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 → Ξ ⁰ _cπ ^-, Ξ ⁰ _c → pK ^-K ^-π ⁺, channel and the mass and lifetime are measured using the Λ ⁰ _b → Λ ⁺ _Cπ ^-, mode as a reference. We measure M (Ξ ^- _b) - M(Λ ⁰ _b)= 178.36 ± 0.46 ± 0.16 MeV=c ², (τξ ^- _B/τΛ ⁰ _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.