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

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 $^{21}_Λ$Ne, where the configurations with the $Λ$ hyperon occupying the first ($Λ_s$) and second ($Λ_p$) lowest-energy states are considered. The results indicate that the positive-parity states are dominated by the $α+^{12}$C+$α+Λ_s$ structure. In contrast, the low-lying negative-parity states are dominated by a strong admixture of $α+^{16}$O+$Λ_s$ structure and $α+^{12}$C+$α+Λ_p$ 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.
9 pages with 5 figures and 2 tables