1212.4907 (C. L. Zhou et al.)

Thermodynamic properties and shear viscosity over entropy density ratio
of nuclear fireball in a quantum-molecular dynamics model    [PDF]

C. L. Zhou, Y. G. Ma, D. Q. Fang, G. Q. Zhang

Thermodynamic and transport properties of nuclear fireball created in the central region of heavy-ion collisions below 200 MeV/nucleon are investigated within the isospin-dependent quantum molecular dynamic (IQMD) model. These properties include time evolutions of the density, temperature, chemical potential, entropy density ($s$) and shear viscosity ($\eta$) as well as density and temperature dependencies of the ratio of shear viscosity over entropy density ($\eta/s$) etc. Based on the shear viscosity parametrization developed by Danilewicz and entropy density which is obtained by a generalized hot Thomas Fermi formalism, the ratio of shear viscosity over entropy density is calculated in the whole collision process as well as in the freeze-out stage. With the collision goes on, a transient minimal $\eta/s$ with the value around 5/$4\pi$ occurs in the largest compression stage. While, the relationship of $\eta/s$ to tempertaure ($T$) in the freeze-out stage displays a local minimum which is about 9-10 times $1/4\pi$ around $T$ = 9-15 MeV, which can be argued as indicative of a liquid gas phase transition. In addition, the influences of nucleon-nucleon cross section ($\sigma_{NN}$) and symmetry energy coefficient ($C_{s}$) are also discussed, and it is found that the results are sensitive to $\sigma_{NN}$ but not to $C_{s}$.

View original: http://arxiv.org/abs/1212.4907