Precision measurement of the mass and lifetime of the $\Xi_b^-$ baryon

We report on measurements of the mass and lifetime of the $\Xi_b^-$ baryon using about 1800 $\Xi_b^-$ decays reconstructed in a proton-proton collision data set corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The decays are reconstructed in the $\Xi_b^-\to\Xi_c^0\pi^-$, $\Xi_c^0\to pK^-K^-\pi^+$ channel and the mass and lifetime are measured using the $\Lambda_b^0\to\Lambda_c^+\pi^-$ mode as a reference. We measure \begin{equation} \ M(\Xi_b^-)-M(\Lambda_b^0)=178.36\pm0.46\pm0.16~MeV/c^2, \end{equation} \begin{equation} \frac{^\tau\Xi_b^-} {^\tau\Lambda_b^0}=1.089\pm0.026\pm0.011, \end{equation} where the uncertainties are statistical and systematic, respectively. These results lead to a factor of two better precision on the $\Xi_b^-$ mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.