ar X iv : h ep - p h / 03 11 10 2 v 1 7 N ov 2 00 3 Strong Decays : Past , Present and Future

In this talk I review the history of models of strong decays, from the original model through applications to charmonium, light and charmed mesons, glueballs and hybrids. Our current rather limited understanding of the QCD mechanism of strong decays is stressed. Regarding current and future applications of strong decay models, we note that in certain channels the very strong coupling predicted between q ¯ q basis states and the two-meson continuum may lead to strongly mixed states and perhaps molecular two-meson bound states. The relevance to the D * sJ (2317) is discussed. Origins of the 3 P 0 model Micu The earliest reference in which the currently widely accepted microscopic physics of strong decays appears is due to Micu [1], in the paper "Decay Rates of Meson Resonances in a Quark Model". Micu was concerned with understanding the light P-wave mesons in the quark model, especially their widths. In the quark model, describing decays required the production of a q ¯ q pair; in lieu of a microscopic model of interactions between quarks she made the plausible assumption that the pair was produced with vacuum (0 ++) quantum numbers, therefore in a 3 P 0 state. No explicit quark model wavefunctions were assumed, so the implicit overlap integrals were described by two free parameters, taken from data. Micu applied this simple model to approximately 30 known light meson decays, and found that it was reasonably successful in explaining the observed partial widths. She concluded that " ... this decay model proves once more the surprising viability of the quark model." This work was follows by a series of decay model calculations by the ORSAY group (LeYaouanc et al.), who introduced explicit nonrelativistic quark model wavefunctions in the calculations of the decay amplitudes and a fundamental pair production amplitude γ. This cast the 3 P 0 decay model in essentially the form in which it is used today.