Observation of the Λb0→χc1 (3872) pK− decay

Abstract

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9 fb−1 of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay Λ0 b → χc1(3872)pK− with χc1(3872) → J/ψ π+π − is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that (58 ± 15)% of the decays proceed via the two-body intermediate state χc1(3872)Λ(1520). The branching fraction with respect to that of the Λ0 b → ψ(2S)pK− decay mode, where the ψ(2S) meson is reconstructed in the J/ψ π+π − final state, is measured to be: B(Λ0b → χc1(3872)pK−)B(Λ0b → ψ(2S)pK−)×B(χc1(3872) → J/ψ π+π−)B(ψ(2S) → J/ψ π+π−)= (5.4 ± 1.1 ± 0.2) × 10−2, where the first uncertainty is statistical and the second is systematic.