Constraints on two-neutron separation energy in the Borromean 22C nucleus

The recently extracted matter radius of carbon isotope 22C allows us to estimate the mean-square distance of a halo neutron with respect to the center-of-mass of this nucleus. By considering this information, we suggest an energy region for an experimental investigation of the unbound 21C virtual state. Our analysis, in a renormalized zero-ranged three-body model, also indicates that the two-neutron separation energy in 22C is expected to be found below ∼0.4MeV, where the 22C is approximated by a Borromean configuration with a pointlike 20C and two s-wave halo neutrons. A virtual-state energy of 21C close to zero, would make the 22C, within Borromean nuclei configurations, the most promising candidate to present an excited bound Efimov state or a continuum three-body resonance.