DSpace at VNU: Search for the X(4140) state in B +→J ψφK + decays

The forward-backward asymmetry of the muons, AFB, the fraction of longitudinal polarization, FL, and the partial branching fraction dB=dq2are determined as a function of the dimuon inva

Differential Branching Fraction and Angular Analysis of the Decay B0 ! K
0
þ


R Aaij et al.*

(LHCb Collaboration)

(Received 15 December 2011; published 3 May 2012) The angular distributions and the partial branching fraction of the decay B0! K
0
þ
 are studied

by using an integrated luminosity of0:37 fb1of data collected with the LHCb detector The

forward-backward asymmetry of the muons, AFB, the fraction of longitudinal polarization, FL, and the partial

branching fraction dB=dq2are determined as a function of the dimuon invariant mass The measurements

are in good agreement with the standard model predictions and are the most precise to date In the dimuon

invariant mass squared range1:00–6:00 GeV2=c4, the results are AFB¼ 0:06þ0:13 0:04, FL¼ 0:55 

0:10  0:03, and dB=dq2¼ ð0:42  0:06  0:03Þ  107c4=GeV2 In each case, the first error is

statistical and the second systematic

DOI: 10.1103/PhysRevLett.108.181806 PACS numbers: 13.20.He

The process B0 ! K
0
þ
 is a flavor changing

neu-tral current decay In the standard model (SM) such decays

are suppressed, as they can proceed only via loop processes

involving electroweak penguin or box diagrams As-yet

undiscovered particles could give additional contributions

with comparable amplitudes, and the decay is therefore a

sensitive probe of new phenomena A number of angular

observables in B0 ! K
0
þ
 decays can be

theoreti-cally predicted with good control of the relevant form

factor uncertainties These include the forward-backward

asymmetry of the muons, AFB, and the fraction of

longitu-dinal polarization, FL, as functions of the dimuon invariant

mass squared, q2 [1] These observables have previously

been measured by the BABAR, Belle, and CDF

experi-ments [2] A more precise determination of AFB is of

particular interest as, in the 1:00 < q2< 6:00 GeV2=c4

region, previous measurements favor an asymmetry with

the opposite sign to that expected in the SM If confirmed,

this would be an unequivocal sign of phenomena not

described by the SM This Letter presents the most precise

measurements of AFB, FL, and the partial branching

frac-tion dB=dq2to date The data used for this analysis were

taken with the LHCb detector at CERN during 2011 and

correspond to an integrated luminosity of 0:37 fb1 The

K
0is reconstructed through its decay into the Kþfinal

state

The LHCb detector [3] is a single-arm spectrometer

designed to study b-hadron decays A silicon strip vertex

detector positioned around the interaction region is used to

measure the trajectory of charged particles and allows the

reconstruction of the primary proton-proton interactions

and the displaced secondary vertices characteristic of B-meson decays A dipole magnetic field and further charged particle tracking stations allow momenta in the range5 < p < 100 GeV=c to be determined with a preci-sion of p=p ¼ 0:4%–0:6% The experiment has an ac-ceptance for charged particles with pseudorapidity between 2 and 5 Two ring imaging Cherenkov detectors allow kaons to be separated from pions or muons over a momentum range2 < p < 100 GeV=c Muons are identi-fied on the basis of the number of hits in detectors inter-leaved with an iron muon filter

The B0 ! K
0
þ
 angular distribution is governed

by six q2-dependent transversity amplitudes The decay can be described by q2 and the three angles l, K, and  For the B0(
B0), lis the angle between the
þ(
) and the opposite of the B0 (
B0) direction in the dimuon rest frame, K the angle between the kaon and the direction opposite to the B meson in the K
0 rest frame, and  the angle between the
þ
and Kþdecay planes in the B rest frame The inclusion of charge conjugate modes is implied throughout this Letter At a given q2, neglecting the muon mass, the normalized partial differential width integrated over Kand  is

1



d2

d cosldq2 ¼3

4FLð1  cos2lÞ

þ3

8ð1  FLÞð1 þ cos2lÞ þ AFBcosl;

(1) and integrated over land  it is

1



d2

d cosKdq2¼3

2FLcos2Kþ3

4ð1  FLÞð1  cos2KÞ:

(2) These expressions do not include any broad S-wave contribution to the B0 ! Kþ
þ
 decay and any

*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 108, 181806 (2012)

contribution from low mass tails of higher K
0resonances.

These contributions are assumed to be small and are

ne-glected in the rest of the analysis

Signal candidates are isolated from the background by

using a set of selection criteria which are detailed below

An event-by-event weight is then used to correct for the

bias induced by the reconstruction, trigger, and selection

criteria In order to extract AFB and FL, simultaneous fits

are made to the Kþ
þ
 invariant mass distribution

and the angular distributions The partial branching

fraction is measured by comparing the efficiency corrected

yield of B0 ! K
0
þ
 decays to the yield of

B0 ! J=cK
0, where J=c !
þ


Candidate B0 ! K
0
þ
 events are first required to

pass a hardware trigger which selects muons with a

trans-verse momentum pT> 1:48 GeV=c In the subsequent

software trigger, at least one of the final state particles is

required to have both pT> 0:8 GeV=c and impact

pa-rameter >100
m with respect to all of the primary

proton-proton interaction vertices in the event [4]

Finally, the tracks of two or more of the final state particles

are required to form a vertex which is significantly

dis-placed from the primary vertices in the event [5]

In the final event selection, candidates with

Kþ
þ
 invariant mass in the range 5100 <

mKþ
þ
< 5600 MeV=c2 and Kþ invariant mass

in the range 792 < mKþ < 992 MeV=c2 are accepted

Two types of backgrounds are then considered:

combina-torial backgrounds, where the particles selected do not

come from a single b-hadron decay, and peaking

back-grounds, where a single decay is selected but with some of

the particle types misidentified In addition, the decays

B0 ! J=cK
0 and B0 !cð2SÞK
0, where J=c,

cð2SÞ !
þ
, are removed by rejecting events

with dimuon invariant mass m
þ
 in the range

2946 < m
þ
< 3176 MeV=c2 or 3586 < m
þ
<

3776 MeV=c2.

The combinatorial background, which is smoothly

dis-tributed in the reconstructed Kþ
þ
invariant mass,

is reduced by using a boosted decision tree (BDT) The

BDT uses information about the event kinematics, vertex

and track quality, impact parameter, and particle

identifi-cation information from the ring imaging Cherenkov and

muon detectors The variables that are used in the BDT are

chosen so as to induce the minimum possible distortion in

the angular and q2 distributions For example, no

addi-tional requirement is made on the pTof both of the muons,

as, at low q2, this would remove a large proportion of

events with j coslj  1 The BDT is trained entirely on

data, using samples that are independent of that which is

used to make the measurements: Triggered and fully

re-constructed B0! J=cK
0 events are used as a proxy for

the signal decay, and events from the upper

B0 ! K
0
þ
 mass sideband (5350 < mKþ
þ
<

5600 MeV=c2) are used as a background sample The

lower mass sideband is not used, as it contains background events formed from partially reconstructed B decays These events make a negligible contribution in the signal region and have properties different from the combinatorial background which is the dominant background in this region

A cut is made on the BDT output in order to optimize the sensitivity to AFBaveraged over all q2 The selected sample has a signal-to-background ratio of three to one

Peaking backgrounds from B0s! 
þ
 (where

 ! KþK), B0 ! J=cK
0, and B0 !cð2SÞK
0 are considered and reduced with a set of vetoes In each case, for the decay to be a potential signal candidate, at least one particle needs to be misidentified For example,

B0! J=cK
0events where a kaon or pion is swapped for one of the muons peak around the nominal B0 mass and evade the J=c veto described above Vetoes for each of these backgrounds are formed by changing the relevant particle mass hypotheses and recomputing the invariant masses and by making use of the particle identification information In order to avoid having a strongly peaking contribution to thecosKangular distribution in the upper mass sideband, Bþ! Kþ
þ
 candidates are removed Events with Kþ
þ
 invariant mass within60 MeV=c2

of the nominal Bþmass are rejected The vetoes for all of these peaking backgrounds remove a negligible amount of signal

After the application of the BDT cut and the above vetoes, a fit is made to the Kþ
þ
 invariant mass distribution in the entire accepted mass range (see Fig.1)

A double-Gaussian distribution is used for the signal mass shape and an exponential function for the background The signal shape is fixed from data using a fit to the

B0! J=cK
0 mass peak In the full q2 range, in a signal mass window of50 MeV=c2 ( 2:5) around the mea-sured B0mass, the fit gives an estimate of337  21 signal events with a background of97  6 events

The residual peaking background is estimated by using simulated events As detailed below, the accuracy of the

]

2

c

[MeV/

-µ + µ -π +

K

m

5100 5200 5300 5400 5500 5600

0 50

100

LHCb

FIG 1 (color online) Kþ
þ
 invariant mass distribu-tion after the applicadistribu-tion of the full selecdistribu-tion as data points with the fit overlaid The signal component is the green (light) line, the background the red (dashed) line, and the full distribution the blue (dark) line

simulation is verified by comparing the particle

(mis)iden-tification probabilities with those derived from control

channels selected from the data The residual peaking

backgrounds are reduced to a level of 6.1 events, i.e.,

1.8% of the 337 observed signal events The backgrounds

from B0s! 
þ
 and B0 ! J=cK
0 decays do not

give rise to any forward-backward asymmetry and are

ignored However, in addition to the above backgrounds,

B0 ! K
0
þ
decays with the kaon and pion swapped

give rise to a 0.7% contribution The change in the sign of

the particle which is taken to be the kaon results in a B0

(
B0) being reconstructed as a
B0 (B0), therefore changing

the sign of AFB for the candidate This misidentification is

accounted for in the fit for the angular observables

The selected B0! K
0
þ
 candidates are weighted

in order to correct for the effects of the reconstruction,

trigger, and selection The weights are derived from

simu-lated B0 ! K
0
þ
events and are normalized such that

the average weight is 1 In order to be independent of the

physics model used in the simulation, the weights are

computed based oncosK,cosl, and q2 on an

event-by-event basis The variation of detector efficiency with the 

angle is small, and ignoring this variation does not bias

the measurements Only events with 0:10 < q2<

19:00 GeV2=c4 are analyzed

Owing to the relatively unbiased selection, 89% of

events have weights between 0.7 and 1.3, and only 3% of

events have a weight above 2 The distortions in the

dis-tributions ofcosK,cosl, and q2that are induced originate

from two main sources First, in order to pass through the

iron muon filter and give hits in the muon stations, tracks

must have at least 3 GeV=c momentum At low q2 this

removes events with j coslj  1 This effect stems from

the geometry of the LHCb detector and is therefore

rela-tively easy to model Second, events withcosK 1, and

hence a slow pion, are removed both by the pion

recon-struction and by the impact parameter requirements used in

the trigger and BDT selection

A number of control samples are used to verify the

simulation quality and to correct for differences with

re-spect to the data The reproduction of the B0 momentum

and pseudorapidity distributions is verified by using

B0 ! J=cK
0decays These decays are also used to check

that the simulation reproduces the measured properties of

selected events The hadron and muon (mis)identification

probabilities are adjusted by using decays where the tested

particle type can be determined without the use of the

particle identification algorithms A tag and probe

approach with J=c !
þ
 decays is used to isolate

a clean sample of genuine muons The decay

D
þ! D0þ, where D0 ! Kþ, is used to give an

unambiguous source of kaons and pions The statistical

precision with which it is possible to make the

data-simulation comparison gives rise to a systematic

uncer-tainty in the weights which is evaluated below

The observables AFBand FLare extracted in bins of q2

In each bin, a simultaneous fit to the Kþ
þ
 invari-ant mass distribution and thecosKandcosldistributions

is performed The angular distributions are fitted both in the signal mass window and in the upper mass sideband which determines the background parameters The angular distributions for the signal are given by Eqs (1) and (2), and a second-order polynomial in cosK and in cosl is used for the background

In order to obtain a positive probability density function over the entire angular range, Eqs (1) and (2) imply that the conditionsjAFBj 3

4ð1  FLÞ and 0 < FL< 1 must be satisfied To account for this, the maximum likelihood values for AFB and FL are extracted by performing a profile-likelihood scan over the allowed range The uncer-tainty on the central value of AFBand FLis calculated by integrating the probability density extracted from the like-lihood, assuming a flat prior in AFB and FL, inside the allowed range This gives an (asymmetric) 68% confidence interval

The partial branching fraction is measured in each of the

q2bins from a fit to the efficiency corrected Kþ
þ
 mass spectrum The efficiencies are determined relative to the B0 ! J=cK
0decay which is used as a normalization mode

The event weighting and fitting procedure is validated

by fitting the angular distribution of B0 ! J=cK
0events, where the physics parameters are known from previous measurements [6] The product of the B0 ! J=cK
0and J=c !
þ
 branching fractions is 75 times larger than the branching fraction of B0 ! K
0
þ
, allowing

a precise test of the procedure to be made Fitting the

B0! J=cK
0 angular distribution, weighted according

to the event-by-event procedure described above, yields values for FLand AFBin good agreement with those found previously

For B0! K
0
þ
, the fit results for AFB, FL, and dB=dq2are shown in Fig.2and are tabulated together with the signal and background yields in Table I The fit pro-jections are available online [7] Signal candidates are observed in each q2 bin with more than 5 significance The compatibility of the fits and the data are assessed by using a binned 2test, and all fits are found to be of good quality The measurements in all three quantities are more precise than those of previous experiments and are in good agreement with the SM predictions The predictions are taken from Ref [8] In the low q2 region, they rely on the factorization approach [9], which loses accuracy when approaching the J=c resonance; in the high q2 region, an operator product expansion in the inverse b-quark mass, 1=mb, and in1=pffiffiffiffiffiq2

is used [10], which is valid only above the open charm threshold In both regions the form factor calculations are taken from Ref [11], and a dimensional estimate is made on the uncertainty from expansion corrections [12]

PRL 108, 181806 (2012)

In the 1:00 < q2< 6:00 GeV2=c4 region, the fit gives

AFB¼ 0:06þ0:13

0:14 0:04, FL¼ 0:55  0:10  0:03,

and dB=dq2 ¼ ð0:42  0:06  0:03Þ  107 c4=GeV2,

where the first error is statistical and the second systematic

The theoretical predictions in the same q2 range

are AFB ¼ 0:04  0:03, FL¼ 0:74þ0:06

0:07, and dB=dq2 ¼ ð0:50þ0:11

0:10Þ  107 c4=GeV2 The LHCb AFB measurement is a factor of 1.5–2.0 more precise than

previous measurements from the Belle, CDF, and BABAR Collaborations [2] which are, respectively, AFB¼ 0:26þ0:27

0:30 0:07, AFB¼ 0:29þ0:20

0:23 0:07, and, for

q2< 6:25 GeV2=c4, AFB ¼ 0:24þ0:18

0:23 0:05 The positive value of AFB preferred in the1:00 < q2< 6:00 GeV2=c4 range in these previous measurements is not favored by the LHCb data The previous measurements of FLin the same

q2 regions are FL¼ 0:67  0:23  0:05 (Belle), FL¼ 0:69þ0:19

0:21 0:08 (CDF), and FL¼ 0:35  0:16  0:04 (BABAR) These are in good agreement with the LHCb result

For the determination of AFB and FL, the dominant systematic uncertainties arise from the event-by-event weights which are extracted from simulated events and from the model used to describe the angular distribution

of the background The uncertainty on the event-by-event weights is evaluated by fluctuating these weights within their statistical uncertainties and repeating the fitting pro-cedure The uncertainty from the background model which

is used is estimated by changing this model to one which uses binned templates from the upper mass sideband rather than a polynomial parameterization

The dominant systematic errors for the determination of dB=dq2 arise from the uncertainties on the particle iden-tification and track reconstruction efficiencies These effi-ciencies are extracted from control channels and are limited by the relevant sample sizes The systematic un-certainty is estimated by fluctuating the efficiencies within the relevant uncertainties and repeating the fitting proce-dure An additional systematic uncertainty of 4% arises from the uncertainty in the B0! J=cK
0 and J=c !
þ
 branching fractions [13]

The total systematic error on each of AFB and FL (dB=dq2) is typically30% (50%) of the statistical error and, hence, adds4% ( 11%) to the total uncertainty

In summary, by using0:37 fb1 of data taken with the LHCb detector during 2011, AFB, FL, and dB=dq2 have been determined for the decay B0 ! K
0
þ
 These are the most precise measurements of these quantities to date

TABLE I Central values with statistical and systematic uncertainties for AFB, FL, and dB=dq2 as a function of q2 The

B0! K
0
þ
signal and background yields in the50 MeV=c2signal mass window with their statistical uncertainties are also

indicated, together with the statistical significance of the signal peak that is observed The significance is computed from the change in the likelihood, fitting with and without the signal component to the mass shape In the case with the signal component, the signal shape

is fixed from data using a fit to the B0! J=c K
0mass peak.

q2

dB=dq2 ( 107c4=GeV2) Signal yield Background yield

Significance () 0:10 < q2< 2:00 0:15  0:20  0:06 0:00þ0:13 0:02 0:61  0:12  0:06 48:6  8:1 16:2  2:3 8.6 2:00 < q2< 4:30 0:05þ0:16 0:04 0:77  0:15  0:03 0:34  0:09  0:02 26:5  6:5 15:7  2:2 5.4 4:30 < q2< 8:68 0:27þ0:06 0:02 0:60þ0:06 0:01 0:69  0:08  0:05 104:7  11:9 31:7  3:3 12.4 10:09 < q2< 12:86 0:27þ0:11 0:02 0:41  0:11  0:03 0:55  0:09  0:07 62:2  9:2 20:4  2:6 9.6 14:18 < q2< 16:00 0:47þ0:06 0:03 0:37  0:09  0:05 0:63  0:11  0:05 44:2  7:0 4:2  1:3 10.2 16:00 < q2< 19:00 0:16þ0:11 0:06 0:26þ0:10 0:03 0:50  0:08  0:05 53:4  8:1 7:0  1:7 9.8 1:00 < q2< 6:00 0:06þ0:13 0:04 0:55  0:10  0:03 0:42  0:06  0:03 76:5  10:6 33:1  3:2 9.9

] 4

c

/ 2 [GeV 2

q

0

0.5

1

1.5

(c)

0

0.5

-0.5

0

LHCb

FIG 2 (color online) AFB (a), FL (b), and dB=dq2 (c) as a

function of q2 The SM prediction is given by the cyan (light)

band, and this prediction rate-averaged across the q2 bins is

indicated by the purple (dark) regions No SM prediction is

shown for the region between the two regimes in which the

theoretical calculations are made (see the text)

All three observables show good agreement with the SM

predictions

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

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S Benson,46J Benton,42R Bernet,39M.-O Bettler,17M van Beuzekom,23A Bien,11S Bifani,12T Bird,50

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P Hopchev,4W Hulsbergen,23P Hunt,51T Huse,48R S Huston,12D Hutchcroft,48D Hynds,47V Iakovenko,41

P Ilten,12J Imong,42R Jacobsson,37A Jaeger,11M Jahjah Hussein,5E Jans,23F Jansen,23P Jaton,38

B Jean-Marie,7F Jing,3M John,51D Johnson,51C R Jones,43B Jost,37M Kaballo,9S Kandybei,40

M Karacson,37T M Karbach,9J Keaveney,12I R Kenyon,55U Kerzel,37T Ketel,24A Keune,38B Khanji,6

Y M Kim,46M Knecht,38P Koppenburg,23A Kozlinskiy,23L Kravchuk,32K Kreplin,11M Kreps,44

G Krocker,11P Krokovny,11F Kruse,9K Kruzelecki,37M Kucharczyk,20,25,37,jT Kvaratskheliya,30,37

V N La Thi,38D Lacarrere,37G Lafferty,50A Lai,15D Lambert,46R W Lambert,24E Lanciotti,37

G Lanfranchi,18C Langenbruch,11T Latham,44C Lazzeroni,55R Le Gac,6J van Leerdam,23J.-P Lees,4

R Lefe`vre,5A Leflat,31,37J Lefranc¸ois,7O Leroy,6T Lesiak,25L Li,3L Li Gioi,5M Lieng,9M Liles,48

R Lindner,37C Linn,11B Liu,3G Liu,37J von Loeben,20J H Lopes,2E Lopez Asamar,35N Lopez-March,38

H Lu,38,3J Luisier,38A Mac Raighne,47F Machefert,7I V Machikhiliyan,4,30F Maciuc,10O Maev,29,37

J Magnin,1S Malde,51R M D Mamunur,37G Manca,15,dG Mancinelli,6N Mangiafave,43U Marconi,14

R Ma¨rki,38J Marks,11G Martellotti,22A Martens,8L Martin,51A Martı´n Sa´nchez,7D Martinez Santos,37

A Massafferri,1Z Mathe,12C Matteuzzi,20M Matveev,29E Maurice,6B Maynard,52A Mazurov,16,32,37

G McGregor,50R McNulty,12M Meissner,11M Merk,23J Merkel,9R Messi,21,kS Miglioranzi,37

D A Milanes,13,37M.-N Minard,4J Molina Rodriguez,54S Monteil,5D Moran,12P Morawski,25R Mountain,52

I Mous,23F Muheim,46K Mu¨ller,39R Muresan,28,38B Muryn,26B Muster,38M Musy,35J Mylroie-Smith,48

P Naik,42T Nakada,38R Nandakumar,45I Nasteva,1M Nedos,9M Needham,46N Neufeld,37C Nguyen-Mau,38,o

M Nicol,7V Niess,5N Nikitin,31A Nomerotski,51A Novoselov,34A Oblakowska-Mucha,26V Obraztsov,34

S Oggero,23S Ogilvy,47O Okhrimenko,41R Oldeman,15,dM Orlandea,28J M Otalora Goicochea,2P Owen,49

K Pal,52J Palacios,39A Palano,13,bM Palutan,18J Panman,37A Papanestis,45M Pappagallo,47C Parkes,50,37

C J Parkinson,49G Passaleva,17G D Patel,48M Patel,49S K Paterson,49G N Patrick,45C Patrignani,19,i

C Pavel-Nicorescu,28A Pazos Alvarez,36A Pellegrino,23G Penso,22,lM Pepe Altarelli,37S Perazzini,14,c

D L Perego,20,jE Perez Trigo,36A Pe´rez-Calero Yzquierdo,35P Perret,5M Perrin-Terrin,6G Pessina,20

A Petrella,16,37A Petrolini,19,iA Phan,52E Picatoste Olloqui,35B Pie Valls,35B Pietrzyk,4T Pilarˇ,44D Pinci,22

R Plackett,47S Playfer,46M Plo Casasus,36G Polok,25A Poluektov,44,33E Polycarpo,2D Popov,10B Popovici,28

C Potterat,35A Powell,51J Prisciandaro,38V Pugatch,41A Puig Navarro,35W Qian,52J H Rademacker,42

B Rakotomiaramanana,38M S Rangel,2I Raniuk,40G Raven,24S Redford,51M M Reid,44A C dos Reis,1

S Ricciardi,45K Rinnert,48D A Roa Romero,5P Robbe,7E Rodrigues,47,50F Rodrigues,2P Rodriguez Perez,36

G J Rogers,43S Roiser,37V Romanovsky,34M Rosello,35,nJ Rouvinet,38T Ruf,37H Ruiz,35G Sabatino,21,k

J J Saborido Silva,36N Sagidova,29P Sail,47B Saitta,15,dC Salzmann,39M Sannino,19,iR Santacesaria,22

C Santamarina Rios,36R Santinelli,37E Santovetti,21,kM Sapunov,6A Sarti,18,lC Satriano,22,mA Satta,21

M Savrie,16,eD Savrina,30P Schaack,49M Schiller,24S Schleich,9M Schlupp,9M Schmelling,10B Schmidt,37

O Schneider,38A Schopper,37M.-H Schune,7R Schwemmer,37B Sciascia,18A Sciubba,18,lM Seco,36

A Semennikov,30K Senderowska,26I Sepp,49N Serra,39J Serrano,6P Seyfert,11M Shapkin,34I Shapoval,40,37

P Shatalov,30Y Shcheglov,29T Shears,48L Shekhtman,33O Shevchenko,40V Shevchenko,30R Silva Coutinho,44

A Shires,49T Skwarnicki,52A C Smith,37N A Smith,48E Smith,51,45K Sobczak,5F J P Soler,47A Solomin,42

F Soomro,18B Souza De Paula,2B Spaan,9A Sparkes,46P Spradlin,47F Stagni,37S Stahl,11O Steinkamp,39

S Stoica,28S Stone,52,37B Storaci,23M Straticiuc,28U Straumann,39V K Subbiah,37S Swientek,9

M Szczekowski,27P Szczypka,38T Szumlak,26S T’Jampens,4E Teodorescu,28F Teubert,37C Thomas,51

E Thomas,37J van Tilburg,11V Tisserand,4M Tobin,39S Topp-Joergensen,51N Torr,51E Tournefier,4,49

M T Tran,38A Tsaregorodtsev,6N Tuning,23M Ubeda Garcia,37A Ukleja,27P Urquijo,52U Uwer,11

V Vagnoni,14G Valenti,14R Vazquez Gomez,35P Vazquez Regueiro,36S Vecchi,16J J Velthuis,42M Veltri,17,g

B Viaud,7I Videau,7X Vilasis-Cardona,35,nJ Visniakov,36A Vollhardt,39D Volyanskyy,10D Voong,42

A Vorobyev,29H Voss,10S Wandernoth,11J Wang,52D R Ward,43N K Watson,55A D Webber,50

D Websdale,49M Whitehead,44D Wiedner,11L Wiggers,23G Wilkinson,51M P Williams,44,45M Williams,49

F F Wilson,45J Wishahi,9M Witek,25W Witzeling,37S A Wotton,43K Wyllie,37Y Xie,46F Xing,51Z Xing,52

Z Yang,3R Young,46O Yushchenko,34M Zavertyaev,10,aF Zhang,3L Zhang,52W C Zhang,12Y Zhang,3

A Zhelezov,11L Zhong,3E Zverev,31and A Zvyagin37

(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

23Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands

24Nikhef National Institute for Subatomic Physics and Vrije Universiteit, Amsterdam, The Netherlands

25Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Kraco´w, Poland

26AGH University of Science and Technology, Kraco´w, Poland

27Soltan Institute for Nuclear Studies, Warsaw, Poland

28Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania

29

Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia

30Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia

31Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow, Russia

32Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN), Moscow, Russia

33Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State University, Novosibirsk, Russia

34Institute for High Energy Physics (IHEP), Protvino, Russia

35Universitat de Barcelona, Barcelona, Spain

36Universidad de Santiago de Compostela, Santiago de Compostela, Spain

37European Organization for Nuclear Research (CERN), Geneva, Switzerland

38

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

39Physik-Institut, Universita¨t Zu¨rich, Zu¨rich, Switzerland

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

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

42H H Wills Physics Laboratory, University of Bristol, Bristol, United Kingdom

43Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom

44Department of Physics, University of Warwick, Coventry, United Kingdom

45STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

46School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom

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

48Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom

49Imperial College London, London, United Kingdom

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

51Department of Physics, University of Oxford, Oxford, United Kingdom

52Syracuse University, Syracuse, New York, USA

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

54

Pontifı´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

55University of Birmingham, Birmingham, United Kingdom

PRL 108, 181806 (2012)

56Physikalisches Institut, Universita¨t Rostock, Rostock, Germany, associated to Physikalisches Institut,

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

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

bAlso at Universita` di Bari, Bari, Italy

cAlso at Universita` di Bologna, Bologna, Italy

dAlso at Universita` di Cagliari, Cagliari, Italy

eAlso at Universita` di Ferrara, Ferrara, Italy

fAlso at Universita` di Firenze, Firenze, Italy

gAlso at Universita` di Urbino, Urbino, Italy

hAlso at Universita` di Modena e Reggio Emilia, Modena, Italy

iAlso at Universita` di Genova, Genova, Italy

jAlso at Universita` di Milano Bicocca, Milano, Italy

kAlso at Universita` di Roma Tor Vergata, Roma, Italy

l

Also at Universita` di Roma La Sapienza, Roma, Italy

mAlso at Universita` della Basilicata, Potenza, Italy

nAlso at LIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

oAlso at Hanoi University of Science, Hanoi, Vietnam