First Observation of a Baryonic B0s Decay

We report the first observation of a baryonic Bs0 decay, Bs0→p Λ ¯K- , using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb-1. The branching fraction is measured to be B (Bs0→p Λ ¯ K- )+B (Bs0→p ¯ Λ K+ )=[5.46 ±0.61 ±0.57 ±0.50 (B )±0.32 (fs/fd)] ×10-6 , where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the B0→p Λ ¯π- decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of b -quark hadronization probabilities fs/fd.