Study of 20-inch PMTs dark count generated large pulses

TL;DR

This study investigates the causes of large pulses in 20-inch PMT dark counts in the JUNO experiment, identifying muons hitting the glass as the main source through measurements and simulation.

Contribution

It provides new insights into the origin of large dark count pulses in large PMTs, combining experimental measurements with simulation analysis.

Findings

Large pulses mainly caused by muons hitting PMT glass

Measurements with muon tagging system confirm muon contribution

Simulation results align with experimental observations

Abstract

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