Effective mass splitting of neutron and proton and isospin emission in heavy-ion collisions

TL;DR

This study uses an isospin and momentum dependent transport model to investigate how effective mass splitting of neutrons and protons influences isospin emission in heavy-ion collisions, providing insights into the symmetry energy at high densities.

Contribution

It systematically analyzes the impact of different neutron-proton effective mass splittings on isospin emission observables in heavy-ion collisions.

Findings

Neutron/proton flow differences are sensitive to symmetry energy stiffness.

Transverse momentum distribution of neutron/proton ratio is affected by symmetry energy.

Elliptic flows at high transverse momentum can distinguish effective mass splitting.

Abstract

Within the framework of an isospin and momentum dependent transport model, the emissions of isospin particles (nucleons and light clusters) squeezed out in heavy-ion collisions are investigated as probes of the poorly known symmetry energy at high baryon density. Two different mass splittings of neutrons and protons in nuclear medium as $m_{n}^{\ast}>m_{p}^{\ast}$ and $m_{n}^{\ast}<m_{p}^{\ast}$ are used in the model and their influence on the isospin emission in heavy-ion collisions is discussed thoroughly. The competition between the stiffness and the momentum dependence of the symmetry potential on reaction dynamics are compared and systematically analyzed. It is found that the difference of the neutron and proton directed flows and the transverse momentum distribution of the neutron/proton ratio are sensitive to the stiffness of the symmetry energy, which can not be changed with the controversial effective mass splitting. The elliptic flows of free nucleons at high transverse momentum within mid-rapidity emission are a promising observable as distinguishing the nucleon effective mass splitting.