The reason that detectors are divided into many components is that each component tests for a special set of particle properties. These components are stacked so that all particles will go through the different layers sequentially. A particle will not be evident until it either interacts with the detector in a measurable fashion, or decays into detectable particles.

A few important things to note:

• Charged particles, like electrons and protons, are detected both in the tracking chamber and the electromagnetic calorimeter.
• Neutral particles, like neutrons and photons, are not detectable in the tracking chamber; they are only evident when they interact with the detector. Photons are detected by the electromagnetic calorimeter, while neutrons are evidenced by the energy they deposit in the hadron calorimeter.
• Each particle type has its own "signature" in the detector. For example, if a physicist detects a particle only in the electromagnetic calorimeter, then he is fairly certain that he observed a photon.

Charge?
Number of Leptons?
Momentum?
Energy?

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