# Study of cryogenic photomultiplier tubes for the future two-phase cryogenic avalanche detector

## TL;DR

This study evaluates various cryogenic photomultiplier tubes for liquid argon detectors, demonstrating high gain and efficiency, with a focus on their suitability for future two-phase cryogenic avalanche detectors.

## Contribution

It provides a comprehensive characterization of multiple cryogenic PMTs, highlighting their performance differences and identifying the most suitable compact tubes for liquid argon applications.

## Key findings

- All tested 3-inch PMTs achieved gains above 5x10^6 in liquid Ar.
- Most 3-inch PMTs had over 95% single electron efficiency.
- Only 12 out of 21 2-inch PMTs met the efficiency and gain criteria.

## Abstract

We report the results of a characterization study of several types of cryogenic photomultipliers manufactured by Hamamatsu Photonics and intended for operation in liquid Ar conditions, namely: compact 2-inch R6041-506MOD tubes, 3-inch R11065-10 and R11065-MOD tubes for operation in liquid Ar and 3-inch R11410-20 tubes originally designed for operation in liquid Xe. These types of PMT are proposed for installation into the future two-phase cryogenic avalanche detector that is developed in the Laboratory of Cosmology and Particle Physics of the Novosibirsk State University jointly with the Budker Institute of Nuclear Physics. Eight R11065 PMTs and seven R11410-20 tubes were tested and all demonstrated excellent performance in liquid Ar in terms of gain and relative single electron efficiency. All 3-inch PMTs showed a maximal gain in liquid Ar above 5x10^6 and relative single electron efficiency higher than 95%. Compact R6041-506MOD tubes have dynode system different from that of the 3-inch photomultipliers and thus their single electron energy resolution and relative efficiency is much worse than that of 3-inch tubes. From 21 2-inch PMTs only 12 tubes were selected with acceptable, i.e. higher than 75%, relative single electron efficiency and the maximal gain higher than 5x10^6. However, these PMTs are very attractive because they are the only compact type of tubes that can operate in liquid Ar.