55804671
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.
119575296
Pion Production in Heavy-ion Collisions in the 1 A GeV region ∗
Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, pion emission in heavy-ion collisions in the region 1 A GeV is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Δ(1232) and N* (1440). The in-medium dependence and Coulomb effects of pion production are included in the calculation. Total pion multiplicity and π−/π+ yields are calculated for the reaction 197Au+197Au in central collisions for selected Skyrme parameters SkP, SLy6, Ska, SIII and compared with the measured data of the FOPI collaboration.
18690672
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.
10170328
Influence of entrance channels on the formation of superheavy nuclei in massive fusion reactions
Within the framework of the dinuclear system (DNS) model, the production cross sections of superheavy nuclei Hs (Z=108) and Z=112 combined with different reaction systems are analyzed systematically. It is found that the mass asymmetries and the reaction Q values of the projectile target combinations play a very important role on the formation cross sections of the evaporation residues. Both methods to obtain the fusion probability by nucleon transfer by solving a set of microscopically derived master equations along the mass asymmetry degree of freedom (ID) and distinguishing protons and neutrons of fragments (2D) are compared with each other and also with the available experimental data. (C) 2010 Elsevier B.V. All rights reserved.
119190579
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.
122097146
PROBING THE SYMMETRY ENERGY AT SUPRA-SATURATION DENSITIES FROM PION EMISSION IN HEAVY-ION COLLISIONS
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 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/ρ0)γs with γs = 2.
122762455
TeV Gamma Ray Survey on the Direction of Fermi-LAT Pulsars with the Tibet Air Shower Array
We search for steady TeV γ-rays from 18 pulsars in the Fermi-LAT pulsar catalog using the Tibet air shower array. We observe 8 sources including the Crab against expected 0.41 sources at a significance of 2σ or more among the 18 pulsars. The chance probability from Poisson statistics is estimated to be 1.4×10-8.With the Crab excluded, it is estimated to be 1.8×10-7. These low chance probabilities clearly show that the Fermi pulsars have a statistically significant correlation with TeV γ-ray excesses observed by the Tibet air shower array.