Effects of incompressibility on the neutron-proton equilibration in ${}^{70}$Zn + ${}^{70}$Zn collisions at 35 MeV/nucleon

Abstract

Background: The primary goal of studying isospin dynamics via heavy-ion reactions is to explore the isospin dependence of effective interactions within the nuclear equation of state (EOS). Purpose: This work aims to investigate the effects of nuclear incompressibility ($K_0$) on neutron-proton equilibration in projectile-like fragments (PLFs). Method: We simulate ${}^{70}$Zn + ${}^{70}$Zn collisions at 35 MeV/nucleon using the isospin-dependent quantum molecular dynamics (IQMD) model, coupled with the statistical decay code GEMINI. Results: The IQMD simulations not only reproduce experimental data patterns but also reveal the dynamic mechanisms underlying the binary breakup of PLFs. The rotation of PLFs is influenced by the transformation of angular momentum, which is connected to the isoscalar component of the EOS. This connection explains why shifts in $K_0$ affect the description of neutron-proton equilibration as measured by PLF rotation. The simulations demonstrate that a model with a smaller $K_0$ paired with a softer symmetry energy, or a larger $K_0$ with a slightly stiffer symmetry energy, both offer better indications of neutron-proton equilibration. Conclusion: Considering the uncertainty in $K_0$, the slope of the symmetry energy is constrained within the range of $L=20\sim 40$ MeV, providing valuable insights into the nuclear equation of state.