We present a systematic analysis of two-pion interferometry for the central Au＋Au collisions at √SNN=3, 5, 7, 11, 17, 27, 39, 62, 130 and 200 GeV/c with the help of a multiphase transport （AMPT） model. Emission source-size radius parameters Rlong, Rout, Rside and the chaotic parameter A are extracted and compared with the experimental data. Transverse momentum and azimuthal angle dependencies of the HBT radii are also discussed for central Au＋Au collisions at 200 GeV/c. The results show that the HBT radii in central collisions do not change much above 7 GeV/c. For central collisions at 200 GeV/c, the radii decrease with the increasing of transverse momentum PT but are not sensitive to the azimuthal angle. These results provide a theoretical reference for the energy scan program of the RHIC-STAR experiment.
With taking electromagnetic field into account for the transport model of Boltzmann-Uehling-Uhlenbeck,electromagnetic effects are studied for ^(208)Pb +^(208)Pb collisions around 100A MeV. Electromagnetic field evolution during the collisions was estimated. It was found that the electric field has an obvious effect on the transverse momentum(p_T) spectra of nucleons during heavy ion collisions, and leads to different minimum position for the peak of p_T spectra of nucleons versus beam energy when the electric field is switched on. For the magnetic field, it affects the z-axis direction distributions of nucleons for central heavy ion collisions at lower energy.
Within the framework of a multiphase transport model, we study the production and properties of Ω andφ in Au ＋ Au collisions with a new set of parameters for （s（NN））^（1/2）= 200 GeV and with the original set of parameters for （s（NN））^（1/2）= 11.5 GeV. The AMPT model with string melting provides a reasonable description at （s（NN））^（1/2）= 200 GeV,while the default AMPT model describes the data well at （s（NN））^（1/2）= 11.5 GeV. This indicates that the system created at top RHIC energy is dominated by partonic interactions, while hadronic interactions become important at lower beam energy, such as （s（NN））^（1/2）= 11.5 GeV. The comparison of N（Ω^＋＋Ω^-）/[2N（φ）] ratio between data and calculations further supports the argument. Our calculations can generally describe the data of nuclear modification factor as well as elliptic flow.
In recent years, the collective motion properties of global rotation of the symmetric colliding system in relativistic energies have been investigated. In addition, the initial geometrical shape effects on the collective flows have been explored using a hydrodynamical model, a transport model, etc. In this work, we study the asymmetric ^(12)C+^(197)Au collision at 200 GeV/c and the effect of the exotic nuclear structure on the global rotation using a multi-phase transport model. The global angular momentum and averaged angular speed were calculated and discussed for the collision system at different evolution stages.
