Searches for $Lambda_{b}^{0}$ and $Xi_{b}^{0}$ decays to $K_{mathrm S}^{0}ppi^{-}$ and $K_{mathrm S}^{0}pK^{-}$ final states with the first observation of the $Lambda_{b}^{0} to K_{S}^{0}ppi^{-}$ decay

A search for previously unobserved decays of beauty baryons to the final states $K^0_{mathrm{S}}ppi^-$ and $K^0_{mathrm{S}}pK^-$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0,mathrm{fb}^{-1}$ of $pp$ collisions. The $Lambda^0_b rightarrow K^0_{mathrm{S}}ppi^-$ decay is observed for the first time with a significance of $8.6,sigma$, and a measurement is made of the $CP$ asymmetry, which is consistent with zero. No significant signals are seen for $Lambda^0_b rightarrow K^0_{mathrm{S}}pK^-$ decays, $Xi^0_b$ decays to both $K^0_{mathrm{S}}ppi^-$ and $K^0_{mathrm{S}}pK^-$ final states, and the $Lambda^0_b rightarrow D^-_s (K^0_{mathrm{S}}K^-)p$ decay, and upper limits on their branching fractions are reported.