We review studies of vortical motion and the resulting global polarization of
and
hyperons in heavy-ion collisions, in particular, within 3FD model. 3FD predictions for the global midrapidity ...polarization in the FAIR-NICA energy range are presented. The 3FD simulations indicate that energy dependence of the observed global polarization of hyperons in the midrapidity region is a consequence of the decrease of the vorticity in the central region with the collision energy rise because of pushing out the vorticity field into the fragmentation regions. At high collision energies this pushing-out results in a peculiar vortical structure consisting of two vortex rings: one ring in the target fragmentation region and another one in the projectile fragmentation region with matter rotation being opposite in these two rings.
A three-fluid hydrodynamic model for simulating relativistic heavy-ion collisions is introduced. Along with two baryon-rich fluids, the new model considers the time-delayed evolution of a third, ...baryon-free (i.e., with zero net baryonic charge) fluid of newly produced particles. Its evolution is delayed because of a formation time {tau}, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After the formation it starts to interact with the baryon-rich fluids and quickly gets thermalized. Within this model with pure hadronic equation of state, a systematic analysis of various observables at incident energies between few and about 160A GeV has been done as well as a comparison with results of transport models. We have succeeded in reasonably reproducing a great body of experimental data in the incident energy range of E{sub lab}{approx_equal} (1-160)A GeV. The list includes proton and pion rapidity distributions, proton transverse-mass spectra, rapidity distributions of {lambda} and {lambda} hyperons, elliptic flow of protons and pions (with the exception of proton v{sub 2} at 40A GeV), multiplicities of pions, positive kaons, {phi} mesons, hyperons, and antihyperons, including multistrange particles. This agreement is achieved on the expense of substantial enhancement of the interflow friction as compared to that estimated proceeding from hadronic free cross sections. However, we have also found out certain problems. The calculated yield of K{sup -} is approximately higher than that in the experiment by a factor of 1.5. We have also failed to describe directed transverse flow of protons and pion at E{sub lab}{>=}40A GeV. This failure apparently indicates that the used EOS is too hard and thereby leaves room for a phase transition.
We present the hybrid model connecting the parton–hadron–string dynamic model (PHSD) and a hydrodynamic model taking into account shear viscosity within the Israel–Stewart approach. The numerical ...scheme, initialization, and particlization procedure are discussed in detail. The performance of the code is tested on the pion and proton rapidity and transverse mass distributions calculated for Au + Au and Pb+Pb collisions at AGS–SPS energies. The influence of the switch time from transport to hydro models, the viscous parameter, and freeze-out time are discussed. Since the applicability of the Israel–Stewart hydrodynamics assumes the perturbative character of the viscous stress tensor,
π
μ
ν
, which should not exceed the ideal energy–momentum tensor,
T
id
μ
ν
, hydrodynamical codes usually rescale the shear stress tensor if the inequality
‖
π
μ
ν
‖
≪
‖
T
id
μ
ν
‖
is not fulfilled in some sense. There are several conditions used in the literature and we analyze in detail the influence of different conditions and values of the cut-off parameter on observables. We show that the form of the corresponding condition plays an important role in the sensitivity of hydrodynamic calculations to the viscous parameter – a ratio of the shear viscosity to the entropy density,
η
/
s
. It is shown that the constraints used in the vHLLE and MUSIC models give the same results for the observables. With these constraints, the rapidity distributions and transverse momentum spectra are most sensitive to a change of the
η
/
s
ratio. We demonstrate that these constraints do not guarantee that each element of the
π
μ
ν
tensor is smaller than the corresponding element
T
id
μ
ν
. As an alternative, a strict condition is used. When applied it reduces the sensitivity of the proton and pion momentum distributions to the viscosity parameter. We performed global fits of the rapidity and transverse mass distributions of pion and protons. It was also found that
η
/
s
as a function of the collision energy monotonically increases from
E
lab
=
6
A
GeV
up to
E
lab
=
40
A
GeV
and saturates for higher SPS energies. We observe that it is difficult to reproduce simultaneously pion and proton rapidity distribution within our model with the present choice of the equation of state without a phase transition.
A multistage hybrid model intended for describing heavy-ion interactions in the energy region of the NICA collider under construction in Dubna is proposed. The model combines the initial, fast, ...interaction stage described by the model of hadron string dynamics (HSD) and the subsequent evolution that the expanding system formed at the first stage experiences at the second stage and which one treats on the basis of ideal hydrodynamics; after the completion of the second stage, the particles involved may still undergo rescattering (third interaction stage). The model admits three freeze-out scenarios: isochronous, isothermal, and isoenergetic. Generally, the HydHSD hybrid model developed in the present study provides fairly good agreement with available experimental data on proton rapidity spectra. It is shown that, within this hybrid model, the two-humped structure of proton rapidity distributions can be obtained either by increasing the freeze-out temperature and energy density or by more lately going over to the hydrodynamic stage. Although the proposed hybrid model reproduces rapidity spectra of protons, it is unable to describe rapidity distributions of pions, systematically underestimating their yield. It is necessary to refine the model by including viscosity effects at the hydrodynamic stage of evolution of the system and by considering in more detail the third interaction stage.
Based on the quasi-particle description of the QCD medium at finite temperature and density we formulate the phenomenological model for the equation of state that exhibits crossover or the ...first-order deconfinement phase transition. The models are constructed in such a way as to be thermodynamically consistent and to satisfy the properties of the ground state nuclear matter complying with constraints from intermediate heavy-ion collision data. Our equations of states show a quite reasonable agreement with the recent lattice findings on the temperature and baryon chemical potential dependence of relevant thermodynamical quantities in the parameter range covering both the hadronic and quark–gluon sectors. The model predictions on the isentropic trajectories in the phase diagram are shown to be consistent with the recent lattice results. Our nuclear equations of state are to be considered as an input to the dynamical models describing the production and the time evolution of a thermalized medium created in heavy-ion collisions in a broad energy range from SIS up to LHC.
A sharp peak in the
K
+
/π
+
ratio in relativistic heavy-ion collision is discussed in the framework of the SU(3) Polyakov-loop extended Nambu-Jona-Lasinio model with vector interaction. In the ...model, the
K
+
/π
+
ratio has been calculated along the chiral phase transition line for different values of the vector coupling
g
V
. It has been shown that the value of the vector coupling hardly affects the behavior of the
K
+
/π
+
ratio.
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