Searches for $\Lambda^0_b$ and $\Xi^0 _b$ decays to $K^0_S p \pi^-$ and $K^0_S pK^-$ final states with first observation of the $\Lambda^0_b \to K^0_S p \pi^-$ decay

A search for previously unobserved decays of beauty baryons to the final states $K^0_S p \pi^-$ and $K^0_S pK^-$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of $pp$ collisions recorded by the LHCb experiment. The $\Lambda^0_b \to K^0_S p \pi^-$ 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.