Precision Determination of the Neutral Weak Form Factor of $^{48}$Ca

TL;DR

This paper reports a precise measurement of the parity-violating asymmetry in elastic electron scattering from $^{48}$Ca, leading to insights into the neutron skin thickness and nuclear structure models.

Contribution

It provides the first precise determination of the weak form factor and neutron skin thickness of $^{48}$Ca, informing nuclear theory and symmetry energy models.

Findings

Measured parity-violating asymmetry $A_{PV}$ with high precision.

Extracted the weak form factor $F_W$ and neutron skin thickness $R_n - R_p$.

Results are consistent with many nuclear model calculations.

Abstract

We report a precise measurement of the parity-violating asymmetry $A_{\rm PV}$ in the elastic scattering of longitudinally polarized electrons from $^{48}{\rm Ca}$. We measure $A_{\rm PV} =2668\pm 106\ {\rm (stat)}\pm 40\ {\rm (syst)}$ parts per billion, leading to an extraction of the neutral weak form factor $F_{\rm W} (q=0.8733$ fm$^{-1}) = 0.1304 \pm 0.0052 \ {\rm (stat)}\pm 0.0020\ {\rm (syst)}$ and the charge minus the weak form factor $F_{\rm ch} - F_{\rm W} = 0.0277\pm 0.0055$. The resulting neutron skin thickness $R_n-R_p=0.121 \pm 0.026\ {\rm (exp)} \pm 0.024\ {\rm (model)}$~fm is relatively thin yet consistent with many model calculations. The combined CREX and PREX results will have implications for future energy density functional calculations and on the density dependence of the symmetry energy of nuclear matter.