Speaker
Description
The LEGEND-1000 experiment, to be hosted at Laboratori Nazionali del Gran Sasso (LNGS) in Italy, seeks to observe neutrinoless double-beta decay with a background index goal of $10^{-5}$ cts/(keV·kg·yr), ($< 10 ^{-6}$ cts/(keV·kg·yr) from cosmogenic sources). At the LNGS depth (approx. 3800 m.w.e.), the in-situ cosmogenic production of $^{77}Ge$ and $^{77m}Ge$ via muon-induced neutrons represents a significant background challenge. The outer liquid argon (LAr) scintillation-light detector system, situated within the atmospheric-sourced LAr volume outside of the tube containing main HPGe detectors array, is optimized to minimize these cosmogenic backgrounds. The initial design utilizes a passive, radiopure Polymethyl methacrylate(PMMA)-based neutron moderator coupled with an active, dedicated light detection system using the argon scintillation properties to the fullest. This system consists of large area light-collecting and wavelength-shifting units with a SiPM-based readout. This contribution details the R&D process dedicated to this background mitigation system.
Furthermore, we report on the LEGENDArYNO test stand, a cryogenic R&D facility recently established at the LNGS laboratory. This apparatus is used to optimize the baseline design of the light detection units, as well as to characterize the mechanical stability, light-guide efficiency, and optical performance of various wavelength-shifting materials. This R&D program is vital for ensuring the reliability and "quasi-background-free" operation of LEGEND-1000 over its multi-decade operational lifetime.
This work is supported by the U.S. DOE, and the NSF, the LANL, ORNL and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak RDA; the Swiss SNF; the UK STFC; the Canadian NSERC and CFI; the LNGS and SURF facilities.