We study the elliptic flow coefficient v2 (η, b) in Au+Au collisions at √ s = 200 A GeV as a function of pseudorapidity η and impact parameter b. Using a hybrid approach which combines early ideal fluid dynamical evolution with late hadronic rescattering, we demonstrate strong dissipative effects from the hadronic rescattering stage on the elliptic flow. With Glauber model initial conditions, hadronic dissipation is shown to be sufficient to fully explain the differences between measured v2 values and ideal hydrodynamic predictions. Initial conditions based on the Color Glass Condensate model generate larger elliptic flow and seem to require additional dissipation during the early quarkgluon plasma stage in order to achieve agreement with experiment.PACS numbers: 25.75.Nq, 12.38.Mh, 12.38.Qk One of the important new discoveries made at the Relativistic Heavy Ion Collider (RHIC) is the large elliptic flow v 2 in non-central Au+Au collisions [1]. At the highest RHIC energy of √ s = 200 A GeV, the observed v 2 values near midrapidity (|η| < ∼ 1), for not too large impact parameters (b < ∼ 7 fm) and transverse momenta (p T < ∼ 1.5 GeV/c), agree with predictions from ideal fluid dynamics [2], including [3,4] the predicted dependence of v 2 on the transverse momentum p T and hadron rest masses [5]. From these observations it has been concluded [6] that in these collisions a quark-gluon plasma (QGP) is created which thermalizes on a very rapid time scale τ therm < 1 fm/c and subsequently evolves as an almost ideal fluid with exceptionally low viscosity.On the other hand, the ideal fluid dynamical description gradually breaks down as one studies collisions at larger impact parameters and at lower energies [7] or moves away from midrapidity [8,9,10,11]. This has been attributed alternatively to incomplete thermalization of the QGP during the early stages of the expansion [13] ("early viscosity") and/or to dissipative effects during the late hadronic expansion stage [14,15,16] ("late viscosity"). It has recently been argued [15,17] that quantum mechanics imposes a lower limit on the shear viscosity of any medium, but that the shear viscosity of the QGP can not exceed this lower limit by a large factor [18]. On the other hand, qualitative arguments were presented in Ref.[16] which emphasize the importance of hadronic dissipation and support a picture of a "nearly perfect fluid strongly coupled QGP (sQGP) core and highly dissipative hadronic corona" in ultrarelativistic heavy-ion collisions. The importance of viscous effects for a successful description of RHIC data on v 2 and v 4 was also emphasized in [19], although this work left it open whether the corresponding lack of thermalization occurs mostly at the beginning or towards the end of the expansion phase. In the present paper we explore this issue more quantitatively, by trying to answer the question how much of the observed deviation of v 2 from the ideal fluid prediction can be attributed to "late viscosity" in the dissipative hadronic phase, and whether or not...

The early stages of a relativistic heavy-ion collision are examined in the framework of an effective classical SU(3) Yang-Mills theory in the transverse plane. We compute the initial energy and number distributions, per unit rapidity, at midrapidity, of gluons produced in high-energy heavy-ion collisions. We discuss the phenomenological implications of our results in light of the recent Relativistic Heavy-Ion Collider data.

A hadronic cascade model based on resonances and strings is used to study mass dependence of relativistic nuclear collisions from p+Be to Au+Au at AGS energies (∼ 10AGeV) systematically. Hadron transverse momentum and rapidity distributions obtained with both cascade calculations and Glauber type calculations are compared with experimental data to perform detailed discussion about the importance of rescattering among hadrons. We find good agreement with the experimental data without any change of model parameters with the cascade model. It is found that rescattering is of importance both for the explanation of high transverse momentum tail and for the multiplicity of produced particles. model based on the string phenomenology implies that some partonic degrees of freedom play some roles in reaction dynamics implicitly. In fact, the estimation of partonic degrees of freedom has been done recently within UrQMD [20]. ARC [16] has shown that 'pure' hadronic model can describe the data at AGS energies. At collider energies, however, explicit treatments of partonic degrees of freedom will be necessary.The main purpose of this work is to perform systematic analyses of collisions from pA to massive AA systems at AGS energies, for which high-quality systematic experimental data are available [39,40], within the hadronic cascade model, JAM1.0, which has been developed recently based on resonances, strings and pQCD.The main features included in JAM are as follows.(1) At low energies, inelastic hh collisions are modeled by the resonance productions based on the idea from RQMD and UrQMD. (2) Above the resonance region, soft string excitation is implemented along the lines of the HIJING model [4]. (3) Multiple minijet production is also included in the same way as the HIJING model in which jet cross section and the number of jet are calculated using an eikonal formalism for perturbative QCD (pQCD) and hard parton-parton scatterings with initial and final state radiation are simulated using PYTHIA [22] program. (4) Rescattering of hadrons which have original constituent quarks can occur with other hadrons assuming the additive quark cross section within a formation time. Since these features of the present hadronic cascade model, JAM1.0, enables us to explore heavy ion collisions in a wide energy range, from 100A MeV to RHIC energies, in a unified way, it is a big challenge for us to make systematic analyses in these energies. In this paper, we focus on the mass dependence of the collision system at AGS energies. Other applications at higher energies are found elsewhere [23].The outline of this paper is as follows. We will present a detailed description of cross sections and modeling of inelastic processes for hh collisions in section II, because elementary hh processes are essential inputs for the hadronic cascade model. In Sec. III, we first study the transverse momentum distributions of protons, pions and kaons in p+Be, p+Al, p+Cu, p+Au, Si+A, Si+Cu and Si+Au collisions at the laboratory incident momentum of 14.6A GeV/c. We ...