Hadronic rareBdecays via exchange or annihilation diagrams

The two-body mesonic $B$ decays induced only via a single $W$-exchange or annihilation quark diagram, such as $B_u^{-}\to D_s^{\mathrm{}(*)-}{K}^{\mathrm{}(*)0}$ and ${\overline{B}}_d^0\to D_s^{\mathrm{}(*)+}{K}^{\mathrm{}(*)-}$, are analyzed in the factorization approximation. We estimate the branching ratios for those transitions into two pseudoscalar mesons, and find them to be negligibly small. The significant effect of final-state rescattering is illustrated by taking $B_u^{-}\to D^{-}{\overline{K}}^0$, for example.