Performance of UV-sensitive MPPC for liquid xenon detector in MEG experiment

In order to upgrade the liquid xenon gamma-ray detector, a new MPPC is being developed in collaboration with Hamamatsu Photonics. It needed to be sensitive for scintillation light of liquid xenon whose wavelength is in vacuum ultra-violet region, as large as 12×12 mm² as one readout channel and capable of counting one photo-electron. Although these requirements were satisfied by previous prototypes, waveform from the prototypes had long decay time. As the countermeasure for this issue, we proposed subdivision and series connection of MPPC active region. We also tested the serial connection in liquid xenon environment with some configurations, and confirmed that waveform is as sharp as that of small (3×3 mm²) MPPC.