Impact of nucleon-nucleon collisions on heavy-ion fusion reactions: An investigation utilizing time-dependent Hartree-Fock theory with the relaxation-time approximation

The role of nucleon-nucleon collisions in heavy-ion fusion reactions is examined using the time-dependent Hartree-Fock (TDHF) approach combined with a relaxation-time approximation (RTA). The investigation focuses on energy dissipation and thermalization in the head-on fusion reaction $^{16}\mathrm{O}+^{16}\mathrm{O}$. The nucleus-nucleus interaction potential, obtained via the density-constraint method, reveals minimal dependence on nucleon-nucleon collisions. However, incorporation of nucleon-nucleon collisions significantly enhances the dissipation of collective kinetic energy, promotes thermalization, and increases the fusion threshold energy above which the system does not fuse. Comparisons with TDHF results indicate that nucleon-nucleon collisions are crucial for achieving equilibrium, a process that pure mean-field models fail to adequately capture. These findings highlight the necessity of beyond mean-field approaches for exploring energy dissipation and thermalization in nuclear-fusion dynamics.