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

TL;DR

This study measures the transverse beam asymmetry in elastic electron scattering from various nuclei, revealing agreement with theory for lighter nuclei and unexpected results for heavy nuclei, indicating new avenues for nuclear structure research.

Contribution

First measurements of $A_n$ for $^4$He, $^{12}$C, and $^{208}$Pb, expanding understanding of two-photon exchange effects in heavy nuclei.

Findings

Agreement with theory for $^1$H, $^4$He, and $^{12}$C

Significantly smaller $A_n$ for $^{208}$Pb than predicted

Potential for $A_n$ to probe heavy nuclear structure

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.