Test results of new CR365-PMTs for the Tibet muon-detector array

Abstract

The Tibet-ASγ experiment has a water-Cherenkov muon-detector array (MD) as a part of 3 different arrays with specific purposes. To increase the ability of getting the primary proton, helium and iron spectra up to 10 16 eV and clarifing their spectral "knee" positions, we need to upgrade current PMT capabiltty in each MD cell. The current dynamic range of the PMTs is 5 to 2000 photoelectrons (PEs) which is enough for the purpose of observation of high-energy celestial gamma rays. However, according to Monte-Carlo simulations, we need a dynamic range of 100 -10 6 PEs for the knee problem. For this end, we have a plan of adding two 8-inch-in-diameter PMTs in each MD cell. We have compared the characteristic features between R5912-PMT made by Japan Hamamatsu and CR365-PMT made by Beijing Hamamatsu, and found that CR365-PMT fulfill our requirements. In this paper, test results of the first batch of 20 CR365-PMTs made by Beijing Hamamatsu for the MD array are shown.