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/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 Λb0 baryons are reconstructed with transverse momentum pT>10 GeV and pseudorapidity |η|<2.1. The measured branching ratio of the Λb0→ψ(2S)Λ0 and Λb0J/ψΛ0 decays is Gcyrillic(Λb0→ψ(2S)Λ0/Gcyrillic(Λb0J/ψΛ0)=0.501±0.033(stat)±0.019(syst), lower than the expectation from the covariant quark model.
Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., et al. (2015). Measurement of the branching ratio Gamma(Λb0→ψ(2S)Λ0)/Gamma(Λb0→J/ψΛ0) with the ATLAS detector. PHYSICS LETTERS. SECTION B, 751, 63-80 [10.1016/j.physletb.2015.10.009].