Measurement of the average B hadron lifetime in Z0 decays

A sample of 689 muon candidates and 665 electron candidates identified in multihadronic Z0 decays has been used to measure the average B hadron lifetime. These data were recorded with the OPAL detector during 1990. Maximum likelihood fits to the distributions of the lepton impact parameters yield an average B hadron lifetime of τb = 1.37 ± 0.07 ± 0.06 ps, 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 the B hadrons produced in Z0 decays.