Heavycc¯andbb¯quarkonium states and unitarity effects

Abstract

We construct a unitarized quarkonium model which uses the quark-pair-creation model for hadronic vertex functions. The mass shifts and mixings induced by $D\overline{D}$, $F\overline{F}$, $D{\overline{D}}^{*}$, etc., loop diagrams are calculated. These improve in particular the fit to the resonances such as $\psi \mathrm{}\left(1D\right)\mathrm{}$ and $\Upsilon \mathrm{}\left(4S\right)\mathrm{}$ which are strongly affected by the first threshold. When comparing the leptonic widths with experiment the unitarized model gives considerably better agreement compared to single-channel $Q\overline{Q}$ potential models. The improvement is partly because of the mixing between different excitations induced by hadronic loops, and partly because of the fact that the wave functions (at the origin) are modified compared to nonunitarized models.