Hadronic B→DX Decays at LHCb and CDF Laurence Carson, Imperial College on 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) – Improved measurements of B s →D s D s (LHCb and CDF) – Improved measurements of B s →D s K and B s →D s π (LHCb) – Observation of B→DKππ decays (LHCb) Many other interesting results not covered here 2

Physics Motivation A variety of interesting physics is accessible using B→DX decays: Different methods to measure γ with B +/- →D 0 K +/- decays [talk of K.Akiba]. The decays B d →D + D - and B s →D s + D s - can be used to measure γ, using U-spin symmetry [e.g. hep-ph/ ]. In addition, B d →D + D - can be used to measure sin(2β). Belle reported unexpectedly large direct CPV in this mode [hep-ex/ ]. The decay B s →D s +/- K -/+ allows a theoretically clean γ measurement, uniquely possible at LHCb, via a flavour-tagged and time-dependent analysis [hep-ph/ , see also talk of K.Akiba]. The same methods used to measure γ using B +/- →D 0 K +/- can also be applied to B +/- →D 0 K +/- π + π - decays [hep-ph/ ]. 3 ( )

The LHCb Experiment Situated on LHC ring; pp collisions at E CM = 7 TeV. (8 TeV in 2012) Forward arm spectrometer, optimised for study of B and D decays. 4 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.

The CDF Experiment Situated on TeVatron ring; pp collisions at E CM = 1.96 TeV Central detector, tracks reconstructed by Si vertex detector and drift chamber (COT). 5 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

B s →DD’ at LHCb D mesons are reconstructed as D 0 →Kπ, D + →Kππ or D s →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 Λ c ) suppressed using combined mass/PID vetoes. 6 LHCb-CONF /fb B s →D s D s B d →D + D s (loose selection) Syst dominated by f s /f d (true for all modes) Preliminary Around five times more precise than previous world average.

B s →DD’ at LHCb First observations of B s →D + D s (10.1σ) and B s →D + D - (10.7σ): 7 B d,s →D + D s (tight selection) B d,s →D + D - Both are in agreement with expectations of ≈|V cd /V cs | 2 = 0.05 and ≈1. Preliminary LHCb-CONF

B s →DD’ at LHCb First observation of B s →D 0 D 0 (5.4σ), and hint of B d →D 0 D 0 (2.1σ): 8 B d,s →D 0 D 0 B - →D 0 D s Again, this is in agreement with expectations. Future plans include measurements of β and γ with B d →D + D - and B s →D s + D s -, once more data has been collected. Preliminary LHCb-CONF

Reconstruct D s →KKπ, with KK in φ window or Kπ in K* window. Soft π 0 or γ from D s *→D s not reconstructed. Normalisation is made to B d →D s D -. B s →D s (*) D s (*) at CDF 9 6.8/fb CDF Note 10721

which is smaller than ΔΓ s measured in B s →J/ψφ [e.g. LHCb-CONF ], suggesting that the three-body contribution is sizeable. and can be used to measure ΔΓ s, ignoring possible contributions from three-body modes [PLB 316, 567] : This yields:, B s →D s (*) D s (*) at CDF 10 The result for B s →D s D s is in agreement with the LHCb value. Third error is from f s /f d and B (B d →D s D - ) The inclusive B is:,

B s →D s h at LHCb An accurate measurement of B (B s →D s K) is an important stepping stone on the path to a γ measurement with this mode [talk of K.Akiba]. High B s →D s π yield allows benchmark B measurement for B s modes. Final selection uses a BDT, trained on B s →D s π data and optimised for significance of the B s →D s K signal. Backgrounds from Λ c are vetoed, similarly to the B→DD’ analysis /fb hep-ex/ B s →D s π B d →D - π (normalisation)

B s →D s h at LHCb: D s K Tight PID criterion applied to bachelor K, to suppress B s →D s π. Performance of PID criteria measured on data using D* + →D 0 (Kπ)π +. Shape of misidentified B s →D s π component determined from data, accounting for effect of PID requirements. D s π yield is left free, and cross-checked against expectation from PID. 12 Background from B d →D - K constrained using misID probability of PID criteria. Cross-check: fitted yield of B d →D s K agrees with expectation from PDG.

B s →D s h at LHCb Experimental systematics include fit model, and translation of PID performance from D* calibration sample to signal B decays. 13 For absolute B measurements, additional external systematics include B (B d →D - π) and LHCb value of f s /f d (from semileptonic decays). – However the D branching fraction uncertainties are subtracted from the f s /f d uncertainty, since f s /f d extraction also depends on these branching fractions. Experimental, plus B (B d →D - π) f s /f d only Total errors are 10% (D s π) and 12% (D s K) respectively. Both measurements significantly improve on the previous world average values of (3.2±0.5)x10 -3 (D s π) and (3.0±0.7)x10 -4 (D s K).

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 /pb (2010) PRL 108, First observations of (c) B d →D - Kππ (7.2σ) and (d) B + →D 0 Kππ (9.0σ). LHCb trigger in 2011/ 2012 contains improvements leading to higher B→Dhhh yields per pb -1 than in 2010 data

Observation of B→DKππ In the future, the B - mode will be used to add sensitivity to the γ measurement with B +/- →D 0 K +/- decays. Also, method to measure γ with B s →D s K can be extended to B s →D s Kππ - search for this mode is underway. 15 Systematics arise from fit model, PID efficiency and Kππ invariant mass distribution. Kππ system consistent with decays of excited strange states, such as K 1 (1270).

Summary Many interesting physics measurements can be made with hadronic B→DX decays. Observations made of many new modes: B s →D + D s, B s →D + D -, B s →D 0 D 0, B d →D - Kππ and B + →D 0 Kππ. Greatly improved measurements of B s →D s D s and B s →D s h. 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

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Semileptonic f s /f d at LHCb Can measure f s /(f u +f d ) using D 0 Xμν, D + Xμν, D s Xμν, after correcting for cross-feeds. 18 f s /(f u + f d ) = ± (stat) – (syst) No dependence on p T or η is seen. Assuming f u =f d, simply doubling this value gives f s /f d. PRD 85,

B→DD’ 19 from hep-ph/ ae iθ is the ratio of penguin to tree amplitudes

Measuring γ with B s →D s K 20 The final state D s - K + is accessible by both B s and B s : 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 - B s or B s to D s + K - or D s - K + From these rates, γ can be extracted in an unambiguous and theoretically clean way.

Measuring γ with B s →D s K 21 Strong phase difference