Evidence for the two-body charmless baryonic decay B + → p Λ ¯ $$ {B}^{+}\to p\overline{\varLambda} $$

A search for the rare two-body charmless baryonic decay $$ {B}^{+}\to p\overline{\varLambda} $$ is performed with pp collision data, corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $$ {B}^{+}\to p\overline{\varLambda} $$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the B + → K S 0 π + decay for normalisation, is $$ \mathrm{\mathcal{B}}\left({B}^{+}\to p\overline{\varLambda}\right)=\left(2.{4}_{-0.8}^{+1.0}\pm 0.3\right)\times 1{0}^{-7}, $$ where the first uncertainty is statistical and the second systematic.