arXiv subjects

M. I. Gorenstein

Publications and source records attributed to M. I. Gorenstein.

At least 55 records · Page 3Linked to original sources

arXiv2016

Entropy production in chemically non-equilibrium quark-gluon plasma created in central Pb+Pb collisions at LHC energies

We study the possibility that partonic matter produced at early stage of ultrarelativistic heavy-ion collisions is out of chemical equilibrium. It is assumed that initially this matter is mostly composed of gluons, but quarks and antiquarks are produced at later times. The dynamical evolution of partonic system is described by the Bjorken-like ideal hydrodynamics with a time dependent quark fugacity. The results of this model are compared with those obtained by assuming the complete chemical equilibrium of partons already at the initial stage. It is shown that in a chemically non-equilibrium scenario the entropy gradually increases, and about 25% of the total final entropy is generated during the hydrodynamic evolution of deconfined matter. We argue that the (anti)quark suppression included in this approach may be responsible for reduced (anti)baryon to meson ratios observed in heavy-ion collisions at LHC energies.

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arXiv2015

Non-Gaussian particle number fluctuations in vicinity of the critical point for van der Waals equation of state

The non-Gaussian measures of the particle number fluctuations -- skewness $Sσ$ and kurtosis $κσ^2$ -- are calculated in a vicinity of the critical point. This point corresponds to the end point of the first-order liquid-gas phase transition. The gaseous phase is characterized by the positive values of skewness while the liquid phase has negative skew. The kurtosis appears to be significantly negative at the critical density and supercritical temperatures. The skewness and kurtosis diverge at the critical point. The classical van der Waals equation of state in the grand canonical ensemble formulation is used in our studies. Neglecting effects of the quantum statistics we succeed to obtain the analytical expressions for the rich structures of the skewness and kurtosis in a wide region around the critical point. These results have universal form, i.e., they do not depend on particular values of the van der Waals parameters $a$ and $b$. The strongly intensive measures of particle number and energy fluctuations are also considered and show singular behavior in the vicinity of the critical point.

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arXiv2015

Undersaturation of quarks at early stages of relativistic nuclear collisions: the hot glue initial scenario and its observable signatures

The early stage of high multiplicity nuclear collisions is represented by a nearly quarkless, hot, deconfined pure gluon plasma. This new scenario should be characterized by a suppression of high $p_T$ photons and dileptons as well as by reduced baryon to meson ratios. We present the numerical results for central Pb+Pb collisions at the LHC energies by using the ideal Bjorken hydrodynamics with time-dependent quark fugacity. It is shown that about 25\% of final total entropy is generated during the hydrodynamic evolution of chemically undersaturated quark-gluon plasma.

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arXiv2015

Scaled variance, skewness, and kurtosis near the critical point of nuclear matter

The van der Waals (VDW) equation of state predicts the existence of a first-order liquid-gas phase transition and contains a critical point. The VDW equation with Fermi statistics is applied to a description of the nuclear matter. The nucleon number fluctuations near the critical point of nuclear matter are studied. The scaled variance, skewness, and kurtosis diverge at the critical point. It is found that the crossover region of the phase diagram is characterized by the large values of the scaled variance, the almost zero skewness, and the significantly negative kurtosis. The rich structures of the skewness and kurtosis are observed in the phase diagram in the wide region around the critical point, namely, they both may attain large positive or negative values.

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arXiv2015

Fluctuations in the Statistical Model of the Early Stage of nucleus-nucleus collisions

Predictions on fluctuations of hadron production properties in central heavy ion collisions are presented. They are based on the Statistical Model of the Early Stage and extend previously published results by considering the strongly intensive measures of fluctuations. In several of the considered cases a significant change in collision energy dependence of calculated quantities as a result of the phase transition is predicted. This provides an opportunity to observe new signals of the onset of deconfinement in heavy ion collisions experiments.

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arXiv2015

Van der Waals Equation of State with Fermi Statistics for Nuclear Matter

The van der Waals (VDW) equation of state is a simple and popular model to describe the pressure function in equilibrium systems of particles with both repulsive and attractive interactions. This equation predicts an existence of a first-order liquid-gas phase transition and contains a critical point. Two steps to extend the VDW equation and make it appropriate for new physical applications are carried out in this paper: 1) the grand canonical ensemble formulation; 2) an inclusion of the quantum statistics. The VDW equation with Fermi statistics is then applied to a description of the system of interacting nucleons. The VDW parameters $a$ and $b$ are fixed to reproduce the properties of nuclear matter at saturation density $n_0=0.16$ fm$^{-3}$ and zero temperature. The model predicts a location of the critical point for the symmetric nuclear matter at temperature $T_c\cong 19.7$ MeV and nucleon number density $n_c \cong 0.07$ fm$^{-3}$.

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arXiv2015

Statistical Model of the Early Stage of nucleus-nucleus collisions with exact strangeness conservation

The Statistical Model of the Early Stage, SMES, describes a transition between confined and deconfined phases of strongly interacting matter created in nucleus-nucleus collisions. The model was formulated in the late 1990s for central Pb+Pb collisions at the CERN SPS energies. It predicted several signals of the transition (onset of deconfinement) which were later observed by the NA49 experiment. The grand canonical ensemble was used to calculate entropy and strangeness production. This approximation is valid for reactions with mean multiplicities of particles carrying conserved charges being significantly larger than one. Recent results of NA61/SHINE on hadron production in inelastic p+p interactions suggest that the deconfinement may also take place in these reactions. However, in this case mean multiplicity of particles with non-zero strange charge is smaller than one. Thus for the modeling of p+p interactions the exact strangeness conservation has to be implemented in the SMES. This extension of the SMES is presented in the paper.

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arXiv2015

Particle Number Fluctuations for van der Waals Equation of State

The van der Waals (VDW) equation of state describes a thermal equilibrium in system of particles, where both repulsive and attractive interactions between them are included. This equation predicts an existence of the 1st order liquid-gas phase transition and the critical point. The standard form of the VDW equation is given by the pressure function in the canonical ensemble (CE) with a fixed number of particles. In the present paper the VDW equation is transformed to the grand canonical ensemble (GCE). We argue that this procedure can be useful for new physical applications. Particularly, the fluctuations of number of particles, which are absent in the CE, can be studied in the GCE. For the VDW equation of state in the GCE the particle number fluctuations are calculated for the whole phase diagram, both outside and inside the liquid-gas mixed phase region. It is shown that the scaled variance of these fluctuations remains finite within the mixed phase and goes to infinity at the critical point. The GCE formulation of the VDW equation of state can be also an important step for its application to a statistical description of hadronic systems, where numbers of different particle species are usually not conserved.

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arXiv2015

Mean transverse mass of hadrons in proton-proton reactions

An energy dependence of the mean transverse mass $\langle m_T\rangle$ at mid-rapidity in proton-proton ($p+p$) reactions is studied within the ultra-relativistic quantum molecular dynamics (UrQMD). The UrQMD model predicts a nonmonotonous dependence of $\langle m_T\rangle$ on collision energy for several hadron species: for $π^+$, $p$, $K^+$, and $Λ$ the mean transverse mass has a maximum at the center of mass energy region $5\le \sqrt{s}\le 8$ GeV. These results are a consequence of an interplay of two contributions: 1) excitations and decays of the baryonic resonances $N^*$ and $Δ$; 2) excitations and decays of the baryonic strings. The UrQMD results do not show any nonmonotonous dependence of $\langle m_T\rangle$ on $\sqrt{s}$ for $π^-$, $K^{-}$, and antiprotons. Whether a nonmonotonous dependence of $\langle m_T\rangle$ at mid-rapidity on the collision energy for $π^+$, $p$, $K^+$, and $Λ$ is relevant for real $p+p$ interactions will be soon checked experimentally by the NA61/SHINE Collaboration.

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arXiv2015

Hadron Resonance Gas Equation of State from Lattice QCD

The Monte Carlo results in lattice QCD for the pressure and energy density at small temperature $T < 155$ MeV and zero baryonic chemical potential are analyzed within the hadron resonance gas model. Two extensions of the ideal hadron resonance gas are considered: the excluded volume model which describes a repulsion of hadrons at short distances and Hagedorn model with the exponential mass spectrum. Considering both of these models one by one we do not find the conclusive evidences in favor of any of them. The controversial results appear because of rather different sensitivities of the pressure and energy density to both excluded volume and Hagedorn mass spectrum effects. On the other hand, we have found a clear evidence for a simultaneous presence of both of them. They lead to rather essential contributions: suppression effects for thermodynamical functions of the hadron resonance gas due to the excluded volume effects and enhancement due to the Hagedorn mass spectrum.

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arXiv2014

System-size and energy dependence of particle momentum spectra: The UrQMD analysis of p+p and Pb+Pb collisions

The UrQMD transport model is used to study a system-size and energy dependence of the pion production in high energy collisions. New data of the NA61/SHINE Collaboration on spectra of negatively charged pions in proton-proton interactions at SPS energies are considered. These results are compared with the corresponding data of the NA49 Collaboration in central Pb+Pb collisions at the same collision energies per nucleon. Mean pion multiplicity per participant nucleon, inverse slope parameter of the transverse momentum spectra, and width of rapidity distribution are investigated. A role of isospin effects is discussed. We find that the UrQMD model predicts a non-monotonous behavior of mean transverse mass with collision energy for positively charged pions at the mid-rapidity in inelastic proton-proton interactions. This will be checked soon experimentally by NA61/SHINE Collaboration.

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arXiv2014

Strangeness Production in Light and Intermediate size Nucleus-Nucleus Collisions

Within the statistical model, the net strangeness conservation and incomplete total strangeness equilibration lead to the suppression of strange particle multiplicities. Furthermore, suppression effects appear to be stronger in small systems. By treating the production of strangeness within the canonical ensemble formulation we developed a simple model which allows to predict the excitation function of $K^+/π^+$ ratio in nucleus-nucleus collisions. In doing so we assumed that different values of $K^+/π^+$, measured in p+p and Pb+Pb interactions at the same collision energy per nucleon, are driven by the finite size effects only. These predictions may serve as a baseline for experimental results from NA61/SHINE at the CERN SPS and the future CBM experiment at FAIR.

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arXiv2014

Recent Developments in the Study of Deconfinement in Nucleus-Nucleus Collisions

Deconfinement refers to the creation of a state of quasi-free quarks and gluons in strongly interacting matter. Model predictions and experimental evidence for the onset of deconfinement in nucleus-nucleus collisions were discussed in our first review on this subject. These results motivated further experimental and theoretical studies. This review addresses two subjects. First, a summary of the past, present and future experimental programmes related to discovery and study of properties of the onset of deconfinement are %briefly presented. Second, recent progress is reviewed on analysis methods and preliminary experimental results for new strongly intensive fluctuation measures are discussed, which are relevant for current and future studies of the onset of deconfinement and searches for the critical point of strongly interacting matter

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arXiv2013

Hadron-Resonance Gas at Freeze-out: Reminder on Importance of Repulsive Interactions

An influence of the repulsive interactions on matter properties is considered within the excluded volume van der Waals hadron-resonance gas model. Quantitative results are presented for matter at the chemical freeze-out in central nucleus-nucleus collisions at relativistic energies. In particular, it is shown that repulsive interactions connected to non-zero size of created particles lead to a significant decrease of collision energy at which the net-baryon density has a maximum. A position of the transition point from baryon to meson dominated matter depends on the difference between baryon and meson hard-core radiuses.

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arXiv2013

Energy and Transverse Momentum Fluctuations in the Equilibrium Quantum Systems

The fluctuations in the ideal quantum gases are studied using the strongly intensive measures $Δ[A,B]$ and $Σ[A,B]$ defined in terms of two extensive quantities $A$ and $B$. In the present paper, these extensive quantities are taken as the motional variable, $A=X$, the system energy $E$ or transverse momentum $P_T$, and number of particles, $B=N$. This choice is most often considered in studying the event-by-event fluctuations and correlations in high energy nucleus-nucleus collisions. The recently proposed special normalization ensures that $Δ$ and $Σ$ are dimensionless and equal to unity for fluctuations given by the independent particle model. In statistical mechanics, the grand canonical ensemble formulation within the Boltzmann approximation gives an example of independent particle model. Our results demonstrate the effects due to the Bose and Fermi statistics. Estimates of the effects of quantum statistics in the hadron gas at temperatures and chemical potentials typical for thermal models of hadron production in high energy collisions are presented. In the case of massless particles and zero chemical potential the $Δ$ and $Σ$ measures are calculated analytically.

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arXiv2013

Shear and bulk viscosities of strongly-interacting 'infinite' parton-hadron matter within the parton-hadron-string transport approach

We study the shear and bulk viscosities of partonic and hadronic matter as functions of temperature T within the parton-hadron-string dynamics (PHSD) off-shell transport approach. Dynamical hadronic and partonic systems in equilibrium are studied by the PHSD simulations in a finite box with periodic boundary conditions. The ratio of the shear viscosity to entropy density η(T)/s(T) from PHSD shows a minimum (with a value of about 0.1) close to the critical temperature T_c, while it approaches the perturbative QCD limit at higher temperatures in line with lattice QCD (lQCD) results. For T<T_c, i.e., in the hadronic phase, the ratio η/s rises fast with decreasing temperature due to a strong decrease of the entropy density $s$ in the hadronic phase at decreasing T. Within statistics, we obtain practically the same results in the Kubo formalism and in the relaxation time approximation. The bulk viscosity ζ(T)---evaluated in the relaxation time approach---is found to strongly depend on the effects of mean fields (or potentials) in the partonic phase. We find a significant rise of the ratio ζ(T)/s(T) in the vicinity of the critical temperature T_c, when consistently including the scalar mean-field from PHSD, which is also in agreement with that from lQCD calculations. Furthermore, we present the results for the ratio (η+ 3ζ/4)/s, which is found to depend nontrivially on temperature and to generally agree with the lQCD calculations as well. Within the PHSD calculations, the strong maximum of ζ(T)/η(T) close to T_c has to be attributed to mean-field (or potential) effects that in PHSD are encoded in the temperature dependence of the quasiparticle masses, which is related to the infrared enhancement of the resummed (effective) coupling g(T).

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arXiv2013

On Normalization of Strongly Intensive Quantities

A special normalization is proposed for strongly intensive quantities used in the study of event-by-event fluctuations in high energy collisions. It ensures that these measures are dimensionless and yields a common scale required for a quantitative comparison of fluctuations of different, in general dimensional, extensive quantities. Namely, the properly normalized strongly intensive quantities assume the value one for fluctuations given by the model of independent particle production and zero in the absence of event-by-event fluctuations.

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arXiv2013

Dynamical equilibration of strongly interacting "infinite" parton matter within the parton-hadron-string dynamics transport approach

We study the kinetic and chemical equilibration in "infinite" parton matter within the parton-hadron-string dynamics off-shell transport approach, which is based on a dynamical quasiparticle model (DQPM) for partons matched to reproduce lattice QCD results-including the partonic equation of state-in thermodynamic equilibrium. The "infinite" parton matter is simulated by a system of quarks and gluons within a cubic box with periodic boundary conditions, at different energy densities, initialized slightly out of kinetic and chemical equilibrium. We investigate the approach of the system to equilibrium and the time scales for the equilibration of different observables. We, furthermore, study particle distributions in the strongly interacting quark-gluon plasma (sQGP) including partonic spectral functions, momentum distributions, abundances of the different parton species and their fluctuations (scaled variance, skewness, and kurtosis) in equilibrium. We also compare the results of the microscopic calculations with the ansatz of the DQPM. It is found that the results of the transport calculations are in equilibrium well matched by the DQPM for quarks and antiquarks, while the gluon spectral function shows a slightly different shape due to the explicit interaction of partons. The time scales for the relaxation of fluctuation observables are found to be shorter than those for the average values. Furthermore, in the local subsystem, a strong change of the fluctuation observables with the size of the local volume is observed. These fluctuations no longer correspond to those of the full system and are reduced to Poissonian distributions when the volume of the local subsystem becomes much smaller than the total volume.

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