Observation of the Ξb−​ → ψ(2S) Ξ− decay and studies of the Ξb∗0 baryon in proton-proton collisions at sqrt(s)= 13 TeV

The first observation of the decay Ξ−𝑏→𝜓⁡(2⁢𝑆)⁢Ξ− and measurement of the branching ratio of Ξ− 𝑏→𝜓⁡(2⁢𝑆)⁢Ξ− to Ξ−𝑏→𝐽/𝜓⁢Ξ− are presented. The 𝐽/𝜓 and 𝜓⁡(2⁢𝑆) 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⁡(2⁢𝑆)⁢Ξ−)/ℬ⁡(Ξ−𝑏→𝐽/𝜓⁢Ξ−)=0.8⁢4+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 Ξ𝑏⁢(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/𝜓⁢Ξ−, 𝜓⁡(2⁢𝑆)⁢Ξ−, 𝐽/𝜓⁢Λ⁢𝐾−, and 𝐽/𝜓⁢Σ0⁢𝐾−. Finally, the fraction of Ξ−𝑏 baryons produced from Ξ𝑏⁢(5945)0 decays is determined.