Highly sensitive micropixel avalanche photodiodes for scintillation counters of the T2K neutrino experiment

Highly sensitive micropixel avalanche photodiodes with a metal-resistor-semiconductor structure (MRS APDs) operating in the restricted Geiger discharge mode and scintillation detectors with wavelength-shifting optical fibers developed for the T2K neutrino oscillation experiment have been investigated. Dependencies of basic MRS APD parameters on the bias voltage, photon wavelength, and temperature have been measured. Characteristics of the scintillation detectors with wavelength-shifting optical fibers and avalanche photodiodes are described.