Messung der Myonpaarproduktion im Prozess e+ e- --> mu+ mu- (gamma) bei Schwerpunktsenergien von 89 GeV bis 183 GeV

Presented are the total cross-sections and forward-backward-asymmetries of the reaction at center of mass energies between 89 GeV and 183 GeV at the LEP-accelerator measured with the L3-Detector from 1995 to 1997. These data include measurements from LEP I on the Z-resonance and from LEP II above the W-pairproduction-threshhold. The myonselection acceptance was increased from polar angles above up to Compared to previous measurements, uncertainties are reduced regarding the assumption of lepton-universality and the determination of the Z-mass and width: Fitting the myonpair-data using a parametrisation in effective coupling constants and yields = (91.196Þ0.013) GeV and = (2.497Þ0.021) GeV. Additionally the Z-mass is determined using the S-matrix-parametrisation without restrictions on the -Z interference term. Adding LEP II data to the LEP I results halves the error on the Z-mass. The results presented in this thesis are obtained by using the FB myonchambersystem - installed before 1995 LEP running - to its full advantage. Myonpair events are used to demonstrate the systemperformance in all components.