Two-Neutron Correlations in a Borromean 20C+n+n System: Sensitivity of Unbound Subsystems

The structure of 22C 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 22C sitting at the edge of the neutron-drip line and its sensitivity to core -n potential. For the present study, we employ a three-body (core + n+ n) structure model designed for describing the Borromean system by explicit coupling of unbound continuum states of the subsystem (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 22C, 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 22C. However, they strongly depend upon the choice of the 20C -n potential as well as the binding energy of 22C, which call for new precise measurements for the low-lying continuum structure of the binary system (20C + n) and the mass of 22C. These measurements will be essential to understand the Borromean three-body system 22C with more accuracy.