Study of dE/dx in a drift chamber with He-C2H6 gas mixture

We studied dE/dx in a small-cell drift chamber filled with a gas mixture of 50% He and 50% C2H6. The dE/dx resolution, measured in terms of the 80% truncated mean of 41 layer samples, was 5.2% when the incident angle of the track with respect to the wire direction was 45 degrees. The beta gamma dependence showed a smaller relativistic rise than in the case of P-10 gas. At an incident angle of 90 degrees, we observed gas gain saturation due to the space charge effect. Although this makes the beta gamma dependence of dE/dx weaker, the dE/dx resolution was improved. As a result, a pi - K separation of 2 sigma is achieved at all incident angles for 2 GeV/c tracks.