D*K ADS

last updated on 20110901

Study of the Suppressed Decays B^- → D^*K^-, D^* → Dπ⁰/γ, D → K⁺π^-

The decay B^- → D^(*)K^- (D = D^(*)0 or D^(*)0) plays an important role for the determination of the CP-violating angle φ₃. The information of φ₃ is extracted from the interference, which occurs when D^(*)0 and D^(*)0 decay to the same final state. The D^* meson can be reconstructed from D^* → Dπ⁰ or D^* → Dγ. So-called ADS method uses the following D decay to K⁺π^-, for which the effect of CP violation can be enhanced by the comparable magnitudes of interfering amplitudes [PRL 78, 3257 (1997), PRD 63, 036005 (2001)]. In 2010, we obtained the first evidence for B^- → DK^-, D → K⁺π^- by introducing improved discrimination of the continuum background from e⁺e^- → qq (q = u, d, s, c) [PRL 106, 231803 (2011)]. In this report, we show a result for B^- → D^*K^-, D^* → Dπ⁰/γ, D → K⁺π^- based on the full 772 million BB pairs collected at Υ(4S) resonance.

The signal yield is extracted by a two dimensional fit on ΔE and NB', where NB' is a varibale for discriminating qq background. We note that NB' is obtained from NB' = ln(NB+0.6)/(1.0-NB) with NB being the varibable used for B^- → DK^-, D → K⁺π^-. In Figs. 1 and 2, we show the result of the fit. We measure the ratio R_{D^*K,Dπ⁰/γ} and the asymmetry A_{D^*K,Dπ⁰/γ} defined by

where r_B^* = |A(B^- → D^*0K^-)/A(B^- → D^*0K^-)|, r_D = |A(D⁰ → K⁺π^-)/A(D⁰ → K^-π⁺)|, δ_B^* = δ(B^- → D^*0K^-) - δ(B^- → D^*0K^-), and δ_D = δ(D⁰ → K^-π⁺) - δ(D⁰ → K⁺π^-). For r_D and δ_D, we have experimental inputs [HFAG page for charm physics]. Obtained results (PRELIMINARY) are

R_D^*K,Dπ⁰ = [1.0 ^+0.8_-0.7 (stat) ^+0.1_-0.2 (syst)] × 10^-2 A_D^*K,Dπ⁰ = 0.4 ^+1.1_-0.7 (stat) ^+0.2_-0.1 (syst)
R_D^*K,Dγ = [3.6 ^+1.4_-1.2 (stat) ±0.2 (syst)] × 10^-2 A_D^*K,Dγ = - 0.51 ^+0.33_-0.29 (stat) ±0.08 (syst)
where the first evidence for D^*K signal is obtaied for the γ mode with a significance of 3.5σ (including systematic error). For r_B^* = 0.1 [CKMfitter page], our results indicate negative cos(δ_B^*+δ_D)cosφ₃ and positive sin(δ_B^*+δ_D)cosφ₃ (consistent with the result obtained by B^- → D^*K^-, D^* → Dπ⁰/γ, D → K_Sπ⁺π^- [PRD 81, 112002 (2010), PRL 105, 121801 (2010)]). Extraction of φ₃ will be given by including other observables later.

Relevant figures:

Fig. 1 (related to R_{D^*K,Dπ⁰/γ}): Result of the fit for the π⁰ mode (left) and the γ mode (right). Charge-conjugate decays are included.
The ΔE distributions (upper) and the NB' distributions (lower) are obtained by projecting in NB' > 1.0 and |ΔE| < 0.03 GeV, respectively.
The fitted sample is shown with dots with error bars and the PDF is shown with the solid blue curve, for which the components are shown
with thicker long-dashed red (D^*K), long-dashed magenta (D^*π), long-dashed brown (DK and Dπ), dash-dotted green (BB background),
and dashed blue (qq background). Better figures (eps format) are obtained by clicking the figures.

Fig. 2 (related to A_{D^*K,Dπ⁰/γ}): ΔE distributions (NB' > 1.0) for the π⁰ mode (upper) and the γ mode (lower).
We show the distributions for B^- (left) and B⁺ (right) candidates. The curves show the same components as in Fig. 1.
Better figures (eps format) are obtained by clicking the figures.