SiPMs for direct scintillation light detection in noble liquids

The extremely low dark count rate of the state-of-the-art vacuum ultraviolet sensitive SiPMs working in cryogenic temperature is about five orders of magnitude lower than at room temperature. However, the dark rate or the corresponding dark current of the same SiPM working in purified noble liquids of Ar, Kr, and Xe are generally higher. We show that the higher dark rate is caused by the nonzero scintillation light events triggered by environmental radio-activity in an ordinary laboratory at sea-level. Although these background scintillation light in noble liquids are in single-photon low light level, in some applications it might be a nonnegligible background.