Measurement of the Ratio of Cross Sections for Neutrino and Antineutrino Scattering from Electrons

Measurements of the ratio R of the purely leptonic weak neutral-current cross sections ${{σ}({{ν}}_{{μ}}e{→}{{ν}}_{{μ}}e)}{{σ}({{{ν}}}_{{μ}}e{→}{{{ν}}}_{{μ}}e)}$ and of the absolute value of ${σ}({{{ν}}}_{{μ}}e{→}{{{ν}}}_{{μ}}e)$ are reported. These yield $R={1.38}_{{-}0.31}+0.40(stat)±{}0.17(syst)$ and ${{σ}({{{ν}}}_{{μ}}e{→}{{{ν}}}_{{μ}}e)}{{E}_{{{{ν}}}_{{μ}}}}=[1.16±{}0.20(stat)±{}0.14(syst)]×{}{10}^{{-}42}$ ${cm}²$/GeV. This value of $R$ determines the fundamental weak neutral-current parameter to be ${{sin}²{θ}}W=0.209±{}0.029(stat)±{}0.013(syst)$.