Two-photon exchange correction in elastic lepton-proton scattering

TL;DR

This paper develops a dispersion relation method to accurately evaluate two-photon exchange effects in elastic lepton-proton scattering, incorporating recent experimental data and providing predictions for upcoming muon-proton experiments.

Contribution

It introduces a novel analytical continuation approach to include inelastic contributions using form factor data and pion electroproduction amplitudes, improving the precision of two-photon exchange calculations.

Findings

Results agree with recent experimental data from CLAS, VEPP-3, and OLYMPUS.

Provides predictions for future muon-proton scattering experiments.

Enhances understanding of two-photon exchange effects at low momentum transfer.

Abstract

We present the dispersion relation approach based on unitarity and analyticity to evaluate the two-photon exchange contribution to elastic electron-proton scattering. The leading elastic and first inelastic $\pi N$ intermediate state contributions are accounted for in the region of small momentum transfer $Q^2 < 1~\mathrm{GeV}^2$ based on the available data input. The novel methods of analytical continuation allow us to exploit the MAMI form factor data and the MAID parameterization for the pion electroproduction amplitudes as input in the calculation. The results are compared to the recent CLAS, VEPP-3 and OLYMPUS data as well as to the full two-photon exchange correction in the near-forward approximation, which is based on the Christy and Bosted unpolarized structure functions fit. Additionally, predictions are given for a forthcoming muon-proton scattering experiment.