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

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 ${}_{\Lambda }^{21}$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.

Comments: 9 pages with 5 figures and 2 tables