Qian, W.

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Measurements of gamma angle using B(s) –> DKK atLHCbW. QianTo cite this version:W. Qian. Measurements of gamma angle using B(s) –>DKK at LHCb. XLVIIIth Rencontres deMoriond - QCD and High Energy Interactions, Mar 2013, La Thuile, Italy. <in2p3-00815898>HAL Id: in2p3-00815898http://hal.in2p3.fr/in2p3-00815898Submitted on 21 Nov 2013HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.Measurement of γ Angle Using B → DK at LHCbWenbin Qianon behalf of the LHCb CollaborationLaboratoire d’Annecy-le-Vieux de Physique des ParticulesUniversite´ de Savoie, CNRS/IN2P3, Annecy-le-Vieux, FranceMeasurements of the CKM angle γ via tree-level b → u and b → c interference are importantfor testing the Standard Model through the CKM unitarity constraint. In these proceedings,CP violation measurements with B → DK decays using 1 fb−1 of data collected in 2011 byLHCb are described, where 2-body (pi+pi−, K+K−, K+pi− and K−pi+), 3-body (Kspi+pi−and KsK+K−) and 4-body (K+pi−pi+pi− and K−pi+pi+pi−) D0 decays are considered. Acombined measurement of γ using the above channels is also presented.1 The LHCb ExperimentThe LHCb apparatus 1 is an single-armed forward spectrometer covering the pseudo rapidityrange 2 < η < 5, designed for the study of particles containing b or c quarks. The trackingsystem has a momentum resolution ∆p/p that varies from 0.4% at 5 GeV/c and 0.6% at 100GeV/c which gives a mass resolution of 10−25 MeV/c2 depending on decay modes. One of thecrucial points for the measurement of γ through B to open charm decays is hadron identification.Two ring-imaging Cherenkov detectors are used to identify charged hadrons and they offer a95% kaon identification efficiency with a 5% pion-to-kaon misidentification rate.The LHCb trigger consists of a hardware trigger based on information from the calorimeterand muon systems, followed by a software stage, which applies a full event reconstruction. Thehardware trigger reduces the event rates from 40 MHz to 1 MHz which is further reduced to 5kHz by the software trigger. It offers an efficiency around 20-50% for B decays with hadrons,depending on final states.During the past two years of operation, the LHCb experiment collected 1.0 fb−1 of data at 7TeV in 2011 and around 2 fb−1 at 8 TeV in 2012 with constant instantaneous luminosity duringeach bunch fill. The constant luminosity makes physics analysis less affected by pile-up effects.The results in this paper are obtained with the first 1 fb−1 of data.2 The CKM Angle γThe CKM angle γ, defined as γ = arg[−VudV∗ub/(VcdV∗cb)], is one of the least well-measured pa-rameters of the CKM unitarity triangle defined through the relation VudV∗ub + VcdV∗cb + VtdV∗tb = 0.A precise measurement of γ from tree-level interference is crucial to overconstrain the unitaritytriangle while the comparison between γ at tree-level and γ at loop-level may shed light onnew physics. As new physics is not expected to affect tree-level processes, γ at tree-level istheoretically clean and the relative precision δγ/γ predicted by Standard Model is at O(10−6).The γ angle can be accessed by different channels with interference between b → c and b → utransitions, it is thus important to combine measurements from different modes for better preci-sion. It has been measured by various experiments 2,3; the current combined precision is around10− 12◦ 4,5Several methods to measure γ in tree decays using B− → DK− a are established, where Dindicates a D0 or D¯0 in this paper. There are three main methods according to different typeof D decays:1. : Gronau-London-Wyler (GLW) method 6: γ is obtained through interference betweenB− → D0K− and B− → D¯0K− where the D0 or D¯0 decays to 2-body CP eigenstates, i.e.D → K+K−, D → pi+pi− etc.2. : Atwood-Dunietz-Soni (ADS) method 7: γ is accessed through interference between thefavoured b → c transition combined with the double-Cabbibo-suppressed D0 → K+pi−decay, and the suppressed b → u transition combined with the Cabbibo-favoured D¯0 →K+pi− decay.3. : Giri-Grossman-Soffer-Zupan (GGSZ) method 8:γ is obtained through interference be-tween B− → D0K− and B− → D¯0K− where theD0 or D¯0 meson decays to self-conjugatedmulti-body final states, i.e. D → Kspi+pi−, D → KsK+K− etc.The decay rate can be generally written as:Γ(B± → D[→ f ]K±) = A2c(r2D + (rKB )2 + 2rKB rDRe(ei(δKB+δD±γ))), (1)where δKB , δD are strong phase difference for B and D decays with different transition; rB is theamplitude ratio between b → u and b → c transitions; rD is the ratio of D decay amplitudes;Ac is the normalisation factor which can be cancelled out. rKB is around 0.1 for B → DK whichgives better sensitivity on γ than B → Dpi decays (rpiB ∼ 0.01)9. Time-integrated CP violationusing the above three methods with B → DK are measured by LHCb and discussed in thefollowing section.3 γ studies with B → DK at LHCb3.1 Two-body D DecaysThe following two-body D decay channels are studied: D → K+K−, D → pi+pi−, D0 →K+pi− and D0 → K−pi+ with which a combined GLW and ADS analysis is performed 10. Theobservables, for the GLW mode, are RCP+ = 2Γ(B−→DCP+K−)+Γ(B+→DCP+K+)Γ(B−→D0K−)+Γ(B+→D¯0K+)and ACP+ =Γ(B−→DCP+K−)−Γ(B+→DCP+K+)Γ(B−→D0K−)+Γ(B+→D¯0K+), which depend on γ by RCP+ = 1 + (rKB )2 + 2rKB cos δKB cos γand ACP+ =2rKBsin δKBsin γRCP+. Similar variables and their relationship with rKB , δKB , γ can be definedand deduced for the ADS mode 7.aCharge-conjugation is implied throughout this paper unless otherwise stated.The above defined variables are calculated using signal yields in B− and B+ decays, wheremost of efficiency effects cancel out except those from detection asymmetry and productionasymmetry which are obtained from control samples. We obtain the following results:RCP+ = 1.007± 0.038± 0.012,ACP+ = 0.145± 0.032± 0.010for the GLW method, averaged over D → K+K− and D → pi+pi−, which corresponds to a CPviolation of 4.5σ significance andRADS(K) = 0.0152± 0.0020± 0.0004,AADS(K) = −0.52± 0.15± 0.02for the B → DK ADS method, which corresponds to a 4.0σ significance CP violation. The firstuncertainty of the result is statistical and the second one is the systematic uncertainty. Com-bining the two methods, we have the first observation of direct CP violation at 5.8σ significancein the 2-body D decays of B → DK.3.2 Three-body D DecaysA model independent method is applied for the GGSZ mode with D → Kspi+pi− and D →KsK+K− 11 using inputs from CLEO measurements 12. The Dalitz plots are divided intodifferent bins (16 for D → Kspi+pi− and 4 for D → KsK+K−) according to the distributionsobtained from Dalitz analysis. It should be noted that the analysis is independent from Dalitzmodelling, any deviation from reality only reduces the sensitivity to γ but does not introducebias. The number of events in each bin is given byN+±i = hB+ [K∓i + (x2+ + y2+)K∓i + 2√KiK−i(x+c±i ∓ y+s±i)], (2)N−±i = hB− [K±i + (x2− + y2−)K∓i + 2√KiK−i(x−c±i ± y−s±i)], (3)where hB± is the normalisation factor for B±, Ki represent the Dalitz distribution in flavour-tagged D decays; ci and si are inputs from CLEO measurements. x± = Re[rKB ei(δKB±γ)] andy± = Im[rKB ei(δKB±γ)] are the quantities to be measured. In total, we have around 660 signals inthe Kspi+pi− mode and 100 signals in the KsK+K− mode. The best fitted value for x± and y±are:x− = (0.0± 4.3± 1.5± 0.6)× 10−2,y− = (2.7± 5.2± 0.8± 2.3)× 10−2,x+ = (−10.3± 4.5± 1.8± 1.4)× 10−2,y+ = (−0.9± 3.7± 0.8± 3.0)× 10−2,where the first error is the statistical uncertainty, the second one is the systematic uncertaintyand the third one is the uncertainty from CLEO inputs. Using the above value, we can extra γfrom the GGSZ mode only, which give a value of (44+43−38)◦.3.3 Four-body D DecaysThere are also measurements using 4-body decays D0 → K−pi+pi−pi+ and D0 → K+pi−pi+pi− 13.An analysis similar to 2-body ADS analysis is performed. There are around 40 signals observedfor the ADS B → DK mode which corresponds to 5.7σ observation and around 160 signals forthe ADS B → Dpi mode which corresponds to more than 10σ observation. The measured valuefor RK3piADS(K) and AK3piADS(K) are 0.0124±0.0027 and −0.42±0.22 respectively. This is then usedto give constraint on rKB which yields rKB = 0.097± 0.011.]°[γ1-CL00.20.40.60.810 20 40 60 80 100 120 140 160 18015.2−+16.1> = 71.1γ<68%95%LHCbPreliminary]°[Bδ1-CL00.20.40.60.810 20 40 60 80 100 120 140 160 18015.5−+12.6> = 112.0Bδ<68%95%LHCbPreliminaryBr0.04 0.06 0.08 0.1 0.12 0.14 0.161-CL00.20.40.60.810.0082−+0.0083> = 0.0919B<r68%95%LHCbPreliminaryFigure 1: 1 - CL curves for γ (left), δB (centre) and rKB (right) from the combination of the measurements usingB → DK decays.3.4 γ CombinationUsing the above measurements, the recent evidence for a difference in the CP asymmetries inD → K+K− and D → pi+pi−, ∆adirCP = (−0.656 ± 0.154) × 10−2 14 and the CLEO inputs 15, acombination is made to extra γ 16. A frequentist technique is used with D mixing effect ignoredat this level. The confidence level (CL) curves of γ, δB and rKB are shown in Fig. 1. The mostprobable value of γ is 71.1 with 68% CL interval [55.4, 87.7]◦ and 95% CL interval [41.4, 101.3]◦.The fitted value for rKB and δKB are 0.092±0.008 and (112.0+12.6−15.5)◦. The results are in agreementwith the combined results measured by Babar 2 and Belle 3 with similar precision.4 ConclusionIn this paper, the results of B → DK measurement at the LHCb experiment using 1 fb−1 ofdata are described. A combination is made which gives γ = 71.1◦ with an uncertainty around16◦; it is in agreement with the combined results published by other experiments.References1. A. A. Alves Jr. et al. (LHCb Collaboration), JINST 3 (2008) S080052. J. P. Lees et al. (BABAR Collaboration), arXiv: 1301.10293. K. Trabelsi (Belle Collaboration), arXiv: 1301.20334. J. Charles et al. (CKMfitter Group), Eur. Phys. J. C41, 1(2005), updated results andplots available at: http://ckmfitter.in2p3.fr5. D. Derkach (UTfit Collaboration), arXiv: 1301.3300, updated results and plots availableat: http://www.utfit.org/UTfit6. M. Gronau and D. Wyler, Phys. Lett. B 253 (1991) 483; M. Gronau and D. London,Phys. Lett. B 265 (1991) 1727. D. Atwood, I. Dunietz and A. Soni, Phys. Rev. Lett. 78 (1997) 32578. A. Giri, Y. Grossman, A. Soffer and J. Zupan, Phys. Rev. D68 (2003) 0540189. J. Beringer et al. (Particle Data Group), Phys. Rev. D86, 010001 (2012)10. R. aaij et al. (LHCb Collaboration), Phys. Lett. B 712 (2012) 203, arXiv: 1203.366211. R. aaij et al. (LHCb Collaboration), Phys. Lett. B 718 (2012) 43, arXiv: 1209.586912. J. Libby et al. (CLEO Collaboration), Phys. Rev. D80, 031105 (2009)13. R. aaij et al. (LHCb Collaboration), arXiv: 1303.464614. Y. Amhis et al. (Heavy Flavor Averaging Group), arXiv: 1207.115815. N. Lowrey et al. (CLEO Collaboration), Phys. Rev. D80, 031105 (2009)16. R. Aaij et al. (LHCb Collaboration), LHCb-CONF-2012-032

Measurements of gamma angle using B(s) --> DKK at LHCb

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