Search

LEGEND-200 is an experiment designed to search for neutrinoless double beta decay of 76Ge by operating up to 200 kg of enriched germanium detectors in liquid argon (LAr). To achieve ultra-low backgrounds, the LAr is instrumented to detect scintillation light emitted upon interactions with ionizing radiation, thus tagging and rejecting backgrounds. The LAr scintillation light is detected with wavelength-shifting fibers coupled to silicon photomultiplier (SiPM) arrays. In this document, we demonstrate the high photoelectron resolution and low noise level of the SiPM signals. We also present the results of special calibration runs performed to determine the light yield and background suppression factors. We show the background suppression performance of the LAr instrumentation on the LEGEND-200 background spectrum before and after the LAr light coincidence cut. Finally, we present the event topology classifier which enables effective particle discrimination, allowing the identification of background types in LEGEND-200.

Noble gas and liquid detectors rely on high chemical purity for successful operation. While gaseous purification has emerged as a reliable method of producing high-purity noble fluids, the requirement for large mass flows drives the development of liquid-phase purification. We constructed a medium-scale liquid argon (LAr) purification system based on a copper catalyst and 4 A molecular sieve capable of purifying 1 t of commercial LAr 5.0 to a long effective triplet lifetime of $\tau_3 \sim 1.3 \mu$s. We further demonstrate that a quenched effective triplet lifetime of $\tau_3 \sim 1 \mu$s, due to contamination by air, can be recovered in loop-mode purification to $\tau_3 \sim 1.3 \mu$s after > 20 volume exchanges., Comment: 8 pages, 2 figures, contribution to LIDINE2023 v2: Added discussion of N2-trapping capability of purifier. Fixed typos, improved text/figure style, and added a reference