Characterization of the Hamamatsu R12699-406-M4 photomultiplier tube in cold xenon environments

The Hamamatsu R12699-406-M4 is a 2×2 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 2·10⁶ at the nominal voltage of -1.0 kV, along with a low dark count rate of 0.4(2) Hz/cm². 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-M4 units were deployed in a small-scale dual-phase xenon time projection chamber. The segmented 2×2 anode structure enabled lateral position reconstruction using a single photomultiplier tube, highlighting the potential of the sensor for effective event localization in future detectors.