Quarkonium Spectroscopy: Beyond One-Gluon Exchange

In this work an improved potential model for quarkonium spectra (charmonium, bottomonium) is constructed. Beside the one-gluon exchange and a linear confinement potential, the model includes systematically effects from two-gluon exchange and the induced interaction (i.e. t-channel exchanges of quark-antiquark bound states). These turn out to be important in order to reproduce correctly the fine- and hyperfine structure of the charmonium and bottomonium states. It is demonstrated that such a satisfactory description of the quarkonium spectra can be obtained with parameters (quark masses, strong coupling constant and string tension) consistent with values of lattice simulations and QCD determinations.