Capability of detecting low energy events in JUNO Central Detector

The Jiangmen Underground Neutrino Observatory (JUNO) is an experimental project designed to determine the neutrino mass ordering and probe the fundamental properties of the neutrino oscillations. The JUNO central detector is a spherical liquid scintillator detector with a diameter of 35.4m and equipped with two independent photomultiplier (PMT) systems, approximately 18,000 20 inch PMTs and 25,000 3 inch PMTs. A trigger threshold of 0.5MeV can be easily achieved by using a common multiplicity trigger and can meet the requirements for measuring the neutrino mass ordering. However, it is essential to further reduce the trigger threshold for detecting solar neutrinos and supernova neutrinos. Based on the 20 inch PMT system, a sophisticated trigger scheme is proposed to achieve a low energy threshold by reducing the rate of events due to radioactivity contaminants and dark noise coincidence. With the new trigger scheme, the event rate of the central detector from different types of sources have been carefully studied by using a detailed detector simulation. It shows that the trigger threshold can be reduced to 0.2 MeV, or even 0.1 MeV, if the concentration of C-14 in liquid scintillator can be well controlled.