The Ugly Duckling and the Swan in heavy ion collisions
Rob Pisarski, Brookhaven National Laboratory
"Aula Magna Enric Casassas", Physics Faculty
Abstract: I begin with a review of gauge theories as they apply to the modern theory of nuclei, which is Quantum ChromoDynamics, or QCD. I discuss why we expect QCD to form a Quark-Gluon Plasma, or QGP, at temperatures of about a trillion degrees, and the possible phase transitions associated with deconfinement and chiral symmetry breaking.
The QGP appears to have been created in the collisions of nuclei at ultra-relativistic energies, at both Brookhaven and CERN. I discuss two notable signals: the success of nearly ideal hydrodynamics, and the quenching of jets in a QGP.
I then discuss the new frontier, which is going down to moderate collision energies, where the baryon chemical potential is significant. This also makes contact with results from the binary collisions of neutron stars. I immodestly suggest that the region of low temperature and high chemical potential in QCD is one of the great problems for physics in the 21st century.