We describe in detail how the different components of a multiphase transport (AMPT) model that uses the heavy ion jet interaction generator (HIJING) for generating the initial conditions, Zhang's parton cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and a relativistic transport (ART) model for treating hadronic scatterings are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the BNL Relativistic Heavy Ion Collider, are then made in order to extract information on the properties of the hot dense matter formed in these collisions.

To study heavy ion collisions at energies available from the Relativistic Heavy Ion Collider ͑RHIC͒, we have developed a multiphase transport model that includes both initial partonic and final hadronic interactions. Specifically, the Zhang's parton cascade ͑ZPC͒ model, which uses as input the parton distribution from the heavy ion jet interaction generator ͑HIJING͒ model, is extended to include the quark-gluon-to-hadronicmatter transition and also final-state hadronic interactions based on a relativistic transport ͑ART͒ model. Predictions of the model for central Au on Au collisions at RHIC are reported.PACS number͑s͒: 25.75. Ϫq, 24.10.Lx, 24.10.Jv The beginning of experiments at the Relativistic Heavy Ion Collider ͑RHIC͒ this year will start an exciting new era in nuclear and particle physics. The estimated high energy density in central heavy ion collisions at RHIC is expected to lead to the formation of a large region of deconfined matter of quarks and gluons, the quark gluon plasma ͑QGP͒. This would give us the opportunity to study the properties of the QGP and its transition to hadronic matter, which would then shed light on the underlying fundamental theory of strong interactions, quantum chromodynamics ͑QCD͒.Because of the complexity of heavy ion collision dynamics, Monte Carlo event generators are needed to relate the experimental observations to the underlying theory. This has already been shown to be the case in heavy ion collisions at existing accelerators such as the SIS, AGS, and SPS ͓1-6͔. As minijet production is expected to play an important role at RHIC energies ͓7͔, models for partonic transport have been studied ͓8,9͔. Furthermore, transport models that include both partonic and hadronic degrees of freedom are being developed ͓10,11͔. We have recently also developed such a multiphase transport ͑AMPT͒ model. It starts from initial conditions that are motivated by perturbative QCD and incorporates the subsequent partonic and hadronic spacetime evolution. In particular, we have used the heavy ion jet interaction generator ͑HIJING͒ model ͓7͔ to generate the initial phase space distribution of partons and the Zhang's parton cascade ͑ZPC͒ model ͓9͔ to follow their rescatterings. A modified HIJING fragmentation scheme is then introduced for treating the hadronization of the partonic matter. The evolution of the resulting hadron system is treated in the framework of a relativistic transport ͑ART͒ model ͓2͔. In this paper, we shall describe this new multiphase transport model and show its predictions for central Au-on-Au collisions at RHIC.In the AMPT model, the initial parton momentum distribution is generated from the HIJING model, which is a Monte Carlo event generator for hadron-hadron, hadronnucleus, and nucleus-nucleus collisions. The HIJING model treats a nucleus-nucleus collision as a superposition of binary nucleon-nucleon collisions. For each pair of nucleons, the impact parameter is determined using the nucleon transverse positions generated from a Woods-Saxon nuclear density distributio...

Using a multiphase transport model that includes both initial partonic and final hadronic interactions, we study the pion interferometry at the Relativistic Heavy-Ion Collider. We find that the two-pion correlation function is sensitive to the magnitude of the parton-scattering cross section, which controls the parton density at which the transition from the partonic to hadronic matter occurs. Also, the emission source of pions is non-Gaussian, leading to source radii that can be more than twice larger than the radius parameters extracted from a Gaussian fit to the correlation function.

Using a multiphase transport model ͑AMPT͒, which includes both initial partonic and final hadronic interactions, we study the rapidity distributions of charged particles such as protons, antiprotons, pions, and kaons in heavy ion collisions at RHIC. The theoretical results for the total charged particle multiplicity at midrapidity are consistent with those measured by the PHOBOS Collaboration in central AuϩAu collisions at ͱsϭ56 and 130 A GeV. We find that these hadronic observables are much more sensitive to the hadronic interactions than to the partonic interactions. DOI: 10.1103/PhysRevC.64.011902 PACS number͑s͒: 25.75.Ϫq, 24.10.Lx Collisions of nuclei at high energies offer the possibility to subject nuclear matter to the extreme conditions of large compression and high excitation energies. Studies based on both nonequilibrium transport models ͓1͔ and equilibrium thermal models ͓2͔ have shown that the experimental data from heavy ion collisions at SIS, AGS, and SPS, where the center of mass collision energies are, respectively, about 3, 5, and 17 A GeV, are consistent with the formation of a hot dense nuclear matter in the initial stage of collisions. With the Relativistic Heavy Ion Collider ͑RHIC͒ at Brookhaven National Laboratory, which can reach a center-of-mass energy of 200A GeV, the initial energy density is expected to exceed that for the transition from the hadronic matter to the quark-gluon plasma. Experiments at RHIC thus provide the opportunity to recreate the matter which is believed to have existed during the first microsecond after the big bang and to study its properties.Recently, charged particle multiplicity near midrapidity has been measured in central AuϩAu collisions at ͱsϭ56and 130 A GeV at RHIC by the PHOBOS Collaboration ͓3͔. The observed charged particle density per participant is found to be compatible with the predictions of the HIJING model that includes particle production from minijets produced in hard-scattering processes ͓4͔. Although the HIJING model implements the parton energy loss via jet quenching ͓5͔, it does not include explicit interactions among minijet partons and the final-state interactions among hadrons. Other models have also been used to understand the data from the PHOBOS Collaboration. The LEXUS model ͓6͔, which is based on a linear extrapolation of ultrarelativistic nucleonnucleon scattering to nucleus-nucleus collisions, predicts too many charged particles compared with the PHOBOS data ͓7͔. On the other hand, the hadronic cascade model LUCIFER ͓8͔ predicts a charged particle multiplicity near midrapidity that is comparable to the PHOBOS data ͓9͔. In this Rapid Communication, we shall use a multiphase transport model ͑AMPT͒ ͓10͔, that includes both partonic and hadronic interactions, to study their effects not only on the total charged particle multiplicity but also on those of kaons, protons, and antiprotons. In the AMPT model, the initial conditions are obtained from the HIJING model ͓4͔ by using a Woods-Saxon radial shape for the colliding nuclei and in...

This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute ‘Heavy Ion Collisions at the LHC—Last Call for Predictions’, held from 14th May to 10th June 2007.