The rare decays $B^0 \to D_s^- K^+$ and $B^+ \to D_s^+ \bar{ K}^0$ can occur only via annihilation type diagrams in the standard model. We calculate these decays in 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. While the decay $B^+ \to D_s^+ \bar{ K}^0$ has a very small branching ratio at ${ \cal O}(10^{ -8})$, due to the suppression from CKM matrix elements $|V_{ ub}^* V_{ cd}|$.
Categories: hep-ph