Alpha-Clustering in Nuclei and Its Impact on Nuclear Symmetry Energy

TL;DR

This paper investigates how alpha-clustering at nuclear surfaces affects the extraction of nuclear symmetry energy from neutron skin measurements, finding significant impact in calcium isotopes but minimal in lead.

Contribution

It introduces the role of alpha-clustering in modifying the relationship between neutron skin thickness and symmetry energy parameters.

Findings

Alpha-clustering probability in $^{208}$Pb is small, minimally affecting symmetry energy extraction.

Alpha-clustering probability in $^{48}$Ca is sizable, requiring correction in symmetry energy analysis.

Alpha-clustering influences the $L$-$R_{ m skin}$ correlation, impacting constraints on nuclear symmetry energy.

Abstract

Nuclear symmetry energy is a fundamental quantity currently under intense investigation in both nuclear physics and astrophysics. The {\it softness} or {\it stiffness} of symmetry energy is still under debate and the extraction of symmetry energy from neutron skin thickness $R_{\rm skin}$ remains a challenge. Parity-violating measurements PREX and CREX provide important opportunities for constraining $R_{\rm skin}$ in $^{208}$Pb and $^{48}$Ca. We investigate the occurrence of $\alpha$-cluster at the surface of nuclei and its impact on the extraction of symmetry energy from $R_{\rm skin}$. Our result indicates that the $\alpha$-clustering probability in $^{208}$Pb is small and the extracted density slope of symmetry energy $L$ is almost unaffected. In contrast, the $\alpha$-clustering probability in $^{48}$Ca is sizeable and the corresponding correction to $L$ should be taken into account. This correction progressively increases with the $\alpha$-clustering probability, leading to a modification of the $L$-$R_{\rm skin}$ correlation, a fact may have important implications in constraining nuclear symmetry energy.