Observation of Parity Nonconservation in Møller Scattering

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