Non factorizable Effetcs in $B \to \chi_{c0} K^- $ from Charmed Meson Rescattering

The $B^{-} \to \chi_{c0} K^{-}$ decay which has no visible factorizable amplitude, could be induced by the Cabibbo-allowed, color-favored $B^{-} \to D_{s}D^{*0}$, $B^{-} \to D^{*0}_{s}D^{0}$ and $B \to D_{s}^{*}D^{*}$ via the rescattering of these charmed mesons to $\chi_{co} K^{-}$. In this talk I would like to discuss a recent calculation \cite{Colangelo} of these effects for $B^{-} \to \chi_{c0} K^{-}$ and $B^{-} \to J/\psi K^{-}$ decays. We find that charmed scattering effects seem capable of producing a large $B^{-} \to \chi_{c0} K^{-}$ branching ratio measured by the Babar and Belle Collaboration and make a significant contribution to the $B^{-} \to J/\psi K^{-}$ branching ratios in agreement with experiments.