Observation of the charmless purely baryonic decay Λb⁰→ Λ pp̄

A bstract A search for the charmless purely baryonic decay Λb⁰→ Λ pp̄ Λ b 0 → Λ p p ¯ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of √s=13 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 Λb⁰→ Λ K⁺K⁻ Λ b 0 → Λ K + K − . Contributions from intermediate charmonium resonances decaying to the pp̄ p p ¯ and K + K − final states are explicitly excluded with a requirement on the invariant mass of the companion hadron system, m(hh̄)<2.85 m h h ¯ < 2.85 GeV, where h stands for a proton or a charged kaon. The relative branching fraction is found to be $$ {B({Λ}_b^0→ Λ pp̄)}{B({Λ}_b^0→ Λ {K}⁺{K}⁻)}=(5.1± {1.3}₍ₛₜₐₜ₎± {0.3}(syst))× {10}⁻². $$ B Λ b 0 → Λ p p ¯ B Λ b 0 → Λ K + K − = 5.1 ± 1.3 stat ± 0.3 syst × 10 − 2 .