Measurement of the averageb hadron lifetime inZ0 decays

A sample of 2610 electron candidates and 2762 muon candidates identified in hadronicZ0 decays has been used to measure the averageb hadron lifetime. These data were recorded with the OPAL detector during 1990 and 1991. Maximum likelihood fits to the distributions of the lepton impact parameters yield an averageb hadron lifetime of$$\tau _b = 1523 \pm 34 \pm 38fs$$, where the first error is statistical and the second systematic. This result is a weighted average over the semileptonic branching fractions and production rates of theb hadrons produced inZ0 decays.