EXPERIMENTAL-STUDY OF AN IMPACT-PARAMETER OPTICAL DISCRIMINATOR

An optical discriminator, sensitive to the impact parameter has been t ested in a particle beam. The device is based on the detection of Cher enkov light produced and trapped in a thin spherical crystal shell vie wed by a fast photodetector. The detector is only sensitive to charged particles with a nonzero impact parameter relative to the centre of t he crystal sphere. A prototype using a LiF crystal has been tested and the experimental results are in agreement with expectations. We outli ne the foreseen developments in order to use such a detector for a fas t selection of B events in fixed-target experiments at proton accelera tors. We also discuss the use of the detector as presently conceived f or the fast selection of strange particles.