DSpace at VNU: Determination of fs fd for 7 TeV pp collisions and measurement of the B0→D-K+ branching fraction

Both ratios are exploited here to measure fs=fd according to the equations [2,3] fs fd ¼ 0:971 VVus ud 2 fK f 2 Bd Bs 1 NaNF DKþ D s þ NDsþ ND Kþ 2 and fs fd ¼ 0:982Bd Bs 1 NaNFNE Dþ

Determination of fs=fdfor 7 TeV pp Collisions and Measurement

of the B0! D
KþBranching Fraction

R Aaij et al.*

(LHCb Collaboration) (Received 28 June 2011; published 14 November 2011) The relative abundance of the three decay modes B0! D
Kþ, B0! D

þ, and B0s ! D

s
þ produced in 7 TeV pp collisions at the LHC is determined from data corresponding to an integrated

luminosity of35 pb
1 The branching fraction of B0! D
Kþis found to beBðB0! D
KþÞ ¼ ð2:01 

0:18stat 0:14systÞ  10
4 The ratio of fragmentation fractions fs=fd is determined through the relative

abundance of B0s ! D

s
þ to B0! D
Kþ and B0! D

þ, leading to fs=fd ¼ 0:253  0:017  0:017  0:020, where the uncertainties are statistical, systematic, and theoretical, respectively

Knowledge of the production rate of B0s mesons is

required to determine any B0s branching fraction This

rate is determined by the b
b production cross section and

the fragmentation probability fs, which is the fraction of

B0s mesons among all weakly decaying bottom hadrons

Similarly, the production rate of B0mesons is driven by the

fragmentation probability fd The measurement of the

branching fraction of the rare decay B0s ! þ
is a

prime example where improved knowledge of fs=fd is

needed to reach the highest sensitivity in the search for

physics beyond the standard model [1] The ratio fs=fdis,

in principle, dependent on collision energy and type as well

as the acceptance region of the detector This is the first

measurement of this quantity at the LHC

The ratio fs=fdcan be extracted if the ratio of branching

fractions of B0 and B0s mesons decaying to particular final

states X1 and X2, respectively, is known:

fs

fd

¼NX 2

NX1

BðB0 ! X1Þ BðB0

s ! X2Þ

ðB0! X1Þ

ðB0s! X2Þ: (1) The ratio of the branching fraction of the B0s ! D

s
þand

B0 ! D
Kþ decays is dominated by contributions from

color-allowed tree-diagram amplitudes and is therefore

theoretically well understood In contrast, the ratio of the

branching ratios of the two decays B0s! D

s
þand B0 !

D

þ can be measured with a smaller statistical

uncer-tainty due to the greater yield of the B0 mode but suffers

from an additional theoretical uncertainty due to the

con-tribution from a W-exchange diagram Both ratios

are exploited here to measure fs=fd according to the

equations [2,3]

fs

fd

¼ 0:971

VVus

ud

2



fK

f

2

Bd

Bs

1

NaNF

D
Kþ

D

s
þ

ND
s
þ

ND
Kþ

(2) and

fs

fd

¼ 0:982Bd

Bs

1

NaNFNE

D

þ

D

s
þ

ND
s
þ

ND

þ

: (3)

Here X is the selection efficiency of decay X (including the branching fraction of the D decay mode used to re-construct it), NX is the observed number of decays of this type, the Vij are elements of the Cabibbo-Kobayashi-Maskawa matrix, fi are the meson decay constants, and the numerical factors take into account the phase space difference for the ratio of the two decay modes Inclusion

of charge conjugate modes is implied throughout The term

Naparametrizes nonfactorizable SUð3Þ-breaking effects;

NF is the ratio of the form factors;NE is an additional correction term to account for the W-exchange diagram in the B0 ! D

þ decay Their values [2,3] are Na¼ 1:00  0:02, NF ¼ 1:24  0:08, and NE¼ 0:966  0:075 The latest world average [4] is used for the B meson lifetime ratio Bs=Bd ¼ 0:973  0:015 The numerical values used for the other factors are jVusj ¼ 0:2252,

jVudj ¼ 0:974 25, f
¼ 130:41, and fK¼ 156:1, with negligible associated uncertainties [5]

The observed yields of these three decay modes in

35 pb
1 of data collected with the LHCb detector in the

2010 running period are used to measure fs=fd averaged over the LHCb acceptance and to improve the current measurement of the branching fraction of the B0!

D
Kþ decay mode [6]

The LHCb experiment [7] is a single-arm spectrometer, designed to study B decays at the LHC, with a pseudor-apidity acceptance of 2 <  < 5 for charged tracks The first trigger level allows the selection of events with B hadronic decays using the transverse energy of hadrons measured in the calorimeter system The event information

*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

is subsequently sent to a software trigger, implemented in a

dedicated processor farm, which performs a final online

selection of events for later offline analysis The tracking

system determines the momenta of B decay products with a

precision of p=p ¼ 0:35%–0:5% Two ring imaging

Cherenkov detectors allow charged kaons and pions to be

distinguished in the momentum range2–100 GeV=c [8]

The three decay modes B0 ! D
ðKþ



Þ
þ, B0 !

D
ðKþ



ÞKþ, and B0s ! D

sðKþK


Þ
þare

topo-logically identical and can therefore be selected by using

identical geometric and kinematic criteria, thus

minimiz-ing efficiency differences between them Events are

se-lected at the first trigger stage by requiring a hadron with

transverse energy greater than 3.6 GeV in the calorimeter

The second, software, stage [9,10] requires a two-, three-,

or four-track secondary vertex with a high sum pT of the

tracks, significant displacement from the primary

interac-tion, and at least one track with exceptionally high pT,

large displacement from the primary interaction, and small

fit 2

The decays of B mesons can be distinguished from the

background by using variables such as the pT and impact

parameter 2 of the B, D, and the final state particles with

respect to the primary interaction In addition, the vertex

quality of the B and D candidates, the B lifetime, and the

angle between the B momentum vector and the vector

joining the B production and decay vertices are used in

the selection The D lifetime and flight distance are not

used in the selection because the lifetimes of the D
s and

D
differ by about a factor of 2

The event sample is first selected by using the gradient

boosted decision tree technique [11], which combines the

geometrical and kinematic variables listed above The

selection is trained on a mixture of simulated B0 !

D

þ decays and combinatorial background selected

from the sidebands of the data mass distributions The

distributions of the input variables for data and simulated

signal events show excellent agreement, justifying the use

of simulated events in the training procedure

Subsequently, D
(D
s) candidates are identified by

requiring the invariant mass under the K

(KK
)

hy-pothesis to fall within the selection window 1870þ24

40

ð1969þ24

40Þ MeV=c2, where the mass resolution is

approxi-mately 10 MeV=c2 The final B0 ! D

þ and B0s !

D
s
þ subsamples consist of events that pass a particle

identification (PID) criterion on the bachelor particle,

based on the difference in log-likelihood between the

charged pion and kaon hypotheses (DLL) of DLLðK

Þ < 0, with an efficiency of 83.0% The B0 ! D
Kþ

subsample consists of events with DLLðK

Þ > 5,

with an efficiency of 70.2% Events not satisfying either

condition are not used

The relative efficiency of the selection procedure is

evaluated for all decay modes using simulated events,

where the appropriate resonances in the charm decays are

taken into account As the analysis is sensitive only to relative efficiencies, the impact of differences between the data and simulation is small The relative efficiencies are D

þ=D
Kþ¼ 1:221  0:021, D
Kþ=D

s
þ¼ 0:917  0:020, and D

þ=D
s
þ¼ 1:1200:025, where the errors are due to the limited size of the simulated event samples

The relative yields of the three decay modes are ex-tracted from unbinned extended maximum likelihood fits

to the mass distributions shown in Fig.2 The signal mass shape is described by an empirical model derived from simulated events The mass distribution in the simulation exhibits non-Gaussian tails on either side of the signal The tail on the right-hand side is due to non-Gaussian detector effects and modeled with a crystal ball function [12] A similar tail is present on the left-hand side of the peak In addition, the low mass tail contains a second contribution due to events where hadrons have radiated photons that are not reconstructed The sum of these contributions is mod-eled with a second crystal ball function The peak values of these two crystal ball functions are constrained to be identical

Various backgrounds have to be considered, in particu-lar, the cross feed between the D
and D
s channels, and the contamination in both samples from b! þ

c

decays, where þ

c ! pK

þ The D
s contamination in the D
data sample is reduced by loose PID requirements, DLLðK

Þ < 10 (with an efficiency of 98.6%) and DLLðK

Þ > 0 (with an efficiency of 95.6%), for the pions and kaons from D decays, respectively The resulting efficiency to reconstruct B0s ! D

s
þ as background is evaluated, by using simulated events, to be 30 times smaller than for B0 ! D

þ and 150 times smaller than for B0 ! D
Kþ within the B0 and D
signal mass win-dows By taking into account the lower production fraction

of B0s mesons, this background is negligible

The contamination from c decays is estimated in a similar way However, different approaches are used for the B0 and B0s decays A contamination of approximately 2% under the B0! D

þmass peak and below 1% under the B0 ! D
Kþ peak is found, and therefore no explicit DLLðp

Þ criterion is needed The cbackground in the

B0ssample is, on the other hand, large enough that it can be fitted for directly

A prominent peaking background to B0! D
Kþ is

B0! D

þ, with the pion misidentified as a kaon The small
! K misidentification rate (of about 4%) is com-pensated by the larger branching fraction, resulting in similar event yields This background is modeled by ob-taining a clean B0 ! D

þ sample from the data and reconstructing it under the B0 ! D
Kþmass hypothesis The resulting mass shape depends on the momentum dis-tribution of the bachelor particle The momentum distribu-tion after the DLLðK

Þ > 5 requirement can be found

by considering the PID performance as a function of PRL 107, 211801 (2011)

momentum This is obtained by using a sample of Dþ!

D0
þ decays and is illustrated in Fig.1 The mass

distri-bution is reweighted by using this momentum distridistri-bution

to reproduce the B0 ! D

þ mass shape following the

DLL cut

The combinatorial background consists of events with

random pions and kaons, forming a fake D
or D
s

candi-date, as well as real D
or D
s mesons that combine with a

random pion or kaon The combinatorial background is

modeled with an exponential shape

Other background components originate from partially

reconstructed B0 and B0s decays In B0! D

þ, these

originate from B0 ! D

þ and B0 ! D
þ decays,

which can also be backgrounds for B0 ! D
Kþ in the

case of a misidentified bachelor pion In B0 ! D
Kþ,

there is additionally background from B0 ! D
Kþ

de-cays The invariant mass distributions for the partially

reconstructed and misidentified backgrounds are taken

from large samples of simulated events, reweighted

ac-cording to the mass hypothesis of the signal being fitted

and the DLL cuts

For B0s! D

s
þ, the B0 ! D

þ background peaks

under the signal with a similar shape In order to suppress

this peaking background, PID requirements are placed on

both kaon tracks The kaon which has the same sign in the

B0s ! D

s
þ and B0 ! D

þ decays is required to

sat-isfy DLLðK

Þ > 0, while the other kaon in the Dþ

s

decay is required to satisfyDLLðK

Þ > 5 Because of

the similar shape, a Gaussian constraint is applied to the

yield of this background The central value of this

con-straint is computed from the
! K misidentification rate

The b! þ

c

background shape is obtained from

simulated events, reweighted according to the PID

effi-ciency, and the yield allowed to float in the fit Finally,

the relative size of the B0s ! D

sþ and B0s ! D

s
þ backgrounds is constrained to the ratio of the

B0! D
þ and B0 ! D

þbackgrounds in the B0!

D

þ fit, with an uncertainty of 20% to account for potential SUð3Þ symmetry breaking effects

The free parameters in the likelihood fits to the mass distributions are the event yields for the different event types, i.e., the combinatorial background, partially recon-structed background, misidentified contributions, and the signal, as well as the peak value of the signal shape In addition, the combinatoric background shape is left free in the B0 ! D

þ and B0s ! D

s
þ fits, and the signal width is left free in the B0! D

þ fit In the B0s!

D
s
þ and B0 ! D
Kþ fits, the signal width is fixed to the value from the B0 ! D

þ fit, corrected by the ratio

of the signal widths for these modes in simulated events

Track Momentum (GeV/c)

0

0.2

0.4

0.6

0.8

1

)>5

π

K,

DLL(K-→

K

)<0

π

,

DLL(K-π π

→π

)>5

π

K,

DLL(K-→

)<0

π

,

DLL(K-π

→

K

FIG 1 Probability, as a function of momentum, to correctly

identify (full symbols) a kaon or a pion when requiring

DLLðK

Þ > 5 or DLLðK

Þ < 0, respectively The

corre-spondent probability to wrongly identify (open symbols) a pion

as a kaon, or a kaon as a pion, is also shown The data are taken

from a calibration sample of D! DðK
Þ
decays; the

statis-tical uncertainties are too small to display

FIG 2 Mass distributions of the B0! D

þ, B0! D
Kþ, and B0s ! D

s
þ candidates (top to bottom) The indicated components are described in the text

The fits to the full B0 ! D

þ, B0 ! D
Kþ, and

B0s ! D

s
þdata samples are shown in Fig.2 The

result-ing B0! D

þ and B0 ! D
Kþ event yields are

4103  75 and 252  21, respectively The number of

misidentified B0 ! D

þ events under the B0 ! D
Kþ

signal as obtained from the fit is 131  19 This agrees

with the number expected from the total number of B0 !

D

þ events, corrected for the misidentification rate

de-termined from the PID calibration sample, of145  5 The

B0s ! D

s
þ event yield is670  34

The stability of the fit results has been investigated by

using different cut values for both the PID requirement on

the bachelor particle and for the multivariate selection

variable In all cases, variations are found to be small in

comparison to the statistical uncertainty

The relative branching fractions are obtained by

correct-ing the event yields by the correspondcorrect-ing efficiency factors;

the dominant correction comes from the PID efficiency The

dominant source of systematic uncertainty is the knowledge

of the B0 ! D

þ branching fraction (for the B0 !

D
Kþ branching fraction measurement) and the

knowl-edge of the D
and D
s branching fractions (for the fs=fd

measurement) An important source of systematic

uncer-tainty is the knowledge of the PID efficiency as a function of

momentum, which is needed to reweight the mass

distribu-tion of the B0 ! D

þ decay under the kaon hypothesis

for the bachelor track This enters in two ways: first as an

uncertainty on the correction factors and second as part of

the systematic uncertainty, since the shape for the

misiden-tified backgrounds relies on correct knowledge of the PID

efficiency as a function of momentum

The performance of the PID calibration is evaluated by

applying the same method from the data to simulated

events, and the maximum discrepancy found between the

calibration method and the true misidentification is

attrib-uted as a systematic uncertainty The fs=fd measurement

using B0! D
Kþ and B0s! D

s
þ is more robust against PID uncertainties, since the final states have the

same number of kaons and pions

Other systematic uncertainties are due to limited

simu-lated event samples (affecting the relative selection

effi-ciencies), neglecting the b! þ

c

and B0s! D

s
þ backgrounds in the B0 ! D

þ fits, and the limited

ac-curacy of the trigger simulation Even though the ratio of

efficiencies is statistically consistent with unity, the

maxi-mum deviation is conservatively assigned as a systematic

uncertainty The difference in interaction probability

be-tween kaons and pions is estimated by using Monte Carlo

simulation The systematic uncertainty due to possible

discrepancies between the data and simulation is expected

to be negligible, and it is not taken into account The

efficiency of the nonresonant Ds decays varies across the

Dalitz plane but has a negligible effect on the total B0s !

D
s
þ efficiency The sources of systematic uncertainty

are summarized in TableI

The efficiency corrected ratio of B0 ! D

þand B0!

D
Kþ yields is combined with the world average of the

B0! D

þ[5] branching ratio to give

B ðB0! D
KþÞ ¼ ð2:01  0:18  0:14Þ  10
4: (4) The first uncertainty is statistical and the second systematic

The theoretically cleaner measurement of fs=fd uses

B0! D
Kþ and B0s! D

s
þ and is made according to

Eq (2) By accounting for the exclusive D branching fractions BðDþ ! K

þ
þÞ ¼ ð9:14  0:20Þ% [13] and BðDþ

s ! K
Kþ
þÞ ¼ ð5:50  0:27Þ% [14], the value of fs=fd is found to be

fs=fd ¼ ð0:310  0:030stat 0:021systÞ 1

NaNF; (5) where the first uncertainty is statistical and the second is systematic The statistical uncertainty is dominated by the yield of the B0 ! D
Kþmode

The statistically more precise but theoretically less clean measurement of fs=fd uses B0 ! D

þ and B0s!

D
s
þand is, from Eq (3),

fs=fd ¼ ð0:307  0:017stat 0:023systÞ 1

NaNFNE:

(6) The two values for fs=fd can be combined into a single value, taking all correlated uncertainties into account and using the theoretical inputs accounting for the SUð3Þ breaking part of the form factor ratio, the nonfactorizable and W-exchange diagram:

fs=fd¼ 0:253  0:017stat 0:017syst 0:020theor: (7)

In summary, with35 pb
1of data collected by using the

LHCb detector during the 2010 LHC operation at a center-of-mass energy of 7 TeV, the branching fraction of the Cabibbo-suppressed B0 decay mode B0 ! D
Kþ has been measured with better precision than the current world average Additionally, two measurements of the fs=fd

production fraction are performed from the relative yields

of B0s ! D

s
þ with respect to B0! D
Kþ and B0!

D

þ These values of fs=fdare numerically close to the values determined at LEP and at the Tevatron [4]

TABLE I Experimental systematic uncertainties for the BðB0! D
KþÞ and the two fs=fd measurements

BðB0! D
KþÞ fs=fd

BðDþ

PRL 107, 211801 (2011)

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 Re´gion Auvergne

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R W Lambert,37E Lanciotti,37G Lanfranchi,18aC Langenbruch,11T Latham,44R Le Gac,6J van Leerdam,23 J.-P Lees,4R Lefe`vre,5A Leflat,31,37J Lefranc¸ois,7O Leroy,6T Lesiak,25L Li,3Y Y Li,43L Li Gioi,5

M Lieng,9R Lindner,37C Linn,11B Liu,3G Liu,37J H Lopes,2E Lopez Asamar,35aN Lopez-March,38a

J Luisier,38aF Machefert,7I V Machikhiliyan,4,30F Maciuc,10aO Maev,29,37J Magnin,1A Maier,37S Malde,51

R M D Mamunur,37G Manca,15a,15bG Mancinelli,6N Mangiafave,43U Marconi,14aR Ma¨rki,38aJ Marks,11

G Martellotti,22aA Martens,7L Martin,51A Martı´n Sa´nchez,7D Martinez Santos,37A Massafferri,1Z Mathe,12

C Matteuzzi,20aM Matveev,29E Maurice,6B Maynard,52A Mazurov,32,16a,37G McGregor,50R McNulty,12

C Mclean,14aM Meissner,11M Merk,23J Merkel,9R Messi,21a,21bS Miglioranzi,37D A Milanes,13a,37 M.-N Minard,4S Monteil,5D Moran,12P Morawski,25J V Morris,45R Mountain,52I Mous,23F Muheim,46

K Mu¨ller,39R Muresan,28,38aB Muryn,26M Musy,35aP Naik,42T Nakada,38aR Nandakumar,45J Nardulli,45

M Nedos,9M Needham,46N Neufeld,37C Nguyen-Mau,38a,38bM Nicol,7S Nies,9V Niess,5N Nikitin,31

A Oblakowska-Mucha,26V Obraztsov,34S Oggero,23S Ogilvy,47O Okhrimenko,41R Oldeman,15a,15b

M Orlandea,28J M Otalora Goicochea,2B Pal,52J Palacios,39M Palutan,18aJ Panman,37A Papanestis,45

M Pappagallo,13a,13bC Parkes,47,37C J Parkinson,49G Passaleva,17aG D Patel,48M Patel,49S K Paterson,49

G N Patrick,45C Patrignani,19a,19bC Pavel-Nicorescu,28A Pazos Alvarez,36A Pellegrino,23G Penso,22a,22b

M Pepe Altarelli,37S Perazzini,14a,14bD L Perego,20a,20bE Perez Trigo,36A Pe´rez-Calero Yzquierdo,35a

P Perret,5M Perrin-Terrin,6G Pessina,20aA Petrella,16a,37A Petrolini,19a,19bB Pie Valls,35aB Pietrzyk,4

T Pilar,44D Pinci,22aR Plackett,47S Playfer,46M Plo Casasus,36G Polok,25A Poluektov,44,33E Polycarpo,2

D Popov,10aB Popovici,28C Potterat,35aA Powell,51T du Pree,23V Pugatch,41A Puig Navarro,35aW Qian,52

J H Rademacker,42B Rakotomiaramanana,38aI 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,47F Rodrigues,2C Rodriguez Cobo,36

P Rodriguez Perez,36G J Rogers,43V Romanovsky,34J Rouvinet,38aT Ruf,37H Ruiz,35aG Sabatino,21a,21b

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

R Santinelli,37E Santovetti,21a,21bM Sapunov,6A Sarti,18a,18bC Satriano,22a,22cA Satta,21aM Savrie,16a,16b

D Savrina,30P Schaack,49M Schiller,11S Schleich,9M Schmelling,10aB Schmidt,37O Schneider,38a

A Schopper,37M.-H Schune,7R Schwemmer,37A Sciubba,18a,18bM Seco,36A Semennikov,30K Senderowska,26

N Serra,39J Serrano,6P Seyfert,11B Shao,3M Shapkin,34I Shapoval,40,37P Shatalov,30Y Shcheglov,29

T Shears,48L Shekhtman,33O Shevchenko,40V Shevchenko,30A Shires,49R Silva Coutinho,54H P Skottowe,43

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

B Souza De Paula,2B Spaan,9A Sparkes,46P Spradlin,47F Stagni,37S Stahl,11O Steinkamp,39S Stoica,28

S Stone,52,37B Storaci,23U Straumann,39N Styles,46S Swientek,9M Szczekowski,27P Szczypka,38a

T Szumlak,26S T’Jampens,4E Teodorescu,28F Teubert,37C Thomas,51,45E Thomas,37J van Tilburg,11

V Tisserand,4M Tobin,39S Topp-Joergensen,51M T Tran,38aA Tsaregorodtsev,6N Tuning,23A Ukleja,27

P Urquijo,52U Uwer,11V Vagnoni,14aG Valenti,14aR Vazquez Gomez,35aP Vazquez Regueiro,36S Vecchi,16a

J J Velthuis,42M Veltri,17a,17cK Vervink,37B Viaud,7I Videau,7X Vilasis-Cardona,35a,35bJ Visniakov,36

A Vollhardt,39D Voong,42A Vorobyev,29H Voss,10aK Wacker,9S Wandernoth,11J Wang,52D R Ward,43

A D Webber,50D Websdale,49M Whitehead,44D Wiedner,11L Wiggers,23G Wilkinson,51M P Williams,44,45

M Williams,49F F Wilson,45J Wishahi,9M Witek,25W Witzeling,37S A Wotton,43K Wyllie,37Y Xie,46

F Xing,51Z Yang,3R Young,46O Yushchenko,34M Zavertyaev,10a,10bL 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

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

5Clermont Universite´, Universite´ Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France PRL 107, 211801 (2011)

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

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

10bP N Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia

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

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

13a

Sezione INFN di Bari, Bari, Italy

13bUniversita` di Bari, Bari, Italy

14aSezione INFN di Bologna, Bologna, Italy

14bUniversita` di Bologna, Bologna, Italy

15aSezione INFN di Cagliari, Cagliari, Italy

15bUniversita` di Cagliari, Cagliari, Italy

16aSezione INFN di Ferrara, Ferrara, Italy

16bUniversita` di Ferrara, Ferrara, Italy

17aSezione INFN di Firenze, Firenze, Italy

17bUniversita` di Firenze, Firenze, Italy

17cUniversita` di Urbino, Urbino, Italy

17dUniversita` di Modena e Reggio Emilia, Modena, Italy

18aLaboratori Nazionali dell’INFN di Frascati, Frascati, Italy

18bUniversita` di Roma La Sapienza, Roma, Italy

19aSezione INFN di Genova, Genova, Italy

19bUniversita` di Genova, Genova, Italy

20a

Sezione INFN di Milano Bicocca, Milano, Italy

20bUniversita` di Milano Bicocca, Milano, Italy

21aSezione INFN di Roma Tor Vergata, Roma, Italy

21bUniversita` di Roma Tor Vergata, Roma, Italy

22aSezione INFN di Roma La Sapienza, Roma, Italy

22bUniversita` di Roma La Sapienza, Roma, Italy

22cUniversita` della Basilicata, Potenza, 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, Cracow, Poland

26Faculty of Physics and Applied Computer Science, Cracow, Poland

27Soltan Institute for Nuclear Studies, Warsaw, Poland

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

29Petersburg 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

35aUniversitat de Barcelona, Barcelona, Spain

35bLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

35cInstitucio´ Catalana de Recerca i Estudis Avanc¸ats (ICREA), Barcelona, Spain

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

37

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

38aEcole Polytechnique Fe´de´rale de Lausanne (EPFL), Lausanne, Switzerland

38bHanoi University of Science, Hanoi, Vietnam

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

45

STFC 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*

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

*Associated member

†

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

PRL 107, 211801 (2011)

the LHC We thank the technical and administrative staff at

CERN and at the LHCb institutes and acknowledge

sup-port from the National...

from the sidebands of the data mass distributions The

distributions of the input variables for data and simulated

signal events show excellent agreement, justifying the use

of. ..

applying the same method from the data to simulated

events, and the maximum discrepancy found between the

calibration method and the true misidentification is

attrib-uted