Calorimeters measure the energy a particle loses as it passes through the detector. It is usually designed to stop entire or “absorb” most of the particles coming from a collision, forcing them to deposit all of their energy within the detector. Calorimeters typically consist of layers of “passive” or “absorbing” high-density material – for example, lead – interleaved with layers of an “active” medium such as solid lead-glass or liquid argon.
Electromagnetic calorimeters measure the energy of electrons and photons as they interact with matter. Hadronic calorimeters sample the energy of hadrons (particles that contain quarks, such as protons and neutrons) as they interact with atomic nuclei. Calorimeters can stop most known particles except muons and neutrinos.
The components of the ATLAS calorimetry system are: the Liquid Argon (LAr) Calorimeter and the Tile Hadronic Calorimeter.
Photo: portion of the Atlas Electromagnetic Calorimeter, CERN- I’ve seen at Museo Nazionale Scienza e Tecnologia Leonardo da Vinci in Milan.