Halo phenomenon in finite many-fermion systems. Atom-positron complexes and large-scale study of atomic nuclei

TL;DR

This study applies a characterization method to various finite many-fermion systems, analyzing how energy density functional parameters influence nuclear halo properties and predicting their occurrence in medium-mass nuclei.

Contribution

It demonstrates the versatility of a halo characterization method across different systems and explores how energy density functional components affect nuclear halo predictions.

Findings

Halo properties are sensitive to the energy density functional parameters.

Pairing correlations significantly influence halo characteristics.

Halo occurrence in medium-mass nuclei is limited to near neutron drip-line regions.

Abstract

The analysis method proposed in Ref. \cite{rotival07a} is applied to characterize halo properties in finite many-fermion systems. First, the versatility of the method is highlighted by applying it to light and medium-mass nuclei as well as to atom-positron and ion-positronium complexes. Second, the dependence of nuclear halo properties on the characteristics of the energy density functional used in self-consistent Hartree-Fock-Bogoliubov calculations is studied. It is found that (a) the low-density behavior of the pairing functional and the regularization/renormalization scheme must be chosen coherently and with care to provide meaningful predictions, (b) the impact of pairing correlations on halo properties is significant and is the result of two competing effects, (c) the detailed characteristics of the pairing functional has however only little importance, (d) halo properties depend significantly on any ingredient of the energy density functional that influences the location of single-particle levels; i.e. the effective mass, the tensor terms and the saturation density of nuclear matter. The latter dependencies give insights to how experimental data on medium-mass drip-line nuclei can be used in the distant future to constrain some characteristics of the nuclear energy density functional. Last but not least, large scale predictions of halos among all spherical even-even nuclei are performed using specific sets of particle-hole and particle-particle energy functionals. It is shown that halos in the ground state of medium-mass nuclei will only be found at the very limit of neutron stability and for a limited number of elements.