Search for the decay ...

Abstract

Abstract

A search for ... decays is performed using 3.0 fb^1- of pp collision data recorded by the LHCb experiment during 2011 and 2012. The f ₀(980) meson is reconstructed through its decay to the [pi] ⁺ [pi] ^- final state in the mass window 900 MeV/c ² < m([pi] ⁺ [pi] ^-) < 1080 MeV/c ². No significant signal is observed. The first upper limits on the branching fraction of ... are set at 90 % (95 %) confidence level. [Figure not available: see fulltext.]

Published for SISSA by Springer

Received: May 8, 2015 Revised: June 15, 2015 Accepted: June 26, 2015 Published: August 3, 2015

Search for the decay B0s ! D0f0(980)

JHEP08(2015)005

The LHCb collaboration

E-mail: mailto:[email protected]

Web End [email protected]

Abstract: A search for B0s ! D0f0(980) decays is performed using 3.0 fb1 of pp collision

data recorded by the LHCb experiment during 2011 and 2012. The f0(980) meson is reconstructed through its decay to the + nal state in the mass window 900 MeV/c2 < m(+) < 1080 MeV/c2. No signicant signal is observed. The rst upper limits on the branching fraction of B(B0s ! D0f0(980)) < 3.1 (3.4) 106 are set at 90 % (95 %)

condence level.

Keywords: Hadron-Hadron Scattering, Branching fraction, B physics, Flavor physics

ArXiv ePrint: 1505.01654

Open Access, Copyright CERN,for the benet of the LHCb Collaboration. Article funded by SCOAP3.

doi:http://dx.doi.org/10.1007/JHEP08(2015)005

Web End =10.1007/JHEP08(2015)005

Contents

1 Introduction 1

2 LHCb detector 2

3 Selection 3

4 Determination of signal yield 4

5 Systematic uncertainties 5

6 Results and summary 8

The LHCb collaboration 14

1 Introduction

Understanding the quark-level substructure of the scalar mesons is one of the main challenges in hadronic physics. The number of observed states, and their masses and branching fractions, suggest that there is a contribution from four-quark wavefunctions in addition to q[notdef]q, and possible gluonic, degrees of freedom [1, 2]. However, the extent of mixing between the di erent components is unclear.

Measurement of the relative production of scalar mesons in B0 and B0s meson decays can help to address this issue [3, 4]. Measurements of B0(s) ! J/ f decays, where f repre

sents either the f0(500) (also known as ) or the f0(980) meson, and f ! + [58] have

already provided important insight into the structure of the scalar mesons [9, 10]. Studies of B0(s) ! D0f decays provide complementary information to the B0(s) ! J/ f case [11].

Measurements of the branching fractions of B0 ! D0f0(500) and B0 ! D0f0(980) decays

have been obtained from Dalitz plot analyses of B0 ! D0+ decays [12, 13], but there

is no experimental result to date on the B0s decays.

In addition, under the assumption that the f0(980) meson has a predominant s[notdef]s component, the B0s ! D0f0(980) decay mode can be used to determine the angle

of the CKM unitarity triangle [14, 15], using the same methods that are applicable for the B0s ! D0 decay mode [1620]. Since the B0s ! D0 decay has recently been ob-

served [21], a signal for the B0s ! D0f0(980) channel is expected if the branching fractions

of the two decays are comparable. An explicit calculation predicts B B0s ! D0f0(980) [parenrightbig]

=

105 [22].

In this paper, the result of a search for the B0s ! D0f0(980) decay is presented. The

inclusion of charge conjugated processes is implied throughout the paper. The nal state

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JHEP08(2015)005

3.50 +1.261.15 +0.560.77

[parenrightbig]

is reconstructed through the D0 ! K+ and f0(980) ! + decays. The decay-time-

integrated branching fraction is measured under the assumption that the B0s ! D0+ decay proceeds uniquely via the f0(980) resonance within the selected mass window, 900 MeV/c2 < m(+) < 1080 MeV/c2. This approach was used for the rst observation of B0s ! J/ f0(980) decays [23]; it is also justied by the fact that no other con

tribution to B0s ! D0+ decays, for example through the B0s ! D + process [24],

is expected at the current level of sensitivity. A further assumption is that the contribution from B0s ! D0f0(980) decays, which is suppressed by the ratio of CKM matrix

elements |VubV cs/(VcbV us)|2 0.1, is negligible. Formally, the measurement is of the decay-

time-integrated sum of the branching fractions for B0s ! D0f0(980) and B0s ! D0f0(980)

decays.

The analysis is based on 3.0 fb1 of LHC pp collision data collected with the LHCb detector, with approximately one third taken at a centre-of-mass energy of 7 TeV during 2011 and the remainder at 8 TeV during 2012. The measurement is obtained by evaluating the ratio of branching fractions

B(B0s ! D0f0(980))

B(B0 ! D0+)

= N(B0s ! D0f0(980))N(B0 ! D0+)

JHEP08(2015)005

fdfs , (1.1)

from which the absolute branching fraction for B0s ! D0f0(980) decays is determined

using the known value of B(B0 ! D0+) [13]. The yields N(B0s ! D0f0(980)) and

N(B0 ! D0+) are determined from separate extended maximum likelihood ts to

the distributions of selected D0f0(980) and D0+ candidates in both the B candidate mass and the output of a neural network (NN) used to separate signal from combinatorial background. The combined reconstruction and selection e ciencies, [epsilon1](B0s ! D0f0(980))

and [epsilon1](B0 ! D0+), are determined from simulated samples with data-driven correc

tions applied. The ratio of fragmentation fractions inside the LHCb acceptance has been measured to be fs/fd = 0.259 0.015 ([25], fs/fd value updated in [26]). Equation (1.1)

corresponds to a branching fraction for f0(980) ! + of 100 %, which is the conventional

way to quote results for decays involving f0(980) mesons.

2 LHCb detector

The LHCb detector [27, 28] is a single-arm forward spectrometer covering the pseudorapidity range 2 < < 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 [29] surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes [30] placed downstream of the magnet. 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 GeV/c. The minimum distance of a track to a primary vertex, the impact parameter (IP), is measured with a resolution of (15 + 29/pT) m, where pT is the component of the momentum transverse to the beam, in GeV/c. Di erent types of charged hadrons are distinguished

2

[epsilon1](B0 ! D0+) [epsilon1](B0s ! D0f0(980))

using information from two ring-imaging Cherenkov detectors [31]. Photon, electron and hadron candidates are identied by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter and a hadronic calorimeter. Muons are identied by a system composed of alternating layers of iron and multiwire proportional chambers [32].

The trigger [33] consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, in which all tracks with pT >

500 (300) MeV are reconstructed for 2011 (2012) data. The software trigger requires a two-, three- or four-track secondary vertex with signicant displacement from the primary pp interaction vertices (PVs). At least one charged particle must have pT > 1.7 GeV/c and be inconsistent with originating from a PV. A multivariate algorithm [34] is used for the identication of secondary vertices consistent with the decay of a b hadron.

Simulated events are used to characterise the detector response to signal and certain types of background events. In the simulation, pp collisions are generated using Pythia [35, 36] with a specic LHCb conguration [37]. Decays of hadronic particles are described by EvtGen [38], in which nal state radiation is generated using Photos [39]. The interaction of the generated particles with the detector and its response are implemented using the Geant4 toolkit [40, 41] as described in ref. [42].

3 Selection

Candidates consistent with the decay chain B0(s) ! D0+ with D0 ! K+ are se

lected. The selection procedure involves applying a preselection to the data sample before using a NN to reduce the combinatorial background. The NN [43] is trained with the preselected D0+ data sample, using the sPlot method [44] with the B candidate mass as discriminating variable to separate statistically the signal and background categories. The input variables to the NN are related to the kinematic properties of the candidate, its isolation from the rest of the pp collision event, and the topology of the signal decay chain. Full details of the preselection and NN training can be found in ref. [45]. The four nal-state tracks must also satisfy particle identication (PID) requirements. Signal candidates are retained for further analysis if they have invariant mass in the range 51005900 MeV/c2.

A requirement that the NN output is greater than 0.7 removes 77 % of combinatorial

background and retains 95 % of B0s ! D0f0(980) decays.

A requirement m(D0) > 2.10 GeV/c2 is used to remove candidates that predominantly originate from B0 ! D + decays. A further requirement, m(D0+) <

5.14 GeV/c2, is used to remove backgrounds from B+ ! D0+ decays combined with a

random candidate. This source of combinatorial background is kinematically excluded from the signal region, but causes structure in the mass distribution at higher B candidate mass. A similar contribution from B+ ! D 0+ decays cannot be vetoed in the same way,

and must therefore be considered further as a source of background.

Following all selection requirements, approximately 1 % of events contain more than one candidate. All candidates are retained for the subsequent analysis; the associated systematic uncertainty is negligible.

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JHEP08(2015)005

4 Determination of signal yield

The yields of B0s ! D0f0(980) and B0 ! D0+ decays are obtained from two separate

extended maximum likelihood ts to the distributions of NN output and B candidate mass for selected candidates. The only di erence between the samples used in the two ts is that the former has an additional requirement of 900 MeV/c2 < m(+) < 1080 MeV/c2. The yield of B0s ! D0+ decays in the latter t is expected to be negligible compared to

the large yields of B0 decays and combinatorial background, and is therefore xed to zero. However, a signicant number of B0 ! D0+ decays are expected to remain within the

f0(980) mass window [13], and therefore both B0 and B0s components are included in the former t.

The data are divided into ve bins of the NN output variable, dened as [0.70, 0.03],

[0.03, 0.54], [0.54, 0.77], [0.77, 0.88] and [0.88, 1.00], and referred to hereafter as bins 1 to 5, respectively. The ve bins contain a similar proportion of signal decays and increase in purity from bin 1 to bin 5. This choice of binning has been found to enhance the sensitivity whilst giving stable t performance.

The ts include components due to signal and combinatorial background as well as from partially reconstructed and misidentied b-hadron decays. The signal invariant mass distribution is described by the sum of two Crystal Ball (CB) [46] functions, with a shared mean and tails on opposite sides described by parameters that are xed to values found in ts to simulated samples.

The combinatorial background is modelled with the sum of two components. The rst has an exponential shape, described by a parameter that is the same in all NN bins. The second originates from B+ ! D 0+ decays combined with a random pion candidate, and

is modelled using a non-parametric shape determined from simulation. The limited sizes of the simulated samples used to obtain this and similar shapes are sources of systematic uncertainty.

Partially reconstructed backgrounds occur from B0 ! D 0+ decays, with D 0 !

D00 and D 0 ! D0 where the neutral pion or photon is not associated with the can

didate, and from B+ ! D0++ decays where one + is also not associated with

the candidate. The invariant mass shapes of these backgrounds are described with non-parametric functions derived from simulation. A global o set of the shape of the partially reconstructed background is determined from the t to data to allow for di erences between data and simulation [47].

Backgrounds from misidentied b-hadron decays arise from B0 ! D( )0K+ and B0s ! D( )0K+ (hereafter collectively referred to as B0(s) ! D( )0K) decays where

the kaon is misidentied as a pion and from 0b ! D( )0p decays where the proton is

misidentied as a pion. Simulation is used to obtain non-parametric descriptions of the invariant mass shapes. To obtain these shapes, the latest knowledge of the phase-space distributions of the decays [45, 48, 49], of the relative branching fractions of the B0 and B0s ! D0K modes [48], and of the relative branching fractions of the decays involving

D0 and D 0 mesons [2], is used. Data-driven estimates of the misidentication probability as a function of particle kinematic properties are also included. The relative yields in the NN bins are taken to be the same as for the signal decays.

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JHEP08(2015)005

A total of 25 parameters are determined from the t to the D0+ sample. These include yields of B0 ! D0+ decays, the total combinatorial background, the total par

tially reconstructed background, and the B0(s) ! D( )0K and 0b ! D( )0p misidentied

backgrounds. For B0 ! D0+ decays, combinatorial and partially reconstructed back

grounds, the fractional yields fi of each component in bins 14 are also free parameters, with the fraction in bin 5 determined as f5 = 1

P4i=1 fi. In addition, the exponential slope parameter of the combinatorial background, the fraction of the combinatorial background from B+ ! D 0+ decays, the fraction of the partially reconstructed background

from B0 ! D 0+ decays and the o set parameter of the partially reconstructed back

ground are determined by the t. Parameters of the signal invariant mass shape (the peak position, the width of the core CB function, and the relative normalisation and ratio of the CB widths) are also allowed to vary. Results of this t are shown in gure 1.

The t to the D0f0(980) subsample includes the same components as the B0 !

D0+ t, with the addition of a second signal component to account for the possible presence of both B0 and B0s decays. The mass di erence between the B0 and B0s mesons is xed to the known value [2]. The shapes for the B0 and B0s components are otherwise identical in both invariant mass and NN output. The following parameters are xed to the values found in the B0 ! D0+ t: the fractional yields fi for the signal and partially

reconstructed background components; the relative normalisation of the two CB functions; the ratio of widths of the CB functions; the fraction of the partially reconstructed background from B0 ! D 0+ decays and the o set parameter of the partially reconstructed

background. In addition, the relative yields of the misidentied background components from B0 ! D( )0K+ and B0s ! D( )0K+ decays are xed to the expected value [48].

The remaining 14 parameters are: the yields for B0s ! D0f0(980) decays, B0 ! D0+

decays, combinatorial and partially reconstructed backgrounds and for the B0(s) ! D( )0K and 0b ! D( )0p misidentied backgrounds; the fractional yields of the combinatorial

background in NN output bins, the exponential slope parameter of the combinatorial background and the fraction of the combinatorial background from B+ ! D 0+ decays; and

the signal peak position and core width. Results of this t are shown in gure 2.

The yields from the ts to the D0f0(980) and D0+ data samples are summarised in table 1. In total, 29 17 B0s ! D0f0(980) decays are found, with a statistical signicance

of 2.2 obtained from p2 ln L, where ln L is the change in log likelihood from the

value obtained in a t with zero signal yield.

5 Systematic uncertainties

The systematic uncertainties that a ect the ratio of branching fractions are summarised in table 2. Various e ects contribute to the systematic uncertainties on the invariant mass t and e ciencies, as described below.

The tail parameters of the signal components for B0s ! D0f0(980) and B0 ! D0+

decays are varied within the uncertainties from the t to simulated events. For the B0s ! D0f0(980) t, the relative normalisation and ratio of widths of the CB functions

are varied according to the uncertainties from the t to the B0 ! D0+ mode. Com-

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LHCb

(a)

2

cCandidates / 8 MeV/

2

cCandidates / 8 MeV/

10

10

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10

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1 5200 5400 5600 5800

1 5200 5400 5600 5800

)2 c

D 0 p + p ) (MeV/(m

)2 c

D 0 p + p ) (MeV/(m

JHEP08(2015)005

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cCandidates / 8 MeV/

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cCandidates / 8 MeV/

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D 0 p + p ) (MeV/(m

)2 c

D 0 p + p ) (MeV/(m

2

cCandidates / 8 MeV/

10

Data Full fit

p

0

0

BComb. bkg. Part. reco. bkg.

+

p

D

+

p

B

0

* 0

( )

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s

K

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0

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+

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p

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* 0

( )

D

b

+

p

p

10

3

2

10

1 5200 5400 5600 5800

)2 c

D 0 p + p ) (MeV/(m

Figure 1. Invariant mass distribution of candidates in the D0+ data sample with t results overlaid, shown on a logarithmic scale. The components are as detailed in the legend. The labels (a) to (e) show the NN bins with increasing purity. The NN binning scheme is described in section 4.

D0+ D0f0(980)

B0 ! D0+ 42 636 362 3 998 87

B0s ! D0f0(980) 29 17

Combinatorial 90 150 481 11 064 145

Partially reconstructed 50 950 493 3 759 88

B0(s) ! D( )0K 9 225 504 852 128

0b ! D( )0p 4 923 415 154 135 Table 1. Yields from the t to the D0+ and D0f0(980) samples.

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JHEP08(2015)005

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Data Full fit

p

0

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0

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+

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BComb. bkg. Part. reco. bkg.

+

p

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f

0 (980)

0

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0

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( )

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s

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B

0

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( )

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K

+

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0

L

* 0

( )

D

b

+

p

p

10

2

10

1

5200 5400 5600 5800

)2 c

D 0 p + p ) (MeV/(m

Figure 2. Invariant mass distribution of candidates in the D0f0(980) data sample with t results overlaid, shown on a logarithmic scale. The components are as detailed in the legend. The labels (a) to (e) show the NN bins with increasing purity. The NN binning scheme is described in section 4.

bined in quadrature these contribute 11.5 % to the systematic uncertainty. The systematic uncertainty from assuming that the NN response is identical for B0s ! D0f0(980)

and B0 ! D0+ decays is evaluated by correcting the fractional yields found in the

B0 ! D0+ t by the ratio of fractional yields found in simulated samples. This

contributes 0.3 % to the systematic uncertainty.

A second-order polynomial function is used to replace the exponential shape for the combinatorial background in both ts, giving a systematic uncertainty of 8.4 %. Varying the smoothing of the non-parametric shape for B+ ! D 0+ decays gives the largest

source of systematic uncertainty of 23.1 %; the size of this e ect is determined by that of

7

the simulated background sample. The fractional yields of the B+ ! D 0+ component

of the combinatorial background are xed to the values found in simulation, rather than using the same fractional yields as the rest of the combinatorial background. This leads to a systematic uncertainty of 1.0 %.

The smoothing of the non-parametric functions for B0 ! D 0+ and B+ ! D0++ is varied in both ts. Additionally, in the B0s ! D0f0(980) sample, the rela

tive normalisation of the shapes is varied within uncertainties from the value found in the B0 ! D0+ t. Combined in quadrature these contribute 6.2 % to the systematic un

certainty. Allowing the fractional yields of the partially reconstructed background to vary in the D0f0(980) t, instead of being xed to values found in the D 0+ t, contributes 3.1 % to the systematic uncertainty.

The misidentied background shapes are also varied by changing the smoothing applied to the non-parametric function. Additionally, the simulation is not reweighted to the known phase-space distributions and the relative normalisation of the B0(s) ! D( )0K

shapes is varied within uncertainties. Together these contribute 6.7 % to the systematic uncertainty. Corrections, derived from simulation, are applied to the fractional yields for the misidentied backgrounds, which are assumed to behave like signal decays in the default t. The sum in quadrature of the individual contributions gives a systematic uncertainty of 8.5 %.

Potential biases in the t procedure are investigated using an ensemble of pseudoexperiments. Each of the pseudoexperiments is tted with the same t model used to describe the data samples. This study shows that the t is stable and well behaved and that the associated systematic uncertainty is negligible.

The uncertainty on the ratio of reconstruction and selection e ciencies for the B0s ! D0f0(980) and B0 ! D0+ nal states contributes 2.5 % to the systematic uncertainty.

This includes statistical uncertainty from the sizes of the simulated samples as well as e ects related to the choice of binning in kinematic variables in the evaluation of the PID e ciency and potential di erences in the response of the hardware trigger. The simulated sample of B0s ! D0f0(980) decays is generated using a relativistic BreitWigner function

with a width of 70 MeV for the f0(980) meson. The true lineshape of the f0(980) meson can di er from the assumed shape in a process-dependent way, which can a ect the fraction of f0(980) ! + decays that fall inside the selected m(+) window. No systematic

uncertainty is assigned due to this choice of f0(980) lineshape. Other possible sources of uncertainty on the ratio of e ciencies are negligible.

The limited knowledge of the ratio of fragmentation fractions, fs/fd = 0.259

0.015 ([25], fs/fd value updated in [26]), contributes 5.8 % to the systematic uncertainty. Combining all of the above sources in quadrature, the total systematic uncertainty on the ratio of branching fractions is found to be 30.7 %.

6 Results and summary

The relative branching fraction of B0s ! D0f0(980) and B0 ! D0+ decays is deter

mined by correcting the ratio of yields for the relative e ciencies and fragmentation frac-

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JHEP08(2015)005

Source Value

Signal shapes 11.5 %

Combinatorial background shapes 24.6 %

Partially reconstructed background shapes 6.9 %

Misidentied background shapes 10.8 %

E ciencies 2.5 %

Fragmentation fraction fs/fd 5.8 %

Total 30.7 %

Table 2. Summary of systematic uncertainties on the ratio of branching fractions.

tions, as shown in eq. (1.1). The total e ciencies are found to be [epsilon1](B0s ! D0f0(980)) =

(0.76 0.02) % and [epsilon1](B0 ! D0+) = (0.57 0.02) %. These values include contri

butions from the LHCb detector acceptance and from selection, trigger and PID requirements. The selection and trigger e ciencies are calculated from simulated samples with data-driven corrections applied. The PID e ciency is measured using a control sample of D ! D0, D0 ! K+ decays. Variation of the B0 ! D0+ e ciency over the

Dalitz plot is taken into account by weighting the simulation according to the observed Dalitz plot distribution [13].

Using eq. (1.1) the ratio of branching fractions is determined to be

B(B0s ! D0f0(980))

B(B0 ! D0+)

= (2.0 1.1 0.6) 103 ,

where the rst uncertainty is statistical and the second systematic. This result is obtained under the assumption that the B0s ! D0+ decays proceed uniquely via the f0(980)

resonance within the range 900 MeV/c2 < m(+) < 1080 MeV/c2; no systematic uncertainty is assigned due to this assumption. The result can be converted into an absolute branching fraction by multiplying by B(B0 ! D0+) = (8.46 0.51) 104 [13] to give

B(B0s ! D0f0(980)) = (1.7 1.0 0.5 0.1) 106 ,

where the third uncertainty is from B(B0 ! D0+). Since the signal yield is not

signicant, upper limits of

B(B0s ! D0f0(980)) < 3.1 (3.4) 106are set at 90 % (95 %) condence level. The statistical likelihood curve obtained from the t is convolved with a Gaussian function of width equal to the systematic uncertainty. The limits obtained are the values within which 90 % (95 %) of the integral of the likelihood in the physical region of non-negative branching fraction are contained.

In summary, a search for the B0s ! D0f0(980) decay has been performed using 3.0 fb1

of pp collision data recorded by the LHCb detector in 2011 and 2012. No signicant

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B(B0 ! D0f0) [13] B(B0s ! D0f0)

f0(500) (11.2 0.8 0.5 2.1 0.5) 105

f0(980) (1.34 0.25 0.10 0.46 0.06) 105 (1.7 1.0 0.5 0.1) 106 Table 3. Results for branching fractions for B0(s) ! D0f0(500) and B0(s) ! D0f0(980) decays. All

quoted results correspond to branching fraction for f0 ! + of 100 %. There is no experimental

result for B(B0s ! D0f0(500)).

signal is observed, and a limit is set on the branching fraction that is below the predicted value [22]. The small yield suggests that much larger data samples will be necessary in order to determine the angle of the CKM unitarity triangle with B0s ! D0f0(980) decays.

Table 3 shows the current experimental status of measurements of the B0(s) ! D0f0(500) and B0(s) ! D0f0(980) branching fractions. The pattern of branching fractions is very

di erent to that for the B0(s) ! J/ f0(500) and B0(s) ! J/ f0(980) modes [58]. These

results may provide insight into the substructure of the scalar mesons.

Acknowledgments

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 sta 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 (U.S.A.). 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 Sk[suppress]lodowska-Curie Actions and ERC (European Union), Conseil g[notdef]n[notdef]ral de Haute-Savoie, Labex ENIGMASS and OCEVU, R[notdef]gion Auvergne (France), RFBR (Russia), XuntaGal and GENCAT (Spain), Royal Society and Royal Commission for the Exhibition of 1851 (United Kingdom).

Open Access. This article is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/

Web End =CC-BY 4.0 ), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

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The LHCb collaboration

R. Aaij38, B. Adeva37, M. Adinol46, A. A older52, 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,g, J. Anderson40, M. Andreotti16,f, J.E. Andrews58, R.B. Appleby54, O. Aquines Gutierrez10, F. Archilli38, P. dArgent11,A. Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,n, 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, 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, T. Bird54, A. Birnkraut9, A. Bizzeti17,i, 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, 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,j, A. Cardini15, P. Carniti20, L. Carson50,K. Carvalho Akiba2,38, R. Casanova Mohr36, G. Casse52, L. Cassina20,k, L. Castillo Garcia38,M. Cattaneo38, Ch. Cauet9, G. Cavallero19, 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. Cli 47, 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. Cunli e53,R. Currie53, C. DAmbrosio38, J. Dalseno46, 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. Deckenho 9, L. Del Buono8, N. D[notdef]l[notdef]age4, D. Derkach55,O. Deschamps5, F. Dettori38, B. Dey40, A. Di Canto38, F. Di Ruscio24, H. Dijkstra38,S. Donleavy52, F. Dordei11, M. Dorigo39, A. Dosil Su[notdef]rez37, 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. F[notdef]arber11, C. Farinelli41, 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, P. Fol53, M. Fontana10, F. Fontanelli19,j, R. Forty38, O. Francisco2, M. Frank38,C. Frei38, M. Frosini17, J. Fu21, E. Furfaro24,l, A. Gallas Torreira37, D. Galli14,d, S. Gallorini22,38,S. Gambetta19,j, M. Gandelman2, P. Gandini55, Y. Gao3, J. Garc[notdef]a Pardi[notdef]as37, J. Garofoli59,J. Garra Tico47, L. Garrido36, D. Gascon36, C. Gaspar38, U. Gastaldi16, R. Gauld55, L. Gavardi9,G. Gazzoni5, A. Geraci21,v, D. Gerick11, E. Gersabeck11, M. Gersabeck54, T. Gershon48,

Ph. Ghez4, A. Gianelle22, S. Gian[notdef]39, V. Gibson47, L. Giubega29, V.V. Gligorov38, C. G[notdef]bel60,D. Golubkov31, A. Golutvin53,31,38, A. Gomes1,a, C. Gotti20,k, M. Grabalosa G[notdef]ndara5,R. Graciani Diaz36, L.A. Granado Cardoso38, E. Graug[notdef]s36, E. Graverini40, G. Graziani17,A. Grecu29, E. Greening55, S. Gregson47, P. Gri th45, L. Grillo11, O. Gr[notdef]nberg63, 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. He[notdef]63, A. Hicheur2, D. Hill55,

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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,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. Kucharczyk26, V. Kudryavtsev34, K. Kurek28,T. Kvaratskheliya31, V.N. La Thi39, D. Lacarrere38, G. La erty54, 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. Lef[notdef]vre5, A. Leat32, J. Lefran[notdef]ois7,O. Leroy6, T. Lesiak26, B. Leverington11, Y. Li7, T. Likhomanenko65,64, M. Liles52, R. Lindner38,C. Linn38, F. Lionetto40, B. Liu15, S. Lohn38, I. Longsta 51, J.H. Lopes2, D. Lucchesi22,r,M. Lucio Martinez37, H. Luo50, A. Lupato22, E. Luppi16,f, O. Lupton55, F. Machefert7,F. Maciuc29, O. Maev30, S. Malde55, A. Malinin64, G. Manca15,e, G. Mancinelli6, P. Manning59,A. Mapelli38, J. Maratas5, J.F. Marchand4, U. Marconi14, C. Marin Benito36, P. Marino23,38,t,R. M[notdef]arki39, J. Marks11, G. Martellotti25, M. Martinelli39, D. Martinez Santos42,F. Martinez Vidal66, D. Martins Tostes2, A. Massa erri1, 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, M. Merk41, D.A. Milanes62, M.-N. Minard4, D.S. Mitzel11, J. Molina Rodriguez60, S. Monteil5,M. Morandin22, P. Morawski27, A. Mord[notdef]6, M.J. Morello23,t, J. Moron27, A.B. Morris50,R. Mountain59, F. Muheim50, J. M[notdef]ller9, K. M[notdef]ller40, V. M[notdef]ller9, M. Mussini14, B. Muster39,P. Naik46, T. Nakada39, R. Nandakumar49, I. Nasteva2, M. Needham50, N. Neri21, S. Neubert11,N. Neufeld38, M. Neuner11, A.D. Nguyen39, T.D. Nguyen39, C. Nguyen-Mau39,q, V. Niess5,R. Niet9, N. Nikitin32, T. Nikodem11, D. Ninci23, A. Novoselov35, D.P. OHanlon48,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,u, M. Palutan18, J. Panman38, A. Papanestis49,M. Pappagallo51, L.L. Pappalardo16,f, C. Parkes54, 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, K. Petridis46, A. Petrolini19,j, M. Petruzzo21,E. Picatoste Olloqui36, B. Pietrzyk4, T. Pila48, D. Pinci25, A. Pistone19, S. Playfer50,M. Plo Casasus37, T. Poikela38, 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,R. Quagliani7,46, 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. Robbe7,38, A.B. Rodrigues1, E. Rodrigues54, J.A. Rodriguez Lopez62, P. Rodriguez Perez54,S. Roiser38, V. Romanovsky35, A. Romero Vidal37, M. Rotondo22, J. Rouvinet39, T. Ruf38,H. Ruiz36, 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, 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,T. Schmelzer9, 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,

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JHEP08(2015)005

V. Shevchenko64, A. Shires9, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46,I. Skillicorn51, T. Skwarnicki59, E. Smith55,49, E. Smith53, J. Smith47, M. Smith54, H. Snoek41, M.D. Sokolo 57,38, F.J.P. Soler51, F. Soomro39, D. Souza46, B. Souza De Paula2, B. Spaan9,P. Spradlin51, S. Sridharan38, F. Stagni38, M. Stahl11, S. Stahl38, 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. Sutcli e53, K. Swientek27, S. Swientek9,V. Syropoulos42, M. Szczekowski28, P. Szczypka39,38, T. Szumlak27, S. TJampens4, 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. Tourneer4, 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. V[notdef]zquez Sierra37, S. Vecchi16, J.J. Velthuis46,M. Veltri17,h, G. Veneziano39, M. Vesterinen11, B. Viaud7, D. Vieira2, M. Vieites Diaz37,X. Vilasis-Cardona36,p, A. Vollhardt40, D. Volyanskyy10, D. Voong46, A. Vorobyev30,V. Vorobyev34, C. Vo[notdef]63, 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, D. Wiedner11, G. Wilkinson55,38, M. Wilkinson59, M. Williams38,

M.P. Williams45, M. Williams56, 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,X. Yuan34, O. Yushchenko35, M. Zangoli14, M. Zavertyaev10,b, L. Zhang3, Y. Zhang3,A. Zhelezov11, A. Zhokhov31, L. Zhong3

1 Centro Brasileiro de Pesquisas Fsicas (CBPF), Rio de Janeiro, Brazil

2 Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

3 Center for High Energy Physics, Tsinghua University, Beijing, China

4 LAPP, Universit Savoie Mont-Blanc, CNRS/IN2P3, Annecy-Le-Vieux, France

5 Clermont Universit, Universit Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France

6 CPPM, Aix-Marseille Universit, CNRS/IN2P3, Marseille, France

7 LAL, Universit Paris-Sud, CNRS/IN2P3, Orsay, France

8 LPNHE, Universit Pierre et Marie Curie, Universit Paris Diderot, CNRS/IN2P3, Paris, France

9 Fakultat Physik, Technische Universitat Dortmund, Dortmund, Germany

10 Max-Planck-Institut fr Kernphysik (MPIK), Heidelberg, Germany

11 Physikalisches Institut, Ruprecht-Karls-Universitat Heidelberg, Heidelberg, Germany

12 School of Physics, University College Dublin, Dublin, Ireland

13 Sezione INFN di Bari, Bari, Italy

14 Sezione INFN di Bologna, Bologna, Italy

15 Sezione INFN di Cagliari, Cagliari, Italy

16 Sezione INFN di Ferrara, Ferrara, Italy

17 Sezione INFN di Firenze, Firenze, Italy

18 Laboratori Nazionali dellINFN di Frascati, Frascati, Italy

19 Sezione INFN di Genova, Genova, Italy

20 Sezione INFN di Milano Bicocca, Milano, Italy

21 Sezione INFN di Milano, Milano, Italy

22 Sezione INFN di Padova, Padova, Italy

23 Sezione INFN di Pisa, Pisa, Italy

24 Sezione INFN di Roma Tor Vergata, Roma, Italy

25 Sezione INFN di Roma La Sapienza, Roma, Italy

26 Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krakw, Poland

27 AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakw, Poland

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28 National Center for Nuclear Research (NCBJ), Warsaw, Poland

29 Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania

30 Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia

31 Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia

32 Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia

33 Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia

34 Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia

35 Institute for High Energy Physics (IHEP), Protvino, Russia

36 Universitat de Barcelona, Barcelona, Spain

37 Universidad de Santiago de Compostela, Santiago de Compostela, Spain

38 European Organization for Nuclear Research (CERN), Geneva, Switzerland

39 Ecole Polytechnique Fdrale de Lausanne (EPFL), Lausanne, Switzerland

40 Physik-Institut, Universitat Zrich, Zrich, Switzerland

41 Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands

42 Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands

43 NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine

44 Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine

45 University of Birmingham, Birmingham, United Kingdom

46 H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom

47 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom

48 Department of Physics, University of Warwick, Coventry, United Kingdom

49 STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

50 School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom

51 School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom

52 Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom

53 Imperial College London, London, United Kingdom

54 School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom

55 Department of Physics, University of Oxford, Oxford, United Kingdom

56 Massachusetts Institute of Technology, Cambridge, MA, United States

57 University of Cincinnati, Cincinnati, OH, United States

58 University of Maryland, College Park, MD, United States

59 Syracuse University, Syracuse, NY, United States

60 Pontifcia Universidade Catlica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to2

61 Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China, associated to3

62 Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia, associated to8

63 Institut fr Physik, Universitat Rostock, Rostock, Germany, associated to11

64 National Research Centre Kurchatov Institute, Moscow, Russia, associated to 31

65 Yandex School of Data Analysis, Moscow, Russia, associated to31

66 Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to36

67 Van Swinderen Institute, University of Groningen, Groningen, The Netherlands, associated to41

a Universidade Federal do Tringulo Mineiro (UFTM), Uberaba-MG, Brazil

b P.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia

c Universit di Bari, Bari, Italy

d Universit di Bologna, Bologna, Italy

e Universit di Cagliari, Cagliari, Italy

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f Universit di Ferrara, Ferrara, Italy

g Universit di Firenze, Firenze, Italy

h Universit di Urbino, Urbino, Italy

i Universit di Modena e Reggio Emilia, Modena, Italy

j Universit di Genova, Genova, Italy

k Universit di Milano Bicocca, Milano, Italy

l Universit di Roma Tor Vergata, Roma, Italy

m Universit di Roma La Sapienza, Roma, Italy

n Universit della Basilicata, Potenza, Italy

o AGH - University of Science and Technology, Faculty of Computer Science, Electronics andTelecommunications, Krakw, Poland

p LIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

q Hanoi University of Science, Hanoi, Viet Nam

r Universit di Padova, Padova, Italy

s Universit di Pisa, Pisa, Italy

t Scuola Normale Superiore, Pisa, Italy

u Universit degli Studi di Milano, Milano, Italy

v Politecnico di Milano, Milano, Italy

Deceased

JHEP08(2015)005

18