Fibers Study to Improve the Liquid Argon Detector for LEGEND-1000 Experiment

The neutrinoless double-beta decay (0𝜈𝛽𝛽) is a hypothetical nuclear process, (A, Z) → (A, Z+2) + 2, which would signal the Majorana nature of neutrinos and demonstrate a violation of lepton number conservation. The LEGEND (Large Enriched Germanium Experiment for Neutrinoless double-beta Decay) Experiment is designed to search for 0𝜈𝛽𝛽 aiming to reach a half-life sensitivity of T_1/2 > 10²⁸ years using 1000 kg of ⁷⁶Ge. One of the systems to veto backgrounds near strings of ⁷⁶Ge-enriched crystals is a liquid argon active shield. Its primary components are light guides to collect scintillation light generated in liquid argon by background radiation. The first phase of the LEGEND program, the LEGEND-200 experiment, uses wavelength-shifting fibers as light guides. In our studies reported here, we investigated improvements in fibers used in LEGEND-200. We have characterized the response of new fibers to common radiation sources by comprehensive measurements of the optical properties of fibers, such as emission spectrum, attenuation length, and light yield. This work also includes optical simulations of a veto system based on new fibers which would lead to improvements of the liquid argon active shield of LEGEND.