Observation of the $\Xi^-_\mathrm{b}$ $\to$ $\psi$(2S)$\Xi^-$ decay and studies of the $\Xi_\mathrm{b}^{\ast{}0}$ 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}^{\ast{}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}^{\ast{}0}$ decays is determined.