is appropriate for comparisons with the lattice data, the following work must be done: 1.) the mass of the heavy quark must be changed whenever the drag coefficient is changed, since we are concerned with results for G ( τ ) with different values of η but the same “effective” mass, 2.) the maximum entropy method must be applied to G ( τ ), so that the spectral function corresponding to the correlation function will be extracted with high precision, 3.) this spectral function must have the zero-mode contribution added and be cut so that the perturbative result for the spectral function is used at large ω instead, and finally 4.) this spectral function should be used to calculate G ( τ ). However, let us note here that this work can be put to greater use in examining quarkonium in heavy-ion collisions. 

Let us argue one last time for treating quarkonium above deconfinement as an open quantum system: typically in particle physics, the rate for the scattering of an N -particle state into another is determined from the square of the matrix element whose indices are the initial and final states, where these states are in the momentum basis. This makes per- fect sense in high-energy experiments, where the incoming and outgoing states are basically each 2-particle momentum eigenstates and the matrix element can be expanded in terms of a small coupling. Such an approach, however, seems entirely inappropriate for quarko- nium formed in a heavy-ion collision, whose constituent quarks are localized in position relative to the surrounding medium and are strongly coupled both to the medium and each other. Non-perturbative techniques and experiment both suggest that quarkonium rapidly thermalizes and interacts strongly with the medium. The most reasonable approach for explaining the observables is to describe quarkonium with a reduced density matrix, whose evolution is determined by a potential and a drag coefficient which are both determined non-perturbatively. 

## V. ACKNOWLEDGMENTS 

We would like to thank E. Shuryak and D. Teaney for very useful and detailed suggestions concerning our work. CY thanks the Institute for Nuclear Theory at the University of Washington for its hospitality during the completion of this work. CY was supported by the US-DOE grants DE-FG02-88ER40388 and DE-FG03-97ER4014. KD was supported by 

