Missed prediction of the neutron halo in $^{37}$Mg

TL;DR

This paper presents a microscopic, self-consistent theoretical description of the neutron halo in $^{37}$Mg using the DRHBc model, successfully reproducing experimental data and clarifying the orbital structure, which was previously missed.

Contribution

It provides the first accurate, parameter-free prediction of the neutron halo in $^{37}$Mg using the deformed relativistic Hartree-Bogoliubov theory in continuum.

Findings

Reproduces neutron separation energies and matter radii of magnesium isotopes.

Identifies the $p$-wave orbital of the halo neutron consistent with experiments.

Predicts higher-order shape decoupling in $^{37}$Mg.

Abstract

Halo phenomena have long been an important frontier in both experimental and theoretical nuclear physics. $^{37}$Mg was identified as a halo nucleus in 2014 and remains the heaviest nuclear halo system to date. While the halo phenomenon in $^{37}$Mg was not predicted before the discovery, its description has been still challenging afterwards. In this Letter, we report a microscopic and self-consistent description of the neutron halo in $^{37}$Mg using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) that was developed in 2010. The experimental neutron separation energies and empirical matter radii of neutron-rich magnesium isotopes as well as the deformed $p$-wave halo characteristics of $^{37}$Mg are well reproduced without any free parameters. In particular, the orbital occupied by the halo neutron in $^{37}$Mg, exhibiting $p$-wave components comparable to those suggested in experiments, remains consistent across various employed density functionals including PC-F1, PC-PK1, NL3*, and PK1. The DRHBc theory investigated only even-even magnesium isotopes in previous works and for that reason missed predicting $^{37}$Mg as a halo nucleus before 2014. Although the core and the halo of $^{37}$Mg are both prolate, higher-order shape decoupling on the hexadecapole and hexacontatetrapole levels is predicted.