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.
Categories: hep-ex