Parity-Violating Electron Deuteron Scattering and the Proton's Neutral Axial Vector Form Factor

The authors report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at the backward angles at electron beam energy of 125 MeV [Q2=0.038 (GeV/c)2]. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon. In addition to the tree level amplitude associated with Z-exchange, the neutral weak axial vector form factor as measured in electron scattering can potentially receive large electroweak corrections, including the anapole moment, that are absent in neutrino scattering. The measured asymmetry A -3.51 ± 0.57 (stat) ± 0.58 (sys) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at 200 MeV [Q2 = 0.091 (GeV/c)2] on a deuterium target. The updated results are also consistent with theoretical predictions on the neutral weal axial vector form factor