Photo-induced Charge Calibration R&D for nEXO

The nEXO experiment is designed to search for the elusive neutrinoless double beta decay of ¹³⁶Xe with a half-life sensitivity goal of >10²⁸ years using a 5-tonne liquid xenon (LXe) 1.3 m diameter cylindrical TPC. The calibration of the ionization and scintillation light response of the detector involves the regular deployment of external radioactive sources, challenging because of the excellent self-shielding properties of LXe, and the occasional injection of ²²⁰Rn and ¹²⁷Xe. Several other risk-mitigating R&D efforts are ongoing to incorporate additional calibration techniques to regularly monitor the drift electrons and the light response of silicon photomultipliers in liquid xenon. This presentation presents the status, including preliminary results, of an effort at the University of Massachusetts Amherst to develop gold photocathodes to generate photoelectrons in LXe using a small, dual grid ionization chamber. The use of multiple such photocathodes could allow to monitor the ionization electron lifetime almost continuously in nEXO.