Studies of parton thermalization at RHIC

We consider the evolution of a parton system which is formed in the central region just after a relativistic heavy ion collision. The parton consist of mostly gluons, minijets, which are produced by elastic scattering between constituent partons of the colliding nuclei. We assume the system can be described by a semi-classical Boltzmann transport equation, which we solve by means of the test particle Monte-Carlo method including retardation. The partons proliferate via secondary radiative $gg \to ggg$ processes until the thermalization is reached for some assumptions. The extended system is thermalized at about $t=1.6$ fm/$c$ with $T = 570$ MeV and stays in equilibrium for about 2 fm/$c$ with breaking temperature $T = 360$ MeV in the rapidity central region.Comment: 14 page

Suppression of High Transverse Momentum π0\pi^0 Spectra in Au+Au Collisions at RHIC

Au+Au, $s^{1/2} = 200$ A GeV measurements at RHIC, obtained with the PHENIX, STAR, PHOBOS and BRAHMS detectors, have all indicated a suppression of neutral pion production, relative to an appropriately normalized NN level. For central collisions and vanishing pseudo-rapidity these experiments exhibit suppression in charged meson production, especially at medium to large transverse momenta. In the PHENIX experiment similar behavior has been reported for $\pi^0$ spectra. In a recent work on the simpler D+Au interaction, to be considered perhaps as a tune-up for Au+Au, we reported on a pre-hadronic cascade mechanism which explains the mixed observation of moderately reduced $p_\perp$ suppression at higher pseudo-rapidity as well as the Cronin enhancement at mid-rapidity. Here we present the extension of this work to the more massive ion-ion collisions. Our major thesis is that much of the suppression is generated in a late stage cascade of colourless pre-hadrons produced after an initial short-lived coloured phase. We present a pQCD argument to justify this approach and to estimate the time duration $\tau_p$ of this initial phase. Of essential importance is the brevity in time of the coloured phase existence relative to that of the strongly interacting pre-hadron phase. The split into two phases is of course not sharp in time, but adequate for treating the suppression of moderate and high $p_\perp$ mesons.Comment: 19 pages, 10 figure

Hydrodynamic afterburner for the CGC at RHIC

Firstly, we give a short review about the hydrodynamic model and its application to the elliptic flow phenomena in relativistic heavy ion collisions. Secondly, we show the first approach to construct a unified model for the description of the dynamics in relativistic heavy ion collisions.Comment: 15 pages, 7 figures, invited talk presented at "Hot Quarks 2004", July 18-24, 2004, Taos Valley, NM, US

Cronin Effect and High-p_T Suppression in pA Collisions

We review the predictions of the theory of Color Glass Condensate for gluon production cross section in p(d)A collisions. We demonstrate that at moderate energies, when the gluon production cross section can be calculated in the framework of McLerran-Venugopalan model, it has only partonic level Cronin effect in it. At higher energies/rapidities corresponding to smaller values of Bjorken x quantum evolution becomes important. The effect of quantum evolution at higher energies/rapidities is to introduce suppression of high-p_T gluons slightly decreasing the Cronin enhancement. At still higher energies/rapidities quantum evolution leads to suppression of produced gluons at all values of p_T.Comment: 32 pages, 8 figures, v2: extended and improved discussion, references adde

CGC, QCD Saturation and RHIC data (Kharzeev-Levin-McLerran-Nardi point of view)

This is the talk given at the Workshop:"Focus on Multiplicitioes", Bari, Italy, 17-19 June,2004.. In this talk, we are going to discuss ion-ion and deuteron - nucleus RHIC data and show that they support, if not more, the idea of the new QCD phase: colour glass condensate with saturated parton density. .Comment: 26 pages with 33 figure

The Colour Glass Condensate: An Introduction

In these lectures, the authors develop the theory of the Colour Glass Condensate. This is the matter made of gluons in the high density environment characteristic of deep inelastic scattering or hadron-hadron collisions at very high energy. The lectures are self contained and comprehensive. They start with a phenomenological introduction, develop the theory of classical gluon fields appropriate for the Colour Glass, and end with a derivation and discussion of the renormalization group equations which determine this effective theory