DSpace at VNU: Measurements of Bc+ production and mass with the Bc+→J ψπ+ decay

Measurements of Bþc Production and Mass with the Bþc!. Aaij et al.* LHCb Collaboration Received 25 September 2012; published 5 December 2012 Measurements of Bþc production and mass are p

Measurements of Bþc Production and Mass with the Bþc ! J= c
þDecay

R Aaij et al.*

(LHCb Collaboration) (Received 25 September 2012; published 5 December 2012) Measurements of Bþc production and mass are performed with the decay mode Bþc ! J=c
þ using

0:37 fb
1 of data collected in pp collisions atpffiffiffis

¼ 7 TeV by the LHCb experiment The ratio of the production cross section times branching fraction between the Bþc ! J=c
þ and the Bþ! J=c Kþ

decays is measured to beð0:68  0:10ðstatÞ  0:03ðsystÞ  0:05ðlifetimeÞÞ% for Bþc and Bþmesons with

transverse momenta pT> 4 GeV=c and pseudorapidities 2:5 <  < 4:5 The Bþc mass is directly

measured to be6273:7  1:3ðstatÞ  1:6ðsystÞ MeV=c2, and the measured mass difference with respect

to the Bþmeson is MðBþcÞ
MðBþÞ ¼ 994:6  1:3ðstatÞ  0:6ðsystÞ MeV=c2.

The Bþc meson is unique in the standard model as it is the

ground state of a family of mesons containing two different

heavy flavor quarks At the 7 TeV LHC center-of-mass

energy, the most probable way to produce BðÞþc mesons is

through the gg-fusion process, gg! BðÞþc þ b þ
c [1]

The production cross section of the Bþc meson has been

calculated by a complete order-4sapproach and using the

fragmentation approach [1] It is predicted to be about

0:4 b [2,3] at ffiffiffi

s

p

¼ 7 TeV including contributions from excited states This is 1 order of magnitude higher than

that predicted at the Tevatron energy pffiffiffis

¼ 1:96 TeV

However, the theoretical predictions suffer from large

uncertainties, and an accurate measurement of the Bþc

production cross section is needed to guide experimental

studies at the LHC As is the case for heavy quarkonia, the

mass of the Bþc meson can be calculated by means of

potential models and lattice QCD, and early predictions

lay in the range from6:2–6:4 GeV=c2[1] The inclusion of

charge conjugate modes is implied throughout this Letter

The Bþc meson was first observed in the semileptonic

decay mode Bþc ! J=cðþ
Þ‘þXð‘ ¼ e;Þ by CDF [4]

The production cross section times branching fraction

for this decay relative to that for Bþ! J=cKþwas

mea-sured to be0:132þ0:041ðstatÞ  0:031ðsystÞþ0:032 (lifetime)

for Bþc and Bþ mesons with transverse momenta pT>

6 GeV=c and rapidities jyj < 1 Measurements of the Bþ

c mass by CDF [5] and D0 [6] using the fully reconstructed

decay Bþc ! J=cðþ
Þ
þ gave MðBþcÞ ¼ 6275:6 

2:9ðstatÞ  2:5ðsystÞ MeV=c2 and MðBþcÞ ¼ 6300 

14ðstatÞ  5ðsystÞ MeV=c2, respectively A more precise

measurement of the Bþc mass would allow for more

stringent tests of predictions from potential models and lattice QCD calculations

In this Letter, we present a measurement of the ratio of the production cross section times branching fraction of

Bþ

c ! J=c
þ relative to that for Bþ! J=cKþ for Bþ

c and Bþ mesons with transverse momenta pT> 4 GeV=c and pseudorapidities2:5 <  < 4:5, and a measurement of the Bþc mass These measurements are performed using 0:37 fb
1of data collected in pp collisions atpffiffiffis

¼ 7 TeV

by the LHCb experiment The LHCb detector [7] is a single-arm forward spectrometer covering the pseudora-pidity range2 <  < 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 ver-tex detector surrounding the pp interaction region, a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes placed downstream The combined tracking system has

a momentum resolution p=p that varies from 0.4% at

5 GeV=c to 0.6% at 100 GeV=c, and an impact parameter (IP) resolution of 20 m for tracks with high transverse momentum Charged hadrons are identified using two ring-imaging Cherenkov detectors 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 muon system composed of alternating layers of iron and multiwire proportional cham-bers The muon identification efficiency is about 97%, with

a misidentification probability ð
! Þ  3%

The Bþc ! J=c
þand Bþ! J=cKþdecay modes are topologically identical and are selected with requirements

as similar as possible to each other Events are selected

by a trigger system consisting of a hardware stage, based

on information from the calorimeter and muon systems, followed by a software stage which applies a full event reconstruction At the hardware trigger stage, events are selected by requiring a single muon candidate or a pair of

*Full author list given at the end of the article

Published by the American Physical Society under the terms of

the Creative Commons Attribution 3.0 License Further

distri-bution of this work must maintain attridistri-bution to the author(s) and

the published article’s title, journal citation, and DOI

PRL 109, 232001 (2012)

muon candidates with high transverse momenta At the

software trigger stage [8,9], events are selected by

requir-ing a pair of muon candidates with invariant mass within

120 MeV=c2of the J=c mass [10], or a two- or three-track

secondary vertex with a large track pT sum, a significant

displacement from the primary interaction, and at least one

track identified as a muon

At the offline selection stage, J=c candidates are

formed from pairs of oppositely charged tracks with

trans-verse momenta pT> 0:9 GeV=c and identified as muons

The two muons are required to originate from a common

vertex Candidates with a dimuon invariant mass between

3.04 and3:14 GeV=c2are combined with charged hadrons

with pT> 1:5 GeV=c to form the Bþ

c and Bþ meson candidates The J=c mass window is about seven times

larger than the mass resolution No particle identification is

used in the selection of the hadrons To improve the Bþc and

Bþ mass resolutions, the mass of the þ
pair is

con-strained to the J=c mass [10] The b-hadron candidates are

required to have pT> 4 GeV=c, decay time t > 0:25 ps

and pseudorapidity in the range2:5 <  < 4:5 The

fidu-cial region is chosen to be well inside the detector

accep-tance to have a reasonably flat efficiency over the phase

space To further suppress background to the Bþc decay, the

IP 2values of the J=c and
þcandidates with respect to

any primary vertex (PV) in the event are required to be

larger than 4 and 25, respectively The IP 2 is defined as

the difference between the 2of the PV reconstructed with

and without the considered particle The IP 2 of the Bþc

candidates with respect to at least one PV in the event is

required to be less than 25 After all selection requirements

are applied, no event has more than one candidate for the

Bþ

c ! J=c
þdecay, and less than 1% of the events have

more than one candidate for the Bþ! J=cKþ decay.

Such multiple candidates are retained and treated the same

as other candidates; the associated systematic uncertainty

is negligible

The ratio of the production cross section times

branch-ing fraction measured in this analysis is

Rc=u¼ðBþcÞBðBþc ! J=c
þÞ

ðBþÞBðBþ! J=cKþÞ

¼NðBþc ! J=c
þÞ

c tot

u tot NðBþ! J=cKþÞ; (1) where ðBþ

cÞ and ðBþÞ are the inclusive production cross

sections of the Bþc and Bþmesons in pp collisions atpffiffiffis

¼

7 TeV, BðBþ

c ! J=c
þÞ and BðBþ! J=cKþÞ are the

branching fractions of the reconstructed decay chains,

NðBþc ! J=c
þÞ and NðBþ! J=cKþÞ are the yields

of the Bþc ! J=c
þ and Bþ! J=cKþ signal decays,

and ctot, utotare the total efficiencies, including

geometri-cal acceptance, reconstruction, selection, and trigger

effects

The signal event yields are obtained from extended unbinned maximum likelihood fits to the invariant mass distributions of the reconstructed Bþc and Bþcandidates in the interval 6:15 < MðJ=c
þÞ < 6:55 GeV=c2 for Bþc candidates and 5:15 < MðJ=cKþÞ < 5:55 GeV=c2 for

Bþ candidates The Bþ

c ! J=c
þ signal mass shape is described by a double-sided Crystal Ball function [11] The power law behaviour toward low mass is due primarily to final state radiation from the bachelor hadron, whereas the high mass tail is mainly due to final state radiation from the muons in combination with the J=c mass constraint The Bþ! J=cKþ signal mass shape is described by the sum of two double-sided Crystal Ball functions that share the same mean but have different resolutions From simu-lated decays, it is found that the tail parameters of the double-sided Crystal Ball function depend mildly on the mass resolution This functional dependence is determined from simulation and included in the mass fit The combi-natorial background is described by an exponential function Background to Bþ! J=cKþ from the Cabibbo-suppressed decay Bþ! J=c
þ is included to improve the fit quality The distribution is determined from the simulated events The ratio of the number of

Bþ! J=c
þ decays to that of the signal is fixed to BðBþ! J=c
þÞ=BðBþ! J=cKþÞ ¼ 3:83% [12] The Cabibbo-suppressed decay Bþc ! J=cKþ is neglected as

a source of background to the Bþc ! J=c
þ decay The invariant mass distributions of the selected Bþc ! J=c
þ and Bþ ! J=cKþ candidates and the fits to the data are shown in Fig.1 The numbers of signal events are162  18 for Bþc ! J=c
þand56243  256 for Bþ! J=cKþ, as obtained from the fits The goodness of fits is checked with a 2 test, which returns a probability of 97% for

Bþ

c ! J=c
þ and 87% for Bþ! J=cKþ. The efficiencies, including geometrical acceptance, reconstruction, selection and trigger effects are determined using simulated signal events The production of the Bþ meson is simulated usingPYTHIA 6.4[13] with the configu-ration described in Ref [14] A dedicated generator

BCVEGPY [15] is used to simulate the Bþc meson produc-tion Decays of Bþc, Bþand J=c mesons are described by

EVTGEN [16] in which final state radiation is generated usingPHOTOS[17] The decay products are traced through the detector by the GEANT4package [18] as described in Ref [19] As the efficiencies depend on pT and , the efficiencies from the simulation are binned in these varia-bles to avoid a bias The signal yield in each bin is obtained from data by subtracting the background contribution using the sPlot technique [20], where the signal and back-ground mass shapes are assumed to be uncorrelated with

pT and  The efficiency-corrected numbers of Bþc ! J=c
þand Bþ! J=cKþ signal decays are2470  350 and364188  2270, respectively, corresponding to a ratio

of Rc=u¼ ð0:68  0:10Þ%, where the uncertainties are statistical only

PRL 109, 232001 (2012)

The systematic uncertainties related to the determination

of the signal yields and efficiencies are described in the

following Concerning the former, studies of simulated

events show that effects due to the fit model on the measured

ratio Rc=ucan be as much as 1%, which is taken as systematic

uncertainty The uncertainties from the contamination due to

the Cabibbo-suppressed decays are found to be negligible

The uncertainties on the determination of the

efficien-cies are dominated by the knowledge of the Bþc lifetime,

which has been measured by CDF [21] and D0 [22] to

give ðBþ

cÞ ¼ 0:453  0:041 ps [10] The distributions of

the Bþc ! J=c
þsimulated events have been reweighted

after changing the Bþc lifetime by one standard deviation

around its mean value and the efficiencies are recomputed

The relative difference of 7.3% between the recomputed

efficiencies and the nominal values is taken as a systematic

uncertainty Since the Bþlifetime is known more precisely,

its contribution to the uncertainty is neglected

The effects of the trigger requirements have been

eval-uated by only using the events triggered by the lifetime

unbiased (di)muon lines, which is about 85% of the total

number of events Repeating the complete analysis, a ratio

of Rc=u¼ ð0:65  0:10Þ% is found, resulting in a

system-atic uncertainty of 4%

The tracking uncertainty includes two components The

first is the difference in track reconstruction efficiency

between data and simulation, estimated with a tag and probe method [23] of J=c ! þ
decays, which is found to be negligible The second is due to the 2% uncertainty on the effect from hadronic interactions assumed in the detector simulation

The uncertainty due to the choice of the (pT, ) binning

is found to be negligible Combining all systematic uncertainties in quadrature, we obtain Rc=u¼ ð0:68  0:10ðstatÞ  0:03ðsystÞ  0:05ðlifetimeÞÞ% for Bþ

c and

Bþ mesons with transverse momenta p

T> 4 GeV=c and pseudorapidities2:5 <  < 4:5

For the mass measurement, different selection criteria are applied All events are used regardless of the trigger line The fiducial region requirement is also removed Only candidates with a good measured mass uncertainty (<20 MeV=c2) are used, and a loose particle identification requirement on the pion of the Bþc ! J=c
þ decay

is introduced to remove the small contamination from

Bþc ! J=cKþdecays.

The alignment of the tracking system and the calibration

of the momentum scale are performed using a sample of J=c ! þ
decays in periods corresponding to differ-ent running conditions, as described in Refs [24] The validity of the calibrated momentum scale has been checked using samples of KS0 !
þ

and ! þ
decays In all cases, the effect of the final state radiation, which cause the fitted masses to be underestimated, is taken into account The difference between the correction factors determined using the J=c and  resonances, 0.06%, is taken as the systematic uncertainty

The Bþc mass is determined with an extended unbinned maximum likelihood fit to the invariant mass distribution

of the selected Bþc ! J=c
þ candidates The mass dif-ference MðBþ

cÞ
MðBþÞ is obtained by fitting the invari-ant mass distributions of the selected Bþc ! J=c
þ and

Bþ! J=cKþcandidates simultaneously The fit model is the same as in the production cross section ratio measure-ment Figure 2 shows the invariant mass distribution for

Bþc ! J=c
þ The Bþc mass is determined to be6273:0  1:3 MeV=c2, with a resolution of 13:4  1:1 MeV=c2, and the mass difference MðBþ

cÞ
MðBþÞ is 994:3  1:3 MeV=c2 The uncertainties are statistical only. The mass measurement is affected by the systematic uncertainties due to the invariant mass model, momentum scale calibration, detector description, and alignment To evaluate the systematic uncertainty, the complete analysis, including the track fit and the momentum scale calibration when needed, is repeated The parameters to which the mass measurement is sensitive are varied within their uncertainties The changes in the central values of the masses obtained from the fits relative to the nominal results are then assigned as systematic uncertainties

Table I summarizes the systematic uncertainties assigned to the measured Bþc mass and mass difference

M ¼ MðBþcÞ
MðBþÞ The main source is the

] 2

c

) [MeV/

± π ψ M(J/

6200 6300 6400 6500

2c

0

10

20

30

40

50

Total Signal Background

LHCb

(a)

] 2

c

) [MeV/

± K ψ M(J/

5200 5300 5400 5500

2

10

3

10

4

Total Signal Background

±

π ψ J/

→

±

B

LHCb

(b)

FIG 1 (color online) Invariant mass distributions of selected

(a) Bþc ! J=c
þcandidates and (b) Bþ! J=c Kþcandidates,

used in the production measurement The fits to the data are

superimposed

PRL 109, 232001 (2012)

uncertainty in the momentum scale calibration After the

calibration procedure a residual0:06% variation of the

momentum scale remains as a function of the particle

pseudorapidity  The impact of this variation is evaluated

by parameterizing the momentum scale as a function of 

The amount of material traversed by a particle in the

tracking system is known to 10% accuracy, the magnitude

of the energy loss correction in the reconstruction is

there-fore varied by 10% To quantify the effects due to the

alignment uncertainty, the horizontal and vertical slopes

of the tracks close to the interaction region, which are

determined by measurements in the vertex detector, are

changed by0:1%, corresponding to the estimated

preci-sion of the length scale along the beam axis [25] To test the

relative alignment of different subdetectors, the analysis is

repeated ignoring the hits of the tracking station between

the vertex detector and the magnet Other uncertainties

arise from the signal and background line shapes The

bias due to the final state radiation is studied using a

simulation based on PHOTOS [17] The mass returned

by the fit model is found to be underestimated by0:7 

0:1 MeV=c2 for the Bþc meson, and by0:4  0:1 MeV=c2

for the Bþ meson The mass and mass difference are corrected accordingly, and the uncertainties are propa-gated The effects of the background shape are evaluated

by using a constant or a first-order polynomial function instead of the nominal exponential function The stability

of the measured Bþc mass is studied by dividing the data samples according to the polarity of the spectrometer magnet and the pion charge The measured Bþc masses are consistent with the nominal result within the statistical uncertainties

In conclusion, using 0:37 fb
1 of data collected in pp collisions at pffiffiffis

¼ 7 TeV by the LHCb experiment, the ratio of the production cross section times branching frac-tion of Bþc ! J=c
þrelative to that for Bþ! J=cKþis measured to be Rc=u¼ ð0:68  0:10ðstatÞ  0:03ðsystÞ  0:05ðlifetimeÞÞ% for Bþ

c and Bþ mesons with transverse momenta pT> 4 GeV=c and pseudorapidities 2:5 <  < 4:5 Given the large theoretical uncertainties on both pro-duction and branching fractions of the Bþc meson, more precise theoretical predictions are required to make a direct comparison with our result The Bþc mass is measured to be 6273:7  1:3ðstatÞ  1:6ðsystÞ MeV=c2. The measured mass difference with respect to the Bþmeson is MðBþ

cÞ
MðBþÞ ¼ 994:6  1:3ðstatÞ  0:6ðsystÞ MeV=c2 Taking the world average Bþ mass [10], we obtain MðBþcÞ ¼ 6273:9  1:3ðstatÞ  0:6ðsystÞ MeV=c2, which has a smaller systematic uncertainty The measured Bþc mass is

in agreement with previous measurements [5,6] and a recent prediction given by the lattice QCD calculations, 6278ð6Þð4Þ MeV=c2 [26] These results represent the most precise determinations of these quantities to date

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 CERN and at the LHCb institutes, and acknowledge sup-port from the National Agencies 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 (The Netherlands); SCSR (Poland); ANCS (Romania); MinES

of Russia and Rosatom (Russia); MICINN, XuntaGal 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 Region Auvergne

[1] N Brambilla et al (Quarkonium Working Group),arXiv: hep-ph/0412158, and references therein

[2] C.-H Chang and X.-G Wu, Eur Phys J C 38, 267 (2004)

[3] Y.-N Gao, J.-B He, P Robbe, M.-H Schune, and Z.-W Yang,Chin Phys Lett 27, 061302 (2010) [4] F Abe et al (CDF Collaboration), Phys Rev Lett 81,

2432 (1998)

TABLE I Systematic uncertainties (in MeV=c2) of the Bþc

mass and mass differenceM ¼ MðBþcÞ
MðBþÞ

Mass fitting

Momentum scale

Detector description

Detector alignment

Vertex detector (track slopes) 0.1   

] 2

c

) [MeV/

± π ψ M(J/

6200 6300 6400 6500

0

10

20

30

40

50

Total Signal Background

LHCb

FIG 2 (color online) Invariant mass distribution of Bþc !

J=c
þ decays, used in the mass measurement The fit to the

data is superimposed

PRL 109, 232001 (2012)

[5] T Aaltonen et al (CDF Collaboration),Phys Rev Lett.

100, 182002 (2008)

[6] V M Abazov et al (D0 Collaboration),Phys Rev Lett

101, 012001 (2008)

[7] A A Alves, Jr et al (LHCb Collaboration), JINST 3,

S08005 (2008)

[8] R Aaij and J Albrecht, Report No

LHCb-PUB-2011-017

[9] V Gligorov, C Thomas, and M Williams, Report

No LHCb-PUB-2011-016

[10] J Beringer et al (Particle Data Group),Phys Rev D 86,

010001 (2012)

[11] T Skwarnicki, PhD thesis, Institute of Nuclear Physics,

Krakow, 1986 Report No DESY-F31-86-02

[12] R Aaij et al (LHCb Collaboration), Phys Rev D 85,

091105 (2012)

[13] T Sjo¨strand, S Mrenna, and P Skands, J High Energy

Phys 05 (2006) 026

[14] I Belyaev et al., Nuclear Science Symposium Conference

Record (NSS/MIC) (IEEE, Bellingham, WA, 2010),

p 1155

[15] C.-H Chang, J.-X Wang, and X.-G Wu,Comput Phys

Commun 174, 241 (2006)

[16] D J Lange,Nucl Instrum Methods Phys Res., Sect A

462, 152 (2001) [17] P Golonka and Z Was,Eur Phys J C 45, 97 (2006) [18] J Allison et al (GEANT4 Collaboration), IEEE Trans Nucl Sci 53, 270 (2006); S Agostinelli et al (GEANT4 Collaboration), Nucl Instrum Methods Phys Res., Sect A 506, 250 (2003)

[19] M Clemencic, G Corti, S Easo, C R Jones, S Miglioranzi, M Pappagallo, and P Robbe,J Phys Conf Ser 331, 032023 (2011)

[20] M Pivk and F R Le Diberder, Nucl Instrum Methods Phys Res., Sect A 555, 356 (2005)

[21] A Abulencia et al (CDF Collaboration),Phys Rev Lett

97, 012002 (2006) [22] V Abazov et al (D0 Collaboration),Phys Rev Lett 102,

092001 (2009) [23] A Jaeger et al., Report No LHCb-PUB-2011-025 [24] R Aaij et al (LHCb Collaboration),Phys Lett B 708,

241 (2012) [25] R Aaij et al (LHCb Collaboration),Phys Lett B 709,

177 (2012) [26] T.-W Chiu and T.-H Hsieh (TWQCD Collaboration), Proc Sci., LAT2006 (2007) 180

R Aaij,38C Abellan Beteta,33,nA Adametz,11B Adeva,34M Adinolfi,43C Adrover,6A Affolder,49Z Ajaltouni,5

J Albrecht,35F Alessio,35M Alexander,48S Ali,38G Alkhazov,27P Alvarez Cartelle,34A A Alves, Jr.,22

S Amato,2Y Amhis,36L Anderlini,17,fJ Anderson,37R B Appleby,51O Aquines Gutierrez,10F Archilli,18,35

A Artamonov,32M Artuso,53E Aslanides,6G Auriemma,22,mS Bachmann,11J J Back,45C Baesso,54

W Baldini,16R J Barlow,51C Barschel,35S Barsuk,7W Barter,44A Bates,48Th Bauer,38A Bay,36J Beddow,48

I Bediaga,1S Belogurov,28K Belous,32I Belyaev,28E Ben-Haim,8M Benayoun,8G Bencivenni,18S Benson,47

J Benton,43A Berezhnoy,29R Bernet,37M.-O Bettler,44M van Beuzekom,38A Bien,11S Bifani,12T Bird,51

A Bizzeti,17,hP M Bjørnstad,51T Blake,35F Blanc,36C Blanks,50J Blouw,11S Blusk,53A Bobrov,31V Bocci,22

A Bondar,31N Bondar,27W Bonivento,15S Borghi,48,51A Borgia,53T J V Bowcock,49C Bozzi,16T Brambach,9

J van den Brand,39J Bressieux,36D Brett,51M Britsch,10T Britton,53N H Brook,43H Brown,49

A Bu¨chler-Germann,37I Burducea,26A Bursche,37J Buytaert,35S Cadeddu,15O Callot,7M Calvi,20,j

M Calvo Gomez,33,nA Camboni,33P Campana,18,35A Carbone,14,cG Carboni,21,kR Cardinale,19,iA Cardini,15

L Carson,50K Carvalho Akiba,2G Casse,49M Cattaneo,35Ch Cauet,9M Charles,52Ph Charpentier,35

P Chen,3,36N Chiapolini,37M Chrzaszcz,23K Ciba,35X Cid Vidal,34G Ciezarek,50P E L Clarke,47

M Clemencic,35H V Cliff,44J Closier,35C Coca,26V Coco,38J Cogan,6E Cogneras,5P Collins,35

A Comerma-Montells,33A Contu,52,15A Cook,43M Coombes,43G Corti,35B Couturier,35G A Cowan,36

D Craik,45S Cunliffe,50R Currie,47C D’Ambrosio,35P David,8P N Y David,38I De Bonis,4K De Bruyn,38

S De Capua,21,kM De Cian,37J M De Miranda,1L De Paula,2P De Simone,18D Decamp,4M Deckenhoff,9

H Degaudenzi,36,35L Del Buono,8C Deplano,15D Derkach,14O Deschamps,5F Dettori,39A Di Canto,11

J Dickens,44H Dijkstra,35P Diniz Batista,1F Domingo Bonal,33,nS Donleavy,49F Dordei,11A Dosil Sua´rez,34

D Dossett,45A Dovbnya,40F Dupertuis,36R Dzhelyadin,32A Dziurda,23A Dzyuba,27S Easo,46U Egede,50

V Egorychev,28S Eidelman,31D van Eijk,38S Eisenhardt,47R Ekelhof,9L Eklund,48I El Rifai,5Ch Elsasser,37

D Elsby,42D Esperante Pereira,34A Falabella,14,eC Fa¨rber,11G Fardell,47C Farinelli,38S Farry,12V Fave,36

V Fernandez Albor,34F Ferreira Rodrigues,1M Ferro-Luzzi,35S Filippov,30C Fitzpatrick,35M Fontana,10

F Fontanelli,19,iR Forty,35O Francisco,2M Frank,35C Frei,35M Frosini,17,fS Furcas,20A Gallas Torreira,34

D Galli,14,cM Gandelman,2P Gandini,52Y Gao,3J.-C Garnier,35J Garofoli,53P Garosi,51J Garra Tico,44

L Garrido,33C Gaspar,35R Gauld,52E Gersabeck,11M Gersabeck,35T Gershon,45,35Ph Ghez,4V Gibson,44

V V Gligorov,35C Go¨bel,54D Golubkov,28A Golutvin,50,28,35A Gomes,2H Gordon,52M Grabalosa Ga´ndara,33

R Graciani Diaz,33L A Granado Cardoso,35E Grauge´s,33G Graziani,17A Grecu,26E Greening,52S Gregson,44

O Gru¨nberg,55B Gui,53E Gushchin,30Yu Guz,32T Gys,35C Hadjivasiliou,53G Haefeli,36C Haen,35 PRL 109, 232001 (2012)

S C Haines,44S Hall,50T Hampson,43S Hansmann-Menzemer,11N Harnew,52S T Harnew,43J Harrison,51

P F Harrison,45T Hartmann,55J He,7V Heijne,38K Hennessy,49P Henrard,5J A Hernando Morata,34

E van Herwijnen,35E Hicks,49D Hill,52M Hoballah,5P Hopchev,4W Hulsbergen,38P Hunt,52T Huse,49

N Hussain,52D Hutchcroft,49D Hynds,48V Iakovenko,41P Ilten,12J Imong,43R Jacobsson,35A Jaeger,11

M Jahjah Hussein,5E Jans,38F Jansen,38P Jaton,36B Jean-Marie,7F Jing,3M John,52D Johnson,52

C R Jones,44B Jost,35M Kaballo,9S Kandybei,40M Karacson,35T M Karbach,35J Keaveney,12I R Kenyon,42

U Kerzel,35T Ketel,39A Keune,36B Khanji,20Y M Kim,47O Kochebina,7V Komarov,36,29R F Koopman,39

P Koppenburg,38M Korolev,29A Kozlinskiy,38L Kravchuk,30K Kreplin,11M Kreps,45G Krocker,11

P Krokovny,31F Kruse,9M Kucharczyk,20,23,jV Kudryavtsev,31T Kvaratskheliya,28,35V N La Thi,36

D Lacarrere,35G Lafferty,51A Lai,15D Lambert,47R W Lambert,39E Lanciotti,35G Lanfranchi,18,35

C Langenbruch,35T Latham,45C Lazzeroni,42R Le Gac,6J van Leerdam,38J.-P Lees,4R Lefe`vre,5A Leflat,29,35

J Lefranc¸ois,7O Leroy,6T Lesiak,23Y Li,3L Li Gioi,5M Liles,49R Lindner,35C Linn,11B Liu,3G Liu,35

J von Loeben,20J H Lopes,2E Lopez Asamar,33N Lopez-March,36H Lu,3J Luisier,36A Mac Raighne,48

F Machefert,7I V Machikhiliyan,4,28F Maciuc,26O Maev,27,35J Magnin,1M Maino,20S Malde,52G Manca,15,d

G Mancinelli,6N Mangiafave,44U Marconi,14R Ma¨rki,36J Marks,11G Martellotti,22A Martens,8L Martin,52

A Martı´n Sa´nchez,7M Martinelli,38D Martinez Santos,35A Massafferri,1Z Mathe,35C Matteuzzi,20

M Matveev,27E Maurice,6A Mazurov,16,30,35,eJ McCarthy,42G McGregor,51R McNulty,12M Meissner,11

M Merk,38J Merkel,9D A Milanes,13M.-N Minard,4J Molina Rodriguez,54S Monteil,5D Moran,51

P Morawski,23R Mountain,53I Mous,38F Muheim,47K Mu¨ller,37R Muresan,26B Muryn,24B Muster,36

J Mylroie-Smith,49P Naik,43T Nakada,36R Nandakumar,46I Nasteva,1M Needham,47N Neufeld,35

A D Nguyen,36C Nguyen-Mau,36,oM Nicol,7V Niess,5N Nikitin,29T Nikodem,11A Nomerotski,52,35

A Novoselov,32A Oblakowska-Mucha,24V Obraztsov,32S Oggero,38S Ogilvy,48O Okhrimenko,41

R Oldeman,15,35,dM Orlandea,26J M Otalora Goicochea,2P Owen,50B K Pal,53A Palano,13,bM Palutan,18

J Panman,35A Papanestis,46M Pappagallo,48C Parkes,51C J Parkinson,50G Passaleva,17G D Patel,49

M Patel,50G N Patrick,46C Patrignani,19,iC Pavel-Nicorescu,26A Pazos Alvarez,34A Pellegrino,38G Penso,22,l

M Pepe Altarelli,35S Perazzini,14,cD L Perego,20,jE Perez Trigo,34A Pe´rez-Calero Yzquierdo,33P Perret,5

M Perrin-Terrin,6G Pessina,20K Petridis,50A Petrolini,19,iA Phan,53E Picatoste Olloqui,33B Pie Valls,33

B Pietrzyk,4T Pilarˇ,45D Pinci,22S Playfer,47M Plo Casasus,34F Polci,8G Polok,23A Poluektov,45,31

E Polycarpo,2D Popov,10B Popovici,26C Potterat,33A Powell,52J Prisciandaro,36V Pugatch,41

A Puig Navarro,36W Qian,3J H Rademacker,43B Rakotomiaramanana,36M S Rangel,2I Raniuk,40

N Rauschmayr,35G Raven,39S Redford,52M M Reid,45A C dos Reis,1S Ricciardi,46A Richards,50

K Rinnert,49V Rives Molina,33D A Roa Romero,5P Robbe,7E Rodrigues,48,51P Rodriguez Perez,34

G J Rogers,44S Roiser,35V Romanovsky,32A Romero Vidal,34J Rouvinet,36T Ruf,35H Ruiz,33G Sabatino,21,k

J J Saborido Silva,34N Sagidova,27P Sail,48B Saitta,15,dC Salzmann,37B Sanmartin Sedes,34M Sannino,19,i

R Santacesaria,22C Santamarina Rios,34R Santinelli,35E Santovetti,21,kM Sapunov,6A Sarti,18,lC Satriano,22,m

A Satta,21M Savrie,16,eP Schaack,50M Schiller,39H Schindler,35S Schleich,9M Schlupp,9M Schmelling,10

B Schmidt,35O Schneider,36A Schopper,35M.-H Schune,7R Schwemmer,35B Sciascia,18A Sciubba,18,l

M Seco,34A Semennikov,28K Senderowska,24I Sepp,50N Serra,37J Serrano,6P Seyfert,11M Shapkin,32

I Shapoval,40,35P Shatalov,28Y Shcheglov,27T Shears,49,35L Shekhtman,31O Shevchenko,40V Shevchenko,28

A Shires,50R Silva Coutinho,45T Skwarnicki,53N A Smith,49E Smith,52,46M Smith,51K Sobczak,5

F J P Soler,48F Soomro,18,35D Souza,43B Souza De Paula,2B Spaan,9A Sparkes,47P Spradlin,48F Stagni,35

S Stahl,11O Steinkamp,37S Stoica,26S Stone,53B Storaci,38M Straticiuc,26U Straumann,37V K Subbiah,35

S Swientek,9M Szczekowski,25P Szczypka,36,35T Szumlak,24S T’Jampens,4M Teklishyn,7E Teodorescu,26

F Teubert,35C Thomas,52E Thomas,35J van Tilburg,11V Tisserand,4M Tobin,37S Tolk,39D Tonelli,35

S Topp-Joergensen,52N Torr,52E Tournefier,4,50S Tourneur,36M T Tran,36A Tsaregorodtsev,6P Tsopelas,38

N Tuning,38M Ubeda Garcia,35A Ukleja,25D Urner,51U Uwer,11V Vagnoni,14G Valenti,14

R Vazquez Gomez,33P Vazquez Regueiro,34S Vecchi,16J J Velthuis,43M Veltri,17,gG Veneziano,36

M Vesterinen,35B Viaud,7I Videau,7D Vieira,2X Vilasis-Cardona,33,nJ Visniakov,34A Vollhardt,37

D Volyanskyy,10D Voong,43A Vorobyev,27V Vorobyev,31H Voss,10C Voß,55R Waldi,55R Wallace,12

S Wandernoth,11J Wang,53D R Ward,44N K Watson,42A D Webber,51D Websdale,50M Whitehead,45

J Wicht,35D Wiedner,11L Wiggers,38G Wilkinson,52M P Williams,45,46M Williams,50,pF F Wilson,46 PRL 109, 232001 (2012)

J Wishahi,9M Witek,23,35W Witzeling,35S A Wotton,44S Wright,44S Wu,3K Wyllie,35Y Xie,47F Xing,52

Z Xing,53Z Yang,3R Young,47X Yuan,3O Yushchenko,32M Zangoli,14M Zavertyaev,10,aF Zhang,3

L Zhang,53W C Zhang,12Y Zhang,3A Zhelezov,11L Zhong,3and A Zvyagin35

(LHCb Collaboration)

1Centro Brasileiro de Pesquisas Fı´sicas (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

4

LAPP, Universite´ de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France

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

6CPPM, Aix-Marseille Universite´, CNRS/IN2P3, Marseille, France

7LAL, Universite´ Paris-Sud, CNRS/IN2P3, Orsay, France

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

9Fakulta¨t Physik, Technische Universita¨t Dortmund, Dortmund, Germany

10Max-Planck-Institut fu¨r Kernphysik (MPIK), Heidelberg, Germany

11Physikalisches Institut, Ruprecht-Karls-Universita¨t Heidelberg, Heidelberg, Germany

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

13

Sezione 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 Roma Tor Vergata, Roma, Italy

22Sezione INFN di Roma La Sapienza, Roma, Italy

23Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krako´w, Poland

24AGH University of Science and Technology, Krako´w, Poland

25National Center for Nuclear Research (NCBJ), Warsaw, Poland

26Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania

27Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia

28Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia

29

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

30Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia

31Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia

32Institute for High Energy Physics (IHEP), Protvino, Russia

33Universitat de Barcelona, Barcelona, Spain

34Universidad de Santiago de Compostela, Santiago de Compostela, Spain

35European Organization for Nuclear Research (CERN), Geneva, Switzerland

36Ecole Polytechnique Fe´de´rale de Lausanne (EPFL), Lausanne, Switzerland

37Physik-Institut, Universita¨t Zu¨rich, Zu¨rich, Switzerland

38

Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands

39Nikhef National Institute for Subatomic Physics and VU University Amsterdam, Amsterdam, The Netherlands

40NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine

41Institute for Nuclear Research of the National Academy of Sciences (KINR), Kyiv, Ukraine

42University of Birmingham, Birmingham, United Kingdom

43H.H Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom

44Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom

45Department of Physics, University of Warwick, Coventry, United Kingdom

46STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

47School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom

48School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom

49Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom

50Imperial College London, London, United Kingdom

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

52Department of Physics, University of Oxford, Oxford, United Kingdom

53Syracuse University, Syracuse, New York, USA PRL 109, 232001 (2012)

54Pontifı´cia Universidade Cato´lica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil (associated with Institution Universidade

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

55Institut fu¨r Physik, Universita¨t Rostock, Rostock, Germany (associated with Institution Physikalisches Institut,

Ruprecht-Karls-Universita¨t Heidelberg, Heidelberg, Germany)

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

bUniversita` di Bari, Bari, Italy

cUniversita` di Bologna, Bologna, Italy

dUniversita` di Cagliari, Cagliari, Italy

eUniversita` di Ferrara, Ferrara, Italy

fUniversita` di Firenze, Firenze, Italy

gUniversita` di Urbino, Urbino, Italy

hUniversita` di Modena e Reggio Emilia, Modena, Italy

iUniversita` di Genova, Genova, Italy

jUniversita` di Milano Bicocca, Milano, Italy

k

Universita` di Roma Tor Vergata, Roma, Italy

lUniversita` di Roma La Sapienza, Roma, Italy

mUniversita` della Basilicata, Potenza, Italy

nLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

oHanoi University of Science, Hanoi, Viet Nam

pMassachusetts Institute of Technology, Cambridge, MA, United States

PRL 109, 232001 (2012)