γZ corrections to forward-angle parity-violating ep scattering

Abstract

We use dispersion relations to evaluate the γZ box contribution to parity-violating electron scattering in the forward limit arising from the axial-vector coupling at the electron vertex. The calculation makes full use of the critical constraints from recent JLab data on electroproduction in the resonance region as well as high-energy data from HERA. At the kinematics of the Qweak experiment, this gives a correction of 0.0047-0.0004+0.0011 to the standard model value 0.0713(8) of the proton weak charge. While the magnitude of the correction is highly significant, the uncertainty is within the anticipated experimental uncertainty of ±0.003.