SPOT-FOCUSING CERENKOV DETECTOR

Tests on a new type of Čerenkov counter have been carried out at CERN in a 50 GeV c-1 positive beam. This detector can be seen as a ring-focusing counter in which a subtraction of a fixed angle θ0 has been performed optically on the Čerenkov angle θ. For a particular value γ0 of the relativistic factor of the particle detected, the Čerenkov angle θ is equal to θ0, and all the Čerenkov light is focused on a spot, which gives its name to the detector. For all other values of γ the spot degenerates into a small ring, much smaller than it would have been in a conventional focusing counter. The radius of the ring provides a determination of the velocity of the particle, and the position of the centre is related to its direction. This counter can be used for the detection of multi-particle events. A description of the detector and its basic design principles are given. Results concerning the velocity resolution and light yield are also presented and compared with computed predictions. © 1979.