University of Birmingham First Observation of a Baryonic Bs0 Decay

We report the first observation of a baryonic B 0 s decay, B 0 s → 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 ð B 0 s → p ¯ Λ K − Þ þ B ð B 0 s → ¯ p Λ K þ Þ ¼ ½ 5 . 46 (cid:2) 0 . 61 (cid:2) 0 . 57 (cid:2) 0 . 50 ð B Þ (cid:2) 0 . 32 ð f s =f d Þ(cid:3) × 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 B 0 → p ¯ Λ π − decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of b -quark hadronization probabilities f s =f d .