After-pulsing and cross-talk in multi-pixel photon counters

Multi-pixel photon counters (MPPC) are pixelated Geiger-mode photon manufactured by Hamamatsu photonics. They will be used for reading out all the scintillator elements within the near detector of the T2K experiment. Their performances photo-detection efficiency, dark noise and gain, and their insensitivity to magnetic field fulfill the ND280 requirements. On the other hand, two known issues, cross-talk and after-pulsing may adversely impact the detector response. In this paper, cross-talk and after-pulsing are precisely measured by recording waveforms and identifying all the avalanche pulses. At an over-voltage of 2 V, an avalanche generates on an average 0.5 additional avalanches due to after-pulsing, whereas it generates 0.13 at 1 V over-voltage. After-pulses follow two independent time constants of 15 and 82 ns. The cross-talk probability is a factor of 3 smaller than the after-puling probability. Simulating the MPPC response, we find that after-pulsing and cross-talk do not degrade the detector performance significantly within the expected operating conditions of the T2K near detector.