Heavy quarkonium correlators at finite temperature: QCD sum rule approach

We investigate the properties of heavy quarkonia at finite temperature in detail using QCD sum rules. Extending previous analyses, we take into account a temperature-dependent effective continuum threshold and derive constraints on the mass, the width, and the varying effective continuum threshold. We find that at least one of these quantities of a charmonium changes abruptly in the vicinity of the phase transition. We also calculate the ratio of the imaginary time correlator to its reconstructed one, G/G_rec, by constructing a model spectral function and compare it to the corresponding lattice QCD results. We demonstrate that the almost constant unity of G/G_rec can be obtained from the destructive interplay of the changes in each part of the spectral modification which are extracted from QCD sum rules.