# Sensitivity of the evaporation residue observables to the symmetry energy

## TL;DR

This study uses a transport model to analyze how the properties of residues in Ni+Ni collisions at 50 MeV/nucleon are sensitive to the symmetry energy's density dependence, revealing potential observables for constraining nuclear matter properties.

## Contribution

It demonstrates that the isospin ratio of pre-equilibrium particles and the size and isotopic ratio of the residue are sensitive to the symmetry energy, providing new tools for constraining the symmetry energy parameters.

## Key findings

- Isospin ratio of pre-equilibrium particles correlates with symmetry energy stiffness.
- Higher symmetry energy at subsaturation densities increases residue size and isotopic ratio.
- Combination of observables can constrain the density dependence of symmetry energy.

## Abstract

The static properties of the heaviest residue and unbound particles produced in central $^{64,58}Ni$ on $^{64,58}Ni$ collisions at 50 MeV/nucleon are predicted within the BUU transport model, in order to explore the sensitivity of those observables to the density dependence of the symmetry energy. We include fluctuations in the collision integral and use a meta-modelling for the mean-field which allows an independent variation of the different empirical parameters of the equation of state. We find that the isospin ratio of pre-equilibrium particles is a good estimator of the stiffness of the symmetry energy, in agreement with previous works. In addition to that, whatever be the functional form of the equation of state, we show that a higher symmetry energy at subsaturation densities leads to an increased size and isotopic ratio for the heaviest residue. This is understood in terms of energy sharing between the pre-equilibrium particles and the (quasi)fused system. The combination of the two observables might be an interesting tool to constrain the different density dependence below and above saturation, which is linked to the relatively poorly known parameter $K_{sym}$.