We study the beam-normal single-spin asymmetry (BNSSA) in high-energy elastic electron scattering from several spin-0 nuclei. Existing theoretical approaches work in the plane-wave formalism and predict the BNSSA to scale as $\sim A/Z$ with the atomic number $Z$ and nuclear mass number $A$. While this prediction holds for light and intermediate nuclei, a striking disagreement in both the sign and the magnitude of BNSSA was observed by the PREX collaboration for ${}^{208}\mathrm{Pb}$, coined the “PREX puzzle.” To shed light on this disagreement, we go beyond the plane-wave approach which neglects Coulomb distortions known to be significant for heavy nuclei. We explicitly investigate the dependence of BNSSA on $A$ and $Z$ by (i) including inelastic intermediate states' contributions into the Coulomb problem in the form of an optical potential, (ii) by accounting for the experimental information on the $A$-dependence of the Compton slope parameter, and (iii) giving a thorough account of the uncertainties of the calculation. Despite of these improvements, the PREX puzzle remains unexplained. We discuss further strategies to resolve this riddle.

中文翻译：

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来自自旋 0 核的电子弹性散射中的束法向单自旋不对称性

我们研究了来自几个自旋 0 原子核的高能弹性电子散射中的束法向单自旋不对称性 (BNSSA)。现有的理论方法适用于平面波形式主义，并预测 BNSSA 将按比例缩放$～\mathrm{一种}/Z$ 与原子序数 $Z$ 和核质量数 $\mathrm{一种}$. 虽然这种预测适用于轻核和中间核，但 PREX 合作观察到了 BNSSA 的符号和大小的惊人分歧${}^{208}铅$，创造了“PREX拼图”。为了阐明这种分歧，我们超越了平面波方法，该方法忽略了已知对重核很重要的库仑畸变。我们明确调查了 BNSSA 对$\mathrm{一种}$ 和 $Z$ 通过 (i) 以光学势的形式将非弹性中间态对库仑问题的贡献包括在内，(ii) 通过考虑关于 $\mathrm{一种}$- 康普顿斜率参数的相关性，以及 (iii) 全面考虑计算的不确定性。尽管有这些改进，但 PREX 难题仍然无法解释。我们讨论了解决这个谜题的进一步策略。