We reconstruct ${\overline{B}}^0\to D_s^{-}{D}^{+}$ decays using a sample of $449\times {10}^6$ $B\overline{B}$ pairs recorded by the Belle experiment, and measure the branching fraction to be $\mathcal{B}({\overline{B}}^0\to D_s^{-}{D}^{+})=[7.5\pm 0.2(\mathrm{stat})\pm 0.8(\mathrm{syst})\pm 0.8({\mathcal{B}}^{\prime }s)]\times {10}^{-3}$. A search for the related decay ${\overline{B}}^0\to D_s^{+}{D}_s^{-}$ is also performed. Since we observe no statistically significant signal, an upper limit on the branching fraction is set at $3.6\times {10}^{-5}$ (90% C.L.).

• Received 27 March 2007

DOI:https://doi.org/10.1103/PhysRevD.75.091102