Discovery of Jet Quenching and Beyond
  Recent observation of high-$p_T$ hadron spectra suppression and mono-jet production in central $Au+Au$ collisions and their absence in $d+Au$ collisions at RHIC have confirmed the long predicted phenomenon of jet quenching in high-energy heavy-ion collisions. Detailed analyses of the experimental data also show parton energy loss as the mechanism for the discovered jet quenching. Using a pQCD parton model that incorporates medium modified parton fragmentation functions and comparing to experimental data from deeply inelastic scattering off nuclei, one can conclude that the initial gluon (energy) density of the hot matter produced in central $Au+Au$ collisions that causes jet quenching at RHIC is about 30 (100) times higher than in a cold $Au$ nucleus. Combined with data on bulk and collective properties of the hot matter, the observed jet quenching provides strong evidence for the formation of a strongly interacting quark gluon plasma in central $Au+Au$ collisions at RHIC. 
Xin-Nian Wang (LBNL)