Measurement of theZ0 line shape parameters and the electroweak couplings of charged leptons

We report on an improved measurement of the mass of theZ⁰ boson, its total width and its partial decay widths into hadrons and leptons, as well as the effective axial vector and vector couplings to charged leptons. These measurements are based on a data set of approximately 160 000 hadronicZ⁰ decays and 18 000 decays into electrons, muons and taus, recorded by the OPAL experiment at centre of mass energies near the mass of theZ⁰. The total width and the partial widths to visible final states, derived from the measured cross sections, are used to extract the invisible width. The effective couplings of theZ⁰ to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at the different centre of mass energy points of theZ⁰ scan. The implications of our results in the context of the Standard Model are discussed.On leave from Research Institute for Computer Peripherals, Hangzhou, China