Detection of internally reflected Cherenkov light

A detector of Internally Reflected Cherenkov light (DIRC) is a design of a Ring imaging Cherenkov detector where Cherenkov light that is captured by total internal reflection inside the solid radiator has its angular information preserved until it reaches the light sensors at the detector perimeter. This requires a precise planar or rectangular cross section of the radiator.

A 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 Cherenkov radiation, provided that $n\beta >1$ (where n is the index of refraction in the quartz and $\beta =v/c$ is the particle's velocity measured in c). 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.

References

• BaBar DIRC homepage
• Nuclear Instruments and Methods in Physics Research A 502 (2003) 211–221