Measurement of electroweak parameters from hadronic and leptonic decays of the Z<SUP>0</SUP>

We have studied the reactions e+ e− GeV. A total luminosity of 5.5 pb− 1, corresponding to approximately 115000 hadronic and 10000 leptonic Z0 decays, has been recorded with the L3 detector. From a simultaneous fit to all of our measured cross section data, we obtain assuming lepton universality: Mz = 91.181 ± 0.010 ± 0.02 (LEP) GeV, Gz = 2501 ± 17 MeV, Ghad = 1742 ± 19 MeV, Gt = 83.6 ± 0.8 MeV. If we do not assume lepton universality, we obtain for the partial decay widths of the Z0 into e+ e− Ge = 83.3 ± 1.1 MeV, Gm = 84.5 ± 2.0 MeV, Gt = 84.0 ± 2.7 MeV. From the measured ratio of the invisible and the leptonic decay widths of the Z0, we determine the number of light neutrino species to be Nv =3.05±0.10. We include our measurements of the forward-backward asymmetry for the leptonic channels in a fit to determine the vector and axial-vector neutral current coupling constants of charged leptons to the Z0. We obtain [(g̅)]V = − 0.046 +0.015−0.012 and [(g̅)]A = − 0.500 ± 0.003. In the framework of the standard model, we estimate the top quark mass to bem t =193−69+52 ±16 (Higgs) GeV, and we derive a value for the weak mixing angle of sin2sin2 θW = 0.2315 ± 0.0025