From QCD to heavy ion collisions

TL;DR

This paper discusses the transition in heavy ion collisions from SPS to LHC energies, highlighting the onset of gluon saturation in QCD and its implications for initial gluon production and evolution.

Contribution

It introduces the concept of gluon saturation at high energies and provides estimates for the saturation scale and initial gluon production at the LHC.

Findings

Gluon production becomes saturated at high energies.

Classical field methods are applicable for large nuclei and energies.

Quantitative estimates for initial gluon production at LHC.

Abstract

This talk will discuss how heavy ion experiments, when moving from SPS (10 + 10 GeV) to RHIC (100+100 GeV) and to LHC (2750+2750 GeV), will enter a new domain of QCD in which the production of even large pT gluons is so abundant that it is simultaneously perturbative but such that the phase space density of gluons is saturated. The saturation scale is estimated, quantitative numbers for the initial production of gluons at the LHC are given and options for their subsequent evolution are outlined. For parametrically large nuclei and energies, classical field methods will be applicable.