Performance of a large area drift chamber operating with a He-iC4H10 mixture

We have measured the performances of a large (115 × 57) cm2 planar drift chamber filled with a He-iC4H10 (70–30) mixture in a beam. The spatial resolution is better than 100 μm along the whole drift cell. Local and integrated efficiencies are 99.3±0.2% and 98.1±0.2% respectively. The coordinate along the wire is measured by the charge division method and the resolution at the center is 0.61% of the wire length