ECT*, Trento, June 17-21: Introduction

h3QCD (high energy, high density and hot QCD)

ECT*, Trento, June 17-21, 2013

Description and main objectives

The main objective of the ongoing heavy ion programs at RHIC and the LHC is the exploration of new phases of nuclear matter which are characterized by high parton densities and strong collective behavior. One of these phases, the Color Glass Condensate, refers to the wavefunctions of the energetic hadrons (protons or nuclei) prior to the collision: the QCD evolution with increasing energy leads to a rapid rise in the density of low-momentum gluons, which is eventually tamed by non-linear effects leading to gluon saturation. When this happens, the occupation number of these soft gluons is so high that a semi-classical description in terms of classical color fields becomes appropriate. In the case of nucleus-nucleus collisions, these classical fields preserve their coherence during the very early stages of the collision, where they extend between the remnants of the two nuclei in the form of color flux tubes. This transient form of dense, coherent matter is known as the Glasma. These flux tubes are unstable and rapidly break into partons that strongly interact with each other because of their high density. These interactions are expected to lead to a state of local thermal equilibrium, the Quark Gluon Plasma. Experimental results suggest that this equilibration is extremely fast and that the ensuing plasma exhibits strong coupling aspects, such as a very low viscosity-to-entropy ratio. These phenomena are insufficiently understood and call for further studies. Furthermore, it is possible to measure the local properties of the quark-gluon plasma by studying its interactions with a "hard probe" -- an energetic parton or jet that loses energy while propagating through the medium. The accompanying phenomena (energy loss, transverse momentum broadening, jet collimation...) are known as "jet quenching".

The purpose of this workshop is to allow for in-depth discussions of various theoretical and phenomenological aspects of the dense partonic stages of hadronic and nuclear collisions. By the time of the workshop, many results of the proton-lead run at the LHC (scheduled early 2013) should be available and allow for a better disentanglement between "initial-state interactions" like saturation and "final-state interactions" like jet quenching. The workshop should provide the opportunity to critically examine our current theoretical understanding of the initial state effects in view of the p-Pb data. Other expected highlights of the workshop include recent theoretical progress in understanding thermalization, strong coupling aspects of the quark-gluon plasma, and medium-induced jet evolution.


François Gelis (CEA/IPhT)    Edmond Iancu (CEA/IPhT)
Cyrille Marquet (CERN)    Dionysis Triantafyllopoulos (ECT*, coordinator)