The Multichannel Quark Model

We discuss the non–relativistic multichannel quark model and describe the techniques developed to solve the resulting equations. We then investigate some simple solutions to demonstrate how the model unifies meson–meson scattering with meson spectroscopy, thereby greatly extending the domain of applicability of the näıve quark model. In the limits of narrow resonance widths and no quark exchange, it reproduces the standard quark model spectroscopy and Breit–Wigner phase description. Outside those limits s–channel resonance masses are lowered by their two–meson couplings, the line–shapes of wide resonances are significantly altered, and the equivalent Breit–Wigner masses and widths show an energy dependence. Because meson–meson interactions are due to coherent s–channel resonance production and t–channel quark exchange (though other interactions can readily be added), the multichannel equations model experimental resonance production and decay in a way that the usual eigenvalue equations cannot.