Yesterday we had a lecture in "Introduction to Particle Detectors"by Frank Hartmann (CERN and KIT - Karlsruhe Institute of Technology)

Before you build a detector, we needed to know the interactions between different elements (photon, charged particles, hadronic interactions, and neutrinos) and what properties we wanted to measure (energy, momentum, charge, life time, decay modes).

The electrons leaves traces in the tracker and in the electromagnetic calorimeter (and stops). The photons leaves traces in the electromagnetic calorimeter (and stops). The hadrons leaves traces in the tracker, the electromagnetic calorimeter and in the hadronic calorimeter (and stops). The muons leaves traces in all of them.

The principal function of  tracking detectors is measure the tracks of emerging particles; determine charge and momentum in connection with a magnetic field; tracks are then reconstructed from measured space-points to determine what the particle actually was!!