Decays of $B^0$ and $B_{ s}^0$ 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 $B_{ s}^0$ 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.
Categories: hep-ex