Pre-thermalization dynamics: initial conditions for QGP at the LHC and RHIC from perturbative QCD

I discuss how the initial conditions for QGP-production in ultrarelativistic heavy ion collisions at the LHC and RHIC can be computed from perturbative QCD.Comment: 11 pages, including 2 figures. A lecture at the International School on the Physics of Quark Gluon Plasma, June 3-6, 1997, Hiroshim

Initial state of the QGP from perturbative QCD + saturation

The production of the initial state of the QGP in very high-energy $AA$ collisions is discussed within the framework of perturbative QCD and saturation. The next-to-leading order computation of the transverse energy of minijets is reviewed. Saturation of parton production, conjectured to occur at a dynamically determinable perturbative scale, leads to estimates of the initial densities. The final state multiplicities are predicted by assuming an isentropic hydrodynamical further evolution. Comparison with RHIC data is shown.Comment: 10 pages, 8 figures. Invited talk at the International Conference on Statistical QCD, August 2001, Bielefel

On the sensitivity of the dijet asymmetry to the physics of jet quenching

The appearance of monojets is among the most striking signature of jet quenching in the context of ultrarelativistic heavy-ion collisions. Experimentally, the disappearance of jets has been quantified by the ATLAS and CMS collaborations in terms of the dijet asymmetry observable A_J. While the experimental findings initially gave rise to claims that the measured A_J would challenge the radiative energy loss paradigm, the results of a systematic investigation of A_J in different models for the medium evolution and for the shower-medium interaction presented here suggest that the observed properties of A_J arise fairly generically and independent of specific model assumptions for a large class of reasonable models. This would imply that rather than posing a challenge to any particular model, the observable prompts the question what model dynamics is not compatible with the data.Comment: 8 pages, 6 figures, added computations of jet R_AA and R=0.2 result

High Energy Nuclear Collisions

Highlights of the results from ultrarelativistic heavy ion collisions at CERN-SPS are reviewed. In particular, I discuss how the experimental results indicate that a collective strongly interacting system has been produced, and what are the implications towards the Quark Gluon Plasma. The physical ideas behind measuring certain observables are introduced. The future program of high energy nuclear collisions at BNL-RHIC and CERN-LHC/ALICE is also briefly discussed.Comment: Plenary talk at the International Europhysics Conference on High Energy Physics, EPS-HEP99, Tampere, Finland, July 1999; 21 page

Minijets in ultrarelativistic heavy ion collisions at future colliders

The role of minijet production as initial conditions for QGP production at $\tau\sim 0.1 fm/c$ in nuclear collisions at the LHC and RHIC energies is discussed.Comment: 15 pages, including 2 figures, an invited article to Comments on Nuclear and Particle Physic

Testing collinear factorization and nuclear parton distributions with pA collisions at the LHC

Global perturbative QCD analyses, based on large data sets from electron-proton and hadron collider experiments, provide tight constraints on the parton distribution function (PDF) in the proton. The extension of these analyses to nuclear parton distributions (nPDF) has attracted much interest in recent years. nPDFs are needed as benchmarks for the characterization of hot QCD matter in nucleus-nucleus collisions, and attract further interest since they may show novel signatures of non- linear density-dependent QCD evolution. However, it is not known from first principles whether the factorization of long-range phenomena into process-independent parton distribution, which underlies global PDF extractions for the proton, extends to nuclear effects. As a consequence, assessing the reliability of nPDFs for benchmark calculations goes beyond testing the numerical accuracy of their extraction and requires phenomenological tests of the factorization assumption. Here we argue that a proton-nucleus collision program at the LHC would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits.Comment: 4 pages, 5 figure

A global DGLAP analysis of nuclear PDFs

In this talk, we shortly report results from our recent global DGLAP analysis of nuclear parton distributions. This is an extension of our former EKS98-analysis improved with an automated $\chi^2$ minimization procedure and uncertainty estimates. Although our new analysis show no significant deviation from EKS98, a sign of a significantly stronger gluon shadowing could be seen in the RHIC BRAHMS data.Comment: Talk given at EPS HEP 200

Hydrodynamics of nuclear collisions with initial conditions from perturbative QCD

We compute the longitudinal hydrodynamic flow in ultrarelativistic heavy ion collisions at $\sqrt{s}$ = 5500 GeV by using boost non-invariant initial conditions following from perturbative QCD. The transfer of entropy and energy from the central region to larger rapidities caused by boost non-invariance is determined and the associated decrease in the lifetime of the system is estimated.Comment: 12 pages, including 6 figure