Probing Meson Structure with Photons

The scalar mesons f(980) and a(985) are two of the best-verified states in the excited meson spectrum. They appear as narrow resonances in the 2 and mass spectra, respectively, as observed in hadroproduction reactions and in the decays of heavier particles such as the J/ and the Z. Although they were once thought to be members of the fundamental nonet of scalar qq' mesons, conventional wisdom is now inclined against that assignment in favor of an exotic (i.e. non-qq') interpretation for these states. These two models are quite different in terms of their charge and current distributions, and so it was suggested early in the 90's (and probably before that) that an experiment using the photon as a probe might distinguish empirically between them. This idea has stimulated a number of experimental searches for these decays by groups working at e+e- colliders in Europe and at Jefferson Lab in the US. Results are now emerging which seem to support a non-quark-model assignment. The status of the analysis and issues surrounding the interpretation of these data will be addressed.

 
1. Physics motivation


2. Phenomenology of the scalar mesons


3. Theoretical models: how to build a molecule


4. Implications of Phi radiative decays


5. Radphi experiment at Jefferson Lab


6. Experiments at Phi factories


7. Present status and future plans