Beam-normal single-spin asymmetry in elastic scattering of electrons from a spin-0 nucleus

TL;DR

This paper investigates the beam-normal single-spin asymmetry in elastic electron scattering from spin-0 nuclei, addressing discrepancies between theory and experiment, especially for heavy nuclei like lead, by including Coulomb distortions and inelastic effects.

Contribution

It extends theoretical models beyond plane-wave approximation by incorporating Coulomb distortions and inelastic states to better understand BNSSA in heavy nuclei.

Findings

The PREX puzzle remains unresolved despite improved modeling.

Coulomb distortions significantly affect BNSSA calculations for heavy nuclei.

Uncertainties in the model are thoroughly analyzed.

Abstract

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 $^{208}$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.