Zhao-Qing Feng

Probing high-density behavior of symmetry energy from pion emission in heavy-ion collisions

Abstract Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation densities is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Δ ( 1232 ) and N ∗ ( 1440 ) . The total pion multiplicities and the π − / π + yields are calculated for selected Skyrme parameters SkP, SLy6, Ska and SIII, and also for the cases of different stiffness of symmetry energy with the parameter SLy6. Preliminary results compared with the measured data by the FOPI Collaboration favor a hard symmetry energy of the potential term proportional to ( ρ / ρ 0 ) γ s with γ s = 2 .

Transverse emission of isospin ratios as a probe of high-density symmetry energy in isotopic nuclear reactions

Abstract Transverse emission of preequilibrium nucleons, light clusters (complex particles) and charged pions from the isotopic Sn 112 , 124 + Sn 112 , 124 reactions at a beam energy of 400 A MeV, to extract the high-density behavior of nuclear symmetry energy, are investigated within an isospin and momentum-dependent transport model. Specifically, the double ratios of neutron/proton, triton/helium-3 and π − / π + in the squeeze-out domain are analyzed systematically, which are favorable in reducing the influence of the Coulomb force and less systematic errors. It is found that the transverse momentum distribution of isospin ratios strongly depend on the stiffness of nuclear symmetry energy, which would be a nice observable to extract the high-density symmetry energy. The collision centrality and the mass splitting of neutron and proton in nuclear medium play a significant role on the distribution structure of the ratios, but do not change the influence of symmetry energy on the spectrum.

Dynamical analysis on heavy-ion fusion reactions near Coulomb barrier

The shell correction is proposed in the improved isospin dependent quantum molecular dynamics (ImIQMD) model, which plays an important role in heavy-ion fusion reactions near Coulomb barrier. By using the ImIQMD model, the static and dynamical fusion barriers, dynamical barrier distribution in the fusion reactions are analyzed systematically. The fusion and capture excitation functions for a series of reaction systems are calculated and compared with experimental data. It is found that the fusion cross sections for neutron-rich systems increase obviously, and the strong shell effects of two colliding nuclei result in a decrease of the fusion cross sections at the sub-barrier energies. The lowering of the dynamical fusion barriers favors the enhancement of the sub-barrier fusion cross sections, which is related to the nucleon transfer and the neck formation in the fusion reactions.

Production of heavy and superheavy nuclei in massive fusion reactions

Within the framework of a dinuclear system (DNS) model, the evaporation-residue excitation functions and the quasi-fission mass yields in the 48Ca induced fusion reactions are investigated systematically and compared with available experimental data. Maximal production cross sections of superheavy nuclei based on stable actinide targets are obtained. Isotopic trends in the production of the superheavy elements Z = 110, 112–118 based on the actinide isotopic targets are analyzed systematically. Optimal evaporation channels and combinations as well as the corresponding excitation energies are proposed. The possible factors that influencing the isotopic dependence of the production cross sections are analyzed. The formation of the superheavy nuclei based on the isotopes U with different projectiles are also investigated and calculated.

Constraining the high-density behavior of the nuclear equation of state from strangeness production in heavy-ion collisions

The dynamics of pions and strange particles in heavy-ion collisions in the region of 1A GeV energies is investigated by the lanzhou quantum molecular dynamics model for probing the nuclear equation of state at suprasaturation densities. The total multiplicities and the ratios obtained in {sup 197}Au+{sup 197}Au over {sup 12}C+{sup 12}C systems are calculated for selected Skyrme parameters SkP, SLy6, Ska, and SIII, which correspond to different modulus of incompressibility of symmetric nuclear matter and different cases of the stiffness of symmetry energy. A decreasing trend of the excitation functions of the ratios for strange particle production with increasing incident energy was observed. The available data of K{sup +} production measured by KaoS collaboration are described well with the parameter SkP, which results in a soft equation of state. The conclusions cannot be modified by an in-medium kaon-nucleon potential.

Production of heavy neutron-rich nuclei in transfer reactions within the dinuclear system model

The dynamics of nucleon transfer processes in heavy-ion collisions is investigated within the dinuclear system model. The production cross sections of nuclei in the reactions 136Xe+208Pb and 238U+248Cm are calculated, and the calculations are in good agreement with the experimental data. The transfer cross sections for the 58Ni+208Pb reaction are calculated and compared with the experimental data. We predict the production cross sections of neutron-rich nuclei Eu, Tb, Ho, and based on the reaction 176Yb+238U. It can be seen that the production cross sections of the neutron-rich nuclei 165Eu, 169Tb, 173Ho, and 181Yb are 2.84 ?b, 6.90 ?b, 46.24 ?b, and 53.61 ?b, respectively, which could be synthesized in experiment.

Effective mass splitting of neutron and proton and isospin emission in heavy-ion collisions

Abstract Within the framework of an isospin and momentum dependent transport model, the emissions of isospin particles (nucleons and light clusters) squeezed out in heavy-ion collisions are investigated as probes of the poorly known symmetry energy at high baryon density. Two different mass splittings of neutrons and protons in nuclear medium as m n ⁎ > m p ⁎ and m n ⁎ m p ⁎ are used in the model and their influence on the isospin emission in heavy-ion collisions is discussed thoroughly. The competition between the stiffness and the momentum dependence of the symmetry potential on reaction dynamics are compared and systematically analyzed. It is found that the difference of the neutron and proton directed flows and the transverse momentum distribution of the neutron/proton ratio are sensitive to the stiffness of the symmetry energy, which cannot be changed with the controversial effective mass splitting. The elliptic flows of free nucleons at high transverse momentum within mid-rapidity emission are to be promising observables as distinguishing the nucleon effective mass splitting.

Comparison of heavy-ion transport simulations: Collision integral in a box

Simulations by transport codes are indispensable to extract valuable physical information from heavy-ion collisions. In order to understand the origins of discrepancies among different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term;i.e., we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within 1% or better) with analytical results, or completely controlled results of a basic cascade code. In order to reach that goal, it was necessary to eliminate correlations within the same pair of colliding particles that can be present depending on the adopted collision prescription. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac toward a Boltzmann distribution. Since the numerical fluctuations are weaker in the Boltzmann-Uehling-Uhlenbeck codes, the Fermi-Dirac statistics is maintained there for a longer time than in the quantum molecular dynamics codes. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean-field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications.

In-medium and isospin effects on particle production near threshold energies in heavy-ion collisions

Dynamics of pseudoscalar mesons (

Dynamics of pion production in heavy-ion collisions around 1A GeV energies

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