First observations of ${\bar{B}}_s^0\to D^{+}{D}^{-}$, $D_s^{+}{D}^{-}$ and $D^0{\bar{D}}^0$ decays

First observations and measurements of the branching fractions of the ${\bar{B}}_s^0\to D^{+}{D}^{-}$, ${\bar{B}}_s^0\to D_s^{+}{D}^{-}$ and $\bar{B}_s^0\to D^0\bar{D}^0$decaysarepresentedusing1.0fb$^{-1}$ of data collected by the LHCb experiment. These branching fractions are normalized to those of ${\bar{B}}^0\to D^{+}{D}^{-}$, $B^0\to D_s^{+}{D}^{-}$ and $B^{-}\to D^0{D}_s^{-}$, respectively. An excess of events consistent with the decay ${\bar{B}}^0\to D^0{\bar{D}}^0$ is also seen, and its branching fraction is measured relative to that of $B^-\to D^0D_s^-$\mathrm{.}Improvedmeasurementsofthebranchingfractions${\cal{B}}(\bar{B}_s^0\to D_s^+D_s^-)$and${\cal{B}}(B^-\to D^0D_s^-)$ are reported, each relative to $\mathcal{B}(B^0\to D_s^{+}{D}^{-})$. The ratios of branching fractions are {-0.2in} {center} {align*} {{\cal{B}}(\bar{B}_s^0\to D^+D^-)\over {\cal{B}}(\bar{B}^0\to D^+D^-)} &= 1.08\pm 0.20\pm0.10, {{\cal{B}}(\bar{B}_s^0\to D_s^+D^-)\over {\cal{B}}(B^0\to D_s^+D^-)} &= 0.050\pm 0.008\pm0.004, {{\cal{B}}(\bar{B}_s^0\to D^0\bar{D}^0)\over {\cal{B}}(B^-\to D^0D_s^-)} &= 0.019\pm 0.003\pm0.003, {{\cal{B}}(\bar{B}^0\to D^0\bar{D}^0)\over {\cal{B}}(B^-\to D^0D_s^-)} &= 0.0014\pm 0.0006\pm0.0002,{{\cal{B}}(\bar{B}_s^0\to D_s^+D_s^-)\over {\cal{B}}(B^0\to D_s^+D^-)} &= 0.56\pm 0.03\pm0.04, {{\cal{B}}(B^-\to D^0D_s^-)\over {\cal{B}}(B^0\to D_s^+D^-)} &= 1.22\pm 0.02\pm0.07, {align*} {center} \noindent where the uncertainties are statistical and systematic, respectively.