First observations of Bˉ0s→D+D−, D+sD− and D0Dˉ0 decays

First observations and measurements of the branching fractions of the Bˉ0s→D+D−, Bˉ0s→D+sD− and Bˉ0s→D0Dˉ0 decays are presented using 1.0~fb−1 of data collected by the LHCb experiment. These branching fractions are normalized to those of Bˉ0→D+D−, B0→D+sD− and B−→D0D−s, respectively. An excess of events consistent with the decay Bˉ0→D0Dˉ0 is also seen, and its branching fraction is measured relative to that of B−→D0D−s. Improved measurements of the branching fractions B(Bˉ0s→D+sD−s) and B(B−→D0D−s) are reported, each relative to B(B0→D+sD−).