Observation of charmless baryonic decays B (s)0 →p p - h+h′-

Decays of B 0 and B 0 s mesons to the charmless baryonic final states p ¯ p h + h ' − , where h and h ′ each denote a kaon or a pion, are searched for using the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3     fb − 1 . Four-body charmless baryonic B 0 s decays are observed for the first time. The decays B 0 s → p ¯ p K + K − , B 0 s → p ¯ p K ± π ∓ , B 0 → p ¯ p K ± π ∓ and B 0 → p ¯ p π + π − are observed with a significance greater than 5 standard deviations; evidence at 4.1 standard deviations is found for the B 0 → p ¯ p K + K − decay and an upper limit is set on the branching fraction for B 0 s → p ¯ p π + π − . Branching fractions in the kinematic region m ( p ¯ p ) < 2850     MeV / c 2 are measured relative to the B 0 → J / ψ ( → p ¯ p ) K ∗ ( 892 ) 0 channel.