Measurements of the b baryon lifetime

Using about 1.5 million hadronic Z decays recorded with the ALEPH detector, the lifetime of the b baryons has been measured using two independent data samples. From a maximum likelihood fit to the impact parameter distribution of leptons in 519 Λl- combinations containing a b baryon sample of 290 decays, the measured b baryon lifetime is τb-baryon = 1.05+0.12-0.11 (stat) +/- 0.09 (syst) ps. The lifetime of the Λ0b baryon from a maximum likelihood fit to the proper time distribution of 58 Λ+cl- candidates containing a Λ0b sample of 44 decays, is τΛ0b = 1.02+0.23-0.18 (stat) +/- 0.06 (syst) ps.