Performance of avalanche photodetectors at cryogenic temperatures: Operations of MPPCs at temperatures below 77 K

We are investigating the possibility of using Silicon Avalanche Photo Detectors (both in proportional and in Geiger mode) to readout inorganic scintillators operated at cryogenic temperatures. Such detectors, that need to operate close to LHe temperatures and in a magnetic field of a few Tesla, was proposed by our group as a way to built an active polarized target to be used for neutrino physics, for the searches of axions and CP violation, as suggested by some theoretical papers. In the present work we have investigated in some details the performance of Hamamatsu MPPCs down to LHe temperature, to verify the temperature range of usability of these devices. Measurement of the most important parameters will be presented: quantum efficiency, dark current, dark rate, gain. These results will be compared to what we measured on Large Area Silicon APDs operating in the same temperature range.