Precision measurement of the mass and lifetime of the Ξ-                      b baryon

We report on measurements of the mass and lifetime of the Ξ- b baryon using about 1800 Ξ- 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 Ξ- b → Ξ0 cπ-, Ξ0 c → pK-K-π+, channel and the mass and lifetime are measured using the Λ0 b → Λ+ Cπ-, mode as a reference. We measure M (Ξ- b) - M(Λ0 b)= 178.36 ± 0.46 ± 0.16 MeV=c2, (τξ- B/τΛ0 b) = 1.089 ± 0.026 ± 0.011, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of 2 better precision on the Ξ- b mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations. © 2014 CERN, for the LHCb Collaboration.