Speaker
Description
Liquefied noble elements, such as liquid xenon and liquid argon, are widely used in low-background physics experiments. They offer self-shielding due to their high density, high scintillation yield, the ability to extract an ionization signal via electron drift, multiple background-rejection techniques including pulse-shape discrimination, and ease of continuous in-situ purification. Despite these advantages, some classes of background remain difficult to address. One example is the β decay of $^{42}$K on the surfaces of the $^{76}$Ge-enriched inverted-coaxial point-contact (ICPC) detectors in LEGEND. With a Q-value of 3.5 MeV, these decays can deposit energy in the 0νββ region of interest at 2039 keV. In LEGEND, the ICPC detectors are immersed in ultra-pure liquid argon, which also serves as an active veto through the readout of its scintillation light. $^{42}$K ions, produced by the β decay of cosmogenic $^{42}$Ar dissolved in the argon, drift toward and collect on the germanium detector surfaces. One possible way to reduce this background to the level required by next-generation experiments is to replace the liquid with a solid-argon active veto, in which $^{42}$K ions are immobilized where they are produced while the scintillation-based veto is retained. In this talk, I will present preliminary projections of the background suppression factor achievable with this technique, followed by first experimental results from a silicon photomultiplier operated in solid argon to characterize its scintillation properties.