A Study of the Rare Decays $B^0\to D_s^{(*)+} π^-$ and $B^0\to D_s^{(*)-} K^+$

We report evidence for the decays $B^0\to D_s^{+} \pi^-$ and $B^0\to D_s^{-} K^+$ and the results of a search for $B^0 \to D_s^{*+} \pi^-$ and $B^0\to D_s^{*-} K^+$ in a sample of 84 milion Y(4S) decays into $B\bar{B}$ pairs collected with the BaBar detector at the PEP II asymmetric-energy $e^{+}e^{-}$ storage ring. We measure the branching fraction Br($B^0 \to D_s^{+} \pi^-) = 3.2 \pm 0.9 ({\rm stat.})\pm 1.0 ({\rm syst.})$. and Br($B^0 \to D_s^{+} \pi^-) = 3.2 \pm 1.0 ({\rm stat.})\pm 1.0 ({\rm syst.})$. We also set 90% C.L. limits BR($B^0 \to D_s^{*+} \pi^-) < 4.1\times 10^{-5}$ at 90% C.L and BR($B^0 \to D_s^{*-} K^+)< 2.5\times 10^{-5}$ at 90% C.L.