Title: Branching ratios of $B \to D_s K$ decays in perturbative QCD approach
Abstract: The rare decays $B^0 \to D_s^- K^+$ and $B^+ \to D_s^+ \overline{K}^0$ can occur only via annihilation type diagrams in the standard model. We calculate these decays in the perturbative QCD approach. We found that the calculated branching ratio of $B^0 \to D_s^- K^+$ agreed with the data which had been observed in the KEK and SLAC B factories. The decay $B^+ \to D_s^+ \overline{K}^0$ has a very small branching ratio at $\cal O(10^{-8})$ , due to the suppression from the CKM matrix elements |V ub * V cd |.