Test of a small prototype of the COMET cylindrical drift chamber

The performance of a small prototype of a cylindrical drift chamber (CDC) used in the COMET Phase-I experiment was studied by using an electron beam. The prototype chamber was constructed with alternating all-stereo wire configuration and operated with the He−iC4H10(90/10) gas mixture without a magnetic field. The drift space–time relation, drift velocity, dE/dx resolution, hit efficiency, and spatial resolution as a function of distance from the wire were investigated. The average spatial resolution of 150 μm with the hit efficiency of 99% was obtained at applied voltages higher than 1800V. We have demonstrated that the design and gas mixture of the prototype match the operation of the COMET CDC.