Measurements of the cross section and forward-backward asymmetry for the
reaction e+e- –> mu+mu- using the DELPHI detector at LEP are presented.
The data come from a scan around the Z0 peak at seven centre of mass
energies, giving a sample of 3858 events in the polar angle region
22-degrees < theta < 158-degrees. From a fit to the cross section for
43-degrees < theta < 137-degrees, a polar angle region for which the
absolute efficiency has been determined, the square root of the product
of the Z0 –> e+e- and Z0 –> mu+mu- partial widths is determined to be
(GAMMA-e-GAMMA-mu)1/2 = 85.0 +/- 0.9 (stat.) +/- 0.8 (syst.) MeV. From
this measurement of the partial width, the value of the effective weak
mixing angle is determined to be sin2(theta-w) = 0.2267 +/- 0.0037. The
ratio of the hadronic to muon pair partial widths is found to be
GAMMA-h/GAMMA-mu = 19.89 +/- 0.40 (stat.) +/- 0.19 (syst.). The
forward-backward asymmetry at the resonance peak energy E(CMS) = 91.22
GeV is found to be A(FB) = 0.028 +/- 0.020 (stat.) +/- 0.005 (syst.).
From a combined fit to the cross section and forward-backward asymmetry
data, the products of the electron and muon vector and axial-vector
coupling constants are determined to be V(e)V-mu = 0.0024 +/- 0.0015
(stat.) +/- 0.0004 (syst.) and A(e)A-mu = 0.253 +/- 0.003 (stat.) +/-
0.003 (syst.). These results are in good agreement with the expectations
of the minimal standard model
