This Demonstration shows the OZI rule applied in the decay of one meson into two. This rule determines which strong processes are preferred and which are allowed but strongly suppressed. Selecting different initial and final quark flavors will display the appropriate diagram.
The OZI rule is an experimentally observed characteristic of strong interaction. It was first published independently by Okubo, Zweig and Iizuka in the 1960s (hence the name OZI). The rule can be summarized as follows: "Decays that correspond to disconnected quark diagrams are forbidden". Due to other physical properties of particles (such as "ideal mixing"), such processes are not completely forbidden, only very strongly suppressed. For example, the meson decay into strange mesons is preferred rather then decay into non-strange mesons or .
For more information about the OZI rule, see for example: Fayyazuddin and Riazuddin, A Modern Introduction to Particle Physics, 2nd ed., Singapore: World Scientific, 2000 p. 177.