Measurement of the Z+b-jet cross-section in pp collisions at [SQRT]s = 7 TeV in the forward region

Abstract

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image)

The associated production of a Z boson or an off-shell photon γ ^sup *^ with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of 7 TeV. The Z bosons are reconstructed in the Z/γ ^sup *^ [arrow right] [mu] ^sup +^ [mu] ^sup -^ final state from muons with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed in the pseudorapidity range 2.0 < [eta] < 4.5. The results are based on data corresponding to 1.0 fb^sup -1^ recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are ...... for p ^sub T^(jet) > 10 GeV, and ...... for p ^sub T^(jet) > 20 GeV. [Figure not available: see fulltext.]

Published for SISSA by Springer

Received: November 6, 2014 Accepted: December 17, 2014

Published: January 13, 2015

Measurement of the Z+b-jet cross-section in pp collisions at ps = 7 TeV in the forward region

JHEP01(2015)064

The LHCb collaboration

E-mail: mailto:[email protected]

Web End [email protected]

Abstract: The associated production of a Z boson or an o -shell photon with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of 7 TeV. The Z bosons are reconstructed in the Z/ ! + nal state from muons

with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed in the pseudorapidity range 2.0 < < 4.5. The results are based on data corresponding to 1.0 fb1 recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are

(Z/ (+) + b-jet) = 295 60 (stat) 51 (syst) 10 (lumi) fb (0.1) for pT(jet) > 10 GeV, and

(Z/ (+) + b-jet) = 128 36 (stat) 22 (syst) 5 (lumi) fb (0.2) for pT(jet) > 20 GeV.

Keywords: Hadron-Hadron Scattering

ArXiv ePrint: 1411.1264

Open Access, Copyright CERN,for the benet of the LHCb Collaboration. Article funded by SCOAP3.

doi:http://dx.doi.org/10.1007/JHEP01(2015)064

Web End =10.1007/JHEP01(2015)064

Contents

1 Introduction 1

2 Detector and samples 2

3 Measurement strategy and event selection 2

4 Systematic uncertainties 4

5 Results 5

6 Summary 7

The LHCb collaboration 10

1 Introduction

The cross-section for the forward production of a Z boson1 in association with a bottom quark (referred to as Z+b-jet) is sensitive to the parton distribution functions (PDF) in the proton in a phase-space region poorly constrained by existing measurements. It is a benchmark measurement for perturbative quantum chromodynamics phenomenology of heavy quarks and allows constraints to be placed on backgrounds in studies of the Standard Model (SM) Higgs boson and searches for non-SM physics.

The ATLAS and CMS collaborations reported measurements of Z+b-jet production with jet transverse momentum2 larger than 25 GeV and jet pseudorapidity | | < 2.1, where

they nd good agreement with next-to-leading order (NLO) predictions [1, 2]. Similar measurements were performed by the CDF [3] and D0 [4] collaborations at the Tevatron, where the dominant contribution comes from the quark-antiquark interaction. The forward acceptance of the LHCb experiment, with a pseudorapidity coverage in the range 2 < < 5, probes a kinematic region complementary to that probed by ATLAS and CMS. The LHCb measurements are sensitive to the parton distribution functions in the proton at low and high values of the Bjorken x variable, where the uncertainties are largest.

In this paper we describe the measurement of the production of Z+b-jet with Z/ !

+ in proton-proton collisions at ps = 7 TeV using the data collected by the LHCb experiment in 2011. The data set corresponds to an integrated luminosity of 1.0 fb1.

The presence of a bottom hadron candidate is used to tag the jet as originating from a bottom quark, following ref. [5]. The results are compared to NLO and leading-order (LO) calculations using massless and massive bottom quarks.

1Throughout this paper Z boson includes both the Z0 and the o -shell photon, , contributions.

2In this paper we use natural units (c = [planckover2pi1] = 1).

1

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2 Detector and samples

The LHCb detector [6] is a single-arm forward spectrometer covering the pseudorapidity range 2 < < 5, designed for the study of particles containing b or c quarks. The detector includes a high-precision tracking system consisting of a silicon-strip vertex detector surrounding the pp interaction region [7], a large-area silicon-strip detector located upstream of a dipole magnet with a bending power of about 4 Tm, and three stations of silicon-strip detectors and straw drift tubes [8] placed downstream of the magnet. The tracking system provides a measurement of momentum, p, with a relative uncertainty that varies from 0.4 % at low momentum to 0.6 % at 100 GeV. The minimum distance of a track to a primary vertex, the impact parameter, is measured with a resolution of (15+29/pT) m, where pT is the transverse momentum in GeV. Di erent types of charged hadrons are distinguished using information from two ring-imaging Cherenkov detectors [9]. Photon, electron and hadron candidates are identied by a calorimeter system consisting of scintillating-pad (SPD) and preshower detectors, an electromagnetic calorimeter and a hadronic calorimeter. The calorimeters have an energy resolution of (E)/E = 10%/pE 1% and (E)/E =

69%/pE 9% (with E in GeV), respectively. Muons are identied by a system com

posed of alternating layers of iron and multiwire proportional chambers [10]. The trigger consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies a full event reconstruction [11].

The events used in this analysis are selected by a trigger that requires the presence of at least one muon candidate with pT > 10 GeV. In addition, the hardware trigger requires a hit multiplicity in the SPD less than 600, in order to reject events whose processing in the software trigger would be too time consuming. This retains about 90 % of the events that contain a Z boson.

Simulated samples of pp collisions are generated with Pythia v6.4 [12] with a specic LHCb conguration [13] using the CTEQ6ll [14] parameterization of the PDFs. Decays of hadronic particles are described by EvtGen [15], while the interaction of the generated particles with the detector, and its response, are implemented using Geant4 [16] as described in ref. [17].

3 Measurement strategy and event selection

The Z! + selection follows that described in ref. [18]. Muon tracks in the ducial vol

ume (2.0 < () < 4.5) are required to have transverse momentum greater than 20 GeV. In order to have good quality muons, the relative uncertainty on the momentum of each muon is required to be less than 10 % and the ~2 probability for the associated track t larger than0.1 %. The dimuon candidate mass is required to be in the 60120 GeV range. The contri

bution from combinatorial background of (0.310.06) %, evaluated in ref. [18], is neglected.

Charged and neutral particles are clustered by the anti-kT algorithm [19] with distance parameter R = 0.5 as implemented in the FastJet software package [20]. As in ref. [18], the jet energy is corrected to the particle level excluding neutrinos and the same jet quality requirements are applied. The jets are required to be reconstructed within the pseudora-

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40

25

Events / (400 MeV)

Data Z+l-jet Z+c-jet Z+b-jet

LHCb

Events / (400 MeV)

35

30

20

Data Z+l-jet Z+c-jet Z+b-jet

LHCb

25

15

20

15

10

10

5

5

0

0

2000 4000 6000

2000 4000 6000

M

[MeV]

corr

M

[MeV]

corr

Figure 1. Mcorr distribution for (left) pT(jet) > 10 GeV and (right) pT(jet) > 20 GeV. Data (black points) are compared to the template t results. The uncertainties shown are statistical only.

pidity range 2.0 < (jet) < 4.5 and two transverse momentum thresholds of 10 and 20 GeV are studied. In addition to those kinematic criteria, jets are required to be isolated from the muons of the Z boson decay ( R(jet, ) > 0.4), where R is the distance in space and is the azimuthal angle.

The Z+b-jet cross-section is determined from the ratio of Z+b-jet to Z+jet event yields corrected for e ciencies and normalized by the Z+jet production cross-section

(Z+b-jet) = "(Z+jet)

"(Z+b-jet)

1 "(b-tag)

JHEP01(2015)064

N (Z+b-jet)

N(Z+jet) (Z+jet), (3.1)

where N (Z+b-jet) is the observed number of Z+b-jet events, N (Z+jet) is the number of observed Z+jet events, "(Z+jet)/"(Z+b-jet) is the ratio of e ciencies for the reconstruction and selection of Z+jet and Z+b-jet events and "(b-tag) is the e ciency of the b-tagging. The production cross-section of a Z boson associated with jets, (Z+jet), was previously measured by LHCb [18]. The same data sample, Z boson selection and jet selection are used but identication of jets originating from bottom quarks is added. By using this approach, the systematic uncertainties and the e ciencies are largely the same as those of ref. [18], except for those related to the b-jet identication.

An algorithm similar to that described in refs. [5, 21] is used for the identication of secondary vertices consistent with the decay of a beauty hadron, using tracks that form the jet. Topological secondary vertices (TOPO), signicantly separated from the primary vertex, are formed by considering all combinations of two, three and four particles within a jet, where particles include both charged particles reconstruced from tracks and reconstruced K0S and hadrons. The requirement of a TOPO candidate greatly reduces the background of jets originating from light partons (l-jets) and charm quarks (c-jets).

The number of b-jets is extracted from an unbinned likelihood t to the corrected mass of the TOPO candidate dened as Mcorr

pM2 + p2 sin2 + p sin . Here, M and p are the invariant mass and momentum of the TOPO candidate and is the angle between its momentum direction and the ight direction inferred from the positions of the primary and secondary vertices [11].

3

0.6

0.55

0.5

0.45

0.4

0.35

0.3

0.25

(b-tag) e

LHCb simulation

JHEP01(2015)064

20 40 60

T

Figure 2. E ciency of b-tagging as function of the jet transverse momentum. The uncertainties shown are statistical only.

Templates for the Mcorr distribution of b-jets, c-jets and l-jets are obtained from simulation of Z+jet, inclusive b-hadron and inclusive c-hadron production. The shapes of the templates for b-jets, c-jets and l-jets in these samples show no dependence on the production process nor on the pT of the jet. The sPlot method [22] is used to estimate the b-jet pT and spectra. Figure 1 shows the Mcorr distribution of b-jet candidates with the t results overlaid.

Jet reconstruction ine ciencies mainly arise from low-momentum particles and calorimeter response, therefore no large di erences between jets originating from heavy quarks and from light quarks and gluons are expected. Hence, the ratio "(Z+jet)/"(Z+b-jet) is assumed to be unity, which is conrmed by simulation.

The b-tagging e ciency, "(b-tag), is determined in simulation as a function of the jet transverse momentum and pseudorapidity. The value of "(b-tag) shows little variation with pseudorapidity in the range 2.0 < (jet) < 4.5, while it rises strongly with pT, reaching a value of 55 % at high pT, as shown in gure 2. The number of Z+b-jet events determined by the template t is corrected for the b-tagging e ciency.

4 Systematic uncertainties

The systematic uncertainties related to the Z boson reconstruction, unfolding, jet energy calibration and nal-state radiation are taken from ref. [18]. Systematic uncertainties related to the Mcorr templates modelling, b-tagging e ciency and jet e ciency avour dependence are studied in this work.

The systematic uncertainty on the Z boson reconstruction takes account of the contributions from the track reconstruction, trigger e ciencies, muon identication e ciencies and the model used to t the Z boson mass. The Z boson reconstruction systematic uncertainty is estimated to be 3.5 % [18].

4

p

(jet) [GeV]

Migrations in the jet transverse momentum distribution are corrected for by unfolding. This correction is applied to the value of (Z+jet) measured in ref. [18] and used in eq. (3.1). Detailed studies show that no dedicated unfolding correction is necessary. The unfolding systematic uncertainty has two contributions. The di erence between the SVD [23] and DAgostini [24] unfolding methods is assigned as one contribution. The second contribution comes from the di erence between the unfolded distribution and the true distribution in an independent simulated sample. This systematic uncertainty is taken from ref. [18] and it is evaluated to be 1.5 %.

An important contribution to the systematic uncertainties related to the jets comes from the jet-energy scale. It is estimated by comparing the transverse momentum of the Z boson and the jet in single jet events, where their momenta are azimuthally opposed, and are expected to be balanced. An additional contribution of 2 % to the jet-energy scale uncertainty comes from the di erences between jets initiated from quarks and gluons. The systematic uncertainty of the jet identication is estimated by comparing the number of candidates in data and simulation with a more stringent selection. The total systematic uncertainty related to jets is 7.8 % as estimated in ref. [18].

The systematic uncertainty associated to nal-state radiation is obtained by direct comparison to the simulation described above and an additional simulation, using HERWIG++[25], as in ref. [18]; it is estimated to be 0.2 %. The systematic uncertainty associated with the knowledge of the luminosity is estimated to be 3.5 % [26].

Possible systematic variations of the nal result due to the extraction of "(b-tag) and Mcorr templates from simulations are controlled using two data samples enriched in b-jets and c-jets. The b-jet (c-jet) enriched sample is selected via one B (D) hadron candidate decaying to J/ K (K ) produced with a large azimuthal opening angle with respect to a probe jet. The b-tagging requirement is applied to the probe jet and a template t is performed. Three studies are performed: 1) the data are divided into two ranges of M, the template t is performed on each and the sum of the resulting b-jet yields is compared with the standard result; 2) a looser b-tagging requirement is applied and the b-jet yields after b-tagging e ciency correction are compared with the default values; and 3) the Mcorr

template is smeared to account for possible di erences between simulation and data, and the impact on the b-jet yields is studied. The Mcorr simulation modelling and TOPO candidate reconstruction e ciency studies are found to a ect this measurement by up to 15 %, where this uncertainty is dominated by the rst of the studies mentioned above.

Using simulation, "(Z+jet)/"(Z+b-jet) is found to be compatible with unity within 2 %, which is taken as the systematic uncertainty due to the avour dependence of the jet e ciency.

The systematic uncertainties are summarized in table 1. They are added in quadrature leading to a total systematic error of 17.8 %.

5 Results

We observe 179 (97) Z+jet events where at least one jet fulls the b-tagging requirement for the pT(jet) > 10 GeV (20 GeV) threshold. No events with more than one b-tagged jet

5

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Source of systematic uncertainty Relative uncertainty (%) Z boson reconstruction 3.5 Unfolding 1.5 Jet-energy scale, resolution and reconstruction 7.8 Final-state radiation 0.2 Luminosity 3.5 Mcorr template and b-tagging 15.0

Jet reconstruction avour dependence 2.0 Total 17.8

Table 1. Relative systematic uncertainty considered for the Z+b-jet cross-section for pT(jet) >20 GeV. The relative uncertainties are similar for the 10 GeV threshold. The rst four contributions are from ref. [18].

are observed. The extended unbinned likelihood t of the Mcorr spectrum using Z+l-jet, Z+c-jet and Z+b-jet templates determines 7215 (3911) Z+b-jet events for the pT(jet) >

10 GeV (20 GeV) threshold. The number of candidates corrected for b-tagging e ciency is found to be 177 36 (76 21) for the pT(jet) > 10 GeV (20 GeV) threshold. Using the

measurements of ref. [18], we determine the cross-section of Z+b-jet production to be

(Z/ (+)+b-jet) = 295 60 (stat) 51 (syst) 10 (lumi) fb

for pT(jet) > 10 GeV, and

(Z/ (+)+b-jet) = 128 36 (stat) 22 (syst) 5 (lumi) fb

for pT(jet) > 20 GeV. These cross-sections are evaluated within the ducial region pT() > 20 GeV, 60 GeV < M(+) < 120 GeV, 2.0 < (jet) < 4.5, 2.0 < () < 4.5 and R(jet, ) > 0.4.

The measurements are compared to predictions of the Z+b-jet cross-section calculated using MCFM [27] in the same kinematic range as for this measurement. The uncertainties include the PDF and theory uncertainties evaluated by varying independently the renormalization and factorization scales by a factor two around their nominal scales. Neither showering nor hadronization are included in MCFM; therefore the same kinematic requirements applied to jets in the data analysis are applied to the bottom quarks in MCFM. An overall correction is calculated by generating Z+b-jet events with Pythia v8.170 with the MSTW08 PDF set [28] where the same acceptance requirements are applied. Jets are reconstructed with FastJet using the anti-kT algorithm with R = 0.5 and then matched with a bottom quark, requiring R(jet,b-quark) < 0.5. The ratio between the number of events with at least one b-jet that fulls the kinematic requirements of this measurement and the number of events with at least one b quark within the acceptance criteria are used as the fragmentation and hadronization correction for the MCFM predictions. The ratio is

6

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LHCb,

= 7 TeV

s

MCFM MSTW08 massive LO MCFM MSTW08 massless LO MCFM MSTW08 massless NLO

100 200 300 400 500

> 10 GeV) [fb]

T

(p

50 100 150 200 250

> 20 GeV) [fb]

T

(p

Z+b

Data

stat

tot

Data

s

Z+b

s

JHEP01(2015)064

Figure 3. Z+b-jet cross-section for two pT(jet) thresholds. The colour band shows the LHCb measurement (with the inner orange band showing the statistical uncertainty, and the outer yellow band showing the total uncertainty). The points with error bars correspond to the theoretical predictions with the inner error bars indicating their PDF uncertainties. These cross-sections are evaluated within the ducial region pT() > 20 GeV, 60 GeV < M(+) < 120 GeV, 2 < (jet) < 4.5, 2 < () < 4.5 and R(jet, ) > 0.4.

0.77 (0.90) for pT(jet) > 10 (20) GeV. Figure 3 shows the cross-section measurements compared to the LO calculation with massive bottom quarks and to LO and NLO calculations neglecting the bottom quark mass.

6 Summary

The cross-section for forward production of a Z boson or an o -shell photon, in the +

channel, and a bottom-quark is measured in ps = 7 TeV proton-proton collisions corresponding to an integrated luminosity of 1.0 fb1 of data collected in 2011 by the LHCb collaboration. Results are reported for the kinematic region 2.0 < () < 4.5, pT() > 20 GeV,

60 < M(+) < 120 GeV, pT(jet) > 10(20) GeV, 2.0 < (jet) < 4.5 and R(jet, ) > 0.4. The measured cross-sections are

(Z/ (+)+b-jet) = 295 60 (stat) 51 (syst) 10 (lumi) fb

for pT(jet)> 10 GeV, and

(Z/ (+)+b-jet) = 128 36 (stat) 22 (syst) 5 (lumi) fb

for pT(jet)> 20 GeV.

The results are in agreement with MCFM predictions for massless and massive bottom quark calculations.

7

Acknowledgments

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 sta at the LHCb institutes. We acknowledge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); NSFC (China); CNRS/IN2P3 (France); BMBF, DFG, HGF and MPG (Germany); SFI (Ireland); INFN (Italy); FOM and NWO (The Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MinES and FANO (Russia); MinECo (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); NSF (U.S.A.). The Tier1 computing centres are supported by IN2P3 (France), KIT and BMBF (Germany), INFN (Italy), NWO and SURF (The Netherlands), PIC (Spain), GridPP (United Kingdom). We are indebted to the communities behind the multiple open source software packages on which we depend. We are also thankful for the computing resources and the access to software R&D tools provided by Yandex LLC (Russia). Individual groups or members have received support from EPLANET, Marie Sk[suppress]lodowska-Curie Actions and ERC (European Union), Conseil g[notdef]n[notdef]ral de Haute-Savoie, Labex ENIG-MASS and OCEVU, R[notdef]gion Auvergne (France), RFBR (Russia), XuntaGal and GENCAT (Spain), Royal Society and Royal Commission for the Exhibition of 1851 (United Kingdom).

Open Access. This article is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/

Web End =CC-BY 4.0 ), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.

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9

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The LHCb collaboration

R. Aaij41, B. Adeva37, M. Adinol46, A. A older52, Z. Ajaltouni5, S. Akar6, J. Albrecht9,F. Alessio38, M. Alexander51, S. Ali41, G. Alkhazov30, P. Alvarez Cartelle37, A.A. Alves Jr25,38,S. Amato2, S. Amerio22, Y. Amhis7, L. An3, L. Anderlini17,g, J. Anderson40, R. Andreassen57,M. Andreotti16,f, J.E. Andrews58, R.B. Appleby54, O. Aquines Gutierrez10, F. Archilli38,A. Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,n, M. Baalouch5, S. Bachmann11, J.J. Back48, A. Badalov36, C. Baesso60, W. Baldini16, R.J. Barlow54, C. Barschel38, S. Barsuk7,W. Barter47, V. Batozskaya28, V. Battista39, A. Bay39, L. Beaucourt4, J. Beddow51,F. Bedeschi23, I. Bediaga1, S. Belogurov31, K. Belous35, I. Belyaev31, E. Ben-Haim8,G. Bencivenni18, S. Benson38, J. Benton46, A. Berezhnoy32, R. Bernet40, AB Bertolin22,M.-O. Bettler47, M. van Beuzekom41, A. Bien11, S. Bifani45, T. Bird54, A. Bizzeti17,i, P.M. Bj[notdef]rnstad54, T. Blake48, F. Blanc39, J. Blouw10, S. Blusk59, V. Bocci25, A. Bondar34,N. Bondar30,38, W. Bonivento15, S. Borghi54, A. Borgia59, M. Borsato7, T.J.V. Bowcock52,E. Bowen40, C. Bozzi16, D. Brett54, M. Britsch10, T. Britton59, J. Brodzicka54, N.H. Brook46,A. Bursche40, J. Buytaert38, S. Cadeddu15, R. Calabrese16,f, M. Calvi20,k, M. Calvo Gomez36,p,P. Campana18, D. Campora Perez38, L. Capriotti54, A. Carbone14,d, G. Carboni24,l,R. Cardinale19,38,j, A. Cardini15, L. Carson50, K. Carvalho Akiba2,38, RCM Casanova Mohr36,G. Casse52, L. Cassina20,k, L. Castillo Garcia38, M. Cattaneo38, Ch. Cauet9, R. Cenci23,t,M. Charles8, Ph. Charpentier38, M. Chefdeville4, S. Chen54, S.-F. Cheung55, N. Chiapolini40,M. Chrzaszcz40,26, X. Cid Vidal38, G. Ciezarek41, P.E.L. Clarke50, M. Clemencic38, H.V. Cli 47,J. Closier38, V. Coco38, J. Cogan6, E. Cogneras5, V. Cogoni15, L. Cojocariu29, G. Collazuol22,P. Collins38, A. Comerma-Montells11, A. Contu15,38, A. Cook46, M. Coombes46, S. Coquereau8,G. Corti38, M. Corvo16,f, I. Counts56, B. Couturier38, G.A. Cowan50, D.C. Craik48,

A.C. Crocombe48, M. Cruz Torres60, S. Cunli e53, R. Currie53, C. DAmbrosio38, J. Dalseno46,P. David8, P.N.Y. David41, A. Davis57, K. De Bruyn41, S. De Capua54, M. De Cian11,

J.M. De Miranda1, L. De Paula2, W. De Silva57, P. De Simone18, C.-T. Dean51, D. Decamp4,M. Deckenho 9, L. Del Buono8, N. D[notdef]l[notdef]age4, D. Derkach55, O. Deschamps5, F. Dettori38,B. Dey40, A. Di Canto38, A Di Domenico25, H. Dijkstra38, S. Donleavy52, F. Dordei11,M. Dorigo39, A. Dosil Su[notdef]rez37, D. Dossett48, A. Dovbnya43, K. Dreimanis52, G. Dujany54,F. Dupertuis39, P. Durante38, R. Dzhelyadin35, A. Dziurda26, A. Dzyuba30, S. Easo49,38,U. Egede53, V. Egorychev31, S. Eidelman34, S. Eisenhardt50, U. Eitschberger9, R. Ekelhof9,L. Eklund51, I. El Rifai5, Ch. Elsasser40, S. Ely59, S. Esen11, H.-M. Evans47, T. Evans55,A. Falabella14, C. F[notdef]arber11, C. Farinelli41, N. Farley45, S. Farry52, R. Fay52, D. Ferguson50,V. Fernandez Albor37, F. Ferreira Rodrigues1, M. Ferro-Luzzi38, S. Filippov33, M. Fiore16,f,M. Fiorini16,f, M. Firlej27, C. Fitzpatrick39, T. Fiutowski27, P. Fol53, M. Fontana10,F. Fontanelli19,j, R. Forty38, O. Francisco2, M. Frank38, C. Frei38, M. Frosini17,g, J. Fu21,38,E. Furfaro24,l, A. Gallas Torreira37, D. Galli14,d, S. Gallorini22,38, S. Gambetta19,j,M. Gandelman2, P. Gandini59, Y. Gao3, J. Garc[notdef]a Pardi[notdef]as37, J. Garofoli59, J. Garra Tico47,L. Garrido36, D. Gascon36, C. Gaspar38, U. Gastaldi16, R. Gauld55, L. Gavardi9, G. Gazzoni5,A. Geraci21,v, E. Gersabeck11, M. Gersabeck54, T. Gershon48, Ph. Ghez4, A. Gianelle22,S. Gian[notdef]39, V. Gibson47, L. Giubega29, V.V. Gligorov38, C. G[notdef]bel60, D. Golubkov31,A. Golutvin53,31,38, A. Gomes1,a, C. Gotti20,k, M. Grabalosa G[notdef]ndara5, R. Graciani Diaz36,L.A. Granado Cardoso38, E. Graug[notdef]s36, E. Graverini40, G. Graziani17, A. Grecu29, E. Greening55,S. Gregson47, P. Gri th45, L. Grillo11, O. Gr[notdef]nberg63, B. Gui59, E. Gushchin33, Yu. Guz35,38,T. Gys38, C. Hadjivasiliou59, G. Haefeli39, C. Haen38, S.C. Haines47, S. Hall53, B. Hamilton58,T. Hampson46, X. Han11, S. Hansmann-Menzemer11, N. Harnew55, S.T. Harnew46, J. Harrison54,J. He38, T. Head39, V. Heijne41, K. Hennessy52, P. Henrard5, L. Henry8, J.A. Hernando Morata37,

10

JHEP01(2015)064

E. van Herwijnen38, M. He[notdef]63, A. Hicheur2, D. Hill55, M. Hoballah5, C. Hombach54,W. Hulsbergen41, N. Hussain55, D. Hutchcroft52, D. Hynds51, M. Idzik27, P. Ilten56,R. Jacobsson38, A. Jaeger11, J. Jalocha55, E. Jans41, A. Jawahery58, F. Jing3, M. John55,D. Johnson38, C.R. Jones47, C. Joram38, B. Jost38, N. Jurik59, S. Kandybei43, W. Kanso6,M. Karacson38, T.M. Karbach38, S. Karodia51, M. Kelsey59, I.R. Kenyon45, T. Ketel42,B. Khanji20,38,k, C. Khurewathanakul39, S. Klaver54, K. Klimaszewski28, O. Kochebina7,M. Kolpin11, I. Komarov39, R.F. Koopman42, P. Koppenburg41,38, M. Korolev32, L. Kravchuk33,K. Kreplin11, M. Kreps48, G. Krocker11, P. Krokovny34, F. Kruse9, W. Kucewicz26,o,M. Kucharczyk20,26,k, V. Kudryavtsev34, K. Kurek28, T. Kvaratskheliya31, V.N. La Thi39,D. Lacarrere38, G. La erty54, A. Lai15, D. Lambert50, R.W. Lambert42, G. Lanfranchi18,C. Langenbruch48, B. Langhans38, T. Latham48, C. Lazzeroni45, R. Le Gac6, J. van Leerdam41,J.-P. Lees4, R. Lef[notdef]vre5, A. Leat32, J. Lefran[notdef]ois7, O. Leroy6, T. Lesiak26, B. Leverington11,Y. Li7, T. Likhomanenko64, M. Liles52, R. Lindner38, C. Linn38, F. Lionetto40, B. Liu15,S. Lohn38, I. Longsta 51, J.H. Lopes2, P. Lowdon40, D. Lucchesi22,r, H. Luo50, A. Lupato22,E. Luppi16,f, O. Lupton55, F. Machefert7, I.V. Machikhiliyan31, F. Maciuc29, O. Maev30,S. Malde55, A. Malinin64, G. Manca15,e, G. Mancinelli6, A. Mapelli38, J. Maratas5,

J.F. Marchand4, U. Marconi14, C. Marin Benito36, P. Marino23,t, R. M[notdef]arki39, J. Marks11,G. Martellotti25, M. Martinelli39, D. Martinez Santos42, F. Martinez Vidal65, D. Martins Tostes2,A. Massa erri1, R. Matev38, Z. Mathe38, C. Matteuzzi20, A. Mazurov45, M. McCann53,J. McCarthy45, A. McNab54, R. McNulty12, B. McSkelly52, B. Meadows57, F. Meier9,M. Meissner11, M. Merk41, D.A. Milanes62, M.-N. Minard4, N. Moggi14, J. Molina Rodriguez60,S. Monteil5, M. Morandin22, P. Morawski27, A. Mord[notdef]6, M.J. Morello23,t, J. Moron27,A.-B. Morris50, R. Mountain59, F. Muheim50, K. M[notdef]ller40, M. Mussini14, B. Muster39, P. Naik46,T. Nakada39, R. Nandakumar49, I. Nasteva2, M. Needham50, N. Neri21, S. Neubert38,N. Neufeld38, M. Neuner11, A.D. Nguyen39, T.D. Nguyen39, C. Nguyen-Mau39,q, M. Nicol7,V. Niess5, R. Niet9, N. Nikitin32, T. Nikodem11, A. Novoselov35, D.P. OHanlon48,A. Oblakowska-Mucha27, V. Obraztsov35, S. Ogilvy51, O. Okhrimenko44, R. Oldeman15,e,

C.J.G. Onderwater66, M. Orlandea29, B. Osorio Rodrigues1, J.M. Otalora Goicochea2, A. Otto38,P. Owen53, A. Oyanguren65, B.K. Pal59, A. Palano13,c, F. Palombo21,u, M. Palutan18,J. Panman38, A. Papanestis49,38, M. Pappagallo51, L.L. Pappalardo16,f, C. Parkes54,

C.J. Parkinson9,45, G. Passaleva17, G.D. Patel52, M. Patel53, C. Patrignani19,j, A. Pearce54,A. Pellegrino41, G. Penso25,m, M. Pepe Altarelli38, S. Perazzini14,d, P. Perret5, L. Pescatore45,E. Pesen67, K. Petridis53, A. Petrolini19,j, E. Picatoste Olloqui36, B. Pietrzyk4, T. Pila48,D. Pinci25, A. Pistone19, S. Playfer50, M. Plo Casasus37, F. Polci8, A. Poluektov48,34,I. Polyakov31, E. Polycarpo2, A. Popov35, D. Popov10, B. Popovici29, C. Potterat2, E. Price46,

J.D. Price52, J. Prisciandaro39, A. Pritchard52, C. Prouve46, V. Pugatch44, A. Puig Navarro39,G. Punzi23,s, W. Qian4, B. Rachwal26, J.H. Rademacker46, B. Rakotomiaramanana39,M. Rama23, M.S. Rangel2, I. Raniuk43, N. Rauschmayr38, G. Raven42, F. Redi53, S. Reichert54, M.M. Reid48, A.C. dos Reis1, S. Ricciardi49, S. Richards46, M. Rihl38, K. Rinnert52,V. Rives Molina36, P. Robbe7, A.B. Rodrigues1, E. Rodrigues54, P. Rodriguez Perez54,S. Roiser38, V. Romanovsky35, A. Romero Vidal37, M. Rotondo22, J. Rouvinet39, T. Ruf38,H. Ruiz36, P. Ruiz Valls65, J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B. Saitta15,e,V. Salustino Guimaraes2, C. Sanchez Mayordomo65, B. Sanmartin Sedes37, R. Santacesaria25,C. Santamarina Rios37, E. Santovetti24,l, A. Sarti18,m, C. Satriano25,n, A. Satta24,

D.M. Saunders46, D. Savrina31,32, M. Schiller38, H. Schindler38, M. Schlupp9, M. Schmelling10,B. Schmidt38, O. Schneider39, A. Schopper38, M.-H. Schune7, R. Schwemmer38, B. Sciascia18,A. Sciubba25,m, A. Semennikov31, I. Sepp53, N. Serra40, J. Serrano6, L. Sestini22, P. Seyfert11,M. Shapkin35, I. Shapoval16,43,f, Y. Shcheglov30, T. Shears52, L. Shekhtman34, V. Shevchenko64,

11

JHEP01(2015)064

A. Shires9, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46, I. Skillicorn51,T. Skwarnicki59, N.A. Smith52, E. Smith55,49, E. Smith53, J. Smith47, M. Smith54, H. Snoek41, M.D. Sokolo 57, F.J.P. Soler51, F. Soomro39, D. Souza46, B. Souza De Paula2, B. Spaan9,P. Spradlin51, S. Sridharan38, F. Stagni38, M. Stahl11, S. Stahl11, O. Steinkamp40, O. Stenyakin35, F Sterpka59, S. Stevenson55, S. Stoica29, S. Stone59, B. Storaci40, S. Stracka23,t, M. Straticiuc29,U. Straumann40, R. Stroili22, L. Sun57, W. Sutcli e53, K. Swientek27, S. Swientek9,V. Syropoulos42, M. Szczekowski28, P. Szczypka39,38, T. Szumlak27, S. TJampens4,M. Teklishyn7, G. Tellarini16,f, F. Teubert38, C. Thomas55, E. Thomas38, J. van Tilburg41,V. Tisserand4, M. Tobin39, J. Todd57, S. Tolk42, L. Tomassetti16,f, D. Tonelli38,S. Topp-Joergensen55, N. Torr55, E. Tourneer4, S. Tourneur39, M.T. Tran39, M. Tresch40,A. Trisovic38, A. Tsaregorodtsev6, P. Tsopelas41, N. Tuning41, M. Ubeda Garcia38, A. Ukleja28,A. Ustyuzhanin64, U. Uwer11, C. Vacca15, V. Vagnoni14, G. Valenti14, A. Vallier7,R. Vazquez Gomez18, P. Vazquez Regueiro37, C. V[notdef]zquez Sierra37, S. Vecchi16, J.J. Velthuis46,M. Veltri17,h, G. Veneziano39, M. Vesterinen11, JVVB Viana Barbosa38, B. Viaud7, D. Vieira2,M. Vieites Diaz37, X. Vilasis-Cardona36,p, A. Vollhardt40, D. Volyanskyy10, D. Voong46,A. Vorobyev30, V. Vorobyev34, C. Vo[notdef]63, J.A. de Vries41, R. Waldi63, C. Wallace48, R. Wallace12,J. Walsh23, S. Wandernoth11, J. Wang59, D.R. Ward47, N.K. Watson45, D. Websdale53,M. Whitehead48, D. Wiedner11, G. Wilkinson55,38, M. Wilkinson59, M.P. Williams45,M. Williams56, H.W. Wilschut66, F.F. Wilson49, J. Wimberley58, J. Wishahi9, W. Wislicki28,M. Witek26, G. Wormser7, S.A. Wotton47, S. Wright47, K. Wyllie38, Y. Xie61, Z. Xing59, Z. Xu39,Z. Yang3, X. Yuan3, O. Yushchenko35, M. Zangoli14, M. Zavertyaev10,b, L. Zhang3, W.C. Zhang12,Y. Zhang3, A. Zhelezov11, A. Zhokhov31 and L. Zhong3.

1 Centro Brasileiro de Pesquisas Fsicas (CBPF), Rio de Janeiro, Brazil

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

3 Center for High Energy Physics, Tsinghua University, Beijing, China

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

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

6 CPPM, Aix-Marseille Universit, CNRS/IN2P3, Marseille, France

7 LAL, Universit Paris-Sud, CNRS/IN2P3, Orsay, France

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

9 Fakultat Physik, Technische Universitat Dortmund, Dortmund, Germany

10 Max-Planck-Institut fr Kernphysik (MPIK), Heidelberg, Germany

11 Physikalisches Institut, Ruprecht-Karls-Universitat Heidelberg, Heidelberg, Germany

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

13 Sezione INFN di Bari, Bari, Italy

14 Sezione INFN di Bologna, Bologna, Italy

15 Sezione INFN di Cagliari, Cagliari, Italy

16 Sezione INFN di Ferrara, Ferrara, Italy

17 Sezione INFN di Firenze, Firenze, Italy

18 Laboratori Nazionali dellINFN di Frascati, Frascati, Italy

19 Sezione INFN di Genova, Genova, Italy

20 Sezione INFN di Milano Bicocca, Milano, Italy

21 Sezione INFN di Milano, Milano, Italy

22 Sezione INFN di Padova, Padova, Italy

23 Sezione INFN di Pisa, Pisa, Italy

24 Sezione INFN di Roma Tor Vergata, Roma, Italy

25 Sezione INFN di Roma La Sapienza, Roma, Italy

26 Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences, Krakw, Poland

27 AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakw, Poland

12

JHEP01(2015)064

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

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

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

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

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

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

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

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

36 Universitat de Barcelona, Barcelona, Spain

37 Universidad de Santiago de Compostela, Santiago de Compostela, Spain

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

39 Ecole Polytechnique Fdrale de Lausanne (EPFL), Lausanne, Switzerland

40 Physik-Institut, Universitat Zrich, Zrich, Switzerland

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

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

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

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

45 University of Birmingham, Birmingham, United Kingdom

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

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

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

49 STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

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

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

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

53 Imperial College London, London, United Kingdom

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

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

56 Massachusetts Institute of Technology, Cambridge, MA, United States

57 University of Cincinnati, Cincinnati, OH, United States

58 University of Maryland, College Park, MD, United States

59 Syracuse University, Syracuse, NY, United States

60 Pontifcia Universidade Catlica do Rio de Janeiro (PUC-Rio), Rio de Janeiro, Brazil, associated to 2

61 Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China, associated to 3

62 Departamento de Fisica , Universidad Nacional de Colombia, Bogota, Colombia, associated to 8

63 Institut fr Physik, Universitat Rostock, Rostock, Germany, associated to 11

64 National Research Centre Kurchatov Institute, Moscow, Russia, associated to 31

65 Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to 36

66 Van Swinderen Institute, University of Groningen, Groningen, The Netherlands, associated to 41

67 Celal Bayar University, Manisa, Turkey, associated to 38

a Universidade Federal do Tringulo Mineiro (UFTM), Uberaba-MG, Brazil

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

c Universit di Bari, Bari, Italy

d Universit di Bologna, Bologna, Italy

e Universit di Cagliari, Cagliari, Italy

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JHEP01(2015)064

f Universit di Ferrara, Ferrara, Italy

g Universit di Firenze, Firenze, Italy

h Universit di Urbino, Urbino, Italy

i Universit di Modena e Reggio Emilia, Modena, Italy

j Universit di Genova, Genova, Italy

k Universit di Milano Bicocca, Milano, Italy

l Universit di Roma Tor Vergata, Roma, Italy

m Universit di Roma La Sapienza, Roma, Italy

n Universit della Basilicata, Potenza, Italy

o AGH - University of Science and Technology, Faculty of Computer Science, Electronics andTelecommunications, Krakw, Poland

p LIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain

q Hanoi University of Science, Hanoi, Viet Nam

r Universit di Padova, Padova, Italy

s Universit di Pisa, Pisa, Italy

t Scuola Normale Superiore, Pisa, Italy

u Universit degli Studi di Milano, Milano, Italy

v Politecnico di Milano, Milano, Italy

JHEP01(2015)064

14