Observation of the Ξ⁻ _b → ψ(2S)Ξ⁻ decay and studies of the Ξ_b(5945)⁰ baryon in proton-proton collisions at √s = 13 TeV

The first observation of the decay Ξ⁻ _b → ψ(2S)Ξ⁻ and measurement of the branching ratio of Ξ⁻ _b → ψ(2S)Ξ⁻ to Ξ⁻ _b → J/ψΞ⁻ are presented. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at √s = 13 TeV in 2016–2018, corresponding to an integrated luminosity of 140 fb⁻¹. The branching fraction ratio is measured to be B(Ξ⁻ _b → ψ(2S)Ξ⁻)/B(Ξ⁻ _b → J/ψΞ⁻) = 0.84^+0.21 _−0.19 (stat) ± 0.10(syst) ± 0.02(B), where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the Ξ_b(5945)⁰ baryon mass and natural width are also presented, using the Ξ⁻ _bπ⁺ final state, where the Ξ⁻ _b baryon is reconstructed through the decays J/ψΞ⁻, ψ(2S)Ξ⁻, J/ψΛK⁻, and J/ψΣ⁰K⁻. Finally, the fraction of Ξ⁻ _b baryons produced from Ξ_b(5945)⁰ decays is determined.