Contribution of Two-Boson-Exchange with $\Delta(1232)$ Excitation to Parity-Violating Elastic Electron-Proton Scattering

TL;DR

This paper calculates two-boson-exchange corrections involving $\Delta(1232)$ excitation to parity-violating electron-proton scattering, revealing significant kinematic-dependent effects on the extraction of strange form factors.

Contribution

It provides the first detailed analysis of $\Delta(1232)$ excitation effects on electroweak corrections in parity-violating scattering experiments.

Findings

$\Delta(1232)$ contributions vary strongly with kinematics.

Total TBE corrections can be as large as 75%.

Corrections are small for A4 experiments.

Abstract

We study the leading electroweak corrections in the precision measurement of the strange form factors. Specifically, we calculate the two-boson-exchange (TBE), two-photon-exchange (TPE) plus $\gamma Z$-exchange ($\gamma Z$E), corrections with $\Delta(1232)$ excitation to the parity-violating asymmetry of the elastic electron-proton scattering. The interplay between nucleon and $\Delta$ contributions is found to depend strongly on the kinematics, as $\delta_\Delta$ begins as negligible at backward angles but becomes very large and negative and dominant at forward angles, while $\delta_N$ always stays positive and decreases monotonically with increasing $\epsilon$. The total TBE corrections to the extracted values of $G^{s}_{E}+\beta G^{s}_{M}$ in recent experiments of HAPPEX and G0 are, depending on kinematics, found to be large and range between 13% to -75% but small in the case of A4 experiments.