Recent STAR data on the bulk observables in the energy range of the Beam-Energy Scan Program at the Relativistic Heavy-Ion Collider are analyzed within the model of the three-fluid dynamics (3FD). The simulations are performed with different equations of state (EoS). The purely hadronic EoS fails to reproduce the data. A good, though imperfect, overall reproduction of the data is found within the deconfinement scenarios. The crossover EoS turns out to be slightly preferable. For this reproduction a fairly strong baryon stopping in the quark-gluon phase is required. The 3FD model does not need two separate freeze-outs (i.e. kinetic and chemical ones) to describe the STAR data. A unified freeze-out is applied at all energies.

Vorticity generated in heavy-ion collisions at energy of √ sNN = 39 GeV is studied. Simulations are performed within a model of the three-fluid dynamics. A peculiar structure consisting of two vortex rings is found: one ring in the target fragmentation region and another one in the projectile fragmentation region. These rings are also formed in central collisions. The matter rotation is opposite in this two rings. These vortex rings are already formed at the early stage of the collision together with primordial fragmentation regions. The average vorticity, responsible for the global polarization of the observed Λ andΛ, is also studied. In the semi-central collisions the average vorticity in the midrapidity region turns out to be more than an order of magnitude lower than the total one. The total vorticity is dominated by the contributions of the fragmentation regions and is produced because of asymmetry of the vortex rings in noncentral collisions. This suggests that in semi-central collisions the global polarization in the fragmentation regions should be at least an order of magnitude higher than that observed by the STAR collaboration in the midrapidity. This polarization should be asymmetrical in the reaction plain and correlate with the corresponding directed flow.

No abstract

The baryon and energy densities attained in fragmentation regions in central Au+Au collisions in the energy range of the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) are estimated within the model of the three-fluid dynamics. It is shown that a considerable part of the baryon charge is stopped in the central fireball. Even at 39 GeV, approximately 70% of the total baryon charge turns out to be stopped. The fraction of this stopped baryon charge decreases with collision energy rise, from 100% at 7.7 GeV to ∼40% at 62 GeV. The highest initial baryon densities of the equilibrated matter, nB/n0 ≈ 10, are reached in the central region of colliding nuclei at √ sNN = 20-40 GeV. These highest densities develop up to quite moderate freeze-out baryon densities at the midrapidity because the matter of the central fireball is pushed out to fragmentation regions by one-dimensional expansion. Therefore, consequences of these high initial baryon densities can be observed only in the fragmentation regions of colliding nuclei in AFTER@LHC experiments in the fixed-target mode.