Determination of the average lifetime of b-baryons

The average lifetime of b-baryons has been studied using 3 x 10(6) hadronic Z(0) decays collected by the DELPHI detector at LEP. Three methods have been used, based on the measurement of different observables: the proper decay time distribution of 206 vertices reconstructed with a Lambda, a lepton and an oppositely charged pion; the impact parameter distribution of 441 muons with high transverse momentum accompanied by a Lambda in the same jet; and the proper decay time distribution of 125 Lambda(c)-lepton decay vertices with the Lambda(c) exclusively reconstructed through its pK pi, pK(0) and Lambda 3 pi decay modes. The combined result is: [GRAPHICS] where the first systematic error is due to experimental uncertainties and the second to the uncertainties in the modelling of the b-baryon production and semi-leptonic decay, Including the measurement recently published by DELPHI based on a sample of proton-muon vertices, the average b-baryon lifetime is: [GRAPHICS] [GRAPHICS]