Observation of Λ0b → ψ(2S) p K− and Λ0b → J/ψ π+ π− p K− Decays and a Measurement of the Λ0b Baryon Mass

The decays Λ0b → ψ(2S) p K− and Λ0b → J/ψ π+ π− p K− are observed in a data sample corresponding to an integrated luminosity of 3 fb^−1, collected in proton-proton collisions at 7 and 8 TeV centre-of-mass energies by the LHCb detector. The ψ(2S) mesons are reconstructed through the decay modes ψ(2S) → μ+ μ− and ψ(2S) → J/ψ π+ π−. The branching fractions relative to that of Λ0b → J/ψ p K− are measured to be B(Λ0b → ψ(2S) p K−)/B(Λ0b → J/ψ p K−) = (20.70 ± 0.76 ± 0.46 ± 0.37) × 10^−2, B(Λ0b → J/ψ π+ π− p K−)/B(Λ0b → J/ψ p K−) = (20.86 ± 0.96 ± 1.34) × 10^−2, where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of J/ψ and ψ(2S) branching fractions. The mass of the Λ0b baryon is measured to be M(Λ0b) = 5619.65 ± 0.17 ± 0.17 MeV/c2, where the uncertainties are statistical and systematic.