Photon and hadron interactions of radially excited states

Abstract

We review the development of the quark model with particular emphasis on the interpretation of quarks as dynamical, confined, hadronic constituents. This interpretation encompasses naturally the phenomenon of radially excited states. The simple vector dominance model is reviewed and an extended vector mason dominance model which includes both radial excitations of the vector mesons, and q(^2)- dependence of the photon-vector meson coupling is applied to radiative decays and photo-production of the vector mesons. The parameters estimated from ψ radiative decay, define a phenomenological prescription in which the radial excitations play a minor role compared with the ground state vector mesons. The predictions of the model for various cross-sections and decay widths are presented and found to be in good agreement with experiment. However we predict a larger total cross-section, σ(_tot)(ψN) than has been recently measured and the suppression of the large phase space decays of excited states is not understood. By re-identifying some of the vector meson states which have been more recently observed coupling to e(^+)e we show that in all flavour sectors the spectra of radial excitations can be well described by a Klein-Gordon type wave equation employing a simple, linear qī potential. The wave-functions obtained by solving the equation are coupled with a quark pair creation hypothesis to predict a number of partial decay widths of the light quark, radially excited states. The suppression of large phase space decays of the excited states is then understood.