Gluon Condensate from Superconvergent QCD Sum Rule*

The potential, or more generally the spectrum of a system of heavy quarks cannot be directly discussed in terms of the OPE (operator product expansion). However, one can use dispersion relations to deduce a number of sum rules relating bound state properties to quantities obtainable via the OPE (“ITEP-type” sum rules). One can then use the estimates of nonperturbative contributions to bound states energies and wave functions to actually go beyond the traditional analysis. Although the sum rules, being global relations, cannot discriminate details one can check consistency and even obtain reasonable estimates on nonperturbative quantities, specifically on the gluon condensate. This last is the aim of the present note, where we will use a method generalizing that proposed by Novikov. To do so we consider the correlator for the vector current of heavy quarks,