Nuclear in-medium effects and collective flows in heavy-ion collisions at intermediate energies

TL;DR

This paper reviews an updated quantum molecular dynamics model incorporating in-medium effects, analyzing how these influence collective flows and isospin emissions in heavy-ion collisions at intermediate energies.

Contribution

It introduces modifications to the Lanzhou quantum molecular dynamics model, including momentum-dependent symmetry potential and effective mass splitting, and evaluates their impact on collision observables.

Findings

In-medium cross sections significantly affect isospin emissions.

Rapidity distribution of neutron-proton flow difference is sensitive to symmetry energy stiffness.

Elliptic flow of energetic nucleons relates to mass splitting of nucleons.

Abstract

A recent updated version of the Lanzhou quantum molecular dynamics is reviewed, in which the momentum dependence of symmetry potential and the effective mass splitting of proton and neutron in nuclear medium are included in the model. The in-medium nucleon-nucleon (NN) elastic cross sections are evaluated with the scaling approach according to the effective mass and their influence on collective flows in heavy-ion collisions are discussed. The inelastic cross sections, in particular for the process of the channel N$\Delta\rightarrow$NN, are parameterized in accordance with the available experimental data. It is found that the in-medium cross sections play a significant role on isospin emissions and result in a flat distribution for transverse flows and elliptic flows of free nucleons comparing with the in-vacuum ones. The rapidity distribution of the difference between neutron and proton transverse flows is sensitive to the stiffness of nuclear symmetry energy as a promising observable, which can not be influenced by the in-medium effect and collision centrality. Furthermore, the elliptic flow of free energetic nucleons in the case of the mass splitting of $m_{n}^{\ast}>m_{p}^{\ast}$ is also related to the symmetry energy. However, the pion flows weakly depend on the symmetry energy and the mass splitting.