Performance of a cylindrical drift chamber for multi-GeV photo-induced experiments

A 50 cm high cylindrical drift chamber (CDC) has been constructed with the z-coordinate determination by the charge division. The active volume extends from 9 to 25 cm in radius, which is divided into 12 jet-type sectors. The performance of the CDC has been investigated using cosmic ray muons in the absence of magnetic field. The CDC was operated with a 70/30 gas mixture of argon and isobutane at atmospheric pressure. A drift velocity of v=52.1±0.7μm/ns was found to be nearly constant at drift distance larger than 0.5 mm. The left–right discrimination of the track was achieved with an accuracy of 98% due to a sense wire staggering. The spatial resolution in r–φ plane was found to be 100–190μm, which depends on the drift distance. The z-coordinate resolution was 2.5–3.5 mm. Observing the direct signal from the sense wire, the difference of the rise times between two wire ends was found to be negligible irrespective of the different pulse height due to different hit positions of the muons.