Physics:Cherenkov counter

Detectors for charged particles using the light emitted by Cherenkov radiation to measure the particle velocity . Combined with knowledge of the particle momentum, determines its mass. Cherenkov counters are therefore most commonly used as detectors for identifying particles, in conjunction with momentum measurements, e.g. in a tracking chamber (see Kleinknecht82). Their index of refraction is carefully optimized for the particle masses and momentum range of the experiment in question. Classification:

• a) Threshold counters record all light produced, thus providing a signal whenever is above the threshold .
• b) Differential counters accept light only in a narrow range of angles ( ) i.e. in a narrow velocity interval. Resolutions of have been reached. As chromatic dispersion ( ) is the major source of error at high momenta, special achromatic counters, called DISC (= directional isochronous self collimating) counters have been developed, which reach to 10^-7. Differential Cherenkov counters suffer from the low acceptance both in angle and .
• c) Ring imaging Cherenkov counters (RICH): In these detectors, particles pass through a radiator, and the radiated photons are usually focused onto a position-sensitive photon detector by a focusing device (mirror). The velocity is determined by a measurement of the radius r of the ring, on which the photons are detected. For more details, Ring Imaging Cherenkov Counter.