Decay dynamics of the unbound $^{25}$O and $^{26}$O nuclei

TL;DR

This paper investigates the decay and structure of unbound $^{25}$O and $^{26}$O nuclei using a three-body model, aligning with new experimental data to elucidate their resonance states, configurations, and halo characteristics.

Contribution

It provides an updated three-body model analysis of $^{26}$O, accurately reproducing the 2$^+$ state energy and revealing detailed configurations of excited states.

Findings

Excellent agreement with experimental 2$^+$ state energy.

Identification of the 0$^+$ excited state at 3.38 MeV mainly as $(f_{7/2})^2$ configuration.

Discussion of di-neutron correlations and halo nature of $^{26}$O.

Abstract

We study the ground and excited resonance states of $^{26}$O with a three-body model of $^{24}$O+n+n taking into account the coupling to the continuum. To this end, we use the new experimental data for the invariant mass spectroscopy of the unbound $^{25}$O and $^{26}$O nuclei, and present an update of three-body model calculations for the two-neutron decay of the $^{26}$O nucleus. With the new model inputs determined with the ground state decay of $^{26}$O, we discuss the di-neurtron correlations and a halo nature of this nucleus, as well as the structure of the excited states. For the energy of the 2$^+$ state, we achieve an excellent agreement with the experimental data with this calculation. We show that the 2$^+$ state consists predominantly of the $(d_{3/2})^2$ configuration, for which the pairing interaction between the valence neutrons slightly decreases its energy from the unperturbed one. We also discuss the structure of excited 0$^+$ states of the $^{26}$O nucleus. In particular, we show the existence of an excited 0$^+$ state at 3.38 MeV, which is mainly composed of the $(f_{7/2})^2$ configuration.