Constraining the symmetry energy content of nuclear matter from nuclear masses: a covariance analysis

TL;DR

This study uses covariance analysis to show that including highly asymmetric nuclei in nuclear mass fits significantly reduces uncertainties in the symmetry energy parameters and neutron-skin thickness, improving their constraints.

Contribution

It demonstrates that incorporating highly asymmetric nuclei in fitting protocols narrows uncertainties in symmetry energy and related nuclear properties.

Findings

Uncertainty in symmetry energy coefficient reduced by ~50%.

Uncertainty in slope parameter reduced by ~50%.

Uncertainty in neutron-skin thickness reduced by ~50%.

Abstract

Elements of nuclear symmetry energy evaluated from different energy density functionals parametrized by fitting selective bulk properties of few representative nuclei are seen to vary widely. Those obtained from experimental data on nuclear masses across the periodic table, however, show that they are better constrained. A possible direction in reconciling this paradox may be gleaned from comparison of results obtained from use of the binding energies in the fitting protocol within a microscopic model with two sets of nuclei, one a representative standard set and another where very highly asymmetric nuclei are additionally included. A covariance analysis reveals that the additional fitting protocol reduces the uncertainties in the nuclear symmetry energy coefficient, its slope parameter as well as the neutron-skin thickness in $^{208}$Pb nucleus by $\sim 50\%$. The central values of these entities are also seen to be slightly reduced.