  The mass difference between the $\Omega^-_b$ and $\Xi^-_b$ 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(\Omega^-_b)- m(\Xi^-_b) = 248.54 \pm 0.51
\text{(stat)} \pm 0.38 \text{(syst)} \, \text{MeV}/c^2. \end{equation} The mass
of the $\Omega^-_b$ baryon is measured to be \begin{equation} m(\Omega^-_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 $\Omega^-_b$ mass
to date. In addition, the production rate of $\Omega^-_b$ baryons relative to
that of $\Xi^-_b$ 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 $2 <
\eta < 6$ and $p_T < 20\,\text{GeV}/c$ with their decays to a $J/\psi$ meson
and a hyperon, the ratio \begin{equation}
\frac{f_{\Omega^-_b}}{f_{\Xi^-_b}}\times\frac{\mathcal{B}(\Omega^-_b \to J/\psi
\Omega^-)}{\mathcal{B}(\Xi^-_b \to J/\psi \Xi^-)} = 0.120 \pm 0.008
\text{(stat)} \pm 0.008 \text{(syst)}, \end{equation} is obtained, where
$f_{\Omega^-_b}$ and $f_{\Xi^-_b}$ are the fragmentation fractions of $b$
quarks into $\Omega^-_b$ and $\Xi^-_b$ baryons, respectively, and $\mathcal{B}$
represents the branching fractions of their respective decays.
