The influence of oxygen contamination on the performance of a mini-jet-cell-type drift chamber for the JLC-CDC

We have studied, using cosmic rays, the influence of oxygen contamination on the performance of a test drift chamber filled with a CO2:iso-C4H10 (90:10) gas mixture. The test chamber has the same mini-jet-cell structure as our proposed central tracker for JLC (JLC-CDC). We observed significant deterioration of its spatial resolution with oxygen contamination in the long drift region, though the wire efficiency stayed essentially 100% up to 50 ppm of oxygen over the full drift length of 5 cm. From the drift-time dependence of signal charge, we evaluated the electron attachment rates at different oxygen concentrations. The results were found to be consistent with a proposed empirical expression for the attachment of thermal electrons.