Efimov states in excited nuclear halos

TL;DR

This paper proposes a systematic method to identify nuclear nuclides exhibiting Efimov states, and identifies $^{90}$Zr and $^{159}$Gd as promising candidates for experimental observation of these universal three-body quantum phenomena in nuclei.

Contribution

The authors introduce a new protocol for detecting Efimov states in nuclear excited states and identify specific stable nuclides as candidates, advancing nuclear Efimov physics.

Findings

Identified $^{90}$Zr and $^{159}$Gd as candidate nuclides for Efimov states.

Proposed a systematic method based on neutron capture cross-sections.

Demonstrated feasibility of observing Efimov states in stable nuclei.

Abstract

Universality -- an essential concept in physics -- implies that different systems show the same phenomenon and can be described by a unified theory. A prime example of the universal quantum phenomena is the Efimov effect, which is the appearance of multiples of low-energy three-body bound states with progressively large sizes dictated by the discrete scale invariance. The Efimov effect, originally proposed in the nuclear physics context, has been observed in cold atoms and $^4\mathrm{He}$ molecules. The search for the Efimov effect in nuclear physics, however, has been a long-standing challenge owing to the difficulty in identifying ideal nuclides with a large $s$-wave scattering length; such nuclides can be unambiguously considered as Efimov states. Here, we propose a systematic method to identify nuclides that exhibit Efimov states in their excited states in the vicinity of the neutron separation threshold. These nuclei are characterised by their enormous low-energy neutron capture cross-sections, hence giant $s$-wave scattering length. Using our protocol, we identified $^{90}$Zr and $^{159}$Gd as novel candidate nuclides that show the Efimov states. They are well inside the valley of stability in the nuclear chart, and are suited for experimental realisation of the Efimov states in nuclear physics.