Investigation of spatial manifestation of $\alpha$ clusters in $^{16}$O via $\alpha$-transfer reactions

TL;DR

This study investigates the surface distribution of $oldsymbol{ ext{alpha}}$ clusters in both ground and excited states of $oldsymbol{^{16} ext{O}}$ using $oldsymbol{ ext{alpha}}$-transfer reactions, revealing state-dependent cluster structures and their spatial localization.

Contribution

It extends previous work by analyzing excited states of $^{16}$O, employing microscopic wave functions and phenomenological models to connect transfer cross sections with cluster wave functions.

Findings

Surface peaks of $ ext{alpha}$-wave functions are sensitive to transfer cross sections.

$^{16} ext{O}$ states show different $ ext{C}+ ext{alpha}$-cluster configurations at specific radii.

The $4_2^+$ state is not dominated by simple $ ext{C}+ ext{alpha}$ configurations.

Abstract

Recently, we have determined surface distributions of $\alpha$ clusters in the ground state of $^{20}\mathrm{Ne}$ from $\alpha$-transfer cross sections, without investigating the properties of its excited states. In this paper we extend our comprehension of $\alpha$-cluster structures in excited states of nuclei through reaction studies. In particular we focus on $^{16}\mathrm{O}$, for which attention has been paid to advances of structure theory and assignment regarding $4^+$-resonance states. We study the surface manifestation of the $\alpha$-cluster states in both the ground and excited states of $^{16}\mathrm{O}$ from the analysis of the $\alpha$-transfer reaction $^{12}\mathrm{C}(^6\mathrm{Li},d)^{16}\mathrm{O}$. The $\alpha$-transfer reaction is described by the distorted-wave Born approximation. We test two microscopic wave functions as an input of reaction calculations. Then a phenomenological potential model is introduced to clarify the correspondence between cluster-wave functions and transfer-cross sections. Surface peaks of the $\alpha$-wave function of $^{16}\mathrm{O}(0^+)$ are sensitively probed by transfer-cross sections at forward angles, while it remains unclear how we trace the surface behavior of $^{16}\mathrm{O}(4^+)$ from the cross sections. We are able to specify that the $\alpha$-cluster structure in the $0_1^+$ and $0_2^+$ states prominently manifests itself at the radii $\sim 4$ and $\sim 4.5$~fm, respectively. It is remarkable that the $4_1^+$ state has the $^{12}\mathrm{C}+\alpha$-cluster component with the surface peak at the radius $\sim 4$ or outer, whereas the $^{12}\mathrm{C}+\alpha$-cluster component in the $4_2^+$ state is found not to be dominant. The $4_2^+$ state is difficult to be interpreted by a simple potential model assuming the $^{12}\mathrm{C}+\alpha$ configuration only.