Study of Beauty Hadron Decays into Pairs of Charm Hadrons

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Abstract

First observations of the decays ${\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{D}_{(s)}^{\ensuremath{-}}$ are reported using data corresponding to an integrated luminosity of $3\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ 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 $\mathcal{B}({B}_{s}^{0}\ensuremath{\rightarrow}{D}^{+}{D}_{s}^{\ensuremath{-}})$ is made and a search is performed for the decays ${B}_{(s)}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\mathrm{\ensuremath{\Lambda}}}_{c}^{\ensuremath{-}}$. The results obtained are $\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{D}^{\ensuremath{-}})/\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{D}_{s}^{\ensuremath{-}})=0.042\ifmmode\pm\else\textpm\fi{}0.003(\text{stat)}\ifmmode\pm\else\textpm\fi{}0.003(\text{syst}),\phantom{\rule{0ex}{0ex}}[\frac{\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{D}_{s}^{\ensuremath{-}})}{\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{+}{D}_{s}^{\ensuremath{-}})}]/[\frac{\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{b}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})}{\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})}]=0.96\ifmmode\pm\else\textpm\fi{}0.02(\text{stat)}\ifmmode\pm\else\textpm\fi{}0.06(\text{syst)},\phantom{\rule{0ex}{0ex}}\mathcal{B}({B}_{s}^{0}\ensuremath{\rightarrow}{D}^{+}{D}_{s}^{\ensuremath{-}})/\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{+}{D}_{s}^{\ensuremath{-}})=0.038\ifmmode\pm\else\textpm\fi{}0.004(\text{stat)}\ifmmode\pm\else\textpm\fi{}0.003(\text{syst)},\phantom{\rule{0ex}{0ex}}\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\mathrm{\ensuremath{\Lambda}}}_{c}^{\ensuremath{-}})/\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{+}{D}_{s}^{\ensuremath{-}})<0.0022[95%\text{ }\text{ }\mathrm{C}.\mathrm{L}.],\phantom{\rule{0ex}{0ex}}\mathcal{B}({B}_{s}^{0}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{+}{\mathrm{\ensuremath{\Lambda}}}_{c}^{\ensuremath{-}})/\mathcal{B}({B}_{s}^{0}\ensuremath{\rightarrow}{D}^{+}{D}_{s}^{\ensuremath{-}})<0.30[95%\text{ }\text{ }\mathrm{C}.\mathrm{L}.].$Measurement of the mass of the ${\mathrm{\ensuremath{\Lambda}}}_{b}^{0}$ baryon relative to the ${\overline{B}}^{0}$ meson gives $M({\mathrm{\ensuremath{\Lambda}}}_{b}^{0})\ensuremath{-}M({\overline{B}}^{0})=339.72\ifmmode\pm\else\textpm\fi{}0.24(\text{stat})\ifmmode\pm\else\textpm\fi{}0.18(\text{syst)}\text{ }\text{ }\mathrm{MeV}/{c}^{2}$. This result provides the most precise measurement of the mass of the ${\mathrm{\ensuremath{\Lambda}}}_{b}^{0}$ baryon to date.

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