A microstrip vertex detector for studying charm hadroproduction

The WA82 experiment has collected data at the Ω facility at CERN for the study of charmed particles produced in hadronic interactions. In order to select charmed particles in the much larger background of ordinary hadronic interactions precise reconstruction of tracks in high-multiplicity events is necessary. The required accuracy, 10 μm in the transverse plane, has been obtained with a telescope made of 23 silicon microstrip detectors, with pitch ranging from 10 to 50 μm. This telescope has been operated in a 1.3 T magnetic field and has been specially designed to select on-line events with secondary vertices. The trigger, based on the measurement of the impact parameter of a track relative to the primary vertex, enriched the charm sample by a factor 15.