Studies of muon-pair production in e+e- annihilations at the LEP collider

Studies of the reaction e+e--μ+ μ- ('muon-pair production') using tbe DELPHI experiment at the LEP Collider are presented. The design and performance of the DELPHI Barrel Muon Detector are described, and some elements of the associated software are discussed. The methods for selecting muon-pair events and for the calculation of backgrounds and efficiencies are described in detail. Results are presented for data coming from a scan around the zo peak at seven centre-of-mass energies from 88.22 GeV to 94.22 GeV. A sample of 1322 muon-pair events is selected in the polar angular range 43° =::; 8 =::; 137°. From a fit to the measured muon-pair cross-sections the square root of the product of the z0-e+e- and the z0-μ+μ- partial widths is determined to be (feef μμ) 1' 2 = 83.8 ± 1.2(sta.t) ± 1.l(sys) MeV. Tbe ratio of the hadronic to muon-pair partial widths is found to be fh/f "'"' = 19.97 ± 0.56(stat) ± 0.45(sys). The forward-backward asymmetry at the centre-of-mass energy nearest the zo peak ,fi = 91.22 GeV is found to be AFB = 0.060 ± 0.040(stat) ± 0.005(sys). From a simultaneous fit to the muon-pair cross-sections and the forward-backward asymmetries across the zo resonance we find that for the vector and axial coupling constants of electrons and muons ( vevμ)1/2 = -0.116!g:~~(stat) ± 0.003(sys) and (aeaμ) 112 = -0.998 ± O.OlO(stat) ± 0.007(sys). All results are in agreement with the expectations of the Standard Model.