The development of the optical discriminator

Abstract New results from the tests of the impact parameter discriminator by the RD30 Collaboration are presented. The device, based on the detection of Cherenkov light produced in a thin crystal, is able to cope with extremely high rates in the GHz range and sign tracks with non-zero impact parameter at a first trigger level. We report experimental results obtained with a sapphire shell surrounded by a liquid cladding compensating chromatic dispersion. An excellent signal to background ratio has been obtained and the sensitivity at low impact parameters reaches the requirements for efficient B-meson selection. The use of such a device for hyperon selection will also be discussed.