EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-PH-EP-2014-296 LHCb-PAPER-2014-063 December 19, 2014

Study of the rare $B^{0}_{s}$ and $B^{0}$ decays into the
$\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ final state

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

A search for the rare decays
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ is performed in a data set
corresponding to an integrated luminosity of 3.0$\mbox{\,fb}^{-1}$ collected
by the LHCb detector in proton-proton collisions at centre-of-mass energies of
7 and 8$\mathrm{\,Te\kern-1.00006ptV}$. Decay candidates with pion pairs that
have invariant mass in the range
0.5–1.3${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ and with muon pairs that do
not originate from a resonance are considered. The first observation of the
decay ${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and the first
evidence of the decay ${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ are
obtained and the branching fractions, restricted to the dipion-mass range
considered, are measured to be
$\mathcal{B}({B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})=(8.6\pm
1.5\,\mathrm{(stat)}\pm 0.7\,\mathrm{(syst)}\pm 0.7\,({\rm norm}))\times
10^{-8}$ and
$\mathcal{B}({B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})=(2.11\pm
0.51\,\mathrm{(stat)}\pm 0.15\,\mathrm{(syst)}\pm 0.16\,({\rm norm}))\times
10^{-8}$, where the third uncertainty is due to the branching fraction of the
decay ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}(\\!\rightarrow\mu^{+}\mu^{-})K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-})}$, used as a normalisation.

Published as Phys. Lett. B743 (2015) 46

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

##  1 Introduction

Decays of the $B^{0}_{s}$ and $B^{0}$ mesons into a
$\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ final state with the muons not originating from
a resonance are flavour-changing neutral-current transitions,111The inclusion
of charge-conjugate processes is implied throughout. which are expected to
proceed mainly from the ${B^{0}_{s}\\!\rightarrow
f_{0}(980)(\\!\rightarrow\pi^{+}\pi^{-})\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow\rho(770)^{0}(\\!\rightarrow\pi^{+}\pi^{-})\mu^{+}\mu^{-}}$
decays, in analogy to what is observed in
${B^{0}_{(s)}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\pi^{+}\pi^{-}}$ decays [1, 2]. In the standard model (SM) these decays
are governed by the ${b\\!\rightarrow s}$ and ${b\\!\rightarrow d}$ weak
transitions and are described by loop diagrams. They are suppressed due to the
Glashow-Iliopoulos-Maiani mechanism [3] and the small values of the Cabibbo-
Kobayashi-Maskawa matrix elements involved [4, 5]. This feature makes the
${B^{0}_{s}\\!\rightarrow f_{0}(980)\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow\rho(770)^{0}\mu^{+}\mu^{-}}$ decays sensitive probes of
several SM extensions, since potential non-SM amplitudes may dominate over the
SM contribution [6, 7, 8, 9, 10]. Current SM predictions of the
${B^{0}_{s}\\!\rightarrow f_{0}(980)\mu^{+}\mu^{-}}$ branching fraction vary
from $10^{-7}$ to $10^{-9}$ [11, 12, 13]; similar values are expected for the
${B^{0}\\!\rightarrow\rho(770)^{0}\mu^{+}\mu^{-}}$ branching fraction [14, 15,
16]. The predictions suffer from uncertainties in the calculation of the
hadronic matrix elements associated with the transitions. For the
${B^{0}_{s}\\!\rightarrow f_{0}(980)\mu^{+}\mu^{-}}$ decay, the limited
knowledge of the quark content of the $f_{0}(980)$ meson results in additional
uncertainties. No experimental information exists on these decays to date.

In this Letter, a search for the
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays is reported.
The analysis is restricted to events with muons that do not originate from
$\phi$, ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$, and $\psi(2S)$
resonances, and with pion pairs with invariant mass in the range
0.5–1.3${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. This mass range is set to
include both $f_{0}(980)$ and $\rho(770)^{0}$ resonances, which overlap
because of their large widths [17]. Other resonances, as well as non-resonant
pions, might contribute [1, 2]. However, due to the limited size of the data
sample, an amplitude analysis of the $\pi^{+}\pi^{-}$ mass spectrum is not
attempted. The analysis is performed in a data set corresponding to an
integrated luminosity of 3.0$\mbox{\,fb}^{-1}$, collected by the LHCb detector
in proton-proton ($pp$) collisions. The first 1.0$\mbox{\,fb}^{-1}$ of data
was collected in 2011 with collisions at the centre-of-mass energy of
7$\mathrm{\,Te\kern-1.00006ptV}$; the remaining 2.0$\mbox{\,fb}^{-1}$ in 2012
at 8$\mathrm{\,Te\kern-1.00006ptV}$. The signal yields are obtained from a fit
to the unbinned $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass distribution of the decay
candidates. The fit modelling and the methods for the background estimation
are validated on data, by fitting the $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass
distribution of
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ decays, while the branching fractions of
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays are
normalised using ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays reconstructed in the same data set.

##  2 Detector and simulation

The LHCb detector [18] 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 [19], 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 [20] placed
downstream of the magnet. The tracking system provides a measurement of
momentum with a relative uncertainty that varies from 0.4% at low momentum to
0.6% at 100${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$. The minimum distance of a
track to a primary vertex (PV), the impact parameter (IP), is measured with a
resolution of 20$\,\upmu\rm m$ for charged particles with high transverse
momentum ($p_{\rm T}$). Different types of charged hadrons are distinguished
using information from two ring-imaging Cherenkov detectors (RICH) [21].
Photon, electron and hadron candidates 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
[22].

Samples of simulated events are used to determine the efficiency of selecting
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays, and to study backgrounds. In the simulation,
$pp$ collisions are generated using Pythia [23, *Sjostrand:2007gs] with a
specific LHCb configuration [25]. Decays of hadronic particles are described
by EvtGen [26], in which final-state radiation is generated using Photos [27].
The model of Refs. [28, 29, 12] is used to describe
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays. The
interaction of the generated particles with the detector and its response are
implemented using the Geant4 toolkit [30, *Agostinelli:2002hh] as described in
Ref. [32].

##  3 Event selection

The online event-selection (trigger) 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 [33]. For this analysis, the
hardware trigger requires at least one muon with ${\mbox{$p_{\rm
T}$}>1.48\,(1.76){\mathrm{\,Ge\kern-1.00006ptV\\!/}c}}$, or two muons with
${\sqrt{\mbox{$p_{\rm T}$}(\mu_{1})\,\mbox{$p_{\rm
T}$}(\mu_{2})}>1.3\,(1.6){\mathrm{\,Ge\kern-1.00006ptV\\!/}c}}$, in the 2011
(2012) data sample. In the software trigger, at least one of the final-state
particles is required to have $\mbox{$p_{\rm
T}$}>1{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and $\rm{IP}>100\,\upmu\rm m$ with
respect to all the primary $pp$ interaction vertices in the event. Finally,
the tracks of two or more final-state particles are required to form a vertex
that is significantly displaced from the PVs. A multivariate algorithm is used
to identify secondary vertices consistent with the decay of a $b$ hadron [34].

In the offline selection, all charged particles are required to have
$\mbox{$p_{\rm T}$}>0.25$${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$ and
trajectories not consistent with originating from the PVs. Two oppositely
charged muon candidates compatible with originating from the same displaced
vertex are considered. To reject ${\phi\\!\rightarrow\mu^{+}\mu^{-}}$,
${{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}\\!\rightarrow\mu^{+}\mu^{-}}$,
and ${\psi(2S)\\!\rightarrow\mu^{+}\mu^{-}}$ decays, candidates having
invariant mass in the ranges 1.010–1.030, 2.796–3.216, or
3.436–3.806${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ are removed;
contributions from other resonances in the $\mu^{+}\mu^{-}$ mass spectrum such
as $\rho(770)^{0}$, $\omega(782)$, and $\psi(4160)$ [35] are negligible. The
muon candidates are combined with a pair of oppositely charged pions with
invariant mass in the range 0.5–1.3${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$
to form ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ candidates.
For the ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}(\\!\rightarrow\mu^{+}\mu^{-})K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-})}$ candidates, the dimuon invariant mass is required to be in the
range 2.796–3.216${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$, and the invariant
mass of the pion and kaon system in the range
0.826–0.966${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. The four tracks are
required to originate from the same $B^{0}_{(s)}$ decay vertex. The
$B^{0}_{(s)}$ momentum vector is required to be within 14 mrad of the vector
that joins the PV with the $B^{0}_{(s)}$ decay vertex (flight distance
vector).

The information from the RICH, the calorimeters, and the muon systems is used
for particle identification (PID), i.e., to define a likelihood for each track
to be associated with a certain particle hypothesis. Requirements on the muon-
identification likelihood are applied to reduce to $\mathcal{O}(10^{-2})$ the
rate of misidentified muon candidates, mainly pions, whilst preserving 95%
signal efficiency. In the case of
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays, PID requirements on kaon candidates are applied
to suppress any contributions from
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ decays with pions misidentified as kaons. In the case
of ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$decays, a
requirement on the PID of pion candidates is applied to reduce the
contamination from $B^{0}\\!\rightarrow K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-})\mu^{+}\mu^{-}$ decays with kaons misidentified as pions; this
background peaks around 5.25${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ in the
$\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass spectrum. A large data set of
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ decays is used to optimise the PID requirement of
pion candidates, assuming that the proportion between misidentified
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ and
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ decays is similar to the proportion between
misidentified ${B^{0}\\!\rightarrow K^{*}(892)^{0}\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays. The requirement
retains about 55% of the signal candidates. Simulations show that additional
contributions from ${B^{0}_{s}\\!\rightarrow\phi(\\!\rightarrow
K^{+}K^{-})\mu^{+}\mu^{-}}$ decays with double kaon-pion misidentification are
negligible. A requirement on the proton-identification likelihood of pion
candidates suppresses the contamination from decays with protons misidentified
as pions, with a $95\%$ signal efficiency. After this selection, simulations
show that contributions from
${\Lambda_{b}^{0}\\!\rightarrow\Lambda(\\!\rightarrow
p\pi^{-})\mu^{+}\mu^{-}}$ and ${\Lambda_{b}^{0}\\!\rightarrow
p\pi^{-}\mu^{+}\mu^{-}}$ decays are negligible, as are contributions from
${\Lambda_{b}^{0}\\!\rightarrow\Lambda(1520)(\\!\rightarrow
pK^{-})\mu^{+}\mu^{-}}$ and ${\Lambda_{b}^{0}\\!\rightarrow
pK^{-}\mu^{+}\mu^{-}}$ decays, where both the proton and the kaon are
misidentified as pions.

In addition to the above requirements, a multivariate selection based on a
boosted decision tree (BDT) [36, 37] is used to suppress the large background
from random combinations of tracks (combinatorial background) present in the
$\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ sample. The BDT is trained using simulated
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ events to model the
signal, and data candidates with $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass in the
range 5.5–5.8${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ for the background.
The training is performed separately for the 2011 and 2012 data, and using
simulations that reproduce the specific operational conditions of each year.
The variables used in the BDT are the significance of the displacement from
the PV of pion and muon tracks, the fit $\chi^{2}$ of the $B^{0}_{(s)}$ decay
vertex, the angle between the $B^{0}_{(s)}$ momentum vector and the flight
distance vector, the $p_{\rm T}$ of the $B^{0}_{(s)}$ candidate, the sum and
the difference of the transverse momenta of pions, the difference of the
transverse momenta of muons, the $B^{0}_{(s)}$ decay time, and the minimum
$p_{\rm T}$ of the pions. The resulting BDT output is independent of the
$\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass and PID variables. A requirement on the
BDT output value is chosen to maximise the figure of merit
$\varepsilon/(\alpha/2+\sqrt{N_{b}})$ [38], where $\varepsilon$ is the signal
efficiency; $N_{b}$ is the number of background events that pass the selection
and have a mass within 30${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ of the
known value of the $B^{0}_{s}$ mass [17]; $\alpha$ represents the desired
significance of the signal, expressed in terms of number of standard
deviations. The value of $\alpha$ is set to 3 (5) for the 2011 (2012) data
set. The resulting selection has around 85% efficiency to select signal
candidates. The same BDT is used to select
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ candidates. The selected samples consist of 364
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ candidates and 52
960 ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ candidates.

The efficiencies of all selection requirements are estimated with simulations,
except for the efficiency of the PID selection for hadrons. The latter is
determined in data using large and low-background samples of
$D^{*+}\rightarrow D^{0}(\rightarrow K^{-}\pi^{+})\pi^{+}$ decays; the
efficiencies are evaluated after reweighting the calibration samples to match
simultaneously the momentum and pseudorapidity distributions of the final-
state particles of ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
(${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$) candidates, and the distribution of the track
multiplicity of the events. The final selection efficiencies for 2011 and 2012
data are reported in Table 1. The statistical uncertainties are due to the
size of the calibration and simulation samples; systematic uncertainties are
described in what follows. The total efficiency varies by approximately 15% in
the $\pi^{+}\pi^{-}$ mass range considered and it is parametrised with a
second-order polynomial. The signal candidates are weighted in order to have a
constant efficiency as a function of the $\pi^{+}\pi^{-}$ mass spectrum.

Table 1:  Selection efficiencies of the 2011 and 2012 data sets; $\varepsilon_{s}$ for the ${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decay, $\varepsilon_{d}$ for the ${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decay, and $\varepsilon_{n}$ for the ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}K^{*}(892)^{0}}$ decay. | 2011 | 2012
---|---|---
$\varepsilon_{s}$ [%] | $36.1\pm 0.3\,\mathrm{(stat)}\pm 2.4\,\mathrm{(syst)}$ | $36.9\pm 0.3\,\mathrm{(stat)}\pm 2.3\,\mathrm{(syst)}$
$\varepsilon_{d}$ [%] | $29.8\pm 0.2\,\mathrm{(stat)}\pm 2.0\,\mathrm{(syst)}$ | $27.5\pm 0.2\,\mathrm{(stat)}\pm 1.7\,\mathrm{(syst)}$
$\varepsilon_{n}$ [%] | $9.33\pm 0.05\,\mathrm{(stat)}\pm 0.35\,\mathrm{(syst)}$ | $9.74\pm 0.08\,\mathrm{(stat)}\pm 0.27\,\mathrm{(syst)}$

Systematic uncertainties of the efficiencies are dominated by the limited
information about the signal decay-models; the main contribution comes from
the unknown angular distributions of
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decay products. To
estimate this uncertainty, the difference in efficiencies between decays
generated according to a phase-space model and to the model of Refs. [28, 29,
12] is considered. The resulting relative uncertainty is $5.4\%$. A relative
uncertainty of $3.7\%$ ($2.8\%$) for 2011 (2012) data is estimated by
considering the difference of the efficiencies evaluated in the simulation and
in data for ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays. The same relative uncertainty is assigned to
the efficiency associated with
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays, as the
cancellation of this uncertainty in the ratio of the efficiencies of signal
and normalisation decays may not be exact. This is due to the fact that the
$p_{\rm T}$ distributions of the final-state particles are different between
the decay modes. An additional $1.6\%$ relative uncertainty is assigned to
$\varepsilon_{s}$, due to the unknown mixture of $B^{0}_{s}$ mass eigenstates
in ${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays, which
results in a $B^{0}_{s}$ effective lifetime that could differ from the value
used in the simulations [39].

##  4 Determination of the signal yields

The ratio of the branching fractions

$\mathcal{R}_{q}\equiv\frac{\mathcal{B}({B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})}{\mathcal{B}(B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}(\\!\rightarrow\mu^{+}\mu^{-})K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-}))},$

with $q=s$ ($d$) for ${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
(${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$) decays, is the quantity
being measured; it is used to express the observed yields of
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays as follows:

$N_{B_{q}}=\frac{f_{q}}{f_{d}}\frac{\varepsilon_{q}}{\varepsilon_{n}}N_{n}\mathcal{R}_{q},$
(1)

where $N_{n}$ is the
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ yield, $f_{s}/f_{d}$ is the ratio of the fragmentation
probabilities for $B^{0}_{s}$ and $B^{0}$ mesons [40], $\varepsilon_{q}$ is
the selection efficiency of
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
(${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$) decays, and
$\varepsilon_{n}$ the one of
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays.

Figure 1: Mass distribution of
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ candidates with fit projections overlaid. The 2011 and
2012 data sets are combined.

The number of events $N_{n}$ in Eq. (1) is obtained from an extended maximum
likelihood fit to the unbinned $\mu^{+}\mu^{-}K^{+}\pi^{-}$ mass distribution
of the ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ candidates in the range
4.97–5.77${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. The
$\mu^{+}\mu^{-}K^{+}\pi^{-}$ mass distribution is shown in Fig. 1 with fit
projections overlaid. A sum of two Gaussian functions, with a power-law tail
on either side derived from simulations, is used to describe the dominant
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ peak and the small
$B^{0}_{s}\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}$ contribution. All function parameters are in common
between the $B^{0}$ and $B^{0}_{s}$ signal functions, except for the mass; the
mass difference between $B^{0}_{s}$ and $B^{0}$ mesons is fixed to the known
value [17]. An exponential function is used to model the combinatorial
background. A small contamination of
$B^{+}\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}K^{+}$ decays
combined with an additional charged pion is modelled with an ARGUS function
[41]. Partially reconstructed $B^{0}$ decays at masses lower than the $B^{0}$
signal are described with another ARGUS function. The fitted yields of
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays are corrected by subtracting a $(6.4\pm 1.0)\%$
contribution of ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{+}\pi^{-}}$ decays [42], where the $K^{+}\pi^{-}$ pair is in a
$S$-wave state and does not originate from the decay of a $K^{*}(892)^{0}$
resonance. The numbers of
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays are $9821\pm 110\,\mathrm{(stat)}\pm
134\,\mathrm{(syst)}\pm 97\,(S\rm{\,wave})$ and $23521\pm
175\,\mathrm{(stat)}\pm 172\,\mathrm{(syst)}\pm 243\,(S\rm{\,wave})$ in the
2011 and 2012 data sets, respectively, where the third uncertainty is due to
the $S$-wave subtraction. The systematic uncertainty accounts for the
uncertainties in the parameters fixed in the fit to the values determined in
simulations, and are calculated with the method described at the end of this
section.

The ratios $\mathcal{R}_{s}$ and $\mathcal{R}_{d}$ are measured from an
extended maximum likelihood fit to the unbinned $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$
mass distribution, where the signal yields are parametrised using Eq. (1), and
all other inputs are fixed. The different centre-of-mass energies result in
different $b\bar{b}$ production cross sections and selection efficiencies in
the 2011 and 2012 data samples. Therefore, the two samples are fitted
simultaneously with different likelihood functions, but with the parameters
$\mathcal{R}_{s}$ and $\mathcal{R}_{d}$ in common. We also fit simultaneously
the ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ samples. The latter are selected with the
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ requirements, except
for the dimuon mass, which is restricted to the
2.796–3.216${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ range. The
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ fit serves as a consistency check of the fit
modelling, since the ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
and ${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ mass distributions are expected to be similar. In
both samples, the fit range is 2${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$
wide and starts from 5.19${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. This
limit is set to remove partially reconstructed decays of the $B^{0}$ mesons
with an unreconstructed $\pi^{0}$. The stability of the fit results is checked
against the extension of the fit range in the lower mass region of the
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ mass distributions, where an additional component is
needed in the fit to describe the partially reconstructed $B^{0}$ decays below
5.19${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. Figure 2 shows the
$\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass distributions of the
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ and
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decay candidates in
the range 5.19–5.99${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ with fit
projections overlaid, where the 2011 and 2012 data sets are combined.

\begin{overpic}[width=223.0721pt]{Fig2a} \put(24.0,78.0){(a)}
\end{overpic}\begin{overpic}[width=223.0721pt]{Fig2b} \put(24.0,78.0){(b)}
\end{overpic}

Figure 2: Mass distributions of (a) the
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ and (b) the
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decay candidates in
the range 5.19–5.99${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ with fit
projections overlaid. The 2011 and 2012 data sets are combined. In (b), the
contribution from ${B^{0}_{s}\\!\rightarrow\phi\mu^{+}\mu^{-}}$ and
${B^{+}\\!\rightarrow K^{+}\mu^{+}\mu^{-}}$ decays are included in the fit,
but they are not visible in the projection, because the corresponding yields
are small.

The ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ signals are described by a model similar to that used
for the ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ signal in the fit of the $\mu^{+}\mu^{-}$
$K^{+}\pi^{-}$ mass distribution. The $B^{0}$ peak position is a common
parameter for the ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
and ${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ fits, as well as the signal resolutions; the
difference between the $B^{0}$ and the $B^{0}_{s}$ masses is fixed to the
known value. The ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
signal widths are multiplied by scale factors, derived from simulations, which
accounts for the different momentum spectra between non-resonant muons and
muons from ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$ meson decays. In
both fits, the combinatorial background is modelled with an exponential
function.

Backgrounds from ${B^{0}\\!\rightarrow K^{*}(892)^{0}\mu^{+}\mu^{-}}$
(${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$) decays, where kaons are misidentified as pions, are
estimated using control samples of these decays reconstructed in data. They
are selected as ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
(${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$) candidates, except for different requirements on the
PID variables of the kaon and pion candidates, as for the normalization decay
mode. To obtain the yields and the shapes of the mass distribution of the
misidentified decays, the kaon candidates are assigned the pion mass, and the
resulting $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass distribution is reweighted to
reproduce the PID selection of the
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ sample. In the final
fit, the yields of the two backgrounds are constrained using Gaussian
functions with means fixed to the values obtained with this method, and widths
that account for a relative uncertainty in the 2011 (2012) data sample of 15%
(10%) for ${B^{0}\\!\rightarrow K^{*}(892)^{0}\mu^{+}\mu^{-}}$ decays, and of
2% (1%) for ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays. The shape of the ${B^{0}\\!\rightarrow
K^{*}(892)^{0}\mu^{+}\mu^{-}}$ background is modelled with a Gaussian function
with a power-law tail on the low-mass side; the shape of the
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ background is modelled with a sum of two Gaussian
functions with different means. All parameters of these functions are fixed
from the values obtained in the fit to the control samples. The background
from ${B^{0}_{s}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays is expected to be less than 0.5% [17] of the
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ yield and is neglected. Similarly, the background from
${B^{0}_{s}\\!\rightarrow K^{*}(892)^{0}\mu^{+}\mu^{-}}$ decays is not
considered.

Backgrounds from decays
${B^{0}_{s}\\!\rightarrow\phi(\\!\rightarrow\pi^{+}\pi^{-}\pi^{0})\mu^{+}\mu^{-}}$
with an unreconstructed $\pi^{0}$,
${B^{0}_{s}\\!\rightarrow\eta^{\prime}(\\!\rightarrow\pi^{+}\pi^{-}\gamma)\mu^{+}\mu^{-}}$
with an unreconstructed $\gamma$, and ${B^{+}\\!\rightarrow
K^{+}\mu^{+}\mu^{-}}$ or ${B^{+}\\!\rightarrow\pi^{+}\mu^{+}\mu^{-}}$ combined
with an additional charged pion, are estimated from simulations. The mass
distributions of these backgrounds are modelled with ARGUS functions with
parameters fixed from fits to simulated events. Backgrounds from similar decay
modes, where the muons come from the ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}$ meson, are described in the
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ fit using the same methods. An additional
contribution is given by
${B_{c}^{+}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\pi^{+}\pi^{-}\pi^{+}}$ decays, where a pion is not reconstructed. This
background is modelled with a sum of two Gaussian functions, one of which has
a power-law tail on the low-mass side. Backgrounds from semileptonic
${B^{0}\\!\rightarrow D^{-}(\\!\rightarrow\rho^{0}\mu^{-}X)\mu^{+}X}$ decays
with ${\rho^{0}\\!\rightarrow\pi^{+}\pi^{-}}$, give a negligible contribution
at $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass greater than
5.19${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$.

##  5 Results

We measure $\mathcal{R}_{s}=(1.67\pm 0.29\,\mathrm{(stat)}\pm
0.13\,\mathrm{(syst)})\times 10^{-3}$ and $\mathcal{R}_{d}=(0.41\pm
0.10\,\mathrm{(stat)}\pm 0.03\,\mathrm{(syst)})\times 10^{-3}$. Systematic
uncertainties are discussed below. These values correspond to $55\pm
10\,\mathrm{(stat)}\pm 5\,\mathrm{(syst)}$
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays and $40\pm
10\,\mathrm{(stat)}\pm 3\,\mathrm{(syst)}$
${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays. The significances
of the observed signals are calculated using Wilks’ theorem [43], and are
$7.2\sigma$ and $4.8\sigma$ for the
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays, respectively. The
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
(${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$) significance is obtained
by considering the ${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
(${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$) yield as a floating
parameter in the fit. The systematic uncertainties are included by multiplying
the significance by the factor
$1/\sqrt{1+(\sigma_{\mathrm{(syst)}}/\sigma_{\mathrm{(stat)}})^{2}}$, where
$\sigma_{\mathrm{(stat)}}$ is the statistical uncertainty, and
$\sigma_{\mathrm{(syst)}}$ is the sum in quadrature of the contributions in
Table 2, except for the uncertainty on $f_{s}/f_{d}$.

Figure 3 compares the $\pi^{+}\pi^{-}$ mass spectra of
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B_{(s)}^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ candidates, separately for the $B^{0}_{s}$ and the
$B^{0}$ decays. The background is subtracted using the sPlot technique [44]
with the $\pi^{+}\pi^{-}\mu^{+}\mu^{-}$ mass as the discriminating variable.
The data show the dominance of the $f_{0}(980)$ resonance in the case of
${B^{0}_{s}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ decays, and of the $\rho(770)^{0}$ resonance in the
case of ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ decays, as expected from previous LHCb analyses [1,
2]. The ${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ data show
indications of a similar composition of the $\pi^{+}\pi^{-}$ mass spectrum,
although the size of the sample is not sufficient to draw a definite
conclusion.

\begin{overpic}[width=218.51521pt]{Fig3a} \put(78.0,80.0){(a)}
\end{overpic}\begin{overpic}[width=218.51521pt]{Fig3b} \put(25.0,80.0){(b)}
\end{overpic}

Figure 3: Background-subtracted distributions of the $\pi^{+}\pi^{-}$
invariant mass for (a) ${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$
and (b) ${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ candidates
(triangular markers). The uncertainties are statistical only. The data are
compared with the background-subtracted $\pi^{+}\pi^{-}$ mass distributions of
(a) ${B^{0}_{s}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ and (b)
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\,\pi^{+}\pi^{-}}$ candidates (histograms).

Several systematic uncertainties on $\mathcal{R}_{s}$ and $\mathcal{R}_{d}$
are considered, as summarised in Table 2. The contribution due to the
uncertainties on parameters that are fixed in the fit, and on the efficiencies
and the yields of ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ decays that are fixed in Eq. (1), is obtained by
repeating the fit, each time with the relevant parameters or inputs fixed to
alternate values. These are sampled from Gaussian distributions centred at the
nominal value, and whose widths correspond to the uncertainties on the fixed
parameters and inputs. Known correlations between fixed parameters are taken
into account. The r.m.s. spreads of the resulting $\mathcal{R}_{s}$ and
$\mathcal{R}_{d}$ values are taken as the systematic uncertainties. The
uncertainties associated with efficiencies are the sums in quadrature of their
statistical and systematic uncertainties, reported in Table 1. The uncertainty
on the ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}}$ yield is the sum in quadrature of the statistical
uncertainty, the systematic uncertainty, and the uncertainty due to the
$S$-wave subtraction. A systematic uncertainty is assigned on the estimation
of the combinatorial background with the following method; pseudo experiments
are generate in an extended mass range from
4.97${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$, where an additional peaking
component is also added to simulate the partially reconstructed $B^{0}$
decays, and the pseudo data are fitted in the nominal range from
5.19${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. The shifts between the average
fitted values and the input values of $\mathcal{R}_{s}$ and $\mathcal{R}_{d}$
are taken as the systematic uncertainties. The contribution to the systematic
uncertainty of $\mathcal{R}_{s}$ due to the uncertainty on the values of
$f_{s}/f_{d}$ is also included. The final systematic uncertainties are the
sums in quadrature of all contributions and correspond to $45\%$ and $28\%$ of
the statistical uncertainties of $\mathcal{R}_{s}$ and $\mathcal{R}_{d}$,
respectively.

Table 2: Summary of systematic uncertainties on $\mathcal{R}_{s}$ and $\mathcal{R}_{d}$. Source |  $\sigma(\mathcal{R}_{s})$ $[10^{-3}]$ |  $\sigma(\mathcal{R}_{d})$ $[10^{-3}]$
---|---|---
Shape of misidentified decays | 0.003 | 0.004
Partially reconstructed decays | 0.003 | 0.004
Combinatorial background | 0.029 | 0.014
Signal shapes | 0.020 | 0.014
Efficiencies | 0.061 | 0.013
Normalisation decay yields | 0.055 | 0.014
$f_{s}/f_{d}$ | 0.093 | –
Quadratic sum | 0.130 | 0.028

##  6 Conclusions

The first observation of the decay
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and the first evidence
of the decay ${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ are obtained
in a data set corresponding to an integrated luminosity of
3.0$\mbox{\,fb}^{-1}$ collected by the LHCb detector in $pp$ collisions at
centre-of-mass energies of 7 and 8$\mathrm{\,Te\kern-1.00006ptV}$. The
analysis is restricted to candidates with muon pairs that do not originate
from $\phi$, ${J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}$, and $\psi(2S)$
resonances, while the pion pairs are required to have invariant mass in the
range 0.5–1.3${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$. About 55
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays and 40
${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays are observed with
significances of $7.2\sigma$ and $4.8\sigma$, respectively. Their branching
fractions relative to the branching fraction of the
${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}(\\!\rightarrow\mu^{+}\mu^{-})K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-})}$ decay are measured to be

$\displaystyle\frac{\mathcal{B}({B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})}{\mathcal{B}(B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}(\\!\rightarrow\mu^{+}\mu^{-})K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-}))}$ $\displaystyle=(1.67\pm 0.29\,\mathrm{(stat)}\pm
0.13\,\mathrm{(syst)})\times 10^{-3},$
$\displaystyle\frac{\mathcal{B}({B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})}{\mathcal{B}(B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}(\\!\rightarrow\mu^{+}\mu^{-})K^{*}(892)^{0}(\\!\rightarrow
K^{+}\pi^{-}))}$ $\displaystyle=(0.41\pm 0.10\,\mathrm{(stat)}\pm
0.03\,\mathrm{(syst)})\times 10^{-3}.$

From these ratios, the following branching fractions are obtained for the
decays with the dipion-mass range considered:

$\displaystyle\mathcal{B}({B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})$
$\displaystyle=(8.6\pm 1.5\,\mathrm{(stat)}\pm 0.7\,\mathrm{(syst)}\pm
0.7\,({\rm norm}))\times 10^{-8}\text{ and}$
$\displaystyle\mathcal{B}({B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}})$
$\displaystyle=(2.11\pm 0.51\,\mathrm{(stat)}\pm 0.15\,\mathrm{(syst)}\pm
0.16\,({\rm norm}))\times 10^{-8},$

where the third uncertainties are due to the uncertainties on the branching
fraction of the normalization decay. We use
$\mathcal{B}({B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}K^{*}(892)^{0}})=(1.30\pm 0.10)\times 10^{-3}$, which is the weighted
average of measurements where the $K^{+}\pi^{-}$ $S$-wave contribution is
subtracted [45, 46, 47], ${\mathcal{B}({J\mskip-3.0mu/\mskip-2.0mu\psi\mskip
2.0mu}\\!\rightarrow\mu^{+}\mu^{-})}$ from Ref. [17], and
${\mathcal{B}(K^{*}(892)^{0}\\!\rightarrow K^{+}\pi^{-})=2/3}$.

Assuming that the decays ${f_{0}(980)\rightarrow\pi^{+}\pi^{-}}$ and
${\rho(770)^{0}\rightarrow\pi^{+}\pi^{-}}$ are the dominant transitions in the
${B^{0}_{s}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ and
${B^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ decays, respectively, and
neglecting other contributions, the
${B_{(s)}^{0}\\!\rightarrow\pi^{+}\pi^{-}\mu^{+}\mu^{-}}$ branching fractions
are corrected to account for the selection efficiencies of the $f_{0}(980)$
and $\rho(770)^{0}$ resonances in the $\pi^{+}\pi^{-}$ mass range considered.
The following values are obtained: $\mathcal{B}({B^{0}_{s}\\!\rightarrow
f_{0}(980)(\\!\rightarrow\pi^{+}\pi^{-})\mu^{+}\mu^{-})=(8.3\pm 1.7)\times
10^{-8}}$ and
$\mathcal{B}({B^{0}\\!\rightarrow\rho(770)^{0}\mu^{+}\mu^{-}})=(1.98\pm
0.53)\times 10^{-8}$, where all uncertainties are summed in quadrature. These
values favour SM expectations of Refs. [12, 14, 15] and disfavour the
$\mathcal{B}({B^{0}_{s}\\!\rightarrow f_{0}(980)\mu^{+}\mu^{-}})$ SM
expectation of Ref. [13].

## 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, HGF 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). The Tier1 computing centres are
supported by IN2P3 (France), KIT and BMBF (Germany), INFN (Italy), NWO and
SURF (The Netherlands), PIC (Spain), GridPP (United Kingdom). We are indebted
to the communities behind the multiple open source software packages on which
we depend. We are also thankful for the computing resources and the access to
software R&D tools provided by Yandex LLC (Russia). Individual groups or
members have received support from EPLANET, Marie Skłodowska-Curie Actions and
ERC (European Union), Conseil général de Haute-Savoie, Labex ENIGMASS and
OCEVU, Région Auvergne (France), RFBR (Russia), XuntaGal and GENCAT (Spain),
Royal Society and Royal Commission for the Exhibition of 1851 (United
Kingdom).

## References

  * [1] LHCb collaboration, R. Aaij et al., Measurement of the resonant and $CP$ components in $\bar{B}^{0}\rightarrow J/\psi\pi^{+}\pi^{-}$ decays, Phys. Rev. D90 (2014) 012003, arXiv:1404.5673
  * [2] LHCb collaboration, R. Aaij et al., Measurement of resonant and $CP$ components in $\bar{B}_{s}^{0}\rightarrow J/\psi\pi^{+}\pi^{-}$ decays, Phys. Rev. D89 (2014) 092006, arXiv:1402.6248
  * [3] S. L. Glashow, J. Iliopoulos, and L. Maiani, Weak interactions with lepton-hadron symmetry, Phys. Rev. D2 (1970) 1285
  * [4] N. Cabibbo, Unitary symmetry and leptonic decays, Phys. Rev. Lett. 10 (1963) 531
  * [5] M. Kobayashi and T. Maskawa, CP-violation in the renormalizable theory of weak interaction, Prog. Theor. Phys. 49 (1973) 652
  * [6] R. Mohanta, Study of some $B^{0}_{s}$ to $f_{0}(980)$ decays in the fourth generation model, Phys. Rev. D84 (2011) 014019, arXiv:1104.4739
  * [7] V. Bashiry and K. Azizi, Systematic analysis of the $B_{s}\rightarrow f_{0}\ell^{+}\ell^{-}$ in the universal extra dimension, JHEP 02 (2012) 021, arXiv:1112.5243
  * [8] E. Iltan, The exclusive $\bar{B}\rightarrow\pi e^{+}e^{-}$ and $\bar{B}\rightarrow\rho e^{+}e^{-}$ decays in the two Higgs doublet model with flavor changing neutral currents, Int. J. Mod. Phys. A14 (1999) 4365, arXiv:hep-ph/9807256
  * [9] T. Aliev and M. Savci, Exclusive $B\rightarrow\pi l^{+}l^{-}$ and $B\rightarrow\rho l^{+}l^{-}$ decays in two Higgs doublet model, Phys. Rev. D60 (1999) 014005, arXiv:hep-ph/9812272
  * [10] J.-J. Wang, R.-M. Wang, Y.-G. Xu, and Y.-D. Yang, Rare decays $B^{+}\rightarrow\pi^{+}l^{+}l^{-},\ \rho^{+}l^{+}l^{-}$ and $B^{0}\rightarrow l^{+}l^{-}$ in the R-parity violating supersymmetry, Phys. Rev. D77 (2008) 014017, arXiv:0711.0321
  * [11] R.-H. Li, C.-D. Lu, W. Wang, and X.-X. Wang, $b\rightarrow s$ transition form factors in the pQCD approach, Phys. Rev. D79 (2009) 014013, arXiv:0811.2648
  * [12] P. Colangelo, F. De Fazio, and W. Wang, $B_{s}\rightarrow f_{0}(980)$ form factors and $B_{s}$ decays into $f_{0}(980)$, Phys. Rev. D81 (2010) 074001, arXiv:1002.2880
  * [13] N. Ghahramany and R. Khosravi, Analysis of the rare semileptonic decays of $B^{0}_{s}$ to $f_{0}(980)$ and $K^{*}(1430)^{0}$ scalar mesons in QCD sum rules, Phys. Rev. D80 (2009) 016009
  * [14] F. Kruger and L. Sehgal, CP violation in the exclusive decays $B\rightarrow\pi e^{+}e^{-}$ and $B\rightarrow\rho e^{+}e^{-}$, Phys. Rev. D56 (1997) 5452, arXiv:hep-ph/9706247
  * [15] D. Melikhov and N. V. Nikitin, Form factors for rare decays $B\rightarrow(\pi,\rho,K,K^{*})l^{+}l^{-}$ in the quark model, arXiv:hep-ph/9609503
  * [16] M. Beneke, T. Feldmann, and D. Seidel, Exclusive radiative and electroweak $b\\!\rightarrow d$ and $b\\!\rightarrow s$ penguin decays at NLO, Eur. Phys. J. C41 (2005) 173, arXiv:hep-ph/0412400
  * [17] Particle Data Group, K. A. Olive et al., Review of particle physics, Chin. Phys. C38 (2014) 090001
  * [18] LHCb collaboration, A. A. Alves Jr. et al., The LHCb detector at the LHC, JINST 3 (2008) S08005
  * [19] R. Aaij et al., Performance of the LHCb Vertex Locator, JINST 9 (2014) P09007, arXiv:1405.7808
  * [20] R. Arink et al., Performance of the LHCb Outer Tracker, JINST 9 (2014) P01002, arXiv:1311.3893
  * [21] M. Adinolfi et al., Performance of the LHCb RICH detector at the LHC, Eur. Phys. J. C73 (2013) 2431, arXiv:1211.6759
  * [22] A. A. Alves Jr. et al., Performance of the LHCb muon system, JINST 8 (2013) P02022, arXiv:1211.1346
  * [23] T. Sjöstrand, S. Mrenna, and P. Skands, PYTHIA 6.4 physics and manual, JHEP 05 (2006) 026, arXiv:hep-ph/0603175
  * [24] T. Sjöstrand, S. Mrenna, and P. Skands, A brief introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852, arXiv:0710.3820
  * [25] I. Belyaev et al., Handling of the generation of primary events in Gauss, the LHCb simulation framework, Nuclear Science Symposium Conference Record (NSS/MIC) IEEE (2010) 1155
  * [26] D. J. Lange, The EvtGen particle decay simulation package, Nucl. Instrum. Meth. A462 (2001) 152
  * [27] 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
  * [28] I. Balakireva, D. Melikhov, N. Nikitin, and D. Tlisov, Forward-backward and $C\\!P$-violating asymmetries in rare $B_{d,s}\rightarrow(\phi,\gamma)l^{+}l^{-}$ decays, Phys. Rev. D81 (2010) 054024, arXiv:0911.0605
  * [29] A. Popov, N. Nikitin, and D. Savrina, The EvtGen-based model for the Monte-Carlo generation of the rare radiative leptonic $B$-decays, PoS QFTHEP2010 (2010) 035
  * [30] Geant4 collaboration, J. Allison et al., Geant4 developments and applications, IEEE Trans. Nucl. Sci. 53 (2006) 270
  * [31] Geant4 collaboration, S. Agostinelli et al., Geant4: a simulation toolkit, Nucl. Instrum. Meth. A506 (2003) 250
  * [32] M. Clemencic et al., The LHCb simulation application, Gauss: design, evolution and experience, J. Phys. Conf. Ser. 331 (2011) 032023
  * [33] R. Aaij et al., The LHCb trigger and its performance in 2011, JINST 8 (2013) P04022, arXiv:1211.3055
  * [34] V. V. Gligorov and M. Williams, Efficient, reliable and fast high-level triggering using a bonsai boosted decision tree, JINST 8 (2013) 2013P, arXiv:1210.6861
  * [35] LHCb collaboration, R. Aaij et al., Observation of a resonance in $B^{+}\rightarrow K^{+}\mu^{+}\mu^{-}$ decays at low recoil, Phys. Rev. Lett. 111 (2013) 112003, arXiv:1307.7595
  * [36] L. Breiman, J. H. Friedman, R. A. Olshen, and C. J. Stone, Classification and regression trees, Wadsworth international group, Belmont, California, USA, 1984
  * [37] R. E. Schapire and Y. Freund, A decision-theoretic generalization of on-line learning and an application to boosting, Jour. Comp. and Syst. Sc. 55 (1997) 119
  * [38] 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
  * [39] K. De Bruyn et al., Branching ratio measurements of $B^{0}_{s}$ decays, Phys. Rev. D86 (2012) 014027, arXiv:1204.1735
  * [40] LHCb collaboration, R. Aaij et al., Measurement of the fragmentation fraction ratio $f_{s}/f_{d}$ and its dependence on $B$ meson kinematics, JHEP 04 (2013) 001, arXiv:1301.5286, $f_{s}/f_{d}$ value updated in LHCb-CONF-2013-011
  * [41] ARGUS collaboration, H. Albrecht et al., Search for $b\rightarrow s\gamma$ in exclusive decays of $B$ mesons, Phys. Lett. B229 (1989), no. 3 304
  * [42] LHCb collaboration, R. Aaij et al., Measurement of the polarization amplitudes in $B^{0}\rightarrow J/\psi K^{*}(892)^{0}$ decays, Phys. Rev. D88 (2013) 052002, arXiv:1307.2782
  * [43] S. S. Wilks, The large-sample distribution of the likelihood ratio for testing composite hypotheses, Ann. Math. Statist. 9 (1938) 60
  * [44] M. Pivk and F. R. Le Diberder, sPlot: a statistical tool to unfold data distributions, Nucl. Instrum. Meth. A555 (2005) 356, arXiv:physics/0402083
  * [45] BaBar collaboration, B. Aubert et al., Evidence for the $B^{0}\\!\rightarrow p\bar{p}K^{*}(892)^{0}$ and $B^{+}\\!\rightarrow\eta_{c}K^{*}(892)^{+}$ decays and study of the decay dynamics of $B$ meson decays into $p\bar{p}h$ final states, Phys. Rev. D76 (2007) 092004, arXiv:0707.1648
  * [46] Belle collaboration, K. Abe et al., Measurements of branching fractions and decay amplitudes in ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}K^{*}(892)^{0}}$ decays, Phys. Lett. B538 (2002) 11, arXiv:hep-ex/0205021
  * [47] CLEO collaboration, C. Jessop et al., Measurement of the decay amplitudes and branching fractions of ${B^{0}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}K^{*}(892)^{0}}$ and $B^{+}\\!\rightarrow{J\mskip-3.0mu/\mskip-2.0mu\psi\mskip 2.0mu}K^{+}$ decays, Phys. Rev. Lett. 79 (1997) 4533, arXiv:hep-ex/9702013

LHCb collaboration

R. Aaij41, B. Adeva37, M. Adinolfi46, A. Affolder52, Z. Ajaltouni5, S. Akar6,
J. Albrecht9, F. Alessio38, M. Alexander51, S. Ali41, G. Alkhazov30, P.
Alvarez Cartelle37, A.A. Alves Jr25,38, S. Amato2, S. Amerio22, Y. Amhis7, L.
An3, L. Anderlini17,g, J. Anderson40, R. Andreassen57, M. Andreotti16,f, J.E.
Andrews58, R.B. Appleby54, O. Aquines Gutierrez10, F. Archilli38, A.
Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,n, M. Baalouch5, S.
Bachmann11, J.J. Back48, A. Badalov36, C. Baesso60, W. Baldini16, R.J.
Barlow54, C. Barschel38, S. Barsuk7, W. Barter47, V. Batozskaya28, V.
Battista39, A. Bay39, L. Beaucourt4, J. Beddow51, F. Bedeschi23, I. Bediaga1,
S. Belogurov31, K. Belous35, I. Belyaev31, E. Ben-Haim8, G. Bencivenni18, S.
Benson38, J. Benton46, A. Berezhnoy32, R. Bernet40, A. Bertolin22, M.-O.
Bettler47, M. van Beuzekom41, A. Bien11, S. Bifani45, T. Bird54, A.
Bizzeti17,i, P.M. Bjørnstad54, T. Blake48, F. Blanc39, J. Blouw10, S. Blusk59,
V. Bocci25, A. Bondar34, N. Bondar30,38, W. Bonivento15, S. Borghi54, A.
Borgia59, M. Borsato7, T.J.V. Bowcock52, E. Bowen40, C. Bozzi16, D. Brett54,
M. Britsch10, T. Britton59, J. Brodzicka54, N.H. Brook46, A. Bursche40, J.
Buytaert38, S. Cadeddu15, R. Calabrese16,f, M. Calvi20,k, M. Calvo Gomez36,p,
P. Campana18, D. Campora Perez38, L. Capriotti54, A. Carbone14,d, G.
Carboni24,l, R. Cardinale19,38,j, A. Cardini15, L. Carson50, K. Carvalho
Akiba2,38, RCM Casanova Mohr36, G. Casse52, L. Cassina20,k, L. Castillo
Garcia38, M. Cattaneo38, Ch. Cauet9, R. Cenci23,t, M. Charles8, Ph.
Charpentier38, M. Chefdeville4, S. Chen54, S.-F. Cheung55, N. Chiapolini40, M.
Chrzaszcz40,26, 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, I. Counts56, B. Couturier38, G.A. Cowan50, D.C. Craik48, A.C.
Crocombe48, M. Cruz Torres60, S. Cunliffe53, R. Currie53, C. D’Ambrosio38, J.
Dalseno46, P. David8, P.N.Y. David41, A. Davis57, K. De Bruyn41, S. De
Capua54, M. De Cian11, J.M. De Miranda1, L. De Paula2, W. De Silva57, P. De
Simone18, C.-T. Dean51, D. Decamp4, M. Deckenhoff9, L. Del Buono8, N.
Déléage4, D. Derkach55, O. Deschamps5, F. Dettori38, B. Dey40, A. Di Canto38,
A Di Domenico25, H. Dijkstra38, S. Donleavy52, F. Dordei11, M. Dorigo39, A.
Dosil Suárez37, D. Dossett48, A. Dovbnya43, K. Dreimanis52, 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. Färber11, C.
Farinelli41, N. Farley45, S. Farry52, R. Fay52, D. Ferguson50, V. Fernandez
Albor37, F. Ferreira Rodrigues1, M. Ferro-Luzzi38, S. Filippov33, M.
Fiore16,f, M. Fiorini16,f, M. Firlej27, C. Fitzpatrick39, T. Fiutowski27, P.
Fol53, M. Fontana10, F. Fontanelli19,j, R. Forty38, O. Francisco2, M. Frank38,
C. Frei38, M. Frosini17, J. Fu21,38, E. Furfaro24,l, A. Gallas Torreira37, D.
Galli14,d, S. Gallorini22,38, S. Gambetta19,j, M. Gandelman2, P. Gandini59, Y.
Gao3, J. García Pardiñas37, J. Garofoli59, J. Garra Tico47, L. Garrido36, D.
Gascon36, C. Gaspar38, U. Gastaldi16, R. Gauld55, L. Gavardi9, G. Gazzoni5, A.
Geraci21,v, E. Gersabeck11, M. Gersabeck54, T. Gershon48, Ph. Ghez4, A.
Gianelle22, S. Gianì39, V. Gibson47, L. Giubega29, V.V. Gligorov38, C.
Göbel60, D. Golubkov31, A. Golutvin53,31,38, A. Gomes1,a, C. Gotti20,k, 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, C. Hadjivasiliou59, G. Haefeli39, C. Haen38, S.C. Haines47, S.
Hall53, B. Hamilton58, T. Hampson46, 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, 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, T. Ketel42, B. Khanji20,38,k, C.
Khurewathanakul39, S. Klaver54, K. Klimaszewski28, O. Kochebina7, M. Kolpin11,
I. Komarov39, R.F. Koopman42, P. Koppenburg41,38, M. Korolev32, L. Kravchuk33,
K. Kreplin11, M. Kreps48, G. Krocker11, P. Krokovny34, F. Kruse9, W.
Kucewicz26,o, M. Kucharczyk20,26,k, V. Kudryavtsev34, K. Kurek28, T.
Kvaratskheliya31, V.N. La Thi39, D. Lacarrere38, G. Lafferty54, A. Lai15, D.
Lambert50, R.W. Lambert42, G. Lanfranchi18, C. Langenbruch48, B. Langhans38,
T. Latham48, C. Lazzeroni45, R. Le Gac6, J. van Leerdam41, J.-P. Lees4, R.
Lefèvre5, A. Leflat32, J. Lefrançois7, O. Leroy6, T. Lesiak26, B.
Leverington11, Y. Li3, T. Likhomanenko64, M. Liles52, R. Lindner38, C. Linn38,
F. Lionetto40, B. Liu15, S. Lohn38, I. Longstaff51, J.H. Lopes2, P. Lowdon40,
D. Lucchesi22,r, H. Luo50, A. Lupato22, E. Luppi16,f, O. Lupton55, F.
Machefert7, I.V. Machikhiliyan31, F. Maciuc29, O. Maev30, S. Malde55, A.
Malinin64, G. Manca15,e, G. Mancinelli6, A. Mapelli38, J. Maratas5, J.F.
Marchand4, U. Marconi14, C. Marin Benito36, P. Marino23,t, R. Märki39, J.
Marks11, G. Martellotti25, M. Martinelli39, D. Martinez Santos42, F. Martinez
Vidal65, D. Martins Tostes2, A. Massafferri1, R. Matev38, Z. Mathe38, C.
Matteuzzi20, A. Mazurov45, M. McCann53, J. McCarthy45, A. McNab54, R.
McNulty12, B. McSkelly52, B. Meadows57, F. Meier9, M. Meissner11, M. Merk41,
D.A. Milanes62, M.-N. Minard4, N. Moggi14, J. Molina Rodriguez60, S. Monteil5,
M. Morandin22, P. Morawski27, A. Mordà6, M.J. Morello23,t, J. Moron27, A.-B.
Morris50, R. Mountain59, F. Muheim50, K. Müller40, M. Mussini14, B. Muster39,
P. Naik46, T. Nakada39, R. Nandakumar49, I. Nasteva2, M. Needham50, N. Neri21,
S. Neubert38, N. Neufeld38, M. Neuner11, A.D. Nguyen39, T.D. Nguyen39, C.
Nguyen-Mau39,q, M. Nicol7, V. Niess5, R. Niet9, N. Nikitin32, T. Nikodem11, A.
Novoselov35, D.P. O’Hanlon48, A. Oblakowska-Mucha27, V. Obraztsov35, S.
Ogilvy51, O. Okhrimenko44, R. Oldeman15,e, C.J.G. Onderwater66, M. Orlandea29,
B. Osorio Rodrigues1, J.M. Otalora Goicochea2, A. Otto38, P. Owen53, A.
Oyanguren65, B.K. Pal59, A. Palano13,c, F. Palombo21,u, M. Palutan18, J.
Panman38, A. Papanestis49,38, M. Pappagallo51, L.L. Pappalardo16,f, C.
Parkes54, C.J. Parkinson9,45, G. Passaleva17, G.D. Patel52, M. Patel53, C.
Patrignani19,j, A. Pearce54,49, A. Pellegrino41, G. Penso25,m, M. Pepe
Altarelli38, S. Perazzini14,d, P. Perret5, L. Pescatore45, E. Pesen67, K.
Petridis53, A. Petrolini19,j, E. Picatoste Olloqui36, B. Pietrzyk4, T.
Pilař48, D. Pinci25, A. Pistone19, S. Playfer50, M. Plo Casasus37, F. Polci8,
A. Poluektov48,34, I. Polyakov31, E. Polycarpo2, A. Popov35, D. Popov10, B.
Popovici29, C. Potterat2, E. Price46, J.D. Price52, J. Prisciandaro39, A.
Pritchard52, C. Prouve46, V. Pugatch44, A. Puig Navarro39, G. Punzi23,s, W.
Qian4, B. Rachwal26, J.H. Rademacker46, B. Rakotomiaramanana39, 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, A.B. Rodrigues1, E.
Rodrigues54, P. Rodriguez Perez54, S. Roiser38, V. Romanovsky35, A. Romero
Vidal37, M. Rotondo22, J. Rouvinet39, T. Ruf38, H. Ruiz36, P. Ruiz Valls65,
J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B. Saitta15,e, V. Salustino
Guimaraes2, C. Sanchez Mayordomo65, B. Sanmartin Sedes37, R. Santacesaria25,
C. Santamarina Rios37, E. Santovetti24,l, A. Sarti18,m, C. Satriano25,n, A.
Satta24, D.M. Saunders46, D. Savrina31,32, M. Schiller38, H. Schindler38, M.
Schlupp9, M. Schmelling10, B. Schmidt38, O. Schneider39, A. Schopper38, M.-H.
Schune7, R. Schwemmer38, B. Sciascia18, A. Sciubba25,m, A. Semennikov31, I.
Sepp53, N. Serra40, J. Serrano6, L. Sestini22, P. Seyfert11, M. Shapkin35, I.
Shapoval16,43,f, Y. Shcheglov30, T. Shears52, L. Shekhtman34, V. Shevchenko64,
A. Shires9, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46, I.
Skillicorn51, T. Skwarnicki59, N.A. Smith52, E. Smith55,49, E. Smith53, J.
Smith47, M. Smith54, H. Snoek41, M.D. Sokoloff57, F.J.P. Soler51, F. Soomro39,
D. Souza46, B. Souza De Paula2, B. Spaan9, P. Spradlin51, S. Sridharan38, F.
Stagni38, M. Stahl11, S. Stahl11, O. Steinkamp40, O. Stenyakin35, F Sterpka59,
S. Stevenson55, S. Stoica29, S. Stone59, B. Storaci40, S. Stracka23,t, M.
Straticiuc29, U. Straumann40, R. Stroili22, L. Sun57, W. Sutcliffe53, K.
Swientek27, S. Swientek9, V. Syropoulos42, M. Szczekowski28, P. Szczypka39,38,
T. Szumlak27, S. T’Jampens4, 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, M.T. Tran39, M. Tresch40, A. Trisovic38, A.
Tsaregorodtsev6, P. Tsopelas41, N. Tuning41, M. Ubeda Garcia38, A. Ukleja28,
A. Ustyuzhanin64, 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,h, G. Veneziano39, M. Vesterinen11,
JVVB Viana Barbosa38, B. Viaud7, D. Vieira2, M. Vieites Diaz37, X. Vilasis-
Cardona36,p, 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, M. Whitehead48, D. Wiedner11, G. Wilkinson55,38, M. Wilkinson59,
M.P. Williams45, M. Williams56, H.W. Wilschut66, F.F. Wilson49, J.
Wimberley58, J. Wishahi9, W. Wislicki28, M. Witek26, G. Wormser7, S.A.
Wotton47, S. Wright47, K. Wyllie38, Y. Xie61, Z. Xing59, Z. Xu39, Z. Yang3, X.
Yuan3, O. Yushchenko35, M. Zangoli14, M. Zavertyaev10,b, L. Zhang3, W.C.
Zhang12, Y. Zhang3, A. Zhelezov11, A. Zhokhov31, L. Zhong3.

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 de Savoie, 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
65Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC,
Valencia, Spain, associated to 36
66Van Swinderen Institute, University of Groningen, Groningen, The
Netherlands, associated to 41
67Celal Bayar University, Manisa, Turkey, associated to 38

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 Firenze, Firenze, Italy
hUniversità di Urbino, Urbino, Italy
iUniversità di Modena e Reggio Emilia, Modena, Italy
jUniversità di Genova, Genova, Italy
kUniversità di Milano Bicocca, Milano, Italy
lUniversità di Roma Tor Vergata, Roma, Italy
mUniversità di Roma La Sapienza, Roma, Italy
nUniversità della Basilicata, Potenza, Italy
oAGH - University of Science and Technology, Faculty of Computer Science,
Electronics and Telecommunications, Kraków, Poland
pLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
qHanoi University of Science, Hanoi, Viet Nam
rUniversità di Padova, Padova, Italy
sUniversità di Pisa, Pisa, Italy
tScuola Normale Superiore, Pisa, Italy
uUniversità degli Studi di Milano, Milano, Italy
vPolitecnico di Milano, Milano, Italy