A determination of electroweak parameters from Z 0 decays into charged leptons

We have measured the partial widths for the three reactions e +e -→Z 0→e +e -, μ +μ -, τ +τ -. The results are Γ ee=84.3±1.3 MeV, √Γ eeΓ μμ=83.3±1.3 MeV, and √Γ eeΓ ττ=83.9±1.4 MeV, where the errors are statistical. The systematic errors are estimated to be 1.0 MeV, 0.9 MeV, and 1.4 MeV, respectively. We perform a simultaneous fit to the cross sections for the e +e -→e +e -, μ +μ -, and τ +τ - data, the differential cross section as a function of polar angle for the electron data, and the forward-backward asymmetry for the muon data. We obtain the leptonic partial with Γ ll=84.0±0.9(stat.) MeV. The systematic error is estimated to be 0.8 MeV. Also, we obtain the axial-vector and vector weak coupling constants of charged leptons, g A=-0.500±0.003 and g v=-0.064 +0.017 -0.013.