Effect of two-boson exchange on parity-violating e-p scattering

TL;DR

This paper calculates two-boson exchange corrections in parity-violating electron-proton scattering, revealing 2-3% effects at low momentum transfer, crucial for accurate extraction of proton's strange form factors.

Contribution

It extends a hadronic formalism to include two-boson exchange effects in the weak sector, improving the accuracy of parity-violation measurements.

Findings

Two-boson exchange effects are 2-3% at low Q^2.

Effects are largest at backward angles and depend strongly on Q^2.

Corrections are provided for relevant experimental kinematics.

Abstract

We compute the corrections from two-photon and photon-Z exchange in parity-violating elastic electron-proton scattering, used to extract the strange form factors of the proton. We use a hadronic formalism that successfully reconciled the earlier discrepancy in the proton's electron to magnetic form factor ratio, suitably extended to the weak sector. Implementing realistic electroweak form factors, we find effects of the order 2-3% at Q^2 < 0.1 GeV^2, which are largest at backward angles, and have a strong Q^2 dependence at low Q^2. Two-boson contributions to the weak axial current are found to be enhanced at low Q^2 and for forward angles. We provide corrections at kinematics relevant for recent and upcoming parity-violating experiments.