Ratio of Shear Viscosity to Entropy Density of Nuclear Participant in the Intermediate Energy Heavy Ion Collisions

The ratio of shear viscosity(η) to entropy density(s) of nuclear fireball created in the central region of intermediate-energy heavy-ion collisions has been investigated within two transport models, namely the Boltzmann-Uehling-Uhlenbeck(BUU) model and the isospin-dependent quantum molecular dynamics(IQMD) model. Different methods are used to calculate η and s. With the collision energy increasing, the η/s displays a saturation value or a local minimum value at a certain beam energy.We argue that the saturation or minimum point corresponds to an occurrence of nuclear liquid gas phase transition.