Observation of the charmless purely baryonic decay $ {\Lambda}_b^0\to \Lambda p\overline{p} $

A search for the charmless purely baryonic decay ${\Lambda}_b^0\to \Lambda p\overline{p}$ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13$ TeV and corresponding to an integrated luminosity of 6 . 0 fb − 1 . The signal decay is observed with a significance of 5.1 standard deviations. Its branching fraction is measured for the first time, relative to that of the topologically similar decay ${\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-}$ . Contributions from intermediate charmonium resonances decaying to the $p\overline{p}$ and K + K − final states are explicitly excluded with a requirement on the invariant mass of the companion hadron system, $ m\left(h\overline{h}\right)