Energy spectrum of neutron-rich helium isotopes: Complex made simple

Abstract

We demonstrate that the intricate energy spectrum of neutron-rich helium isotopes can be straightforwardly described by taking advantage of the low-energy properties of neutron-neutron interaction and the scale separation that is present in diluted dripline systems. By using arguments based on the halo effective field theory, we carry out a parameter reduction of the complex-energy configuration interaction framework in the spd space, including resonant and scattering states. By adjusting only one parameter, the strength of the spin-singlet central neutron-neutron interaction, we reproduce experimental energies and widths of 5−8 He within tens of keV precision. We predict a parity inversion of narrow resonances in 9 He and show that the ground state of 10 He is an s-wave-dominated threshold configuration that could decay through two-neutron emission.Introduction.-The neutron-rich helium isotopes 5−10 He epitomize novel aspects of nuclear structure at and beyond the limit of nuclear binding. Experimentally, the even-even isotopes 6 He [1] and 8 He [2, 3] are Borromean halos, they have no bound excited states, and they exhibit an abnormal pattern of the one-and two-neutron emission thresholds. The odd-N isotopes 5 He [1,4,5] and 7 He [6,7] are neutron-unbound. Presently, too little is known about the elusive 9 He [8,9] and 10 He [3,4,[10][11][12][13][14][15][16][17][18][19] isotopes to firmly conclude whether they represent genuine nuclear systems or not. The current experimental information on the energy spectrum of 5−10 He is displayed in Fig. 1.

A Guided Tour of ab initio Nuclear Many-Body Theory

“…Common to all these approaches is that a configuration space interaction that is given in terms of SHO matrix elements is expanded on a basis containing SHO and Berggren states, hence it is still an open question how a direct implementation of the interactions in a basis with continuum degrees of freedom might modify existing results. It is worth noting that such a construction has been achieved for phenomenological GSM interactions that have been tuned for light nuclei [217][218][219][220][221][222]. In light nuclei, the NCSMC has been applied with impressive success to describe a variety of exotic nuclei with up to three-cluster structures.…”

“…sections 2.3.8 and 3.2.4), as well as the GSM Coupled Channel (GSM-CC) approach, which was developed to describe reactions between light projectiles and targets that are treated in the GSM with a core [221,328,329]. Thus far, applications of the GSM-CC have been based on phenomenological valence-space interactions, but new efforts are underway to directly construct suitable Hamiltonians based on EFT principles [220,330], or derive the effective interactions from chiral forces with the techniques discussed in section 2.3 (see [214,215]). Of course, the GSM-CC ideas could also be applied to the No-Core GSM [153,155,218], although the computational complexity would limit such an approach to light nuclei.…”

Gamow Shell Model description of Li isotopes and their mirror partners

“…We want to mention here that a similar approach was employed in Ref. [29] to construct an effective neutronneutron interaction for the description of the helium isotopic chain in the Berggren basis. In that case, using only the central term V 01 c , a good reproduction of weaklybound and unbound states in helium nuclei was achieved.…”

“…By means of the principal-component analysis, it was concluded that a very reasonable description of energies of 6 ≤ A ≤ 9 nuclei (rms deviation from experiment of 250 keV) could be achieved with only four interaction parameters. In the follow-up paper [29], carried out in the spd space, experimental energies and widths of 5−8 He could be reproduced within tens of keV precision by adjusting only one parameter (the strength of spinsinglet central neutron-neutron term). In this work, we construct the minimal GSM model to describe binding energies and spectra of 5 ≤ A ≤ 11 nuclei in the sp space by carrying out simultaneous optimization of the corenucleon potential and the valence two-body interaction with the mass-dependent interaction scaling to effectively account for the missing three-body forces.…”

Local two- and three-nucleon chiral interactions

“…These drawbacks include the scaling behavior as a function of mass number, the convergence of observables as a function of basis states, the validity of many-body truncations, and constraints regarding which nuclear interactions can be used. A special but related challenge is the development, within the basic model, of approaches accounting for the coupling to the continuum-these are mandatory to describe, for instance, weakly bound nuclear systems [18,19].…”