Researchers from SYSU and IHEP have developed a unique muon veto detector system for TAO, a satellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO). This system features a top veto tracker system with remarkable characteristics such as high light yield, distinct signal-background differentiation and high detection efficiency even at high thresholds, provides the TAO experiment with a robust capability to suppress cosmic muon induced fast neutron and radioisotope events which are significant correlated backgrounds for the neutrino signal. This scalable solution establishes a transferable technique for next-generation neutrino detectors requiring muon identification efficiency >99.5% across multi-ton volumes.
Unique Design for Enhanced Performance
For ground-near neutrino or low-background detectors, muon veto systems are crucial. TAO features a top veto tracker system. It comprises 160 modules, each constructed from PS strips, embedded WLS-fibers, and silicon photomultipliers. The optimized WLS fiber arrangement, with fibers uniformly bent in the PS and combined with fiber focusing readout at the end, is a standout design feature. This design not only improves the light yield but also enhances the muon detection efficiency.
"This unique design is a significant step forward in muon veto detection" said Prof. Wei Wang, the corresponding author. "Innovative fiber arrangement and readout techniques are used, which provide valuable experience and references for other related experiments."
High Light Yield and Clear Signal-Background Differentiation
The research reveals that the further the muon strikes toward the two ends of the PS strip, the higher the total light yield, although with greater asymmetry. The most probable signal strength output from one end of a 2000-mm PS module is at least greater than 40.8 p.e. with a clear differentiation between background and muon signals, and for a 1500-mm PS module, it is at least greater than 51.5 p.e.. Using optical grease to couple the SiPM and WLS fiber increases the effective light yield by 12.5%. This high light yield and distinct signal-background separation ensure that the detector can accurately identify muons and remove associated events, which is crucial for the success of neutrino and low-background experiments.
High Detection Efficiency Even At High Thresholds
Three types of trigger modes and their efficiencies were defined to comprehensively evaluate the performance of this unique design. In "module" mode (Summing signals from both ends of the PS to exceed the threshold), the detection efficiency of the PS exceeded 99.67% at a 30-photoelectron threshold, and even in "AND" mode (Simultaneously exceeding the threshold at both ends of the PS), it surpassed 99.60% at a 15-photoelectron threshold.
Maintaining high detection efficiency even at high thresholds ensures that the detector operates with high reliability and accuracy, meeting the strict requirements of the TAO experiment with 99.00% compliance. This capability provides a robust and reliable detection solution not only for the TAO experiment but also for other applications in the fields of neutrino and low-background detection.
This research on the muon veto detector system for the TAO experiment outlines a potential path toward more efficient and reliable detection technologies. By combining a unique design with high light yield, clear signal-background differentiation and high detection efficiency even at high thresholds, the system may influence the future of such experiments. With growing global demand for enhanced detection capabilities, these advancements offer a reliable auxiliary system. The complete study is accessible via DOI: 10.1007/s41365-025-01696-2
