Speaker
Description
The Jiangmen Underground Neutrino Observatory (JUNO) features a 20-kton liquid scintillator detector located 700 meters underground, with the primary goal of determining the neutrino mass ordering. To effectively identify cosmic muons and suppress associated backgrounds, a dedicated Water Cherenkov veto system has been constructed. This system surrounds the central detector and is filled with high-purity water. Cherenkov light produced by muons passing through the water is detected by an array of 2,399 microchannel plate photomultiplier tubes (MCP-PMTs). The inner surfaces of the veto system are lined with Tyvek reflector to maximize photon collection efficiency. A water purification and circulation system maintains the required ultrapure water quality, ensuring long-term detector stability and performance. This presentation will provide a detailed overview of the veto detector, focusing on its key subsystems: the veto PMTs, Earth Magnetic Field shielding coils, water system, and Tyvek reflector. The detector currently operates stably with excellent performance, achieving a muon detection efficiency >99.9% for muons going through the central detector.