Alpha-Clustering in Nuclei and Its Impact 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 $R_{\mathrm{skin}}$ remains a challenge. Parity-violating measurements PREX and CREX provide important opportunities for constraining $R_{\mathrm{skin}}$ 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 $R_{\mathrm{skin}}$. 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 $L$-$R_{\mathrm{skin}}$ correlation, a fact may have important implications in constraining nuclear symmetry energy.

Comments: 6 pages, 5 figures, accepted for publication in Physical Review C