Study of $\Xi^-_b$ and $\Omega^-_b$ decays to $\Lambda_c^+ h^- h^{\prime -}$ final states

Decays of $\Xi_b^-$ and $\Omega_b^-$ baryons to $\Lambda_c^+ h^- h^{\prime -}$ final states, with $h^- h^{\prime -}$ being $\pi^-\pi^-$, $K^-\pi^-$ and $K^-K^-$, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of $8.7 \,{\rm fb}^{-1}$ of $pp$ collisions collected at centre-of-mass energies $\sqrt{s} = 7$, $8$ and $13 \,{\rm TeV}$. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the $B^- \to \Lambda_c^+ \overline{p} \pi^-$ mode, are measured, with $\Xi_b^- \to \Lambda_c^+ K^- \pi^-$, $\Xi_b^- \to \Lambda_c^+ K^- K^-$ and $\Omega^-_b \to \Lambda_c^+ K^- K^-$ being observed at over $5\,\sigma$ significance. In addition, the $B^- \to \Lambda_c^+ \overline{p} K^-$ decay is observed for the first time, and its branching fraction is measured relative to that of the $B^- \to \Lambda_c^+ \overline{p} \pi^-$ mode.