The Influence of in-medium NN cross-sections, symmetry potential and impact parameter on the isospin observables

TL;DR

This study investigates how in-medium NN cross-sections, symmetry potential, and impact parameter influence isospin-sensitive observables in heavy-ion collisions, highlighting the dominant role of symmetry potential density dependence.

Contribution

It demonstrates that symmetry potential density dependence significantly affects isospin observables more than in-medium NN cross sections at high incident velocities.

Findings

Density dependence of symmetry potential impacts $DR(n/p)$ and $R_i$ more than NN cross sections.

Isospin transport ratios vary with impact parameter and fragment group.

Projectile rapidity fragments with $Z extgreater20$ show higher isospin ratios.

Abstract

We explore the influence of in-medium nucleon-nucleon cross section, symmetry potential and impact parameter on isospin sensitive observables in intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified version of Quantum Molecular Dynamics model. At incident velocities above the Fermi velocity, we find that the density dependence of symmetry potential plays a more important role on the double neutron to proton ratio $DR(n/p)$ and the isospin transport ratio $R_i$ than the in-medium nucleon-nucleon cross sections, provided that the latter are constrained to a fixed total NN collision rate. We also explore both $DR(n/p)$ and $R_i$ as a function of the impact parameter. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediate-energy heavy-ion collisions, we examine the isospin transport ratios constructed from different groups of fragments. We find that the values of the isospin transport ratios for projectile rapidity fragments with $Z\ge20$ are greater than those constructed from the entire projectile rapidity source. We believe experimental investigations of this phenomenon can be performed. These may provide significant tests of fragmentation time scales predicted by ImQMD calculations.