Speaker
Description
Hyper-Kamiokande is a next-generation water Cherenkov detector under construction in Japan, scheduled to start observations in 2027. The physics goals of Hyper-Kamiokande experiment include leptonic CP phase measurements, proton decay searches, and observations of atmospheric neutrinos and neutrinos from solar and supernova explosions. The effective volume of the detector will be about eight times that of Super-Kamiokande. Approximately 20,000 photomultiplier tubes with a diameter of 50 cm (ID PMTs) will be installed in the inner detector (ID) region. In order to improve physical sensitivity through higher statistics, higher precision, and lower background measurement, the performance of PMTs has been improved. The developed photomultiplier tubes have been installed in the Super-Kamiokande. It was confirmed that the detection efficiency, time resolution, and charge resolution improved approximately twice each.
Production and delivery of 50 cm diameter photomultiplier tubes for Hyper-Kamiokande are underway. Long-term measurements are being conducted to ensure stable performance during the production period. Two cold dark rooms were prepared as an environment in which 16 photomultiplier tubes could be measured simultaneously, and measurements were taken with a mu-metal magnetic shield for individual PMTs. In the measurement, Scaler, ADC, and TDC data of the signal from the photomultiplier tube are acquired, and the variation is monitored for about 0.5-1 month for each item (dark noise rate, gain amplification rate, charge resolution, Peak-to-Vally ratio of one photoelectron distribution, time resolution, probability of after-pulse occurrence). Measurements began in December 2021, and as of July 2022, more than 170 photomultiplier tubes have been monitored for their performance. In the established measurement environment, stable performance was confirmed for each item within the measurement period.
This poster will introduce the data acquisition system for the long-term measurements, show the performance of Hyper-Kamiokande 50 cm diameter photomultiplier tubes obtained from the long-term measurements with comparisons to required performance, and present the understanding of the detector performance obtained so far and prospects.
