The Two-Photon-Exchange and \gamma Z-Exchange Corrections to parity-Violating Elastic Electron-Proton Scattering

TL;DR

This paper calculates two-photon and gamma-Z exchange corrections to parity-violating elastic electron-proton scattering, showing they can significantly affect the extraction of strange form factors in precision experiments.

Contribution

It provides the first detailed estimate of TPE and gamma-Z exchange corrections including proton finite size effects in a simple hadronic model.

Findings

Corrections can reach a few percent, comparable to experimental strange-quark effects.

Gamma-Z exchange generally larger than TPE, especially at low Q^2.

Combined effects can alter extracted form factors by up to -40%.

Abstract

Leading electroweak corrections play an important role in precision measurements of the strange form factors. We calculate the two-photon-exchange (TPE) and $\gamma Z$-exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the finite size of the proton. We find both can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. The effect of $\gamma Z$-exchange is in general larger than that of TPE, especially at low momentum transfer $Q^2\le 1 GeV^2$. Their combined effects on the values of $G^s_E+\beta G^s_M$ extracted in recent experiments can be as large as -40% in certain kinematics.