Heavy-Quark diffusion in the Quark-Gluon Plasma

The Quark-Gluon Plasma (QGP) is a hot and dense state of matter predicted by Quantum Chromo Dynamics (QCD) to exist at temperatures above T~200MeV ($\sim 10^{12}$~Kelvin). The QGP is believed to have prevailed in the first few microseconds after the big bang. Experiments at the Relativistic Heavy Ion Collider (RHIC) are trying to recreate, for a short moment, the QGP in the laboratory. It has been found that the matter produced in high-energy Au-Au collisions is a strongly coupled quark-gluon liquid with very low viscosity and high opacity. To understand the properties of this strongly coupled QGP (sQGP) heavy quarks (charm and bottom) are a particularly valuable probe: they are produced early in the reaction and subsequently diffuse in the putative sQGP. In this talk we develop a model for nonperturbative interactions between heavy and light quarks in the sQGP and apply it to experimental spectra at RHIC. Good agreement with data allows for a quantitative estimate of the heavy-quark diffusion coefficient in the sQGP.