Energy Spectrum of Neutron-Rich Helium Isotopes: Complex Made Simple

TL;DR

This paper simplifies the complex energy spectrum of neutron-rich helium isotopes using effective field theory and minimal parameter adjustment, accurately reproducing experimental data and predicting new phenomena.

Contribution

It introduces a simplified model based on halo effective field theory that reduces parameters and accurately describes helium isotope spectra.

Findings

Reproduces experimental energies and widths within tens of keV.

Predicts parity inversion in $^{9}$He resonances.

Suggests $^{10}$He ground state is an $s$-wave threshold configuration.

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.