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arXiv · 2608.01943

Long-Delayed Afterpulse Measurement of JUNO 20-inch Photomultiplier Tubes

Xiaojie Luo·Cailian Jiang·Haojie Dong·Yuduo Guan·Gaosong Li·Zhonghua Qin·Zhenning Qu·Junyu Shao·Liangjian Wen·Zeyuan Yu·Boyi Zheng
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Abstract

In large-scale liquid scintillator detectors such as the Jiangmen Underground Neutrino Observatory (JUNO), high-intensity events like cosmic muons induce photomultiplier tube (PMT) afterpulses that can interfere with the analysis of delayed physics signals. To systematically evaluate this instrumental background, we present a dedicated measurement of long-delayed afterpulses in two types of JUNO 20-inch PMTs: a dynode-based PMT and a microchannel-plate (MCP) PMT. The afterpulse time profiles were first characterized within a direct 1.8~ms waveform window and were further extended to 20~ms using a sliding-window readout strategy. Distinct long-delayed components are observed, revealing a strong dependence on the PMT multiplication structure. The dynode PMT exhibits a broad afterpulse component peaking at approximately 260~$\mu$s, whereas the MCP-PMT shows a pronounced peak around 90~$\mu$s, an additional component around 550~$\mu$s, and a much smaller, broadly distributed millisecond-scale component. For the microsecond-scale components, the afterpulse yield per primary photoelectron is at the $10^{-3}$ level in the selected delayed windows and increases approximately linearly with the primary light intensity. The accumulated delayed activity can therefore become non-negligible following high-intensity events. These quantitative findings provide critical inputs for PMT response characterization and for the accurate modeling of delayed correlated backgrounds in high-precision neutrino experiments.

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Xiaojie Luo, Cailian Jiang, Haojie Dong, Yuduo Guan, Gaosong Li, Zhonghua Qin, Zhenning Qu, Junyu Shao, Liangjian Wen, Zeyuan Yu, Boyi Zheng. 2026-08-03. Long-Delayed Afterpulse Measurement of JUNO 20-inch Photomultiplier Tubes. https://arxiv.org/abs/2608.01943

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