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 (A(n)) in the elastic scattering of 0.95 and 2.18 GeV electrons off C-12, Ca-40, Ca-48, and Pb-208 at very forward angles where the most detailed theoretical calculations have been performed. The first measurements of A(n) for Ca-40 and Ca-48 are found to be similar to that of C-12, consistent with expectations and thus demonstrating the validity of theoretical calculations for nuclei with Z <= 20. We also report A(n) for Pb-208 at two new momentum transfers (Q(2)) 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 A(n) for nuclei containing less than or similar to 50 nucleons, but point to the need for further investigation to understand the unusual A(n) behavior discovered for scattering off Pb-208.

Automated summary

Precision determinations of the beam-normal single spin asymmetries (A(n)) in the elastic scattering of 0.95 and 2.18 GeV electrons off C-12, Ca-40, Ca-48, and Pb-208 were reported. The measurement results for Ca-40 and Ca-48 are similar to that of C-12, consistent with expectations and validating the theoretical calculations for nuclei with Z ≤ 20. However, the A(n) measurements for Pb-208 show significant disagreement with the results for Z ≤ 20 nuclei, indicating the need for further investigation.