Measurement of spatial resolutions and drift velocities in a drift-chamber filled with a helium-DME mixture

Abstract We have measured spatial resolutions in a quadratic drift cell using as drift gas pure DME or a mixture of 70% He and 30% DME at atmospheric pressure. For a maximum drift distance of 5 mm we obtained in the He-DME mixture a resolution σ r = 80 μ m over 60% of the drift cell and for pure DME σ r = 40 μ m over 80% of the drift cell. The drift velocity of electrons is approximately three times faster in this mixture than in pure DME. A systematic study of the electric field dependence of the drift velocities in various He-DME mixtures is also presented.