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K. A. Bugaev

Publications and source records attributed to K. A. Bugaev.

At least 91 records · Page 5Linked to original sources
arXiv2005

Hagedorn Thermostat: A Novel View of Hadronic Thermodynamics

A microcanonical treatment of Hagedorn systems, i.e. finite mass hadronic resonances with an exponential mass spectrum controlled by the Hagedorn temperature $T_H$, is performed. We show that, in the absence of any restrictions, a Hagedorn system is a perfect thermostat, i.e. it imparts its temperature $T_H$ to any other system in thermal contact with it. We study the thermodynamic effects of the lower mass cut-off in the Hagedorn mass spectrum. We show that in the presence of a single Hagedorn resonance the temperature of any number of $N_B$ Boltzmann particles differs only slightly from $T_H$ up to the kinematically allowed limit $N_B^{kin}$. For $N_B > N_B^{kin}$ however, the low mass cut-off leads to a decrease of the temperature as $N_B$ grows. The properties of Hagedorn thermostats naturally explain a single value of hadronization temperature observed in elementary particle collisions at high energies and lead to some experimental predictions.

hep-ph↗
arXiv2005

The Hagedorn thermostat

A system H with a Hagedorn-like mass spectrum imparts its unique temperature TH to any other system coupled to it. An H system radiates particles in preexisting physical and chemical equilibrium. These particles form a saturated vapor at temperature TH. This coexistence describes a first order phase transition. An H system is nearly indifferent to fragmentation into smaller H systems. A lower mass cut-off in the spectrum does not significantly alter the general picture

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arXiv2005

Exactly Soluble Models for Surface Partition

The surface partition of large clusters is studied analytically within a frame-work of the ``Hills and Dales Model''. Three formulations are solved exactly by using the Laplace-Fourier transformation method. In the limit of small amplitude deformations, the ``Hills and Dales Model'' gives upper and lower bounds for the surface entropy coefficient of large clusters. A comparison with the 2- and 3-dimensional Ising model surface entropy coefficients is made.

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arXiv2004

Surface Partition of Large Fragments

The surface partition of large fragments is derived analytically within a simple statistical model by the Laplace-Fourier transformation method. In the limit of small amplitude deformations, a suggested Hills and Dales Model reproduces the leading term of the famous Fisher result for the surface entropy with an accuracy of a few percent. The surface partition of finite fragments is discussed as well.

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arXiv2004

Boundary Conditions of the Hydro-Cascade Model and Relativistic Kinetic Equations for Finite Domains

A detailed analysis of the coupled relativistic kinetic equations for two domains separated by a hypersurface having both space- and time-like parts is presented. Integrating the derived set of transport equations, we obtain the correct system of the hydro+cascade equations to model the relativistic nuclear collision process. Remarkably, the conservation laws on the boundary between domains conserve separately both the incoming and outgoing components of energy, momentum and baryonic charge. Thus, the relativistic kinetic theory generates twice the number of conservation laws compared to traditional hydrodynamics. Our analysis shows that these boundary conditions between domains, the three flux discontinuity, can be satisfied only by a special superposition of two cut-off distribution functions for the ``out'' domain. All these results are applied to the case of the phase transition between quark gluon plasma and hadronic matter. The possible consequences for an improved hydro+cascade description of the relativistic nuclear collisions are discussed. The unique properties of the three flux discontinuity and their effect on the space-time evolution of the transverse expansion are also analyzed. The possible modifications of both transversal radii from pion correlations generated by a correct hydro+cascade approach are discussed.

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arXiv2002

Hadron Spectra and QGP Hadronization in Au+Au Collisions at RHIC

The transverse mass spectra of Omega hyperons and phi mesons measured recently by STAR Collaboration in Au+Au collisions at sqrt(s_NN) = 130 GeV are described within a hydrodynamic model of the quark gluon plasma expansion and hadronization. The flow parameters at the plasma hadronization extracted by fitting these data are used to predict the transverse mass spectra of J/psi and psi' mesons.

hep-ph↗
arXiv2002

Relativistic Kinetic Equations for Finite Domains and Freeze-out Problem

The relativistic kinetic equations for the two domains separated by the hypersurface with both space- and time-like parts are derived. The particle exchange between the domains separated by the time-like boundaries generates source terms and modifies the collision term of the kinetic equation. The correct hydrodynamic equations for the ``hydro+cascade'' models are obtained and their differences from existing freeze-out models of the hadronic matter are discussed.

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arXiv2002

Equation of State for the Two-component Van der Waals Gas with Relativistic Excluded Volumes

A canonical partition function for the two-component excluded volume model is derived, leading to two different van der Waals approximations. The one is known as the Lorentz-Berthelot mixture and the other has been proposed recently. Both models are analysed in the canonical and grand canonical ensemble. In comparison with the one-component van der Waals excluded volume model the suppression of particle densities is reduced in these two-component formulations, but in two essentially different ways. Presently used multi-component models have no such reduction. They are shown to be not correct when used for components with different hard-core radii. For high temperatures the excluded volume interaction is refined by accounting for the Lorentz contraction of the spherical excluded volumes, which leads to a distinct enhancement of lighter particles. The resulting effects on pion yield ratios are studied for AGS and SPS data.

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arXiv2002

Omega, J/psi and psi' Transverse Mass Spectra at RHIC

The transverse mass spectra of J/psi and psi' mesons and Omega hyperons produced in central Au+Au collisions at RHIC energies are discussed within a statistical model used successfully for the interpretation of the SPS results. The comparison of the presented model with the future RHIC data should serve as a further crucial test of the hypothesis of statistical production of charmonia at hadronization. Finally, in case of validity, the approach should allow to estimate the mean transverse flow velocity at the quark gluon plasma hadronization.

hep-ph↗
arXiv2001

Critical Exponents of the Statistical Multifragmentation Model

For the statistical multifragmentation model the critical indices $α^\prime, β, γ^\prime, δ$ are calculated as functions of the Fisher parameter $τ$. It is found that these indices have different values than in Fisher's droplet model. Some peculiarities of the scaling relations are discussed. The basic model predicts for the index $τ$ a narrow range of values, $1.799< τ< 1.846$, which is consistent with two experiments on nuclear multifragmentation.

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arXiv2001

Transverse Momentum Spectra of $J/ψ$ and $ψ^{\prime}$ Mesons from Quark Gluon Plasma Hadronization in Nuclear Collisions

Recent results on transverse mass spectra of $J/ψ$ and $ψ^{\prime}$ mesons in central Pb+Pb collisions at 158 A$\cdot$GeV are considered. It is shown that those results support a hypothesis of statistical production of charmonia at hadronization and suggest the early thermal freeze--out of $J/ψ$ and $ψ^{\prime}$ mesons. Based on this approach the collective transverse velocity of hadronizing quark gluon plasma is estimated to be $ \approx 0.2$. Predictions for transverse mass spectra of hidden and open charm mesons at SPS and RHIC are discussed.

hep-ph↗
arXiv2001

Statistical Multifragmentation in Thermodynamical Limit: An Exact Solution for Phase Transitions

An exact analytical solution of the statistical multifragmentation model is found in thermodynamic limit. Excluded volume effects are taken into account in the thermodynamically self-consistent way. The model exhibits a 1-st order phase transition of the liquid-gas type. An extension of the model including the Fisher's term is also studied. The possibility of the second order phase transition at or above the critical point is discussed. The mixed phase region of the phase diagram, where the gas of nuclear fragments coexists with the infinite liquid condensate, is unambiguously identified. The peculiar thermodynamic properties of the model near the boundary between the mixed phase and the pure gaseous phase are studied. The results for the caloric curve and specific heat are presented and a physical picture of the nuclear liquid-gas phase transition is clarified.

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arXiv2000

Statistical Multifragmentation in Thermodynamic Limit

An exact analytical solution of the statistical multifragmentation model is found in thermodynamic limit. The model exhibits a 1-st order phase transition of the liquid-gas type. The mixed phase region of the phase diagram, where the gas of nuclear fragments coexists with the infinite liquid condensate, is unambiguously identified. The peculiar thermodynamic properties of the model near the boundary between the mixed phase and the pure gaseous phase are studied. The results for the caloric curve and specific heat are presented and a physical picture of the nuclear liquid-gas phase transition is clarified.

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arXiv2000

Exactly Soluble Model for Nuclear Liquid-Gas Phase Transition

Thermodynamical properties of nuclear matter undergoing multifragmentation are studied within a simplified version of the statistical model. An exact analytical solution has been found for the grand canonical ensemble. Excluded volume effects are taken into account in the thermodynamically self-consistent way. In thermodynamic limit the model exhibits a first order liquid-gas phase transition with specific mixed phase properties. An extension of the model including the Fisher's term is also studied. The possibility of the second order phase transition at or above the critical point is demonstrated. The fragment mass distributions in the different regions of the phase diagram are discussed.

nucl-th↗
arXiv2000

Van der Waals Excluded Volume Model for Lorentz Contracted Rigid Spheres

Conventional cluster and virial expansions are generalized to momentum dependent inter-particle potentials. The model with Lorentz contracted hard core potentials is considered, e.g. as hadron gas model. A Van der Waals-type model with a temperature dependent excluded volume is derived. Lorentz contraction effects at given temperature are stronger for light particles and make their effective excluded volume smaller than that of heavy ones.

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