First evidence for the two-body charmless baryonic decay $ {B^0}\to p\overline{p} $

Abstract The results of a search for the rare two-body charmless baryonic decays $ {B^0}\to p\overline{p} $ and $ B_s^0\to p\overline{p} $ are reported. The analysis uses a data sample, corresponding to an integrated luminosity of 0.9 fb−1, of pp collision data collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. An excess of $ {B^0}\to p\overline{p} $ candidates with respect to background expectations is seen with a statistical significance of 3.3 standard deviations. This is the first evidence for a two-body charmless baryonic B 0 decay. No significant $ B_s^0\to p\overline{p} $ signal is observed, leading to an improvement of three orders of magnitude over previous bounds. If the excess events are interpreted as signal, the 68.3% confidence level intervals on the branching fractions are $ \begin{array}{*{20}{c}} {\mathcal{B}\left( {{B^0}\to p\overline{p}} \right)=1.47_{-0.51-0.14}^{+0.62+0.35}\times {10^{-8 }},} \hfill \\ {\mathcal{B}\left( {{B^s}\to p\overline{p}} \right)=2.84_{-1.68-0.18}^{+2.03+0.85}\times {10^{-8 }},} \hfill \\ \end{array} $ where the first uncertainty is statistical and the second is systematic.