New Measurements of the Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering over a Range of Spin-0 Nuclei

We report precision determinations of the beam-normal single spin asymmetries (An) in the elastic scattering of 0.95 and 2.18 GeV electrons off C12, Ca40, Ca48, and Pb208 at very forward angles where the most detailed theoretical calculations have been performed. The first measurements of An for Ca40 and Ca48 are found to be similar to that of C12, consistent with expectations and thus demonstrating the validity of theoretical calculations for nuclei with Z≤20. We also report An for Pb208 at two new momentum transfers (Q2) extending the previous measurement. Our new data confirm the surprising result previously reported, with all three data points showing significant disagreement with the results from the Z≤20 nuclei. These data confirm our basic understanding of the underlying dynamics that govern An for nuclei containing 50 nucleons, but point to the need for further investigation to understand the unusual An behavior discovered for scattering off Pb208