Two-photon exchange measurements with positrons and electrons

TL;DR

This paper discusses the importance of two-photon exchange effects in charged lepton scattering, highlighting recent findings that suggest larger corrections than previously thought and proposing further positron measurements at Jefferson Lab.

Contribution

It emphasizes the need for new positron scattering experiments to better understand two-photon exchange contributions across various reactions.

Findings

Recent data indicate larger two-photon exchange effects than earlier believed.

Historical positron scattering data were limited in kinematic coverage.

Further measurements at Jefferson Lab could clarify these effects.

Abstract

Two-photon exchange contributions have potentially broad ranging impact on several charged lepton scattering measurements. Previously believed to be extremely small, based in part on comparisons of positron scattering and electron scattering in the 1950s and 1960s, recent data suggest that the corrections may be larger than expected, in particular in kinematic regions that were inaccessible in these early positron scattering measurements. Additional measurements using positron beams at Jefferson Lab would allow for a detailed investigation of these contributions in a range of reactions and observables.