A measurement of electron production in hadronicZ0 decays and a determination of

The production rate of electrons with momentump>4 GeV/c and large momentum transverse to the jet containing the electron has been measured in 136000 hadronic decays of theZ0 recorded with the OPAL detector at LEP in 1990. The dominant source of these electrons is the semileptonic decay of hadrons containingb quarks. If we assume that the semileptonic branching fraction ofb hadrons produced on theZ0 resonance is the same as the branching fraction measured at the ϒ(4S) resonance, we determine$$\Gamma _{b\bar b} = 394 \pm 13 \pm 32$$ MeV, where the first error is statistical and the second error is systematic. The sensitivity of the result to this assumption is discussed. We have reduced the dependence of our result on the model ofb hadron semileptonic decay by taking into account the correlation between the model dependence of the branching fractions measured at the ϒ(4S) and of our kinematic acceptance for electrons.