Evidence for the two-body charmless baryonic decay $B^+ \to p \kern 0.1em\overline{\kern -0.1em\Lambda}$

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.