12,113 research outputs found
Estimation of the Shear Viscosity from 3FD Simulations of Au+Au Collisions at 3.3--39 GeV
An effective shear viscosity in central Au+Au collisions is estimated in the
range of incident energies 3.3 GeV 39 GeV. The
simulations are performed within a three-fluid model employing three different
equations of state with and without the deconfinement transition. In order to
estimate this effective viscosity, we consider the entropy produced in the 3FD
simulations as if it is generated within the conventional one-fluid viscous
hydrodynamics. It is found that the effective viscosity within different
considered scenarios is very similar at the expansion stage of the collision:
as a function of temperature () the viscosity-to-entropy ratio behaves as
; as a function of net-baryon density (), , i.e. it is mainly determined by the density dependence of the entropy
density. The above dependencies take place along the dynamical trajectories of
Au+Au collisions. At the final stages of the expansion the values are
ranged from 0.05 at highest considered energies to 0.5 at the
lowest ones.Comment: 4 pages, 3 figures, to be published in Eur. Phys. Journ.
Entropy Production and Effective Viscosity in Heavy-Ion Collisions
Entropy production and an effective viscosity in central Au+Au collisions are
estimated in a wide range of incident energies 3.3 GeV
39 GeV. The simulations are performed within a three-fluid model employing
three different equations of state with and without deconfinement transition,
which are equally good in reproduction of the momentum-integrated elliptic flow
of charged particles in the considered energy range. It is found that more that
80\% entropy is prodused during a short early collision stage which lasts
1 fm/c at highest considered energies 20 GeV. The
estimated values of the viscosity-to-entropy ratio () are approximately
the same in all considered scenarios. At final stages of the system expansion
they range from 0.05 at highest considered energies to 0.5 lowest
ones. It is found that the ratio decreases with the temperature ()
rise approximately as and exhibits a rather weak dependence on the
net-baryon density.Comment: 10 pages, 9 figures. Version accepted for publication in the European
Physical Journal
Light fragment production at CERN Super Proton Synchrotron
Recent data on the deutron and He production in central Pb+Pb collisions
at the CERN Super Proton Synchrotron (SPS) energies measured by the NA49
collaboration are analyzed within the model of the three-fluid dynamics (3FD)
complemented by the coalescence model for the light-fragment production. The
simulations are performed with different equations of state---with and without
deconfinement transition. It is found that scenarios with the deconfinement
transition are preferable for reproduction rapidity distributions of deuterons
and He, the corresponding results well agree with the experimental data. At
the same time the calculated transverse-mass spectra of He at midrapidity
do not that nice agree with the experimental data. The latter apparently
indicates that coalescence coefficients should be temperature and/or momentum
dependent.Comment: 7 pages, 7 figures, 1 table, version accepted for publication in Eur.
Phys. J.
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