Study of 20-inch PMTs dark count generated large pulses

Abstract The main goal of the JUNO experiment is to determine neutrino mass ordering with a 20 kt liquid-scintillator detector. 20-inch PMT crucial as one key instruments realize an excellent energy resolution at least 3% 1 MeV. knowledge on PMT's characterisation and feature critical for detector performance understanding. Large pulses from dark count such flasher or others are serious concerns noise control. Focusing large count, this paper trying investigate causes by measurements muon tagging system. It found that pules contributed mainly muons hitting glass, we have preliminary understanding results simulation based Geant4.