High-precision calibration of gain and characterization of single-photoelectron response in photomultiplier tubes

Accurate gain calibration of photomultiplier tubes is crucial because their fundamental function is to detect photon counts under low-light conditions. Traditional photomultiplier tube calibration methods require assumptions about the single photoelectron response in the charge spectrum, which are then used to construct the complete photomultiplier tube response function. However, discrepancies between these assumptions and actual single photoelectron responses can introduce calibration bias. This paper presents a novel method utilizing a joint analysis of charge and amplitude spectra. This approach enables precise calibration of the photomultiplier tube gain and provides an authentic single photoelectron response.