Characterization of the Hamamatsu R12699-406-M4 Photomultiplier Tube in Cold Xenon Environments

TL;DR

This paper thoroughly characterizes the Hamamatsu R12699-406-M4 photomultiplier tube in cold xenon environments, demonstrating its high gain, low dark count rate, and suitability for dark matter detection experiments with position reconstruction capabilities.

Contribution

It provides the first detailed characterization of the R12699-406-M4 in cold xenon, including performance metrics and its application in a small-scale detector for event localization.

Findings

Gain exceeds 2×10^6 at -1.0 kV

Dark count rate is approximately 0.4 Hz/cm^2

Effective position reconstruction demonstrated in a dual-phase xenon TPC

Abstract

The Hamamatsu R12699-406-M2 is a $2\times2$ multi-anode 2-inch photomultiplier tube that offers a compact form factor, low intrinsic radioactivity, and high photocathode coverage. These characteristics make it a promising candidate for next-generation xenon-based direct detection dark matter experiments, such as XLZD and PandaX-xT. We present a detailed characterization of this photosensor operated in cold xenon environments, focusing on its single photoelectron response, dark count rate, light emission, and afterpulsing behavior. The device demonstrated a gain exceeding $2\cdot 10^6$ at the nominal voltage of -1.0 kV, along with a low dark count rate of $(0.4\pm0.2)\;\text{Hz/cm}^2$. Due to the compact design, afterpulses exhibited short delay times, resulting in some cases in an overlap with the light-induced signal. To evaluate its applicability in a realistic detector environment, two R12699-406-M2 units were deployed in a small-scale dual-phase xenon time projection chamber. The segmented $2\times2$ anode structure enabled lateral position reconstruction using a single photomultiplier tube, highlighting the potential of the sensor for effective event localization in future detectors.