90 research outputs found
Collision term dependence of the hadronic shear viscosity and diffusion coefficients
In this work the shear viscosity and the diffusion coefficients of
conserved charges with of hadronic matter are
investigated within the hadronic transport approach SMASH. We systematically
study the effect of multi-particle reactions, angular distributions and
additional elastic cross sections via the additive quark model description, the
numbers of degrees of freedom and the baryon density on the transport
coefficients using the Green-Kubo formalism. We find that multi-particle
reactions decrease the shear viscosity in a simplified hadron gas whereas the
electric charge diffusion coefficient is not modified. Furthermore, additional
elastic cross sections have a strong impact on both and
whereas anisotropic scatterings enhance the shear viscosity in the full hadron
gas. When increasing the number of degrees of freedom the shear viscosity is
only slightly modified in comparison to the diffusion coefficients. Finally,
the calculation within a finite baryon chemical potential reveals that the
shear viscosity itself does not depend on but on the ratio .
The diffusion coefficients show a strong dependency which we compare to
Chapman-Enskog calculations
Fate of critical fluctuations in an interacting hadronic medium using maximum entropy distributions
We study the evolution of critical fluctuations in an expanding system within
a hadronic transport approach. The initialization of the system with critical
fluctuations is achieved by coupling the ideal hadron resonance gas cumulants
to the ones from the 3d Ising model and generating the net and total particle
number distribution from the principle of maximum entropy. These distributions
are then evolved using realistic hadronic interactions. We systematically
investigate the evolution of the critical fluctuations initialized at various
temperatures and chemical potentials along a freeze-out line. We find that
resonance regeneration and isospin randomization processes have the strongest
influence on the evolution of the fluctuations. Additionally, the sets of
particles coupled to the critical mode are modified to assess the strength of
the propagation of correlations through interactions. We find that in the
scaling region of the critical point correlations are propagated through the
whole collisional history and are still present after the kinetic freeze-out of
the matter if the coupling strength is large enough
Particle production in a hybrid approach for a beam energy scan of Au+Au/Pb+Pb collisions between = 4.3 GeV and = 200.0 GeV
Heavy-ion collisions at varying collision energies provide access to
different regions of the QCD phase diagram. In particular collisions at
intermediate energies are promising candidates to experimentally identify the
postulated first order phase transition and critical end point.
While heavy-ion collisions at low and high collision energies are
theoretically well described by transport approaches and
hydrodynamics+transport hybrid approaches, respectively, intermediate energy
collisions remain a challenge.
In this work, a modular hybrid approach, the SMASH-vHLLE-hybrid coupling 3+1D
viscous hydrodynamics (vHLLE) to hadronic transport (SMASH), is introduced. It
is validated and subsequently applied in Au+Au/Pb+Pb collisions between
= 4.3 GeV and = 200.0 GeV to
study the rapidity and transverse mass distributions of identified particles as
well as excitation functions for and
. A good agreement with experimental measurements
is obtained, including the baryon stopping dynamics. The transition from a
Gaussian rapidity spectrum of protons at lower energies to the double-hump
structure at high energies is reproduced. The centrality and energy dependence
of charged particle is also described reasonably well. This work serves
as a basis for further studies, e.g. systematic investigations of different
equations of state or transport coefficients
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