Measurements of cross sections and forward-backward
at the Z resonance and
of electroweak parameters
The L3 Collaboration
M.Acciarri26 - et al.
26 INFN-Sezione di Milano, 20133 Milan, Italy
Received: 4 February 2000
/ Published online: 18 May 2000
- © Springer-Verlag 2000
Dedicated to the memory of Prof. Dr. Klaus Schultze
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 was collected at centre-of-mass energies and which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results:
An invisible width of is derived which in the Standard Model yields for the number of light neutrino species . 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 and . Including our measurements of the forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of 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 is set at 95% confidence level.
Copyright Società Italiana di Fisica, Springer-Verlag 2000