First observations of the decays ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{D}_{(s)}^{-}$ are reported using data corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$ collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction $\mathcal{B}(B_s^0\to D^{+}{D}_s^{-})$ is made and a search is performed for the decays $B_{(s)}^0\to {\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-}$. The results obtained are $$\begin{gathered} \mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{D}^{-})/\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{D}_s^{-})=0.042\pm 0.003(\text{stat)}\pm 0.003(\text{syst}), \\ \left[\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{D}_s^{-})}{\mathcal{B}({\overline{B}}^0\to D^{+}{D}_s^{-})}\right]/\left[\frac{\mathcal{B}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\pi }^{-})}{\mathcal{B}({\overline{B}}^0\to D^{+}{\pi }^{-})}\right]=0.96\pm 0.02(\text{stat)}\pm 0.06(\text{syst)}, \\ \mathcal{B}(B_s^0\to D^{+}{D}_s^{-})/\mathcal{B}({\overline{B}}^0\to D^{+}{D}_s^{-})=0.038\pm 0.004(\text{stat)}\pm 0.003(\text{syst)}, \\ \mathcal{B}({\overline{B}}^0\to {\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-})/\mathcal{B}({\overline{B}}^0\to D^{+}{D}_s^{-})<0.0022[95\%\mathrm{C}\mathrm{.}\mathrm{L}\mathrm{.}], \\ \mathcal{B}(B_s^0\to {\mathrm{\Lambda }}_c^{+}{\mathrm{\Lambda }}_c^{-})/\mathcal{B}(B_s^0\to D^{+}{D}_s^{-})<0.30[95\%\mathrm{C}\mathrm{.}\mathrm{L}\mathrm{.}]. \end{gathered}$$Measurement of the mass of the ${\mathrm{\Lambda }}_b^0$ baryon relative to the ${\overline{B}}^0$ meson gives $M({\mathrm{\Lambda }}_b^0)-M({\overline{B}}^0)=339.72\pm 0.24(\text{stat})\pm 0.18(\text{syst)}\mathrm{MeV}/c^2$. This result provides the most precise measurement of the mass of the ${\mathrm{\Lambda }}_b^0$ baryon to date.

• Received 17 March 2014

DOI:https://doi.org/10.1103/PhysRevLett.112.202001

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© 2014 CERN, for the LHCb Collaboration