The following picture gallery contains the information about Feynman diagrams necessary to understand the explanations on the following pages. This information uses as an example the muon, a popular particle among the physicists, although unknown to most human beings, that flies through our body regularly. Approximately one muon goes every minute through an area of the size of a finger nail at sea level. (How many muons cross your body within a year?)



The 3 images on the left illustrate the sequence of the decay of the muon, and the last image depicts a muon-antimuon annihilation.

  • These cosmic ray muons have a lifetime of 1/500 of a millisecond before they decay. In this picture you can find the Feynman diagram describing this decay of the muon into a W- particle and a muon neutrino. The W- itself decays into an electron and an electron anti-neutrino. You can gather the chronological sequence from the horizontal axis (time, abbreviated with t) in this diagram. The spatial sequence can be gathered from the perpendicular axis (s for space). There are always ingoing particles (here: muon) and outgoing particles (here: neutrinos and electron) inside a Feynman diagram. Leptons are displayed as straight lines with a little arrow in the middle of the line whereas the messenger particles of the weak (W, Z) and electromagnetic (γ) interactions are shown by wavy lines. Anti-leptons are always displayed with an arrow that points backward in time.
  • Interaction are described by vertices (here: red coloured). They also mark places where charge, momentum and energy conservation must be valid. The first vertex represent the process that happens earlier. There a W- particle is emitted. This is called emission of a messenger particle.
  • The second vertex shows the creation of particles. Here, the W particle is transformed into an electron and an electron anti-neutrino.
  • And what if by chance a muon hits an anti-muon during its flight through the earth's atmosphere? They both annihilate, destroy each other, and create either a photon or a Z particle. This process is called annihilation.


As a matter of fact, Feynman diagrams (proposed and developed by Richard Feynman - Nobel Prize in Physics 1965), are depictions of decays and interactions between particles, with a proper mathematical treatment described by quantum field theory. Using these pictures, complicated processes can be illustrated and occurrence probabilities can be computed more easily.

Here you get back to the beta decay website.
Here you get back to the W particle website.