Contribution of hard photon emission to charge asymmetry in elastic (anti)lepton-proton scattering

TL;DR

This paper evaluates the impact of hard photon emission on charge asymmetry in elastic lepton-proton scattering, considering lepton mass effects beyond the ultrarelativistic approximation, and provides numerical analysis relevant to experimental conditions.

Contribution

It is the first to analyze the hard photon emission contribution to charge asymmetry beyond the ultrarelativistic limit while including lepton mass effects.

Findings

Hard photon emission significantly affects charge asymmetry.

Infrared divergences are canceled by soft two-photon exchange contributions.

Numerical results align with Jefferson Lab and MUSE experimental conditions.

Abstract

The influence of the hard photon emission on the charge asymmetry in the (anti)lepton-proton elastic scattering was evaluated for the first time beyond the ultrarelativistic limit, while retaining the lepton mass at all steps of the calculation. This contribution - responsible for the charge asymmetry - is induced by interference between real photon emission from the lepton and proton. During the calculation any excited states of the intermediated proton are not considered, allowing us to use the standard fermionic propagator for this particle. The infrared divergence extracted using Lorenz-invariant approach of Bardin-Shumeiko is canceled by the corresponding soft part of the two-photon exchange contribution. Numerical analysis was performed within kinematic conditions of Jefferson Lab measurements and MUSE experiment in PSI.