  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^- --> Xi_c^0 pi^-, Xi_c^0
--> pK-K-pi+ channel and the mass and lifetime are measured using the
Lambda_b^0 --> Lambda_c^+ pi- mode as a reference. We measure M(Xi_b^-) -
M(Lambda_b^0) = 178.36 +- 0.46 +- 0.16 MeV/c^2 and tau(Xi_b^-)/tau(Lambda_b^0)
= 1.089 +- 0.026 +- 0.011, 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.
