Dispersion $\gamma Z$-box correction to the weak charge of the proton

TL;DR

This paper calculates the dispersion $oxdot$-box corrections to the proton's weak charge in elastic electron-proton scattering, highlighting their significance for interpreting parity violation experiments like QWEAK.

Contribution

It provides a dispersion calculation of $oxdot$-box corrections at GeV energies, which were previously not fully accounted for in experimental analyses.

Findings

$oxdot$-box corrections are significant at GeV energies.

Current uncertainties in PV measurements may be underestimated.

More accurate dispersion correction calculations are necessary.

Abstract

We consider elastic scattering of electrons off a proton target. The parity violating (PV) asymmetry arises at leading order in $\alpha$ due to interference of $\gamma$ and $Z$ exchange. The radiative corrections to this leading mechanism were calculated in the literature and included in experimental analyses, except for $\gamma Z$ box and cross-box contributions. We present here a dispersion calculation of these corrections in forward kinematics. We demonstrate that at the GeV energies of current PV experiments, such corrections are not suppressed by the small vector weak charge of the electron, as occurs in the atomic PV. Our results suggest that the current theoretical uncertainty in the analysis of the QWEAK experiment might be substantially underestimated, and more accurate account of the dispersion corrections are needed in order to interprete the PV data.