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

While the nucleus of an atom can decay into a less massive nucleus by splitting apart, how does a fundamental particle decay into other fundamental particles? Fundamental particles cannot split apart, because they have no constituents, but rather they somehow turn into other particles.

It turns out that when a particle decays it changes into a less massive particle and a force-carrier particle (always a W boson if it is a fundamental particle; some hadrons may decay with gluons or photons resulting). These force carriers may then re-emerge as other particles. So, a particle does not just change into another particle type; there is an intermediate force-carrier particle which mediates particle decays.

In many cases, these temporary force-carrier particles seem to violate the conservation of energy because their mass is greater than the available energy in the reaction. However, these particles exist so briefly that, because of Heisenberg's Uncertainty Principle, no rules are broken. These are called virtual particles.

A particle decays into a less massive particle and a force-carrier particle, which then decays into other particles (in this illustration, a W boson decays to u and d quarks).