How much do heavy quarks thermalize in a heavy ion collision?

We investigate the thermalization of charm quarks in high-energy heavy-ion collisions. To this end, we calculate the diffusion coefficient in the perturbative quark gluon plasma and relate it to collisional energy loss and momentum broadening. We then use these transport properties to formulate a Langevin model for the evolution of the heavy quark spectrum in the hot medium. The model is strictly valid in the nonrelativistic limit and for all velocities $\ensuremath{\gamma}v<\ensuremath{\alpha}{s}^{\ensuremath{-}1/2}$ to leading logarithm in $T/{m}_{D}$. The corresponding Fokker-Planck equation can be solved analytically for a Bjorken expansion and the solution gives a simple estimate for the medium…