THE OZI RULE AND NUCLEONS

The title of this lecture series raises two questions: (1) what is the OZI rule? (2) what is a nucleon. In the lectures both questions were addressed in parallel and the material moved back and forth between them. In a written version it seems more appropriate to treat the two questions separately, beginning with trying to understand the structure of the nucleon. Experimental evidence for the symmetry and quark structure of hadrons is reviewed with a historical introduction and updated by presenting constituent quark model relations for hadron masses and magnetic moments. Three definitions of the OZI rule are presented, all of which forbid decays like ϕ → ρπ but making different selection rules for more complicated reactions. All suffer from the higher order paradox that a forbidden process can take place via a two-step transition in which each step is allowed; e.g. [Formula: see text]. No prescription is given for estimating the strength of forbidden processes. The role of cancellations between different higher order diagrams is discussed.