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Register a new userRatio of shear viscosity to entropy density in multifragmentation of Au + Au
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The ratio of the shear viscosity ($eta$) to entropy density ($s$) for the intermediate energy heavy-ion collisions has been calculated by using the Green-Kubo method in the framework of the quantum molecular dynamics model. The theoretical curve of $eta/s$ as a function of the incident energy for the head-on Au+Au collisions displays that a minimum region of $eta/s$ has been approached at higher incident energies, where the minimum $eta/s$ value is about 7 times Kovtun-Son- Starinets (KSS) bound (1/4$pi$). We argue that the onset of minimum $eta/s$ region at higher incident energies corresponds to the nuclear liquid gas phase transition in nuclear multifragmentation.
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The ratio of shear viscosity ($eta$) to entropy density ($s$) for an equilibrated system is investigated in intermediate energy heavy ion collisions below 100$A$ MeV within the framework of the Boltzmann-Uehling-Uhlenbeck (BUU) model . After the collision system almost reaches a local equilibration, the temperature, pressure and energy density are obtained from the phase space information and {$eta/s$} is calculated using the Green-Kubo formulas. The results show that {$eta$}/$s$ decreases with incident energy and tend towards a smaller value around 0.5, which is not so drastically different from the BNL Relativistic Heavy Ion Collider results in the present model.
Equilibration of highly excited baryon-rich matter is studied within the microscopic model calculations in A+A collisions at energies of BES, FAIR and NICA. It is shown that the system evolution from the very beginning of the collision can be approximated by relativistic hydrodynamics, although the hot and dense nuclear matter is not in local equilibrium yet. During the evolution of the fireball the extracted values of energy density, net baryon and net strangeness densities are used as an input to Statistical Model (SM) in order to calculate temperature $T$, chemical potentials $mu_B$ and $mu_S$, and entropy density $s$ of the system. Also, they are used as an input for the box with periodic boundary conditions to investigate the momentum correlators in the infinite nuclear matter. Shear viscosity $eta$ is calculated according to the Green-Kubo formalism. At all energies, shear viscosity to entropy density ratio shows minimum at time corresponding to maximum baryon density. The ratio dependence on $T, mu_B, mu_S$ is investigated for both in- and out of equilibrium cases.
We performed a systematic study of the formation of fragments with different mass ranges in 197Au+197Au collisions at incident energies between 20 - 1000 MeV/nucleon and at impact para- meter between ^b = 0-0.98. The aim of present study is to understand the complex dependence of fragment production on incident energy and impact parameter. Our results clearly indicate that the QMD simulations of 197Au+197Au predict different behavior for different mass ranges than for IMFs with a change in incident energy and impact parameter. All charge yields can be parameterized by a power law and no signal of liquid-gas phase transition is seen as no unique dependence of tau on impact parameter is seen.
Onset of multifragmentation and vaporization in Au-Au collisions
We study the collision energy dependence of (anti-)deuteron and (anti-)triton production in the most central Au+Au collisions at $sqrt{s_mathrm{NN}}=$ 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV, using the nucleon coalescence model. The needed phase-space distribution of nucleons at the kinetic freeze-out is generated from a new 3D hybrid dynamical model (texttt{iEBE-MUSIC}) by using a smooth crossover equation of state (EoS) without a QCD critical point. Our model calculations predict that the coalescence parameters of (anti-)deuteron ($B_2(d)$ and $B_2(bar{d})$) decrease monotonically as the collision energy increases, and the light nuclei yield ratio $N_t N_p/N_d^2$ remains approximately a constant with respect to the collision energy. These calculated observables fail to reproduce the non-monotonic behavior of the corresponding data from the STAR Collaboration. Without including any effects of the critical point in our model, our results serve as the baseline predictions for the yields of light nuclei in the search for the possible QCD critical points from the experimental beam energy scan of heavy ion collisions.
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