Speaker
Description
Hyper-Kamiokande (HK) is a next-generation water Cherenkov detector aimed at searching for leptonic CP violation and observing proton decay. HK is currently under construction, with observations scheduled to begin in 2028. Approximately 20,000 50 cm photomultiplier tubes (PMTs) will be installed in a water tank 72 m in height and 68 m in diameter. HK aims for a measurement energy error of less than 1 %, therefore it is important to accurately understand the PMT gain across a wide range of light intensities.
This presentation reports on the detected light intensity reproducibility of the 50 cm PMT (Hamamatsu Photonics R12860) used in HK. The input-output nonlinearity of the R12860 can be attributed to over-linearity in the light intensity region below 500 photoelectrons, and to saturation effects in the electron multiplier section that appear in the high light intensity region.
In this study, it was confirmed that, for the R12860, the longer the pulse width of the incident light, the smaller the effects of both the over-linearity at low light intensities and the saturation at high light intensities.
In addition, methods for reproducing gain were examined in order to achieve good consistency across a wide range of light intensities. Deriving gain from the single-photoelectron charge distribution is susceptible to the influence of the low-charge tail and can produce errors of several percent. To understand this effect, the light-intensity dependence of gain was investigated from various perspectives, including evaluation via a statistical method that uses the mean and variance at each light intensity for multiple photoelectrons.