Study of the suppressed B meson decay B^- -> D K^-, D -> K^+ \pi^-

TL;DR

This study investigates the suppressed B^- -> D K^- decay to measure CP violation, setting an upper limit on the amplitude ratio and analyzing related decay modes with significant findings on decay rates and asymmetries.

Contribution

The paper provides the first upper limit on the suppressed decay mode B^- -> D K^- and measures related decay ratios and asymmetries using a large data sample.

Findings

No significant evidence for B^- -> D K^- decay; upper limit r_B < 0.19.

Measured B(B^- -> D^0 K^-)/B(B^- -> D^0 ) ratio as (6.77 1.0) 10^{-2}.

Observed a 6.6 significance signal for B^- -> D   with charge asymmetry -0.02^{+0.15}_{-0.16}.

Abstract

We report a study of the suppressed B meson decay B^- -> D K^- followed by D -> K^+ \pi^-, where D indicates a D^0 or \bar{D}^0 state. The two decay paths interfere and provide information on the CP-violating angle \phi_3. We use a data sample containing 657 x 10^6 B\bar{B} pairs recorded at the \Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- storage ring. We do not find significant evidence for the mode B^- -> D K^-, D -> K^+ \pi^-, and set an upper limit of r_B < 0.19, where r_B is the magnitude of the ratio of amplitudes |A(B^- -> \bar{D}^0 K^-)/A(B^- -> D^0 K^-)|. The decay B^- -> D \pi^-, D -> K^+ \pi^- is also analyzed as a reference, for which we observe a signal with 6.6\sigma significance, and measure the charge asymmetry A_{D\pi} to be -0.02^{+0.15}_{-0.16}(stat) \pm 0.04(syst). In addition, the ratio B(B^- -> D^0 K^-)/B(B^- -> D^0 \pi^-) is measured to be [6.77 \pm 0.23(stat) \pm 0.30(syst)] x 10^{-2}.