Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. IX: Constraint of pairing force to $^1S_0$ neutron-matter gap

TL;DR

This paper introduces a new Skyrme-HFB mass model, HFB-16, which constrains the pairing force to neutron matter gaps, resulting in improved nuclear mass predictions and relevance for astrophysical phenomena.

Contribution

The study develops a Skyrme-HFB model with pairing force constrained by neutron matter gaps, achieving better mass fits and consistent pairing gaps without additional flexibility.

Findings

Achieved rms error of 0.632 MeV on 2149 nuclear masses.

Improved predictions for neutron-rich nuclei.

Spectral pairing gaps align with experimental level densities.

Abstract

In this latest of our series of Skyrme-HFB mass models, HFB-16, we introduce the new feature of requiring that the contact pairing force reproduce at each density the $^1S_0$ pairing gap of neutron matter as determined in microscopic calculations with realistic nucleon-nucleon forces. We retain the earlier constraints on the Skyrme force of reproducing the energy-density curve of neutron matter, and of having an isoscalar effective mass of $0.8M$ in symmetric infinite nuclear matter at the saturation density; we also keep the recently adopted device of dropping Coulomb exchange. Furthermore, the correction term for the spurious energy of collective motion has a form that is known to favour fission barriers that are in good agreement with experiment. Despite the extra constraints on the effective force, we have achieved a better fit to the mass data than any other mean field model, the rms error on the 2149 measured masses of nuclei with $N$ and $Z \ge$ 8 having been reduced to 0.632 MeV; the improvement is particularly striking for the most neutron-rich nuclei. Moreover, it turns out that even with no flexibility at all remaining for the pairing force, the spectral pairing gaps that we find suggest that level densities in good agreement with experiment should be obtained. This new force is thus particularly well-suited for astrophysical applications, such as stellar nucleosynthesis and neutron-star crusts.