New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei

Abstract

We have measured the beam-normal single-spin asymmetry $A_n$ in the elastic scattering of 1-3 GeV transversely polarized electrons from ${}^1$H and for the first time from ${}^4$He, ${}^{12}$C, and ${}^{208}$Pb. For ${}^1$H, ${}^4$He and ${}^{12}$C, 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 ${}^{208}$Pb 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.

5 pages, 3 figures, accepted by PRL. v3: fixed one author name and affiliation, otherwise no change