EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-EP-2016-006 LHCb-PAPER-2015-033 January 20, 2016

Observation of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 2.07352pt\phi$ decay

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

The ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay is observed in $pp$ collision data
corresponding to an integrated luminosity of 3$\mbox{\,fb}^{-1}$ recorded by
the LHCb detector at centre-of-mass energies of
7$\mathrm{\,Te\kern-1.00006ptV}$ and 8$\mathrm{\,Te\kern-1.00006ptV}$. This is
the first observation of this decay channel, with a statistical significance
of 15 standard deviations. The mass of the ${B}^{0}_{s}$ meson is measured to
be
$5367.08\,\\!\pm\,\\!0.38\,\\!\pm\,\\!0.15{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$.
The branching fraction ratio ${\cal
B}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi)/{\cal
B}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)$ is measured to be
$0.0115\,\\!\pm\,\\!0.0012\;^{+0.0005}_{-0.0009}$. In both cases, the first
uncertainty is statistical and the second is systematic. No evidence for non-
resonant ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt{{K}^{+}}{{K}^{-}}$ or
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\kern 1.19995pt{{K}^{+}}{{K}^{-}}{{K}^{+}}{{K}^{-}}$ decays is found.

Published in JHEP 03 (2016) 040

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

##  1 Introduction

The study of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay, previously unobserved, allows a precise
measurement of the ${B}^{0}_{s}$ meson mass and a search for possible
resonances in the $\phi\,\phi$ and ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ invariant mass spectra, similar to what has been reported for the
$B^{+}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\,\phi\,K^{+}\;$ decay mode [1, 2, 3] (the inclusion of charge
conjugate processes is implied throughout). The most recent theoretical
predictions for heavy hadron masses, based on lattice QCD calculations, can be
found in Refs. [4, 5, 6]. The current experimental knowledge of the
${B}^{0}_{s}$ mass, as summarized in Ref. [7], is dominated by results from
the LHCb experiment [8], which were obtained with the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay using a small fraction of the integrated luminosity
collected in the 2010–2012 LHC run. The ${B}^{0}_{s}$ mass measurement using
this decay is limited by the precision of the momentum scale. The
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay mode is a good alternative to
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ since the kinetic energy available to the final-state particles
($Q$-value) is much lower, leading to a 65% reduction in the systematic
uncertainty arising from the precision of the momentum scale.

The ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay is also of interest in searches for
intermediate states in the ${B}^{0}_{s}$ decay chain. In recent years, many
new charmonium or charmonium-like states have been discovered, which are not
easily accommodated in the quark model of hadrons [9, 10]. In a study of
$B^{+}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi\,K^{+}$
decays, the CDF collaboration reported evidence for a state, in the
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\,\phi$ invariant mass
spectrum, called $Y(4140)$ with mass and width values of $m=4143.0\pm
2.9\,(\mathrm{stat})\pm
1.2\,(\mathrm{syst})~{}\\!{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ and
$\Gamma=11.7^{+8.3}_{-5.0}\,(\mathrm{stat})\pm
3.7\,(\mathrm{syst})~{}\\!\mathrm{\,Me\kern-1.00006ptV}$ [3]. The Belle and
BaBar collaborations searched for the $Y(4140)$ using the same ${{B}^{+}}$
decay mode [11, 1] and found no significant signal, although the upper limits
on the production rate did not contradict the CDF measurement. Recently, the
D0 collaboration reported a similar structure [12]. At the LHC, both the LHCb
and CMS collaborations have searched for the state in question. The LHCb
collaboration found no evidence with 0.37$\mbox{\,fb}^{-1}$ of $pp$ collision
data [2], in $2.4\,\sigma$ disagreement with the CDF measurement. A CMS search
for the same signature [13] supports the CDF observation. With two out of five
experiments failing to observe the $Y(4140)$ resonance the question of its
existence still remains open. The search for resonances in the $\phi\,\phi$
invariant mass spectrum is also of interest. Several experiments have reported
a near-threshold enhancement in the $\phi\,\phi$ invariant mass distribution
from the $J/\psi\rightarrow\gamma\,\phi\,\phi$ decay [14, 15, 16]. A partial-
wave analysis showed that the structure is dominated by a $0^{-+}$ state
called $\eta(2225)$. This resonance is still controversial and its observation
in a different decay mode would be conclusive.

Theoretical predictions of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ branching fraction are difficult due to the
presence of three vector mesons in the final states. The
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay is the ${B}^{0}_{s}$ counterpart of the
measured $B^{+}\rightarrow J/\psi\,\phi\,K^{+}$ and $B^{0}\rightarrow
J/\psi\,\phi\,K^{0}$ decays [17]. All these channels are strongly suppressed
with respect to the similar decays without the additional $\phi$ meson in the
final state. The suppression factors of the last two channels are $0.048\pm
0.004$ and $0.057\pm 0.012$ for the charged and neutral decays [7]. A
qualitative comparison with these branching fractions can be done considering
that the phase space of the decay
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ is smaller by a factor of seven, so the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ branching fraction is expected to be $\sim
10^{-5}$.

This paper presents the first observation of the decay
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ and the decay branching fraction measurement
with respect to the reference decay
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$. A measurement of the ${B}^{0}_{s}$ mass is also presented. The
data sample corresponds to an integrated luminosity of 3.0$\mbox{\,fb}^{-1}$
$pp$ collisions collected by the LHCb experiment. The data were recorded in
the years 2011 and 2012 at centre-of-mass energies of
7$\mathrm{\,Te\kern-1.00006ptV}$ and 8$\mathrm{\,Te\kern-1.00006ptV}$,
respectively.

##  2 The LHCb detector

The LHCb detector [18, 19] 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 $4{\rm\,Tm}$, and three stations
of silicon-strip detectors and straw drift tubes placed downstream of the
magnet. The polarity of the dipole magnet is reversed periodically throughout
data-taking. The tracking system provides a measurement of momentum, $p$, of
charged particles with a relative uncertainty that varies from 0.5% at low
momentum to 1.0% at 200${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The minimum
distance of a track to a primary vertex (PV), the impact parameter, is
measured with a resolution of $(15+29/\mbox{$p_{\rm T}$}){\,\upmu\rm m}$,
where $p_{\rm T}$ is the component of the momentum transverse to the beam, in
${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. Different types of charged hadrons are
distinguished using information from two ring-imaging Cherenkov detectors.
Photons, electrons and hadrons are identified by a calorimeter system
consisting of scintillating-pad and preshower detectors, an electromagnetic
calorimeter and a hadronic calorimeter. Muons are identified by a system
composed of alternating layers of iron and multiwire proportional chambers.
The online event selection is performed by a trigger, which consists of a
hardware stage, based on information from the calorimeter and muon systems,
followed by a software stage, which applies a full event reconstruction.

Simulated events are used to determine trigger, reconstruction and selection
efficiencies and reconstructed mass distributions. In addition, simulated
samples are used to estimate possible peaking backgrounds from $B$ meson
decays that can mimic the ${{B}^{0}_{s}}\rightarrow J/\psi\,\phi\,(\phi)$
final states. In the simulation, $pp$ collisions are generated using Pythia 6
[20] with a specific LHCb configuration [21]. Decays of hadronic particles are
described by EvtGen [22], in which final-state radiation is generated using
Photos [23]. The interaction of the generated particles with the detector, and
its response, are implemented using the Geant4 toolkit [24,
*Agostinelli:2002hh] as described in Ref. [26].

##  3 Event selection

The final states of the signal and reference channels differ only by the
presence of an extra $\phi$ meson in the former mode. The selections of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ and
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ candidates are done in almost the same way, allowing a partial
cancellation of systematic uncertainties in the evaluation of the efficiency
ratio. The ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ meson is
reconstructed in the $J/\psi\rightarrow\mu^{+}\mu^{-}$ decay while the $\phi$
meson is reconstructed in the $\phi\rightarrow K^{+}K^{-}$ decay.

Events are selected by the hardware triggers requiring a single muon with
transverse momentum $p_{\rm T}$ $>1.48{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ or
a muon pair with product of transverse momenta greater than
$(1.3{\mathrm{\,Ge\kern-1.00006ptV\\!/}c})^{2}$. At the first stage of the
software trigger, events are selected that contain two muon tracks with
$p_{\rm T}$ $>$ 0.5 GeV/c and invariant mass
$m(\mu^{+}\mu^{-})>2.7{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$, or a single
muon track with $\mbox{$p_{\rm T}$}>1{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and
$\chi^{2}_{\rm IP}>16$ with respect to any PV. The quantity $\chi^{2}_{\rm
IP}$ is the difference between the $\chi^{2}$ values of a given PV
reconstructed with and without the track considered. The second stage of the
software trigger selects a muon pair with an invariant mass that is consistent
with the known ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ mass [7]. The
decay length significance of the reconstructed
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ candidate, $S_{L}$, is required
to be greater than 3, where $S_{L}$ is the distance between the
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ vertex and the PV, divided by
its uncertainty.

The offline analysis uses a cut-based preselection, followed by a multivariate
analysis. In the preselection all the tracks are required to have a good-
quality track fit. In the $\phi\rightarrow K^{+}K^{-}$ decay reconstruction,
kaons are selected with $p>3{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and
$\mbox{$p_{\rm T}$}>200{\mathrm{\,Me\kern-1.00006ptV\\!/}c}$, and the vertex
is required to have a good-quality fit. Particle identification (PID) is
performed using information from all the subdetectors. A loose requirement is
applied to the PID discriminant of kaons with respect to the pion
misidentification $\mathrm{DLL}_{{K}{\pi}}>0$, where
$\mathrm{DLL}_{x{\pi}}=\ln\mathcal{L}_{x}-\ln\mathcal{L}_{\pi}$ is the delta-
log-likelihood for the $x$ particle hypothesis with respect to the pion. For
the ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\rightarrow\mu^{+}\mu^{-}$
decay, the two muons are required to have
$p>5{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and to satisfy a loose PID
selection, $\mathrm{DLL}_{{\mu}\pi}>-1$. The invariant mass of the
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ candidate is required to be in
the interval [3036, 3156]${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$,
corresponding to a $\pm 4\sigma$ interval around the nominal mass of the
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ meson [7]. To select the final
$B^{0}_{s}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\,(\phi)$ decay, the $\phi$ and
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ meson candidates are required
to pass the selection cuts $\mbox{$p_{\rm
T}$}(\phi)>300{\mathrm{\,Me\kern-1.00006ptV\\!/}c}$ and $\mbox{$p_{\rm
T}$}({{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}})>400{\mathrm{\,Me\kern-1.00006ptV\\!/}c}$, and to form a good-quality
displaced vertex. The collinearity angle, defined as the angle between the
reconstructed ${B}^{0}_{s}$ momentum and the flight direction determined from
the secondary vertex, is required to be smaller than 1.8°. In the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay selection, to reduce the contamination from non-resonant
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\kern 1.19995pt{{K}^{+}}{{K}^{-}}$ decays, the dikaon invariant mass is
required to be in the range [980,
1080]${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. To improve the mass and
decay-time resolutions, a kinematic fit [27] is applied to both ${B}^{0}_{s}$
decays, constraining the mass of the ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}$ candidate to its known value [7] and the ${B}^{0}_{s}$ momentum to
point to the PV. Finally, the ${B}^{0}_{s}$ candidate invariant mass is
required to be in the interval [5250,
5490]${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$.

Different multivariate selection algorithms, based on a boosted decision tree
(BDT) [28, 29] with the AdaBoost algorithm[30], are used to select the signal
and the reference channel samples. The BDT is trained with simulated
${B}^{0}_{s}$ samples for the signals, while for the background, a sample of
40 million simulated events containing inclusive
$B\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}X$ decays is used.
For the ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay channel, the simulated sample is
generated according to phase space. The BDT input variables are the $p_{\rm
T}$ of the $\phi$ and ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ mesons
and the vertex $\chi^{2}$, flight distance significance, $S_{L}$, collinearity
angle and the impact parameter of the ${B}^{0}_{s}$ meson with respect to the
PV. The BDT discriminant threshold is chosen to maximise the figure of merit,
$\epsilon/(3/2+\sqrt{b})$ [31], where $\epsilon$ is the signal efficiency
determined using simulated events and $b$ is the number of expected background
candidates estimated using mass sideband events in the data. For the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ channel the BDT discriminant is selected to maximize
$s/\sqrt{s+b}$, where $s$ and $b$ are the expected signal and background
yields, estimated from simulated events and sideband data, respectively.

In the ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ selection, no restriction is initially put on
the $K^{+}K^{-}$ system invariant mass, with both the resonant and the non-
resonant $B^{0}_{s}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\,(K^{+}K^{-})\,(K^{+}K^{-})$ selected. If the candidate
$B^{0}_{s}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}(K_{1}^{+}K_{1}^{-})\,(K_{2}^{+}K_{2}^{-})$ passes the selection cuts,
almost always the candidate
$B^{0}_{s}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}(K_{1}^{+}K_{2}^{-})\,(K_{2}^{+}K_{1}^{-})$ also passes the cuts,
resulting in a duplicated candidate. So a genuine resonant
$B^{0}_{s}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi(K^{+}K^{-})\,\phi(K^{+}K^{-})$ event will most of the time produce
also a “fake” non-resonant candidate, given the low probability that the
invariant mass of two wrongly-coupled kaons is around the $\phi$ mass. In
order to remove these “fake” candidates, the $K^{+}K^{-}$ system masses are
required to satisfy
$|m(K^{+}K^{-})-m_{\phi}|<15{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. After
this cut, 1.8% of events contain double candidates. For each of these events,
one candidate is chosen at random. In the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay selection, this ambiguity problem is not present, so a
tight cut on the $|m(K^{+}K^{-})-m_{\phi}|$ is not applied.

##  4 Results

The ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay branching fraction is measured with
respect to the reference decay
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ as

$\frac{\mathcal{B}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern
1.19995pt\phi)}{\mathcal{B}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)}=\frac{N_{\mathrm{obs}}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern
1.19995pt\phi)}{\epsilon({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern
1.19995pt\phi)}\cdot\frac{\epsilon({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)}{N_{\mathrm{obs}}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)}\cdot\frac{1}{\mathcal{B}(\phi\rightarrow K^{+}K^{-})}\,,$

where
$N_{\mathrm{obs}}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi)$ and
$N_{\mathrm{obs}}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)$ are the numbers of observed events and
$\epsilon({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi)$ and
$\epsilon({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)$ are the selection efficiencies.

Figure 1 shows the invariant mass of the reconstructed
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay, for all the candidates surviving the
pre-selection, the BDT and the selection on the $m(K^{+}K^{-})$ around the
$\phi$ mass. In order to evaluate the number of signal decays, an unbinned
extended maximum likelihood fit is performed assuming a Gaussian signal peak
and an exponential combinatorial background. The observed signal yield is
$128\pm 13$ events, where the uncertainty is statistical. Using Wilks’s
theorem [32], the statistical significance is found to be 15 standard
deviations. As expected, the mass resolution is good, $\sigma=3.05\pm
0.41$${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$, due to the low $Q$-value of
the decay.

Figure 1: Invariant mass of reconstructed
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ candidates. The result of the fit to the
distribution is also shown.

In the reference channel, in order to discriminate between the resonant
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ and the non-resonant
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\kern 1.19995pt{{K}^{+}}{{K}^{-}}$ decays, a fit to the $K^{+}K^{-}$
mass spectrum is made, where the combinatorial background in the ${B}^{0}_{s}$
mass window is statistically removed using the sPlot technique [33]. Figure 2
(left) shows the mass distribution of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\kern 1.19995pt{{K}^{+}}{{K}^{-}}$ candidates with the fit results
superimposed. The ${B}^{0}_{s}$ peak is described by a double Crystal Ball
function [34], while the underlying combinatorial background is described by
an exponential function plus a second-order polynomial. Figure 2 (right) shows
the $K^{+}K^{-}$ mass distribution superimposed with the result of the fit.
The fit is performed using a relativistic Breit-Wigner convolved with a
Gaussian resolution function for the $\phi$ signal and a second-order
polynomial for the non-resonant component. The observed
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ yield is $82120\pm 330$ events where the uncertainty is
statistical.

Figure 2: (left) Invariant mass distribution of reconstructed
$B^{0}_{s}\rightarrow J/\psi\,K^{+}K^{-}$ candidates; (right) invariant mass
distribution of the $K^{+}K^{-}$ system, for those candidates which come from
a ${B}^{0}_{s}$ decay. For both distributions, the fit result is shown.

All the efficiencies (detector acceptance, reconstruction, trigger and
selection) are evaluated using the simulated samples together with a data-
driven method [35] for tracking and PID. To check the reliability of the
simulation, a comparison is made between data and simulation for all of the
kinematic variables used in the selection; good agreement is found. Since the
ratio of
$\epsilon$(${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$) over
$\epsilon$(${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$) is evaluated, many systematic effects, related to possible small
deviation of simulation with respect to data, cancel or are significantly
reduced.

The efficiency ratio
$\epsilon({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern
1.19995pt\phi)/\epsilon({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)$ is evaluated to be $0.2778\pm 0.0015$, where the uncertainty is
statistical, due to the limited simulated sample sizes. As expected, the
efficiency of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ channel is lower than that of
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ one, due to the presence of the additional $\phi\rightarrow
K^{+}K^{-}$ decay and the fact that on average the decay products have a
smaller transverse momentum.

From the event yields and the ratio of efficiencies, and using the known
$\phi\rightarrow K^{+}K^{-}$ branching fraction [7], the branching fraction
ratio is measured to be

$\frac{\mathcal{B}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern
1.19995pt\phi)}{\mathcal{B}({{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi)}=0.0115\pm
0.0012\;(\mathrm{stat})\;^{+0.0005}_{-0.0009}\;(\mathrm{syst})\,.$

The systematic uncertainty will be discussed in Section 5.

From the fit to the ${B}^{0}_{s}$ invariant mass distribution in the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay, the mass of the ${B}^{0}_{s}$ meson is
measured to be

$m(B^{0}_{s})=5367.08\pm 0.38\;\mathrm{(stat)}\pm
0.15\;\mathrm{(syst)}{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}.$

The ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi$ and $\phi\,\phi$ mass
distributions are shown in Fig. 3 for both data and simulation. For the data,
the sPlot techique is used to subtract the background from the signal. Since
the ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ process is a decay of a pseudoscalar into
three vector mesons, its accurate description is complex and affected by large
theoretical uncertainty. Here, to simulate the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay, a simple phase-space decay model is
used, which turns out not to provide a satisfactory description of the data.
The disagreement can be due to either intermediate resonances or the
simplified description of the decay. More data are needed to resolve the
issue. Presently, due to the low statistics and the unknown decay dynamics, it
is difficult to draw any conclusions from the two mass distributions.

Figure 3: Invariant mass of the ($\phi,\phi$) (left) and ($J/\psi,\phi$)
(right) pairs, in the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay. In the $J/\psi\,\phi$ plot, for each
candidate two values are calculated, one for each $\phi$ meson. The
distribution of data and simulation (phase space) are shown. To compare the
shape, the two distributions are normalised to the same area.

##  5 Systematic uncertainties

A summary of the systematic uncertainties on the measurement of the branching
fraction ratio is given in Table 1. Since the various effects are
uncorrelated, the total systematic uncertainty is evaluated by adding all
terms in quadrature.

The average multiplicity of
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ candidates in the simulated sample is 1.006
compared to 1.018 of the data. The relative difference (1.2%) is assigned as a
systematic uncertainty.

The use of a simplified decay model affects the determination of the detection
efficiency and introduces some bias in the measurement. In order to evaluate
the effect, the simulated sample is used to study the efficiency of the
selection as a function of the two masses $m(\phi,\phi)$ and $m(J/\psi,\phi)$.
The efficiency is then evaluated in a simulated sample reweighted in such a
way as to reproduce the mass distributions in the data. A relative difference
$\Delta\epsilon/\epsilon=1.0\%$ is found and is assigned as a systematic
uncertainty due to the unknown decay model.

Alternative functions for describing the signal component are tested: double
Gaussian or double Crystal Ball function for the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ and single Gaussian or single Crystal Ball function for
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$. In both cases a negligible change in yields
is observed and therefore no systematic uncertainty is assigned. Conversely,
different choices of the background parametrisation in the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ data can lead to sizeable difference in the results. In order to
estimate a systematic uncertainty, the fits are repeated using an exponential,
a second-order polynomial and the sum of the two (the nominal fit). The
largest difference in yield, 1.6%, between the nominal fit and the fit with
the exponential, is taken as the systematic uncertainty. The same procedure
applied to the signal channel results in a 0.8% change in yield. The two
systematic uncertainties are added in quadrature to give an overall
uncertainty of 1.8% in the modelling of the signal and backgrounds.

To evaluate the contamination from non-resonant
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt{{K}^{+}}{{K}^{-}}$ and $B^{0}_{s}\rightarrow
J/\psi\kern 1.19995ptK^{+}K^{-}K^{+}K^{-}$ decays, a dedicated search is
performed for these two channels in the whole allowed kinematic region
(without any requirement on the $K^{+}K^{-}$ mass). The yields are then
extrapolated to the restricted kinematic region of the signal. For the
$B^{0}_{s}\rightarrow J/\psi\,K^{+}K^{-}K^{+}K^{-}$ decay, the sPlot technique
is first used to select the ${B}^{0}_{s}$ decay and then the two $K^{+}K^{-}$
mass spectra are fitted simultaneously to determine the yield of the fully
resonant decay candidates and the non-resonant ones. The non-resonant
component is the sum of true non-resonant decays plus the candidates obtained
by exchanging the kaons pairings in the resonant decays. When the latter
component is subtracted from the measured yield, the number of non-resonant
candidates is found to be $22\pm 18$. Extrapolating this number to the $\phi$
meson mass region and using the Feldman-Cousins method [36] gives an upper
limit of 1.5 events in the signal region at 68.3% confidence level. A similar
procedure is followed for the $B^{0}_{s}\rightarrow J/\psi\,\phi\,K^{+}K^{-}$
decay. One $K^{+}K^{-}$ pair is required to have the mass in the non-resonant
range, $m(K^{+}K^{-})>1080{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. In these
events, no evidence of a mass peak is found in the mass spectrum
$m(J/\psi\,K^{+}K^{-}K^{+}K^{-})$ nor in the mass spectrum of the other kaon
pair. Using the Feldman-Cousins method an estimated contamination of 6.2
events is found at 68.3% confidence level. The uncertainties on the two non-
resonant modes are added linearly, resulting in an asymmetric relative
uncertainty of $-6\%$.

The data-driven method used to correct the tracking efficiency for the two
additional kaons in the final state of
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ with respect to
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay has an uncertainty of 1.5% per track, resulting in an
overall relative uncertainty of 3.0%. This term also takes into account the
uncertainty of hadronic interactions in the detector material.

Due to the decay time requirement on the selected events, the lack of
knowledge of the admixture of $B^{0}_{sH}$ and $B^{0}_{sL}$ eigenstates in the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay is a further source of systematic
uncertainty [37]. While for the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay the simulation uses the measured fractions of $B^{0}_{sH}$
and $B^{0}_{sL}$ states [38], the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay is simulated assuming a completely
symmetric combination. In order to evaluate the systematic effect, the
simulated sample is reweighted assuming the two extreme cases where the
$B_{s}$ meson is a complete $B^{0}_{sH}$ or a $B^{0}_{sL}$ state. The observed
difference in the efficiency is $2.1\%$ and this number is assigned as the
systematic uncertainty.

A detailed comparison between data and simulation is performed for all the
variables used in the BDT selection. For both the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ and
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay channels, all variables show good agreement and the
relative branching fraction result is stable against changes in the threshold
of the BDT response. The total systematic uncertainty on the ratio of
branching fractions is found to be ${}^{+4.4}_{-7.4}\,\%$.

Table 1: Summary of the relative systematic uncertainties (in percentage) on the branching fraction ratio measurement. Source | Value
---|---
Candidate multiplicity | $\pm 1.2$
Decay model | $\pm 1.0$
Signal and background modelling | $\pm 1.8$
Contamination from non-resonant decays | $-6.0$
Track efficiency | $\pm 3.0$
$B^{0}_{sH}/B^{0}_{sL}$ fractions | $\pm 2.1$
Total | ${}^{+4.4}_{-7.4}$

Table 2 gives a summary of the systematic uncertainties of the ${B}^{0}_{s}$
mass measurement. For the ${B}^{0}_{s}$ mass determination, the momentum scale
calibration is the main source of systematic uncertainty. The momentum scale
takes into account the limited knowledge of the detector alignment. By
comparing measured mass values for several charmed mesons with precisely known
values, an uncertainty of 0.03% on the momentum scale is estimated [39]. The
corresponding uncertainty in the ${B}^{0}_{s}$ mass value is $\pm
0.12{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$.

The uncertainty in the kaon mass [7] will affect the ${B}^{0}_{s}$ mass
determination, while the uncertainty on the
${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ mass has a negligible effect.
The effect is estimated by repeating the fit with the kaon mass shifted by
$\pm\sigma$, where $\sigma$ is the uncertainty on the known kaon mass. The
observed mass variation, $\pm 0.06{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$,
is assigned as a systematic uncertainty.

The fit model for the signal and background of the invariant mass
distributions is another source of systematic uncertainty. The effect is
estimated by comparing to the nominal case the fit results with those from
alternative functions. The systematic uncertainty from this effect is $\pm
0.02{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$.

The energy loss of the kaons in the detector is another possible source of
bias in the mass measurement. A detailed study of this effect has been
performed in Ref. [8] for the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay. Following the same procedure in
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay, the effect is found to be $\pm
0.06{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$, which is assigned as a
systematic uncertainty. The bias for neglecting the QED radiative corrections
in the final state is negligible due to the restricted phase space [8]. The
uncertainty due to detector alignment is also negligible. Combining all of the
above sources in quadrature, the total systematic uncertainty on the mass
measurement is found to be $\pm 0.15{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$.

As a cross check, the mass measurement is performed separately in the two
data-taking periods and in two samples with opposite magnet polarity. All the
measurements are consistent within the uncertainties.

Table 2: Summary of the absolute systematic uncertainties (in ${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$) affecting the ${B}^{0}_{s}$ mass determination from the ${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi\kern 1.19995pt\phi$ decay. Source | Value
---|---
Momentum scale | 0.12
Kaon mass | 0.06
Kaon energy loss | 0.06
Signal and background modelling | 0.02
Total | 0.15

##  6 Conclusions

This paper presents the first observation of the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay channel, with a signal yield of $128\pm
13$. Taking the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi$ decay as the reference channel the relative branching fraction is
measured to be

$\frac{\mathcal{B}(B_{s}\rightarrow
J/\psi\,\phi\,\phi)}{\mathcal{B}(B_{s}\rightarrow J/\psi\,\phi)}=0.0115\pm
0.0012\;(\mathrm{stat})\;^{+0.0005}_{-0.0009}\;(\mathrm{syst})\,.$

From a fit to the ${B}^{0}_{s}$ invariant mass distribution in the
${{B}^{0}_{s}}\\!\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}}\phi\kern 1.19995pt\phi$ decay, the mass of the ${B}^{0}_{s}$ meson is
measured to be

$m(B^{0}_{s})=5367.08\pm 0.38\;\mathrm{(stat)}\pm
0.15\;\mathrm{(syst)}\;{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}.$

This value is consistent with previous LHCb results [8] and with the world
average [7]. The overall uncertainty is 20% larger than the current most
precise measurement. As the systematic uncertainty is a factor of two smaller,
further improvement can be expected when larger datasets become available.

## 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); NSFC
(China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN (Italy); FOM
and NWO (The Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MinES
and FANO (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine);
STFC (United Kingdom); NSF (USA). We acknowledge the computing resources that
are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy),
SURF (The Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and Yandex
LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-GRID
(Poland) and OSC (USA). We are indebted to the communities behind the multiple
open source software packages on which we depend. Individual groups or members
have received support from AvH Foundation (Germany), EPLANET, Marie
Skłodowska-Curie Actions and ERC (European Union), Conseil Général de Haute-
Savoie, Labex ENIGMASS and OCEVU, Région Auvergne (France), RFBR and Yandex
LLC (Russia), GVA, XuntaGal and GENCAT (Spain), The Royal Society, Royal
Commission for the Exhibition of 1851 and the Leverhulme Trust (United
Kingdom).

## References

  * [1] BaBar collaboration, J. P. Lees et al., _Study of $B^{\pm,0}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}K^{+}K^{-}K^{\pm,0}$ and search for $B^{0}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi$ at BaBar_, Phys. Rev. D91 (2015) 012003, arXiv:1407.7244
  * [2] LHCb collaboration, R. Aaij et al., _Search for the $X(4140)$ state in $B^{+}\rightarrow J/\psi\phi K^{+}$ decays_, Phys. Rev. D85 (2012) 091103(R), arXiv:1202.5087
  * [3] CDF collaboration, T. Aaltonen et al., _Evidence for a narrow near-threshold structure in the ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi$ mass spectrum in $B^{+}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi K^{+}$ decays_, Phys. Rev. Lett. 102 (2009) 242002, arXiv:0903.2229
  * [4] E. B. Gregory et al., _Precise B, $B_{s}$ and $B_{c}$ meson spectroscopy from full lattice QCD_, Phys. Rev. D83 (2011) 014506, arXiv:1010.3848
  * [5] C. McNeile et al., _Heavy meson masses and decay constants from relativistic heavy quarks in full lattice QCD_ , Phys. Rev. D86 (2012) 074503, arXiv:1207.0994
  * [6] R. Lewis and R. M. Woloshyn, _Bottom baryons from a dynamical lattice QCD simulation_ , Phys. Rev. D79 (2009) 014502, arXiv:0806.4783
  * [7] Particle Data Group, K. A. Olive et al., _Review of particle physics_ , Chin. Phys. C38 (2014) 090001 and 2015 update
  * [8] LHCb collaboration, R. Aaij et al., _Measurement of $b$-hadron masses_, Phys. Lett. B708 (2012) 241, arXiv:1112.4896
  * [9] E. S. Swanson, _The new heavy mesons: A status report_ , Phys. Rept. 429 (2006) 243, arXiv:hep-ph/0601110
  * [10] E. Klempt and A. Zaitsev, _Glueballs, hybrids, multiquarks: Experimental facts versus QCD inspired concepts_ , Phys. Rept. 454 (2007) 1, arXiv:0708.4016
  * [11] Belle collaboration, C. P. Shen et al., _Evidence for a new resonance and search for the $Y(4140)$ in the $\gamma\gamma\rightarrow\phi{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}$ process_, Phys. Rev. Lett. 104 (2010) 112004, arXiv:0912.2383
  * [12] D0 collaboration, V. M. Abazov et al., _Search for the $X(4140)$ state in $B^{+}\rightarrow J/\psi\phi K^{+}$ decay with the D0 detector_, Phys. Rev. D89 (2014) 012004, arXiv:1309.6580
  * [13] CMS collaboration, S. Chatrchyan et al., _Observation of a peaking structure in the $J/\psi\phi$ mass spectrum from $B^{\pm}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\phi K^{\pm}$ decays_, Phys. Lett. B734 (2014) 261, arXiv:1309.6920
  * [14] BES collaboration, M. Ablikim et al., _Partial wave analysis of ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\rightarrow\gamma\phi\phi$_, Phys. Lett. B662 (2008) 330, arXiv:0801.3885
  * [15] Z. Bai et al., _Observation of a pseudoscalar state in ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\rightarrow\gamma\phi\phi$ near $\phi\phi$ threshold_, Phys. Rev. Lett. 65 (1990) 1309
  * [16] DM2 collaboration, D. Bisello et al., _Search of glueballs in the ${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}\rightarrow\gamma\phi\phi$ decay_, Phys. Lett. B179 (1986) 294
  * [17] BaBar collaboration, B. Aubert et al., _Rare $B$ decays into states containing a ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ meson and a meson with $s\bar{s}$ quark content_, Phys. Rev. Lett. 91 (2003) 71801, arXiv:hep-ex/0304014
  * [18] LHCb collaboration, A. A. Alves Jr. et al., _The LHCb detector at the LHC_, JINST 3 (2008) S08005
  * [19] LHCb collaboration, R. Aaij et al., _LHCb detector performance_, Int. J. Mod. Phys. A30 (2015), no. 07 1530022, arXiv:1412.6352
  * [20] T. Sjöstrand, S. Mrenna, and P. Skands, _PYTHIA 6.4 physics and manual_ , JHEP 05 (2006) 026, arXiv:hep-ph/0603175
  * [21] I. Belyaev et al., _Handling of the generation of primary events in Gauss, the LHCb simulation framework_ , J. Phys. Conf. Ser. 331 (2011) 032047
  * [22] D. J. Lange, _The EvtGen particle decay simulation package_ , Nucl. Instrum. Meth. A462 (2001) 152
  * [23] P. Golonka and Z. Was, _PHOTOS Monte Carlo: A precision tool for QED corrections in $Z$ and $W$ decays_, Eur. Phys. J. C45 (2006) 97, arXiv:hep-ph/0506026
  * [24] GEANT4 collaboration, J. Allison et al., _Geant4 developments and applications_ , IEEE Trans. Nucl. Sci. 53 (2006) 270
  * [25] GEANT4 collaboration, S. Agostinelli et al., _GEANT4: A simulation toolkit_ , Nucl. Instrum. Meth. A506 (2003) 250
  * [26] M. Clemencic et al., _The LHCb simulation application, Gauss: Design, evolution and experience_, J. Phys. Conf. Ser. 331 (2011) 032023
  * [27] W. D. Hulsbergen, _Decay chain fitting with a Kalman filter_ , Nucl. Instr. Meth. A552 (2005) 566, arXiv:physics/0503191
  * [28] L. Breiman, J. H. Friedman, R. A. Olshen, and C. J. Stone, Classification and regression trees, Wadsworth international group, Belmont, California, USA, 1984
  * [29] B. P. Roe et al., _Boosted decision trees as an alternative to artificial neural networks for particle identification_ , Nucl. Instrum. Meth. A543 (2005) 577, arXiv:physics/0408124
  * [30] R. E. Schapire and Y. Freund, _A decision-theoretic generalization of on-line learning and an application to boosting_ , J. Comput. Syst. Sci. 55 (1997) 119
  * [31] G. Punzi, _Sensitivity of searches for new signals and its optimization_ , in Statistical Problems in Particle Physics, Astrophysics, and Cosmology (L. Lyons, R. Mount, and R. Reitmeyer, eds.), p. 79, 2003.  arXiv:physics/0308063
  * [32] S. S. Wilks, _The large-sample distribution of the likelihood ratio for testing composite hypotheses_ , Ann. Math. Stat. 9 (1938) 60
  * [33] M. Pivk and F. R. Le Diberder, _sPlot: A statistical tool to unfold data distributions_ , Nucl. Instrum. Meth. A555 (2005) 356, arXiv:physics/0402083
  * [34] T. Skwarnicki, A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, DESY-F31-86-02
  * [35] LHCb collaboration, R. Aaij et al., _Measurement of the track reconstruction efficiency at LHCb_, JINST 10 (2015) P02007, arXiv:1408.1251
  * [36] G. J. Feldman and R. D. Cousins, _Unified approach to the classical statistical analysis of small signals_ , Phys. Rev. D57 (1998) 3873, arXiv:physics/9711021
  * [37] K. De Bruyn et al., _Branching ratio measurements of $B_{s}$ decays_, Phys. Rev. D86 (2012) 014027, arXiv:1204.1735
  * [38] LHCb collaboration, R. Aaij et al., _Precision measurement of CP violation in $B^{0}_{s}\rightarrow{{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}}K^{+}K^{-}$ decays_, Phys. Rev. Lett. 114 (2015) 041801, arXiv:1411.3104
  * [39] LHCb collaboration, R. Aaij et al., _Precision measurement of D meson mass differences_ , JHEP 06 (2013) 065, arXiv:1304.6865

LHCb collaboration

R. Aaij38, B. Adeva37, M. Adinolfi46, A. Affolder52, Z. Ajaltouni5, S. Akar6,
J. Albrecht9, F. Alessio38, M. Alexander51, S. Ali41, G. Alkhazov30, P.
Alvarez Cartelle53, A.A. Alves Jr57, S. Amato2, S. Amerio22, Y. Amhis7, L.
An3, L. Anderlini17, J. Anderson40, G. Andreassi39, M. Andreotti16,f, J.E.
Andrews58, R.B. Appleby54, O. Aquines Gutierrez10, F. Archilli38, P.
d’Argent11, A. Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,m, M.
Baalouch5, S. Bachmann11, J.J. Back48, A. Badalov36, C. Baesso60, W.
Baldini16,38, R.J. Barlow54, C. Barschel38, S. Barsuk7, W. Barter38, V.
Batozskaya28, V. Battista39, A. Bay39, L. Beaucourt4, J. Beddow51, F.
Bedeschi23, I. Bediaga1, L.J. Bel41, V. Bellee39, N. Belloli20, I. Belyaev31,
E. Ben-Haim8, G. Bencivenni18, S. Benson38, J. Benton46, A. Berezhnoy32, R.
Bernet40, A. Bertolin22, M.-O. Bettler38, M. van Beuzekom41, A. Bien11, S.
Bifani45, P. Billoir8, T. Bird54, A. Birnkraut9, A. Bizzeti17,h, T. Blake48,
F. Blanc39, J. Blouw10, S. Blusk59, V. Bocci25, A. Bondar34, N. Bondar30,38,
W. Bonivento15, S. Borghi54, M. Borsato7, T.J.V. Bowcock52, E. Bowen40, C.
Bozzi16, S. Braun11, M. Britsch10, T. Britton59, J. Brodzicka54, N.H. Brook46,
A. Bursche40, J. Buytaert38, S. Cadeddu15, R. Calabrese16,f, M. Calvi20,j, M.
Calvo Gomez36,o, P. Campana18, D. Campora Perez38, L. Capriotti54, A.
Carbone14,d, G. Carboni24,k, R. Cardinale19,i, A. Cardini15, P. Carniti20, L.
Carson50, K. Carvalho Akiba2,38, G. Casse52, L. Cassina20,j, L. Castillo
Garcia38, M. Cattaneo38, Ch. Cauet9, G. Cavallero19, R. Cenci23,s, M.
Charles8, Ph. Charpentier38, M. Chefdeville4, S. Chen54, S.-F. Cheung55, N.
Chiapolini40, M. Chrzaszcz40, X. Cid Vidal38, G. Ciezarek41, P.E.L. Clarke50,
M. Clemencic38, H.V. Cliff47, J. Closier38, V. Coco38, J. Cogan6, E.
Cogneras5, V. Cogoni15,e, L. Cojocariu29, G. Collazuol22, P. Collins38, A.
Comerma-Montells11, A. Contu15,38, A. Cook46, M. Coombes46, S. Coquereau8, G.
Corti38, M. Corvo16,f, B. Couturier38, G.A. Cowan50, D.C. Craik48, A.
Crocombe48, M. Cruz Torres60, S. Cunliffe53, R. Currie53, C. D’Ambrosio38, E.
Dall’Occo41, J. Dalseno46, P.N.Y. David41, A. Davis57, K. De Bruyn41, S. De
Capua54, M. De Cian11, J.M. De Miranda1, L. De Paula2, P. De Simone18, C.-T.
Dean51, D. Decamp4, M. Deckenhoff9, L. Del Buono8, N. Déléage4, M. Demmer9, D.
Derkach55, O. Deschamps5, F. Dettori38, B. Dey21, A. Di Canto38, F. Di
Ruscio24, H. Dijkstra38, S. Donleavy52, F. Dordei11, M. Dorigo39, A. Dosil
Suárez37, D. Dossett48, A. Dovbnya43, K. Dreimanis52, L. Dufour41, G.
Dujany54, F. Dupertuis39, P. Durante38, R. Dzhelyadin35, A. Dziurda26, A.
Dzyuba30, S. Easo49,38, U. Egede53, V. Egorychev31, S. Eidelman34, S.
Eisenhardt50, U. Eitschberger9, R. Ekelhof9, L. Eklund51, I. El Rifai5, Ch.
Elsasser40, S. Ely59, S. Esen11, H.M. Evans47, T. Evans55, A. Falabella14, C.
Färber38, N. Farley45, S. Farry52, R. Fay52, D. Ferguson50, V. Fernandez
Albor37, F. Ferrari14, F. Ferreira Rodrigues1, M. Ferro-Luzzi38, S.
Filippov33, M. Fiore16,38,f, M. Fiorini16,f, M. Firlej27, C. Fitzpatrick39, T.
Fiutowski27, K. Fohl38, P. Fol53, M. Fontana15, F. Fontanelli19,i, R. Forty38,
O. Francisco2, M. Frank38, C. Frei38, M. Frosini17, J. Fu21, E. Furfaro24,k,
A. Gallas Torreira37, D. Galli14,d, S. Gallorini22,38, S. Gambetta50, M.
Gandelman2, P. Gandini55, Y. Gao3, J. García Pardiñas37, J. Garra Tico47, L.
Garrido36, D. Gascon36, C. Gaspar38, R. Gauld55, L. Gavardi9, G. Gazzoni5, A.
Geraci21,u, D. Gerick11, E. Gersabeck11, M. Gersabeck54, T. Gershon48, Ph.
Ghez4, A. Gianelle22, S. Gianì39, V. Gibson47, O. G. Girard39, L. Giubega29,
V.V. Gligorov38, C. Göbel60, D. Golubkov31, A. Golutvin53,31,38, A. Gomes1,a,
C. Gotti20,j, M. Grabalosa Gándara5, R. Graciani Diaz36, L.A. Granado
Cardoso38, E. Graugés36, E. Graverini40, G. Graziani17, A. Grecu29, E.
Greening55, S. Gregson47, P. Griffith45, L. Grillo11, O. Grünberg63, B. Gui59,
E. Gushchin33, Yu. Guz35,38, T. Gys38, T. Hadavizadeh55, C. Hadjivasiliou59,
G. Haefeli39, C. Haen38, S.C. Haines47, S. Hall53, B. Hamilton58, X. Han11, S.
Hansmann-Menzemer11, N. Harnew55, S.T. Harnew46, J. Harrison54, J. He38, T.
Head39, V. Heijne41, K. Hennessy52, P. Henrard5, L. Henry8, J.A. Hernando
Morata37, E. van Herwijnen38, M. Heß63, A. Hicheur2, D. Hill55, M. Hoballah5,
C. Hombach54, W. Hulsbergen41, T. Humair53, N. Hussain55, D. Hutchcroft52, D.
Hynds51, M. Idzik27, P. Ilten56, R. Jacobsson38, A. Jaeger11, J. Jalocha55, E.
Jans41, A. Jawahery58, F. Jing3, M. John55, D. Johnson38, C.R. Jones47, C.
Joram38, B. Jost38, N. Jurik59, S. Kandybei43, W. Kanso6, M. Karacson38, T.M.
Karbach38,†, S. Karodia51, M. Kelsey59, I.R. Kenyon45, M. Kenzie38, T.
Ketel42, B. Khanji20,38,j, C. Khurewathanakul39, S. Klaver54, K.
Klimaszewski28, O. Kochebina7, M. Kolpin11, I. Komarov39, R.F. Koopman42, P.
Koppenburg41,38, M. Kozeiha5, L. Kravchuk33, K. Kreplin11, M. Kreps48, G.
Krocker11, P. Krokovny34, F. Kruse9, W. Krzemien28, W. Kucewicz26,n, M.
Kucharczyk26, V. Kudryavtsev34, A. K. Kuonen39, K. Kurek28, T.
Kvaratskheliya31, D. Lacarrere38, G. Lafferty54, A. Lai15, D. Lambert50, G.
Lanfranchi18, C. Langenbruch48, B. Langhans38, T. Latham48, C. Lazzeroni45, R.
Le Gac6, J. van Leerdam41, J.-P. Lees4, R. Lefèvre5, A. Leflat32,38, J.
Lefrançois7, E. Lemos Cid37, O. Leroy6, T. Lesiak26, B. Leverington11, Y. Li7,
T. Likhomanenko65,64, M. Liles52, R. Lindner38, C. Linn38, F. Lionetto40, B.
Liu15, X. Liu3, D. Loh48, I. Longstaff51, J.H. Lopes2, D. Lucchesi22,q, M.
Lucio Martinez37, H. Luo50, A. Lupato22, E. Luppi16,f, O. Lupton55, N.
Lusardi21, F. Machefert7, F. Maciuc29, O. Maev30, K. Maguire54, S. Malde55, A.
Malinin64, G. Manca7, G. Mancinelli6, P. Manning59, A. Mapelli38, J. Maratas5,
J.F. Marchand4, U. Marconi14, C. Marin Benito36, P. Marino23,38,s, J. Marks11,
G. Martellotti25, M. Martin6, M. Martinelli39, D. Martinez Santos37, F.
Martinez Vidal66, D. Martins Tostes2, A. Massafferri1, R. Matev38, A.
Mathad48, Z. Mathe38, C. Matteuzzi20, K. Matthieu11, A. Mauri40, B. Maurin39,
A. Mazurov45, M. McCann53, J. McCarthy45, A. McNab54, R. McNulty12, B.
Meadows57, F. Meier9, M. Meissner11, D. Melnychuk28, M. Merk41, D.A.
Milanes62, M.-N. Minard4, D.S. Mitzel11, J. Molina Rodriguez60, I.A. Monroy62,
S. Monteil5, M. Morandin22, P. Morawski27, A. Mordà6, M.J. Morello23,s, J.
Moron27, A.B. Morris50, R. Mountain59, F. Muheim50, J. Müller9, K. Müller40,
V. Müller9, M. Mussini14, B. Muster39, P. Naik46, T. Nakada39, R.
Nandakumar49, A. Nandi55, I. Nasteva2, M. Needham50, N. Neri21, S. Neubert11,
N. Neufeld38, M. Neuner11, A.D. Nguyen39, T.D. Nguyen39, C. Nguyen-Mau39,p, V.
Niess5, R. Niet9, N. Nikitin32, T. Nikodem11, D. Ninci23, A. Novoselov35, D.P.
O’Hanlon48, A. Oblakowska-Mucha27, V. Obraztsov35, S. Ogilvy51, O.
Okhrimenko44, R. Oldeman15,e, C.J.G. Onderwater67, B. Osorio Rodrigues1, J.M.
Otalora Goicochea2, A. Otto38, P. Owen53, A. Oyanguren66, A. Palano13,c, F.
Palombo21,t, M. Palutan18, J. Panman38, A. Papanestis49, M. Pappagallo51, L.L.
Pappalardo16,f, C. Pappenheimer57, C. Parkes54, G. Passaleva17, G.D. Patel52,
M. Patel53, C. Patrignani19,i, A. Pearce54,49, A. Pellegrino41, G. Penso25,l,
M. Pepe Altarelli38, S. Perazzini14,d, P. Perret5, L. Pescatore45, K.
Petridis46, A. Petrolini19,i, M. Petruzzo21, E. Picatoste Olloqui36, B.
Pietrzyk4, T. Pilař48, D. Pinci25, A. Pistone19, A. Piucci11, S. Playfer50, M.
Plo Casasus37, T. Poikela38, F. Polci8, A. Poluektov48,34, I. Polyakov31, E.
Polycarpo2, A. Popov35, D. Popov10,38, B. Popovici29, C. Potterat2, E.
Price46, J.D. Price52, J. Prisciandaro39, A. Pritchard52, C. Prouve46, V.
Pugatch44, A. Puig Navarro39, G. Punzi23,r, W. Qian4, R. Quagliani7,46, B.
Rachwal26, J.H. Rademacker46, M. Rama23, M.S. Rangel2, I. Raniuk43, N.
Rauschmayr38, G. Raven42, F. Redi53, S. Reichert54, M.M. Reid48, A.C. dos
Reis1, S. Ricciardi49, S. Richards46, M. Rihl38, K. Rinnert52, V. Rives
Molina36, P. Robbe7,38, A.B. Rodrigues1, E. Rodrigues54, J.A. Rodriguez
Lopez62, P. Rodriguez Perez54, S. Roiser38, V. Romanovsky35, A. Romero
Vidal37, J. W. Ronayne12, M. Rotondo22, J. Rouvinet39, T. Ruf38, P. Ruiz
Valls66, J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B. Saitta15,e, V.
Salustino Guimaraes2, C. Sanchez Mayordomo66, B. Sanmartin Sedes37, R.
Santacesaria25, C. Santamarina Rios37, M. Santimaria18, E. Santovetti24,k, A.
Sarti18,l, C. Satriano25,m, A. Satta24, D.M. Saunders46, D. Savrina31,32, M.
Schiller38, H. Schindler38, M. Schlupp9, M. Schmelling10, T. Schmelzer9, B.
Schmidt38, O. Schneider39, A. Schopper38, M. Schubiger39, M.-H. Schune7, R.
Schwemmer38, B. Sciascia18, A. Sciubba25,l, A. Semennikov31, N. Serra40, J.
Serrano6, L. Sestini22, P. Seyfert20, M. Shapkin35, I. Shapoval16,43,f, Y.
Shcheglov30, T. Shears52, L. Shekhtman34, V. Shevchenko64, A. Shires9, B.G.
Siddi16, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46, I.
Skillicorn51, T. Skwarnicki59, E. Smith55,49, E. Smith53, I. T. Smith50, J.
Smith47, M. Smith54, H. Snoek41, M.D. Sokoloff57,38, F.J.P. Soler51, F.
Soomro39, D. Souza46, B. Souza De Paula2, B. Spaan9, P. Spradlin51, S.
Sridharan38, F. Stagni38, M. Stahl11, S. Stahl38, S. Stefkova53, O.
Steinkamp40, O. Stenyakin35, S. Stevenson55, S. Stoica29, S. Stone59, B.
Storaci40, S. Stracka23,s, M. Straticiuc29, U. Straumann40, L. Sun57, W.
Sutcliffe53, K. Swientek27, S. Swientek9, V. Syropoulos42, M. Szczekowski28,
P. Szczypka39,38, T. Szumlak27, S. T’Jampens4, A. Tayduganov6, T. Tekampe9, M.
Teklishyn7, G. Tellarini16,f, F. Teubert38, C. Thomas55, E. Thomas38, J. van
Tilburg41, V. Tisserand4, M. Tobin39, J. Todd57, S. Tolk42, L. Tomassetti16,f,
D. Tonelli38, S. Topp-Joergensen55, N. Torr55, E. Tournefier4, S. Tourneur39,
K. Trabelsi39, M.T. Tran39, M. Tresch40, A. Trisovic38, A. Tsaregorodtsev6, P.
Tsopelas41, N. Tuning41,38, A. Ukleja28, A. Ustyuzhanin65,64, U. Uwer11, C.
Vacca15,e, V. Vagnoni14, G. Valenti14, A. Vallier7, R. Vazquez Gomez18, P.
Vazquez Regueiro37, C. Vázquez Sierra37, S. Vecchi16, J.J. Velthuis46, M.
Veltri17,g, G. Veneziano39, M. Vesterinen11, B. Viaud7, D. Vieira2, M. Vieites
Diaz37, X. Vilasis-Cardona36,o, A. Vollhardt40, D. Volyanskyy10, D. Voong46,
A. Vorobyev30, V. Vorobyev34, C. Voß63, J.A. de Vries41, R. Waldi63, C.
Wallace48, R. Wallace12, J. Walsh23, S. Wandernoth11, J. Wang59, D.R. Ward47,
N.K. Watson45, D. Websdale53, A. Weiden40, M. Whitehead48, G. Wilkinson55,38,
M. Wilkinson59, M. Williams38, M.P. Williams45, M. Williams56, T. Williams45,
F.F. Wilson49, J. Wimberley58, J. Wishahi9, W. Wislicki28, M. Witek26, G.
Wormser7, S.A. Wotton47, S. Wright47, K. Wyllie38, Y. Xie61, Z. Xu39, Z.
Yang3, J. Yu61, X. Yuan34, O. Yushchenko35, M. Zangoli14, M. Zavertyaev10,b,
L. Zhang3, Y. Zhang3, A. Zhelezov11, A. Zhokhov31, L. Zhong3, S. Zucchelli14.

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

aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil
bP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS),
Moscow, Russia
cUniversità di Bari, Bari, Italy
dUniversità di Bologna, Bologna, Italy
eUniversità di Cagliari, Cagliari, Italy
fUniversità di Ferrara, Ferrara, Italy
gUniversità di Urbino, Urbino, Italy
hUniversità di Modena e Reggio Emilia, Modena, Italy
iUniversità di Genova, Genova, Italy
jUniversità di Milano Bicocca, Milano, Italy
kUniversità di Roma Tor Vergata, Roma, Italy
lUniversità di Roma La Sapienza, Roma, Italy
mUniversità della Basilicata, Potenza, Italy
nAGH - University of Science and Technology, Faculty of Computer Science,
Electronics and Telecommunications, Kraków, Poland
oLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
pHanoi University of Science, Hanoi, Viet Nam
qUniversità di Padova, Padova, Italy
rUniversità di Pisa, Pisa, Italy
sScuola Normale Superiore, Pisa, Italy
tUniversità degli Studi di Milano, Milano, Italy
uPolitecnico di Milano, Milano, Italy
†Deceased