PoS - Proceedings of Science
Volume 441 - XVIII International Conference on Topics in Astroparticle and Underground Physics (TAUP2023) - Neutrino Physics and Astrophysics
Muon Veto of the LEGEND Experiment
G. Grünauer*  on behalf of the LEGEND Collaboration
Full text: pdf
Supplementary files:
Pre-published on: January 09, 2024
Published on: March 22, 2024
The $\mathbf{L}$arge $\mathbf{E}$nriched $\mathbf{G}$ermanium $\mathbf{E}$xperiment for $\mathbf{N}$eutrinoless $\beta \beta$ $\mathbf{D}$ecay (LEGEND) is an experiment searching for neutrinoless $\beta \beta$ decay of the $^{76}$Ge isotope. LEGEND-1000, with 1000 kg of $^{76}$Ge mass, is designed to reach half-life sensitivity of $T_{\frac{1}{2}} > 10^{28}$ years. To be sensitive to such a half life, a number of measures are required to reduce background events.
For the current experimental phase LEGEND-200, a Water-Cherenkov-Veto system actively reduces background from radioactive isotopes and cosmic radiation like muons. It uses photomultiplier tubes (PMTs) as light sensors in a water-tank covered with a reflective foil to increase the light yield inside the water volume.
This muon veto has been stably taking data since March 2023. Regular calibration of the PMTs ensures measurements of up to 100 photoelectrons per PMT. A first look on the data of the muon veto shows a stable total muon rate of $\approx 35$ mHz over two months. A small area of the muon veto directly below the cryostat, called the ''Pillbox'', can increase the detection efficiency of muons in the experiment through determining coincidences between the muon veto and the liquid argon (LAr) instrumentation or High Purity Germanium (HPGe) detectors. It has been demonstrated that $20 \%$ of the muon veto PMTs can detect $\approx 70.8 \%$ of the coincident muon events.
Considering these results, plans for the improved LEGEND-1000 muon veto are presented, including an optimised PMT distribution.
DOI: https://doi.org/10.22323/1.441.0261
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