Neutron-pair structure in the continuum spectrum of O 26

Abstract

Background: The structure of O26 is currently being investigated on both theoretical and experimental fronts. It is well established that it is unbound and the resonance parameters are fairly well known. The theoretical analysis may involved two- and three-body interactions as well as correlations with the continuum spectrum of energy. Purpose: In order to properly assess the structure of the ground and excited states, it is imperative to include a large single-particle representation with the right asymptotic behavior. The purpose of this paper is to provide details of the single-particle continuum configurations of the ground and excited 0+ states. Method: We use a large complex energy single-particle basis, formed by resonances and complex energy scattering states, the so-called Berggren basis, and a separable interaction, which is convenient to solve in a large model space. Results: Three 0+ states were found in the complex energy plane. Changes in the resonant parameters, i.e., energy and width, were analyzed as a function of strength of the residual interaction. It is shown how a subtle difference in the interaction could change the unbound character of O26 into a Borromean nucleus. Conclusions: Only one of the two excited states can be considered as a candidate for a physical meaningful resonance. The calculated occupation probabilities are in agreement with other theoretical approaches although the calculated half-life is three orders of magnitude smaller than the experimental one.