A measurement of the average lifetime of b-flavoured baryons

The average lifetime of baryons containing a b quark has been measured with the OPAL detector using data collected between 1990 and 1992. Semileptonically decaying b-flavoured baryons which produce a Λ are identified through the charge correlation of the λ and lepton. The decay point of the baryon is estimated by the λ-lepton vertex, and the observed distribution of decay lengths is fitted to determine the average lifetime. In the data sample consisting of 261 right-sign and 104 wrong-sign λ-lepton charge combinations, the average b baryon lifetime is found to be τ = 1.05+0.23-0.20±0.08 ps, where the first error is statistical and the second systematic.