<IMG SRC="navi.gif" WIDTH=160 HEIGHT=440 usemap="#navi" BORDER=0> Particle Decays And Annihilations : Different Interactions

Strong, electromagnetic, and weak interactions cause particle decays. There are three particle properties that determine which interaction and force-carrier particle will mediate a given decay:

Flavor:

"Flavor" refers to a particle's type. When a fundamental particle decays from one type of particle to another, we say it "changes flavor." If a down quark decays into an up quark, the down quark does not cease to be: it simply changes flavor. Only the weak interaction (via the W boson) can change flavor and allow the decay of a truly fundamental particle.

Electromagnetic Charge:

Particles with electromagnetic charge attract particles with opposite electric charge and repel particles with similar charges. Photons carry the electromagnetic interaction.

Color Charge:

Just as some particles can be electromagnetically charged, particles can have a different kind of charge called color charge. The strong interaction causes the attraction between color charged particles.

The strong force-carrier particle, the gluon, mediates decays involving color changes. The weak force-carrier particles, W+ and W-, mediate decays in which particles change flavor (and electric charge).