Improved measurement of B0bar -> D_s^-D^+ and search for B0bar ->   D_s^+D_s^- at Belle
  We reconstruct B0bar -> D_s^-D^+ decays using a sample of 275 million BBbar pairs recorded by the Belle experiment, and we measure the branching fraction to be [7.42 +- 0.23(stat) +- 1.36(syst)] x 10^(-3). We also search for the related decay B0bar -> D_s^+D_s^-. We observe no statistically significant signal and set an upper limit on the branching fraction of 2.0 x 10^(-4) at 90% C.L. 
K. Abe, et al. (for the Belle Collaboration)