Z-Path

• Introducing the Z boson
• Introducing the Higgs boson
• Identifying particles
• Identifying Events
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Knowledge Center

• The Standard Model
• Research at the LHC
• More about the Z boson
• Energy units
• Momentum
• Vectors
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• Radioactivity
• Feynman diagrams

The following picture gallery contains all information about Feynman diagrams that are necessary to understand the explanations on the following pages. These information are given by using a popular particle at least for physicists that is nevertheless unknown to most human beings although its representatives fly through our own bodies regularly: the muon. Approximately one muon flies every minute through an area of the size of a finger nail at sea level. (How many muons cross your body within a year?)

We will use them as pictures that illustrates the sequence of an interaction between particles (collisions, scattering, decays) in space-time-diagrams.

• 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 (named after Richard Feynman) are figurative depictions of contributions from interactions between particles, which are described by quantum field theory. By using these pictures, complicated processes are illustrated and their appearance probabilities can be more easily calculated.

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