Measurement of the Quantum Efficiency of Electrode Materials for VUV Photons in Liquid Xenon

Abstract

Light dark matter searches using ionization signals in dual-phase liquid xenon (LXe) time projection chambers (TPCs) are limited by low-energy ionization backgrounds, including those from the photoelectric effect on the electrodes. To address this, we measured the quantum efficiency (QE) of various electrode materials for vacuum ultraviolet (VUV) photons in LXe, including platinum (Pt), stainless steel (SUS304), and magnesium fluoride (MgF$_{2}$)-coated aluminum (Al). Our results show that MgF$_{2}$-coated Al exhibits the lowest QE among the tested materials. The QE for VUV photons with a mean wavelength of 179.5~nm was measured to be $(7.2 \pm 2.3) \times 10^{-5}$, corresponding to a reduction by a factor of 4.4 compared to SUS304, a commonly used electrode material in direct dark matter experiments with LXe. These findings suggest that employing low-QE electrodes can help mitigate photoelectric-induced backgrounds, potentially improving the sensitivity of LXe TPCs in light dark matter searches.