Performance of new 8-inch photomultiplier tube used for the Tibet muon-detector array

TL;DR

This study compares two types of 8-inch photomultiplier tubes (PMTs) for use in the Tibet muon-detector array, aiming to enhance measurement range and accuracy for cosmic ray composition analysis.

Contribution

First comparison of R5912-PMT and CR365-PMT, informing the selection of PMTs for wide dynamic range measurements in cosmic ray experiments.

Findings

R5912-PMT and CR365-PMT have similar characteristic features

Both PMTs can be used to cover the required dynamic range in MD cells

Addition of two PMTs extends measurement range over six orders of magnitude

Abstract

A new hybrid experiment has been constructed to measure the chemical composition of cosmic rays around the "knee" in the wide energy range by the Tibet AS$\gamma$ collaboration at Tibet, China, since 2014. They consist of a high-energy air-shower-core array (YAC-II), a high-density air-shower array (Tibet-III) and a large underground water-Cherenkov muon-detector array (MD). In order to obtain the primary proton, helium and iron spectra and their "knee" positions in the energy range lower than $10^{16}$ eV, each of PMTs equipped to the MD cell is required to measure the number of photons capable of covering a wide dynamic range of 100 - $10^{6}$ photoelectrons (PEs) according to Monte Carlo simulations. In this paper, we firstly compare the characteristic features between R5912-PMT made by Japan Hamamatsu and CR365-PMT made by Beijing Hamamatsu. This is the first comparison between R5912-PMT and CR365-PMT. If there exists no serious difference, we will then add two 8-inch-in-diameter PMTs to meet our requirements in each MD cell, which are responsible for the range of 100 - 10000 PEs and 2000 - 1000000 PEs, respectively. That is, MD cell is expected to be able to measure the number of muons over 6 orders of magnitude.