Charmonium: Comparison with experiment

The charmonium model, formulated in detail in an earlier publication, is compared in a comprehensive fashion with the data on the family. The parameters of the "naive" model, in which the system is described as a cc pair, are determined from the observed positions of, ^', and the P states. The model then yields a successful description of the spectrum of spin-triplet states above the charm threshold. It also accounts for the ratio of the leptonic widths of ^' and. When the cc potential is applied to the family, it accounts, without any readjustment of parameters, for the positions of the 2S and 3S levels and for the leptonic widths of and ^' relative to that of. The model does not give acceptable values of the absolute leptonic widths, a shortcoming which is ascribed to large quantum-chromodynamic corrections to the van Royen-Weisskopf formula. The calculated E1 rates are about twice the values observed in the family. This naive model is also extended with considerable success to mesons composed of one heavy and one light quark. A significant extension of the model is achieved by incorporating coupling to charmed-meson decay channels. This gives a satisfactory understanding of (3772) as the 1^3D₁ cc state, mixed via open and closed decay channels to 2^3S. The model has decay amplitudes that are oscillatory functions of the decay momentum; these oscillations are a direct consequence of the radial nodes in the cc parent states. These amplitudes provide a qualitative understanding of the observed peculiar branching ratios into various charmed-meson channels near the resonance at 4. 03 GeV, which is assigned to 3^3S. The coupling of the cc states below the charm threshold to closed decay channels modifies the bound states and leads to reduction of about 20% in E1 rates in comparison to those of the naive model.