## Abstract

Decays of $B^0$ and $B^0_s$ mesons to the charmless baryonic final states $p\overline{p}h^+h^{\prime -}$, where $h$ and $h^{\prime}$ 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 $B^0_s \to p\overline{p}K^+K^-, B^0_s \to p\overline{p}K^{\pm}\pi^{\mp}, B^0 \to p\overline{p}K^{\pm}\pi^{\mp}$ and $B^0 \to p\overline{p}\pi^+\pi^-$ are observed with a significance greater than 5 standard deviations; evidence at 4.1 standard deviations is found for the $B^0 \to p\overline{p}K^+K^-$ decay and an upper limit is set on the branching fraction for $B^0_s \to p\overline{p}\pi^+\pi^-$. Branching fractions in the kinematic region $m(p\overline{p}) < 2850 MeV/c^2$ are measured relative to the $B^0 \to J/\psi(\to p\overline{p})K^*(892)^0$ channel.