DSpace at VNU: First evidence of direct CP violation in charmless two-body decays of Bs0 mesons

Unbinned maximum likelihood fits to the K mass spectra of the selected events are performed.. KþK cross-feed background yields are determined from fits to the þ and KþK mass spectra, res

First Evidence of Direct CP Violation in Charmless Two-Body Decays of B0s Mesons

R Aaij et al.*

(LHCb Collaboration)

(Received 29 February 2012; published 16 May 2012) Using a data sample corresponding to an integrated luminosity of 0:35 fb
1collected by LHCb in 2011,

we report the first evidence of CP violation in the decays of B0

smesons to K
pairs, ACPðB0

0:27  0:08ðstatÞ  0:02ðsystÞ, with a significance of 3:3 Furthermore, we report the most precise

measurement of CP violation in the decays of B0mesons to K
 pairs, ACPðB0! K
Þ ¼
0:088 

0:011ðstatÞ  0:008ðsystÞ, with a significance exceeding 6

DOI: 10.1103/PhysRevLett.108.201601 PACS numbers: 11.30.Er, 13.25.Hw

The violation of CP symmetry, i.e., the noninvariance of

fundamental forces under the combined action of the

charge conjugation (C) and parity (P) transformations, is

well established in the K0 and B0 meson systems [1 4]

Recent results from the LHCb collaboration have also

provided evidence for CP violation in the decays of D0

mesons [5] Consequently, there now remains only one

neutral heavy meson system, the B0, where CP violation

has not yet been seen All current experimental

measure-ments of CP violation in the quark flavor sector are well

described by the Cabibbo-Kobayashi-Maskawa

mecha-nism [6,7] which is embedded in the framework of the

standard model (SM) However, it is believed that the size

of CP violation in the SM is not sufficient to account for

the asymmetry between matter and antimatter in the

Universe [8]; hence, additional sources of CP violation

are being searched for as manifestations of physics beyond

the SM

In this Letter, we report measurements of direct CP

violating asymmetries in B0! Kþ

and B0 ! K

þ

decays using data collected with the LHCb detector The

inclusion of charge-conjugate modes is implied except in

the asymmetry definitions CP violation in charmless

two-body B decays could potentially reveal the presence of

physics beyond the SM [9 13], and has been extensively

studied at the B factories and at the Tevatron [14–16] The

direct CP asymmetry in the B0ðsÞdecay rate to the final state

fðsÞ, with f ¼ Kþ

and fs¼ K

þ, is defined as

ACP¼
½ð B0

ðsÞ! fðsÞÞ; ðB0

ðsÞ! fðsÞÞ; (1) where
½X; Y ¼ ðX
YÞ=ðX þ YÞ and fðsÞ denotes the

charge conjugate of fðsÞ

LHCb is a forward spectrometer covering the

pseudor-apidity range 2 <  < 5, designed to perform flavor

physics measurements at the LHC A detailed description

of the detector can be found in Ref [17] The analysis is based on pp collision data collected in the first half of 2011

at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 0:35 fb
1 The polarity of the LHCb magnetic field is reversed from time to time in order

to partially cancel the effects of instrumental charge asym-metries, and about 0:15 fb
1were acquired with one polar-ity and 0:20 fb
1with the opposite polarity

The LHCb trigger system comprises a hardware trigger followed by a high level trigger (HLT) implemented in software The hadronic hardware trigger selects high verse energy clusters in the hadronic calorimeter A trans-verse energy threshold of 3.5 GeV has been adopted for the data set under study The HLT first selects events with at least one large transverse momentum track characterized

by a large impact parameter, and then uses algorithms to reconstruct D and B meson decays Most of the events containing the decays under study have been acquired by means of a dedicated two-body HLT selection To discrimi-nate between signal and background events, this trigger selection imposes requirements on the quality of the online-reconstructed tracks (2 per degree of freedom), their transverse momenta (pT), and their impact parame-ters (dIP, defined as the distance between the reconstructed trajectory of the track and the pp collision vertex), the distance of closest approach of the decay products of the B meson candidate (dCA), its transverse momentum (pB

T), its impact parameter (dBIP), and the decay time in its rest frame (t

, calculated assuming the decay into
þ

) Only B candidates within the

invariant mass range 4:7–5:9 GeV=c2 are accepted The

mass hypothesis

is conventionally chosen to select all charmless two-body

B decays using the same criteria

Offline selection requirements are subsequently applied Two sets of criteria have been optimized with the aim

of minimizing the expected uncertainty either on

ACPðB0 ! K
Þ or on ACPðB0 ! K
Þ In addition to more selective requirements on the kinematic variables already used in the HLT, two further requirements on the larger of the transverse momenta and of the impact

*Full author list given at the end of the article

Published by the American Physical Society under the terms of

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

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

PRL 108, 201601 (2012)

parameters of the daughter tracks are applied A summary

of the two distinct sets of selection criteria is reported in

TableI In the case of B0 ! K
decays, a tighter selection

is needed because the probability for a b quark to decay as

B0 ! K
is about 14 times smaller than that to decay as

B0 ! K
[18], and consequently a stronger rejection of

combinatorial background (Comb bkg.) is required The

two samples passing the event selection are then

subdi-vided into different final states using the particle

identifi-cation (PID) provided by the two ring-imaging Cherenkov

(RICH) detectors Again two sets of PID selection criteria

are applied: a loose set optimized for the measurement of

ACPðB0 ! K
Þ and a tight set for that of ACPðB0! K
Þ

To estimate the background from other two-body B

decays with a misidentified pion or kaon (cross-feed

back-ground), the relative efficiencies of the RICH PID selection

criteria must be determined The high production rate of

charged D mesons at the LHC and the kinematic

charac-teristics of the Dþ! D0ðK

þÞ
þ decay chain make

such events an appropriate calibration sample for the PID

of kaons and pions In addition, for calibrating the response

of the RICH system for protons, a sample of  ! p

decays is used PID information is not used to select either

sample, as the selection of pure final states can be realized

by means of kinematic criteria alone The production and

decay kinematics of the D0! K

þ and  ! p

channels differ from those of the B decays under study

Since the RICH PID information is momentum dependent,

the distributions obtained from calibration samples are

reweighted according to the momentum distributions of

B daughter tracks observed in data

Unbinned maximum likelihood fits to the K
mass

spectra of the selected events are performed The B0 !

K
and B0 ! K
signal components are described by

single Gaussian functions convolved with a function which

describes the effect of final state radiation on the mass line

shape [19] The background due to partially reconstructed

three-body B decays is parametrized by means of an

ARGUS function [20] convolved with a Gaussian

resolu-tion funcresolu-tion The combinatorial background is modeled

by an exponential and the shapes of the cross-feed

backgrounds, mainly due to B0 !
þ

and B0!

KþK
decays with one misidentified particle in the final state, are obtained from Monte Carlo simulations The

B0!
þ

and B0 ! KþK
cross-feed background yields are determined from fits to the
þ

and KþK
mass spectra, respectively, using events selected by the same offline selection as the signal and taking into account the appropriate PID efficiency factors The Kþ

and

K

þ mass spectra for the events passing the two offline selections are shown in Fig.1

From the two mass fits we determine, respectively, the signal yields NðB0! K
Þ ¼ 13 250  150 and NðB0! K
Þ ¼ 314  27, as well as the raw yield asymmetries

ArawðB0! K
Þ ¼
0:095  0:011 and ArawðB0!K
Þ¼ 0:280:08, where the uncertainties are statistical only In order to determine the CP asymmetries from the observed raw asymmetries, effects induced by the detector acceptance and event reconstruction, as well as due to strong interac-tions of final state particles with the detector material, need

to be taken into account Furthermore, the possible presence

of a B0 ðsÞ
B0 ðsÞproduction asymmetry must also be consid-ered The CP asymmetry is related to the raw asymmetry by

ACP¼ Araw
A, where the correction A is defined as

AðB0 ðsÞ! K
Þ ¼ dðsÞADðK
Þ þ dðsÞAPðB0

ðsÞÞ; (2) where d¼ 1 and s¼
1, following the sign convention for f and fs in Eq (1) The instrumental asymmetry

ADðK
Þ is given in terms of the detection efficiencies "D

of the charge-conjugate final states by ADðK
Þ ¼

½"DðK

þÞ; "DðKþ

Þ, and the production asymmetry

APðB0 ðsÞÞ is defined in terms of the B0

ðsÞ and B0

ðsÞ production rates, Rð B0

ðsÞÞ and RðB0

ðsÞÞ, as APðB0

ðsÞÞ ¼

½Rð B0ðsÞÞ; RðB0

ðsÞÞ The factor dðsÞ takes into account di-lution due to neutral B0

ðsÞmeson mixing, and is defined as

dðsÞ¼

R1

0 e
dðsÞ tcosðmdðsÞtÞ"ðB0ðsÞ! K
; tÞdt

R1

0 e
dðsÞ tcoshðdðsÞ

2 tÞ"ðB0

ðsÞ! K
; tÞdt; (3) where "ðB0 ! K
; tÞ and "ðB0 ! K
; tÞ are the accep-tances as functions of the decay time for the two recon-structed decays To calculate d and s we assume that

d ¼ 0 and we use the world averages for d, md, s,

ms, and s [4] The shapes of the acceptance functions are parametrized using signal decay time distributions ex-tracted from data We obtain d¼ 0:303  0:005 and s¼

0:033  0:003, where the uncertainties are statistical only

In contrast to d, the factor sis small, owing to the large B0 oscillation frequency, thus leading to a negligible impact of

a possible production asymmetry of B0 mesons on the corresponding CP asymmetry measurement

The instrumental charge asymmetry ADðK
Þ can be expressed in terms of two distinct contributions

ADðK
Þ ¼ AIðK
Þ þ ðK
ÞARðK
Þ, where AIðK
Þ is

an asymmetry due to the different strong interaction cross

TABLE I Summary of selection criteria adopted for the

mea-surement of ACPðB0! K
Þ and ACPðB0

s! K
Þ

maxðpK

T; p

maxðdK

IP; d

pB

PRL 108, 201601 (2012)

sections with the detector material of Kþ

and K

þ

final state particles, and ARðK
Þ arises from the possible

presence of a reconstruction or detection asymmetry The

quantity AIðK
Þ does not change its value by reversing the

magnetic field, as the difference in the interaction lengths

seen by the positive and negative particles for opposite

polarities is small By contrast, ARðK
Þ changes its sign

when the magnetic field polarity is reversed The factor

ðK
Þ accounts for different signal yields in the data sets

with opposite polarities, due to the different values of the

corresponding integrated luminosities and to changing

trigger conditions in the course of the run It is estimated

by using the yields of the largest decay mode, i.e., B0 !

K
, determined from the mass fits applied to the two data

sets separately We obtain ðK
Þ ¼
½NupðB0! K
Þ;

NdownðB0 ! K
Þ ¼
0:202  0:011, where ‘‘up’’ and

‘‘down’’ denote the direction of the main component of

the dipole field

The instrumental asymmetries for the final state K
are

measured from data using large samples of tagged Dþ!

D0ðK

þÞ
þand Dþ! D0ðK
KþÞ
þdecays, and

un-tagged D0 ! K

þdecays The combination of the

inte-grated raw asymmetries of all these decay modes is

necessary to disentangle the various contributions to the

raw asymmetries of each mode, notably including the K

instrumental asymmetry as well as that of the pion from the

Dþdecay, and the production asymmetries of the Dþand

D0 mesons In order to determine the raw asymmetry of the D0 ! K
decay, a maximum likelihood fit to the

K

þ and Kþ

mass spectra is performed For the decays Dþ! D0ðK

þÞ
þ and Dþ! D0ðK
KþÞ
þ,

we perform maximum likelihood fits to the discriminating variable m ¼ MD
MD0, where MD and MD0 are the reconstructed D and D0 invariant masses, respectively Approximately 54  106 D0 ! K

þ decays, 7:5  106

Dþ!D0ðK

þÞ
þand 1:1106Dþ! D0ðK
KþÞ
þ decays are used The mass distributions are shown in Figs 2(a)–2(c) The D0! K

þ signal component is modeled as the sum of two Gaussian functions with the common mean convolved with a function accounting for final state radiation [19], on top of an exponential combi-natorial background The Dþ! D0ðK

þÞ
þ and

Dþ! D0ðK
KþÞ
þ signal components are modeled as the sum of two Gaussian functions convolved with a func-tion taking account of the asymmetric shape of the mea-sured distribution [5] The background is described by an empirical function of the form 1
e
ðm
m0 Þ= , where

m0 and are free parameters Using the current world average of the integrated CP asymmetry for the D0!

K
Kþ decay [21] and neglecting CP violation in the Cabibbo-favored D0 ! K

þ decay [22], from the raw yield asymmetries returned by the mass fits we determine

AIðK
Þ ¼ ð
1:00:2Þ10
2 and ARðK
Þ ¼ ð
1:8  0:2Þ  10
3, where the uncertainties are statistical only

0 500 1000 1500 2000 2500

3000

(a)

)

2

invariant mass (GeV/c

− π

+

0 500 1000 1500 2000 2500

3000

LHCb (b)

B →Kπ

B →Kπ

B →ππ

B →KK

B →3-body

Comb bkg

0 0 0 0 s s

0 50 100 150 200 250 300 350

400

) 2 invariant mass (GeV/c

−

π

+ K

LHCb (c)

0 50 100 150 200 250 300 350

400

) 2 invariant mass (GeV/c +

π

−

K

LHCb (d)

FIG 1 (color online) Invariant K
mass spectra obtained using the event selection adopted for the best sensitivity on (a), (b) ACPðB0! K
Þ and (c), (d) ACPðB0

s ! K
Þ Plots (a) and (c) represent the Kþ

invariant mass whereas plots (b) and (d) represent the K

þ invariant mass The results of the unbinned maximum likelihood fits are overlaid The main components contributing to the fit model are also shown

PRL 108, 201601 (2012)

The possible existence of a B0- B0 production

asymme-try is studied by reconstructing a sample of B0 ! J=cK0

decays CP violation in b ! c cs transitions, which

is predicted in the SM to be at the 10
3 level [23], is

neglected The raw asymmetry ArawðB0!J=cK0Þ is

de-termined from an unbinned maximum likelihood fit to the

J=c þ
ÞK0ðKþ

Þ and J=c þ
Þ K0ðK

þÞ

mass spectra The signal mass peak is modeled as the

sum of two Gaussian functions with a common mean,

whereas the combinatorial background is modeled by an

exponential The data sample contains approximately

25 400 B0 ! J=cK0 decays The mass distribution is

shown in Fig.2(d) To determine the production

asymme-try we need to correct for the presence of instrumental

asymmetries Once the necessary corrections are applied,

we obtain a value for the B0 production asymmetry

APðB0Þ ¼ 0:010  0:013, where the uncertainty is

statisti-cal only

By using the instrumental and production

asymme-tries, the correction factor to the raw asymmetry

AðB0 ! K
Þ ¼
0:007  0:006 is obtained Since the

B0 meson has no valence quarks in common with those of

the incident protons, its production asymmetry is expected

to be smaller than for the B0, an expectation that is

sup-ported by hadronization models as discussed in Ref [24]

Even conservatively assuming a value of the production

asymmetry equal to that for the B0, owing to the small

value of s the effect of APðB0Þ is negligible, and we find

AðB0 ! K
Þ ¼ 0:010  0:002

The systematic uncertainties on the asymmetries fall

into the following main categories, related to (a) PID

cali-bration, (b) modeling of the signal and background

components in the maximum likelihood fits, and

(c) instrumental and production asymmetries Knowledge

of PID efficiencies is necessary in this analysis to compute

the number of cross-feed background events affecting the mass fit of the B0 ! K
and B0 ! K
decay channels In order to estimate the impact of imperfect PID calibration,

we perform unbinned maximum likelihood fits after having altered the number of cross-feed background events present in the relevant mass spectra according to the sys-tematic uncertainties affecting the PID efficiencies An estimate of the uncertainty due to possible imperfections

in the description of the final state radiation is determined

by varying, over a wide range, the amount of emitted radiation [19] in the signal line shape parametrization The possibility of an incorrect description of the core distribution in the signal mass model is investigated by replacing the single Gaussian with the sum of two Gaussian functions with a common mean The impact of additional three-body B decays in the K
spectrum, not accounted for in the baseline fit—namely B !


where one pion is missed in the reconstruction and another

is misidentified as a kaon—is investigated The mass line shape of this background component is determined from Monte Carlo simulations, and then the fit is repeated after having modified the baseline parametrization accordingly For the modeling of the combinatorial background compo-nent, the fit is repeated using a first-order polynomial Finally, for the case of the cross-feed backgrounds, two distinct systematic uncertainties are estimated: one due to a relative bias in the mass scale of the simulated distributions with respect to the signal distributions in data, and another accounting for the difference in mass resolution between simulation and data All the shifts from the relevant base-line values are accounted for as systematic uncertainties Differences in the kinematic properties of B decays with respect to the charm control samples, as well as different triggers and offline selections, are taken into account by introducing a systematic uncertainty on the values of the

A corrections This uncertainty dominates the total sys-tematic uncertainty related to the instrumental and produc-tion asymmetries, and can be reduced in future measurements with a better understanding of the depen-dence of such asymmetries on the kinematics of selected signal and control samples The systematic uncertainties for ACPðB0 ! K
Þ and ACPðB0 ! K
Þ are summarized in TableII

In conclusion we obtain the following measurements of the CP asymmetries:

ACPðB0 ! K
Þ ¼
0:088  0:011ðstatÞ  0:008ðsystÞ; and

ACPðB0 ! K
Þ ¼ 0:27  0:08ðstatÞ  0:02ðsystÞ: The result for ACPðB0! K
Þ constitutes the most precise measurement available to date It is in good agreement with the current world average provided by the Heavy Flavor Averaging Group ACPðB0 ! K
Þ ¼
0:098þ0:012

0:011

) 2 invariant mass (GeV/c

π

K

1.82 1.84 1.86 1.88 1.90

Events / ( 0.9 MeV/c 0

500

1000

1500

2000

2500 ×10 3

LHCb

(a)

) 2 ) (MeV/c

0

M(D*)-M(D

140 142 144 146 148 150

Events / ( 0.12 MeV/c 0

100 200 300 400

500 ×10 3

LHCb

(b)

) 2 ) (MeV/c 0 M(D*)-M(D

140 142 144 146 148 150

Events / ( 0.12 MeV/c 0

10

20

30

40

50

60

70

80

LHCb 3

10

×

(c)

) 2 invariant mass (GeV/c

*0 K

ψ

J/

5.22 5.24 5.26 5.28 5.30 5.32 5.34

0 500 1000 1500 2000

(d)

FIG 2 (color online) Distributions of the invariant mass or

(b) Dþ! D0ðK

þÞ
þ, (c) Dþ! D0ðK
KþÞ
þ, and

(d) B0! J= þ
ÞK0ðKþ

Þ The results of the maximum

likelihood fits are overlaid

PRL 108, 201601 (2012)

[21] Dividing the central value of ACPðB0! K
Þ by the

sum in quadrature of the statistical and systematic

uncer-tainties, the significance of the measured deviation from

zero exceeds 6, making this the first observation (greater

than 5) of CP violation in the B meson sector at a hadron

collider The same significance computed for ACPðB0 !

K
Þ is 3:3; therefore, this is the first evidence for CP

violation in the decays of B0 mesons The result for

ACPðB0 ! K
Þ is in agreement with the only

measure-ment previously available [16]

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 Contract No FP7 and the Region of

Auvergne

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R Aaij,38C Abellan Beteta,33,aB Adeva,34M Adinolfi,43C Adrover,6A Affolder,49Z Ajaltouni,5J Albrecht,35

F Alessio,35M Alexander,48S Ali,38G Alkhazov,27P Alvarez Cartelle,34A A Alves Jr,22S Amato,2Y Amhis,36

J Anderson,37R B Appleby,51O Aquines Gutierrez,10F Archilli,18,35L Arrabito,55A Artamonov,32

M Artuso,53,35E Aslanides,6G Auriemma,22,bS Bachmann,11J J Back,45V Balagura,28,35W Baldini,16

R J Barlow,51C Barschel,35S Barsuk,7W Barter,44A Bates,48C Bauer,10Th Bauer,38A Bay,36I Bediaga,1

S Belogurov,28K Belous,32I Belyaev,28E Ben-Haim,8M Benayoun,8G Bencivenni,18S Benson,47J Benton,43

R Bernet,37M.-O Bettler,17M van Beuzekom,38A Bien,11S Bifani,12T Bird,51A Bizzeti,17,cP M Bjørnstad,51

T Blake,35F Blanc,36C Blanks,50J Blouw,11S Blusk,53A Bobrov,31V Bocci,22A Bondar,31N Bondar,27

W Bonivento,15S Borghi,48,51A Borgia,53T J V Bowcock,49C Bozzi,16T Brambach,9J van den Brand,39

J Bressieux,36D Brett,51M Britsch,10T Britton,53N H Brook,43H Brown,49A Bu¨chler-Germann,37

I Burducea,26A Bursche,37J Buytaert,35S Cadeddu,15O Callot,7M Calvi,20,dM Calvo Gomez,33,a

TABLE II Summary of systematic uncertainties on ACPðB0!

K
Þ and ACPðB0

s ! K
Þ The categories (a), (b), and (c) defined

in the text are also indicated The total systematic uncertainties

given in the last row are obtained by summing the individual

contributions in quadrature

PRL 108, 201601 (2012)

A Camboni,33P Campana,18,35A Carbone,14G Carboni,21,eR Cardinale,19,35,fA Cardini,15L Carson,50

K Carvalho Akiba,2G Casse,49M Cattaneo,35Ch Cauet,9M Charles,52Ph Charpentier,35N Chiapolini,37

K Ciba,35X Cid Vidal,34G Ciezarek,50P E L Clarke,47M Clemencic,35H V Cliff,44J Closier,35C Coca,26

V Coco,38J Cogan,6P Collins,35A Comerma-Montells,33A Contu,52A Cook,43M Coombes,43G Corti,35

B Couturier,35G A Cowan,36R Currie,47C D’Ambrosio,35P David,8P N Y David,38I De Bonis,4

K De Bruyn,38S De Capua,21,eM De Cian,37F De Lorenzi,12J M De Miranda,1L De Paula,2P De Simone,18

D Decamp,4M Deckenhoff,9H Degaudenzi,36,35L Del Buono,8C Deplano,15D Derkach,14,35O Deschamps,5

F Dettori,39J Dickens,44H Dijkstra,35P Diniz Batista,1F Domingo Bonal,33,aS Donleavy,49F Dordei,11

A Dosil Sua´rez,34D Dossett,45A Dovbnya,40F Dupertuis,36R Dzhelyadin,32A Dziurda,23S Easo,46U Egede,50

V Egorychev,28S Eidelman,31D van Eijk,38F Eisele,11S Eisenhardt,47R Ekelhof,9L Eklund,48Ch Elsasser,37

D Elsby,42D Esperante Pereira,34A Falabella,16,14,gC Fa¨rber,11G Fardell,47C Farinelli,38S Farry,12V Fave,36

V Fernandez Albor,34M Ferro-Luzzi,35S Filippov,30C Fitzpatrick,47M Fontana,10F Fontanelli,19,fR Forty,35

O Francisco,2M Frank,35C Frei,35M Frosini,17,hS Furcas,20A Gallas Torreira,34D Galli,14,iM Gandelman,2

P Gandini,52Y Gao,3J-C Garnier,35J Garofoli,53J Garra Tico,44L Garrido,33D Gascon,33C Gaspar,35

R Gauld,52N Gauvin,36M Gersabeck,35T Gershon,45,35Ph Ghez,4V Gibson,44V V Gligorov,35C Go¨bel,54

D Golubkov,28A Golutvin,50,28,35A Gomes,2H Gordon,52M Grabalosa Ga´ndara,33R Graciani Diaz,33

L A Granado Cardoso,35E Grauge´s,33G Graziani,17A Grecu,26E Greening,52S Gregson,44B Gui,53

E Gushchin,30Yu Guz,32T Gys,35C Hadjivasiliou,53G Haefeli,36C Haen,35S C Haines,44T Hampson,43

S Hansmann-Menzemer,11R Harji,50N Harnew,52J Harrison,51P F Harrison,45T Hartmann,56J He,7

V Heijne,38K Hennessy,49P Henrard,5J A Hernando Morata,34E van Herwijnen,35E Hicks,49K Holubyev,11

P Hopchev,4W Hulsbergen,38P Hunt,52T Huse,49R S Huston,12D Hutchcroft,49D Hynds,48V Iakovenko,41

P Ilten,12J Imong,43R Jacobsson,35A Jaeger,11M Jahjah Hussein,5E Jans,38F Jansen,38P Jaton,36

B Jean-Marie,7F Jing,3M John,52D Johnson,52C R Jones,44B Jost,35M Kaballo,9S Kandybei,40

M Karacson,35T M Karbach,9J Keaveney,12I R Kenyon,42U Kerzel,35T Ketel,39A Keune,36B Khanji,6

Y M Kim,47M Knecht,36R F Koopman,39P Koppenburg,38M Korolev,29A Kozlinskiy,38L Kravchuk,30

K Kreplin,11M Kreps,45G Krocker,11P Krokovny,31F Kruse,9K Kruzelecki,35M Kucharczyk,20,23,35,d

V Kudryavtsev,31T Kvaratskheliya,28,35V N La Thi,36D Lacarrere,35G Lafferty,51A Lai,15D Lambert,47

R W Lambert,39E Lanciotti,35G Lanfranchi,18C Langenbruch,11T Latham,45C Lazzeroni,42R Le Gac,6

J van Leerdam,38J.-P Lees,4R Lefe`vre,5A Leflat,29,35J Lefranc¸ois,7O Leroy,6T Lesiak,23L Li,3L Li Gioi,5

M Lieng,9M Liles,49R Lindner,35C Linn,11B Liu,3G Liu,35J von Loeben,20J H Lopes,2E Lopez Asamar,33

N Lopez-March,36H Lu,3J Luisier,36A Mac Raighne,48F Machefert,7I V Machikhiliyan,4,28F Maciuc,10

O Maev,27,35J Magnin,1S Malde,52R M D Mamunur,35G Manca,15,jG Mancinelli,6N Mangiafave,44

U Marconi,14R Ma¨rki,36J Marks,11G Martellotti,22A Martens,8L Martin,52A Martı´n Sa´nchez,7

M Martinelli,38D Martinez Santos,35A Massafferri,1Z Mathe,12C Matteuzzi,20M Matveev,27E Maurice,6

B Maynard,53A Mazurov,16,30,35G McGregor,51R McNulty,12M Meissner,11M Merk,38J Merkel,9

S Miglioranzi,35D A Milanes,13M.-N Minard,4J Molina Rodriguez,54S Monteil,5D Moran,12P Morawski,23

R Mountain,53I Mous,38F Muheim,47K Mu¨ller,37R Muresan,26B Muryn,24B Muster,36J Mylroie-Smith,49

P Naik,43T Nakada,36R Nandakumar,46I Nasteva,1M Needham,47N Neufeld,35A D Nguyen,36

C Nguyen-Mau,36,kM Nicol,7V Niess,5N Nikitin,29T Nikodem,11A Nomerotski,52,35A Novoselov,32

A Oblakowska-Mucha,24V Obraztsov,32S Oggero,38S Ogilvy,48O Okhrimenko,41R Oldeman,15,35,j

M Orlandea,26J M Otalora Goicochea,2P Owen,50K B Pal,53J Palacios,37A Palano,13,lM Palutan,18

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

M Patel,50S K Paterson,50G N Patrick,46C Patrignani,19,fC Pavel-Nicorescu,26A Pazos Alvarez,34

A Pellegrino,38G Penso,22,mM Pepe Altarelli,35S Perazzini,14,iD L Perego,20,dE Perez Trigo,34

A Pe´rez-Calero Yzquierdo,33P Perret,5M Perrin-Terrin,6G Pessina,20A Petrolini,19,fA Phan,53

E Picatoste Olloqui,33B Pie Valls,33B Pietrzyk,4T Pilarˇ,45D Pinci,22R Plackett,48S Playfer,47

M Plo Casasus,34G Polok,23A Poluektov,45,31E Polycarpo,2D Popov,10B Popovici,26C Potterat,33A Powell,52

J Prisciandaro,36V Pugatch,41A Puig Navarro,33W Qian,53J H Rademacker,43B Rakotomiaramanana,36

M S Rangel,2I Raniuk,40G Raven,39S Redford,52M M Reid,45A C dos Reis,1S Ricciardi,46A Richards,50

K Rinnert,49D A Roa Romero,5P Robbe,7E Rodrigues,48,51F Rodrigues,2P Rodriguez Perez,34G J Rogers,44

S Roiser,35V Romanovsky,32M Rosello,33,aJ Rouvinet,36T Ruf,35H Ruiz,33G Sabatino,21,e

PRL 108, 201601 (2012)

J J Saborido Silva,34N Sagidova,27P Sail,48B Saitta,15,jC Salzmann,37M Sannino,19,fR Santacesaria,22

C Santamarina Rios,34R Santinelli,35E Santovetti,21,eM Sapunov,6A Sarti,18,mC Satriano,22,bA Satta,21

M Savrie,16,gD Savrina,28P Schaack,50M Schiller,39S Schleich,9M Schlupp,9M Schmelling,10B Schmidt,35

O Schneider,36A Schopper,35M.-H Schune,7R Schwemmer,35B Sciascia,18A Sciubba,18,mM Seco,34

A Semennikov,28K Senderowska,24I Sepp,50N Serra,37J Serrano,6P Seyfert,11M Shapkin,32I Shapoval,40,35

P Shatalov,28Y Shcheglov,27T Shears,49L Shekhtman,31O Shevchenko,40V Shevchenko,28A Shires,50

R Silva Coutinho,45T Skwarnicki,53N A Smith,49E Smith,52,46K Sobczak,5F J P Soler,48A Solomin,43

F Soomro,18,35B Souza De Paula,2B Spaan,9A Sparkes,47P Spradlin,48F Stagni,35S Stahl,11O Steinkamp,37

S Stoica,26S Stone,53,35B Storaci,38M Straticiuc,26U Straumann,37V K Subbiah,35S Swientek,9

M Szczekowski,25P Szczypka,36T Szumlak,24S T’Jampens,4E Teodorescu,26F Teubert,35C Thomas,52

E Thomas,35J van Tilburg,11V Tisserand,4M Tobin,37S Tolk,39S Topp-Joergensen,52N Torr,52

E Tournefier,4,50S Tourneur,36M T Tran,36A Tsaregorodtsev,6N Tuning,38M Ubeda Garcia,35A Ukleja,25

P Urquijo,53U Uwer,11V Vagnoni,14G Valenti,14R Vazquez Gomez,33P Vazquez Regueiro,34S Vecchi,16

J J Velthuis,43M Veltri,17,nB Viaud,7I Videau,7D Vieira,2X Vilasis-Cardona,33,aJ Visniakov,34A Vollhardt,37

D Volyanskyy,10D Voong,43A Vorobyev,27V Vorobyev,31H Voss,10R Waldi,56S Wandernoth,11J Wang,53

D R Ward,44N K Watson,42A D Webber,51D Websdale,50M Whitehead,45D Wiedner,11L Wiggers,38

G Wilkinson,52M P Williams,45,46M Williams,50F F Wilson,46J Wishahi,9M Witek,23W Witzeling,35

S A Wotton,44K Wyllie,35Y Xie,47F Xing,52Z Xing,53Z Yang,3R Young,47O Yushchenko,32M Zangoli,14

M Zavertyaev,10,oF Zhang,3L 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

4LAPP, Universite´ de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France

5

Clermont 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

13Sezione INFN di Bari, Bari, Italy

14

Sezione 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

25Soltan Institute for Nuclear Studies, 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

29Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia

30

Institute 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

PRL 108, 201601 (2012)

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

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

38Nikhef 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

44

Cavendish 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, United States, USA

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

associated to Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

55CC-IN2P3, CNRS/IN2P3, Lyon-Villeurbanne, France associated to CPPM, Aix-Marseille Universite´,

CNRS/IN2P3, Marseille, France

56Institut fu¨r Physik, Universita¨t Rostock, Rostock, Germany associated to Physikalisches Institut,

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

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

bUniversita` della Basilicata, Potenza, Italy

cUniversita` di Modena e Reggio Emilia, Modena, Italy

dUniversita` di Milano Bicocca, Milano, Italy

eUniversita` di Roma Tor Vergata, Roma, Italy

fUniversita` di Genova, Genova, Italy

g

Universita` di Ferrara, Ferrara, Italy

hUniversita` di Firenze, Firenze, Italy

iUniversita` di Bologna, Bologna, Italy

jUniversita` di Cagliari, Cagliari, Italy

kHanoi University of Science, Hanoi, Viet Nam

lUniversita` di Bari, Bari, Italy

mUniversita` di Roma La Sapienza, Roma, Italy

nUniversita` di Urbino, Urbino, Italy

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

PRL 108, 201601 (2012)