The JUNO (Jiangmen Underground Neutrino Observatory) experiment is under preparation in China by the international collaboration. The main goal of the project is to determine the neutrino mass hierarchy by precise measurement of the energy spectrum of the antineutrinos from the nuclear reactors with help of the 20 kt liquid scintillator underground detector located at a distance of 53 km. Data taking should begin in 2020.
Performance of the JUNO experiment is related to its capability to suppress or at least to control the background processes, which may have the same signature as the antineutrino signal. There are several sources of the background but most dangerous is due to cosmogenic isotopes produced in nuclear spallation processes in cosmic muons interactions.
The Veto system of the JUNO detector is used for muon detection, muon induced background study and its reduction. It consists of the Top Tracker system and the Water Cherenkov detector. The Water Cherenkov detector is a pool filled with purified water and instrumented with PMTs surrounding the central antineutrino detector. The Top Tracker made of scintillating strips and covering ∼1/3 of the top area with 3 layers has to reconstruct the cosmic muons’ direction. This independent muon information will help muon tagging, track reconstruction and efficiency study to understand and reduce cosmogenic backgrounds.
Effect of cosmic muons, cosmogenic isotopes, spallation neutrons, and natural radioactivity as well as the design of the Veto system detectors, their performances and the strategy for the background reduction are presented.