Speaker
Description
We present a standalone measurement of afterpulses in the 20-inch photomultiplier tubes (PMTs) used in the Jiangmen Underground Neutrino Observatory (JUNO) experiment. A dedicated afterpulse test setup was constructed, in which intense external light pulses were injected into the PMTs. The afterpulse time distributions were obtained by recording subsequent hits following the primary signals over an extended time window with several milliseconds.
The measurements reveal the presence of significant ultra-slow afterpulse components that had not been previously identified. Both MCP-PMTs and dynode-PMTs used in JUNO exhibit distinct ultra-slow afterpulses, clustered around approximately 90 μs and 260 μs, respectively, with probabilities at the level of 10⁻³ relative to the main signal. The dependence of the afterpulse probability on the incident light intensity is studied in detail, and the charge distributions of the afterpulses are also characterized.
Furthermore, the experimental results are compared with anomalous signals observed in JUNO detector data. The good agreement between the measured afterpulse features and the detector observations confirms that these anomalous events originate from PMT afterpulse effects, validating both the interpretation of the detector data and the reliability of the present measurements.