Effects of in-medium nucleon-nucleon cross section on collective flow and nuclear stopping in heavy-ion collisions in the Fermi-energy domain

TL;DR

This study uses an updated UrQMD model to analyze how in-medium nucleon-nucleon cross sections affect collective flow and nuclear stopping in gold-gold collisions at Fermi energies, comparing results with experimental data.

Contribution

It introduces a systematic investigation of in-medium nucleon-nucleon cross sections' effects on collision observables using an updated UrQMD model, including a new density- and momentum-dependent parametrization.

Findings

Optimal in-medium correction factors vary with beam energy.

The FU3FP1 parametrization reproduces experimental data well.

Nuclear stopping increases with beam energy in experiments.

Abstract

With the newly updated version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, a systematic investigation of the effects of in-medium nucleon-nucleon ($NN$) elastic cross section on the collective flow and the stopping observables in $^{197}\text{Au}+^{197}\text{Au}$ collisions at beam energies from 40 to 150 MeV/nucleon is performed. Simulations with the medium correction factor $\mathcal{F}=\sigma^{\text{in-medium}}_{NN}/\sigma^{\text{free}}_{NN}=0.2,~0.3,~0.5$, and the one obtained with the FU3FP1 parametrization which depends on both the density and the momentum are compared to the FOPI and INDRA experimental data. It is found that, to best fit the experimental data of the slope of the directed flow and the elliptic flow at mid-rapidity as well as the nuclear stopping, the correction factor $\mathcal{F}$=0.2 and 0.5 are required for reactions at beam energies of 40 and 150 MeV/nucleon, respectively. While calculations with the FU3FP1 parametrization can simultaneously reproduce these experimental data reasonably well. And, the observed increasing nuclear stopping with increasing beam energy in experimental data can also be reproduced by using the FU3FP1 parametrization, while the calculated stopping power in Au+Au collisions with beam energies from 40 to 150 MeV$/$nucleon almost keeps constant when take $\mathcal{F}$ equal to a fixed value.