Commissioning of the Cylindrical Drift Chamber for the COMET experiment

A cylindrical drift chamber (CDC) has been developed for the COMET Phase-I experiment. To search for the muon-to-electron conversion with a sensitivity of $3 \times 10^{-15}$, the CDC is required to have momentum resolution of 200 keV/$c$ for 100-MeV/$c$ electrons. In order to reduce the multiple scattering, we have selected a chamber gas mixture of 90% helium with 10% isobutane. Construction of the CDC was successfully conducted, and performance evaluation is being carried out. We have confirmed stable operation without a magnetic field thus far based on cosmic-ray tests. In this paper, the motivation, design, construction, and commissioning status of the CDC are presented.