Observation of Decays $B^0\to D_s^{(*)+}\pi^-$ and$B^0\to D_s^{(*)-}K^+$

The authors report the observation of decays B{sup 0} {yields} D{sub s}{sup (*)+} {pi}{sup -} and B{sup 0} {yields} D{sub s}{sup (*)-} K{sup +} in a sample of 230 x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} events recorded with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} storage ring. They measure the branching fractions {Beta}(B{sup 0} {yields} D{sub s}{sup +}{pi}{sup -}) = (1.3 {+-} 0.3(stat) {+-} 0.2(syst)) x 10{sup -5}, {Beta}(B{sup 0} {yields} D{sub s}{sup -}K{sup +}) = (2.5 {+-} 0.4(stat) {+-} 0.4(syst)) x 10{sup -5}, {Beta}(B{sup 0} {yields} D*{sub s}{sup +} {pi}{sup -}) = (2.8 {+-} 0.6(stat) {+-} 0.5 (syst)) x 10{sup -5}, and {Beta}(B{sup 0} {yields} D*{sub s}{sup -} K{sup +}) = (2.0 {+-} 0.5(stat) {+-} 0.4(syst)) x 10{sup -5}. The significance of the measurements to differ from zero are 5, 9, 6, and 5 standard deviations, respectively