EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-PH-EP-2014-226

Precision measurement of the mass and lifetime of the Ξ−b baryon The LHCb collaboration† 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 → Ξ0c pi−, Ξ0c → pK−K−pi+ channel and the mass and lifetime are measured using the Λ0b → Λ+c pi − 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 two better precision on the Ξ−b mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations. Submitted to Physical Review Letters c © CERN on behalf of the LHCb collaboration, license CC-BY-4.0. †Authors are listed at the end of this Letter. a