24/08/2005LHCb UK Meeting, Dublin1 First steps toward γ from B + →D 0 (K 0 π + π - )K + with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby

24/08/2005 LHCb UK Meeting, Dublin 2 γ is the weak phase between b→cus (  V cb ) and b→ucs (  V ub )  can be extracted from the interference of these two processes in charged B  D 0 K decays with D 0 /D 0 decaying to a common final state  r B is the relative colour suppression between the two modes O(0.1) – dilutes sensitivity to γ  δ is the strong phase difference-invariant under CP Several methods available to extract γ from two-body decays of the D 0 /D 0 (Gronau- London-Wyler and Atwood-Dunietz-Soffer) Requires 3+charge conjugate modes to extract the parameters  some of these modes have very small BFs which are not observed with current B-factory statistics  Will be interesting for LHCb (see reoptimised TDR for GLW): but γ ambiguities and doubly Cabbibo suppressed decays interfere Measuring γ: B + →D 0 (K 0 π + π - )K + No need for a time-dependent analysis

24/08/2005 LHCb UK Meeting, Dublin 3 Measuring γ: B + →D 0 (K 0 π + π - )K + A method proposed by ADS/Giri, Grossman, Soffer and Zupan alleviates some of the problems by utilising three body Cabbibo allowed decays of the D 0 /D 0 BR(D 0 →K 0 π + π - )=(5.97±0.35)% BR(D 0 →K + K - )=(3.89±0.14)×10 -3 % Also, large strong phases between the intermediate resonances allows the the extraction of r B, δ and γ by studying the Dalitz distribution of events where PRD 63, (2001) and PRD 68, (2003)

24/08/2005 LHCb UK Meeting, Dublin 4 Not everything in black and white makes sense ρ(770) Doubly Cabbibo suppressed K * 2 nd derivative of likelihood w.r.t. γ Regions of the Dalitz plot with the largest interferences are most sensitive to γ Need good model for Dalitz amplitudes Belle/Babar have use an isobar model with: Breit-Wigner + non-resonant

24/08/2005 LHCb UK Meeting, Dublin 5 Measuring the Dalitz model B-factories use a O(100k) samples of D + *→D 0 π +,D 0 →K 0 π + π - to measure amplitudes and phases-vary model for systematics LHCb can exploit these and results from CLEO-c K*(892) DCS K*(892) ρ(770)

24/08/2005 LHCb UK Meeting, Dublin 6 Measuring γ: B + →D 0 (K 0 π + π - )K +  = 70° ± 31° ± 11° ± 13° D* and D combined Dalitz Model error Belle do significantly better: reason is measured r B = 0.21±0.08  = 68° ± 14° ± 13° ± 11° γ(deg) 1σ1σ 2σ2σ r B vs σ(  ) Exp. systematic hep-ex/ PRD 70, (2004) B+ BB

24/08/2005 LHCb UK Meeting, Dublin 7 Selection studies so far (T. Barber) Selection to maximise signal to background:  1 year signal yield = 6300  No events in 1.6×10 5 incl. B and 3×10 4 min. bias Limited statistic samples  Selection in DC04v2 stripping Currently being revisited but a very promising start LL K0S DD K0S

24/08/2005 LHCb UK Meeting, Dublin 8 Next steps: selection and backgrounds Understanding Dalitz acceptance key to the analysis  Assessing this from Tom’s selection Selection optimisation and improvement  Understand and cross check current selection, then  Optimisation non-standard due to extraction from fit to Dalitz space and importance of systematic uncertainties Statistical limits in background MC samples  Sideband techniques for data  Good understanding of Dalitz distribution of background

24/08/2005 LHCb UK Meeting, Dublin 9 HLT K 0 S complicates this significantly Only long tracks: 30% of selected signal events LL K short ε HLT /track ≈93%, therefore 5-track efficiency ≈70% overall reduces yield to 1300/annum Including DD non-trivial as topology is under constrained for a kinematic fit No need to panic yet as B-factories are performing measurements with 5 times less statistics-but clearly increased yields desirable IP B+B+ D0D0 K+K+ π+π+ π-π- π+π+ π-π- K0SK0S

24/08/2005 LHCb UK Meeting, Dublin 10 Event model Complex Dalitz model required:  Current simulation phase space: OK for Dalitz efficiency then reweight to any model….. unless the correlations amongst the daughters distort Dalitz acceptance  In LHCb isobar model already implemented for B 0 →D 0 K* studies Want event model in LHCb framework and Standalone: acceptance studies and fitting K-matrix  Transfer BABAR/Belle/CLEO-C measurements

24/08/2005 LHCb UK Meeting, Dublin 11 B + →D 0 (K 0 K + K - )K + Same method works with π→K in D 0 decay  Reduced BF: BF(D 0 →K 0 K + K - ) = (1.03±0.10)% BF(D 0 →K 0 π + π - ) = (5.97±0.35)%  But using RICH info maybe a big help for background suppression Dalitz model has less resonances but complex threshold effects (Babar hep-ex/ )  what is the sensitivity to γ? Generated samples in Cambridge to study in parallel to the Kππ mode PDG ‘04

24/08/2005 LHCb UK Meeting, Dublin 12 Outlook Other issues to feedback to the optimization studies:  fitting for γ,  and r B and  systematics Understanding acceptance, B + →D 0 (K 0 K + K - )K + and HLT first Looking forward to a successful Oxbridge collaboration…..

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