# Target-normal single-spin asymmetry in elastic electron-nucleon scattering

## TL;DR

This paper models the target-normal single-spin asymmetry in elastic electron-nucleon scattering at forward angles, linking it to two-photon exchange amplitudes and providing predictions for proton and neutron targets.

## Contribution

It introduces a novel parametrization of the doubly virtual Compton scattering tensor for nearly forward angles, ensuring consistency with known forward limit data.

## Key findings

- Provides asymmetry predictions for elastic electron-proton scattering.
- Extends the model to electron-neutron scattering.
- Discusses the applicability limits of the developed model.

## Abstract

We estimate the target-normal single-spin asymmetry at nearly forward angles in elastic electron-nucleon scattering. In the leading-order approximation, this asymmetry is proportional to the imaginary part of the two-photon exchange (TPE) amplitude, which can be expressed as an integral over the doubly virtual Compton scattering (VVCS) tensor. We develop a model that parametrizes the VVCS tensor for the case of nearly forward scattering angles. Our parametrization ensures a proper normalization of the imaginary part of the TPE amplitude on the well-known forward limit expression, which is given in terms of nucleon structure functions measurable in inelastic electron-nucleon scattering experiments. We discuss applicability limits of our theory and provide target-normal single-spin asymmetry predictions for both elastic electron-proton and electron-neutron scattering.