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First steps toward γ from B + →D 0 (K 0 π + π - )K + with

First steps toward γ from B + →D 0 (K 0 π + π - )K + with. Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby. Measuring γ : B + →D 0 (K 0 π + π - )K +. γ is the weak phase between b→cus (  V cb ) and b→ucs (  V ub )

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First steps toward γ from B + →D 0 (K 0 π + π - )K + with

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  1. First steps toward γfrom B+→D0(K0π+π-)K+ with Tom Barber, Val Gibson, Cristina Lazzeroni and Jim Libby LHCb UK Meeting, Dublin

  2. Measuring γ: B+→D0(K0π+π-)K+ • γ is the weak phase between b→cus (Vcb) and b→ucs (Vub) • g can be extracted from the interference of these two processes in charged BD0K decays with D0/D0 decaying to a common final state • rBis 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 D0/D0(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 No need for a time-dependent analysis LHCb UK Meeting, Dublin

  3. Measuring γ: B+→D0(K0π+π-)K+ PRD 63, 036005 (2001) and PRD 68, 054018 (2003) • A method proposed by ADS/Giri, Grossman, Soffer and Zupan alleviates some of the problems by utilising three body Cabbibo allowed decays of the D0/D0 • BR(D0→K0π+π-)=(5.97±0.35)% • BR(D0→K+K-)=(3.89±0.14)×10-3% • Also, large strong phases between the intermediate resonances allows the the extraction of rB, δ and γ by studying the Dalitz distribution of events where LHCb UK Meeting, Dublin

  4. Not everything in black and white makes sense 2nd 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: ρ(770) Doubly Cabbibo suppressed K* Breit-Wigner + non-resonant LHCb UK Meeting, Dublin

  5. Measuring the Dalitz model • B-factories use a O(100k) samples of D+*→D0π+,D0→K0π+π- to measure amplitudes and phases-vary model for systematics • LHCb can exploit these and results from CLEO-c K*(892) ρ(770) DCS K*(892) LHCb UK Meeting, Dublin

  6. γ(deg) 1σ 2σ Measuring γ: B+→D0(K0π+π-)K+ hep-ex/0504039 B+ B- g = 70°±31°±11°±13° D* and D combined Exp. systematic Dalitz Model error Belle do significantly better: reason is measured rB=0.21±0.08 rB vs σ() PRD 70, 072003 (2004) g = 68°±14°±13°±11° 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 1.6×105 incl. B and 3×104 min. bias • Limited statistic samples • Selection in DC04v2 stripping • Currently being revisited but a very promising start LL K0S DD K0S 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 LHCb UK Meeting, Dublin

  9. π+ π- B+ D0 π+ K0S IP π- K+ HLT • K0S complicates this significantly • Only long tracks: • 30% of selected signal events LL K short • εHLT/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 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 B0→D0 K* studies • Want event model in LHCb framework and • Standalone: acceptance studies and fitting • K-matrix • Transfer BABAR/Belle/CLEO-C measurements LHCb UK Meeting, Dublin

  11. B+→D0(K0K+K-)K+ • Same method works with π→K in D0decay • Reduced BF: • BF(D0→K0K+K-) = (1.03±0.10)% • BF(D0→K0 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/0507026) • what is the sensitivity to γ? • Generated samples in Cambridge to study in parallel to the Kππ mode PDG ‘04 LHCb UK Meeting, Dublin

  12. Outlook • Other issues to feedback to the optimization studies: • fitting for γ,  and rB and • systematics • Understanding acceptance, B+→D0(K0K+K-)K+ and HLT first • Looking forward to a successful Oxbridge collaboration….. LHCb UK Meeting, Dublin

  13. LHCb UK Meeting, Dublin

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