EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-EP-2019-225 LHCb-PAPER-2019-032 January 13, 2020

Updated measurement of decay-time-dependent $C\\!P$ asymmetries in
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays

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

A search for decay-time-dependent charge-parity ($C\\!P$) asymmetry in
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays is performed at the LHCb
experiment using proton-proton collision data recorded at a center-of-mass
energy of 13 TeV, and corresponding to an integrated luminosity of
5.4$\text{\,fb}^{-1}$. The ${D}^{0}$ mesons are required to originate from
semileptonic decays of $b$ hadrons, such that the charge of the muon
identifies the flavor of the neutral $D$ meson at production. The asymmetries
in the effective decay widths of ${D}^{0}$ and ${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mesons are determined to be
$A_{\Gamma}({{K}^{+}}{{K}^{-}})=(-4.3\pm 3.6\pm 0.5)\times 10^{-4}$ and
$A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})=(2.2\pm 7.0\pm 0.8)\times 10^{-4}$, where
the uncertainties are statistical and systematic, respectively. The results
are consistent with $C\\!P$ symmetry and, when combined with previous LHCb
results, yield $A_{\Gamma}({{K}^{+}}{{K}^{-}})=(-4.4\pm 2.3\pm 0.6)\times
10^{-4}$ and $A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})=(2.5\pm 4.3\pm 0.7)\times
10^{-4}$.

Published in Phys. Rev. D101 (2020) 012005

© 2024 CERN for the benefit of the LHCb collaboration. CC-BY-4.0 licence.

##  1 Introduction

Charge-parity ($C\\!P$) violation is one of the key ingredients that are
needed to generate the asymmetry between matter and antimatter observed in the
Universe [1]. The Standard Model (SM) of particle physics, where all known
$C\\!P$-violating processes arise from the irreducible phase of the Cabibbo-
Kobayashi-Maskawa matrix [2, 3] is ,however, unable to explain the observed
asymmetry [4, 5]. New dynamics that lead to a significant enhancement of
$C\\!P$-violating processes are required, making searches for $C\\!P$
violation a powerful probe for physics beyond the SM. Although $C\\!P$
violation has been experimentally observed in the down-type quark sector with
measurements of $K$ and $B$ mesons [6, 7, 8, 9, 10], no indication of new
dynamics has been reported yet. Only recently has $C\\!P$ violation been
observed in the decay of charmed mesons [11]. The limited precision of the SM
predictions, together with the limited amount of experimental information
available [12], is, however, not yet sufficient to establish whether the
observed signal could be explained by the SM [13, 14, 15, 16, 17, 18].
Additional searches for $C\\!P$ violation in the charm sector, and
particularly for more suppressed and yet-to-be-observed signs of
$C\\!P$-violating effects induced by ${D}^{0}$–${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mixing, have unique potential to
probe for the existence of beyond-the-SM dynamics, which couple preferentially
to up-type quarks [19, 20, 21, 22, 23, 24].

This paper reports a search for $C\\!P$ violation in ${D}^{0}$–${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mixing, or in the interference
between mixing and decay, through the measurement of the asymmetry between the
effective decay widths, $\hat{\Gamma}$, of mesons initially produced as
${D}^{0}$ and ${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ and
decaying into the $C\\!P$-even final states $f={{K}^{+}}{{K}^{-}}$,
${{\pi}^{+}}{{\pi}^{-}}$:

$A_{\Gamma}(f)\equiv\frac{\hat{\Gamma}({{{D}^{0}}\rightarrow
f})-\hat{\Gamma}({{{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}\rightarrow
f})}{\hat{\Gamma}({{{D}^{0}}\rightarrow f})+\hat{\Gamma}({{{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}\rightarrow f})}.$ (1)

Several measurements of the parameter $A_{\Gamma}(f)$ have been performed by
the BaBar [25], CDF [26], Belle [27], and LHCb [28, 29, 30] Collaborations,
leading to the current world-average value of $(-3.2\pm 2.6)\times 10^{-4}$
[12], when neglecting differences between the
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays.111Throughout the paper,
the inclusion of the charge-conjugate decay mode is implied unless otherwise
stated. The achieved sensitivity is still 1 order of magnitude larger than the
theoretical predictions of $A_{\Gamma}\approx 3\times 10^{-5}$ [31]. This
paper updates the LHCb measurements of Refs. [28, 29, 30] using the data
sample of proton-proton collisions collected at a center-of-mass energy of 13
TeV during 2016–2018, and corresponding to an integrated luminosity of
5.4$\text{\,fb}^{-1}$. The analysis is performed using ${D}^{0}$ mesons
originating from semileptonic decays of $b$ hadrons, where the $b$-hadron
candidates are only partially reconstructed. The charge of the muon identifies
(“tags”) the flavor of the ${D}^{0}$ meson at its production. The samples are
dominated by ${{{B}^{-}}}\rightarrow{{D}^{0}}{\mu^{-}}X$ and ${{\kern
1.79993pt\overline{\kern-1.79993ptB}}{}^{0}}\rightarrow{{D}^{0}}{\mu^{-}}X$
decays, where $X$ denotes any set of final-state particles that are not
reconstructed.

The paper is structured as follows: the analysis strategy is described in Sec.
2. The LHCb detector is sketched in Sec. 3; Sec. 4 details the criteria used
to select the signal and control samples; Sec. 5 describes the fit method, and
its validation using ${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays; the
determination of the systematic uncertainties is outlined in Sec. 6, before
concluding with the presentation of the final results in Sec. 7.

##  2 Analysis strategy

Due to the weak interactions, the mass eigenstates of neutral charm mesons,
$D_{1}$ and $D_{2}$, are a superposition of the flavor states, ${D}^{0}$ and
${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$: $|D_{1,2}\rangle\equiv
p|{{D}^{0}}\rangle\pm q|{{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}\rangle$, where $q$ and $p$ are
complex coefficients satisfying $\lvert p\rvert^{2}+\lvert q\rvert^{2}=1$.
Hence, an originally produced ${D}^{0}$ meson can oscillate as a function of
time into a ${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ meson, and
vice versa, before decaying. In the limit of $C\\!P$ symmetry, $q$ equals $p$
and the oscillations are characterized by only two dimensionless parameters,
$x\equiv(m_{1}-m_{2})c^{2}/\Gamma$ and
$y\equiv(\Gamma_{1}-\Gamma_{2})/2\Gamma$, where $m_{1(2)}$ and $\Gamma_{1(2)}$
are the mass and decay width of the $C\\!P$-even (odd) eigenstate $D_{1(2)}$,
respectively, and $\Gamma\equiv(\Gamma_{1}+\Gamma_{2})/2$ is the average decay
width [32]. The values of $x$ and $y$ have been measured to be of the order of
1% or smaller [12]. In the presence of $C\\!P$ violation, the mixing rates for
mesons produced as ${D}^{0}$ and ${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ differ, further enriching the
phenomenology. As an example, indicating with $A_{f}$ ($\bar{A}_{f}$) the
decay amplitude of a ${D}^{0}$ (${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$) meson into the final state $f$,
three different manifestations of $C\\!P$ violation can be measured: (i)
$C\\!P$ violation in the decay if
${{\mathcal{A}}^{\text{dir}}_{{C\\!P}}}(f)\equiv(|{A_{f}}|^{2}-|{\bar{A}_{f}}|^{2})/(|{A_{f}}|^{2}+|{\bar{A}_{f}}|^{2})$
differs from zero, (ii) $C\\!P$ violation in mixing if $|q/p|$ differs from
unity, and (iii) $C\\!P$ violation in the interference between mixing and
decay if $\phi_{f}\equiv\arg[(q{\bar{A}_{f}})/(p{A_{f}})]$ differs from zero.
The latter two can be accessed by measuring the decay-time-dependent $C\\!P$
asymmetry

${{\mathcal{A}}_{{C\\!P}}}({{D}^{0}}\rightarrow
f;t)=\frac{\Gamma({{D}^{0}}(t)\rightarrow f)-\Gamma({{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}(t)\rightarrow
f)}{\Gamma({{D}^{0}}(t)\rightarrow f)+\Gamma({{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}(t)\rightarrow f)}.$ (2)

In the limit of small mixing parameters, Eq. (2) can be approximated as a
linear function of decay time [33, 34],

${{\mathcal{A}}_{{C\\!P}}}({{D}^{0}}\rightarrow
f;t)\approx{{\mathcal{A}}^{\text{dir}}_{{C\\!P}}}(f)-A_{\Gamma}(f)\
\frac{t}{\tau},$ (3)

where $\tau=1/\Gamma$ is the average lifetime of neutral $D$ mesons. The
coefficient $A_{\Gamma}(f)$ is related to the mixing and $C\\!P$-violation
parameters by [35]

$A_{\Gamma}(f)\approx-x\phi_{f}+y\left(|q/p|-1\right)-y{{\mathcal{A}}^{\text{dir}}_{{C\\!P}}}(f).$
(4)

Contrarily to the measurement reported in Ref. [11], which is sensitive to
${{\mathcal{A}}^{\text{dir}}_{{C\\!P}}}({{K}^{+}}{{K}^{-}})-{{\mathcal{A}}^{\text{dir}}_{{C\\!P}}}({{\pi}^{+}}{{\pi}^{-}})$,
$A_{\Gamma}(f)$ is mostly sensitive to $C\\!P$ violation in mixing or in the
interference between mixing and decay, because the term
$y{{\mathcal{A}}^{\text{dir}}_{{C\\!P}}}(f)\leqslant 10^{-5}$ [12] can be
neglected at the current level of experimental precision. Moreover, neglecting
the $\mathcal{O}(10^{-3})$ difference between the weak phases of the decay
amplitudes to the $C\\!P$-even final states ${{K}^{+}}{{K}^{-}}$ and
${{\pi}^{+}}{{\pi}^{-}}$, $\phi_{f}\approx\phi\equiv\arg(q/p)$ becomes
universal and $A_{\Gamma}$ independent of $f$ [22].

Experimentally, the partial rate asymmetry of Eq. (2) cannot be measured
directly because of charge-asymmetric detection efficiencies and asymmetric
production rates of ${D}^{0}$ and ${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mesons from semileptonic
$b$-hadron decays in proton-proton collisions. Instead, the “raw” asymmetry
between the ${D}^{0}$ and ${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$
mesons yields,

${A_{\text{raw}}}({{D}^{0}}\rightarrow f)=\frac{N({\kern
1.79993pt\overline{\kern-1.79993ptB}}\rightarrow{{D}^{0}}(\rightarrow
f)\mu^{-}X)-N({B}\rightarrow{{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}(\rightarrow f)\mu^{+}X)}{N({\kern
1.79993pt\overline{\kern-1.79993ptB}}\rightarrow{{D}^{0}}(\rightarrow
f)\mu^{-}X)+N({B}\rightarrow{{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}(\rightarrow f)\mu^{+}X)},$ (5)

is measured as a function of decay time. Neglecting higher-order terms in the
involved asymmetries, which are at most $\mathcal{O}(1\%)$, the raw asymmetry
can be approximated as

${A_{\text{raw}}}({{D}^{0}}\rightarrow
f;t)\approx{{\mathcal{A}}_{{C\\!P}}}({{D}^{0}}\rightarrow
f;t)+A_{D}(\mu)+A_{P}({D}),$ (6)

where $A_{D}(\mu)$ and $A_{P}({D})$ are the nuisance asymmetries due to the
detection efficiency of the tagging muon and to the production rates of the
neutral $D$ mesons, respectively. The parameter $A_{\Gamma}$ corresponds to
the slope of the decay-time-dependent raw asymmetry only if $A_{D}$ and
$A_{P}$ are independent of decay time. In this analysis, a possible time
dependence of $A_{D}$ and $A_{P}$ is considered as a source of systematic
uncertainty. The analysis procedure is validated on data using a control
sample of Cabibbo-favored ${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays,
whose size exceeds that of the ${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ signal modes by approximately 1
order of magnitude, and where measured asymmetries can be attributed solely to
instrumental effects because no $C\\!P$ violation is expected. To avoid
potential experimenter’s bias, the measured values of
$A_{\Gamma}({{K}^{+}}{{K}^{-}})$ and $A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})$
remained unknown during the development of the analysis and were examined only
after the analysis procedure and the evaluation of the systematic
uncertainties were finalized.

##  3 Detector

The LHCb detector [36, 37] is a single-arm forward spectrometer covering the
pseudorapidity range $2<\eta<5$, designed for the study of particles
containing $b$ or $c$ quarks. The detector includes a high-precision tracking
system consisting of a silicon-strip vertex detector surrounding the $pp$
interaction region, a large-area silicon-strip detector located upstream of a
dipole magnet with a bending power of about $4{\mathrm{\,Tm}}$, and three
stations of silicon-strip detectors and straw drift tubes placed downstream of
the magnet. The tracking system provides a measurement of the momentum, $p$,
of charged particles with relative uncertainty that varies from 0.5% at low
momentum to 1.0% at 200$\text{\,Ge\kern-1.00006ptV\\!/}c$. The minimum
distance of a track to a primary vertex (PV), the impact parameter, is
measured with a resolution of $(15+29/p_{\mathrm{T}})\,\upmu\text{m}$, where
$p_{\mathrm{T}}$ is the component of the momentum transverse to the beam, in
$\text{\,Ge\kern-1.00006ptV\\!/}c$. Different types of charged hadrons are
distinguished using information from two ring-imaging Cherenkov detectors.
Photons, electrons, and hadrons are identified by a calorimeter system
consisting of scintillating-pad and preshower detectors, an electromagnetic
and a hadronic calorimeter. Muons are identified by a system composed of
alternating layers of iron and multiwire proportional chambers. The magnetic-
field polarity is reversed periodically during data taking to mitigate the
differences of reconstruction efficiencies of particles with opposite charges.

The on-line event selection is performed by a trigger, which consists of a
hardware stage followed by a two-level software stage. In between the two
software stages, an alignment and calibration of the detector is performed in
near real time [38]. The same alignment and calibration information is
propagated to the off-line reconstruction, ensuring consistent and high-
quality particle identification information between the trigger and off-line
software. The identical performance of the on-line and off-line reconstruction
offers the opportunity to perform physics analyses directly using candidates
reconstructed in the trigger [39, 40], which the present analysis exploits.

##  4 Selection

The selection criteria are mainly inherited from the measurement of the
difference between the decay-time-integrated $C\\!P$ asymmetries in
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays [11], which uses the same
sample of proton-proton collisions. Signal candidates are first required to
pass the hardware trigger, which selects events containing at least one
charged particle with high transverse momentum that leaves a track in the muon
system. At the first stage of the software trigger, events are selected if
they contain at least one track having large transverse momentum and being
incompatible with originating from any PV, or if any two-track combination
forming a secondary vertex passes a multivariate classifier. If a particle is
identified as a muon, a lower $p_{\mathrm{T}}$ threshold is applied. At the
second stage of the software trigger, the full event reconstruction is
performed, and requirements on kinematic, topological, and particle-
identification criteria are placed on the signal candidates. A ${D}^{0}$
candidate is formed by combining two well-reconstructed, oppositely charged
tracks such that they are consistent with originating from a common vertex.
The ${D}^{0}$ candidate must satisfy requirements on the vertex quality and
has to be well separated from all PVs in the event. At the next step, the
${D}^{0}$ candidate is combined with a muon to form a $B$ candidate. Only
candidates where the ${D}^{0}$ meson decays downstream along the beam axis
with respect to the $B$ candidate are further considered. The $B$ candidate
must have a visible mass, $m({{D}^{0}}\mu)$, and a corrected mass, $m_{\rm
corr}({B})$, consistent with a signal decay. The corrected mass is computed as
$m_{\rm
corr}(B)\equiv\sqrt{m^{2}({{D}^{0}}\mu)+p_{\perp}^{2}({{D}^{0}}\mu)}+p_{\perp}({{D}^{0}}\mu)$,
where $p_{\perp}({{D}^{0}}\mu)$ is the momentum of the ${{D}^{0}}\mu$ system
transverse to the $B$ flight direction, to partially correct for the
unreconstructed particles in the decay of the $B$ hadron.

In the off-line selection, trigger signals are associated with reconstructed
particles. Particle-identification criteria and requirements on
$m({{D}^{0}}\mu)$ and $m_{\rm corr}({B})$ are tightened with respect to the
on-line selection. The mass of the ${D}^{0}$ candidate is required to be in
the ranges $[1825,1925]\text{\,Me\kern-1.00006ptV\\!/}c^{2}$,
$[1820,1939]\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ and
$[1780,1940]\text{\,Me\kern-1.00006ptV\\!/}c^{2}$ for
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$,
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$, and
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays, respectively, to reduce the
amount of background decays with misidentified final-state particles to a
negligible level. The reconstructed decay time is computed from the distance,
$L$, between the measured ${D}^{0}$ and $B$ decay vertices and from the
${D}^{0}$ momentum, $p({{D}^{0}})$, as $t=m_{{D}^{0}}L/[p({{D}^{0}})c]$, where
$m_{{D}^{0}}$ is the known ${D}^{0}$ mass [32]. All ${D}^{0}$ candidates with
a reconstructed decay time that is either negative or exceeds 10 times the
${D}^{0}$ lifetime are discarded. Mass vetoes suppress background from
misreconstructed $B$ decays to final states involving a charmonium resonance,
such as ${B}^{-}\rightarrow\psi^{(^{\prime})}(\rightarrow\mu^{+}\mu^{-})h^{-}$
with $h=\pi$ or $K$, where a muon is misidentified as a pion or kaon and is
used in the ${D}^{0}$ final state. Tag muons reconstructed in regions of phase
space with large instrumental asymmetries, due to muons of one charge either
being bent out of the detector acceptance or deflected into the LHC beam pipe,
are vetoed. The fraction of signal candidates removed by this requirement is
$10\%$. In addition, for ${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays,
candidates with kaon $p_{\mathrm{T}}<800\text{\,Me\kern-1.00006ptV\\!/}c$ are
removed to reduce instrumental asymmetry between the detection of negatively
and positively charged kaons. Since these requirements do not reduce the
background to a sufficiently low level for
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays, a dedicated boosted
decision tree (BDT) is trained to isolate the signal candidates from
background made of accidental combinations of charged particles
(“combinatorial background”). The variables used in the BDT to discriminate
signal from combinatorial background are the fit quality of the ${D}^{0}$ and
the $B$ decay vertices, the ${D}^{0}$ flight distance; the ${D}^{0}$ impact
parameter with respect to the closest PV, the transverse momenta of the
${D}^{0}$ decay products, the significance of the distance between the
${D}^{0}$ and $B$ decay vertices, and the visible and corrected masses of the
$B$-hadron candidate. The BDT is trained using
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays as signal proxies and
candidates from the ${D}^{0}$ mass sidebands of the signal decay modes as
background. The optimal requirement on the BDT discriminant is chosen by
maximizing the figure of merit $\mathcal{S}/\sqrt{\mathcal{S+B}}$ in a range
corresponding to approximately 3 times the mass resolution around the
${D}^{0}$ mass, where $\mathcal{S}$ and $\mathcal{B}$ denote the signal and
background yields, respectively. If an event contains more than one candidate
after the full selection, one is chosen at random. The fraction of candidates
removed by this requirement is $0.4\%$.

\begin{overpic}[width=216.81pt]{Fig1a} \put(21.0,55.0){$(a)$}
\end{overpic}\begin{overpic}[width=216.81pt]{Fig1b} \put(21.0,55.0){$(b)$}
\end{overpic}

\begin{overpic}[width=216.81pt]{Fig1c} \put(21.0,55.0){$(c)$} \end{overpic}

Figure 1: Mass distributions of (a) ${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$,
(b) ${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ and (c)
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ candidates with fit projections
overlaid.

The mass distributions of the selected signal- and control-decay candidates
are shown in Fig. 1. Details about the fit model are given in the next
section. Approximately $9\times 10^{6}$, $3\times 10^{6}$, and $76\times
10^{6}$ signal ${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$,
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$, and
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays, respectively, are
reconstructed over a smooth background dominated by accidental combinations of
charged particles.

##  5 Fit method

The samples of selected ${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$,
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ and
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ candidates are split into 20
approximately equally populated subsets (“bins”) of decay time in the range
$[0,10]\tau$. In each decay-time bin, the raw asymmetry $A_{\text{raw}}$ is
determined by a simultaneous binned $\chi^{2}$ fit to the $m({{D}^{0}})$
distributions of the ${D}^{0}$ and ${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ candidates, split according to
the muon tag. The total signal yields and asymmetries are treated as shared
floating parameters of the fit. The fits include two components: signal and
combinatorial background. The signal is described with a sum of a Gaussian and
a Johnson’s $S_{U}$ distribution [41], with parameters determined from a fit
to the decay-time-integrated mass spectra. To account for the observed
dependence of the signal mass shape on decay time, the means and widths of the
signal distributions are left free to float individually for each decay-time
bin. The mass shape is assumed to be the same for ${D}^{0}$ and ${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ candidates for charge-symmetric
final states of the signal modes, and allowed to differ for
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ and ${{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}\rightarrow{{K}^{+}}{{\pi}^{-}}$
candidates. The combinatorial background is described by a linear function,
with a slope that floats independently in each decay-time bin and is allowed
to differ between ${D}^{0}$ and ${\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ candidates.

The raw asymmetry measured in decay-time bin $i$ is fit by minimizing the
least squares with respect to the linear function
${A_{\text{raw}}}(0)-A_{\Gamma}\langle t\rangle_{i}/\tau$. The decay-time-
independent terms of Eqs. (3) and (6) are incorporated into a single
parameter, ${A_{\text{raw}}}(0)$, that is determined by the fit together with
$A_{\Gamma}$. The average decay time in each bin $i$, $\langle t\rangle_{i}$,
is computed using the decay-time distribution of background-subtracted
${D}^{0}$ candidates. Statistically consistent values are found for the
control and signal modes. The ${D}^{0}$ lifetime $\tau$ is set to its known
value [32]. Using large samples of simulated experiments, it is verified that
the analysis procedure leads to unbiased estimates of the fit parameters and
of their uncertainties. Figure 2 shows the projection of the decay-time-
dependent fit to the ${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ control
sample. Here $A_{\Gamma}$ is measured to be $(1.6\pm 1.2)\times 10^{-4}$,
where the uncertainty is statistical only. The measured value is consistent
with zero as expected, confirming the validity of the assumption of decay-
time-independent nuisance asymmetries. In
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ decays, due to their charge-
asymmetric final states, detection asymmetries are more pronounced compared to
the signal modes, where these asymmetries are only caused by the muons used to
tag the flavor of the ${D}^{0}$ mesons.

Figure 2: Raw asymmetry as a function of decay time with fit projection
overlaid for ${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ signal candidates.

##  6 Systematic uncertainties

The systematic uncertainty is dominated by the following contributions: the
impact of decay-time acceptance and resolution, the effect of neglected
background from combinations of real ${D}^{0}$ candidates with unrelated muons
(which might lead to a wrong identification of the neutral $D$-meson flavor),
and the impact of the assumed parametrization of the signal and background
mass shapes. These effects are studied using large samples of
pseudoexperiments, where the above sources of systematic biases are simulated.

The average decay-time resolution is estimated to be $127\text{\,fs}$ using
simulated decays. In the generation of the pseudoexperiments, the resolution
is increased by 10% to account for differences between data and simulation.
The decay-time acceptance is estimated from data by comparing the background-
subtracted decay-time distributions of
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ candidates with an exponential
function convoluted with the decay-time resolution. Different sets of
pseudoexperiments, simulating the effect of decay-time acceptance and
resolution, are generated with values of $A_{\Gamma}$ in the range
$[-30,30]\times 10^{-4}$. Each pseudoexperiment is then fit with the default
analysis approach, and the difference between the measured and the input
values of $A_{\Gamma}$ is used to determine the systematic bias. As the bias
is found to depend linearly on the true value of $A_{\Gamma}$, the largest
bias observed within the $68\%$ confidence-level interval of the current world
average [12] is taken as the systematic uncertainty. This amounts to
$0.3\times 10^{-4}$ ($0.4\times 10^{-4}$) for
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$
(${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$) decays.

The probability to wrongly associate unrelated muons with the ${D}^{0}$
candidates is estimated using the yields of “wrong-sign”
${{D}^{0}}(\rightarrow K^{-}\pi^{+})\mu^{+}$ and ${{\kern
1.79993pt\overline{\kern-1.79993ptD}}{}^{0}}(\rightarrow K^{+}\pi^{-})\mu^{-}$
candidates in data, which are corrected for the rate of doubly Cabibbo-
suppressed decays and decays due to flavor oscillation using the measurements
reported in Ref. [42]. Mistag probabilities between 1% at low decay times and
3% at high decay times are observed. Also in this case the bias observed in
pseudoexperiments depends linearly on the true value of $A_{\Gamma}$.
Following the same strategy as discussed above, a systematic uncertainty of
$0.3\times 10^{-4}$ ($0.6\times 10^{-4}$) is assigned for
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$
(${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$) decays.

To estimate any potential bias due to the specific choice of the mass model
used in the fits that determine the raw asymmetries, samples of
pseudoexperiments are generated using alternative signal and background models
that describe the data equally well. The observed bias is independent of the
input $A_{\Gamma}$ and results in an additional systematic uncertainty of
$0.3\times 10^{-4}$ for both signal decay channels.

Uncertainties on $\langle t\rangle_{i}/\tau$ arising from relative
misalignments of subdetectors and from the uncertainty on the input value of
the ${D}^{0}$ lifetime [32] give negligible contributions. Furthermore,
unexpected biases due to a possible decay-time dependence of the nuisance
asymmetries and due to the selection procedure are investigated using the
${{D}^{0}}\rightarrow{{K}^{-}}{{\pi}^{+}}$ control sample and/or by measuring
$A_{\Gamma}$ in disjoint subsamples split by magnetic-field polarity, year of
data taking, and kinematic variables of the $B$ hadron, ${D}^{0}$ meson and
muon candidates. No unexpected variations are observed, and no additional
systematic uncertainties are assigned.

Table 1: Summary of the dominant contributions to the systematic uncertainty on $A_{\Gamma}({{K}^{+}}{{K}^{-}})$ and $A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})$. Source of uncertainty |  $A_{\Gamma}({{K}^{+}}{{K}^{-}})$ [$10^{-4}$] |  $A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})$ [$10^{-4}$]
---|---|---
Decay-time resolution and acceptance | $0.3$ | $0.4$
Mistag probability | $0.3$ | $0.6$
Mass-fit model | $0.3$ | $0.3$
Total | 0.5 | 0.8

A summary of the relevant systematic uncertainties is given in Table 1. The
total systematic uncertainty is obtained by summing in quadrature the
individual components and amounts to $0.5\times 10^{-4}$ and $0.8\times
10^{-4}$ for $A_{\Gamma}({{K}^{+}}{{K}^{-}})$ and
$A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})$, respectively.

##  7 Results and conclusions

A search for decay-time-dependent $C\\!P$ violation in
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays is performed using proton-
proton collision data recorded with the LHCb detector at a center-of-mass
energy of 13 TeV, and corresponding to an integrated luminosity of
5.4$\text{\,fb}^{-1}$. The ${D}^{0}$ mesons are required to originate from
semileptonic $b$-hadron decays, such that the charge of the muon identifies
the flavor of the neutral $D$ meson at the moment of its production. The
parameter $A_{\Gamma}$ is determined from a fit to the asymmetry between
${D}^{0}$ and ${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ yields as a
function of decay time. The projections of the fits for both
${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ samples are shown in Fig. 3. The
results are

$\displaystyle A_{\Gamma}({{K}^{+}}{{K}^{-}})$ $\displaystyle=(-4.3\pm 3.6\pm
0.5)\times 10^{-4},$ $\displaystyle A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})$
$\displaystyle=(\phantom{-}2.2\pm 7.0\pm 0.8)\times 10^{-4},$

where the uncertainties are statistical and systematic, respectively.

\begin{overpic}[width=303.53267pt]{Fig3a} \put(85.0,35.0){$(a)$} \end{overpic}

\begin{overpic}[width=303.53267pt]{Fig3b} \put(85.0,35.0){$(b)$} \end{overpic}

Figure 3: Raw asymmetry as a function of decay time with fit projection
overlaid for (a) ${{D}^{0}}\rightarrow{{K}^{+}}{{K}^{-}}$ and (b)
${{D}^{0}}\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ signal candidates.

The measured values are combined with previous LHCb measurements based on data
corresponding to 3$\text{\,fb}^{-1}$ collected at center-of-mass energies of 7
and 8 TeV, and where the neutral $D$ mesons originate either from semileptonic
$b$-hadron decays [28] or from promptly produced ${{D}^{*+}}(2010)$ mesons
[29], with which they are consistent. The combination accounts for
correlations in the systematic uncertainties and yields

$\displaystyle A_{\Gamma}({{K}^{+}}{{K}^{-}})$ $\displaystyle=(-4.4\pm 2.3\pm
0.6)\times 10^{-4},$ $\displaystyle A_{\Gamma}({{\pi}^{+}}{{\pi}^{-}})$
$\displaystyle=(\phantom{-}2.5\pm 4.3\pm 0.7)\times 10^{-4}.$

Assuming $A_{\Gamma}$ to be universal, the above two results can be averaged
to yield $A_{\Gamma}=(-2.9\pm 2.0\pm 0.6)\times 10^{-4}$. The results do not
show any indication of $C\\!P$ violation in charm mixing or in the
interference between mixing and decay.

## Acknowledgements

We express our gratitude to our colleagues in the CERN accelerator departments
for the excellent performance of the LHC. We thank the technical and
administrative staff at the LHCb institutes. We acknowledge support from CERN
and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); MOST
and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN
(Italy); NWO (Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MSHE
(Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC
(United Kingdom); DOE NP and NSF (USA). We acknowledge the computing resources
that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN
(Italy), SURF (Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and
Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-
GRID (Poland) and OSC (USA). We are indebted to the communities behind the
multiple open-source software packages on which we depend. Individual groups
or members have received support from AvH Foundation (Germany); EPLANET, Marie
Skłodowska-Curie Actions and ERC (European Union); ANR, Labex P2IO and OCEVU,
and Région Auvergne-Rhône-Alpes (France); Key Research Program of Frontier
Sciences of CAS, CAS PIFI, and the Thousand Talents Program (China); RFBR, RSF
and Yandex LLC (Russia); GVA, XuntaGal and GENCAT (Spain); the Royal Society
and the Leverhulme Trust (United Kingdom).

## References

  * [1] A. D. Sakharov, _Violation of $C\\!P$ invariance, $C$ asymmetry, and baryon asymmetry of the universe_, Pisma Zh. Eksp. Teor. Fiz. 5 (1967) 32, Usp. Fiz. Nauk 161 (1991) 61
  * [2] N. Cabibbo, _Unitary symmetry and leptonic decays_ , Phys. Rev. Lett. 10 (1963) 531
  * [3] M. Kobayashi and T. Maskawa, _$C\\!P$ -violation in the renormalizable theory of weak interaction_, Prog. Theor. Phys. 49 (1973) 652
  * [4] P. Huet and E. Sather, _Electroweak baryogenesis and standard model $C\\!P$ violation_, Phys. Rev. D51 (1995) 379, arXiv:hep-ph/9404302
  * [5] M. Dine and A. Kusenko, _The origin of the matter–antimatter asymmetry_ , Rev. Mod. Phys. 76 (2003) 1, arXiv:hep-ph/0303065
  * [6] J. H. Christenson, J. W. Cronin, V. L. Fitch, and R. Turlay, _Evidence for the $2\pi$ decay of the $K_{2}^{0}$ meson_, Phys. Rev. Lett. 13 (1964) 138
  * [7] BaBar collaboration, B. Aubert et al., _Direct CP violating asymmetry in $B^{0}\rightarrow K^{+}\pi^{-}$ decays_, Phys. Rev. Lett. 93 (2004) 131801, arXiv:hep-ex/0407057
  * [8] Belle collaboration, Y. Chao et al., _Evidence for direct CP violation in $B^{0}\rightarrow{{K}^{+}}{{\pi}^{-}}$ decays_, Phys. Rev. Lett. 93 (2004) 191802, arXiv:hep-ex/0408100
  * [9] LHCb collaboration, R. Aaij et al., _First observation of $C\\!P$ violation in the decays of ${B}^{0}_{s}$ mesons_, Phys. Rev. Lett. 110 (2013) 221601, arXiv:1304.6173
  * [10] LHCb collaboration, R. Aaij et al., _Observation of $C\\!P$ violation in ${{B}^{\pm}}\\!\rightarrow{D}{{K}^{\pm}}$ decays_, Phys. Lett. B712 (2012) 203, Erratum ibid. B713 (2012) 351, arXiv:1203.3662
  * [11] LHCb collaboration, R. Aaij et al., _Observation of $C\\!P$ violation in charm decays_, Phys. Rev. Lett. 122 (2019) 211803, arXiv:1903.08726
  * [12] Heavy Flavor Averaging Group, Y. Amhis et al., _Averages of $b$-hadron, $c$-hadron, and $\tau$-lepton properties as of summer 2018_, arXiv:1909.12524, updated results and plots available at https://hflav.web.cern.ch
  * [13] M. Chala, A. Lenz, A. V. Rusov, and J. Scholtz, _$\Delta A_{{C\\!P}}$ within the Standard Model and beyond_, JHEP 07 (2019) 161, arXiv:1903.10490
  * [14] H.-N. Li, C.-D. Lü, and F.-S. Yu, _Implications on the first observation of charm $C\\!PV$ at LHCb_, arXiv:1903.10638
  * [15] Y. Grossman and S. Schacht, _The emergence of the $\Delta U=0$ rule in charm physics_, JHEP 07 (2019) 020, arXiv:1903.10952
  * [16] A. Soni, _Resonance enhancement of charm $C\\!P$_, arXiv:1905.00907
  * [17] F. Buccella, A. Paul, and P. Santorelli, _$SU(3)_{F}$ breaking through final state interactions and $C\\!P$ asymmetries in $D\rightarrow PP$ decays_, Phys. Rev. D99 (2019) 113001, arXiv:1902.05564
  * [18] H.-Y. Cheng and C.-W. Chiang, _Revisiting $C\\!P$ violation in $D\rightarrow P\\!P$ and $V\\!P$ decays_, arXiv:1909.03063
  * [19] M. Golden and B. Grinstein, _Enhanced $C\\!P$ violations in hadronic charm decays_, Phys. Lett. B222 (1989) 501
  * [20] F. Buccella et al., _Nonleptonic weak decays of charmed mesons_ , Phys. Rev. D51 (1995) 3478, arXiv:hep-ph/9411286
  * [21] S. Bianco, F. L. Fabbri, D. Benson, and I. Bigi, _A Cicerone for the physics of charm_ , Riv. Nuovo Cim. 26N7 (2003) 1, arXiv:hep-ex/0309021
  * [22] Y. Grossman, A. L. Kagan, and Y. Nir, _New physics and CP violation in singly Cabibbo suppressed D decays_ , Phys. Rev. D75 (2007) 036008, arXiv:hep-ph/0609178
  * [23] M. Artuso, B. Meadows, and A. A. Petrov, _Charm meson decays_ , Ann. Rev. Nucl. Part. Sci. 58 (2008) 249, arXiv:0802.2934
  * [24] A. Khodjamirian and A. A. Petrov, _Direct CP asymmetry in $D\rightarrow\pi^{-}\pi^{+}$ and $D\rightarrow K^{-}K^{+}$ in QCD-based approach_, Phys. Lett. B774 (2017) 235, arXiv:1706.07780
  * [25] BaBar collaboration, J. P. Lees et al., _Measurement of ${D}^{0}$–${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mixing and CP violation in two-body ${D}^{0}$ decays_, Phys. Rev. D87 (2013) 012004, arXiv:1209.3896
  * [26] CDF collaboration, T. Aaltonen et al., _Measurement of indirect CP-violating asymmetries in $D^{0}\rightarrow K^{+}K^{-}$ and $D^{0}\rightarrow\pi^{+}\pi^{-}$ decays at CDF_, Phys. Rev. D90 (2014) 111103, arXiv:1410.5435
  * [27] Belle collaboration, M. Starič et al., _Measurement of ${D}^{0}$–${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mixing and search for CP violation in $D^{0}\rightarrow K^{+}K^{-},\pi^{+}\pi^{-}$ decays with the full Belle data set_, Phys. Lett. B753 (2016) 412, arXiv:1509.08266
  * [28] LHCb collaboration, R. Aaij et al., _Measurement of indirect $C\\!P$ asymmetries in ${{D}^{0}}\\!\rightarrow{{K}^{-}}{{K}^{+}}$ and ${{D}^{0}}\\!\rightarrow{{\pi}^{-}}{{\pi}^{+}}$ decays using semileptonic $B$ decays_, JHEP 04 (2015) 043, arXiv:1501.06777
  * [29] LHCb collaboration, R. Aaij et al., _Measurement of the $C\\!P$ violation parameter $A_{\Gamma}$ in ${{D}^{0}}\\!\rightarrow{{K}^{+}}{{K}^{-}}$ and ${{D}^{0}}\\!\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays_, Phys. Rev. Lett. 118 (2017) 261803, arXiv:1702.06490
  * [30] LHCb collaboration, R. Aaij et al., _Measurement of the mass difference between neutral charm-meson eigenstates_ , Phys. Rev. Lett. 122 (2019) 231802, arXiv:1903.03074
  * [31] A. Cerri et al., _Opportunities in flavour physics at the HL-LHC and HE-LHC_ , arXiv:1812.07638
  * [32] Particle Data Group, M. Tanabashi et al., _Review of particle physics_ , Phys. Rev. D98 (2018) 030001
  * [33] CDF collaboration, T. Aaltonen et al., _Measurement of $C\\!P$-violating asymmetries in $D^{0}\rightarrow\pi^{+}\pi^{-}$ and $D^{0}\rightarrow K^{+}K^{-}$ decays at CDF_, Phys. Rev. D85 (2012) 012009, arXiv:1111.5023
  * [34] M. Gersabeck et al., _On the interplay of direct and indirect CP violation in the charm sector_ , J. Phys. G39 (2012) 045005, arXiv:1111.6515
  * [35] LHCb collaboration, _Search for time-dependent $C\\!P$ violation in ${{D}^{0}}\\!\rightarrow{{K}^{+}}{{K}^{-}}$ and ${{D}^{0}}\\!\rightarrow{{\pi}^{+}}{{\pi}^{-}}$ decays_, LHCb-CONF-2019-001, 2019
  * [36] LHCb collaboration, A. A. Alves Jr. et al., _The LHCb detector at the LHC_, JINST 3 (2008) S08005
  * [37] LHCb collaboration, R. Aaij et al., _LHCb detector performance_ , Int. J. Mod. Phys. A30 (2015) 1530022, arXiv:1412.6352
  * [38] G. Dujany and B. Storaci, _Real-time alignment and calibration of the LHCb Detector in Run II_ , J. Phys. Conf. Ser. 664 (2015) 082010
  * [39] R. Aaij et al., _The LHCb trigger and its performance in 2011_, JINST 8 (2013) P04022, arXiv:1211.3055
  * [40] R. Aaij et al., _Tesla: an application for real-time data analysis in High Energy Physics_ , Comput. Phys. Commun. 208 (2016) 35, arXiv:1604.05596
  * [41] N. L. Johnson, _Systems of frequency curves generated by methods of translation_ , Biometrika 36 (1949) 149
  * [42] LHCb collaboration, R. Aaij et al., _Updated determination of ${D}^{0}$–${\kern 1.79993pt\overline{\kern-1.79993ptD}}{}^{0}$ mixing and $C\\!P$ violation parameters with ${{D}^{0}}\\!\rightarrow{{K}^{+}}{{\pi}^{-}}$ decays_, Phys. Rev. D97 (2018) 031101, arXiv:1712.03220

LHCb collaboration

R. Aaij28, C. Abellán Beteta46, T. Ackernley56, B. Adeva43, M. Adinolfi50, H.
Afsharnia6, C.A. Aidala77, S. Aiola22, Z. Ajaltouni6, S. Akar61, P.
Albicocco19, J. Albrecht11, F. Alessio44, M. Alexander55, A. Alfonso Albero42,
G. Alkhazov34, P. Alvarez Cartelle57, A.A. Alves Jr61, S. Amato2, Y. Amhis8,
L. An18, L. Anderlini18, G. Andreassi45, M. Andreotti17, F. Archilli13, P.
d’Argent13, J. Arnau Romeu7, A. Artamonov41, M. Artuso63, K. Arzymatov38, E.
Aslanides7, M. Atzeni46, B. Audurier23, S. Bachmann13, J.J. Back52, S.
Baker57, V. Balagura8,b, W. Baldini17,44, A. Baranov38, R.J. Barlow58, S.
Barsuk8, W. Barter57, M. Bartolini20,44,h, F. Baryshnikov74, G. Bassi25, V.
Batozskaya32, B. Batsukh63, A. Battig11, V. Battista45, A. Bay45, M. Becker11,
F. Bedeschi25, I. Bediaga1, A. Beiter63, L.J. Bel28, V. Belavin38, S. Belin23,
N. Beliy66, V. Bellee45, K. Belous41, I. Belyaev35, E. Ben-Haim9, G.
Bencivenni19, S. Benson28, S. Beranek10, A. Berezhnoy36, R. Bernet46, D.
Berninghoff13, H.C. Bernstein63, E. Bertholet9, A. Bertolin24, C.
Betancourt46, F. Betti16,e, M.O. Bettler51, M. van Beuzekom28, Ia.
Bezshyiko46, S. Bhasin50, J. Bhom30, M.S. Bieker11, S. Bifani49, P. Billoir9,
A. Bizzeti18,u, M. Bjørn59, M.P. Blago44, T. Blake52, F. Blanc45, S. Blusk63,
D. Bobulska55, V. Bocci27, O. Boente Garcia43, T. Boettcher60, A. Boldyrev39,
A. Bondar40,x, N. Bondar34, S. Borghi58,44, M. Borisyak38, M. Borsato13, J.T.
Borsuk30, T.J.V. Bowcock56, C. Bozzi17, S. Braun13, A. Brea Rodriguez43, M.
Brodski44, J. Brodzicka30, A. Brossa Gonzalo52, D. Brundu23, E. Buchanan50, A.
Buonaura46, C. Burr44, A. Bursche23, J.S. Butter28, J. Buytaert44, W.
Byczynski44, S. Cadeddu23, H. Cai68, R. Calabrese17,g, L. Calero Diaz19, S.
Cali19, R. Calladine49, M. Calvi21,i, M. Calvo Gomez42,m, A. Camboni42, P.
Campana19, D.H. Campora Perez44, L. Capriotti16,e, A. Carbone16,e, G.
Carboni26, R. Cardinale20,h, A. Cardini23, P. Carniti21,i, K. Carvalho
Akiba28, A. Casais Vidal43, G. Casse56, M. Cattaneo44, G. Cavallero44, R.
Cenci25,p, J. Cerasoli7, M.G. Chapman50, M. Charles9,44, Ph. Charpentier44, G.
Chatzikonstantinidis49, M. Chefdeville5, V. Chekalina38, C. Chen3, S. Chen23,
A. Chernov30, S.-G. Chitic44, V. Chobanova43, M. Chrzaszcz44, A. Chubykin34,
P. Ciambrone19, M.F. Cicala52, X. Cid Vidal43, G. Ciezarek44, F. Cindolo16,
P.E.L. Clarke54, M. Clemencic44, H.V. Cliff51, J. Closier44, J.L.
Cobbledick58, V. Coco44, J.A.B. Coelho8, J. Cogan7, E. Cogneras6, L.
Cojocariu33, P. Collins44, T. Colombo44, A. Comerma-Montells13, A. Contu23, N.
Cooke49, G. Coombs55, S. Coquereau42, G. Corti44, C.M. Costa Sobral52, B.
Couturier44, D.C. Craik60, J. Crkovska78, A. Crocombe52, M. Cruz Torres1, R.
Currie54, C. D’Ambrosio44, C.L. Da Silva78, E. Dall’Occo28, J. Dalseno43,50,
A. Danilina35, A. Davis58, O. De Aguiar Francisco44, K. De Bruyn44, S. De
Capua58, M. De Cian45, J.M. De Miranda1, L. De Paula2, M. De Serio15,d, P. De
Simone19, C.T. Dean78, W. Dean77, D. Decamp5, L. Del Buono9, B. Delaney51,
H.-P. Dembinski12, M. Demmer11, A. Dendek31, V. Denysenko46, D. Derkach39, O.
Deschamps6, F. Desse8, F. Dettori23, B. Dey69, A. Di Canto44, P. Di Nezza19,
S. Didenko74, H. Dijkstra44, F. Dordei23, M. Dorigo25,y, L. Douglas55, A.
Dovbnya47, K. Dreimanis56, M.W. Dudek30, L. Dufour44, G. Dujany9, P.
Durante44, J.M. Durham78, D. Dutta58, R. Dzhelyadin41,†, M. Dziewiecki13, A.
Dziurda30, A. Dzyuba34, S. Easo53, U. Egede57, V. Egorychev35, S.
Eidelman40,x, S. Eisenhardt54, S. Ek-In45, R. Ekelhof11, L. Eklund55, S.
Ely63, A. Ene33, S. Escher10, S. Esen28, T. Evans44, A. Falabella16, J. Fan3,
N. Farley49, S. Farry56, D. Fazzini8, P. Fernandez Declara44, A. Fernandez
Prieto43, F. Ferrari16,e, L. Ferreira Lopes45, F. Ferreira Rodrigues2, S.
Ferreres Sole28, M. Ferrillo46, M. Ferro-Luzzi44, S. Filippov37, R.A. Fini15,
M. Fiorini17,g, M. Firlej31, K.M. Fischer59, C. Fitzpatrick44, T. Fiutowski31,
F. Fleuret8,b, M. Fontana44, F. Fontanelli20,h, R. Forty44, V. Franco Lima56,
M. Franco Sevilla62, M. Frank44, C. Frei44, D.A. Friday55, J. Fu22,q, M.
Fuehring11, W. Funk44, M. Féo44, E. Gabriel54, A. Gallas Torreira43, D.
Galli16,e, S. Gallorini24, S. Gambetta54, Y. Gan3, M. Gandelman2, P.
Gandini22, Y. Gao3, L.M. Garcia Martin76, B. Garcia Plana43, F.A. Garcia
Rosales8, J. García Pardiñas46, J. Garra Tico51, L. Garrido42, D. Gascon42, C.
Gaspar44, D. Gerick13, E. Gersabeck58, M. Gersabeck58, T. Gershon52, D.
Gerstel7, Ph. Ghez5, V. Gibson51, A. Gioventù43, O.G. Girard45, P. Gironella
Gironell42, L. Giubega33, C. Giugliano17, K. Gizdov54, V.V. Gligorov9, D.
Golubkov35, A. Golutvin57,74, A. Gomes1,a, P. Gorbounov35,4, I.V. Gorelov36,
C. Gotti21,i, E. Govorkova28, J.P. Grabowski13, R. Graciani Diaz42, T.
Grammatico9, L.A. Granado Cardoso44, E. Graugés42, E. Graverini45, G.
Graziani18, A. Grecu33, R. Greim28, P. Griffith17, L. Grillo58, L. Gruber44,
B.R. Gruberg Cazon59, C. Gu3, X. Guo67, E. Gushchin37, A. Guth10, Yu.
Guz41,44, T. Gys44, C. Göbel65, T. Hadavizadeh59, G. Haefeli45, C. Haen44,
S.C. Haines51, P.M. Hamilton62, Q. Han69, X. Han13, T.H. Hancock59, S.
Hansmann-Menzemer13, N. Harnew59, T. Harrison56, R. Hart28, C. Hasse44, M.
Hatch44, J. He66, M. Hecker57, K. Heijhoff28, K. Heinicke11, A. Heister11,
A.M. Hennequin44, K. Hennessy56, L. Henry76, E. van Herwijnen44, J. Heuel10,
A. Hicheur64, R. Hidalgo Charman58, D. Hill59, M. Hilton58, P.H. Hopchev45, J.
Hu13, W. Hu69, W. Huang66, W. Hulsbergen28, T. Humair57, R.J. Hunter52, M.
Hushchyn39, D. Hutchcroft56, D. Hynds28, P. Ibis11, M. Idzik31, P. Ilten49, A.
Inglessi34, A. Inyakin41, K. Ivshin34, R. Jacobsson44, S. Jakobsen44, J.
Jalocha59, E. Jans28, B.K. Jashal76, A. Jawahery62, V. Jevtic11, F. Jiang3, M.
John59, D. Johnson44, C.R. Jones51, B. Jost44, N. Jurik59, S. Kandybei47, M.
Karacson44, J.M. Kariuki50, N. Kazeev39, M. Kecke13, F. Keizer51, M. Kelsey63,
M. Kenzie51, T. Ketel29, B. Khanji44, A. Kharisova75, K.E. Kim63, T. Kirn10,
V.S. Kirsebom45, S. Klaver19, K. Klimaszewski32, S. Koliiev48, A.
Kondybayeva74, A. Konoplyannikov35, P. Kopciewicz31, R. Kopecna13, P.
Koppenburg28, I. Kostiuk28,48, O. Kot48, S. Kotriakhova34, L. Kravchuk37, R.D.
Krawczyk44, M. Kreps52, F. Kress57, S. Kretzschmar10, P. Krokovny40,x, W.
Krupa31, W. Krzemien32, W. Kucewicz30,l, M. Kucharczyk30, V. Kudryavtsev40,x,
H.S. Kuindersma28, G.J. Kunde78, A.K. Kuonen45, T. Kvaratskheliya35, D.
Lacarrere44, G. Lafferty58, A. Lai23, D. Lancierini46, J.J. Lane58, G.
Lanfranchi19, C. Langenbruch10, T. Latham52, F. Lazzari25,v, C. Lazzeroni49,
R. Le Gac7, A. Leflat36, R. Lefèvre6, F. Lemaitre44, O. Leroy7, T. Lesiak30,
B. Leverington13, H. Li67, X. Li78, Y. Li4, Z. Li63, X. Liang63, R. Lindner44,
P. Ling67, F. Lionetto46, V. Lisovskyi8, G. Liu67, X. Liu3, D. Loh52, A.
Loi23, J. Lomba Castro43, I. Longstaff55, J.H. Lopes2, G. Loustau46, G.H.
Lovell51, Y. Lu4, D. Lucchesi24,o, M. Lucio Martinez28, Y. Luo3, A. Lupato24,
E. Luppi17,g, O. Lupton52, A. Lusiani25, X. Lyu66, R. Ma67, S. Maccolini16,e,
F. Machefert8, F. Maciuc33, V. Macko45, P. Mackowiak11, S. Maddrell-Mander50,
L.R. Madhan Mohan50, O. Maev34,44, A. Maevskiy39, K. Maguire58, D.
Maisuzenko34, M.W. Majewski31, S. Malde59, B. Malecki44, A. Malinin73, T.
Maltsev40,x, H. Malygina13, G. Manca23,f, G. Mancinelli7, R. Manera
Escalero42, D. Manuzzi16,e, D. Marangotto22,q, J. Maratas6,w, J.F. Marchand5,
U. Marconi16, S. Mariani18, C. Marin Benito8, M. Marinangeli45, P. Marino45,
J. Marks13, P.J. Marshall56, G. Martellotti27, L. Martinazzoli44, M.
Martinelli21, D. Martinez Santos43, F. Martinez Vidal76, A. Massafferri1, M.
Materok10, R. Matev44, A. Mathad46, Z. Mathe44, V. Matiunin35, C. Matteuzzi21,
K.R. Mattioli77, A. Mauri46, E. Maurice8,b, M. McCann57,44, L. Mcconnell14, A.
McNab58, R. McNulty14, J.V. Mead56, B. Meadows61, C. Meaux7, G. Meier11, N.
Meinert71, D. Melnychuk32, S. Meloni21,i, M. Merk28, A. Merli22, M.
Mikhasenko44, D.A. Milanes70, E. Millard52, M.-N. Minard5, O. Mineev35, L.
Minzoni17,g, S.E. Mitchell54, B. Mitreska58, D.S. Mitzel44, A. Mogini9, R.D.
Moise57, T. Mombächer11, I.A. Monroy70, S. Monteil6, M. Morandin24, G.
Morello19, M.J. Morello25,t, J. Moron31, A.B. Morris7, A.G. Morris52, R.
Mountain63, H. Mu3, F. Muheim54, M. Mukherjee69, M. Mulder28, C.H. Murphy59,
D. Murray58, P. Muzzetto23, A. Mödden 11, D. Müller44, K. Müller46, V.
Müller11, P. Naik50, T. Nakada45, R. Nandakumar53, A. Nandi59, T. Nanut45, I.
Nasteva2, M. Needham54, N. Neri22,q, S. Neubert13, N. Neufeld44, R.
Newcombe57, T.D. Nguyen45, C. Nguyen-Mau45,n, E.M. Niel8, S. Nieswand10, N.
Nikitin36, N.S. Nolte44, C. Nunez77, D.P. O’Hanlon16, A. Oblakowska-Mucha31,
V. Obraztsov41, S. Ogilvy55, R. Oldeman23,f, C.J.G. Onderwater72, J. D.
Osborn77, A. Ossowska30, J.M. Otalora Goicochea2, T. Ovsiannikova35, P.
Owen46, A. Oyanguren76, P.R. Pais45, T. Pajero25,t, A. Palano15, M. Palutan19,
G. Panshin75, A. Papanestis53, M. Pappagallo54, L.L. Pappalardo17,g, C.
Pappenheimer61, W. Parker62, C. Parkes58,44, G. Passaleva18,44, A. Pastore15,
M. Patel57, C. Patrignani16,e, A. Pearce44, A. Pellegrino28, M. Pepe
Altarelli44, S. Perazzini16, D. Pereima35, P. Perret6, L. Pescatore45, K.
Petridis50, A. Petrolini20,h, A. Petrov73, S. Petrucci54, M. Petruzzo22,q, B.
Pietrzyk5, G. Pietrzyk45, M. Pikies30, M. Pili59, D. Pinci27, J. Pinzino44, F.
Pisani44, A. Piucci13, V. Placinta33, S. Playfer54, J. Plews49, M. Plo
Casasus43, F. Polci9, M. Poli Lener19, M. Poliakova63, A. Poluektov7, N.
Polukhina74,c, I. Polyakov63, E. Polycarpo2, G.J. Pomery50, S. Ponce44, A.
Popov41, D. Popov49, S. Poslavskii41, K. Prasanth30, L. Promberger44, C.
Prouve43, V. Pugatch48, A. Puig Navarro46, H. Pullen59, G. Punzi25,p, W.
Qian66, J. Qin66, R. Quagliani9, B. Quintana6, N.V. Raab14, R.I. Rabadan
Trejo7, B. Rachwal31, J.H. Rademacker50, M. Rama25, M. Ramos Pernas43, M.S.
Rangel2, F. Ratnikov38,39, G. Raven29, M. Ravonel Salzgeber44, M. Reboud5, F.
Redi45, S. Reichert11, A.C. dos Reis1, F. Reiss9, C. Remon Alepuz76, Z. Ren3,
V. Renaudin59, S. Ricciardi53, S. Richards50, K. Rinnert56, P. Robbe8, A.
Robert9, A.B. Rodrigues45, E. Rodrigues61, J.A. Rodriguez Lopez70, M.
Roehrken44, S. Roiser44, A. Rollings59, V. Romanovskiy41, M. Romero Lamas43,
A. Romero Vidal43, J.D. Roth77, M. Rotondo19, M.S. Rudolph63, T. Ruf44, J.
Ruiz Vidal76, J. Ryzka31, J.J. Saborido Silva43, N. Sagidova34, B. Saitta23,f,
C. Sanchez Gras28, C. Sanchez Mayordomo76, B. Sanmartin Sedes43, R.
Santacesaria27, C. Santamarina Rios43, M. Santimaria19, E. Santovetti26,j, G.
Sarpis58, A. Sarti27, C. Satriano27,s, A. Satta26, M. Saur66, D. Savrina35,36,
L.G. Scantlebury Smead59, S. Schael10, M. Schellenberg11, M. Schiller55, H.
Schindler44, M. Schmelling12, T. Schmelzer11, B. Schmidt44, O. Schneider45, A.
Schopper44, H.F. Schreiner61, M. Schubiger28, S. Schulte45, M.H. Schune8, R.
Schwemmer44, B. Sciascia19, A. Sciubba27,k, S. Sellam64, A. Semennikov35, A.
Sergi49,44, N. Serra46, J. Serrano7, L. Sestini24, A. Seuthe11, P. Seyfert44,
D.M. Shangase77, M. Shapkin41, T. Shears56, L. Shekhtman40,x, V.
Shevchenko73,74, E. Shmanin74, J.D. Shupperd63, B.G. Siddi17, R. Silva
Coutinho46, L. Silva de Oliveira2, G. Simi24,o, S. Simone15,d, I. Skiba17, N.
Skidmore13, T. Skwarnicki63, M.W. Slater49, J.G. Smeaton51, A. Smetkina35, E.
Smith10, I.T. Smith54, M. Smith57, A. Snoch28, M. Soares16, L. Soares Lavra1,
M.D. Sokoloff61, F.J.P. Soler55, B. Souza De Paula2, B. Spaan11, E. Spadaro
Norella22,q, P. Spradlin55, F. Stagni44, M. Stahl61, S. Stahl44, P. Stefko45,
S. Stefkova57, O. Steinkamp46, S. Stemmle13, O. Stenyakin41, M. Stepanova34,
H. Stevens11, A. Stocchi8, S. Stone63, S. Stracka25, M.E. Stramaglia45, M.
Straticiuc33, S. Strokov75, J. Sun3, L. Sun68, Y. Sun62, P. Svihra58, K.
Swientek31, A. Szabelski32, T. Szumlak31, M. Szymanski66, S. T’Jampens5, S.
Taneja58, Z. Tang3, T. Tekampe11, G. Tellarini17, F. Teubert44, E. Thomas44,
K.A. Thomson56, J. van Tilburg28, M.J. Tilley57, V. Tisserand6, M. Tobin4, S.
Tolk44, L. Tomassetti17,g, D. Tonelli25, D.Y. Tou9, E. Tournefier5, M.
Traill55, M.T. Tran45, C. Trippl45, A. Trisovic51, A. Tsaregorodtsev7, G.
Tuci25,44,p, A. Tully45, N. Tuning28, A. Ukleja32, D.J. Unverzagt13, A.
Usachov8, A. Ustyuzhanin38,39, U. Uwer13, A. Vagner75, V. Vagnoni16, A.
Valassi44, G. Valenti16, H. Van Hecke78, C.B. Van Hulse14, R. Vazquez Gomez42,
P. Vazquez Regueiro43, S. Vecchi17, M. van Veghel72, J.J. Velthuis50, M.
Veltri18,r, A. Venkateswaran63, M. Vernet6, M. Veronesi28, M. Vesterinen52,
J.V. Viana Barbosa44, D. Vieira66, M. Vieites Diaz45, H. Viemann71, X.
Vilasis-Cardona42,m, A. Vitkovskiy28, V. Volkov36, A. Vollhardt46, D. Vom
Bruch9, A. Vorobyev34, V. Vorobyev40,x, N. Voropaev34, J.A. de Vries28, C.
Vázquez Sierra28, R. Waldi71, J. Walsh25, J. Wang4, J. Wang3, J. Wang68, M.
Wang3, Y. Wang69, Z. Wang46, D.R. Ward51, H.M. Wark56, N.K. Watson49, D.
Websdale57, A. Weiden46, C. Weisser60, B.D.C. Westhenry50, D.J. White58, M.
Whitehead10, D. Wiedner11, G. Wilkinson59, M. Wilkinson63, I. Williams51,
M.R.J. Williams58, M. Williams60, T. Williams49, F.F. Wilson53, M. Winn8, W.
Wislicki32, M. Witek30, G. Wormser8, S.A. Wotton51, H. Wu63, K. Wyllie44, Z.
Xiang66, D. Xiao69, Y. Xie69, H. Xing67, A. Xu3, L. Xu3, M. Xu69, Q. Xu66, Z.
Xu3, Z. Xu5, Z. Yang3, Z. Yang62, Y. Yao63, L.E. Yeomans56, H. Yin69, J.
Yu69,aa, X. Yuan63, O. Yushchenko41, K.A. Zarebski49, M. Zavertyaev12,c, M.
Zdybal30, M. Zeng3, D. Zhang69, L. Zhang3, S. Zhang3, W.C. Zhang3,z, Y.
Zhang44, A. Zhelezov13, Y. Zheng66, X. Zhou66, Y. Zhou66, X. Zhu3, V.
Zhukov10,36, J.B. Zonneveld54, S. Zucchelli16,e.

1Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil
2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3Center for High Energy Physics, Tsinghua University, Beijing, China
4Institute Of High Energy Physics (IHEP), Beijing, China
5Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IN2P3-LAPP, Annecy,
France
6Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
7Aix Marseille Univ, CNRS/IN2P3, CPPM, Marseille, France
8LAL, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France
9LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3,
Paris, France
10I. Physikalisches Institut, RWTH Aachen University, Aachen, Germany
11Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
12Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany
13Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
14School of Physics, University College Dublin, Dublin, Ireland
15INFN Sezione di Bari, Bari, Italy
16INFN Sezione di Bologna, Bologna, Italy
17INFN Sezione di Ferrara, Ferrara, Italy
18INFN Sezione di Firenze, Firenze, Italy
19INFN Laboratori Nazionali di Frascati, Frascati, Italy
20INFN Sezione di Genova, Genova, Italy
21INFN Sezione di Milano-Bicocca, Milano, Italy
22INFN Sezione di Milano, Milano, Italy
23INFN Sezione di Cagliari, Monserrato, Italy
24INFN Sezione di Padova, Padova, Italy
25INFN Sezione di Pisa, Pisa, Italy
26INFN Sezione di Roma Tor Vergata, Roma, Italy
27INFN Sezione di Roma La Sapienza, Roma, Italy
28Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands
29Nikhef National Institute for Subatomic Physics and VU University Amsterdam,
Amsterdam, Netherlands
30Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of
Sciences, Kraków, Poland
31AGH - University of Science and Technology, Faculty of Physics and Applied
Computer Science, Kraków, Poland
32National Center for Nuclear Research (NCBJ), Warsaw, Poland
33Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest-Magurele, Romania
34Petersburg Nuclear Physics Institute NRC Kurchatov Institute (PNPI NRC KI),
Gatchina, Russia
35Institute of Theoretical and Experimental Physics NRC Kurchatov Institute
(ITEP NRC KI), Moscow, Russia, Moscow, Russia
36Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow,
Russia
37Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS),
Moscow, Russia
38Yandex School of Data Analysis, Moscow, Russia
39National Research University Higher School of Economics, Moscow, Russia
40Budker Institute of Nuclear Physics (SB RAS), Novosibirsk, Russia
41Institute for High Energy Physics NRC Kurchatov Institute (IHEP NRC KI),
Protvino, Russia, Protvino, Russia
42ICCUB, Universitat de Barcelona, Barcelona, Spain
43Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de
Santiago de Compostela, Santiago de Compostela, Spain
44European Organization for Nuclear Research (CERN), Geneva, Switzerland
45Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL),
Lausanne, Switzerland
46Physik-Institut, Universität Zürich, Zürich, Switzerland
47NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
48Institute for Nuclear Research of the National Academy of Sciences (KINR),
Kyiv, Ukraine
49University of Birmingham, Birmingham, United Kingdom
50H.H. Wills Physics Laboratory, University of Bristol, Bristol, United
Kingdom
51Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
52Department of Physics, University of Warwick, Coventry, United Kingdom
53STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
54School of Physics and Astronomy, University of Edinburgh, Edinburgh, United
Kingdom
55School of Physics and Astronomy, University of Glasgow, Glasgow, United
Kingdom
56Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
57Imperial College London, London, United Kingdom
58Department of Physics and Astronomy, University of Manchester, Manchester,
United Kingdom
59Department of Physics, University of Oxford, Oxford, United Kingdom
60Massachusetts Institute of Technology, Cambridge, MA, United States
61University of Cincinnati, Cincinnati, OH, United States
62University of Maryland, College Park, MD, United States
63Syracuse University, Syracuse, NY, United States
64Laboratory of Mathematical and Subatomic Physics , Constantine, Algeria,
associated to 2
65Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de
Janeiro, Brazil, associated to 2
66University of Chinese Academy of Sciences, Beijing, China, associated to 3
67South China Normal University, Guangzhou, China, associated to 3
68School of Physics and Technology, Wuhan University, Wuhan, China, associated
to 3
69Institute of Particle Physics, Central China Normal University, Wuhan,
Hubei, China, associated to 3
70Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia,
associated to 9
71Institut für Physik, Universität Rostock, Rostock, Germany, associated to 13
72Van Swinderen Institute, University of Groningen, Groningen, Netherlands,
associated to 28
73National Research Centre Kurchatov Institute, Moscow, Russia, associated to
35
74National University of Science and Technology “MISIS”, Moscow, Russia,
associated to 35
75National Research Tomsk Polytechnic University, Tomsk, Russia, associated to
35
76Instituto de Fisica Corpuscular, Centro Mixto Universidad de Valencia -
CSIC, Valencia, Spain, associated to 42
77University of Michigan, Ann Arbor, United States, associated to 63
78Los Alamos National Laboratory (LANL), Los Alamos, United States, associated
to 63

aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil
bLaboratoire Leprince-Ringuet, Palaiseau, France
cP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS),
Moscow, Russia
dUniversità di Bari, Bari, Italy
eUniversità di Bologna, Bologna, Italy
fUniversità di Cagliari, Cagliari, Italy
gUniversità di Ferrara, Ferrara, Italy
hUniversità di Genova, Genova, Italy
iUniversità di Milano Bicocca, Milano, Italy
jUniversità di Roma Tor Vergata, Roma, Italy
kUniversità di Roma La Sapienza, Roma, Italy
lAGH - University of Science and Technology, Faculty of Computer Science,
Electronics and Telecommunications, Kraków, Poland
mLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
nHanoi University of Science, Hanoi, Vietnam
oUniversità di Padova, Padova, Italy
pUniversità di Pisa, Pisa, Italy
qUniversità degli Studi di Milano, Milano, Italy
rUniversità di Urbino, Urbino, Italy
sUniversità della Basilicata, Potenza, Italy
tScuola Normale Superiore, Pisa, Italy
uUniversità di Modena e Reggio Emilia, Modena, Italy
vUniversità di Siena, Siena, Italy
wMSU - Iligan Institute of Technology (MSU-IIT), Iligan, Philippines
xNovosibirsk State University, Novosibirsk, Russia
ySezione INFN di Trieste, Trieste, Italy
zSchool of Physics and Information Technology, Shaanxi Normal University
(SNNU), Xi’an, China
aaPhysics and Micro Electronic College, Hunan University, Changsha City, China
†Deceased