Probing Equilibration in HICs and Symmetry Energy by Using Isospin-Related Observables

Abstract：

We have studied the equilibration with respect to isospin degree of freedom in four systems ⁹⁶Ru+⁹⁶Ru,⁹⁶ Ru+⁹⁶Zr,⁹⁶Zr+⁹⁶Ru,⁹⁶Zr+⁹⁶Zr at 100 MeV/u and 400MeV/u with isospin dependent QMD. It is proposed in this paper that the neutron-proton differential rapidity distribution is a sensitive probe to the degree of equilibration with respect to the isospin degree of freedom. By analyzing the average N/Z ratio of emitted nucleons, light charged particles (LCP) and intermediate mass fragments (IMF), it is found that there exists memory effect in multifragmentation process. The average N/Z ratio of IMF reduces largely as beam energy increases from 100MeV/u to 400MeV/u, which may result from the change of the behavior of the isotope distribution of IMF. The isotope distribution of IMF does also show certain memory effect at 100 MeV/u case but not at 400 MeV/u case. We also found the rapidity distribution of differential neutron-proton counting in neutron rich nucleus-nucleus collisions at intermediate energies is sensitive to the isospin dependent part of nuclear potential. In conclusion, based on these studies we have found it's an effective way to explore whether the final equilibration could be reached in intermediate HICs by constructing a set of isospin (a)symmetry nuclear-nuclear collision systems with same mass and different charge.