Electroweak studies ine+e−collisions: 12<√s<46.78 GeV

The Mark J Collaboration at the DESY $e^{+}$ $e^{\mathrm{-}}$ collider PETRA presents results on the electroweak reactions ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$ ${\mathrm{\tau }}^{+}$ ${\mathrm{\tau }}^{\mathrm{-}}$,${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$γ, and $e^{+}$ $e^{\mathrm{-}}$ ${\mu }^{+}$ ${\mu }^{\mathrm{-}}$. The c.m. energy range is 12 to 46.78 GeV. In the ${\mu }^{+}$ ${\mu }^{\mathrm{-}}$ and ${\tau }^{+}$ ${\tau }^{\mathrm{-}}$ 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 τ’s are compatible with universality and with the predictions of the standard model. In the ${\mu }^{+}$ ${\mu }^{\mathrm{-}}$γ 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, $e^{+}$ $e^{\mathrm{-}}$ ${\mu }^{+}$ ${\mu }^{\mathrm{-}}$, agrees with QED to order ${\alpha }^4$ over the entire energy range and the $Q^2$ range from 0.7 to 166 ${\mathrm{GeV}}^2$.