Drift chambers with controlled charge collection geometry for the NA34/Helios experiment

Abstract We report on the design and performance of a set of drift chambers for the NA34/HELIOS experiment at the CERN-SPS. The chambers are operated with CO 2 at low drift velocity and have a field geometry allowing a controllable track sample length and isochronous charge collection. In beam tests using a silicon microstrip hodoscope as external track reference, we measure a two-track separation of 600 μm and, at a drift velocity of 8.9 μm/ns, an absolute single track percision of 60 μ on average the total drift distance of 20 mm. The influence of the track sample length on the chamber performance is studied and a value of 2.5–3.0 mm is found as an optimum.