Mean-field analysis of ground state and low-lying electric dipole strength in $^{22}$C

TL;DR

This study uses mean-field and RPA methods with Skyrme functionals to analyze the ground state and low-lying electric dipole strength in neutron-rich $^{22}$C, highlighting the role of core excitations near the neutron threshold.

Contribution

It introduces a modified Skyrme potential to simulate experimental properties of $^{22}$C and investigates the development of low-lying $E1$ strength including core excitations.

Findings

Low-lying $E1$ strength exceeds the energy-weighted cluster sum rule near the neutron threshold.

Core excitations involving the $1d_{5/2}$ orbit are significant in $^{22}$C.

The neutron Fermi level approaching zero enhances low-lying $E1$ strength.

Abstract

Properties of neutron-rich $^{22}$C are studied using the mean-field approach with Skyrme energy density functionals. Its weak binding and large total reaction cross section, which are suggested by recent experiments, are simulated by modifying the central part of Skyrme potential. Calculating $E1$ strength distribution by using the random-phase approximation, we investigate developments of low-lying electric dipole ($E1$) strength and a contribution of core excitations of $^{20}$C. As the neutron Fermi level approaches the zero energy threshold ($\varepsilon_F >\sim -1$ MeV), we find that the low-lying $E1$ strength exceeds the energy-weighted cluster sum rule, which indicates an importance of the core excitations with the $1d_{5/2}$ orbit.