Analysis of Z⁰ couplings to charged leptons

The couplings of the Z⁰ to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at centre of mass energies near to the mass of the Z⁰. The data are consistent with lepton universality. Using a parametrisation of the lepton pair differential cross section which assumes that the Z⁰ has only vector and axial couplings to leptons, the charged leptonic partial decay width of the Z⁰ is determined to be G{cyrillic}_ol+ol- = 83.1±1.9 MeV and the square of the product of the effective axial vector and vector coupling constants of the Z⁰ to charged leptons to be a ̌² _ol v ̌² _ol = 0.0039± 0.0083, in agreement with the standard model. A parametrisation in the form of the improved Born approximation gives effective leptonic axial vector and vector coupling constants a ̌² _ol = 0.998±0.024 and v ̌² _ol = 0.0044±0.0083. In the framework of the standard model, the values of the parameters ρ{variant}_z and sin²θ_w are found to be 0.998±0.024 and 0.233^+0.045 _-0.012 respectively. Using the relationship in the minimal standard model between ρ{variant}_z and sin²θ_w, the results sin²θ^SM _w = 0.233^+0.007 _-0.006 is obtained. Our previously published measurement of the ratio of the hadronic to the leptonic partial width of the Z⁰ is update: R_z = 21.72^+0.71 _-0.65.