Measurement of the mass difference and relative production rate of the $\hat{I}{\text{c◯}}_b^{-}$ and $\hat{I}{ž}_b^{-}$ baryons

Abstract

The mass difference between the $\hat{I}{\text{c◯}}_b^{-}$ and $\hat{I}{ž}_b^{-}$ baryons is measured using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9{\text{fb}}^{-1}$, and is found to be \begin{equation} m(Ω^-_b)- m(Ξ^-_b) = 248.54 \pm 0.51 \text{(stat)} \pm 0.38 \text{(syst)} \, \text{MeV}/c^2. \end{equation} The mass of the $\hat{I}{\text{c◯}}_b^{-}$ baryon is measured to be \begin{equation} m(Ω^-_b)= 6045.9 \pm 0.5 \text{(stat)} \pm 0.6 \text{(syst)} \, \text{MeV}/c^2. \end{equation} This is the most precise determination of the $\hat{I}{\text{c◯}}_b^{-}$ mass to date. In addition, the production rate of $\hat{I}{\text{c◯}}_b^{-}$ baryons relative to that of $\hat{I}{ž}_b^{-}$ baryons is measured for the first time in $pp$ collisions, using an LHCb dataset collected at a center-of-mass energy of $13\text{TeV}$ and corresponding to an integrated luminosity of $6{\text{fb}}^{-1}$. Reconstructing beauty baryons in the kinematic region $2<\hat{I}\cdot <6$ and $p_T<20\text{GeV}/c$ with their decays to a $J/\ddot{I}ˆ$ meson and a hyperon, the ratio \begin{equation} \frac{f_{Ω^-_b}}{f_{Ξ^-_b}}\times\frac{\mathcal{B}(Ω^-_b \to J/ψΩ^-)}{\mathcal{B}(Ξ^-_b \to J/ψΞ^-)} = 0.120 \pm 0.008 \text{(stat)} \pm 0.008 \text{(syst)}, \end{equation} is obtained, where $f_{\hat{I}{\text{c◯}}_b^{-}}$ and $f_{\hat{I}{ž}_b^{-}}$ are the fragmentation fractions of $b$ quarks into $\hat{I}{\text{c◯}}_b^{-}$ and $\hat{I}{ž}_b^{-}$ baryons, respectively, and $\mathcal{B}$ represents the branching fractions of their respective decays.

23 pages, 3 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-053.html (LHCb public pages)