We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 = 0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state, and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A_n provides a direct probe of the imaginary component of the 2-gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.
@article{arxiv.0705.1525,
title = {Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering},
author = {G0 Collaboration and D. S. Armstrong},
journal= {arXiv preprint arXiv:0705.1525},
year = {2010}
}