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Measurements of Cross Sections and Forward-Backward Asymmetries at the Z Resonance and Determination of Electroweak Parameters / L3 collaboration
We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years $1993-95$.A total luminosity of 103 pb$^{-1}$ was collected at centre-of-mass energies $\sqrt{s} \approx m_\mathrm{Z}$ and $\sqrt{s} \approx m_\mathrm{Z} \pm 1.8$ GeVwhich corresponds to 2.5 million hadronic and 245 thousand leptonic events selected.These data lead to a significantly improved determination of Z parameters.From the total cross sections, combined with our measurements in $1990-92$,we obtain the final results:%%%\begin{eqnarr ay*} m_\mathrm{Z} = 91189.8 \pm 3.1\ \mathrm{MeV} \, , & & \Gamma_\mathrm{Z} = 2502.4 \pm 4.2\ \mathrm{MeV} \, , \\ \Gamma_\mathrm{had} = 1741.1 \pm 3.8\ \mathrm{MeV} \, , & & \Gamma_\ell = 84.14 \pm 0.17\ \mathrm{MeV} \,. \label{eq:Zpara_abstract}\end{eqnarray*}%%%An invisible width of $\Gamma_\mathrm{inv} = 499.1 \pm 2.9$ MeV is derived which in the Standard Model yields for the numberof light neutrino species $N_\nu = 2.978 \pm 0.014$.Adding our results on the leptonic forward-backward asymmetries and thetau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be $\bar{g}_{\mathrm{V}}^\ell = -0.0397\pm 0.0017$ and $\bar{g}_{\mathrm{A}}^\ell = -0.50153 \pm 0.00053$.Including our measurements of the Z $\rightarrow \mathrm{b}\bar{\mathrm{b}}$ forward-backward and quark charge asymmetries a value for the effective electroweakmixing angle of $\sin^2\!\overline{\theta}_{\mathrm{W}} = 0.23093 \pm 0.00066$ is derived. [...]
hep-ex/0002046; CERN-EP-2000-022; CERN-EP-2000-022; CERN-L3-202.- Geneva : CERN, 2000 - 97 p. - Published in : Eur. Phys. J. C 16 (2000) 1-40 Fulltext: ep-2000-022 - PDF; arXiv:hep-ex_0002046 - PDF; External link: Preprint - Please contact the library if you need to access this document.

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