Experimental study of an impact-parameter optical discriminator

Abstract An optical discriminator, sensitive to the impact parameter has been tested in a particle beam. The device is based on the detection of Cherenkov light produced and trapped in a thin spherical crystal shell viewed by a fast photodetector. The detector is only sensitive to charged particles with a nonzero impact parameter relative to the centre of the crystal sphere. A prototype using a LiF crystal has been tested and the experimental results are in agreement with expectations. We outline the foreseen developments in order to use such a detector for a fast selection of B events in fixed-target experiments at proton accelerators. We also discuss the use of the detector as presently conceived for the fast selection of strange particles.