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Description
Aiming at the calibration requirements of neutrino detectors, the single-photoelectron (SPE) responses of an MCP-PMT and a conventional dynode PMT are compared at the waveform level. By analyzing approximately 9 million digitized waveforms, we find that the MCP-PMT charge spectrum exhibits a pronounced high-charge tail. The fraction of events with charges above 3 p.e. is 0.66%, approximately 160 times higher than that of the dynode PMT, indicating a significant deviation from the Poisson-Gaussian model. The excess is not accompanied by a comparable increase in peak amplitude or resolved multiple pulses, but is instead associated with increased charge integration due to significantly broader pulse widths, as characterized by the full width at half maximum (FWHM). In addition, the MCP-PMT exhibits a distinct but narrower delayed component at approximately 42 ns. These results indicate that the MCP-PMT charge response is strongly dependent on pulse shape, suggesting that its calibration should incorporate waveform-level diagnostics rather than directly following conventional PMT calibration procedures.