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Register a new userEquation of state dependence of directed flow in a microscopic transport model
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We study the sensitivities of the directed flow in Au+Au collisions on the equation of state (EoS), employing the transport theoretical model JAM. The EoS is modified by introducing a new collision term in order to control the pressure of a system by appropriately selecting an azimuthal angle in two-body collisions according to a given EoS. It is shown that this approach is an efficient method to modify the EoS in a transport model. The beam energy dependence of the directed flow of protons is examined with two different EoS, a first-order phase transition and crossover. It is found that our approach yields quite similar results as hydrodynamical predictions on the beam energy dependence of the directed flow; Transport theory predicts a minimum in the excitation function of the slope of proton directed flow and does indeed yield negative directed flow, if the EoS with a first-order phase transition is employed. Our result strongly suggests that the highest sensitivity for the critical point can be seen in the beam energy range of $4.7leqsrtNNleq11.5$ GeV.
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We investigate the effects of nuclear mean-field as well as the formation and decay of nuclear clusters on the directed flow $v_1$ in high energy nucleus-nucleus collisions from $sqrt{s_{NN}}=7.7$ GeV to 27 GeV incident energies within a transport model. Specifically, we use the JAM transport model in which potentials are implemented based on the framework of the relativistic quantum molecular dynamics. Our approach reproduces the rapidity dependence of directed flow data up to $sqrt{s_{NN}}approx 8$ GeV showing the significant importance of mean-field. However, the slopes of $dv_1/dy$ at mid-rapidity are calculated to be positive at $sqrt{s_{NN}}=11.7$ and 19.6 GeV, and becomes negative above 27 GeV. Thus the result from the JAM hadronic transport model with nuclear mean-field approach is incompatible with the data. Therefore within our approach, we conclude that the excitation function of the directed flow cannot be explained by the hadronic degree of freedom alone.
We calculate the kaon HBT radius parameters for high energy heavy ion collisions, assuming a first order phase transition from a thermalized Quark-Gluon-Plasma to a gas of hadrons. At high transverse momenta K_T ~ 1 GeV/c direct emission from the phase boundary becomes important, the emission duration signal, i.e., the R_out/R_side ratio, and its sensitivity to T_c (and thus to the latent heat of the phase transition) are enlarged. Moreover, the QGP+hadronic rescattering transport model calculations do not yield unusual large radii (R_i<9fm). Finite momentum resolution effects have a strong impact on the extracted HBT parameters (R_i and lambda) as well as on the ratio R_out/R_side.
We analyse various flow coefficients of anisotropic momentum distribution of final state particles in mid-central ($b$ $=$ 5--9 $fm$) Au + Au collisions in the beam energy range $rm E_{rm Lab}$ $=$ $1A -158A$ GeV. Different variants of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, namely the pure transport (cascade) mode and the hybrid mode, are employed for this investigation. In the hybrid UrQMD model, the ideal hydrodynamical evolution is integrated with the pure transport calculation for description of the evolution of the fireball. We opt for the different available equations of state (EoS) replicating the hadronic as well as partonic degrees of freedom together with possible phase transitions, viz. hadron gas, chiral + deconfinement EoS and bag model EoS, to investigate their effect on the properties of the final state particles. We also attempt to gain insights about the dynamics of the medium by studying different features of particle production such as particle ratios and net-proton rapidity distribution. The results and conclusions drawn here would be useful to understand the response of various observables to the underlying physics of the model as well as to make comparisons with the upcoming measurements of the future experiments at Facility for Antiproton and Ion Research (FAIR) and Nuclotron-based Ion Collider fAcility (NICA).
The time evolution of Mach-like structure (the splitting of the away side peak in di-hadron $Deltaphi$ correlation) is presented in the framework of a dynamical partonic transport model. With the increasing of the lifetime of partonic matter, Mach-like structure can be produced and developed by strong parton cascade process. Not only the splitting parameter but also the number of associated hadrons ($N_{h}^{assoc}$) increases with the lifetime of partonic matter and partonic interaction cross section. Both the explosion of $N_{h}^{assoc}$ following the formation of Mach-like structure and the corresponding results of three-particle correlation support that a partonic Mach-like shock wave can be formed by strong parton cascade mechanism. Therefore, the studies about Mach-like structure may give us some critical information, such as the lifetime of partonic matter and hadronization time.
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