Observation of Parity Nonconservation in Møller Scattering

Abstract

We report a measurement of the parity-violating asymmetry in fixed target electron-electron (M\o{}ller) scattering: ${A}_{\mathrm{PV}}=[\ensuremath{-}175\ifmmode\pm\else\textpm\fi{}30(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}20(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$. This first direct observation of parity nonconservation in M\o{}ller scattering leads to a measurement of the electron's weak charge at low energy ${Q}_{W}^{e}=\ensuremath{-}0.053\ifmmode\pm\else\textpm\fi{}0.011$. This is consistent with the standard model expectation at the current level of precision: ${sin}^{2}{\ensuremath{\theta}}_{\mathrm{W}}({M}_{Z}{)}_{\overline{\mathrm{MS}}}=0.2293\ifmmode\pm\else\textpm\fi{}0.0024(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.0016(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.0006(\mathrm{theory})$.