Effect of gas composition on CMS Cathode Strip Chamber performance

Cathode strip chambers (CSCs) are multiwire proportional counters that will be used as muon detectors in the Compact Muon Solenoid (CMS) experiment at the European Center for Nuclear Research (CERN). The composition of the gas inside the chamber influences important chamber parameters, such as gas gain and operational voltage range. Differences in these parameters were examined under variations in concentration of argon, carbon dioxide, and carbon tetrafluoride around the baseline mixture of Ar + CO2 + CF4 = 40 + 50 + 10. Gas gain was found to be dependent on Ar concentration, but independent of CF4 or CO2 relative concentration. Operational voltage range of ~370V has no dependence on Ar concentration in the range of 60%40% Ar, and has a weak dependence on the amount of CF4 (at fixed 40% Ar): ~340V at 0% CF4 to ~430V at 20% CF4.