Electroweak studies in e/sup +/e/sup -/ collisions: 12<. sqrt. s<46. 78 GeV

The Mark J Collaboration at the DESY e/sup +/e/sup -/ collider PETRA presents results on the electroweak reactions e/sup +/e/sup -/..--> mu../sup +/..mu../sup -/tau/sup +/tau/sup -/,..mu../sup +/..mu../sup -/..gamma.., and e/sup +/e/sup -/..mu../sup +/..mu../sup -/. The c.m. energy range is 12 to 46.78 GeV. In the ..mu../sup +/..mu../sup -/ and tau/sup +/tau/sup -/ channels the total cross sections and the forward-backward asymmetries are reported and compared with other experiments. The results are in excellent agreement with the standard model. The weak-neutral-current vector and axial-vector coupling constants are determined. The values for muons and tau's are compatible with universality and with the predictions of the standard model. In the ..mu../sup +/..mu../sup -/..gamma.. channel, all measured distributions, including the forward-backward muon asymmetry, are in excellent agreement with the electroweak theory. Our data on the two-photon process, e/sup +/e/sup -/..mu../sup +/..mu../sup -/, agrees with QED to order ..cap alpha../sup 4/ over the entire energy range and the Q/sup 2/ range from 0.7 to 166 GeV/sup 2/.