Determination of $f_s/f_d$ for 7 TeV pp Collisions and Measurement of the $B^0 \to D^-K^+$ Branching Fraction

arXiv:1106.4435v2 [hep-ex] 2 Dec 2011

fraction of the decay

B

→

D

−

K

R. Aaij et al., (The LHCb Collaboration)

The relative abundance of the three decay modes B0 _{→ D}−_K+_{, B}0 _{→ D}−_π+_{and B}0 s → D−

sπ+produced in 7 TeV pp collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb−1_{. The branching fraction of B}0 _{→ D}−_K+_{is found to be} B B0 _→D−_K+
_{= (2.01 ± 0.18}stat_±0.14syst_{) × 10}−4_{. The ratio of fragmentation fractions f}

s/fdis determined through the relative abundance of B0

s → Ds−π+to B0 → D−K+and B0 → D−π+, leading to fs/fd = 0.253 ± 0.017 ± 0.017 ± 0.020, where the uncertainties are statistical, systematic, and theoretical respectively.

PACS numbers: 12.38.Qk, 13.60.Le, 13.87.Fh

Knowledge of the production rate of B0

s mesons is

re-quired to determine any B0

s branching fraction. This

rate is determined by the b¯b production cross-section and the fragmentation probability fs, which is the

frac-tion of B0

s mesons amongst all weakly-decaying bottom

hadrons. Similarly the production rate of B0 _{mesons is}

driven by the fragmentation probability fd. The

mea-surement of the branching fraction of the rare decay B0

s→ µ

+_{µ− is a prime example where improved}

knowl-edge of fs/fd is needed to reach the highest sensitivity

in the search for physics beyond the Standard Model [1]. The ratio fs/fd is in principle dependent on collision

en-ergy and type as well as the acceptance region of the detector. This is the first measurement of this quantity at the LHC.

The ratio fs/fdcan be extracted if the ratio of

branch-ing fractions of B0_{and B}0

s mesons decaying to particular

final states X1 and X2, respectively, is known:

fs fd = NX2 NX1 B(B0_{→ X} 1) B(B0 s → X2) ǫ(B0_{→ X} 1) ǫ(B0 s→ X2) . (1)

The ratio of the branching fraction of the B0

s →

D−

sπ+and B0 → D−K+decays is dominated by

con-tributions from colour-allowed tree-diagram amplitudes and is therefore theoretically well understood. In con-trast, the ratio of the branching ratios of the two de-cays B0

s → D−sπ+and B0 → D−π+can be measured

with a smaller statistical uncertainty due to the greater yield of the B0 _{mode, but suffers from an additional}

theoretical uncertainty due to the contribution from a W -exchange diagram. Both ratios are exploited here to measure fs/fd according to the equations [2, 3]

fs fd = 0.971 ·     Vus Vud     2  fK fπ 2 τBd τBs 1 NaNF ǫD−K+ ǫ_D−_sπ+ N_D− sπ+ ND−K+ , (2) and fs fd = 0.982 · τBd τBs 1 NaNFNE ǫD−π+ ǫ_Ds−_π+ ND−_sπ+ ND−π+ . (3) Here ǫX is the selection efficiency of decay X (including

the branching fraction of the D decay mode used to

re-construct it), NX is the observed number of decays of

this type, the Vij are elements of the CKM matrix, fi

are the meson decay constants and the numerical factors take into account the phase space difference for the ratio of the two decay modes. Inclusion of charge conjugate modes is implied throughout. The term Na parametrizes

non-factorizable SU(3)-breaking effects; NF is the ratio

of the form factors; NE is an additional correction term

to account for the W -exchange diagram in the B0 _→

D−_π+_{decay. Their values [2, 3] are Na = 1.00 ± 0.02,}

NF = 1.24 ± 0.08, and NE = 0.966 ± 0.075. The latest

world average [4] is used for the B meson lifetime ratio τBs/τBd= 0.973 ± 0.015. The numerical values used for the other factors are: |Vus| = 0.2252, |Vud| = 0.97425,

fπ = 130.41 and fK = 156.1, with negligible associated

uncertainties [5].

The observed yields of these three decay modes in 35 pb−1 _{of data collected with the LHCb detector in}

the 2010 running period are used to measure fs/fd

av-eraged over the LHCb acceptance and to improve the current measurement of the branching fraction of the B0_{→ D−K}+_{decay mode [6].}

The LHCb experiment [7] is a single-arm spectrometer, designed to study B decays at the LHC, with a pseudo-rapidity acceptance of 2 < η < 5 for charged tracks. The first trigger level allows the selection of events with B hadronic decays using the transverse energy of hadrons measured in the calorimeter system. The event infor-mation is subsequently sent to a software trigger, imple-mented in a dedicated processor farm, which performs a final online selection of events for later offline analysis. The tracking system determines the momenta of B de-cay products with a precision of δp/p = 0.35–0.5%. Two Ring Imaging Cherenkov (RICH) detectors allow charged kaons and pions to be distinguished in the momentum range 2–100 GeV/c [8].

The three decay modes, B0 _{→ D}−_(K+_π−_π−_)π+_,

B0 _{→ D}−_(K+_π−_π−_)K+ _{and B}0

s → Ds−(K+K−π−)π+,

are topologically identical and can therefore be selected using identical geometric and kinematic criteria, thus minimizing efficiency differences between them. Events

are selected at the first trigger stage by requiring a hadron with transverse energy greater than 3.6 GeV in the calorimeter. The second, software, stage [9, 10] re-quires a two, three, or four track secondary vertex with a high sum pT of the tracks, significant displacement from

the primary interaction, and at least one track with ex-ceptionally high pT, large displacement from the primary

interaction, and small fit χ2_.

The decays of B mesons can be distinguished from background using variables such as the pT and impact

parameter χ2 _{of the B, D, and the final state particles}

with respect to the primary interaction. In addition the vertex quality of the B and D candidates, the B lifetime, and the angle between the B momentum vector and the vector joining the B production and decay vertices are used in the selection. The D lifetime and flight distance are not used in the selection because the lifetimes of the D−

s and D− differ by about a factor of two.

The event sample is first selected using the gradient boosted decision tree technique [11], which combines the geometrical and kinematic variables listed above. The selection is trained on a mixture of simulated B0 _→

D−_π+ _{decays and combinatorial background selected}

from the sidebands of the data mass distributions. The distributions of the input variables for data and simu-lated signal events show excellent agreement, justifying the use of simulated events in the training procedure.

Subsequently, D− _(D−

s) candidates are identified by

requiring the invariant mass under the Kππ (KKπ) hypothesis to fall within the selection window 1870+24 −40

(1969+24

−40) MeV/c

2_{, where the mass resolution is}

ap-proximately 10 MeV/c2_{. The final B}0 _{→ D}−_π+_and

B0

s → Ds−π

+_{subsamples consist of events that pass a}

particle identification (PID) criterion on the bachelor particle, based on the difference in log-likelihood be-tween the charged pion and kaon hypotheses (DLL) of DLL(K − π) < 0, with an efficiency of 83.0%. The B0_→

D−_K+_{subsample consists of events with DLL(K − π) >}

5, with an efficiency of 70.2%. Events not satisfying ei-ther condition are not used.

The relative efficiency of the selection procedure is evaluated for all decay modes using simulated events, where the appropriate resonances in the charm decays are taken into account. As the analysis is only sensi-tive to relasensi-tive efficiencies, the impact of differences be-tween data and simulation is small. The relative efficien-cies are ǫD−π+/ǫ_D−K+= 1.221 ± 0.021, ǫ_D−K+/ǫ

D−

sπ+=

0.917 ± 0.020, and ǫD−π+/ǫ

D−_sπ+ = 1.120 ± 0.025, where the errors are due to the limited size of the simulated event samples.

The relative yields of the three decay modes are ex-tracted from unbinned extended maximum likelihood fits to the mass distributions shown in Fig. 2. The signal mass shape is described by an empirical model derived from simulated events. The mass distribution in the sim-ulation exhibits non-Gaussian tails on either side of the

signal. The tail on the right-hand side is due to non-Gaussian detector effects and modeled with a Crystal Ball (CB) function [12]. A similar tail is present on the left-hand side of the peak. In addition, the low mass tail contains a second contribution due to events where hadrons have radiated photons that are not recon-structed. The sum of these contributions is modeled with a second CB function. The peak values of these two CB functions are constrained to be identical.

Various backgrounds have to be considered, in par-ticular the crossfeed between the D− _{and D}−

s

chan-nels, and the contamination in both samples from Λb→

Λ+

cπ−decays, where Λ+c → pK−π+. The D−s

contami-nation in the D− _{data sample is reduced by loose PID}

requirements, DLL(K − π) < 10 (with an efficiency of 98.6%) and DLL(K−π) > 0 (with an efficiency of 95.6%), for the pions and kaons from D decays, respectively. The resulting efficiency to reconstruct B0

s → Ds−π

+_as

back-ground is evaluated, using simulated events, to be 30 times smaller than for B0_{→ D−π}+_{and 150 times smaller}

than for B0_{→ D−K}+_{within the B}0_{and D−signal mass}

windows. Taking into account the lower production frac-tion of B0

s mesons, this background is negligible.

The contamination from Λc decays is estimated in a

similar way. However, different approaches are used for the B0 _{and B}0

s decays. A contamination of

approxi-mately 2% under the B0_{→ D−π}+_{mass peak and below}

1% under the B0 _{→ D−K}+_{peak is found, and}

there-fore no explicit DLL(p − π) criterion is needed. The Λc

background in the B0

s sample is, on the other hand, large

enough that it can be fitted for directly.

A prominent peaking background to B0 _{→ D}−_K+_is

B0 _{→ D}−_π+_{, with the pion misidentified as a kaon.}

The small π → K misidentification rate (of about 4%) is compensated by the larger branching fraction, resulting in similar event yields. This background is modeled by obtaining a clean B0_{→ D−π}+_{sample from the data and}

reconstructing it under the B0 _{→ D−K}+_mass

hypoth-esis. The resulting mass shape depends on the tum distribution of the bachelor particle. The momen-tum distribution after the DLL(K − π) > 5 requirement can be found by considering the PID performance as a function of momentum. This is obtained using a sample of D∗+ _{→ D}0_π+_{decays, and is illustrated in Fig. 1. The}

mass distribution is reweighted using this momentum dis-tribution to reproduce the B0 _{→ D}−_π+_{mass shape}

fol-lowing the DLL cut.

The combinatorial background consists of events with random pions and kaons, forming a fake D− _{or D}−

s

can-didate, as well as real, D− _{or D}−

s mesons that combine

with a random pion or kaon. The combinatorial back-ground is modeled with an exponential shape.

Other background components originate from par-tially reconstructed B0 _{and B}0

s decays. In B

0 _→

D−_π+_{these originate from B}0 _{→ D}∗−_π+_{and B}0 _→

Track Momentum (GeV/c) 0 20 40 60 80 100 Efficiency 0 0.2 0.4 0.6 0.8 1 )>5 π K, DLL(K-→ K )<0 π , DLL(K-π → π )>5 π K, DLL(K-→ π )<0 π , DLL(K-π → K

FIG. 1: Probability, as a function of momentum, to cor-rectly identify (full symbols) a kaon or a pion when requiring DLL(K − π) > 5 or DLL(K − π) < 0, respectively. The cor-respondent probability to wrongly identify (open symbols) a pion as a kaon, or a kaon as a pion is also shown. The data are taken from a calibration sample of D∗_{→D(Kπ)π decays;} the statistical uncertainties are too small to display.

D−_K+_{in the case of a misidentified bachelor pion. In}

B0 _{→ D}−_K+_{there is additionally background from}

B0 _{→ D}∗−_K+_{decays. The invariant mass distributions}

for the partially reconstructed and misidentified back-grounds are taken from large samples of simulated events, reweighted according to the mass hypothesis of the signal being fitted and the DLL cuts.

For B0

s → D−sπ+, the B0→ D−π+background peaks

under the signal with a similar shape. In order to sup-press this peaking background, PID requirements are placed on both kaon tracks. The kaon which has the same sign in the B0

s→ D−sπ+and B0→ D−π+decays is

required to satisfy DLL(K − π) > 0, while the other kaon in the D+

s decay is required to satisfy DLL(K − π) > 5.

Because of the similar shape, a Gaussian constraint is ap-plied to the yield of this background. The central value of this constraint is computed from the π → K misiden-tification rate. The Λb → Λ+cπ−background shape is

obtained from simulated events, reweighted according to the PID efficiency, and the yield allowed to float in the fit. Finally, the relative size of the B0

s → D−sρ+and

B0

s → Ds∗−π+backgrounds is constrained to the ratio of

the B0_{→ D−ρ}+_{and B}0 _{→ D∗−π}+_{backgrounds in the}

B0 _{→ D−π}+_{fit, with an uncertainty of 20% to account}

for potential SU(3) symmetry breaking effects.

The free parameters in the likelihood fits to the mass distributions are the event yields for the different event types, i.e. the combinatorial background, partially re-constructed background, misidentified contributions, the signal, as well as the peak value of the signal shape. In addition the combinatoric background shape is left free in the B0 _{→ D−π}+_{and B}0

s → Ds−π

+_{fits, and the}

sig-nal width is left free in the B0 _{→ D−π}+_{fit. In the}

B0

s → D−sπ+and B0 → D−K+fits the signal width is

fixed to the value from the B0_{→ D−π}+_{fit, corrected by}

the ratio of the signal widths for these modes in simulated events.

The fits to the full B0 _{→ D}−_π+_{, B}0 _{→ D}−_K+_,

and B0

s → D−sπ+data samples are shown in Fig. 2.

The resulting B0 _{→ D}−_π+_{and B}0 _{→ D}−_K+_event

yields are 4103 ± 75 and 252 ± 21, respectively. The number of misidentified B0 _{→ D}−_π+_{events under the}

B0_{→ D}−_K+_{signal as obtained from the fit is 131 ± 19.}

This agrees with the number expected from the total number of B0_{→ D}−_π+_{events, corrected for the}

misiden-tification rate determined from the PID calibration sam-ple, of 145 ± 5. The B0 s→ D−sπ+event yield is 670 ± 34.

5000

0

5200

5400

_{Mass (MeV/c²)}

5600

5800

200

400

600

Ev

en

ts

/ (8

M

eV/

c²)

ND−_π+=

4103

±

75

B0_→D−_π+ B0_→D∗−_π+ B0_→D−_ρ+

Combinatorial

5000

0

5200

5400

_{Mass (MeV/c²)}

5600

5800

25

50

75

100

Ev

en

ts

/ (1

6 M

eV/

c²)

ND−_K+=

252

±

21

B0_→D−_K+ B0_→D−_π+ B0_→D∗−_K+ B0_→D−_ρ+

Combinatorial

5000

0

5200

5400

_{Mass (MeV/c²)}

5600

5800

40

80

120

160

Ev

en

ts

/ (8

M

eV/

c²)

_ND− sπ+=

670

±

34

B0 s →Ds−π+ B0_→D−_π+ B0 s →Ds∗−π+ B0 s →Ds−(

3

π)+ B0 s →Ds−ρ+ Λb→Λc+π−

Combinatorial

FIG. 2: Mass distributions of the B0 _{→ D}−_π+_{, B}0 _→ D−_K+_{, and B}0

s →Ds−π+candidates (top to bottom). The indicated components are described in the text.

The stability of the fit results has been investigated using different cut values for both the PID requirement on the bachelor particle and for the multivariate selection variable. In all cases variations are found to be small in comparison to the statistical uncertainty.

The relative branching fractions are obtained by cor-recting the event yields by the corresponding efficiency factors; the dominant correction comes from the PID ef-ficiency. The dominant source of systematic uncertainty is the knowledge on the B0_{→ D−π}+_{branching fraction}

(for the B0 _{→ D−K}+_{branching fraction measurement)}

and the knowledge of the D− _{and D}−

s branching

frac-tions (for the fs/fdmeasurement). An important source

of systematic uncertainty is the knowledge of the PID ef-ficiency as a function of momentum, which is needed to reweight the mass distribution of the B0_{→ D}−_π+_decay

under the kaon hypothesis for the bachelor track. This enters in two ways: firstly as an uncertainty on the cor-rection factors, and secondly as part of the systematic uncertainty, since the shape for the misidentified back-grounds relies on correct knowledge of the PID efficiency as a function of momentum.

The performance of the PID calibration is evaluated by applying the same method from data to simulated events, and the maximum discrepancy found between the calibration method and the true mis-identification is at-tributed as a systematic uncertainty. The fs/fd

mea-surement using B0 _{→ D−K}+_{and B}0

s → Ds−π+is more

robust against PID uncertainties, since the final states have the same number of kaons and pions.

Other systematic uncertainties are due to limited sim-ulated event samples (affecting the relative selection efficiencies), neglecting the Λb → Λ+cπ− and Bs0 →

D−

sπ+backgrounds in the B0→ D−π+fits, and the

lim-ited accuracy of the trigger simulation. Even though the ratio of efficiencies is statistically consistent with unity, the maximum deviation is conservatively assigned as a systematic uncertainty. The difference in interac-tion probability between kaons and pions is estimated using MC simulation. The systematic uncertainty due to possible discrepancies between data and simulation is expected to be negligible and it is not taken into account. The efficiency of the non-resonant Dsdecays varies across

the Dalitz plane, but has a negligible effect on the total B0

s → D−sπ+efficiency. The sources of systematic

uncer-tainty are summarized in Tab. I.

The efficiency corrected ratio of B0 _{→ D}−_π+_and

B0 _{→ D}−_K+_{yields is combined with the world average}

of the B0_{→ D}−_π+ _{[5] branching ratio to give}

B B0_{→ D−}

K+
= (2.01 ± 0.18 ± 0.14) × 10−4_{. (4)}

The first uncertainty is statistical and the second system-atic.

The theoretically cleaner measurement of fs/fd uses

B0_{→ D−K}+_{and B}0

s→ D−sπ+and is made according to

Eq. 2. Accounting for the exclusive D branching fractions

TABLE I: Experimental systematic uncertainties for the B B0_→D−_K+
_{and the two f}

s/fdmeasurements. B B0_→D−_K+
fs/fd PID calibration 2.5% 1.0%/2.5% Fit model 2.8% 2.8% Trigger simulation 2.0% 2.0% B_(B0 _→D−_π+_{) 4.9%} B_(D+ s →K+K−π+) 4.9% B(D+_→K−_π+_π+_{) 2.2%} τBs/τBd 1.5% B(D+_{→ K}−_π+_π+_{) = (9.14 ± 0.20)% [13] and B(D}+ s → K−_K+_π+_{) = (5.50 ± 0.27)% [14], the value of f} s/fd is found to be fs/fd = (0.310 ± 0.030stat± 0.021syst) × 1 NaNF , (5) where the first uncertainty is statistical and the second is systematic. The statistical uncertainty is dominated by the yield of the B0_{→ D}−_K+_mode.

The statistically more precise but theoretically less clean measurement of fs/fd uses B0→ D−π+and B0s→

D−

sπ+and is, from Eq. 3,

fs/fd = (0.307 ± 0.017stat± 0.023syst) ×

1 NaNFNE

. (6) The two values for fs/fd can be combined into a

sin-gle value, taking all correlated uncertainties into ac-count and using the theoretical inputs acac-counting for the SU (3) breaking part of the form factor ratio, the non-factorizable and W-exchange diagram:

fs/fd = 0.253 ± 0.017stat± 0.017syst± 0.020theor. (7)

In summary, with 35 pb−1 _{of data collected using}

the LHCb detector during the 2010 LHC operation at a centre-of-mass energy of 7 TeV, the branching frac-tion of the Cabibbo-suppressed B0 _{decay mode B}0 _→

D−_K+_{has been measured with better precision than}

the current world average. Additionally, two measure-ments of the fs/fd production fraction are performed

from the relative yields of B0

s → D−sπ+with respect

to B0 _{→ D}−_K+_{and B}0 _{→ D}−_π+_{. These values of}

fs/fd are numerically close to the values determined at

LEP and at the Tevatron [4].

Acknowledgments

We express our gratitude to our colleagues in the CERN accelerator departments for the excellent per-formance of the LHC. We thank the technical and ad-ministrative staff at CERN and at the LHCb insti-tutes, and acknowledge support from the National Agen-cies: CAPES, CNPq, FAPERJ and FINEP (Brazil);

CERN; NSFC (China); CNRS/IN2P3 (France); BMBF, DFG, HGF and MPG (Germany); SFI (Ireland); INFN (Italy); FOM and NWO (Netherlands); SCSR (Poland); ANCS (Romania); MinES of Russia and Rosatom (Rus-sia); MICINN, XUNGAL and GENCAT (Spain); SNSF and SER (Switzerland); NAS Ukraine (Ukraine); STFC (United Kingdom); NSF (USA). We also acknowledge the support received from the ERC under FP7 and the R´egion Auvergne.

[1] Aaij, R. et al. (LHCb Collaboration). Phys. Lett. B, 699:330, 2011. arXiv:1103.2465[hep-ex].

[2] R. Fleischer, N. Serra, and N. Tuning. Phys. Rev., D83:014017, 2011. arXiv:1012.2784[hep-ph].

[3] R. Fleischer, N. Serra, and N. Tuning. Phys. Rev., D82:034038, 2010. arXiv:1004.3982[hep-ph].

[4] D. Asner et al. arXiv:1010.1589[hep-ex], 2010. [5] K. Nakamura et al. J. Phys. G, 37(075021), 2010. [6] Abe, K. et al. (BELLE Collaboration). Phys. Rev. Lett.,

87:111801, 2001. arXiv:0104051[hep-ex].

[7] A. A. Alves Jr. et al. (LHCb Collaboration). JINST, 3:S08005, 2008.

[8] A. A. Alves Jr. et al. The LHCb Detector at the LHC. JINST, 3:S08005, 2008.

[9] V. V. Gligorov. LHCb-PUB-2011-003. [10] M. Williams et al. LHCb-PUB-2011-002. [11] A. Hoecker et al. PoS, ACAT:040, 2007. [12] T. Skwarnicki. DESY F31-86-02, 1986.

[13] Dobbs, S. et al. (CLEO Collaboration). Phys. Rev., D76:112001, 2007. arXiv:0709.3783[hep-ex].

[14] Alexander, J. P. et al. (CLEO Collaboration). Phys. Rev. Lett., 100:161804, 2008. arXiv:0801.0680[hep-ex].

The LHCb Collaboration

R. Aaij23_{, B. Adeva}36_{, M. Adinolfi}42_{, C. Adrover}6_{, A. Affolder}48_{, Z. Ajaltouni}5_{, J. Albrecht}37_{, F. Alessio}6,37_{, M. Alexander}47_, G. Alkhazov29_{, P. Alvarez Cartelle}36_{, A.A. Alves Jr}22_{, S. Amato}2_{, Y. Amhis}38_{, J. Amoraal}23_{, J. Anderson}39_{, R.B. Appleby}50_, O. Aquines Gutierrez10_{, L. Arrabito}53_{, A. Artamonov}34_{, M. Artuso}52,37_{, E. Aslanides}6_{, G. Auriemma}22,m_{, S. Bachmann}11_, J.J. Back44_{, D.S. Bailey}50_{, V. Balagura}30,37_{, W. Baldini}16_{, R.J. Barlow}50_{, C. Barschel}37_{, S. Barsuk}7_{, W. Barter}43_{, A. Bates}47_,

C. Bauer10_{, Th. Bauer}23_{, A. Bay}38_{, I. Bediaga}1_{, K. Belous}34_{, I. Belyaev}30,37_{, E. Ben-Haim}8_{, M. Benayoun}8_{, G. Bencivenni}18_, S. Benson46_{, J. Benton}42_{, R. Bernet}39_{, M.-O. Bettler}17,37_{, M. van Beuzekom}23_{, A. Bien}11_{, S. Bifani}12_{, A. Bizzeti}17,h_, P.M. Bjørnstad50_{, T. Blake}49_{, F. Blanc}38_{, C. Blanks}49_{, J. Blouw}11_{, S. Blusk}52_{, A. Bobrov}33_{, V. Bocci}22_{, A. Bondar}33_, N. Bondar29_{, W. Bonivento}15_{, S. Borghi}47_{, A. Borgia}52_{, T.J.V. Bowcock}48_{, C. Bozzi}16_{, T. Brambach}9_{, J. van den Brand}24_, J. Bressieux38_{, S. Brisbane}51_{, M. Britsch}10_{, T. Britton}52_{, N.H. Brook}42_{, A. B¨uchler-Germann}39_{, A. Bursche}39_{, J. Buytaert}37_,

S. Cadeddu15_{, J.M. Caicedo Carvajal}37_{, O. Callot}7_{, M. Calvi}20,j_{, M. Calvo Gomez}35,n_{, A. Camboni}35_{, P. Campana}18,37_, A. Carbone14_{, G. Carboni}21,k_{, R. Cardinale}19,i_{, A. Cardini}15_{, L. Carson}36_{, K. Carvalho Akiba}23_{, G. Casse}48_{, M. Cattaneo}37_, M. Charles51_{, Ph. Charpentier}37_{, N. Chiapolini}39_{, X. Cid Vidal}36_{, P.E.L. Clarke}46_{, M. Clemencic}37_{, H.V. Cliff}43_{, J. Closier}37_,

C. Coca28_{, V. Coco}23_{, J. Cogan}6_{, P. Collins}37_{, F. Constantin}28_{, G. Conti}38_{, A. Contu}51_{, A. Cook}42_{, M. Coombes}42_, G. Corti37_{, G.A. Cowan}38_{, R. Currie}46_{, B. D’Almagne}7_{, C. D’Ambrosio}37_{, P. David}8_{, P.N.Y. David}23_{, I. De Bonis}4_, S. De Capua21,k_{, M. De Cian}39_{, F. De Lorenzi}12_{, J.M. De Miranda}1_{, L. De Paula}2_{, P. De Simone}18_{, D. Decamp}4_, M. Deckenhoff9_{, H. Degaudenzi}38,37_{, M. Deissenroth}11_{, L. Del Buono}8_{, C. Deplano}15_{, O. Deschamps}5_{, F. Dettori}15,d_, J. Dickens43_{, H. Dijkstra}37_{, P. Diniz Batista}1_{, D. Dossett}44_{, A. Dovbnya}40_{, F. Dupertuis}38_{, R. Dzhelyadin}34_{, C. Eames}49_, S. Easo45_{, U. Egede}49_{, V. Egorychev}30_{, S. Eidelman}33_{, D. van Eijk}23_{, F. Eisele}11_{, S. Eisenhardt}46_{, R. Ekelhof}9_{, L. Eklund}47_,

Ch. Elsasser39_{, D.G. d’Enterria}35,o_{, D. Esperante Pereira}36_{, L. Est`eve}43_{, A. Falabella}16,e_{, E. Fanchini}20,j_{, C. F¨arber}11_, G. Fardell46_{, C. Farinelli}23_{, S. Farry}12_{, V. Fave}38_{, V. Fernandez Albor}36_{, M. Ferro-Luzzi}37_{, S. Filippov}32_{, C. Fitzpatrick}46_,

M. Fontana10_{, F. Fontanelli}19,i_{, R. Forty}37_{, M. Frank}37_{, C. Frei}37_{, M. Frosini}17,f,37_{, S. Furcas}20_{, A. Gallas Torreira}36_, D. Galli14,c_{, M. Gandelman}2_{, P. Gandini}51_{, Y. Gao}3_{, J-C. Garnier}37_{, J. Garofoli}52_{, L. Garrido}35_{, C. Gaspar}37_{, N. Gauvin}38_,

M. Gersabeck37_{, T. Gershon}44_{, Ph. Ghez}4_{, V. Gibson}43_{, V.V. Gligorov}37_{, C. G¨obel}54_{, D. Golubkov}30_{, A. Golutvin}49,30,37_, A. Gomes2_{, H. Gordon}51_{, M. Grabalosa G´andara}35_{, R. Graciani Diaz}35_{, L.A. Granado Cardoso}37_{, E. Graug´es}35_, G. Graziani17_{, A. Grecu}28_{, S. Gregson}43_{, B. Gui}52_{, E. Gushchin}32_{, Yu. Guz}34_{, T. Gys}37_{, G. Haefeli}38_{, S.C. Haines}43_, T. Hampson42_{, S. Hansmann-Menzemer}11_{, R. Harji}49_{, N. Harnew}51_{, J. Harrison}50_{, P.F. Harrison}44_{, J. He}7_{, V. Heijne}23_, K. Hennessy48_{, P. Henrard}5_{, J.A. Hernando Morata}36_{, E. van Herwijnen}37_{, W. Hofmann}10_{, K. Holubyev}11_{, P. Hopchev}4_, W. Hulsbergen23_{, P. Hunt}51_{, T. Huse}48_{, R.S. Huston}12_{, D. Hutchcroft}48_{, D. Hynds}47_{, V. Iakovenko}41_{, P. Ilten}12_{, J. Imong}42_, R. Jacobsson37_{, M. Jahjah Hussein}5_{, E. Jans}23_{, F. Jansen}23_{, P. Jaton}38_{, B. Jean-Marie}7_{, F. Jing}3_{, M. John}51_{, D. Johnson}51_, C.R. Jones43_{, B. Jost}37_{, S. Kandybei}40_{, T.M. Karbach}9_{, J. Keaveney}12_{, U. Kerzel}37_{, T. Ketel}24_{, A. Keune}38_{, B. Khanji}6_,

Y.M. Kim46_{, M. Knecht}38_{, S. Koblitz}37_{, P. Koppenburg}23_{, A. Kozlinskiy}23_{, L. Kravchuk}32_{, K. Kreplin}11_{, G. Krocker}11_, P. Krokovny11_{, F. Kruse}9_{, K. Kruzelecki}37_{, M. Kucharczyk}20,25_{, S. Kukulak}25_{, R. Kumar}14,37_{, T. Kvaratskheliya}30,37_, V.N. La Thi38_{, D. Lacarrere}37_{, G. Lafferty}50_{, A. Lai}15_{, D. Lambert}46_{, R.W. Lambert}37_{, E. Lanciotti}37_{, G. Lanfranchi}18_,

C. Langenbruch11_{, T. Latham}44_{, R. Le Gac}6_{, J. van Leerdam}23_{, J.-P. Lees}4_{, R. Lef`evre}5_{, A. Leflat}31,37_{, J. Lefran¸cois}7_, O. Leroy6_{, T. Lesiak}25_{, L. Li}3_{, Y.Y. Li}43_{, L. Li Gioi}5_{, M. Lieng}9_{, R. Lindner}37_{, C. Linn}11_{, B. Liu}3_{, G. Liu}37_{, J.H. Lopes}2_,

E. Lopez Asamar35_{, N. Lopez-March}38_{, J. Luisier}38_{, F. Machefert}7_{, I.V. Machikhiliyan}4,30_{, F. Maciuc}10_{, O. Maev}29,37_, J. Magnin1_{, A. Maier}37_{, S. Malde}51_{, R.M.D. Mamunur}37_{, G. Manca}15,d_{, G. Mancinelli}6_{, N. Mangiafave}43_{, U. Marconi}14_,

R. M¨arki38_{, J. Marks}11_{, G. Martellotti}22_{, A. Martens}7_{, L. Martin}51_{, A. Mart´ın S´anchez}7_{, D. Martinez Santos}37_, A. Massafferri1_{, Z. Mathe}12_{, C. Matteuzzi}20_{, M. Matveev}29_{, E. Maurice}6_{, B. Maynard}52_{, A. Mazurov}32,16,37_{, G. McGregor}50_,

R. McNulty12_{, C. Mclean}14_{, M. Meissner}11_{, M. Merk}23_{, J. Merkel}9_{, R. Messi}21,k_{, S. Miglioranzi}37_{, D.A. Milanes}13,37_, M.-N. Minard4_{, S. Monteil}5_{, D. Moran}12_{, P. Morawski}25_{, J.V. Morris}45_{, R. Mountain}52_{, I. Mous}23_{, F. Muheim}46_{, K. M¨uller}39_,

R. Muresan28,38_{, B. Muryn}26_{, M. Musy}35_{, P. Naik}42_{, T. Nakada}38_{, R. Nandakumar}45_{, J. Nardulli}45_{, M. Nedos}9_, M. Needham46_{, N. Neufeld}37_{, C. Nguyen-Mau}38,p_{, M. Nicol}7_{, S. Nies}9_{, V. Niess}5_{, N. Nikitin}31_{, A. Oblakowska-Mucha}26_,

V. Obraztsov34_{, S. Oggero}23_{, S. Ogilvy}47_{, O. Okhrimenko}41_{, R. Oldeman}15,d_{, M. Orlandea}28_{, J.M. Otalora Goicochea}2_, B. Pal52_{, J. Palacios}39_{, M. Palutan}18_{, J. Panman}37_{, A. Papanestis}45_{, M. Pappagallo}13,b_{, C. Parkes}47,37_{, C.J. Parkinson}49_,

G. Passaleva17_{, G.D. Patel}48_{, M. Patel}49_{, S.K. Paterson}49_{, G.N. Patrick}45_{, C. Patrignani}19,i_{, C. Pavel-Nicorescu}28_, A. Pazos Alvarez36_{, A. Pellegrino}23_{, G. Penso}22,l_{, M. Pepe Altarelli}37_{, S. Perazzini}14,c_{, D.L. Perego}20,j_{, E. Perez Trigo}36_, A. P´erez-Calero Yzquierdo35_{, P. Perret}5_{, M. Perrin-Terrin}6_{, G. Pessina}20_{, A. Petrella}16,37_{, A. Petrolini}19,i_{, B. Pie Valls}35_,

B. Pietrzyk4_{, T. Pilar}44_{, D. Pinci}22_{, R. Plackett}47_{, S. Playfer}46_{, M. Plo Casasus}36_{, G. Polok}25_{, A. Poluektov}44,33_, E. Polycarpo2_{, D. Popov}10_{, B. Popovici}28_{, C. Potterat}35_{, A. Powell}51_{, T. du Pree}23_{, V. Pugatch}41_{, A. Puig Navarro}35_,

W. Qian52_{, J.H. Rademacker}42_{, B. Rakotomiaramanana}38_{, I. Raniuk}40_{, G. Raven}24_{, S. Redford}51_{, M.M. Reid}44_, A.C. dos Reis1_{, S. Ricciardi}45_{, K. Rinnert}48_{, D.A. Roa Romero}5_{, P. Robbe}7_{, E. Rodrigues}47_{, F. Rodrigues}2_, C. Rodriguez Cobo36_{, P. Rodriguez Perez}36_{, G.J. Rogers}43_{, V. Romanovsky}34_{, J. Rouvinet}38_{, T. Ruf}37_{, H. Ruiz}35_,

G. Sabatino21,k_{, J.J. Saborido Silva}36_{, N. Sagidova}29_{, P. Sail}47_{, B. Saitta}15,d_{, C. Salzmann}39_{, M. Sannino}19,i_, R. Santacesaria22_{, R. Santinelli}37_{, E. Santovetti}21,k_{, M. Sapunov}6_{, A. Sarti}18,l_{, C. Satriano}22,m_{, A. Satta}21_{, M. Savrie}16,e_,

D. Savrina30_{, P. Schaack}49_{, M. Schiller}11_{, S. Schleich}9_{, M. Schmelling}10_{, B. Schmidt}37_{, O. Schneider}38_{, A. Schopper}37_, M.-H. Schune7_{, R. Schwemmer}37_{, A. Sciubba}18,l_{, M. Seco}36_{, A. Semennikov}30_{, K. Senderowska}26_{, N. Serra}39_{, J. Serrano}6_,

P. Seyfert11_{, B. Shao}3_{, M. Shapkin}34_{, I. Shapoval}40,37_{, P. Shatalov}30_{, Y. Shcheglov}29_{, T. Shears}48_{, L. Shekhtman}33_, O. Shevchenko40_{, V. Shevchenko}30_{, A. Shires}49_{, R. Silva Coutinho}54_{, H.P. Skottowe}43_{, T. Skwarnicki}52_{, A.C. Smith}37_, N.A. Smith48_{, K. Sobczak}5_{, F.J.P. Soler}47_{, A. Solomin}42_{, F. Soomro}49_{, B. Souza De Paula}2_{, B. Spaan}9_{, A. Sparkes}46_, P. Spradlin47_{, F. Stagni}37_{, S. Stahl}11_{, O. Steinkamp}39_{, S. Stoica}28_{, S. Stone}52,37_{, B. Storaci}23_{, U. Straumann}39_{, N. Styles}46_, S. Swientek9_{, M. Szczekowski}27_{, P. Szczypka}38_{, T. Szumlak}26_{, S. T’Jampens}4_{, E. Teodorescu}28_{, F. Teubert}37_{, C. Thomas}51,45_,

E. Thomas37_{, J. van Tilburg}11_{, V. Tisserand}4_{, M. Tobin}39_{, S. Topp-Joergensen}51_{, M.T. Tran}38_{, A. Tsaregorodtsev}6_, N. Tuning23_{, A. Ukleja}27_{, P. Urquijo}52_{, U. Uwer}11_{, V. Vagnoni}14_{, G. Valenti}14_{, R. Vazquez Gomez}35_{, P. Vazquez Regueiro}36_,

S. Vecchi16_{, J.J. Velthuis}42_{, M. Veltri}17,g_{, K. Vervink}37_{, B. Viaud}7_{, I. Videau}7_{, X. Vilasis-Cardona}35,n_{, J. Visniakov}36_, A. Vollhardt39_{, D. Voong}42_{, A. Vorobyev}29_{, H. Voss}10_{, K. Wacker}9_{, S. Wandernoth}11_{, J. Wang}52_{, D.R. Ward}43_, A.D. Webber50_{, D. Websdale}49_{, M. Whitehead}44_{, D. Wiedner}11_{, L. Wiggers}23_{, G. Wilkinson}51_{, M.P. Williams}44,45_, M. Williams49_{, F.F. Wilson}45_{, J. Wishahi}9_{, M. Witek}25_{, W. Witzeling}37_{, S.A. Wotton}43_{, K. Wyllie}37_{, Y. Xie}46_{, F. Xing}51_, Z. Yang3_{, R. Young}46_{, O. Yushchenko}34_{, M. Zavertyaev}10,a_{, L. Zhang}52_{, W.C. Zhang}12_{, Y. Zhang}3_{, A. Zhelezov}11_{, L. Zhong}3_,

E. Zverev31_{, A. Zvyagin}37_.

1_{Centro Brasileiro de Pesquisas F´ısicas (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´e de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France}

5_{Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France} 6_{CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France}

7_{LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France}

8_{LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France} 9_{Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany}

10_{Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany}

11_{Physikalisches Institut, Ruprecht-Karls-Universit¨at 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 dell’INFN di Frascati, Frascati, Italy} 19_{Sezione INFN di Genova, Genova, Italy}

20_{Sezione INFN di Milano Bicocca, Milano, Italy} 21_{Sezione INFN di Roma Tor Vergata, Roma, Italy} 22_{Sezione INFN di Roma La Sapienza, Roma, Italy}

23_{Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands}

24_{Nikhef National Institute for Subatomic Physics and Vrije Universiteit, Amsterdam, Netherlands} 25_{Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Cracow, Poland}

26_{Faculty of Physics & Applied Computer Science, Cracow, Poland} 27_{Soltan Institute for Nuclear Studies, Warsaw, Poland}

28_{Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania} 29_{Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia}

30_{Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia} 31_{Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia} 32_{Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia} 33_{Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia}

34_{Institute for High Energy Physics (IHEP), Protvino, Russia} 35_{Universitat de Barcelona, Barcelona, Spain}

36_{Universidad de Santiago de Compostela, Santiago de Compostela, Spain} 37_{European Organization for Nuclear Research (CERN), Geneva, Switzerland}

38_{Ecole Polytechnique F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland} 39_{Physik-Institut, Universit¨at Z¨urich, Z¨urich, Switzerland}

40_{NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine} 41_{Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine}

42_{H.H. Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom} 43_{Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom}

44_{Department of Physics, University of Warwick, Coventry, United Kingdom} 45_{STFC Rutherford Appleton Laboratory, Didcot, United Kingdom}

46_{School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom} 47_{School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom}

48_{Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom} 49_{Imperial College London, London, United Kingdom}

50_{School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom} 51_{Department of Physics, University of Oxford, Oxford, United Kingdom}

52_{Syracuse University, Syracuse, NY, United States}

53_{CC-IN2P3, CNRS/IN2P3, Lyon-Villeurbanne, France, associated member}

54_{Pontif´ıcia Universidade Cat´olica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to} 2

b_{Universit`a di Bari, Bari, Italy</sub> c<sub>Universit`a di Bologna, Bologna, Italy} d_{Universit`a di Cagliari, Cagliari, Italy</sub> e<sub>Universit`a di Ferrara, Ferrara, Italy} f_{Universit`a di Firenze, Firenze, Italy</sub> g<sub>Universit`a di Urbino, Urbino, Italy}

h_{Universit`a di Modena e Reggio Emilia, Modena, Italy</sub> i<sub>Universit`a di Genova, Genova, Italy}

j_{Universit`a di Milano Bicocca, Milano, Italy</sub> k<sub>Universit`a di Roma Tor Vergata, Roma, Italy} l_{Universit`a di Roma La Sapienza, Roma, Italy</sub> m<sub>Universit`a della Basilicata, Potenza, Italy}

n_{LIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain} o_{Instituci´o Catalana de Recerca i Estudis Avan¸cats (ICREA), Barcelona, Spain}

p_{Hanoi University of Science, Hanoi, Viet Nam} (The LHCb Collaboration)