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

Abstract

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 \sqrt{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^−_b π^+ final state, where the Ξ^−_b baryon is reconstructed through the decays J/ψΞ^−, ψ(2S)Ξ^−, J/ψΛK^−, and J/ψΣ^0K−. Finally, the fraction of Ξ^−_b baryons produced from Ξ_b(5945)^0 decays is determined.