  The China Dark Matter Experiment (CDEX) Collaboration will carry out a direct
search for weakly interacting massive particles with germanium detectors.
Liquid argon will be utilized as an anti-Compton and cooling material for the
germanium detectors. A low-background and large-area photomultiplier tube (PMT)
immersed in liquid argon will be used to read out the light signal from the
argon. In this paper we carry out a careful evaluation on the performance of
the PMT operating at both room and cryogenic temperatures. Based on the single
photoelectron response model, the absolute gain and resolution of the PMT were
measured. This has laid a foundation for PMT selection, calibration and signal
analysis in the forthcoming CDEX experiments.
