New measurements of the transverse beam asymmetry for elastic electron scattering from selected nuclei

We have measured the beam-normal single-spin asymmetry A n in the elastic scattering of 1-3 GeV transversely polarized electrons from H1 and for the first time from He4, C12, and Pb208. For H1, He4, and C12, the measurements are in agreement with calculations that relate A n to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the Pb208 result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new A n measurements might emerge as a new and sensitive probe of the structure of heavy nuclei. © 2012 American Physical Society.