Detector of internally-reflected Cherenkov light

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The Detector of Internally Reflected Čerenkov light (DIRC) was first proposed by Blair Ratcliff as a tool for particle ID at a B-Factory. As a particle traveling close to the speed of light passes through the quartz it emits Čerenkov radiation, provided that $n β > 1$ (where n is the index of refraction in the quartz and $\beta = \frac{v}{c}$ is proportional to the particle's velocity). This radiation is transmitted through internal reflections to a stand-off box which contains photomultipliers. Knowledge of the angle at which the radiation was produced, combined with the track angle and the particle's momentum (measured in a drift chamber) may be used to calculate the particle's mass.

The DIRC differs from earlier RICH and CRID Cherenkov light detectors in that the quartz bars used as radiators also transmit the light. The design was first used by the BaBar Collaboration at SLAC.