Observation of Cabibbo suppressed $B\to D^{(\ast )}{K}^{-}$ decays at Belle

Abstract

Cabibbo-suppressed decays $B\to D^{(\ast )}{K}^{-}$ using a 10.4 fb${}^{-1}$ data sample accumulated at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ storage ring. The high-momentum particle identification system of Belle is used to isolate signals for $B\to D^0{K}^{-}$, $D^{+}{K}^{-}$, $D^{\ast 0}{K}^{-}$ and $D^{\ast +}{K}^{-}$ from the $B\to D^{(\ast )}{\pi }^{-}$ decay processes which have much larger branching fractions. We report ratios of Cabibbo-suppressed to Cabibbo-favored branching fractions of: $\mathcal{B}(B^{-}\to D^0{K}^{-})/\mathcal{B}(B^{-}\to D^0{\pi }^{-})=0.079\pm 0.009\pm 0.006$; $\mathcal{B}(\overline{B^0}\to D^{+}{K}^{-})/\mathcal{B}(\overline{B^0}\to D^{+}{\pi }^{-})=0.068\pm 0.015\pm 0.007$; $\mathcal{B}(B^{-}\to D^{\ast 0}{K}^{-})/\mathcal{B}(B^{-}\to D^{\ast 0}{\pi }^{-})=0.078\pm 0.019\pm 0.009$; and $\mathcal{B}({\bar{B}}^0\to D^{\ast +}{K}^{-})/\mathcal{B}({\bar{B}}^0\to D^{\ast +}{\pi }^{-})=0.074\pm 0.015\pm 0.006$. The first error is statistical and the second is systematic. These are the first reported observations of the $B\to D^{+}{K}^{-}$, $D^{\ast 0}{K}^{-}$ and $D^{\ast +}{K}^{-}$ decay processes.

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