Abstract
We have studied the reactionse + e −→hadrons,e + e −, μ+ μ− and τ+ τ−, in the energy range 88.2\( \leqq \sqrt s \leqq 94.2\) GeV. A total luminosity of 5.5 pb−1, corresponding to approximately 115000 hadronic and 10000 leptonicZ 0 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:
If we do not assume lepton universality, we obtain for the partial decay widths of theZ 0 intoe + e − μ+ μ− and τ+ τ−:
From the measured ratio of the invisible and the leptonic decay widths of theZ 0, we determine the number of light neutrino species to beN v =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 theZ 0. We obtain\(\bar g_V = - 0.046_{ - 0.012}^{ + 0.015}\) and\(\bar g_A = - 0.500 \pm 0.003\). In the framework of the Standard Model, we estimate the top quark mass to bem t =193 +52−69 ±16 (Higgs) GeV, and we derive a value for the weak mixing angle of sin2θ W =1−(M W /M Z )2=0.222 ± 0.008, corresponding to an effective weak mixing angle of\(\sin ^2 \bar \theta _W = 0.2315 \pm 0.0025\).
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L3 Collaboration., Adeva, B., Adriani, O. et al. Measurement of electroweak parameters from hadronic and leptonic decays of theZ 0 . Z. Phys. C - Particles and Fields 51, 179–203 (1991). https://doi.org/10.1007/BF01475788
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DOI: https://doi.org/10.1007/BF01475788