55846865
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.
58937358
Particle production in antiproton-induced nuclear reactions
The quantum molecular dynamics model has been improved to investigate the reaction dynamics induced by antiprotons. The reaction channels of elastic scattering, annihilation, charge exchange, and inelastic collisions have been included in the model. Dynamics on particle production, in particular pions, kaons, antikaons, and hyperons, is investigated in collisions of (p) over bar on C-12, Ne-20, Ca-40, Sn-112, Ta-181, Au-197, and U-238 from a low to high incident momentum. The rapidity and momentum distributions of pi(+) and protons from the LEAR measurements can be well reproduced. The impacts of system size and incident momentum on particle emissions are investigated from the inclusive spectra, transverse momentum, and rapidity distributions. It is found that the annihilations of (p) over bar on nucleons are of importance on the particle production. Hyperons are mainly produced via meson induced reactions on nucleons and strangeness exchange collisions when the incident momentum is below the threshold value of annihilation reaction. A higher nuclear temperature is obtained from the kaon emission, but it has a lower value for hyperon production.
120114037
Nuclear stopping and compression in heavy-ion collisions at intermediate energies
Abstract The nuclear stopping and the radial flow are investigated with an isospin-dependent quantum molecular dynamics (IQMD) model for Ni + Ni and Pb + Pb from 0.4 to and 1.2 GeV/u. The expansion velocity as well as the degree of nuclear stopping are higher in the heavier system at all energies. The ratio between the flow energy and the total available energy in center of mass of the colliding systems exhibits a positive correlation to the degree of nuclear stopping. The maximum density ( ρ max ) achieved in the compression is comparable to the hydrodynamics prediction only if the non-zero collision time effect is taken into account in the later. Due to the partial transparency, the growing of the maximum density achieved in the central region of the fireball with the increase of beam energy becomes gradually flat in the 1 GeV/u energy regime.
56089077
Dynamics of strangeness production in heavy-ion collisions near threshold energies
Within the framework of the improved isospin-dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K{sup 0,+}, {Lambda}, and {Sigma}{sup -,0,+}) production in heavy-ion collisions near threshold energies is investigated systematically, with the strange particles considered to be produced mainly by inelastic collisions of baryon-baryon and pion-baryon. Collisions in the region of suprasaturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. Total multiplicities as functions of incident energies and collision centralities are calculated with the Skyrme parameter SLy6. The excitation function of strangeness production is analyzed and also compared with the KaoS data for K{sup +} production in the reactions {sup 12}C+{sup 12}C and {sup 197}Au+{sup 197}Au.
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.
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.
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.