Model dependence of isospin sensitive observables at high densities

TL;DR

This paper compares two isospin-dependent transport models, IBUU04 and UrQMD, revealing significant differences in key observables that depend on model inputs, emphasizing the need for detailed input studies to better understand nuclear symmetry energy.

Contribution

It highlights the model dependence of isospin-sensitive observables and underscores the importance of detailed input parameter studies for accurate nuclear symmetry energy determination.

Findings

Significant differences in n/p ratio, pi-/pi+ ratio, and isospin flows between models.

Discrepancies mainly due to different symmetry potentials and cross sections.

Calls for detailed studies of model inputs like symmetry potential and cross sections.

Abstract

Within two different frameworks of isospin-dependent transport model, i.e., Boltzmann-Uehling-Uhlenbeck (IBUU04) and Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport models, sensitive probes of nuclear symmetry energy are simulated and compared. It is shown that neutron to proton ratio of free nucleons, pi-/pi+ ratio as well as isospin-sensitive transverse and elliptic flows given by the two transport models with their "best settings", all have obvious differences. Discrepancy of numerical value of isospin-sensitive n/p ratio of free nucleon from the two models mainly originates from different symmetry potentials used and discrepancies of numerical value of charged pi-/pi+ ratio and isospin-sensitive flows mainly originate from different isospin-dependent nucleon-nucleon cross sections. These demonstrations call for more detailed studies on the model inputs (i.e., the density- and momentum-dependent symmetry potential and the isospin-dependent nucleon-nucleon cross section in medium) of isospin-dependent transport model used. The studies of model dependence of isospin sensitive observables can help nuclear physicists to pin down the density dependence of nuclear symmetry energy through comparison between experiments and theoretical simulations scientifically.