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Measurements of cross sections and forward-backward asymmetries at the Z resonance and determination of electroweak parameters

CollaborationWith : Achard, Pablo / Ambrosi, Giovanni / Bourquin, Maurice / Braccini, Saverio / Chamizo Llatas, Maria / Deglon, Patrick / Extermann, Pierre / Field, John / Fredj, Lotfi / Kienzle, Maria-Novella / Muheim, Franz / Pohl, Martin / Produit, Nicolas / Sciarrino, Deborah
Published in European Physical Journal. C. 2000, vol. 16, no. 1, p. 1-40
Abstract 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 103pb−1 was collected at centre-of-mass energies s√≈mZ and s√≈mZ±1.8GeV which 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: mZ=91189.8±3.1MeV,ΓZ=2502.4±4.2MeV,Γhad=1751.1±3.8MeV,Γℓ=84.14±0.17MeV. An invisible width of Γinv=499.1±2.9MeV is derived which in the Standard Model yields for the number of light neutrino species Nν=2.978±0.014 . Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be g¯ℓV=−0.0397±0.0017 and g¯ℓA=−0.50153±0.00053 . Including our measurements of the Z→bb¯ forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin2θ¯W=0.23093±0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of mH<133 GeV is set at 95% confidence level.
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L3 COLLABORATION. Measurements of cross sections and forward-backward asymmetries at the Z resonance and determination of electroweak parameters. In: European Physical Journal. C, 2000, vol. 16, n° 1, p. 1-40. https://archive-ouverte.unige.ch/unige:47337

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Deposited on : 2015-02-27

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