arXiv subjects

Yu-Gang Ma

Publications and source records attributed to Yu-Gang Ma.

156 records · Page 9Linked to original sources

arXiv2014

Effect of initial fluctuations on the collective flow in intermediate-energy heavy ion collisions

A systemical analysis of the initial fluctuation effect on the collective flows for Au+Au at 1$A$ GeV has been presented in the framework of Isospin-dependent Quantum Molecular Dynamics model (IQMD), and a special focus on the initial fluctuation effect on the squeeze-out is emphasized. The flows calculated by the participant plane reconstructedby the initial geometry in coordinate space are compared with those calculated by both the ideal reaction plane and event plane methods. It is found that initial fluctuation weakens squeeze-out effect, and somediscrepancies between the flows extracted by the above different plane methods appearwhich indicate that the flows are affected by the evolution of dynamics. In addition, we found that the squeeze-out flow is also proportional to initial eccentricity. Our calculations also qualitatively give the similar trend for the excitation function of the elliptic flow of the FOPI experimental data. Finally we address the nucleon number scaling of the flows for light particles. Even though initial fluctuation decreases the ratio of $v_4/v_2^2$ as well as $v_3/(v_1v_2$) a lot, all fragments to mass number 4 keep the same curve and shows independent of transverse momentum.

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arXiv2014

Production of Kaon and $Λ$ in nucleus-nucleus collisions at ultra-relativistic energy from a blast wave model

The particle production of Kaon and $Λ$ are studied in nucleus-nucleus collisions at relativistic energy based on a chemical equilibrium blast-wave model. The transverse momentum spectra of Kaon and $Λ$ at the kinetic freeze-out stage from our model are in good agreement with the experimental results. The kinetic freeze-out parameters of temperature ($T_{kin}$) and radial flow parameter $ρ_{0}$ are presented for the FOPI, RHIC and LHC energies. And the resonance decay effect is also discussed. The systematic study for beam energy dependence of the strangeness particle production will help us to better understand the properties of the matter created in heavy-ion collisions at the kinetic freeze-out stage.

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arXiv2014

Charge separation with fluctuating domains in relativistic heavy-ion collisions

Charge separation induced by the chiral magnetic effect suggested that some ${\cal P}$- or ${\cal CP}$-odd metastable domains could be produced in a QCD vacuum in the early stage of relativistic heavy-ion collisions. Based on a multi-phase transport model, our results suggest that a domain-based scenario with final state interactions can describe the solenoidal tracker at RHIC detector (STAR) measurements of both same- and opposite-charge azimuthal angle correlations, $<\cos(ϕ_α+ϕ_β)>$, in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV. The occupancy factor of the total volume of domains over the fireball volume is small, which indicates that the size and number of metastable domains should be relatively small in the early stage of a quark-gluon plasma.

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arXiv2013

Shear viscosity of neutron-rich nucleonic matter near its liquid-gas phase transition

Within a relaxation time approach using free nucleon-nucleon cross sections modified by the in-medium nucleon masses that are determined from an isospin- and momentum-dependent effective nucleon-nucleon interaction, we investigate the specific shear viscosity ($η/s$) of neutron-rich nucleonic matter near its liquid-gas phase transition. It is found that as the nucleonic matter is heated at fixed pressure or compressed at fixed temperature, its specific shear viscosity shows a valley shape in the temperature or density dependence, with the minimum located at the boundary of the phase transition. Moreover, the value of $η/s$ drops suddenly at the first-order liquid-gas phase transition temperature, reaching as low as $4\sim5$ times the KSS bound of $\hbar/4π$. However, it varies smoothly for the second-order liquid-gas phase transition. Effects of the isospin degree of freedom and the nuclear symmetry energy on the value of $η/s$ are also discussed.

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arXiv2013

Energy dependence of pion in-medium effects on π^-/π^+ ratio in heavy-ion collisions

Within the framework of a thermal model with its parameters fitted to the results from an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, we study the pion in-medium effect on the charged-pion ratio in heavy-ion collisions at various energies. We find that due to the cancellation between the effects from pion-nucleon s-wave and p-wave interactions in nuclear medium, the π^-/π^+ ratio generally decreases after including the pion in-medium effect. The effect is larger at lower collision energies as a result of narrower pion spectral functions at lower temperatures.

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arXiv2013

Symmetry energy and nucleon-nucleon cross sections

The extension of the Boltzmann-Uehling-Uhlenbeck model of nucleus-nucleus collision is presented. The isospin-dependent nucleon-nucleon cross sections are estimated using the proper volume extracted from the equation of state of the nuclear matter transformed into the form of the Van der Waals equation of state. The results of such simulations demonstrate the dependence on symmetry energy which typically varies strongly from the results obtained using only the isospin-dependent mean-field. The evolution of the n/p multiplicity ratio with angle and kinetic energy, in combination with the elliptic flow of neutrons and protons, provides a suitable set of observables for determination of the density dependence of the symmetry energy. The model thus provides an environment for testing of equations of state, used for various applications in nuclear physics and astrophysics.

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arXiv2012

Hypernclear in the improved quark mass density- dependent model

The improved quark mass density- dependent model, which has been successfully used to describe the properties of both finite nuclei and bulk nuclear matter, is extended to include the strange quark. The parameters of the model are determined by the saturation properties of bulk matter. Then the given parameter set is employed to investigate both the properties of strange hadronic matter and those of $Λ$ hypernuclei. Bulk strange hadronic matter consisting of nucleons, $Λ$- hyperons and $Ξ$- hyperons is studied under mean-field approximation. Among others, density dependence of the effective baryon mass, saturation properties and stability of the physical system are discussed. For single-$Λ$ hypernuclei, single particle energies of $Λ$ hyperon is evaluated. In particular, it is found that the present model produces a small spin-orbit interaction, which is in agreement with the experimental observations. The above results show that the present model can consistently describe the properties of strange hadronic matter, as well as those of single $Λ$ hypernuclei within an uniform parameterization.

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arXiv2012

Quark deconfinement phase transition in nuclear matter for improved quark mass density-dependent model

The improved quark mass density-dependent (IQMDD) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to investigate the properties of quark deconfinement phase transition. By using the finite-temperature quantum field theory, we calculate the finite temperature effective potential and extend the IQMDD model to finite temperature and finite nuclear matter density. The critical temperature and the critical density of nuclear matter are given and the QCD phase diagram is addressed. It is shown that this model can not only describe the saturation properties of nuclear matter, but also explain the quark deconfinement phase transition successfully.

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arXiv2011

Isobaric yield ratios in heavy-ion reactions, and symmetry energy of neutron-rich nuclei at intermediate energies

The isobaric yield ratios of the fragments produced in the neutron-rich 48Ca and 64Ni projectile fragmentation are analyzed in the framework of a modified Fisher model. The correlations between the isobaric yield ratios (R) and the energy coefficients in the Weiszäcker-Beth semiclassical mass formula (the symmetry-energy term asym, the Coulomb-energy term ac, and the pairing-energy term ap) and the difference between the chemical potentials of the neutron and proton (μn-μp) are investigated. Simple correlations between (μn-μp)/T, ac/T, asym/T, and ap/T (where T is the temperature), and lnR are obtained. It is suggested that (μn-μp)/T, ac/T, asym/T, and ap/T of neutron-rich nuclei can be extracted using isobaric yield ratios for heavy-ion collisions at intermediate energies.

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arXiv2001

Cluster Emission and Phase Transition Behavior in the Nuclear Disassembly

The features of the emissions of light particles ($LP$), charged particles ($CP$), intermediate mass fragments ($IMF$) and the largest fragment ($MAX$) are investigated for $^{129}Xe$ as functions of temperature and "freeze-out" density in the frameworks of isospin dependent lattice gas model and classical molecular dynamics model. Definite turning points for the slopes of average multiplicity of $LP$, CP and $IMF$, and of the mean mass of the largest fragment ($A_{max}$) are shown around a liquid gas phase transition temperature and while the largest variances of the distributions of $LP$, $CP$, $IMF$, and $MAX$ appear there. It indicates that the cluster emission rate can be taken as a probe of nuclear liquid gas phase transition and while the largest fluctuation is simultaneously accompanied at the point of the phase transition within lattice gas model and molecular dynamics model as the traditional thermodynamical theory requires when a phase transition occurs.

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arXiv2001

Application of Information Theory in Nuclear Liquid Gas Phase Transition

Information entropy and Zipf's law in the field of information theory have been used for studying the disassembly of nuclei in the framework of the isospin dependent lattice gas model and molecular dynamical model. We found that the information entropy in the event space is maximum at the phase transition point and the mass of the cluster show exactly inversely to its rank, i.e. Zipf's law appears. Both novel criteria are useful in searching the nuclear liquid gas phase transition experimentally and theoretically.

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arXiv1999

Isospin Effects of the Critical Behavior in the Lattice Gas Model

Isospin effects of the critical phenomena were studied via Xe isotopes in the frame of lattice gas model. All the critical temperatures for four Xe isotopes are close to 5.5 MeV at the same freeze-out density of about 0.39 $ρ_0$. The critical values of power law parameter of mass distribution, mean multiplicity of intermediate mass fragments (IMF), information entropy and Campi's second moment show minor dependence on the isospin at the critical point.

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