Influence of Transport Variables on Isospin Transport Ratios

TL;DR

This paper investigates how various transport model parameters influence isospin diffusion ratios in heavy ion collisions, highlighting the importance of model inputs like cross sections and cluster production in constraining the symmetry energy.

Contribution

The study systematically examines the effects of symmetry energy, mean field properties, cross sections, and cluster production on isospin diffusion within a transport model.

Findings

Cross sections and cluster production significantly affect isospin diffusion.

Differences in transport ratios depend on whether residue or all fragments are used.

Measurements comparing these two methods can constrain model inputs.

Abstract

The symmetry energy in the nuclear equation of state affects many aspects of nuclear astrophysics, nuclear structure, and nuclear reactions. Recent constraints from heavy ion collisions, including isospin diffusion observables, have started to put constraints on the symmetry energy below nuclear saturation density, but these constraints depend on the employed transport model and input physics other than the symmetry energy. To understand these dependencies, we study the influence of the symmetry energy, isoscaler mean field compressibility and momentum dependence, in-medium nucleon-nucleon cross sections, and light cluster production on isospin diffusion within the pBUU transport code. In addition to the symmetry energy, several uncertain issues strongly affect isospin diffusion, most notably the cross sections and cluster production. In addition, there is a difference in the calculated isospin transport ratios, depending upon whether they are computed using the isospin asymmetry of either the residue or of all forward moving fragments. Measurements that compare the isospin transport ratios of these two quantities would help place constraints on the input physics, such as the density dependence of the symmetry energy.