Observation of B^0 -> p anti lamda D^(*)-

We report the first observation of the decays B^0 -> p anti lamda D^(*)-. the data sample of 711 fb^-1 used in this analysis corresponds to 772 million B B bar pairs, collected at the Y(4S) resonance by the Belle detector at the KEKB asymmetric-energy e+e- collider. We observe 19.8σ and 10.8σ excesses of events for the two decay modes and measure the branching fractions ofB^0 -> p anti lamda D^- and B^0 -> p anti lamda D^*- to be (25.1 +/- 2.6 +/- 3.5) x 10^-6 and (33.6 +/- 6.3 +/- 4.4) x 10^-6, respectively, where the first predictions based on the generalized factorization approach. In addition, a threshold enhancement in the di-baryon (p anti lamda) consistent with that observed in similar B decays.