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Hadronic B→DX Decays at LHCb and CDF

Hadronic B→DX Decays at LHCb and CDF. Laurence Carson, Imperial College o n behalf of the LHCb Collaboration CIPANP 2012, St. Petersburg,FL. Outline. Physics motivation: why study hadronic B→DX decays? Selection of recent measurements: Observation of new B s →DD ’ decays ( LHCb )

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Hadronic B→DX Decays at LHCb and CDF

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  1. HadronicB→DX Decays at LHCb and CDF Laurence Carson, Imperial College on behalf of the LHCb Collaboration CIPANP 2012, St. Petersburg,FL

  2. Outline • Physics motivation: why study hadronicB→DX decays? • Selection of recent measurements: • Observation of new Bs→DD’ decays (LHCb) • Improved measurements of Bs→DsDs(LHCb and CDF) • Improved measurements of Bs→DsK and Bs→Dsπ (LHCb) • Observation of B→DKππ decays (LHCb) • Many other interesting results not covered here

  3. Physics Motivation • A variety of interesting physics is accessible using B→DX decays: • Different methods to measure γ with B+/-→D0K+/- decays [talk of K.Akiba]. • The decays Bd→D+D- and Bs→Ds+Ds- can be used to measure γ, using U-spin symmetry [e.g. hep-ph/0310252]. • In addition, Bd→D+D-can be used to measure sin(2β). Belle reported unexpectedly large direct CPV in this mode [hep-ex/0702031]. • The decay Bs→Ds+/-K-/+ allows a theoretically clean γ measurement, uniquely possible at LHCb, via a flavour-tagged and time-dependent analysis [hep-ph/0304027, see also talk of K.Akiba]. • The same methods used to measure γ using B+/-→D0K+/- can also be applied to B+/-→D0K+/-π+π-decays [hep-ph/0211282]. ( )

  4. The LHCb Experiment • Situated on LHC ring; pp collisions at ECM = 7 TeV. (8 TeV in 2012) • Forward arm spectrometer, optimised for study of B and D decays. Hardware trigger reduces event rate to 1MHz, followed by software trigger reducing to several kHz. This allows high trigger efficiency, even on purely hadronic final states.

  5. The CDF Experiment • Situated on TeVatronring; pp collisions at ECM = 1.96 TeV • Central detector, tracks reconstructed by Si vertex detector and drift chamber (COT). • Charged hadron PID using • dE/dx in COT • TOF system between COT and solenoid • Hadronic trigger searches for two oppositely-charged tracks with vertex displaced from primary interaction

  6. Bs→DD’ at LHCb • D mesons are reconstructed as D0→Kπ , D+→Kππ or Ds→KKπ. • Final selection based on BDT for each D type, trained on data using relevant B(s)→Dπ decay (signal) and D mass sidebands (background). • Cross-feeds (and Λc) suppressed using combined mass/PID vetoes. Bd→D+Ds(loose selection) Bs→DsDs LHCb-CONF- 2012-009 1.0/fb Syst dominated by fs/fd(true for all modes) Preliminary • Around five times more precise than previous world average.

  7. Bs→DD’ at LHCb • First observations of Bs→D+Ds (10.1σ) and Bs→D+D-(10.7σ): Preliminary • Both are in agreement with expectations of ≈|Vcd/Vcs|2 = 0.05 and ≈1. Bd,s→D+D- Bd,s→D+Ds(tight selection) LHCb-CONF- 2012-009

  8. Bs→DD’ at LHCb • First observation of Bs→D0D0 (5.4σ), and hint of Bd→D0D0 (2.1σ): Preliminary • Again, this is in agreement with expectations. B-→D0Ds Bd,s→D0D0 LHCb-CONF- 2012-009 • Future plans include measurements of β and γ with Bd→D+D- and Bs→Ds+Ds-, once more data has been collected.

  9. Bs→Ds(*)Ds(*) at CDF • Reconstruct Ds→KKπ, with KK in φ window or Kπ in K* window. • Soft π0 or γ from Ds*→Ds not reconstructed. • Normalisation is made to Bd→DsD-. CDF Note 10721 6.8/fb

  10. Bs→Ds(*)Ds(*) at CDF Third error is from fs/fd and B(Bd→DsD-) • The result for Bs→DsDs is in agreement with the LHCb value. • The inclusive B is: , and can be used to measure ΔΓs, ignoring possible contributions from three-body modes [PLB 316, 567]: • This yields: , which is smaller than ΔΓs measured in Bs→J/ψφ[e.g. LHCb-CONF-2012-002], suggesting that the three-body contribution is sizeable.

  11. Bs→Dsh at LHCb • An accurate measurement of B(Bs→DsK) is an important stepping stone on the path to a γ measurement with this mode [talk of K.Akiba]. • High Bs→Dsπ yield allows benchmark B measurement for Bsmodes. • Final selection uses a BDT, trained on Bs→Dsπdata and optimised for significance of the Bs→DsK signal. • Backgrounds from Λc are vetoed, similarly to the B→DD’ analysis. 0.37/fb hep-ex/ 12041237 Bs→Dsπ Bd→D-π(normalisation)

  12. Bs→Dsh at LHCb: DsK • Tight PID criterion applied to bachelor K, to suppress Bs→Dsπ. • Performance of PID criteria measured on data using D*+→D0(Kπ)π+. • Shape of misidentified Bs→Dsπcomponent determined from data, accounting for effect of PID requirements. • Dsπ yield is left free, and cross-checked against expectation from PID. • Background from Bd→D-K constrained using misID probability of PID criteria. • Cross-check: fitted yield of Bd→DsKagrees with expectation from PDG.

  13. Bs→Dsh at LHCb • Experimental systematics include fit model, and translation of PID performance from D* calibration sample to signal B decays. • For absolute B measurements, additional external systematics include B(Bd→D-π) and LHCb value of fs/fd(from semileptonic decays). • However the D branching fraction uncertainties are subtracted from the fs/fd uncertainty, since fs/fdextraction also depends on these branching fractions. fs/fdonly Experimental, plus B(Bd→D-π) • Total errors are 10% (Dsπ) and 12% (DsK) respectively. • Both measurements significantly improve on the previous world average valuesof (3.2±0.5)x10-3 (Dsπ) and (3.0±0.7)x10-4(DsK).

  14. Observation of B→DKππ • B measured relative to the Cabibbo-favoured B→Dπππ modes. • Tight PID criterion is applied to bachelor K, to suppress B→Dπππ. First observations of (c)Bd→D-Kππ (7.2σ) and (d) B+→D0Kππ(9.0σ). 35/pb (2010) PRL 108, 161801 LHCb trigger in 2011/ 2012 contains improvements leading to higher B→Dhhh yields per pb-1 than in 2010 data

  15. Observation of B→DKππ • In the future, the B- mode will be used to add sensitivity to the γ measurement with B+/-→D0K+/-decays. • Also, method to measure γ with Bs→DsKcan be extended to Bs→DsKππ - search for this mode is underway. • Systematics arise from fit model, PID efficiency and Kππ invariant mass distribution. • Kππ system consistent with decays of excited strange states, such as K1(1270).

  16. Summary • Many interesting physics measurements can be made with hadronicB→DX decays. • Observations made of many new modes: Bs→D+Ds, Bs→D+D-, Bs→D0D0, Bd→D-Kππ and B+→D0Kππ. • Greatly improved measurements of Bs→DsDsand Bs→Dsh. • These measurements open the road to new ways to measure physics parameters such as γ. • Stay tuned for more results in the future! • LHCb expects to collect ≈1.5/fb at 8 TeV in 2012

  17. Backup

  18. Semileptonicfs/fd at LHCb • Can measure fs/(fu+fd) using D0Xμν, D+Xμν, DsXμν, after correcting for cross-feeds. PRD 85, 032008 + 0.011 (syst) fs/(fu + fd) = 0.134 ± 0.004 (stat) – 0.010 • No dependence on pT or η is seen. • Assuming fu=fd, simply doubling this value gives fs/fd.

  19. B→DD’ from hep-ph/07054421 aeiθ is the ratio of penguin to tree amplitudes

  20. Measuring γ with Bs→DsK • The final state Ds-K+ is accessible by both Bs and Bs: • Both diagrams have similar magnitudes, hence large interference between them is possible. • Using a flavour-tagged, time-dependent analysis, we can measure four decay rates - Bsor Bs to Ds+K- or Ds-K+ • From these rates, γ can be extracted in an unambiguous and theoretically clean way.

  21. Measuring γ with Bs→DsK Strong phase difference

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