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Abstract

A relative calibration of the Fine-Grained Detector (FGD) in the T2K experiment is presented, with emphasis on the saturation calibration effects in Hamamatsu's multi-pixel photon counters (MPPCs). The calibration is produced on a test bed with a Hamamatsu Pico-Second Pulsed laser, on a small model of the FGD on a sample of fibers and MPPCs. The wavelength shifting fiber-MPPC complex used in the FGD is found to have an effective pixel count of 518, and to exhibit an effective after-pulsing and crosstalk fraction of 1.6% when measured between 0.6 and 0.9 Volts over-voltage (V OV).