# Neutron skins as laboratory constraints on properties of neutron stars and on what we can learn from heavy ion fragmentation reactions

## TL;DR

This paper investigates how measurements of nuclear reaction fragments involving neutron-rich nuclei at high energies can constrain the neutron skin and the symmetry energy component of the nuclear equation of state, informing neutron star properties.

## Contribution

It introduces a method to use high-energy neutron-rich nuclear reactions to probe neutron skins and the symmetry energy, connecting nuclear experiments with astrophysical neutron star models.

## Key findings

- Reaction fragment measurements are sensitive to neutron skin variations.
- Different reaction channels provide complementary constraints.
- The approach links nuclear reaction data to neutron star EOS properties.

## Abstract

The equation of state (EOS) of infinite nuclear matter with a small proton/neutron fraction is a crucial input to determine the properties of neutron stars and compare model predictions to astronomical observations. The so-called `symmetry energy' is the part of the EOS accounting for the difference in the number of neutrons and protons. Numerous experiments have been devised to assess the symmetry energy and constrain its functional dependence with the nucleon density. Further constraints follow from a stellar modeling using the EOS to reproduce astronomical observations such as neutron star masses and radii. The recent detection of gravitational waves emitted from neutron star mergers and the nucleosynthesis ensuing from these events caused a surge of interest for such studies. Several types of nuclear reactions have been proposed to study the symmetry energy part of the EOS. Some of them consist in determining the neutron skin in nuclei and exploit its correlation with the slope parameter of the symmetry energy. In this article we explore a particular set of reactions using high energy ($E_{lab} \sim 1$ GeV/nucleon) neutron-rich projectiles. We explore measurements of all reaction fragments (a) in the same isotopic chain, i.e., only by removal of neutrons, (b) in all charge-changing channels, and (c) total interaction cross sections. Using Hartree-Fock-Bogoliubov (HBF) predictions for neutron and proton densities with Skyrme interactions, we explore the sensitivity of these cross sections with the neutron skin in nuclei.