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 → Ξ0cπ-, Ξ0c → pK-K-π+, channel and the mass and lifetime are measured using the Λ0b → Λ+Cπ-, mode as a reference. We measure M (Ξ-b) - M(Λ0b)= 178.36 ± 0.46 ± 0.16 MeV=c2, (τξ-B/τΛ0b) = 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.