Event Display Pictures : Muon-Pair Production
An initial electron and positron annihilate and the resulting Z-particle decays producing a muon and an anti-muon.
The fast-moving muons, a much heavier "copy" of electrons, are too massive to be affected much by atomic electric fields, so no electromagnetic shower develops. They also have no strong interactions, so no hadron shower develops either. The two decay particles, therefore, pass all the way through the detector before decaying somewhere outside of it. In fact, muons are the only charged particles that can get all the way through the detector. Hence, the outer layer, the Warm Iron Calorimeter (WIC), is used as a muon detector -- charged particles which leave a single track all the way to the outside of the detector are identified as muons.
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Notice in the picture the two muons leave "tracks" (the pattern of hits has been computer-connected to make this picture) in the drift chamber and discrete red "hits" in the yellow octagonal WIC. Almost no energy is lost in the inner calorimeter (pictured in blue).
Drift chamber hit pattern, enlarged.
