Speakers
Description
The Liquid Argon (LAr) instrumentation of the neutrinoless double-beta decay experiment LEGEND-200 builds on its precursor [1] operated in the completed GERDA experiment. Thanks to its efficient background recognition capabilities, it was pivotal to search for neutrinoless double-beta decays of $^{76}$Ge quasi-free of background events [2]. An improved version has been developed and is deployed in LEGEND-200 at the Laboratori Nazionali del Gran Sasso. The low-background LAr instrumentation detects the argon scintillation light created by energy depositions in the liquid argon that accompanies energy depositions in the high-purity germanium detectors. Such background events originate from $\alpha$, $ \beta$, $ \gamma$ or neutron interactions, originating from primordial, anthropogenic radioisotopes or cosmogenic produced unstable isotopes. They must be discriminated from neutrinoless double beta decay signals, which have energy deposition inside the germanium detectors and no energy deposition in the liquid argon. The LAr instrumentation consists of two concentric curtains of WaveLength Shifting (WLS) fibers, realized by evaporation of the fibers with TetraPhenyl Butadiene (TPB) and read out with arrays of Silicon PhotoMultipliers (SiPM). The TPB first shifts the LAr scintillation light from 128 nm vacuum ultraviolet to blue light. Subsequently, the blue light is absorbed inside the fibers and shifted to the green, and guided by total internal reflection to the low-background SiPM arrays mounted on both ends of the fiber module. The electrical signals are transmitted via differential transmission lines and amplified outside the liquid argon. The full traces are recorded with a flash-ADC system and stored for offline analysis. Transparent, TPB coated nylon shrouds complement the LAr instrumentation surrounding germanium detector strings and a reflecting and WaveLength Shifting Reflector (WLSR) of cylinder geometry enclosing the germanium and fiber arrays. The poster will cover the phases of the LAr instrumentation: from the design and its requirements to the first analysis of commissioning data.
[1] Optical fiber read-out for liquid argon scintillation light, J. Janicskó Csáthy, T.Bode, J. Kratz, S. Schönert, Ch. Wiesinger, https://doi.org/10.48550/arXiv.1606.04254.
[2] Final Results of GERDA on the Search for Neutrinoless Double-$ \beta $ Decay, GERDA Collaboration M. Agostini et. al., PRL 125, 252502 (2020).
| Collaboration | LEGEND Collaboration |
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