Two-neutron correlations in a Borromean $^{20}{\rm C}+n+n$ system: Sensitivity of unbound subsystems

TL;DR

This study investigates two-neutron correlations in the Borromean nucleus $^{22}$C using a three-body model, highlighting the sensitivity of its structure to the core-neutron potential and emphasizing the need for precise experimental data.

Contribution

The paper introduces a three-body model explicitly coupling continuum states to analyze $^{22}$C's structure and its sensitivity to potential parameters, advancing understanding of Borromean systems.

Findings

More configuration mixing than previous studies.

Strong dependence on $^{20}$C-$n$ potential and binding energy.

Highlights need for precise measurements of continuum structure.

Abstract

The structure of $^{22}$C plays a vital role in the new physics at subshell closure of $N=16$ in the neutron-rich region. We study the two-neutron correlations in the ground state of the weakly-bound Borromean nucleus $^{22}$C sitting at the edge of the neutron-drip line and its sensitivity to ${\rm core}$-$n$ potential. For the present study, we employ a three-body (${\rm core}+n+n$) structure model designed for describing the Borromean system by explicit coupling of unbound continuum states of the subsystem (${\rm core}+n$). We use a density-independent contact-delta interaction to describe the neutron-neutron interaction and its strength is varied to fix the binding energy. Along with the ground-state properties of $^{22}$C, we investigate its electric-dipole and monopole responses, discussing the contribution of various configurations. Our results indicate more configuration mixing as compared to the previous studies in the ground state of $^{22}$C. However, they strongly depend upon the choice of the $^{20}{\rm C}$-$n$ potential as well as the binding energy of $^{22}$C, which call for new precise measurements for the low-lying continuum structure of the binary system ($^{20}{\rm C}+n$) and the mass of $^{22}$C. These measurements will be essential to understand the Borromean three-body system $^{22}$C with more accuracy.