# Measurement of the mass and production rate of ${\Xi }_{b}^{-}$ baryons

23 March 2019

Abstract: The first measurement of the production rate of ${\Xi }_{b}^{-}$ baryons in $pp$ collisions relative to that of ${\Lambda }_{b}^{0}$ baryons is reported, using data samples collected by the LHCb experiment, and corresponding to integrated luminosities of 1, 2 and $1.6\text{}\text{}{\mathrm{fb}}^{-1}$ at $\sqrt{s}=7$, 8 and 13 TeV, respectively. In the kinematic region $2<\eta <6$ and ${p}_{T}<20\text{}\text{}\mathrm{GeV}/c$, we measure $\frac{{f}_{{\Xi }_{b}^{-}}}{{f}_{{\Lambda }_{b}^{0}}}\frac{B\left({\Xi }_{b}^{-}\to J/\psi {\Xi }^{-}\right)}{B\left({\Lambda }_{b}^{0}\to J/\psi \Lambda \right)}=\left(10.8±0.9±0.8\right)×{10}^{-2}$ [$\sqrt{s}=7,8\text{}\text{}\mathrm{TeV}$], $\frac{{f}_{{\Xi }_{b}^{-}}}{{f}_{{\Lambda }_{b}^{0}}}\frac{B\left({\Xi }_{b}^{-}\to J/\psi {\Xi }^{-}\right)}{B\left({\Lambda }_{b}^{0}\to J/\psi \Lambda \right)}=\left(13.1±1.1±1.0\right)×{10}^{-2}$ [$\sqrt{s}=13\text{}\text{}\mathrm{TeV}$], where ${f}_{{\Xi }_{b}^{-}}$ and ${f}_{{\Lambda }_{b}^{0}}$ are the fragmentation fractions of $b$ quarks into ${\Xi }_{b}^{-}$ and ${\Lambda }_{b}^{0}$ baryons, respectively; $B$ represents branching fractions; and the uncertainties are due to statistical and experimental systematic sources. The values of ${f}_{{\Xi }_{b}^{-}}/{f}_{{\Lambda }_{b}^{0}}$ are obtained by invoking SU(3) symmetry in the ${\Xi }_{b}^{-}\to J/\psi {\Xi }^{-}$ and ${\Lambda }_{b}^{0}\to J/\psi \Lambda$ decays. Production asymmetries between ${\Xi }_{b}^{-}$ and ${\overline{\Xi }}_{b}^{+}$ baryons are also reported. The mass of the ${\Xi }_{b}^{-}$ baryon is also measured relative to that of the ${\Lambda }_{b}^{0}$ baryon, from which it is found that $m\left({\Xi }_{b}^{-}\right)=5796.70±0.39±0.15±0.17\text{}\text{}\mathrm{MeV}/{c}^{2}$, where the last uncertainty is due to the precision on the known ${\Lambda }_{b}^{0}$ mass. This result represents the most precise determination of the ${\Xi }_{b}^{-}$ mass.

Published in: Physical Review D 99 (2019)