Observation of the $${{{\varLambda } ^0_{b}} \!\rightarrow {{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} {{\varXi } ^-} {{K} ^+} }$$ and $${{{{\varXi } ^0_{b}} \!\rightarrow {{J \hspace{-1.66656pt}/\hspace{-1.111pt}\psi }} {{\varXi } ^-} {{\pi } ^+} }}$$ decays

The first observation of the Ξb0→J/ψΞ-π+ decay and the most precise measurement of the branching fraction of the Λb0→J/ψΞ-K+ decay are reported, using proton-proton collision data from the LHCb experiment collected in 2016–2018 at a centre-of-mass energy of 13\,TeV, corresponding to an integrated luminosity of 5.4\,fb-1. Using the Λb0→J/ψΛ and Ξb-→J/ψΞ- decays as normalisation channels, the ratios of branching fractions are measured to be (Formula presented.) where the first uncertainty is statistical and the second systematic. [The LHCb Collaboration]