Search for CP violation using T-odd correlations in D 0 → K + K −π+π− decays

JHEP10(2014)005 Published for SISSA by Springer Received:August 7, 2014 Accepted:September 10, 2014 Published:October 1, 2014 Search for CP violation using T-odd correlations in D0→K+K−π+π−decays The LHCb collaboration E-mail: [email protected] Abstract: A search for CP violation using T -odd correlations is performed using the four-body D0→K+K−π+π− decay, selected from semileptonic B decays. The data sample corresponds to integrated luminosities of 1.0 fb −1 and 2.0 fb −1 recorded at the centre-of-mass energies of 7 TeV and 8 TeV, respectively. The CP -violating asymmetry aT-odd CP is measured to be (0 . 18 ± 0 . 29 ( stat ) ± 0 . 04 ( syst ))%. Searches for CP violation in different regions of phase space of the four-body decay, and as a function of the D0 decay time, are also presented. No significant deviation from the CP conservation hypothesis is found. Keywords: CP violation, Charm physics, Hadron-Hadron Scattering, Flavor physics ArXiv ePrint: 1408.1299 Open Access, Copyright CERN, for the benefit of the LHCb Collaboration. Article funded by SCOAP3. doi:10.1007/JHEP10(2014)005 JHEP10(2014)005 Contents 1 Introduction 1 2 Detector 2 3 Selection 3 4 Asymmetry measurements 4 5 Systematic uncertainties 8 6 Conclusions 10 A Measured asymmetries in regions of phase space 11 B Measured asymmetries in intervals of D0decay time 13 The LHCb collaboration 16 1 Introduction Violation of the CP symmetry in charm decays is expected to be very small in the Standard Model (SM) [ 1 , 2 ], however, asymmetries at a few times 10 −3 within the SM cannot be excluded according to recent calculations [ 3 – 5 ]. A significant excess of CP violation ( CPV ) with respect to the theoretical predictions would be a signature of physics beyond the SM. The study of CPV in singly Cabibbo-suppressed charm decays is uniquely sensitive to physics beyond the SM, in particular through new contributions in strong penguin and chromomagnetic dipole operators [ 2 ]. The analysis of singly Cabibbo-suppressed D0→K+K−π+π−1 decays allows localised CPV in different regions of phase space to be probed. This approach enhances the sensitivity due to several interfering amplitudes with different relative strong phases contributing to the decay. The analysis in ref. [ 6 ] quotes a p -value of 9.1% for the compatibility with the CP conservation hypothesis, using D∗ -tagged promptly-produced D0 mesons. In the present analysis, a sample of D0→K+K−π+π− decays, selected from semileptonic B decays, is used to measure a CP -violating parameter based on T -odd correlations characterised by different sensitivity to CPV [ 7 , 8 ]. Using triple products of final state particle momenta in the D0 centre-of-mass frame, CT≡~pK+· ( ~pπ+×~pπ− ) for D0 and CT≡~pK−· ( ~pπ−×~pπ+ ) for ¯ D0decays, two T-odd observables, AT≡ΓD0(CT>0) −ΓD0(CT<0) ΓD0(CT>0) + ΓD0(CT<0), AT≡Γ¯ D0(−CT>0) −Γ¯ D0(−CT<0) Γ¯ D0(−CT>0) + Γ ¯ D0(−CT<0),(1.1) 1Throughout this paper the use of charge conjugate reactions is implied, unless otherwise indicated. – 1 – JHEP10(2014)005 can be studied [ 9 ], where Γ D0 (Γ ¯ D0 ) is the partial decay width of D0 ( ¯ D0 ) decays to K+K−π+π− in the indicated CT ( CT ) range. However, because final state interaction (FSI) effects could introduce fake asymmetries [ 9 , 10 ], these are not theoretically clean CP-violating observables. A well defined CP-violating observable is aT-odd CP ≡1 2(AT−AT),(1.2) as FSI effects cancel out in the difference. In contrast to the asymmetry between the phase-space integrated rates in a D0→V1V2 decay (where Vi indicates a vector meson), aT-odd CP is sensitive to CP violation in interference between even- and oddpartial waves of the V1V2system [7]. Previous measurements of aT-odd CP are compatible with no CPV : FOCUS measured aT-odd CP = (1.0±5.7±3.7)% [11], and BaBar measured aT-odd CP = (0.10 ±0.51 ±0.44)% [12]. The physics observables, AT , AT , and aT-odd CP are by construction insensitive to D0 / ¯ D0 production asymmetries, detector- and reconstruction-induced charge asymmetries. The measurement described in this paper determines the CP -violating observable aT-odd CP with an improved precision. For the first time, aT-odd CP is measured in different regions of phase space and in bins of D0 decay time, allowing to probe for CP violation both in the decay amplitude and in its interference with the mixing amplitude. 2 Detector The LHCb detector [ 13 ] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 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 [ 14 ], 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 [ 15 ] 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/c . The minimum distance of a track to a primary vertex, the impact parameter, is measured with a resolution of (15 + (29 GeV/c ) /pT ) µ m, where pT is the component of p transverse to the beam. Different types of charged hadrons are distinguished using information from two ring-imaging Cherenkov (RICH) detectors [ 16 ]. Photon, electron and hadron candidates are identified by a calorimeter system consisting of scintillating-pad and preshower detectors, an electromagnetic calorimeter and a hadronic calorimeter. Muons are identified by a system composed of alternating layers of iron and multiwire proportional chambers [ 17 ]. The trigger [ 18 ] 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. Events are required to pass both hardware and software trigger selections. The software trigger identifies D0→K+K−π+π− (signal) and D0→K−π+π−π+ (control sample) events from B→D0µ−X decays, where X indicates any system composed of charged and neutral particles, by requiring a four-track secondary vertex with a scalar sum of pT of the tracks – 2 – JHEP10(2014)005 greater than 1 . 8 GeV/c . The D0 daughter tracks are required to have pT> 0 . 3 GeV/c and momentum p > 2 GeV/c . The muon track is selected with pT> 1 . 2 GeV/c and p > 2 GeV/c . Tracks have to be compatible with detached decay vertices of B and D0 decays. Therefore, a requirement is imposed for all the tracks in the signal candidate on the χ2 IP , i.e. the difference in χ2 of a given primary vertex reconstructed with and without the considered particle, to be greater than 9. The invariant mass of the D0µ system is required to be less than 6.2 GeV/c2. In the simulation, pp collisions are generated using Pythia [ 19 , 20 ] with a specific LHCb configuration [ 21 ]. Decays of hadronic particles are described by EvtGen [ 22 ]. The interaction of the generated particles with the detector and its response are implemented using the Geant4 toolkit [23,24] as described in ref. [25]. 3 Selection The analysis is based on data recorded by the LHCb experiment, at center-of-mass energies of 7 TeV and 8 TeV, corresponding to integrated luminosities of 1 . 0 fb−1 and 2 . 0 fb−1 , respectively. The D0 candidates are formed from combinations of kaon and pion candidate tracks and then combined with a muon candidate track to reconstruct the semileptonic B decay. The flavour of the D0 is identified by the charge of the muon, i.e. a negative charge identifies a D0 meson and a positive charge identifies a ¯ D0 meson. The information from the RICH system is used to distinguish between kaons and pions, while the information from the muon system is used to identify muon candidates. The D0 meson decay vertex is required to be downstream of the B decay vertex. The invariant mass of the D0µ system is required to be in the range [2.6,5.2] GeV/c2. Two main sources of peaking background in m ( K+K−π+π− ), the reconstructed inviariant mass of D0 candidates, are present and consist of D0→K0 SK+K− decays, and D0→K+K−π+π− decays from D0 mesons that originate at the interaction point, referred to as “prompt” charm decays in the following. The small component of D0→K0 SK+K− events is vetoed by requiring the invariant mass of the π+π− system to be more than 3 σ away from the known K0 S mass [ 26 ], where σ = 4 . 5 MeV/c2 is the resolution determined from the fit to data. The contribution of prompt charm decays is estimated by fitting the distribution of the logarithm of the χ2 IP of the D0 meson. The prompt component and the signal component from semileptonic B decays accumulate at 0 and at 5, respectively. The fraction of prompt D0 decays in our sample is measured to be fprompt = (1 . 20 ± 0 . 08)% and the effect of its presence is accounted for as a systematic uncertainty. The distributions of D0 decays where pions and kaons have not been correctly identified have been studied and do not peak in m ( K+K−π+π− ). When multiple candidates are reconstructed, one candidate per event is retained, by random choice. This happens in 0.7% of the events. The signal yield for D0→K+K−π+π− from B→D0µ−X decays, obtained from an extended maximum likelihood fit to the m ( K+K−π+π− ) distribution, is (171 . 3 ± 0 . 6) × 10 3 events with a sample purity of about 75%. – 3 – JHEP10(2014)005 Sample Signal Decays D0,CT>0 39 628 ±256 D0,CT<0 45 762 ±272 ¯ D0,−CT>0 39 709 ±256 ¯ D0,−CT<0 46 162 ±274 Table 1 . Number of signal decays obtained from the fit to data for each of the four samples defined by the D0/¯ D0flavour and the sign of CTor CT. By using identical kinematic selection criteria as for the signal, Cabibbo-favoured D0→K−π+π−π+ decays are also reconstructed with a signal yield of about of 6 . 211 × 10 6 and a purity of about 95%. These decays are used for control checks and for assessing systematic uncertainties. 4 Asymmetry measurements The selected data sample is split into four subsamples according to the charge of the muon candidate, which determines the flavour of the D0 , and the sign of CT ( CT ). The reconstruction efficiencies are equal, within their uncertainties, for CT> 0 ( −CT> 0) and for CT< 0 ( −CT< 0) according to studies based on simulated events and on the D0→K−π+π−π+ control sample. A simultaneous maximum likelihood fit to the m ( K+K−π+π− ) distribution of the four subsamples is used to determine the number of signal and background events, and the asymmetries AT and AT . The fit model consists of two Gaussian functions with common mean for the signal and an exponential function for the background. The two asymmetries ATand ATare included in the fit model as ND0,CT>0=1 2ND0(1 + AT), ND0,CT<0=1 2ND0(1 −AT), N¯ D0,−CT>0=1 2N¯ D0(1 + AT), N¯ D0,−CT<0=1 2N¯ D0(1 −AT). (4.1) The CP -violating asymmetry aT-odd CP is then calculated from AT and AT . Negligible correlation is found between these two asymmetries. The results of the fit are shown in figure 1. The number of signal decays for each subsample are listed in table 1. Three different approaches have been followed to search for CPV : a measurement integrated over the phase space, measurements in different regions of phase space, and measurements as a function of the D0 decay time. The results of the first approach are obtained by fitting the full data sample and are AT = ( − 7 . 18 ± 0 . 41)%, and AT = ( − 7 . 55 ± 0 . 41)%, where the uncertainties are statistical only. The CP -violating asymmetry calculated from the two partial asymmetries is aT-odd CP = (0.18 ±0.29)%. – 4 – JHEP10(2014)005 ] 2 c) [GeV/ − π + π − K + (Km 1.85 1.9 ) 2 c Candidates / (1.1 MeV/ 0 500 1000 1500 2000 2500 3000 3500 4000 4500 >0) T (C 0 (a) D LHCb Pull 3− 0 +3 ] 2 c) [GeV/ − π + π − K + (Km 1.85 1.9 ) 2 c Candidates / (1.1 MeV/ 0 500 1000 1500 2000 2500 3000 3500 4000 4500 <0) T (C 0 (b) D LHCb Pull 3− 0 +3 ] 2 c) [GeV/ − π + π − K + (Km 1.85 1.9 ) 2 c Candidates / (1.1 MeV/ 0 500 1000 1500 2000 2500 3000 3500 4000 4500 >0) T C(- 0 D(c) LHCb Pull 3− 0 +3 ] 2 c) [GeV/ − π + π − K + (Km 1.85 1.9 ) 2 c Candidates / (1.1 MeV/ 0 500 1000 1500 2000 2500 3000 3500 4000 4500 <0) T C(- 0 D(d) LHCb Pull 3− 0 +3 Figure 1 . Distributions of the K+K− π+π − invariant mass in the four samples defined by D0 ( ¯ D0 ) flavour and the sign of CT ( CT ). The results of the fit are overlaid as a solid line, and a dashed line is used for representing the background. The normalised residuals (pulls) of the difference between the fit results and the data points, divided by their uncertainties, are shown on top of each distribution. The relatively large asymmetries observed in AT and AT are due to FSI effects [ 9 , 10 ], which are known to be relevant in charm mesons decays. These effects are difficult to predict, since they involve non-perturbative strong interactions [ 27 ]. However, experimental measurements provide solid anchor points for future calculations. The measurement in different regions of the phase space is performed by dividing the sample using a binning scheme based on the Cabibbo-Maksimowicz [ 28 ] variables mK+K− , mπ+π− , cos ( θK+ ), cos ( θπ+ ), Φ, defined as the K+K− and π+π− invariant masses, the cosine of the angle of the K+ ( π+ ) with respect to the opposite direction to the D0 momentum in the K+K− ( π+π− ) rest frame, and the angle between the planes described by the two kaons and pions in the D0rest frame, respectively. The background-subtracted distributions for D0 ( ¯ D0 ) events with CT> 0 and CT< 0 ( −CT> 0 and −CT< 0) in mπ+π− and mK+K− are shown in figure 2. The background subtraction is performed using m ( K+K−π+π− ) sidebands. Clear indications of ρ0→π+π− – 5 – JHEP10(2014)005 ] 2 c) [GeV/ − π + π(m 0.4 0.6 0.8 ) 2 cCandidates / (11.7 MeV/ 0 500 1000 1500 2000 2500 3000 >0) T (C 0 D <0) T (C 0 D (a) ] 2 c) [GeV/ − π + π(m 0.4 0.6 0.8 (b) LHCb >0) T C(- 0 D <0) T C(- 0 D ] 2 c) [GeV/ − K + (Km 1 1.2 1.4 1.6 ) 2 cCandidates / (13.2 MeV/ 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 >0) T (C 0 D <0) T (C 0 D (c) ] 2 c) [GeV/ − K + (Km 1 1.2 1.4 1.6 (d) LHCb >0) T C(- 0 D <0) T C(- 0 D Figure 2 . Sideband-subtracted distributions of D0 ( ¯ D0 ) candidates in variables of (a, b) mπ+π− and (c, d) mK+K− for different values of CT ( CT ). The veto for D0→K0 SK+K− decays is visible in the mπ+π−distribution. and φ→K+K− resonances are seen in the data. The distributions of cos ( θK+ ), cos ( θπ+ ), and Φ variables are shown in figure 3, where FSI-induced differences are clearly evident [ 29 ]. Effects of CPV would lead to different distributions for D0and ¯ D0events. The phase space is divided in 32 regions such that the number of signal events is similar in each region; the definition of the 32 regions is reported in table 3in appendix A. The same fit model used for the integrated measurement is separately fitted to data in each bin. The signal shapes are consistent among different bins, while significant variations are found in the distribution of the combinatorial background. The distributions of the measured asymmetries in the 32-region binning scheme are shown in figure 4and the results are reported in table 4in appendix A. The compatibility with the CP conservation hypothesis is tested by means of a χ2 test, where the χ2 is defined as RTV−1R , where R is the array of aT-odd CP measurements, and V−1 is the inverse of the covariance matrix V , defined as the sum of the statistical and systematic covariance matrices. An average systematic uncertainty, whose evaluation is discussed in section 5, is assumed for the different bins. The statistical uncertainties are considered uncorrelated among the bins, while systematic uncertainties are assumed to be fully correlated. The contribution of systematic uncertainties is small compared to the statistical ones, as shown in table 2. The results are consistent with the CP conservation – 6 – JHEP10(2014)005 ) K θcos( -1 -0.5 0 0.5 1 Candidates / 0.04 0 200 400 600 800 1000 1200 1400 1600 1800 2000 >0) T (C 0 D <0) T (C 0 D (a) ) K θcos( -1 -0.5 0 0.5 1 (b) LHCb >0) T C(- 0 D <0) T C(- 0 D ) π θcos( -1 -0.5 0 0.5 1 Candidates / 0.04 0 200 400 600 800 1000 1200 1400 1600 1800 2000 >0) T (C 0 D <0) T (C 0 D (c) ) π θcos( -1 -0.5 0 0.5 1 (d) LHCb >0) T C(- 0 D <0) T C(- 0 D [rad]Φ 0 1 2 3 Candidates / (0.05 rad) 0 200 400 600 800 1000 1200 1400 1600 1800 2000 >0) T (C 0 D <0) T (C 0 D (e) [rad]Φ 0 1 2 3 (f) LHCb >0) T C(- 0 D <0) T C(- 0 D Figure 3 . Sideband-subtracted distributions of D0 ( ¯ D0 ) candidates in variables of (a, b) cos ( θK+ ), (c, d) cos ( θπ+ ), and (e, f) Φ for different values of CT ( CT ). The asymmetric distributions with respect to 0 for cos ( θK+ ) and cos ( θπ+ ) variables, and with respect to π/ 2 for the Φ variable, are due to the dynamics of the four-body decay. hypothesis with a p -value of 74%, based on χ2/ndf = 26 . 4 / 32, where ndf is the number of degrees of freedom. Four alternative binning schemes, one with 8 regions and three with 16 regions, are also tested. These are described in appendix A. Results are compatible with the CP conservation hypothesis with a p -value of 24% for the case of 8 regions and 28%, 62%, 82% for the three different phase space divisions in 16 regions. The AT and AT asymmetries are significantly different among the different regions. This effect can be explained by the rich resonant structure of the hadronic four-body decay [ 30 ] that produces different FSI effects over the phase space. – 7 – JHEP10(2014)005 Phase space region 0 10 20 30 ] -2 [10 T A -40 -30 -20 -10 0 10 20 30 40 (a) LHCb Phase space region 0 10 20 30 ] -2 [10 T A -40 -30 -20 -10 0 10 20 30 40 (b) LHCb Phase space region 0 10 20 30 ] -2 [10 CP -oddT a -8 -6 -4 -2 0 2 4 6 8 10 (c) LHCb /ndf = 26.4/32 2 χ Figure 4 . Distributions of the asymmetry parameters (a) AT , (b) AT and (c) aT-odd CP in 32 regions of the phase space. -1 -1 -0.9 ] -2 [10 T A -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 decay time [ps] 0 D 0 0.2 0.4 0.6 (a) LHCb 4 3.9 4 -1 -1 -0.9 ] -2 [10 T A -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 decay time [ps] 0 D 0 0.2 0.4 0.6 (b) LHCb 4 3.9 4 -1 -1 -0.9 ] -2 [10 CP -oddT a -8 -6 -4 -2 0 2 4 6 8 10 decay time [ps] 0 D 0 0.2 0.4 0.6 (c) LHCb /ndf = 1.3/4 2 χ 4 3.9 4 Figure 5 . Distributions of the asymmetry parameters (a) AT , (b) AT and (c) aT-odd CP as a function of the D0 decay time. For aT-odd CP , the value of the χ2/ndf for the CP conservation hypothesis, represented by a dashed line, is also quoted. The scale is broken for the first and last bin. The aT-odd CP distribution in D0 decay time is shown in figure 5and the results for the different decay time bins are reported in table 5in appendix B. The compatibility with the CP conservation hypothesis is verified by means of a χ2 test considering statistical and systematic uncertainties as in the previous case; a value of χ2/ndf = 1 . 3 / 4 is obtained, corresponding to a p -value of 86%. Consistent results are obtained when using different divisions of the decay time in 3 and 5 intervals compatible with the CP conservation hypothesis with p -values of 92% and 83%, respectively. This result is consistent with no time-dependent CPV . The AT and AT asymmetry parameters do not show any significant dependence as a function of the decay time, and the results are compatible with constant functions with p-values of 80% and 38%, respectively. 5 Systematic uncertainties The sources of systematic uncertainty and their relative contributions to the total uncertainty are listed in table 2. The contamination from prompt D0 decays affects the asymmetry A according to A→A (1 −f ) + fAd , where f is the fraction of the contamination in the selected sample – 8 – JHEP10(2014)005 [21] I. Belyaev et al., Handling of the generation of primary events in Gauss, the LHCb simulation framework,IEEE Nucl. Sci. Symp. Conf. Rec. 2010 (2010) 1155. [22] D.J. Lange, The EvtGen particle decay simulation package,Nucl. Instrum. Meth. A 462 (2001) 152 [INSPIRE]. [23] GEANT4 collaboration, J. Allison et al., GEANT4: developments and applications,IEEE Trans. Nucl. Sci. 53 (2006) 270. [24] GEANT4 collaboration, S. Agostinelli et al., GEANT4: a simulation toolkit,Nucl. Instrum. Meth. A 506 (2003) 250 [INSPIRE]. [25] M. Clemencic et al., The LHCb simulation application, Gauss: design, evolution and experience,J. Phys. Conf. Ser. 331 (2011) 032023 [INSPIRE]. [26] Particle Data Group collaboration, J. Beringer et al., Review of Particle Physics (RPP), Phys. Rev. D 86 (2012) 010001 [INSPIRE]. [27] M. Gronau, Resonant two-body D decays,Phys. Rev. Lett. 83 (1999) 4005 [hep-ph/9908237] [INSPIRE]. [28] N. Cabibbo and A. Maksymowicz, Angular correlations in Ke-4 decays and determination of low-energy π−πphase shifts,Phys. Rev. 137 (1965) B438. [29] J.F. Donoghue, Is D0→ϕK0 really a clear signal for the annihilation diagram?,Phys. Rev. D 33 (1986) 1516 [INSPIRE]. [30] CLEO collaboration, M. Artuso et al., Amplitude analysis of D0→K+K−π+π− ,Phys. Rev. D 85 (2012) 122002 [arXiv:1201.5716] [INSPIRE]. – 15 – JHEP10(2014)005 The LHCb collaboration R. Aaij41, B. Adeva37, M. Adinolfi46, A. Affolder52, 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, 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, M.-O. Bettler47, M. van Beuzekom41, A. Bien11, S. Bifani45, T. Bird54, A. Bizzeti17,i, P.M. Bjørnstad54, T. Blake48, F. Blanc39, J. Blouw10, S. Blusk59, V. Bocci25, A. Bondar34, N. Bondar30,38, W. Bonivento15,38, S. Borghi54, A. Borgia59, M. Borsato 7 , T.J.V. Bowcock 52 , E. Bowen 40 , C. Bozzi 16 , T. Brambach 9 , J. Bressieux 39 , D. Brett 54 , M. Britsch 10 , T. Britton 59 , J. Brodzicka 54 , N.H. Brook 46 , H. Brown 52 , A. Bursche 40 , G. Busetto 22,r , J. Buytaert 38 , S. Cadeddu 15 , R. Calabrese 16,f , M. Calvi 20,k , M. Calvo Gomez 36,p , P. Campana 18,38 , D. Campora Perez 38 , A. Carbone 14,d , G. Carboni 24,l , R. Cardinale 19,38,j , A. Cardini 15 , L. Carson 50 , K. Carvalho Akiba2, G. Casse52, L. Cassina20, L. Castillo Garcia38, M. Cattaneo38, Ch. Cauet9, R. Cenci58, M. Charles8, Ph. Charpentier38, M. Chefdeville4, S. Chen54, S.-F. Cheung55, N. Chiapolini40, M. Chrzaszcz40,26, K. Ciba38, X. Cid Vidal38, G. Ciezarek53, P.E.L. Clarke50, M. Clemencic38, H.V. Cliff47, J. Closier38, V. Coco38, J. Cogan6, E. Cogneras5, L. Cojocariu29, P. Collins38, A. Comerma-Montells11, A. Contu15, A. Cook46, M. Coombes46, S. Coquereau8, G. Corti38, M. Corvo16,f , I. Counts56, B. Couturier38, G.A. Cowan50, D.C. Craik48, M. Cruz Torres60, S. Cunliffe53, R. Currie50, C. D’Ambrosio38, 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, D. Decamp4, M. Deckenhoff9, L. Del Buono8, N. D´el´eage4, D. Derkach55, O. Deschamps5, F. Dettori38, A. Di Canto38, H. Dijkstra38, S. Donleavy52, F. Dordei11, M. Dorigo39, A. Dosil Su´arez37, 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¨arber11, C. Farinelli41, N. Farley45, S. Farry52, RF 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. Frosini17,38,g, J. Fu21,38, E. Furfaro24,l, A. Gallas Torreira37, D. Galli14,d, S. Gallorini22, S. Gambetta19,j, M. Gandelman2, P. Gandini59, Y. Gao3, J. Garc´ıa Pardi˜nas37, J. Garofoli59, J. Garra Tico47, L. Garrido36, C. Gaspar38, R. Gauld55, L. Gavardi9, G. Gavrilov30, A. Geraci21,v, E. Gersabeck11, M. Gersabeck54, T. Gershon48, Ph. Ghez4, A. Gianelle22, S. Gian`ı39, V. Gibson47, L. Giubega29, V.V. Gligorov38, C. G¨obel60, D. Golubkov31, A. Golutvin53,31,38, A. Gomes1,a, C. Gotti20, M. Grabalosa G´andara 5 , R. Graciani Diaz 36 , L.A. Granado Cardoso 38 , E. Graug´es 36 , G. Graziani 17 , A. Grecu29, E. Greening55, S. Gregson47, P. Griffith45, L. Grillo11, O. Gr¨unberg62, 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. Head38, V. Heijne41, K. Hennessy52, P. Henrard5, L. Henry8, J.A. Hernando Morata37, E. van Herwijnen38, M. Heß62, A. Hicheur1, D. Hill55, M. Hoballah5, C. Hombach54, W. Hulsbergen41, P. Hunt55, N. Hussain55, D. Hutchcroft52, D. Hynds 51 , M. Idzik 27 , P. Ilten 56 , R. Jacobsson 38 , A. Jaeger 11 , J. Jalocha 55 , E. Jans 41 , P. Jaton 39 , – 16 – JHEP10(2014)005 A. Jawahery 58 , F. Jing 3 , M. John 55 , D. Johnson 55 , C.R. Jones 47 , C. Joram 38 , B. Jost 38 , N. Jurik 59 , M. Kaballo9, S. Kandybei43, W. Kanso6, M. Karacson38, T.M. Karbach38, S. Karodia51, M. Kelsey59, I.R. Kenyon45, T. Ketel42, B. Khanji20, C. Khurewathanakul39, S. Klaver54, K. Klimaszewski28, O. Kochebina7, M. Kolpin11, I. Komarov39, R.F. Koopman42, P. Koppenburg41,38, M. Korolev32, A. Kozlinskiy41, L. Kravchuk33, K. Kreplin11, M. Kreps48, G. Krocker11, P. Krokovny34, F. Kruse9, W. Kucewicz26,o, M. Kucharczyk20,26,38,k, V. Kudryavtsev34, K. Kurek28, T. Kvaratskheliya31, V.N. La Thi39, D. Lacarrere38, G. Lafferty54, 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`evre5, A. Leflat32, J. Lefran¸cois7, S. Leo23, O. Leroy6, T. Lesiak26, B. Leverington11, Y. Li3, T. Likhomanenko63, M. Liles 52 , R. Lindner 38 , C. Linn 38 , F. Lionetto 40 , B. Liu 15 , S. Lohn 38 , I. Longstaff 51 , J.H. Lopes 2 , N. Lopez-March39, P. Lowdon40, H. Lu3, D. Lucchesi22,r, H. Luo50, A. Lupato22, E. Luppi16,f , O. Lupton55, F. Machefert7, I.V. Machikhiliyan31, F. Maciuc29, O. Maev30, S. Malde55, A. Malinin63, G. Manca15,e, G. Mancinelli6, A. Mapelli38, J. Maratas5, J.F. Marchand4, U. Marconi14, C. Marin Benito36, P. Marino23,t, R. M¨arki39, J. Marks11, G. Martellotti25, A. Martens8, A. Mart´ın S´anchez7, M. Martinelli39, D. Martinez Santos42, F. Martinez Vidal64, D. Martins Tostes2, A. Massafferri1, 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. Milanes8, M.-N. Minard4, N. Moggi14, J. Molina Rodriguez60, S. Monteil5, M. Morandin22, P. Morawski27, A. Mord`a6, M.J. Morello23,t, J. Moron 27 , A.-B. Morris 50 , R. Mountain 59 , F. Muheim 50 , K. M¨uller 40 , M. Mussini 14 , B. Muster 39 , 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. O’Hanlon48, A. Oblakowska-Mucha27, V. Obraztsov35, S. Oggero41, S. Ogilvy51, O. Okhrimenko44, R. Oldeman15,e, G. Onderwater65, M. Orlandea29, J.M. Otalora Goicochea2, P. Owen53, A. Oyanguren64, 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. Pazos Alvarez37, A. Pearce54, A. Pellegrino41, M. Pepe Altarelli38, S. Perazzini14,d, E. Perez Trigo37, P. Perret5, M. Perrin-Terrin 6 , L. Pescatore 45 , E. Pesen 66 , K. Petridis 53 , A. Petrolini 19,j , E. Picatoste Olloqui 36 , B. Pietrzyk4, T. Pilaˇr48, D. Pinci25, A. Pistone19, S. Playfer50, M. Plo Casasus37, F. Polci8, A. Poluektov 48,34 , E. Polycarpo 2 , A. Popov 35 , D. Popov 10 , B. Popovici 29 , C. Potterat 2 , E. Price 46 , J.D. Price52, J. Prisciandaro39, A. Pritchard52, C. Prouve46, V. Pugatch44, A. Puig Navarro39, G. Punzi 23,s , W. Qian 4 , B. Rachwal 26 , J.H. Rademacker 46 , B. Rakotomiaramanana 39 , M. Rama 18 , 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. Robbe 7 , A.B. Rodrigues 1 , E. Rodrigues 54 , P. Rodriguez Perez 54 , S. Roiser 38 , V. Romanovsky 35 , A. Romero Vidal37, M. Rotondo22, J. Rouvinet39, T. Ruf38, H. Ruiz36, P. Ruiz Valls64, J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B. Saitta15,e, V. Salustino Guimaraes2, C. Sanchez Mayordomo64, B. Sanmartin Sedes37, R. Santacesaria25, C. Santamarina Rios37, E. Santovetti24,l, A. Sarti18,m, C. Satriano25,n, A. Satta24, D.M. Saunders46, M. Savrie16,f , D. Savrina31,32, M. Schiller42, H. Schindler38, M. Schlupp9, M. Schmelling10, B. Schmidt38, O. Schneider39, A. Schopper38, M.-H. Schune7, R. Schwemmer38, B. Sciascia18, A. Sciubba25, M. Seco37, 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. Shevchenko63, A. Shires9, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46, T. Skwarnicki59, N.A. Smith52, E. Smith55,49, E. Smith53, J. Smith47, M. Smith54, H. Snoek41, M.D. Sokoloff57, – 17 – JHEP10(2014)005 F.J.P. Soler51, F. Soomro39, D. Souza46, B. Souza De Paula2, B. Spaan9, A. Sparkes50, P. Spradlin51, S. Sridharan38, F. Stagni38, M. Stahl11, S. Stahl11, O. Steinkamp40, O. Stenyakin35, S. Stevenson55, S. Stoica29, S. Stone59, B. Storaci40, S. Stracka23,38, M. Straticiuc29, U. Straumann 40 , R. Stroili 22 , V.K. Subbiah 38 , L. Sun 57 , W. Sutcliffe 53 , K. Swientek 27 , S. Swientek 9 , V. Syropoulos42, M. Szczekowski28, P. Szczypka39,38, D. Szilard2, T. Szumlak27, S. T’Jampens4, M. Teklishyn7, G. Tellarini16,f , F. Teubert38, C. Thomas55, E. Thomas38, J. van Tilburg41, V. Tisserand4, M. Tobin39, S. Tolk42, L. Tomassetti16,f , D. Tonelli38, S. Topp-Joergensen55, N. Torr55, E. Tournefier4, S. Tourneur39, M.T. Tran39, M. Tresch40, A. Tsaregorodtsev6, P. Tsopelas41, N. Tuning41, M. Ubeda Garcia38, A. Ukleja28, A. Ustyuzhanin63, U. Uwer11, C. Vacca15, V. Vagnoni14, G. Valenti14, A. Vallier7, R. Vazquez Gomez18, P. Vazquez Regueiro37, C. V´azquez Sierra37, S. Vecchi16, J.J. Velthuis46, M. Veltri17,h, G. Veneziano39, M. Vesterinen11, B. Viaud 7 , D. Vieira 2 , M. Vieites Diaz 37 , X. Vilasis-Cardona 36,p , A. Vollhardt 40 , D. Volyanskyy 10 , D. Voong46, A. Vorobyev30, V. Vorobyev34, C. Voß62, H. Voss10, J.A. de Vries41, R. Waldi62, C. Wallace 48 , R. Wallace 12 , J. Walsh 23 , S. Wandernoth 11 , J. Wang 59 , D.R. Ward 47 , N.K. Watson 45 , D. Websdale53, M. Whitehead48, J. Wicht38, D. Wiedner11, G. Wilkinson55, M.P. Williams45, M. Williams56, H.W. Wilschut65, 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. Yang 3 , X. Yuan 3 , O. Yushchenko 35 , M. Zangoli 14 , M. Zavertyaev 10,b , L. Zhang 59 , W.C. Zhang 12 , Y. Zhang3, A. Zhelezov11, A. Zhokhov31, L. Zhong3, A. Zvyagin38 1Centro Brasileiro de Pesquisas F´ısicas (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, Universit´e de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France 5Clermont Universit´e, Universit´e Blaise Pascal, CNRS/IN2P3, LPC, Clermont-Ferrand, France 6CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France 7LAL, Universit´e Paris-Sud, CNRS/IN2P3, Orsay, France 8LPNHE, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, CNRS/IN2P3, Paris, France 9Fakult¨at Physik, Technische Universit¨at Dortmund, Dortmund, Germany 10 Max-Planck-Institut f¨ur Kernphysik (MPIK), Heidelberg, Germany 11 Physikalisches Institut, Ruprecht-Karls-Universit¨at 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 dell’INFN 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, Krak´ow, Poland 27 AGH - University of Science and Technology, Faculty of Physics and Applied Computer Science, Krak´ow, Poland 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 – 18 – JHEP10(2014)005 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 F´ed´erale de Lausanne (EPFL), Lausanne, Switzerland 40 Physik-Institut, Universit¨at Z¨urich, Z¨urich, 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 Pontif´ıcia Universidade Cat´olica 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 Institut f¨ur Physik, Universit¨at Rostock, Rostock, Germany, associated to 11 63 National Research Centre Kurchatov Institute, Moscow, Russia, associated to 31 64 Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC, Valencia, Spain, associated to 36 65 KVI - University of Groningen, Groningen, The Netherlands, associated to 41 66 Celal Bayar University, Manisa, Turkey, associated to 38 aUniversidade Federal do Triˆangulo Mineiro (UFTM), Uberaba-MG, Brazil bP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS), Moscow, Russia cUniversit`a di Bari, Bari, Italy dUniversit`a di Bologna, Bologna, Italy eUniversit`a di Cagliari, Cagliari, Italy fUniversit`a di Ferrara, Ferrara, Italy gUniversit`a di Firenze, Firenze, Italy hUniversit`a di Urbino, Urbino, Italy iUniversit`a di Modena e Reggio Emilia, Modena, Italy jUniversit`a di Genova, Genova, Italy kUniversit`a di Milano Bicocca, Milano, Italy lUniversit`a di Roma Tor Vergata, Roma, Italy – 19 – JHEP10(2014)005 mUniversit`a di Roma La Sapienza, Roma, Italy nUniversit`a della Basilicata, Potenza, Italy oAGH - University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications, Krak´ow, Poland pLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain qHanoi University of Science, Hanoi, Viet Nam rUniversit`a di Padova, Padova, Italy sUniversit`a di Pisa, Pisa, Italy tScuola Normale Superiore, Pisa, Italy uUniversit`a degli Studi di Milano, Milano, Italy vPolitecnico di Milano, Milano, Italy – 20 –