Measurement of electroweak parameters from hadronic and leptonic decays of the Z<sup>0</sup>
We have studied the reactions e+e−→hadrons, e+e−, μ+ μ− and τ+τ−, in the energy range 88.2 ≦ √s ≦ 94.2 GeV. A total luminosity of 5.5 pb<sup>−1</sup>, corresponding to approximately 115000 hadronic and 10000 leptonic Z<sup>0</sup> decays, has been recorded with the L3 detect...
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| Autores principales: | , |
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| Formato: | Articulo |
| Lenguaje: | Inglés |
| Publicado: |
1991
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| Materias: | |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/81060 |
| Aporte de: |
| Sumario: | We have studied the reactions e+e−→hadrons, e+e−, μ+ μ− and τ+τ−, in the energy range 88.2 ≦ √s ≦ 94.2 GeV. A total luminosity of 5.5 pb<sup>−1</sup>, corresponding to approximately 115000 hadronic and 10000 leptonic Z<sup>0</sup> 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:
M<sub>z</sub> = 91.181 ± 0.010 ± 0.02 (LEP) GeV,
Γ<sub>z</sub> = 2501 ± 17 MeV,
Γ<sub>had</sub>= 1742 ± 19 MeV, Γ<sub>t</sub> = 83.6 ± 0.8 MeV.
If we do not assume lepton universality, we obtain for the partial decay widths of the Z<sup>0</sup> into e+e−, μ+μ− and τ+ τ−:
Γ<sub>e</sub> = 83.3 ± 1.1 MeV, Γ<sub>μ</sub> = 84.5 ± 2.0 MeV,
Γ<sub>τ</sub> = 84.0 ± 2.7 MeV.
From the measured ratio of the invisible and the leptonic decay widths of the Z<sup>0</sup>, 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 Z<sup>0</sup>. We obtain g¯<sub>V</sub> = −0.046<sup>+0.015</sup><sub>−0.012</sub> and g¯<sub>A</sub> = −0.500 ± 0.003. In the framework of the Standard Model, we estimate the top quark mass to be m<sub>t</sub> =193<sup>+52</sup><sub>−69</sub> ± 16 (Higgs) GeV, and we derive a value for the weak mixing angle of sin<sup>2</sup>θ<sub>W</sub> ≡ 1 − (M<sub>W</sub>/M<sub>Z</sub>)<sup>2</sup> = 0.222 ± 0.008, corresponding to an effective weak mixing angle of sin<sup>2</sup>θ¯<sub>W</sub> = 0.2315 ± 0.0025. |
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