Purification of large volume of liquid argon for LEGEND-200

The design, construction and performance of the system capable of purifying 65m$^{3}$ of liquid argon to sub-ppm level designed for LEGEND–200 experiment is presented. The quality of the purified liquid argon is monitored in real-time during the purification process, by measuring the argon triplet state lifetime and simultaneous direct measurements of the concentrations of impurities such as water, oxygen, and nitrogen with a sensitivity of 0.1 ppm. The achieved argon triplet lifetime value measured inside the LEGEND cryostat, when filled in 70% of its capacity, was at the level of $\tau_{3}$ = 1.3 μs. If needed, the system may also be used later to purify liquid argon already filled into the LEGEND cryostat in the loop mode

Present and Future of 0ν2β Searches with Germanium

Among the several experiments and techniques conceived of to search for neutrinoless double β decay (0ν2β) in a handful of isotopes, presently the best lower limit on the half-life for this rare process, is provided by those using 76Ge, a rare isotope of germanium. Such a lower limit is of 1.8 × 1026 y. Building from such a successful achievement of the GERDA and Majorana Demonstrator experiments, the baton with 76Ge passes now to the LEGEND experiment. Using a two-stage approach with about 200 kg and then 1 t of germanium, LEGEND aims to attain a sensitivity of around 1028 y, which will enable it to probe the standard inverted-ordering neutrino mass scenario. We touch upon the past generation of experiments to illustrate their strong and weak points, review the general concept and design of LEGEND, and describe the LEGEND-200 detector and its preliminary performance. We also illustrate how the backgrounds can have a dramatic effect on the search and in which way the latter can be mitigated

The LEGEND-200 Liquid Argon Instrumentation: From a simple veto to a full-fledged detector

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

Purification of large volume of liquid argon for LEGEND-200

The design, construction and performance of the system capable of purifying 65m$^{3}$ of liquid argon to sub-ppm level designed for LEGEND–200 experiment is presented. The quality of the purified liquid argon is monitored in real-time during the purification process, by measuring the argon triplet state lifetime and simultaneous direct measurements of the concentrations of impurities such as water, oxygen, and nitrogen with a sensitivity of 0.1 ppm. The achieved argon triplet lifetime value measured inside the LEGEND cryostat, when filled in 70% of its capacity, was at the level of $\tau_{3}$ = 1.3 μs. If needed, the system may also be used later to purify liquid argon already filled into the LEGEND cryostat in the loop mode