Precision measurement of the ${\mathrm{\Xi }}_b^{-}$ baryon lifetime

A sample of $pp$ collision data, corresponding to an integrated luminosity of 5.5 fb${}^{-1}$ and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the ${\mathrm{\Xi }}_b^{-}$ baryon to that of the ${\mathrm{\Lambda }}_b^0$ baryon, $r_{\tau }\equiv {\tau }_{{\mathrm{\Xi }}_b^{-}}\mathrm{/}{\tau }_{{\mathrm{\Lambda }}_b^0}$. The value $r_{\tau }=1.076\pm 0.013\pm 0.006$ is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain $r_{\tau }^{\mathrm{R}\mathrm{u}\mathrm{n}1,2}=1.078\pm 0.012\pm 0.007$. Multiplying by the world-average value of the ${\mathrm{\Lambda }}_b^0$ lifetime yields ${\tau }_{{\mathrm{\Xi }}_b^{-}}^{\mathrm{R}\mathrm{u}\mathrm{n}1,2}=1.578\pm 0.018\pm 0.010\pm 0.011$ ps, where the uncertainties are statistical, systematic, and due to the limited knowledge of the ${\mathrm{\Lambda }}_b^0$ lifetime. This measurement improves the precision of the current world average of the ${\mathrm{\Xi }}_b^{-}$ lifetime by about a factor of two, and is in good agreement with the most recent theoretical predictions.