Two-photon exchange and elastic scattering of electrons/positrons on the proton. (Proposal for an experiment at VEPP-3)

TL;DR

This paper proposes an experiment to compare electron-proton and positron-proton scattering at moderate Q^2 to investigate if two-photon exchange effects can resolve discrepancies in proton form factor measurements.

Contribution

It introduces a new experimental approach to directly measure two-photon exchange effects by comparing electron and positron scattering at specific momentum transfer.

Findings

Potential to clarify two-photon exchange contributions

Improved understanding of proton form factor discrepancies

Guidance for future experimental and theoretical work

Abstract

It has been suggested that two-photon exchange corrections could explain the discrepancy between Rosenbluth extractions of the proton form factors and recent polarization transfer measurements. We propose a precise comparison of electron-proton and positron-proton scattering at Q^2=1.6 GeV^2 to determine if two-photon exchange at moderate Q^2 values is in fact able to explain the discrepancy.