OPEN-CHANNEL EFFECTS ON HEAVY-QUARKONIUM SPECTRA - A PHENOMENOLOGICALSTUDY WITHIN A ONE-OPEN-CHANNEL APPROXIMATION

Open-channel effects on charmonium (S-and D-waves) and bottomonium (S- wave) J(P) = 1(-) spectra are investigated within a one-open-channel a pproximation. Mass shifts and decay widths of these states just above the threshold are obtained by taking into account a coupling between c onfined quarkonium states and decaying states of the open channel. The final-state interaction (FSI) between the decaying meson and antimeso n plays a very important role in producing a reasonable magnitude of c oupling; the FSI provides the open-channel poles (R-1, R-2) at the app ropriate positions on the complex energy plane. The result is found to be independent of the detailed form of the transition potential and t he final-state interaction.