The calorimeter measures the energies
of charged and neutral particles. It consists of metal plates
(absorbers) and sensing elements. Interactions in the absorbers
transform the incident energy into a "shower" of particles that
are detected by the sensing elements.
In the inner sections of the calorimeter, the
sensing element is liquid argon. The showers in the argon liberate
electrons that are collected and recorded.
In the outer sections, the sensors are tiles of
scintillating plastic. The showers cause the plastic to emit light
which is detected and recorded.