Observation of the $Ξ^-_\mathrm{b}$ $\to$ $ψ$(2S)$Ξ^-$ decay and studies of the $Ξ_\mathrm{b}$(5945)$^{0}$ baryon in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract: The first observation of the decay $\Xi^-_\mathrm{b}$ $\to$ $\psi$(2S)$\Xi^-$ and measurement of the branching ratio of $\Xi^-_\mathrm{b}$ $\to$ $\psi$(2S)$\Xi^-$ to $\Xi^-_\mathrm{b}$ $\to$ J/$\psi$$\Xi^-$ are presented. The J/$\psi$ and $\psi$(2S) mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at $\sqrt{s}$ = 13 TeV in 2016-2018, corresponding to an integrated luminosity of 140 fb$^{-1}$. The branching fraction ratio is measured to be $\mathcal{B}$($\Xi^-_\mathrm{b}$ $\to$ $\psi$(2S)$\Xi^-$) / $\mathcal{B}$($\Xi^-_\mathrm{b}$ $\to$ J/$\psi$$\Xi^-$) = 0.84 $^{+0.21}_{-0.19}$ (stat) $\pm$ 0.10 (syst) $\pm$ 0.02 ($\mathcal{B}$), where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the $\Xi_\mathrm{b}$(5945)$^{0}$ baryon mass and natural width are also presented, using the $\Xi_\mathrm{b}^-\pi^+$ final state, where the $\Xi^-_\mathrm{b}$ baryon is reconstructed through the decays J/$\psi \Xi^-$, $\psi$(2S)$\Xi^-$, J/$\psi \Lambda$K$^-$, and J/$\psi \Sigma^0$K$^-$. Finally, the fraction of the $\Xi^-_\mathrm{b}$ baryons produced from $\Xi_\mathrm{b}$(5945)$^{0}$ decays is determined.