Two-photon exchange correction in elastic unpolarized electron-proton scattering at small momentum transfer

TL;DR

This paper calculates the two-photon exchange correction in elastic electron-proton scattering at small momentum transfer, incorporating inelastic intermediate states and proton structure functions, improving accuracy over previous approximations.

Contribution

It provides a comprehensive calculation of TPE corrections including full Q^2 dependence, aligning well with empirical data at small momentum transfer.

Findings

Reproduces leading terms in Q^2 expansion of TPE correction.

Goes beyond approximation by including full Q^2 dependence.

Results agree with empirical TPE fits at small Q^2.

Abstract

We evaluate the two-photon exchange (TPE) correction to the unpolarized elastic electron-proton scattering at small momentum transfer $ Q^2 $. We account for the inelastic intermediate states approximating the double virtual Compton scattering by the unpolarized forward virtual Compton scattering. The unpolarized proton structure functions are used as input for the numerical evaluation of the inelastic contribution. Our calculation reproduces the leading terms in the $ Q^2 $ expansion of the TPE correction and goes beyond this approximation by keeping the full $ Q^2 $ dependence of the proton structure functions. In the range of small momentum transfer, our result is in good agreement with the empirical TPE fit to existing data.