QCD MIXING EFFECTS IN A GAUGE-INVARIANT QUARK-MODEL FOR PHOTOPRODUCTION AND ELECTROPRODUCTION OF BARYON RESONANCES

The photo- and electroproduction of baryon resonances are calculated in the constituent quark model with chromodynamics of Isgur and Karl consistently to O(v2c2) for the quarks. We find that the successes of the nonrelativistic quark model are preserved, some problems are removed, and QCD mixing effects may become important with increasing q2 in electroproduction. For the first time both spectroscopy and transitions receive a unified treatment within the framework of a potential quark model. © 1990 The American Physical Society.