The interplay of single-particle and collective motions in the low-lying states of $^{21}_\Lambda$Ne with quadrupole-octupole correlations

TL;DR

This paper extends the beyond mean-field approach to hypernuclear states by incorporating both single-particle and quadrupole-octupole collective excitations, revealing new structural insights into $^{21}_\Lambda$Ne.

Contribution

It introduces a mixed configuration method based on covariant density functional theory to study low-lying hypernuclear states, including octupole correlations.

Findings

Positive-parity states are dominated by $ ext{α}+^{12} ext{C}+ ext{α}+ ext{Λ}_s$ structure.

Negative-parity states show strong admixture of different configurations due to octupole correlations.

Negative-parity states are significantly lowered in energy and transition strengths are quenched.

Abstract

The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the configurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordinate method based on a covariant density functional theory. The method is demonstrated in the application to the low-lying states of $^{21}_\Lambda$Ne, where the configurations with the $\Lambda$ hyperon occupying the first ($\Lambda_s$) and second ($\Lambda_p$) lowest-energy states are considered. The results indicate that the positive-parity states are dominated by the $\alpha+^{12}$C+$\alpha+\Lambda_s$ structure. In contrast, the low-lying negative-parity states are dominated by a strong admixture of $\alpha+^{16}$O+$\Lambda_s$ structure and $\alpha+^{12}$C+$\alpha+\Lambda_p$ structure due to the inclusion of octupole correlations. As a result, the low-lying negative-parity states become much lower than what is expected from the previous studies without the mixing, and the electric multipole transition strengths are significantly quenched.