If charged particles travel faster than light in such a medium, they give up some of their energy by emitting blue light. In a transparent medium like water, ice, oil or gas, the blue light can escape and transmit the information that a fast charged particle has passed through. Using various media to optimize the size of the light cone around the particle's direction, physicists build Cerenkov detectors that contain light-sensitive devices called photomultipliers. Calorimeters - Most particles interact with matter when they travel through it. Depending on the type of interaction, a particle can lose a fraction or all of its energy.
Calorimeters measure the energy lost and determine the total energy of the incoming particle.
Hadronic calorimeters monitor the energy of particles containing quarks as they interact with atomic nuclei. To build calorimeters, physicists use a wide variety of materials including solid lead-glass, cesium iodide, liquid argon and silica aerogel. A semiconductor with a voltage applied across its junction constitutes a sensitive, high-precision tracking device. Physicists build silicon detectors that consist of layers of small pads with many tiny silicon strips a fraction of a millimeter wide. Charged particles passing through the silicon create electric signals that exactly indicate which strips the particles have crossed.