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 $^1$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. 
The HAPPEX and PREX Collaborations: S. Abrahamyan, A. Acha, A.   Afanasev, Z. Ahmed, H. Albataineh, K. Aniol, D. S. Armstron...
nucl-ex