arXiv subjects

V. N. Russkikh

Publications and source records attributed to V. N. Russkikh.

11 recordsLinked to original sources

arXiv2009

Elliptic Flow and Dissipation in Heavy-Ion Collisions at E_{lab} = (1--160)A GeV

Elliptic flow in heavy-ion collisions at incident energies $E_{lab}\simeq$ (1--160)A GeV is analyzed within the model of 3-fluid dynamics (3FD). We show that a simple correction factor, taking into account dissipative affects, allows us to adjust the 3FD results to experimental data. This single-parameter fit results in a good reproduction of the elliptic flow as a function of the incident energy, centrality of the collision and rapidity. The experimental scaling of pion eccentricity-scaled elliptic flow versus charged-hadron-multiplicity density per unit transverse area turns out to be also reasonably described. Proceeding from values of the Knudsen number, deduced from this fit, we estimate the upper limit the shear viscosity-to-entropy ratio as $η/s \sim 1-2$ at the SPS incident energies. This value is of the order of minimal $η/s$ observed in water and liquid nitrogen.

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arXiv2008

On freeze-out problem in relativistic hydrodynamics

A finite unbound system which is equilibrium in one reference frame is in general nonequilibrium in another frame. This is a consequence of the relative character of the time synchronization in the relativistic physics. This puzzle was a prime motivation of the Cooper--Frye approach to the freeze-out in relativistic hydrodynamics. Solution of the puzzle reveals that the Cooper--Frye recipe is far not a unique phenomenological method that meets requirements of energy-momentum conservation. Alternative freeze-out recipes are considered and discussed.

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arXiv2008

Transverse-Mass Spectra in Heavy-Ion Collisions at energies E_{lab} = 2--160 GeV/nucleon

Transverse-mass spectra of protons, pions and kaons produced in collisions of heavy nuclei are analyzed within the model of 3-fluid dynamics. It was demonstrated that this model consistently reproduces these spectra in wide ranges of incident energies E_{lab}, from 4A GeV to 160A GeV, rapidity bins and centralities of the collisions. In particular, the model describes the "step-like" dependence of kaon inverse slopes on the incident energy. The key point of this explanation is interplay of hydrodynamic expansion of the system with its dynamical freeze-out.

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arXiv2008

Transverse-Mass Effective Temperature in Heavy-Ion Collisions from AGS to SPS

Transverse-mass spectra in Au+Au and Pb+Pb collisions in incident energy range from 2A to 160A GeV are analyzed within the model of 3-fluid dynamics. It is shown that dynamical description of freeze-out, accepted in this model, naturally explains the incident energy behavior of inverse-slope parameters of these spectra observed in experiment. Simultaneous reproduction of the inverse-slopes of all considered particles (protons, pions and kaons) suggests that these particles belong to the same hydrodynamic flow at the instant of their freeze-out.

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arXiv2007

What we have learned so far from 3-fluid hydrodynamics

Available data on heavy-ion collisions at AGS and SPS energies are analyzed using a 3-fluid dynamical model within a purely hadronic scenario. We investigate the problems met in reproducing these data within this scheme. In particular, we try to indicate those data which could point towards the occurrence of a phase transition into the quark-gluon phase. We also discuss the success of the model in reproducing the transverse-mass spectra of various hadrons. We argue that the simultaneous reproduction of the inverse-slope parameters of all considered particles may imply that these particles belong to the same hydrodynamic flow at the instant of their freeze-out rather than that it signals the onset of a phase transition.

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arXiv2007

Dynamical Freeze-out in 3-Fluid Hydrodynamics

Freeze-out procedure accepted in the model of 3-fluid dynamics (3FD) is analyzed. This procedure is formulated in terms of drain terms in hydrodynamic equations. Dynamics of the freeze-out is illustrated by 1-dimensional simulations. It is demonstrated that the resulting freeze-out reveals a nontrivial dynamics depending on initial conditions in the expanding ``fireball''. The freeze-out front is not defined just ``geometrically'' on the condition of the freeze-out criterion met but rather is a subject the fluid evolution. It competes with the fluid flow and not always reaches the place where the freeze-out criterion is met. Dynamics of the freeze-out in 3D simulations is analyzed. It is demonstrated that the late stage of central nuclear collisions at top SPS energies is of the form of three (two baryon-rich and one baryon-free) fireballs separated from each other.

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arXiv2006

Dynamical phase trajectories for relativistic nuclear collisions

Central collisions of gold nuclei are simulated by several existing models and the central net baryon density rho and the energy density eps are extracted at successive times, for beam kinetic energies of 5-40 GeV per nucleon. The resulting trajectories in the (rho,eps) phase plane are discussed from the perspective of experimentally exploring the expected first-order hadronization phase transition with the planned FAIR at GSI or in a low-energy campaign at RHIC.

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arXiv2006

Collective Flow in Heavy-Ion Collisions from AGS to SPS

Collective transverse flow in heavy-ion collisions at incident energies E_{lab} = (1 -160)A GeV is analyzed within the model of 3-fluid dynamics (3FD). Simulations are performed with purely hadronic equation of state (EoS). At the AGS energies the flow turns out to be sensitive to the stopping power of nuclear matter rather than only to the stiffness of the EoS. When the stopping power is fixed to reproduce other observables, the flow data favor more and more soft EoS with the incident energy rise, which can be associated with ``a transition from hadronic to string matter'' reported in the Hadron-String-Dynamics (HSD) model. Problems, which are met in simultaneous reproduction of directed and elliptic flows within the 3FD, suggest that the transverse flow is very sensitive to the character of the transverse-momentum nonequilibrium at the initial stage of collision. Arguments in favor of "early-stage" nature of the flow observable are put forward. This suggests that the flow (especially the directed one) is determined by early-stage evolution of the collision rather than freeze-out stage.

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arXiv2006

Relativistic Heavy-Ion Collisions within 3-Fluid Hydrodynamics: Hadronic Scenario

A 3-fluid hydrodynamic model for simulating relativistic heavy-ion collisions is introduced. Alongside with two baryon-rich fluids, the new model considers time-delayed evolution of a third, baryon-free (i.e. with zero net baryonic charge) fluid of newly produced particles. Its evolution is delayed due to a formation time, 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 comparison with results of transport models. We have succeeded to reasonably reproduce a great body of experimental data in the incident energy range of E_{lab} = (1-160)A GeV. The list includes proton and pion rapidity distributions, proton transverse-mass spectra, rapidity distributions of Lambda and antiLambda hyperons, elliptic flow of protons and pions (with the exception of proton v2 at 40A GeV), multiplicities of pions, positive kaons, phi-mesons, hyperons and antihyperons, including multi-strange 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^- is approximately by a factor of 1.5 higher than that in the experiment. We have also failed to describe directed transverse flow of protons and pion at E_{lab} > 40A GeV. This failure apparently indicates that the used EoS is too hard and thereby leaves room for a phase transition.

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arXiv2003

Evolution of Baryon-Free Matter Produced in Relativistic Heavy-Ion Collisions

A 3-fluid hydrodynamic model is introduced for simulating heavy-ion collisions at incident energies between few and about 200 AGeV. In addition to the two baryon-rich fluids of 2-fluid models, the new model incorporates a third, baryon-free (i.e. with zero net baryonic charge) fluid which is created in the mid-rapidity region. Its evolution is delayed due to a formation time $τ$, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After formation it thermalizes and starts to interact with the baryon-rich fluids. It is found that for $τ$=0 the interaction strongly affects the baryon-free fluid. However, at reasonable finite formation time, $τ$=1 fm/c, the effect of this interaction turns out to be substantially reduced although still noticeable. Baryonic observables are only slightly affected by the interaction with the baryon-free fluid.

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arXiv2003

Three-Fluid Simulations of Relativistic Heavy-Ion Collisions

A relativistic 3-fluid 3D hydrodynamic model has been developed for describing heavy-ion collisions at incident energies between few and $\sim$ 200 A$\cdot$GeV. In addition to two baryon-rich fluids which simulate mutually decelerating counterflows of target and projectile nucleons, the new model incorporates evolution of a third, retarded baryon-free fluid created by this decelerated baryonic matter. Different equations of state, including those with the deconfinement phase transition, are treated. A reasonable agreement with experiment is illustrated by proton rapidity spectra, their dependence on collision centrality and beam energy.

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