71] for the propagation of the generated
particles through the detector. The background samples were obtained in data
from the sideband region of the invariant-mass distribution $\Delta
M=M(\mathrm{K}\uppi\uppi)-M(\mathrm{K}\uppi)$. The sideband region was chosen
as the invariant-mass interval $\Delta M>150~{}\mathrm{MeV}/c^{2}$, where no
$\mathrm{D^{*+}}$ signal is present. Independent BDTs were trained for the
high-multiplicity and minimum-bias samples in three different $p_{\mathrm{T}}$
intervals, i.e. $5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$,
$7<p_{\mathrm{T}}<10~{}\mathrm{GeV}/c$, and
$10<p_{\mathrm{T}}<20~{}\mathrm{GeV}/c$. Subsequently, they were applied to
the real data sample in which the type of candidate is unknown. The BDT
outputs are related to the candidate probability to be a prompt
$\mathrm{D^{*+}}$ meson, non-prompt $\mathrm{D^{*+}}$ meson, or combinatorial
background.

The selection based on the probability to be background was optimised to yield
a good statistical significance and purity of the signal. By selecting high
probability to be prompt or non-prompt $\mathrm{D^{*+}}$ mesons, the samples
of candidates were further separated to the charm-enhanced (significant
contribution of prompt $\mathrm{D^{*+}}$ mesons) and the beauty-enhanced
(significant contribution of non-prompt $\mathrm{D^{*+}}$ mesons) samples. The
threshold values were tuned as a function of $p_{\mathrm{T}}$ using MC
simulations. The fractions of prompt ($f_{\mathrm{prompt}}$) and non-prompt
($f_{\mathrm{non\text{-}prompt}}$) $\mathrm{D^{*+}}$ mesons in each sample
were evaluated with a data-driven method based on the sampling of the raw
yield $Y_{\mathrm{i}}$ at different values of the BDT-output score related to
the probability of being a non-prompt $\mathrm{D^{*+}}$ meson. These fractions
can be computed by solving a system of equations that relate raw yields to the
corrected yields of prompt ($N_{\mathrm{prompt}}$) and non-prompt
($N_{\mathrm{non\text{-}prompt}}$) $\mathrm{D^{*+}}$ mesons by the product of
the geometrical acceptance and the reconstruction and selection (including
BDT) efficiency factors ($\mathrm{Acc}\times\epsilon$) for prompt and non-
prompt $\mathrm{D^{*+}}$ mesons. Each equation, obtained for a set of BDT
selections $i$, can be expressed as

$(\mathrm{Acc}\times\epsilon)_{\mathrm{prompt},i}\times
N_{\mathrm{prompt}}+(\mathrm{Acc}\times\epsilon)_{\mathrm{non\text{-}prompt},i}\times
N_{\mathrm{non\text{-}prompt}}-Y_{i}=\delta_{\mathrm{i}},$ (2)

where $\delta_{\mathrm{i}}$ is the residual originating from the uncertainties
on $Y_{i}$, $(\mathrm{Acc}\times\epsilon)_{\mathrm{non\text{-}prompt},i}$, and
$(\mathrm{Acc}\times\epsilon)_{\mathrm{prompt},i}$. To define the sets of
selections, the BDT-output response related to the probability of a candidate
to be a non-prompt $\mathrm{D^{*+}}$ meson was sampled monotonically, to
obtain $n$ selections ordered in such a way that the $i^{\mathrm{th}}$
selected sample was completely included in the $(i-1)^{\mathrm{th}}$ one. The
system of equation is then solved via a $\chi^{2}$ minimisation, which
provides as output the corrected yields of prompt ($N_{\mathrm{prompt}}$) and
non-prompt ($N_{\mathrm{non\text{-}prompt}}$) $\mathrm{D^{*+}}$ mesons and
their covariance matrix. A detailed description of this method is presented in
Refs. [72, 73, 74]. For each $p_{\mathrm{T}}$ interval, the raw yields of
$\mathrm{D^{*+}}$ mesons were extracted with a fit to the distribution of the
invariant mass $\Delta M$.

The distribution was fitted with a combination of the Gaussian function
corresponding to the $\mathrm{D^{*+}}$ signal and a background function. The
shape of the background distribution can be described with the function
$p_{0}\sqrt{\Delta M-M_{\uppi}}\text{ }e^{p_{1}(\Delta M-M_{\uppi})}$, where
$p_{0}$ and $p_{1}$ are free parameters and $M_{\uppi}$ is the pion mass. The
corresponding $\mathrm{Acc}\times\epsilon$ factors were obtained with MC
simulations analogous to those used for the BDT trainings. Finally, the
fraction of (non-)prompt $\mathrm{D^{*+}}$ mesons for a given set of
selections was computed as

$f_{\mathrm{(non\text{-})prompt},j}=\frac{(\mathrm{Acc}\times\epsilon)_{\mathrm{(non\text{-})prompt},j}\times
N_{\mathrm{(non\text{-})prompt}}}{(\mathrm{Acc}\times\epsilon)_{\mathrm{prompt},j}\times
N_{\mathrm{prompt}}+(\mathrm{Acc}\times\epsilon)_{\mathrm{non\text{-}prompt},j}\times
N_{\mathrm{non\text{-}prompt}}}.$ (3)

A different index "$j$" is used here to underline the fact that not all of
these sets are used for the $\chi^{2}$ minimisation given by Eq. 2. The
uncertainty of $f_{\mathrm{(non\text{-})prompt},j}$ is computed considering
the covariance matrix of $N_{\mathrm{prompt}}$ and
$N_{\mathrm{non\text{-}prompt}}$ obtained in the $\chi^{2}$-minimisation
procedure. Figure 1 shows an example of a raw-yield extracted as a function of
the BDT selection employed in the minimisation procedure for $\mathrm{D^{*+}}$
mesons with $5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$ in high-multiplicity
triggered pp collisions at $\sqrt{s}=13~{}\mathrm{TeV}$. The leftmost data
point of the distribution is the raw yield corresponding to the loosest
selection on the BDT output related to the candidate probability of being a
non-prompt $\mathrm{D^{*+}}$ meson, while the rightmost one corresponds to the
strictest selection, which is expected to preferentially select non-prompt
$\mathrm{D^{*+}}$ mesons. The $\mathrm{Acc}\times\epsilon$ factors obtained
for these selections ranged from about 10% to 0.1% for prompt
$\mathrm{D^{*+}}$ mesons, and from about 30% to 10% for non-prompt
$\mathrm{D^{*+}}$ mesons. The prompt and non-prompt components are represented
by the red and blue filled histograms, respectively, while their sum is
depicted by the green histogram. The $f_{\mathrm{prompt}}$ factor obtained in
the charm-enhanced sample is higher than 90% for both the high-multiplicity
and minimum-bias triggered events, while the $f_{\mathrm{non\text{-}prompt}}$
in the beauty-enhanced sample is $\sim 60\%$ and $\sim 40\%$ almost
independent of $p_{\mathrm{T}}$ for high-multiplicity and minimum-bias
triggered events, respectively.

Figure 1: Raw yield as a function of the BDT selection and extracted
contributions from prompt and non-prompt $\mathrm{D^{*+}}$ mesons with
$5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$ and $|y|<0.8$ in the high-multiplicity
triggered pp collisions at $\sqrt{s}=13~{}\mathrm{TeV}$. Figure 2: Invariant-
mass distributions $\Delta M$ for the charm-enhanced (left panel) and the
beauty-enhanced (right panel) samples in pp collisions at
$\sqrt{s}=13~{}\mathrm{TeV}$, selected with the high-multiplicity trigger. The
distributions are obtained at midrapidity ($|y|<0.8$) in
$5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$ and $0.0<\cos{\theta^{*}}<0.2$.

The raw yields of $\mathrm{D^{*+}}$ mesons were extracted in different
$\cos{\theta^{*}}$ and $p_{\mathrm{T}}$ intervals for both the beauty- and the
charm-enhanced samples. Figure 2 shows the $\Delta M$ distributions in
$5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$ and $0.0<\cos{\theta^{*}}<0.2$ intervals
for the beauty- and charm-enhanced samples in high-multiplicity triggered pp
collisions at $\sqrt{s}=13~{}\mathrm{TeV}$. The width of the Gaussian function
for the $\mathrm{D^{*+}}$ signal was fixed to the value from the MC
simulation.

Figure 3: Acceptance and efficiency corrected angular distributions of the
decay product in the rest frame of the $\mathrm{D^{*+}}$ meson with respect to
the helicity axis. The left panel shows the angular distribution for the
charm-enhanced $\mathrm{D^{*+}}$ sample in pp collisions at
$\sqrt{s}=13~{}\mathrm{TeV}$, selected with the high-multiplicity trigger and
the right panel shows the same but for the beauty-enhanced $\mathrm{D^{*+}}$
sample. The distributions are obtained at midrapidity ($|y|<0.8$) in
$5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$ and are fitted with Eq. 1 to extract the
$\rho_{00}$ values. Only statistical uncertainties are shown.

The raw yields were corrected for the corresponding
$\mathrm{Acc}\times\epsilon$ factors in each $\cos{\theta^{*}}$ and
$p_{\mathrm{T}}$ intervals. The impact on the $\rho_{00}$ measurement due to
the shape of the $\cos{\theta^{*}}$ and $p_{\mathrm{T}}$ distributions in the
MC simulations was studied by weighting the generated MC distributions in
order to reproduce the measured $\cos{\theta^{*}}$ and $p_{\mathrm{T}}$
distributions, and the effect on the $\mathrm{Acc}\times\epsilon$ values was
found to be smaller than 0.1% in the analysed $p_{\mathrm{T}}$ intervals. The
efficiency and acceptance corrected angular distributions at midrapidity for
the selected $p_{\mathrm{T}}$ interval in high-multiplicity triggered pp
collisions at $\sqrt{s}=13~{}\mathrm{TeV}$ are shown in Fig. 3. The left panel
of Fig. 3 shows the angular distribution of the charm-enhanced
$\mathrm{D^{*+}}$ sample and the right panel shows the same but for the
beauty-enhanced $\mathrm{D^{*+}}$ sample. The absolute value of
$\cos{\theta^{*}}$ was considered due to the limited size of the analysed
sample. The angular distributions were further fitted with the functional form
given in Eq. 1 to extract the $\rho_{00}$ values for both the charm- and the
beauty-enhanced samples in each $p_{\mathrm{T}}$ interval.

It was verified with a MC simulation that the $\rho_{00}$ parameter linearly
depends on the fraction of non-prompt $\mathrm{D^{*+}}$ meson in the analysed
sample. Hence, a linear fit of the measured $\rho_{00}$ parameters obtained
for the charm- and beauty-enhanced samples as a function of the
$f_{\mathrm{non\text{-}prompt}}$ was performed to obtain the $\rho_{00}$
values for prompt and non-prompt $\mathrm{D^{*+}}$ mesons. The charm- and the
beauty-enhanced selections used in this analysis provided two samples of
independent candidates. Moreover, the samples of candidates in the minimum-
bias and high-multiplicity triggered events are statistically independent.
Considering that the measured $\rho_{00}$ parameter can be decomposed as a
linear combination of the prompt and non-prompt components,

$\rho_{00}=f_{\mathrm{prompt}}\times\rho_{00}^{\mathrm{prompt}}+f_{\mathrm{non\text{-}prompt}}\times\rho_{00}^{\mathrm{non\text{-}prompt}},$
(4)

the four independent measurements corresponding to the charm- and beauty-
enhanced samples for both minimum-bias and high-multiplicity events were
fitted with a linear function in order to extrapolate it to
$f_{\mathrm{non\text{-}prompt}}=0$ and $f_{\mathrm{non\text{-}prompt}}=1$. A
similar procedure was adopted in Ref. [75] to measure the elliptic flow of
prompt and non-prompt D mesons. With the current data samples it is not
possible to perform the linear extrapolation of the $\rho_{00}$ parameter
independently for the minimum-bias and high-multiplicity collisions, which may
have different physical origin, and the reported results are for the combined
sample. Figure 4 shows the linear fit of $\rho_{00}$ as a function of
$f_{\mathrm{non\text{-}prompt}}$ in $5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$. The
filled (empty) markers correspond to the measurements performed in the
minimum-bias (high-multiplicity) pp collisions. The coloured band represents
the $1\sigma$ confidence interval obtained from the linear fit. The
$\rho_{00}$ parameter for prompt and non-prompt $\mathrm{D^{*+}}$ mesons is
then obtained by evaluating the fit function for
$f_{\mathrm{non\text{-}prompt}}=0$ and $f_{\mathrm{non\text{-}prompt}}=1$,
respectively.

Figure 4: The spin density matrix element ($\rho_{00}$) as a function of
$f_{\mathrm{non\text{-}prompt}}$ in $5<p_{\mathrm{T}}<7~{}\mathrm{GeV}/c$ for
charm- and beauty-enhanced samples obtained for minimum-bias and high-
multiplicity triggered pp collisions at $\sqrt{s}=13~{}\mathrm{TeV}$. Only
statistical uncertainties are shown. The blue line represents the linear fit
to the data with the blue band indicating its $1\sigma$ confidence interval.

##  3 Systematic uncertainties

There are four major sources of systematic uncertainties in the measurement of
$\rho_{00}$ for prompt and non-prompt $\mathrm{D^{*+}}$ mesons. These
uncertainties are related to: i) the signal extraction, ii) the track
reconstruction and selection efficiencies, iii) the BDT selection efficiency,
and iv) the (non-)prompt fraction estimation. The systematic uncertainty
arising from the signal extraction was estimated by varying the invariant-mass
fit range, leaving the Gaussian width free in the fit, and using a bin-
counting method for the raw-yield extraction. In the bin-counting method the
signal yield is extracted by integrating the invariant-mass distribution after
subtracting the background estimated from the background fit function. The
systematic uncertainty associated with the track selection and reconstruction
efficiency was evaluated by varying the track-quality selection criteria as
described in Ref. [76]. The systematic uncertainty on the selection efficiency
originates from imperfections in the description of the decay kinematics as
well as the detector resolution and alignment in the simulation. It was
estimated by comparing the $\rho_{00}$ parameters obtained for prompt and non-
prompt $\mathrm{D^{*+}}$ mesons with different BDT selection criteria. The
uncertainty associated with the (non-)prompt fraction estimation was evaluated
by varying the selection criteria described in Sec. 2, as well as the
configuration of the invariant-mass fits. All of the above mentioned
variations were performed independently and, assuming they are uncorrelated
with each other, added in quadrature to obtain the total systematic
uncertainties. Table 1 summarises the values of the systematic uncertainties
for the lowest and highest $p_{\mathrm{T}}$ intervals, reporting separately
the various sources for prompt and non-prompt $\mathrm{D^{*+}}$ mesons. The
total systematic uncertainty ranges between 2.5% and 3.5% for prompt
$\mathrm{D^{*+}}$ mesons, and between 6.5% and 8% for non-prompt
$\mathrm{D^{*+}}$ mesons. These systematic uncertainties were considered as
fully correlated as a function of $p_{\mathrm{T}}$.

Table 1: Summary of the relative systematic uncertainties on the $\rho_{00}$ parameter of prompt and non-prompt $\mathrm{D^{*+}}$ mesons for different $p_{\mathrm{T}}$ intervals. | Prompt | Non-prompt
---|---|---
$p_{\mathrm{T}}~{}(\mathrm{GeV}/c)$ |  $5\mbox{--}7$ |  $10\mbox{--}20$ |  $5\mbox{--}7$ |  $10\mbox{--}20$
Signal yield |  2.0% |  0.5% |  4.0% |  2.0%
Tracking efficiency |  negl. |  1.0% |  2.0% |  4.0%
BDT efficiency |  0.5% |  3.5% |  6.0% |  5.0%
(Non-)prompt fraction |  negl. |  negl. |  0.5% |  negl.
Total |  2.5% |  3.5% |  8.0% |  6.5%

In order to validate the results of the measurements, an additional analysis
was performed with respect to a random quantisation axis (random unit vector
direction in 3-dimensional space) which breaks the correlation between the
helicity axis and the daughter momentum direction, due to helicity
conservation. As expected, the extracted $\rho_{00}$ values for both prompt
and non-prompt $\mathrm{D^{*+}}$ mesons are consistent with $1/3$.

##  4 Results

Figure 5: The spin density matrix element ($\rho_{00}$) for prompt and non-
prompt $\mathrm{D^{*+}}$ mesons as a function of $p_{\mathrm{T}}$ in pp
collisions at $\sqrt{s}=13~{}\mathrm{TeV}$. Measurements are carried out with
respect to the helicity axis at $|y|<0.8$. Statistical and systematic
uncertainties are represented by bars and boxes, respectively. The
measurements are compared with the estimations from the QCD-based MC event
generator Pythia 8 \+ EvtGen [70, 77]. Model estimations are shown by colour
bands where the width of the band corresponds to the statistical uncertainty
in model calculations.

Figure 5 shows the $\rho_{00}$ values with respect to the helicity axis for
prompt and non-prompt $\mathrm{D^{*+}}$ mesons as a function of
$p_{\mathrm{T}}$ in pp collisions at $\sqrt{s}=13~{}\mathrm{TeV}$. The
measurements are performed in $|y|<0.8$. The $\rho_{00}$ values for prompt
$\mathrm{D^{*+}}$ mesons are consistent with $1/3$, while for non-prompt
$\mathrm{D^{*+}}$ mesons they are significantly larger than $1/3$ throughout
the studied $p_{\mathrm{T}}$ range. The values measured in the three
$p_{\mathrm{T}}$ intervals were averaged using the corrected yields of prompt
and non-prompt $\mathrm{D^{*+}}$ mesons as weights. The resulting $\rho_{00}$
values in the $p_{\mathrm{T}}$ interval between $5$ and $20~{}\mathrm{GeV}/c$
are

$\displaystyle\rho_{00}(\text{prompt }\mathrm{D^{*+}})$
$\displaystyle=0.324\pm 0.004(\text{stat.})\pm 0.008(\text{syst.}),$ (5)
$\displaystyle\rho_{00}(\text{non-prompt }\mathrm{D^{*+}})$
$\displaystyle=0.455\pm 0.022(\text{stat.})\pm 0.035(\text{syst.}).$

This finding implies no spin alignment for prompt $\mathrm{D^{*+}}$ mesons
with a simultaneous non-zero spin alignment of non-prompt $\mathrm{D^{*+}}$
mesons in high-energy pp collisions. The evidence of non-prompt
$\mathrm{D^{*+}}$-meson spin alignment can be understood as a consequence of
helicity conservation in the decay of beauty scalar mesons to vector mesons.
Measured $\rho_{00}$ values are further compared with the MC event generator
Pythia 8 \+ EvtGen [70, 77]. The EvtGen decay package, which conserves the
helicity and account for the V$-$A nature in the decay of beauty mesons, is
used in place of the default Pythia 8 decayer. In this case, model
calculations are found to be in agreement with the extracted $\rho_{00}$
values for both prompt and non-prompt $\mathrm{D^{*+}}$ mesons, while if the
EvtGen package is not used, the $\rho_{00}$ parameter is found to be
compatible with $1/3$ for both prompt and non-prompt $\mathrm{D^{*+}}$ mesons.
The measured $\rho_{00}$ for non-prompt $\mathrm{D^{*+}}$ mesons is
qualitatively consistent with the longitudinal polarisation fraction
($f_{\mathrm{L}}$) observed by the LHCb collaboration in the
$\mathrm{B^{0}}\rightarrow\mathrm{D^{*-}}\mathrm{D_{s}^{*+}}$ decay with
respect to a different quantisation axis defined by the B-meson momentum
direction [55]. The direct comparison between the magnitudes of
$f_{\mathrm{L}}$ and $\rho_{00}$ measured by the LHCb and ALICE Collaborations
is not possible due to the different quantisation axis and the different decay
channels. Therefore, dedicated model calculations are required for a
quantitative comparison of the ALICE and LHCb data.

Figure 6: Model simulation based on the MC event generator Pythia 8 \+ EvtGen
[70, 77] for the spin density matrix element ($\rho_{00}$) for
$\mathrm{D^{*+}}$ mesons with respect to the direction perpendicular to the
reaction plane as a function of $f_{\mathrm{non\text{-}prompt}}$. Model
simulations are carried out for $\mathrm{D^{*+}}$ mesons at midrapidity
($|y|<0.8$) with two input values of $v_{2}$.

After the validation of the helicity conservation in the
$\mathrm{H_{b}\to\mathrm{D^{*+}}+X}$ decays via the comparison with the
measurement presented in this letter, the predicted $\rho_{00}$ value obtained
with Pythia 8 and the EvtGen decay package can be used to estimate the
magnitude of the corresponding contribution to the spin alignment in heavy-ion
collisions. In particular, the spin alignment of non-prompt $\mathrm{D^{*+}}$
meson with respect to the helicity axis can affect the measurements of
$\mathrm{D^{*+}}$ spin alignment with respect to the reaction plane in heavy-
ion collisions. Due to the elliptic flow of the non-prompt $\mathrm{D^{*+}}$
mesons [78, 79, 80, 50, 51] in heavy-ion collisions, the helicity axis is
correlated to the direction of the angular momentum and the magnetic field,
which are perpendicular to the orientation of the reaction plane [50]. In
order to obtain a quantitative estimate of this effect for heavy-ion
collisions, a combination of Pythia 8 and the EvtGen decay package, which are
in good agreement with ALICE measurements as shown in Fig. 5, is used to model
the spin alignment of non-prompt $\mathrm{D^{*+}}$-mesons with respect to the
helicity axis. Elliptic flow modulations of non-prompt $\mathrm{D^{*+}}$
mesons are introduced in the simulation by an appropriate rotation of the
$\mathrm{D^{*+}}$ and its decay product momentum in the azimuthal plane.
Introducing $v_{2}$ modulation aligns the momentum direction of non-prompt
$\mathrm{D^{*+}}$ in the direction perpendicular to the reaction plane. Two
different calculations with $v_{2}$ values of 0.05 and 0.1 were performed.
These values were chosen to mimic measurements reported by the ALICE and ATLAS
Collaborations of leptons from beauty-hadron decays for midcentral Pb–Pb
collisions [81, 82]. Figure 6 shows the calculated $\rho_{00}$ values for
$\mathrm{D^{*+}}$ mesons as a function of $f_{\mathrm{non\text{-}prompt}}$
with respect to the direction perpendicular to the reaction plane. It is found
that in the presence of $v_{2}$, helicity conservation in the beauty-meson
decay leads to a value of $\rho_{00}$ less than $1/3$. The opposite direction
with respect to $1/3$ compared to the measurement presented in this letter is
due to the different quantisation axis. In the recombination hadronisation
scenario of polarised quarks, the expected value of $\rho_{00}$ for both the
magnetic field and angular momentum is also less than $1/3$ [42]. Therefore,
in the presence of $v_{2}$ the spin alignment of non-prompt $\mathrm{D^{*+}}$
mesons due to the helicity conservation in beauty-meson decays mimics the
signal of global spin alignment, expected due to the presence of large angular
momentum and magnetic field in midcentral heavy-ion collisions. In the
presence of additional non-flow correlations (i.e. correlations not induced by
the collective expansion but rather by decays and jet contributions) [83],
this effect can get further enhanced. A sizeable fraction of non-prompt
$\mathrm{D^{*+}}$ mesons, e.g. $f_{\mathrm{non\text{-}prompt}}=0.2$ [72, 74]
can give on the order of 5% deviation from the $\rho_{00}=1/3$. This
contribution is not negligible considering the recent $\mathrm{J}/\uppsi$
polarisation measurement in Pb–Pb collisions by the ALICE Collaboration where
a deviation up to 10% from the $\rho_{00}=1/3$ was observed [52]. Thanks to
the higher luminosity and improved spatial resolution of the upgraded ITS
installed in ALICE for the LHC Run 3 [84, 85], future measurements with non-
prompt charm hadrons of the spin alignment in pp collisions and azimuthal
anisotropy in heavy-ion collisions will provide a more accurate baseline for
understanding effects induced by the initial angular momentum and magnetic
field in non-central heavy-ion collisions.

##  5 Summary

The first measurements for prompt and non-prompt $\mathrm{D^{*+}}$ meson spin
alignment with respect to the helicity axis at midrapidity in pp collisions at
$\sqrt{s}=13~{}\mathrm{TeV}$ are presented. No spin alignment is observed for
the prompt $\mathrm{D^{*+}}$ mesons in pp collisions, with measured
$\rho_{00}$ values being consistent with $1/3$. This observation is consistent
with previous measurements in $\mathrm{e^{+}e^{-}}$ collisions far from the
$\mathrm{Z}^{0}$ resonance and suggests that charm quarks are either produced
unpolarised or their polarisation is washed out during the hadronisation
process. The measured value for the non-prompt $\mathrm{D^{*+}}$-meson spin
density element is $\rho_{00}=0.455\pm 0.022(\text{stat.})\pm
0.035(\text{syst.})$ in the $5<p_{\mathrm{T}}<20~{}\mathrm{GeV}/c$ interval.
The measured value is compatible with the prediction from Pythia 8 \+ EvtGen
simulations and is interpreted as an evidence of spin alignment of non-prompt
$\mathrm{D^{*+}}$ mesons with respect to the helicity axis due to the helicity
conservation in beauty-meson decays. Based on the measurements and MC
simulations, it was estimated that the spin alignment of the non-prompt
$\mathrm{D^{*+}}$ mesons in the presence of elliptic flow can mimic the signal
of global spin alignment in heavy-ion collisions. The new data presented in
this letter provide an important baseline for future spin alignment
measurements of $\mathrm{D^{*+}}$ vector mesons in heavy-ion collisions, which
probe the initial angular momentum and magnetic field.

## 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: A. I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation (ANSL), State Committee of Science and World Federation of Scientists (WFS), Armenia; Austrian Academy of Sciences, Austrian Science Fund (FWF): [M 2467-N36] and Nationalstiftung für Forschung, Technologie und Entwicklung, Austria; Ministry of Communications and High Technologies, National Nuclear Research Center, Azerbaijan; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Financiadora de Estudos e Projetos (Finep), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Universidade Federal do Rio Grande do Sul (UFRGS), Brazil; Bulgarian Ministry of Education and Science, within the National Roadmap for Research Infrastructures 2020-2027 (object CERN), Bulgaria; Ministry of Education of China (MOEC) , Ministry of Science & Technology of China (MSTC) and National Natural Science Foundation of China (NSFC), China; Ministry of Science and Education and Croatian Science Foundation, Croatia; Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Cubaenergía, Cuba; Ministry of Education, Youth and Sports of the Czech Republic, Czech Republic; The Danish Council for Independent Research | Natural Sciences, the VILLUM FONDEN and Danish National Research Foundation (DNRF), Denmark; Helsinki Institute of Physics (HIP), Finland; Commissariat à l’Energie Atomique (CEA) and Institut National de Physique Nucléaire et de Physique des Particules (IN2P3) and Centre National de la Recherche Scientifique (CNRS), France; Bundesministerium für Bildung und Forschung (BMBF) and GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany; General Secretariat for Research and Technology, Ministry of Education, Research and Religions, Greece; National Research, Development and Innovation Office, Hungary; Department of Atomic Energy Government of India (DAE), Department of Science and Technology, Government of India (DST), University Grants Commission, Government of India (UGC) and Council of Scientific and Industrial Research (CSIR), India; National Research and Innovation Agency - BRIN, Indonesia; Istituto Nazionale di Fisica Nucleare (INFN), Italy; Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and Japan Society for the Promotion of Science (JSPS) KAKENHI, Japan; Consejo Nacional de Ciencia (CONACYT) y Tecnología, through Fondo de Cooperación Internacional en Ciencia y Tecnología (FONCICYT) and Dirección General de Asuntos del Personal Academico (DGAPA), Mexico; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), Netherlands; The Research Council of Norway, Norway; Commission on Science and Technology for Sustainable Development in the South (COMSATS), Pakistan; Pontificia Universidad Católica del Perú, Peru; Ministry of Education and Science, National Science Centre and WUT ID-UB, Poland; Korea Institute of Science and Technology Information and National Research Foundation of Korea (NRF), Republic of Korea; Ministry of Education and Scientific Research, Institute of Atomic Physics, Ministry of Research and Innovation and Institute of Atomic Physics and University Politehnica of Bucharest, Romania; Ministry of Education, Science, Research and Sport of the Slovak Republic, Slovakia; National Research Foundation of South Africa, South Africa; Swedish Research Council (VR) and Knut & Alice Wallenberg Foundation (KAW), Sweden; European Organization for Nuclear Research, Switzerland; Suranaree University of Technology (SUT), National Science and Technology Development Agency (NSTDA) and National Science, Research and Innovation Fund (NSRF via PMU-B B05F650021), Thailand; Turkish Energy, Nuclear and Mineral Research Agency (TENMAK), Turkey; National Academy of Sciences of Ukraine, Ukraine; Science and Technology Facilities Council (STFC), United Kingdom; National Science Foundation of the United States of America (NSF) and United States Department of Energy, Office of Nuclear Physics (DOE NP), United States of America. In addition, individual groups or members have received support from: European Research Council, Strong 2020 - Horizon 2020, Marie Skłodowska Curie (grant nos. 950692, 824093, 896850), European Union; Academy of Finland (Center of Excellence in Quark Matter) (grant nos. 346327, 346328), Finland; Programa de Apoyos para la Superación del Personal Académico, UNAM, Mexico.

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##  Appendix A The ALICE Collaboration

S. Acharya 124, D. Adamová 85, A. Adler69, G. Aglieri Rinella 32, M. Agnello
29, N. Agrawal 50, Z. Ahammed 132, S. Ahmad 15, S.U. Ahn 70, I. Ahuja 37, A.
Akindinov 140, M. Al-Turany 96, D. Aleksandrov 140, B. Alessandro 55, H.M.
Alfanda 6, R. Alfaro Molina 66, B. Ali 15, A. Alici 25, N. Alizadehvandchali
113, A. Alkin 32, J. Alme 20, G. Alocco 51, T. Alt 63, I. Altsybeev 140, M.N.
Anaam 6, C. Andrei 45, A. Andronic 135, V. Anguelov 93, F. Antinori 53, P.
Antonioli 50, N. Apadula 73, L. Aphecetche 102, H. Appelshäuser 63, C. Arata
72, S. Arcelli 25, M. Aresti 51, R. Arnaldi 55, J.G.M.C.A. Arneiro 109, I.C.
Arsene 19, M. Arslandok 137, A. Augustinus 32, R. Averbeck 96, M.D. Azmi 15,
A. Badalà 52, J. Bae 103, Y.W. Baek 40, X. Bai 117, R. Bailhache 63, Y.
Bailung 47, A. Balbino 29, A. Baldisseri 127, B. Balis 2, D. Banerjee 4, Z.
Banoo 90, R. Barbera 26, F. Barile 31, L. Barioglio 94, M. Barlou77, G.G.
Barnaföldi 136, L.S. Barnby 84, V. Barret 124, L. Barreto 109, C. Bartels 116,
K. Barth 32, E. Bartsch 63, N. Bastid 124, S. Basu 74, G. Batigne 102, D.
Battistini 94, B. Batyunya 141, D. Bauri46, J.L. Bazo Alba 100, I.G. Bearden
82, C. Beattie 137, P. Becht 96, D. Behera 47, I. Belikov 126, A.D.C. Bell
Hechavarria 135, F. Bellini 25, R. Bellwied 113, S. Belokurova 140, V. Belyaev
140, G. Bencedi 136, S. Beole 24, A. Bercuci 45, Y. Berdnikov 140, A.
Berdnikova 93, L. Bergmann 93, M.G. Besoiu 62, L. Betev 32, P.P. Bhaduri 132,
A. Bhasin 90, M.A. Bhat 4, B. Bhattacharjee 41, L. Bianchi 24, N. Bianchi 48,
J. Bielčík 35, J. Bielčíková 85, J. Biernat 106, A.P. Bigot 126, A. Bilandzic
94, G. Biro 136, S. Biswas 4, N. Bize 102, J.T. Blair 107, D. Blau 140, M.B.
Blidaru 96, N. Bluhme38, C. Blume 63, G. Boca 21,54, F. Bock 86, T. Bodova 20,
A. Bogdanov140, S. Boi 22, J. Bok 57, L. Boldizsár 136, M. Bombara 37, P.M.
Bond 32, G. Bonomi 131,54, H. Borel 127, A. Borissov 140, A.G. Borquez Carcamo
93, H. Bossi 137, E. Botta 24, Y.E.M. Bouziani 63, L. Bratrud 63, P. Braun-
Munzinger 96, M. Bregant 109, M. Broz 35, G.E. Bruno 95,31, M.D. Buckland 23,
D. Budnikov 140, H. Buesching 63, S. Bufalino 29, O. Bugnon102, P. Buhler 101,
Z. Buthelezi 67,120, S.A. Bysiak106, M. Cai 6, H. Caines 137, A. Caliva 96, E.
Calvo Villar 100, J.M.M. Camacho 108, P. Camerini 23, F.D.M. Canedo 109, M.
Carabas 123, A.A. Carballo 32, F. Carnesecchi 32, R. Caron 125, L.A.D.
Carvalho 109, J. Castillo Castellanos 127, F. Catalano 24, C. Ceballos Sanchez
141, I. Chakaberia 73, P. Chakraborty 46, S. Chandra 132, S. Chapeland 32, M.
Chartier 116, S. Chattopadhyay 132, S. Chattopadhyay 98, T.G. Chavez 44, T.
Cheng 96,6, C. Cheshkov 125, B. Cheynis 125, V. Chibante Barroso 32, D.D.
Chinellato 110, E.S. Chizzali II,94, J. Cho 57, S. Cho 57, P. Chochula 32, P.
Christakoglou 83, C.H. Christensen 82, P. Christiansen 74, T. Chujo 122, M.
Ciacco 29, C. Cicalo 51, F. Cindolo 50, M.R. Ciupek96, G. ClaiIII,50, F.
Colamaria 49, J.S. Colburn99, D. Colella 95,31, M. Colocci 32, M. Concas
IV,55, G. Conesa Balbastre 72, Z. Conesa del Valle 128, G. Contin 23, J.G.
Contreras 35, M.L. Coquet 127, T.M. CormierI,86, P. Cortese 130,55, M.R.
Cosentino 111, F. Costa 32, S. Costanza 21,54, C. Cot 128, J. Crkovská 93, P.
Crochet 124, R. Cruz-Torres 73, E. Cuautle64, P. Cui 6, A. Dainese 53, M.C.
Danisch 93, A. Danu 62, P. Das 79, P. Das 4, S. Das 4, A.R. Dash 135, S. Dash
46, R.M.H. David44, A. De Caro 28, G. de Cataldo 49, J. de Cuveland38, A. De
Falco 22, D. De Gruttola 28, N. De Marco 55, C. De Martin 23, S. De Pasquale
28, S. Deb 47, R.J. Debski 2, K.R. Deja133, R. Del Grande 94, L. Dello Stritto
28, W. Deng 6, P. Dhankher 18, D. Di Bari 31, A. Di Mauro 32, R.A. Diaz 141,7,
T. Dietel 112, Y. Ding 125,6, R. Divià 32, D.U. Dixit 18, Ø. Djuvsland20, U.
Dmitrieva 140, A. Dobrin 62, B. Dönigus 63, J.M. Dubinski 133, A. Dubla 96, S.
Dudi 89, P. Dupieux 124, M. Durkac105, N. Dzalaiova12, T.M. Eder 135, R.J.
Ehlers 86, V.N. Eikeland20, F. Eisenhut 63, D. Elia 49, B. Erazmus 102, F.
Ercolessi 25, F. Erhardt 88, M.R. Ersdal20, B. Espagnon 128, G. Eulisse 32, D.
Evans 99, S. Evdokimov 140, L. Fabbietti 94, M. Faggin 27, J. Faivre 72, F.
Fan 6, W. Fan 73, A. Fantoni 48, M. Fasel 86, P. Fecchio29, A. Feliciello 55,
G. Feofilov 140, A. Fernández Téllez 44, L. Ferrandi 109, M.B. Ferrer 32, A.
Ferrero 127, C. Ferrero 55, A. Ferretti 24, V.J.G. Feuillard 93, V. Filova 35,
D. Finogeev 140, F.M. Fionda 51, F. Flor 113, A.N. Flores 107, S. Foertsch 67,
I. Fokin 93, S. Fokin 140, E. Fragiacomo 56, E. Frajna 136, U. Fuchs 32, N.
Funicello 28, C. Furget 72, A. Furs 140, T. Fusayasu 97, J.J. Gaardhøje 82, M.
Gagliardi 24, A.M. Gago 100, C.D. Galvan 108, D.R. Gangadharan 113, P. Ganoti
77, C. Garabatos 96, J.R.A. Garcia 44, E. Garcia-Solis 9, K. Garg 102, C.
Gargiulo 32, K. Garner135, P. Gasik 96, A. Gautam 115, M.B. Gay Ducati 65, M.
Germain 102, A. Ghimouz122, C. Ghosh132, M. Giacalone 50,25, P. Giubellino
96,55, P. Giubilato 27, A.M.C. Glaenzer 127, P. Glässel 93, E. Glimos 119,
D.J.Q. Goh75, V. Gonzalez 134, L.H. González-Trueba 66, M. Gorgon 2, S.
Gotovac33, V. Grabski 66, L.K. Graczykowski 133, E. Grecka 85, A. Grelli 58,
C. Grigoras 32, V. Grigoriev 140, S. Grigoryan 141,1, F. Grosa 32, J.F.
Grosse-Oetringhaus 32, R. Grosso 96, D. Grund 35, G.G. Guardiano 110, R.
Guernane 72, M. Guilbaud 102, K. Gulbrandsen 82, T. Gündem 63, T. Gunji 121,
W. Guo 6, A. Gupta 90, R. Gupta 90, S.P. Guzman 44, L. Gyulai 136, M.K.
Habib96, C. Hadjidakis 128, F.U. Haider 90, H. Hamagaki 75, A. Hamdi 73, M.
Hamid6, Y. Han 138, R. Hannigan 107, M.R. Haque 133, J.W. Harris 137, A.
Harton 9, H. Hassan 86, D. Hatzifotiadou 50, P. Hauer 42, L.B. Havener 137,
S.T. Heckel 94, E. Hellbär 96, H. Helstrup 34, M. Hemmer 63, T. Herman 35, G.
Herrera Corral 8, F. Herrmann135, S. Herrmann 125, K.F. Hetland 34, B. Heybeck
63, H. Hillemanns 32, C. Hills 116, B. Hippolyte 126, F.W. Hoffmann 69, B.
Hofman 58, B. Hohlweger 83, G.H. Hong 138, M. Horst 94, A. Horzyk 2, Y. Hou 6,
P. Hristov 32, C. Hughes 119, P. Huhn63, L.M. Huhta 114, C.V. Hulse 128, T.J.
Humanic 87, A. Hutson 113, D. Hutter 38, J.P. Iddon 116, R. Ilkaev140, H.
Ilyas 13, M. Inaba 122, G.M. Innocenti 32, M. Ippolitov 140, A. Isakov 85, T.
Isidori 115, M.S. Islam 98, M. Ivanov 96, M. Ivanov12, V. Ivanov 140, M.
Jablonski 2, B. Jacak 73, N. Jacazio 32, P.M. Jacobs 73, S. Jadlovska105, J.
Jadlovsky105, S. Jaelani 81, L. Jaffe38, C. Jahnke 110, M.J. Jakubowska 133,
M.A. Janik 133, T. Janson69, M. Jercic88, S. Jia 10, A.A.P. Jimenez 64, F.
Jonas 86, J.M. Jowett 32,96, J. Jung 63, M. Jung 63, A. Junique 32, A. Jusko
99, M.J. Kabus 32,133, J. Kaewjai104, P. Kalinak 59, A.S. Kalteyer 96, A.
Kalweit 32, V. Kaplin 140, A. Karasu Uysal 71, D. Karatovic 88, O. Karavichev
140, T. Karavicheva 140, P. Karczmarczyk 133, E. Karpechev 140, U. Kebschull
69, R. Keidel 139, D.L.D. Keijdener58, M. Keil 32, B. Ketzer 42, A.M. Khan 6,
S. Khan 15, A. Khanzadeev 140, Y. Kharlov 140, A. Khatun 115,15, A. Khuntia
106, M.B. Kidson112, B. Kileng 34, B. Kim 16, C. Kim 16, D.J. Kim 114, E.J.
Kim 68, J. Kim 138, J.S. Kim 40, J. Kim 68, M. Kim 18,93, S. Kim 17, T. Kim
138, K. Kimura 91, S. Kirsch 63, I. Kisel 38, S. Kiselev 140, A. Kisiel 133,
J.P. Kitowski 2, J.L. Klay 5, J. Klein 32, S. Klein 73, C. Klein-Bösing 135,
M. Kleiner 63, T. Klemenz 94, A. Kluge 32, A.G. Knospe 113, C. Kobdaj 104, T.
Kollegger96, A. Kondratyev 141, N. Kondratyeva 140, E. Kondratyuk 140, J.
Konig 63, S.A. Konigstorfer 94, P.J. Konopka 32, G. Kornakov 133, M. Korwieser
94, S.D. Koryciak 2, A. Kotliarov 85, V. Kovalenko 140, M. Kowalski 106, V.
Kozhuharov 36, I. Králik 59, A. Kravčáková 37, L. Kreis96, M. Krivda 99,59, F.
Krizek 85, K. Krizkova Gajdosova 35, M. Kroesen 93, M. Krüger 63, D.M. Krupova
35, E. Kryshen 140, V. Kučera 32, C. Kuhn 126, P.G. Kuijer 83, T. Kumaoka122,
D. Kumar132, L. Kumar 89, N. Kumar89, S. Kumar 31, S. Kundu 32, P. Kurashvili
78, A. Kurepin 140, A.B. Kurepin 140, A. Kuryakin 140, S. Kushpil 85, J.
Kvapil 99, M.J. Kweon 57, J.Y. Kwon 57, Y. Kwon 138, S.L. La Pointe 38, P. La
Rocca 26, Y.S. Lai73, A. Lakrathok104, M. Lamanna 32, R. Langoy 118, P.
Larionov 32, E. Laudi 32, L. Lautner 32,94, R. Lavicka 101, T. Lazareva 140,
R. Lea 131,54, H. Lee 103, G. Legras 135, J. Lehrbach 38, R.C. Lemmon 84, I.
León Monzón 108, M.M. Lesch 94, E.D. Lesser 18, M. Lettrich94, P. Lévai 136,
X. Li10, X.L. Li6, J. Lien 118, R. Lietava 99, I. Likmeta 113, B. Lim 24,16,
S.H. Lim 16, V. Lindenstruth 38, A. Lindner45, C. Lippmann 96, A. Liu 18, D.H.
Liu 6, J. Liu 116, I.M. Lofnes 20, C. Loizides 86, S. Lokos 106, J. Lomker 58,
P. Loncar 33, J.A. Lopez 93, X. Lopez 124, E. López Torres 7, P. Lu 96,117,
J.R. Luhder 135, M. Lunardon 27, G. Luparello 56, Y.G. Ma 39, A. Maevskaya140,
M. Mager 32, T. Mahmoud42, A. Maire 126, M.V. Makariev 36, M. Malaev 140, G.
Malfattore 25, N.M. Malik 90, Q.W. Malik19, S.K. Malik 90, L. Malinina
VII,141, D. Mal’Kevich 140, D. Mallick 79, N. Mallick 47, G. Mandaglio 30,52,
S.K. Mandal 78, V. Manko 140, F. Manso 124, V. Manzari 49, Y. Mao 6, G.V.
Margagliotti 23, A. Margotti 50, A. Marín 96, C. Markert 107, P. Martinengo
32, J.L. Martinez113, M.I. Martínez 44, G. Martínez García 102, S. Masciocchi
96, M. Masera 24, A. Masoni 51, L. Massacrier 128, A. Mastroserio 129,49, O.
Matonoha 74, P.F.T. Matuoka109, A. Matyja 106, C. Mayer 106, A.L. Mazuecos 32,
F. Mazzaschi 24, M. Mazzilli 32, J.E. Mdhluli 120, A.F. Mechler63, Y. Melikyan
43,140, A. Menchaca-Rocha 66, E. Meninno 101,28, A.S. Menon 113, M. Meres 12,
S. Mhlanga112,67, Y. Miake122, L. Micheletti 55, L.C. Migliorin125, D.L.
Mihaylov 94, K. Mikhaylov 141,140, A.N. Mishra 136, D. Miśkowiec 96, A. Modak
4, A.P. Mohanty 58, B. Mohanty79, M. Mohisin Khan V,15, M.A. Molander 43, Z.
Moravcova 82, C. Mordasini 94, D.A. Moreira De Godoy 135, I. Morozov 140, A.
Morsch 32, T. Mrnjavac 32, V. Muccifora 48, S. Muhuri 132, J.D. Mulligan 73,
A. Mulliri22, M.G. Munhoz 109, R.H. Munzer 63, H. Murakami 121, S. Murray 112,
L. Musa 32, J. Musinsky 59, J.W. Myrcha 133, B. Naik 120, A.I. Nambrath 18,
B.K. Nandi 46, R. Nania 50, E. Nappi 49, A.F. Nassirpour 74, A. Nath 93, C.
Nattrass 119, M.N. Naydenov 36, A. Neagu19, A. Negru123, L. Nellen 64, S.V.
Nesbo34, G. Neskovic 38, D. Nesterov 140, B.S. Nielsen 82, E.G. Nielsen 82, S.
Nikolaev 140, S. Nikulin 140, V. Nikulin 140, F. Noferini 50, S. Noh 11, P.
Nomokonov 141, J. Norman 116, N. Novitzky 122, P. Nowakowski 133, A. Nyanin
140, J. Nystrand 20, M. Ogino 75, A. Ohlson 74, V.A. Okorokov 140, J. Oleniacz
133, A.C. Oliveira Da Silva 119, M.H. Oliver 137, A. Onnerstad 114, C.
Oppedisano 55, A. Ortiz Velasquez 64, J. Otwinowski 106, M. Oya91, K. Oyama
75, Y. Pachmayer 93, S. Padhan 46, D. Pagano 131,54, G. Paić 64, A. Palasciano
49, S. Panebianco 127, H. Park 122, H. Park 103, J. Park 57, J.E. Parkkila 32,
R.N. Patra90, B. Paul 22, H. Pei 6, T. Peitzmann 58, X. Peng 6, M. Pennisi 24,
L.G. Pereira 65, D. Peresunko 140, G.M. Perez 7, S. Perrin 127, Y. Pestov140,
V. Petráček 35, V. Petrov 140, M. Petrovici 45, R.P. Pezzi 102,65, S. Piano
56, M. Pikna 12, P. Pillot 102, O. Pinazza 50,32, L. Pinsky113, C. Pinto 94,
S. Pisano 48, M. Płoskoń 73, M. Planinic88, F. Pliquett63, M.G. Poghosyan 86,
B. Polichtchouk 140, S. Politano 29, N. Poljak 88, A. Pop 45, S. Porteboeuf-
Houssais 124, V. Pozdniakov 141, K.K. Pradhan 47, S.K. Prasad 4, S. Prasad 47,
R. Preghenella 50, F. Prino 55, C.A. Pruneau 134, I. Pshenichnov 140, M.
Puccio 32, S. Pucillo 24, Z. Pugelova105, S. Qiu 83, L. Quaglia 24, R.E.
Quishpe113, S. Ragoni 14,99, A. Rakotozafindrabe 127, L. Ramello 130,55, F.
Rami 126, S.A.R. Ramirez 44, T.A. Rancien72, M. Rasa 26, S.S. Räsänen 43, R.
Rath 50, M.P. Rauch 20, I. Ravasenga 83, K.F. Read 86,119, C. Reckziegel 111,
A.R. Redelbach 38, K. Redlich VI,78, C.A. Reetz 96, A. Rehman20, F. Reidt 32,
H.A. Reme-Ness 34, Z. Rescakova37, K. Reygers 93, A. Riabov 140, V. Riabov
140, R. Ricci 28, M. Richter 19, A.A. Riedel 94, W. Riegler 32, C. Ristea 62,
M. Rodríguez Cahuantzi 44, K. Røed 19, R. Rogalev 140, E. Rogochaya 141, T.S.
Rogoschinski 63, D. Rohr 32, D. Röhrich 20, P.F. Rojas44, S. Rojas Torres 35,
P.S. Rokita 133, G. Romanenko 141, F. Ronchetti 48, A. Rosano 30,52, E.D.
Rosas64, K. Roslon 133, A. Rossi 53, A. Roy 47, S. Roy 46, N. Rubini 25, D.
Ruggiano 133, R. Rui 23, B. Rumyantsev141, P.G. Russek 2, R. Russo 83, A.
Rustamov 80, E. Ryabinkin 140, Y. Ryabov 140, A. Rybicki 106, H. Rytkonen 114,
W. Rzesa 133, O.A.M. Saarimaki 43, R. Sadek 102, S. Sadhu 31, S. Sadovsky 140,
J. Saetre 20, K. Šafařík 35, S.K. Saha 4, S. Saha 79, B. Sahoo 46, R. Sahoo
47, S. Sahoo60, D. Sahu 47, P.K. Sahu 60, J. Saini 132, K. Sajdakova37, S.
Sakai 122, M.P. Salvan 96, S. Sambyal 90, I. Sanna 32,94, T.B. Saramela109, D.
Sarkar 134, N. Sarkar132, P. Sarma 41, V. Sarritzu 22, V.M. Sarti 94, M.H.P.
Sas 137, J. Schambach 86, H.S. Scheid 63, C. Schiaua 45, R. Schicker 93, A.
Schmah93, C. Schmidt 96, H.R. Schmidt92, M.O. Schmidt 32, M. Schmidt92, N.V.
Schmidt 86, A.R. Schmier 119, R. Schotter 126, A. Schröter 38, J. Schukraft
32, K. Schwarz96, K. Schweda 96, G. Scioli 25, E. Scomparin 55, J.E. Seger 14,
Y. Sekiguchi121, D. Sekihata 121, I. Selyuzhenkov 96,140, S. Senyukov 126,
J.J. Seo 57, D. Serebryakov 140, L. Šerkšnytė 94, A. Sevcenco 62, T.J. Shaba
67, A. Shabetai 102, R. Shahoyan32, A. Shangaraev 140, A. Sharma89, B. Sharma
90, D. Sharma 46, H. Sharma 106, M. Sharma 90, S. Sharma 75, S. Sharma 90, U.
Sharma 90, A. Shatat 128, O. Sheibani113, K. Shigaki 91, M. Shimomura76, J.
Shin11, S. Shirinkin 140, Q. Shou 39, Y. Sibiriak 140, S. Siddhanta 51, T.
Siemiarczuk 78, T.F. Silva 109, D. Silvermyr 74, T. Simantathammakul104, R.
Simeonov 36, B. Singh90, B. Singh 94, R. Singh 79, R. Singh 90, R. Singh 47,
S. Singh 15, V.K. Singh 132, V. Singhal 132, T. Sinha 98, B. Sitar 12, M.
Sitta 130,55, T.B. Skaali19, G. Skorodumovs 93, M. Slupecki 43, N. Smirnov
137, R.J.M. Snellings 58, E.H. Solheim 19, J. Song 113, A. Songmoolnak104, F.
Soramel 27, R. Spijkers 83, I. Sputowska 106, J. Staa 74, J. Stachel 93, I.
Stan 62, P.J. Steffanic 119, S.F. Stiefelmaier 93, D. Stocco 102, I. Storehaug
19, P. Stratmann 135, S. Strazzi 25, C.P. Stylianidis83, A.A.P. Suaide 109, C.
Suire 128, M. Sukhanov 140, M. Suljic 32, R. Sultanov 140, V. Sumberia 90, S.
Sumowidagdo 81, S. Swain60, I. Szarka 12, M. Szymkowski 133, S.F. Taghavi 94,
G. Taillepied 96, J. Takahashi 110, G.J. Tambave 20, S. Tang 124,6, Z. Tang
117, J.D. Tapia Takaki 115, N. Tapus123, L.A. Tarasovicova 135, M.G. Tarzila
45, G.F. Tassielli 31, A. Tauro 32, G. Tejeda Muñoz 44, A. Telesca 32, L.
Terlizzi 24, C. Terrevoli 113, G. Tersimonov3, S. Thakur 4, D. Thomas 107, A.
Tikhonov 140, A.R. Timmins 113, M. Tkacik105, T. Tkacik 105, A. Toia 63, R.
Tokumoto91, N. Topilskaya 140, M. Toppi 48, F. Torales-Acosta18, T. Tork 128,
A.G. Torres Ramos 31, A. Trifiró 30,52, A.S. Triolo 30,52, S. Tripathy 50, T.
Tripathy 46, S. Trogolo 32, V. Trubnikov 3, W.H. Trzaska 114, T.P. Trzcinski
133, A. Tumkin 140, R. Turrisi 53, T.S. Tveter 19, K. Ullaland 20, B. Ulukutlu
94, A. Uras 125, M. Urioni 54,131, G.L. Usai 22, M. Vala37, N. Valle 21,
L.V.R. van Doremalen58, M. van Leeuwen 83, C.A. van Veen 93, R.J.G. van
Weelden 83, P. Vande Vyvre 32, D. Varga 136, Z. Varga 136, M. Vasileiou 77, A.
Vasiliev 140, O. Vázquez Doce 48, O. Vazquez Rueda 113,74, V. Vechernin 140,
E. Vercellin 24, S. Vergara Limón44, L. Vermunt 96, R. Vértesi 136, M. Verweij
58, L. Vickovic33, Z. Vilakazi120, O. Villalobos Baillie 99, A. Villani 23, G.
Vino 49, A. Vinogradov 140, T. Virgili 28, V. Vislavicius74, A. Vodopyanov
141, B. Volkel 32, M.A. Völkl 93, K. Voloshin140, S.A. Voloshin 134, G. Volpe
31, B. von Haller 32, I. Vorobyev 94, N. Vozniuk 140, J. Vrláková 37, C. Wang
39, D. Wang39, Y. Wang 39, A. Wegrzynek 32, F.T. Weiglhofer38, S.C. Wenzel 32,
J.P. Wessels 135, S.L. Weyhmiller 137, J. Wiechula 63, J. Wikne 19, G. Wilk
78, J. Wilkinson 96, G.A. Willems 135, B. Windelband 93, M. Winn 127, J.R.
Wright 107, W. Wu39, Y. Wu 117, R. Xu 6, A. Yadav 42, A.K. Yadav 132, S.
Yalcin 71, Y. Yamaguchi 91, S. Yang20, S. Yano 91, Z. Yin 6, I.-K. Yoo 16,
J.H. Yoon 57, S. Yuan20, A. Yuncu 93, V. Zaccolo 23, C. Zampolli 32, F. Zanone
93, N. Zardoshti 32,99, A. Zarochentsev 140, P. Závada 61, N. Zaviyalov140, M.
Zhalov 140, B. Zhang 6, L. Zhang 39, S. Zhang 39, X. Zhang 6, Y. Zhang117, Z.
Zhang 6, M. Zhao 10, V. Zherebchevskii 140, Y. Zhi10, D. Zhou 6, Y. Zhou 82,
J. Zhu 96,6, Y. Zhu6, S.C. Zugravel 55, N. Zurlo 131,54

## Affiliation Notes

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

## Collaboration Institutes

1 A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute)
Foundation, Yerevan, Armenia
2 AGH University of Krakow, Cracow, Poland
3 Bogolyubov Institute for Theoretical Physics, National Academy of Sciences
of Ukraine, Kiev, Ukraine
4 Bose Institute, Department of Physics and Centre for Astroparticle Physics
and Space Science (CAPSS), Kolkata, India
5 California Polytechnic State University, San Luis Obispo, California, United
States
6 Central China Normal University, Wuhan, China
7 Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana,
Cuba
8 Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and
Mérida, Mexico
9 Chicago State University, Chicago, Illinois, United States
10 China Institute of Atomic Energy, Beijing, China
11 Chungbuk National University, Cheongju, Republic of Korea
12 Comenius University Bratislava, Faculty of Mathematics, Physics and
Informatics, Bratislava, Slovak Republic
13 COMSATS University Islamabad, Islamabad, Pakistan
14 Creighton University, Omaha, Nebraska, United States
15 Department of Physics, Aligarh Muslim University, Aligarh, India
16 Department of Physics, Pusan National University, Pusan, Republic of Korea
17 Department of Physics, Sejong University, Seoul, Republic of Korea
18 Department of Physics, University of California, Berkeley, California,
United States
19 Department of Physics, University of Oslo, Oslo, Norway
20 Department of Physics and Technology, University of Bergen, Bergen, Norway
21 Dipartimento di Fisica, Università di Pavia, Pavia, Italy
22 Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
23 Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
24 Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy
25 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Bologna, Italy
26 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Catania, Italy
27 Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN,
Padova, Italy
28 Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo
Collegato INFN, Salerno, Italy
29 Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy
30 Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy
31 Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari,
Italy
32 European Organization for Nuclear Research (CERN), Geneva, Switzerland
33 Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, Split, Croatia
34 Faculty of Engineering and Science, Western Norway University of Applied
Sciences, Bergen, Norway
35 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical
University in Prague, Prague, Czech Republic
36 Faculty of Physics, Sofia University, Sofia, Bulgaria
37 Faculty of Science, P.J. Šafárik University, Košice, Slovak Republic
38 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-
Universität Frankfurt, Frankfurt, Germany
39 Fudan University, Shanghai, China
40 Gangneung-Wonju National University, Gangneung, Republic of Korea
41 Gauhati University, Department of Physics, Guwahati, India
42 Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-
Wilhelms-Universität Bonn, Bonn, Germany
43 Helsinki Institute of Physics (HIP), Helsinki, Finland
44 High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico
45 Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest, Romania
46 Indian Institute of Technology Bombay (IIT), Mumbai, India
47 Indian Institute of Technology Indore, Indore, India
48 INFN, Laboratori Nazionali di Frascati, Frascati, Italy
49 INFN, Sezione di Bari, Bari, Italy
50 INFN, Sezione di Bologna, Bologna, Italy
51 INFN, Sezione di Cagliari, Cagliari, Italy
52 INFN, Sezione di Catania, Catania, Italy
53 INFN, Sezione di Padova, Padova, Italy
54 INFN, Sezione di Pavia, Pavia, Italy
55 INFN, Sezione di Torino, Turin, Italy
56 INFN, Sezione di Trieste, Trieste, Italy
57 Inha University, Incheon, Republic of Korea
58 Institute for Gravitational and Subatomic Physics (GRASP), Utrecht
University/Nikhef, Utrecht, Netherlands
59 Institute of Experimental Physics, Slovak Academy of Sciences, Košice,
Slovak Republic
60 Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India
61 Institute of Physics of the Czech Academy of Sciences, Prague, Czech
Republic
62 Institute of Space Science (ISS), Bucharest, Romania
63 Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt,
Frankfurt, Germany
64 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México,
Mexico City, Mexico
65 Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS),
Porto Alegre, Brazil
66 Instituto de Física, Universidad Nacional Autónoma de México, Mexico City,
Mexico
67 iThemba LABS, National Research Foundation, Somerset West, South Africa
68 Jeonbuk National University, Jeonju, Republic of Korea
69 Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik,
Fachbereich Informatik und Mathematik, Frankfurt, Germany
70 Korea Institute of Science and Technology Information, Daejeon, Republic of
Korea
71 KTO Karatay University, Konya, Turkey
72 Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-
Alpes, CNRS-IN2P3, Grenoble, France
73 Lawrence Berkeley National Laboratory, Berkeley, California, United States
74 Lund University Department of Physics, Division of Particle Physics, Lund,
Sweden
75 Nagasaki Institute of Applied Science, Nagasaki, Japan
76 Nara Women’s University (NWU), Nara, Japan
77 National and Kapodistrian University of Athens, School of Science,
Department of Physics , Athens, Greece
78 National Centre for Nuclear Research, Warsaw, Poland
79 National Institute of Science Education and Research, Homi Bhabha National
Institute, Jatni, India
80 National Nuclear Research Center, Baku, Azerbaijan
81 National Research and Innovation Agency - BRIN, Jakarta, Indonesia
82 Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
83 Nikhef, National institute for subatomic physics, Amsterdam, Netherlands
84 Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, United Kingdom
85 Nuclear Physics Institute of the Czech Academy of Sciences, Husinec-Řež,
Czech Republic
86 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
87 Ohio State University, Columbus, Ohio, United States
88 Physics department, Faculty of science, University of Zagreb, Zagreb,
Croatia
89 Physics Department, Panjab University, Chandigarh, India
90 Physics Department, University of Jammu, Jammu, India
91 Physics Program and International Institute for Sustainability with Knotted
Chiral Meta Matter (SKCM2), Hiroshima University, Hiroshima, Japan
92 Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen,
Germany
93 Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
94 Physik Department, Technische Universität München, Munich, Germany
95 Politecnico di Bari and Sezione INFN, Bari, Italy
96 Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum
für Schwerionenforschung GmbH, Darmstadt, Germany
97 Saga University, Saga, Japan
98 Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata,
India
99 School of Physics and Astronomy, University of Birmingham, Birmingham,
United Kingdom
100 Sección Física, Departamento de Ciencias, Pontificia Universidad Católica
del Perú, Lima, Peru
101 Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
102 SUBATECH, IMT Atlantique, Nantes Université, CNRS-IN2P3, Nantes, France
103 Sungkyunkwan University, Suwon City, Republic of Korea
104 Suranaree University of Technology, Nakhon Ratchasima, Thailand
105 Technical University of Košice, Košice, Slovak Republic
106 The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of
Sciences, Cracow, Poland
107 The University of Texas at Austin, Austin, Texas, United States
108 Universidad Autónoma de Sinaloa, Culiacán, Mexico
109 Universidade de São Paulo (USP), São Paulo, Brazil
110 Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
111 Universidade Federal do ABC, Santo Andre, Brazil
112 University of Cape Town, Cape Town, South Africa
113 University of Houston, Houston, Texas, United States
114 University of Jyväskylä, Jyväskylä, Finland
115 University of Kansas, Lawrence, Kansas, United States
116 University of Liverpool, Liverpool, United Kingdom
117 University of Science and Technology of China, Hefei, China
118 University of South-Eastern Norway, Kongsberg, Norway
119 University of Tennessee, Knoxville, Tennessee, United States
120 University of the Witwatersrand, Johannesburg, South Africa
121 University of Tokyo, Tokyo, Japan
122 University of Tsukuba, Tsukuba, Japan
123 University Politehnica of Bucharest, Bucharest, Romania
124 Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
125 Université de Lyon, CNRS/IN2P3, Institut de Physique des 2 Infinis de
Lyon, Lyon, France
126 Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France,
Strasbourg, France
127 Université Paris-Saclay, Centre d’Etudes de Saclay (CEA), IRFU, Départment
de Physique Nucléaire (DPhN), Saclay, France
128 Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
129 Università degli Studi di Foggia, Foggia, Italy
130 Università del Piemonte Orientale, Vercelli, Italy
131 Università di Brescia, Brescia, Italy
132 Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata,
India
133 Warsaw University of Technology, Warsaw, Poland
134 Wayne State University, Detroit, Michigan, United States
135 Westfälische Wilhelms-Universität Münster, Institut für Kernphysik,
Münster, Germany
136 Wigner Research Centre for Physics, Budapest, Hungary
137 Yale University, New Haven, Connecticut, United States
138 Yonsei University, Seoul, Republic of Korea
139 Zentrum für Technologie und Transfer (ZTT), Worms, Germany
140 Affiliated with an institute covered by a cooperation agreement with CERN
141 Affiliated with an international laboratory covered by a cooperation
agreement with CERN.