Long-Delayed Afterpulse Measurement of JUNO 20-inch Photomultiplier Tubes
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~μs, whereas the MCP-PMT shows a pronounced peak around 90~μs, an additional component around 550~μs, 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.
Related
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BibTeX
@misc{luo2026longdelayed,
title = {{Long-Delayed Afterpulse Measurement of JUNO 20-inch Photomultiplier Tubes}},
author = {Xiaojie Luo and Cailian Jiang and Haojie Dong and Yuduo Guan and Gaosong Li and Zhonghua Qin and Zhenning Qu and Junyu Shao and Mingxia Sun and Liangjian Wen and Zeyuan Yu and Boyi Zheng},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.01943},
eprint = {2608.01943},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.01943},
}
RIS
TY - UNPB
TI - Long-Delayed Afterpulse Measurement of JUNO 20-inch Photomultiplier Tubes
AU - Xiaojie Luo
AU - Cailian Jiang
AU - Haojie Dong
AU - Yuduo Guan
AU - Gaosong Li
AU - Zhonghua Qin
AU - Zhenning Qu
AU - Junyu Shao
AU - Mingxia Sun
AU - Liangjian Wen
AU - Zeyuan Yu
AU - Boyi Zheng
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2608.01943
UR - https://arxiv.org/abs/2608.01943
AB - 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~μs, whereas the MCP-PMT shows a pronounced peak around 90~μs, an additional component around 550~μs, 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.
ER -