First observation of the rare purely baryonic decay $B^0 \to p\overline{p}$

Abstract

The first observation of the decay of a $B^0$ meson to a purely baryonic final state, $B^0 \to p\overline{p}$, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb$^{−1}$. The branching fraction is determined to be $\mathcal{B}(B^0 \to p\overline{p}) = (1.25 \pm 0.27 \pm 0.18) \times 10^{−8}$, where the first uncertainty is statistical and the second systematic. The decay mode $B^0 \to p\overline{p}$ is the rarest decay of the $B^0$ meson observed to date. The decay $B^0_s \to p\overline{p}$ is also investigated. No signal is seen and the upper limit $\mathcal{B}(B^0 \to p\overline{p}) < 1.5 \times 10^{−8}$ at 90% confidence level is set on the branching fraction.