PUB - Publikationen an der Universität Bielefeld

Motivated by indications that heavy (charm and bottom) quarks interactstrongly at temperatures generated in heavy ion collision experiments, wesuggest a non-perturbative definition of a heavy quark chemical equilibrationrate as a transport coefficient. Within leading-order perturbation theory(corresponding to 3-loop level), the definition is argued to reduce to anexpression obtained from the Boltzmann equation. Around T ~ 400 MeV, anorder-of-magnitude estimate for charm yields a rate Gamma^{-1}_{chem} > 60 fm/cwhich remains too slow to play a practical role in current experiments.However, the rate increases rapidly with T and, due to non-linear effects, alsoif the initial state contains an overabundance of heavy quarks.