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

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/Nc expansion of low-energy QCD and combines N and Δ intermediate and final states using the contracted SU(4) spin-flavor symmetry. The normal spin asymmetry obtained in leading-order accuracy in 1/Nc has magnitude ∼10−2 and different sign in ep and en scattering. It can be measured in electron scattering at lab energies ∼0.5–1.5 GeV and provides a clean probe of two-photon exchange dynamics.