Measurement of the branching ratio Γ(Λb0→ψ(2S)Λ0)/Γ(Λb0→J/ψΛ0) with the ATLAS detector

An observation of the Λb0→ψ(2S)Λ0 decay and a comparison of its branching fraction with that of the Λb0→J/ψΛ0 decay has been made with the ATLAS detector in proton–proton collisions at s=8 TeV at the LHC using an integrated luminosity of 20.6 fb−1. The J/ψJ/ψ and ψ(2S)ψ(2S) mesons are reconstructed in their decays to a muon pair, while the Λ0→pπ−Λ0→pπ− decay is exploited for the Λ0Λ0 baryon reconstruction. The Λb0 baryons are reconstructed with transverse momentum pT>10 GeVpT>10 GeV and pseudorapidity |η|<2.1|η|<2.1. The measured branching ratio of the Λb0→ψ(2S)Λ0 and Λb0→J/ψΛ0 decays is Γ(Λb0→ψ(2S)Λ0)/Γ(Λb0→J/ψΛ0)=0.501±0.033(stat)±0.019(syst), lower than the expectation from the covariant quark model.