Measurement of the Branching Ratio Γ ({Λ_b⁰} → ψ(2s)Λ⁰) / Γ ({Λ_b⁰} → J/ψΛ⁰) with the ATLAS Detector

An observation of the Γ_b^{Λ0} > ψ(2s)Λ⁰ decay and a comparison of its branching fraction with that of the Λ_b^0 > ψ(2s)Λ⁰ decay has been made with the ATLAS detector in proton-proton collisions at √s̅ = 8 TeV at the LHC using an integrated luminosity of 20.6 fb⁻¹. The J/ψ and ψ(2s) mesons are reconstructed in their decays to a muon pair, while the Λ⁰ > pπ⁻ decay is exploited for the Λ⁰ baryon reconstruction. The Λ_b^0 baryons are reconstructed with transverse momentum p_T > 10 GeV and pseudorapidity |η| < 2.1. The measured branching ratio of the Λ_b^0 → ψ(2s)Λ⁰ and Λ_b^0 and Λ_b^0 → J/ψΛ⁰ decay is Γ(Λ_b^0 / Γ(Λ_b^0 → J/ψΛ⁰) = 0.501 ± 0.033(stat) ± 0.019(syst), lower than the expectation from the covariant quark model.