Target normal single-spin asymmetry in inclusive electron-nucleon scattering with two-photon exchange: Analysis using $1/N_c$ expansion

TL;DR

This paper calculates the target normal single-spin asymmetry in inclusive electron-nucleon scattering caused by two-photon exchange, using a $1/N_c$ expansion of QCD, revealing measurable asymmetries that differ for proton and neutron.

Contribution

It introduces a novel analysis of two-photon exchange effects in electron-nucleon scattering using the $1/N_c$ expansion and spin-flavor symmetry, providing predictions for asymmetry magnitudes.

Findings

Asymmetry magnitude ~ 10^{-2}

Different signs for ep and en scattering

Measurable at lab energies 0.5-1.5 GeV

Abstract

We calculate the target normal single-spin asymmetry caused by two-photon exchange in inclusive electron-nucleon scattering in the resonance region. Our analysis uses the $1/N_c$ expansion of low-energy QCD and combines $N$ and $\Delta$ intermediate and final states using the contracted $SU(4)$ spin-flavor symmetry. The normal spin asymmetry obtained in leading-order accuracy in $1/N_c$ has magnitude $\sim 10^{-2}$ and different sign in $ep$ and $en$ scattering. It can be measured in electron scattering at lab energies $\sim$ 0.5-1.5 GeV and provides a clean probe of two-photon exchange dynamics.