arXiv subjects

V. D. Toneev

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

At least 37 records · Page 2Linked to original sources

arXiv2013

The QGP dynamics in relativistic heavy-ion collisions

The dynamics of partons and hadrons in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for the partonic phase (DQPM) including a dynamical hadronization scheme. The PHSD model reproduces a large variety of observables from SPS to LHC energies, e.g. the quark-number scaling of elliptic flow, transverse mass and rapidity spectra of charged hadrons, dilepton spectra, open and hidden charm production, collective flow coefficients etc., which are associated with the observation of a sQGP. The highlights of the latest results on collective flow are presented and open questions/perspectives are discussed.

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arXiv2012

Event-by-event background in estimates of the chiral magnetic effect

In terms of the parton-hadron-string-dynamics (PHSD) approach - including the retarded electromagnetic field - we investigate the role of fluctuations of the correlation function in the azimuthal angle $ψ$ of charged hadrons that is expected to be a sensitive signal of local strong parity violation. For the early time we consider fluctuations in the position of charged spectators resulting in electromagnetic field fluctuations as well as in the position of participant baryons defining the event plane. For partonic and hadronic phases in intermediate stages of the interaction we study the possible formation of excited matter in electric charge dipole and quadrupole form as generated by fluctuations. The role of the transverse momentum and local charge conservation laws in the observed azimuthal asymmetry is investigated, too. All these above-mentioned effects are incorporated in our analysis based on event-by-event PHSD calculations. Furthermore, the azimuthal angular correlations from Au+Au collisions observed in the recent STAR measurements within the RHIC Beam-Energy-Scan (BES) program are studied. It is shown that the STAR correlation data at the collision energies of $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV can be reasonably reproduced within the PHSD. At higher energies the model fails to describe the $ψ$ correlation data resulting in an overestimation of the partonic scalar field involved. We conclude that an additional transverse anisotropy fluctuating source is needed which with a comparable strength acts on both in- and out-of-plane components.

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arXiv2012

Collective properties of nucleus-nucleus collisions from AGS to LHC energies

The azimuthal anisotropies of the collective transverse flow of charged hadrons are investigated in a wide range of heavy-ion collision energies within the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which incorporates explicit partonic degrees-of-freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ of charged hadrons with collision energy is successfully described in terms of the PHSD approach. The analysis of higher-order harmonics $v_3$ and $v_4$ in the azimuthal angular distribution shows a similar tendency of growing deviations between partonic and purely hadronic models with increasing collision energy. This demonstrates that the excitation functions of azimuthal anisotropies reflect the increasing role of quark-gluon degrees of freedom in the early phase of relativistic heavy-ion collisions. Furthermore, the specific variation of the ratio $v_4/(v_2)^2$ with respect to bombarding energy, centrality and transverse momentum is found to provide valuable information on the underlying partonic dynamics.

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arXiv2012

Azimuthal anisotropies for Au+Au collisions in the parton-hadron transient energy range

The azimuthal anisotropies of the collective transverse flow of charged hadrons are investigated in a wide range of heavy-ion collision energies within the microscopic parton-hadron-string dynamics (PHSD) transport approach which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation of state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ of charged hadrons with collision energy is successfully described in terms of the PHSD approach. The PHSD scaling properties of various collective observables are confronted with experimental data as well as with hydrodynamic predictions. The analysis of higher-order harmonics $v_3$ and $v_4$ in the azimuthal angular distribution shows a similar tendency of growing deviations between partonic and purely hadronic models with increasing collision energy. This demonstrates that the excitation functions of azimuthal anisotropies reflect the increasing role of quark-gluon degrees of freedom in the early phase of relativistic heavy-ion collisions. Furthermore, the specific variation of the ratio $v_4/(v_2)^2$ with respect to bombarding energy, centrality and transverse momentum is found to provide valuable information on the underlying dynamics.

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arXiv2012

Theoretical analysis of a possible observation of the chiral magnetic effect in Au + Au collisions within the RHIC beam energy scan program

In terms of the hadron-string-dynamics (HSD) approach we investigate the correlation function in the azimuthal angle $ψ$ of charged hadrons that is expected to be sensitive to a signal of local strong parity violation. Our analysis of Au+Au collisions is based on the recent STAR data within the RHIC Beam-Energy-Scan (BES) program. The HSD model reasonably reproduces STAR data for $\sqrt{s_{NN}}=$7.7 GeV, while there are some deviations from the experiment at the collision energy of 11.5 GeV and an increase of deviations between theory and experiment at $\sqrt{s_{NN}}=$39 GeV. For reference, the results for $\sqrt{s_{NN}}=$ 200 GeV are given as well. The role of the retarded electromagnetic field is discussed and a compensation effect for the action of its electric and magnetic components is pointed out. We conclude that the recent RHIC BES data at $\sqrt{s_{NN}}=$7.7 and 11.5 GeV can be understood on the hadronic level without involving the idea of a strong parity violation; however, at $\sqrt{s_{NN}}\sim$40 GeV and above one needs to take into consideration explicit partonic (quark-qluon) degrees-of-freedom for a proper treatment of the dynamics.

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arXiv2012

The QGP phase in relativistic heavy-ion collisions

The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results - including the partonic equation of state - in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color neutrality as well as energy-momentum conservation. The PHSD approach is applied to nucleus-nucleus collisions from low SIS to RHIC energies. The traces of partonic interactions are found in particular in the elliptic flow of hadrons as well as in their transverse mass spectra.

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arXiv2011

Chiral Magnetic Effect and evolution of electromagnetic field

The energy dependence of observable two particle correlator in search for the local strong parity violation in Au+Au collisions is estimated within a simple phenomenological model. The model reproduces available RHIC data but at LHC predicts that the Chiral Magnetic effect (CME) will be about 20 times weaker than at RHIC, contrary to the first LHC measurements. In the lower energy range this effect should vanish sharply at energy somewhere above the top SPS one with agreement with the preliminary results of the Beam Energy Scan program. To elucidate CME background effects a transport HSD model including magnetic field evolution is put forward and electromagnetic dynamics at the RHIC energy is investigated. It is observed that the electromagnetic field included into the hadronic model does not influence on observables due to mutual compensation of effects of electric and magnetic fields.

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arXiv2011

Effects of Model Parameters in Thermodynamics of the PNJL Model

The thermodynamic behavior of the two-flavor($N_f=$2) three-color ($N_c=3$) Polyakov-loop-extended Nambu-Jona-Lasinio model at the finite chemical potential is investigated. New lattice gluon data for gluon thermodynamics are used defining the effective potential within polynomial and logarithmic forms of its approximation. We study the effects of using different sets of data and different forms of the potential on thermodynamic properties of hot and dense matter. It is found that the PNJL thermodynamics depends stronger on the form of the effective potential than on the used lattice data set. Particular attention is paid to the phase diagram in the $(T,μ)$ plane.

hep-ph↗

arXiv2011

Relaxation time ansatz and shear and bulk viscosities of gluon matter

Shear and bulk viscosity-to-entropy density ratios are calculated for the pure gluon matter in a non-equilibrium mean-field quasiparticle approach within the relaxation time approximation. We study how different approximations used in the literature affect the results for the shear and bulk viscosities. Though the results for the shear viscosity turned out to be quite robust, all evaluations of the shear and bulk viscosities obtained in the framework of the relaxation time approximation can be considered only as rough estimations.

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arXiv2011

Decay of a scalar $σ$-meson near the critical end-point in the PNJL model

Properties of a scalar $σ$-meson are investigated in the two-flavor Nambu-Jona-Lasinio model with the Polyakov loop. Model analysis of the phase diagram of strong interacting matter is performed. The temperature dependence of the $σ\rightarrowππ$ decay width is studied at the zero chemical potential and near the critical end-point. The calculated strong coupling constant $g_{σππ}$ and the decay width are compared with available experimental data and other model results. Nonthermal enhancement of the total decay width is noted for the $σ$ meson near the critical end-point when the condition $m_σ\geq2m_π$ is broken.

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arXiv2011

Shear and bulk viscosities for pure glue matter

Shear $η$ and bulk $ζ$ viscosities are calculated in a quasiparticle model within a relaxation time approximation for pure gluon matter. Below $T_c$ the confined sector is described within a quasiparticle glueball model. Particular attention is paid to behavior of the shear and bulk viscosities near $T_c$. The constructed equation of state reproduces the first-order phase transition for the glue matter. It is shown that with this equation of state it is possible to describe the temperature dependence of the shear viscosity to entropy ratio $η/s$ and the bulk viscosity to entropy ratio $ζ/s$ in reasonable agreement with available lattice data but absolute values of the $ζ/s$ ratio underestimate the upper limits of this ratio in the lattice measurements typically by an order of magnitude.

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arXiv2011

Thermodynamics in NJL-like models

Thermodynamic behavior of conventional Nambu-Jona-Lasinio and Polyakov-loop-extended Nambu-Jona-Lasinio models is compared. A particular attention is paid to the phase diagram in the ($T -μ$) plane.

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arXiv2010

The Chiral Magnetic Effect: Beam-energy and system-size dependence

We consider the energy dependence of the local ${\cal P}$ and ${\cal CP}$ violation in Au+Au and Cu+Cu collisions over a large energy range within a simple phenomenological model. It is expected that at LHC the chiral magnetic effect will be about 20 times weaker than at RHIC. At lower energy range this effect should vanish sharply at energy somewhere above the top SPS one. To elucidate CME background effects a transport model including magnetic field evolution is put forward.

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arXiv2010

Beam-energy and system-size dependence of the CME

The energy dependence of the local ${\cal P}$ and ${\cal CP}$ violation in Au+Au and Cu+Cu collisions in a large energy range is estimated within a simple phenomenological model. It is expected that at LHC the Chiral Magnetic effect (CME) will be about 20 times weaker than at RHIC. In the lower energy range this effect should vanish sharply at energy somewhere above the top SPS one. To elucidate CME background effects a transport model including magnetic field evolution is put forward.

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arXiv2010

Viscosity coefficients for hadron and quark-gluon phases

The shear ($η$) and bulk ($ζ$) viscosities are calculated in a quasiparticle relaxation time approximation. The hadron phase is described within the relativistic mean field based model with scaled hadron masses and couplings. The quark phase is treated in terms of the heavy quark bag model fitted to the lattice data. A two-phase model allowing for the first order phase transition from the hadron phase to the strongly coupled quark gluon plasma is constructed by means of the Gibbs conditions. Temperature and baryon density dependence of the calculated viscosity-to-entropy ratios ($η/s$, $ζ/s$) are analyzed and compared with those obtained in other models. Special attention is paid to the behavior of viscosity coefficients near the critical temperature, from both hadron and quark-gluon side. Effects of resonance widths on viscosities and viscosity-to-entropy ratios are estimated.

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arXiv2009

Viscosity of hadron matter within relativistic mean-field based model with scaled hadron masses and couplings

The shear ($η$) and bulk ($ζ$) viscosities are calculated in a quasiparticle relaxation time approximation for a hadron matter described within the relativistic mean-field based model with scaled hadron masses and couplings. Comparison with results of other models is presented. We demonstrate that a small value of the shear viscosity to entropy density ratio required for explaining a large elliptic flow observed at RHIC may be reached in the hadron phase. Large values of the bulk viscosity are noted in case of the baryon enriched matter.

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arXiv2009

Resonance Structure in the $γγ$ Invariant Mass Spectrum in $p$C- and $d$C-Interactions

Along with $π^0$ and $η$ mesons, a resonance structure in the invariant mass spectrum of two photons at $M_{γγ}= 360 \pm 7 \pm 9$ MeV is observed in the reaction $d C\toγ+ γ+X$ at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are $Γ= 63.7 \pm 17.8$ MeV and $σ_{γγ}=98\pm24^{+93}_{-67} {\rm μb}$, respectively. The collected statistics amount to $2339 \pm 340$ events of $1.5\cdot 10^6$ triggered interactions of a total number $\sim 10^{12}$ of $d$C-interactions. This resonance structure is not observed in $p$C collisions at the beam momentum 5.5 GeV/c. Possible mechanisms of this ABC-like effect are discussed.

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arXiv2008

Relativistic Mean-Field Model with Scaled Hadron Masses and Couplings

Here we continue to elaborate properties of the relativistic mean-field based model (SHMC) proposed in ref. [6] where hadron masses and coupling constants depend on the $σ$-meson field. The validity of approximations used in [6] is discussed. We additionally incorporate contribution of meson excitations to the equations of motion. We also estimate the effects of the particle width. It is demonstrated that the inclusion of the baryon-baryon hole and baryon-antibaryon loop terms, if performed perturbatively, destroys the consistency of the model.

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