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V. D. Toneev

Publications and source records attributed to V. D. Toneev.

At least 73 records · Page 4Linked to original sources
arXiv2003

Strangeness Production in Nuclear Matter and Expansion Dynamics

Thermodynamical properties of hot and dense nuclear matter are analyzed and compared for different equation of state (EoS). It is argued that the softest point of the equation of state and the strangeness separation on the phase boundary can manifest themselves in observables. The influence of the EoS and the order of the phase transition on the expansion dynamics of nuclear matter and strangeness excitation function is analyzed. It is shown that bulk properties of strangeness production in A-A collisions depend only weakly on the particular form of the EoS. The predictions of different models are related with experimental data on strangeness production.

hep-ph↗
arXiv2002

Observable Consequences of Crossover-type Deconfinement Phase Transition

Equation of State (EoS) for hot and dense nuclear matter with a quark-hadron phase transition is constructed within a statistical mixed-phase model assuming coexistence of unbound quarks in nuclear surrounding. This model predicts the deconfinement phase transition of the crossover type. The so-called "softest point" effect of EoS is analyzed and confronted to that for other equations of state which exhibit the first order phase transition (two-phase bag model) or no transition at all (hadron resonance gas). It is demonstrated that the beam energy dependence of the directed flow is a smooth function in the whole range from SIS till SPS energies and allows to disentangle different EoS, being in good agreement with experimental data for the statistical mixed-phase model. In contrast, excitation functions for relative strangeness abundance turn out to be insensitive to the order of phase transition.

nucl-th↗
arXiv2002

Quark-gluon evolution in early stage of ultra-relativistic heavy-ion collisions

A set of coupled kinetic equations describing in the Abelian approximation a mixture of quarks and self-interacting gluons is formulated and solved numerically. The model includes the Schwinger-like mechanism for particle creation in a strong field as well as two-particle elastic collisions between all mixture components in the Landau approximation of small-angle scattering. The process of equilibration at the initial energy density exhibits a dominant quark creation in the very early time of interaction. It is shown that damping of energy density oscillations due to elastic scattering of perturbative quarks and gluons is not strong enough to reach thermodynamic equilibrium in a reasonable relaxation time. A possible account for a such behavior is discussed.

hep-ph↗
arXiv2002

Comparative Study of Multifragmentation of Gold Nuclei Induced by Relativistic Protons, $^4$He, and $^{12}$C

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, $^4$He and $^{12}$C on Au with the $4π$ setup FASA. The mean IMF multiplicities (for the events with at least one IMF) are saturating at the value of $2.2\pm0.2$ for the incident energies above 6 GeV. The observed IMF multiplicities cannot be described in a two-stage scenario, a fast cascade followed by a statistical multifragmentation. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate phase and modifying empirically the excitation energies and masses of the remnants. The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of ``thermal'' multifragmentation of a hot and diluted target spectator. In the case of $^{12}$C+Au(22.4 GeV) and $^4$He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow.

nucl-ex↗
arXiv2002

Towards thermodynamical consistency of qusiparticle picture

The purpose of the present article is to call attention to some realistic quasiparticle-based description of the quark/gluon matter and its consistent implementation in thermodynamics. A simple and transparent representation of the thermodynamical consistency conditions is given. This representation allows one to review critically and systemize available phenomenological approaches to the deconfinement problem with respect to their thermodynamical consistency. A particular attention is paid to the development of a method for treating the string screening in the dense matter of unbound color charges. The proposed method yields an integrable effective pair potential which can be incorporated into the mean-field picture. The results of its application are in reasonable agreement with lattice data on the QCD thermodynamics.

nucl-th↗
arXiv2001

Fragile Signs of Criticality in the Nuclear Multifragmentation

Deviations from an idealized equilibrium phase transition picture in nuclear multifragmentation is studied in terms of the entropic index. We investigate different heat-capacity features in the canonical quantum statistical model of nuclear multifragmentation generalized in the framework of Tsallis nonextensive thermostatistics. We find that the negative branch of heat capacity observed in quasi-peripheral Au+Au collisions is caused primarily by the non-generic nonextensivity effects.

nucl-th↗
arXiv2001

Plasma production and thermalisation in a strong field

Aspects of the formation and equilibration of a quark-gluon plasma are explored using a quantum kinetic equation, which involves a non-Markovian, Abelian source term for quark and antiquark production and, for the collision term, a relaxation time approximation that defines a time-dependent quasi-equilibrium temperature and collective velocity. The strong Abelian field is determined via the simultaneous solution of Maxwell's equation. A particular feature of this approach is the appearance of plasma oscillations in all thermodynamic observables. Their presence can lead to a sharp increase in the time-integrated dilepton yield.

nucl-th↗
arXiv2001

Transition from Thermal to Rapid Expansion in Multifragmentation of Gold Induced by Light Relativistic Projectiles

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, $^4$He and $^{12}$C on Au with the $4π$ setup FASA. In the case of $^{12}$C(22.4 GeV)+Au and $^4$He(14.6 GeV)+Au collisions, the deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments: the spectra are harder than calculated and than measured in p-induced collisions. This difference is attributed to a collective flow with the expansion velocity on the surface about 0.1 $c$ (for $^{12}$C+Au collisions).

nucl-ex↗
arXiv2000

Dynamical interpretation of chemical freeze-out in heavy ion collisions

It is demonstrated that there exists a direct correlation between chemical freeze-out point and the softest point of the equation of state where the pressure divided by the energy density, $p(ε)/ε$, has a minimum. A dynamical model is given as an example where the passage of the softest point coincides with the condition for chemical freeze-out, namely an average energy per hadron $\approx$ 1 GeV. The sensitivity of the result to the equation of state used is discussed.

nucl-th↗
arXiv2000

Directed Flow of Baryons in Heavy-Ion Collisions

The collective motion of nucleons from high-energy heavy-ion collisions is analyzed within a relativistic two-fluid model for different equations of state (EoS). As function of beam energy the theoretical slope parameter F_y of the differential directed flow is in good agreement with experimental data, when calculated for the QCD-consistent EoS described by the statistical mixed-phase model. Within this model, which takes the deconfinement phase transition into account, the excitation function of the directed flow turns out to be a smooth function in the whole range from SIS till SPS energies. This function is close to that for pure hadronic EoS and exhibits no minimum predicted earlier for a two-phase bag-model EoS. Attention is also called to a possible formation of nucleon antiflow (F_y < 0) at energies of the order of 100 A GeV.

nucl-th↗
arXiv2000

Anomalous radial expansion in central heavy-ion reactions

The expansion velocity profile in central heavy-ion reactions in the Fermi energy domain is examined. The radial expansion is non-hubblean and in the surface region it scales proportional to a higher exponent ($α> 1$) of the radius. The anomalous expansion velocity profile is accompanied by a power law nucleon density profile in the surface region. Both these features of central heavy-ion reactions disappear at higher energies, and the system follows a uniform Hubble expansion ($α\simeq 1$).

nucl-th↗
arXiv2000

Nuclear Multifragmentation in the Non-extensive Statistics - Canonical Formulation

We apply the canonical quantum statistical model of nuclear multifragmentation generalized in the framework of recently proposed Tsallis non-extensive thermostatistics for the description of nuclear multifragmentation process. The test calculation in the system with A=197 nucleons show strong modification of the 'critical' behaviour associated with the nuclear liquid-gas phase transition for small deviations from the conventional Boltzmann-Gibbs statistical mechanics.

nucl-th↗
arXiv1999

Quantum Statistical Model of Nuclear Multifragmentation in the Canonical Ensemble Method

A quantum statistical model of nuclear multifragmentation is proposed. The recurrence equation method used within the canonical ensemble makes the model solvable and transparent to physical assumptions and allows to get results without involving the Monte Carlo technique. The model exhibits the first order phase transition. Quantum statistics effects are clearly seen on the microscopic level of occupation numbers but are almost washed out for global thermodynamic variables and the averaged observables studied. In the latter case, the recurrence relations for multiplicity distributions of both intermediate-mass and all fragments are derived and the specific changes in the shape of multiplicity distributions in the narrow region of the transition temperature is stressed. The temperature domain favorable to search for the HBT effect is noted.

nucl-th↗
arXiv1999

The non-equilibrium distribution function of particles and anti-particles created in strong fields

We investigate the quantum Vlasov equation with a source term describing the spontaneous particle creation in strong fields. The back-reaction problem is treated by solving this kinetic equation together with the Maxwell equation which determines the induced time-dependent electric field in the system. The evolution of distribution functions for bosons and fermions is studied numerically. We found that the system shows a regular dynamic behavior if the back-reaction is neglected. But if the back-reaction is included, it is not the case and some stochastic features are clearly revealed in the non-equilibrium distribution function..

hep-ph↗
arXiv1999

Multifragmentation of non-spherical nuclei

The shape influence of decaying thermalized source on various characteristics of multifragmentation as well as its interplay with effects of angular momentum and collective expansion are first studied and the most pertinent variables are proposed. The analysis is based on the extension of the statistical microcanonical multifragmentation model.

nucl-th↗
arXiv1999

Dynamical Interpretation of Chemical Freeze-Out Parameters

It is shown that the condition for chemical freeze-out, average energy per hadron approximately 1 GeV, selects the softest point of the equation of state, namely the point where the pressure divided by the energy density has a minimum. The sensitivity to the equation of state used is discussed. The previously proposed mixed phase model, which is consistent with lattice QCD data naturally leads to the chemical freeze-out condition.

nucl-th↗
arXiv1998

Non-Markovian effects in strong-field pair creation

We analyze a quantum kinetic equation describing both boson and fermion pair production and explore analytically and numerically the solution of the non-Markovian kinetic equation. In the Markovian limit of the kinetic equation we find an analytical solution for the single particle distribution function of bosons and fermions. The numerical investigation for a homogeneous, constant electric field shows an enhancement (bosons) or a suppression (fermions) of the pair creation rate according to the symmetry character of the produced particles. For strong fields non-Markovian effects are important while they disappear for weak fields. Hence it is sufficient to apply the low density limit for weak fields but necessary to take into account memory effects for strong fields.

hep-ph↗