~4He +n+n Continuum within an Ab initio Framework

摘要

The low-lying continuum spectrum of the ~6He nucleus is investigated for the first time within an ab initio framework that encompasses the ~4He + n + n three-cluster dynamics characterizing its lowest decay channel. This is achieved through an extension of the no-core shell model combined with the resonating-group method, in which energy-independent nonlocal interactions among three nuclear fragments can be calculated microscopically, starting from realistic nucleon-nucleon interactions and consistent ab initio many-body wave functions of the clusters. The three-cluster Schroedinger equation is solved with three-body scattering boundary conditions by means of the hyperspherical-harmonics method on a Lagrange mesh. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we find the known J~π = 2~+ resonance as well as a result consistent with a new low-lying second 2~+ resonance recently observed at GANIL at 2.6 MeV above the ~6He ground state. We also find resonances in the 2~-, 1~+, and 0~-channels, while no low-lying resonances are present in the 0~+ and 1~-channels.