Calorimeters measure the energy of particles, and determine whether they have electromagnetic or hadronic interactions. Particle Identification in a calorimeter is a destructive measurement. All particles except muons and neutrinos deposit all their energy in the calorimeter system by production of electromagnetic or hadronic showers. Photons, electrons and positrons deposit all their energy in an electromagnetic calorimeter. Their showers are indistinguishable, but a photon can be identified by the non-existence of a track in the tracking system that is associated to the shower.