Study of the Suppressed Decays $B^- \to [K^+π^-]_D K^-$ and $B^- \to [K^+π^-]_D π^-$

Abstract

We report a study of the suppressed decays $B^- \to [K^+π^-]_D K^-$ and $B^- \to [K^+π^-]_D π^-$, where $[K^+π^-]_D$ indicates that the $K^+π^-$ pair originates from a neutral $D$ meson. These decay modes are sensitive to the Unitarity Triangle angle $ϕ_3$. We use a data sample containing 275 million $B\bar{B}$ pairs recorded at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric $e^+e^-$ storage ring. The signal for $B^- \to [K^+π^-]_D K^-$ is not statistically significant, and we set a limit $r_B < 0.27$ at 90% confidence level, where $r_B$ is the magnitude of the ratio of amplitudes $| A(B^- \to \bar{D}^0K^-) / A(B^- \to D^0K^-) |$. We observe a signal with $6.4σ$ statistical significance in the related mode, $B^- \to [K^+π^-]_D π^-$.