Operation of Multi-Pixel Photon Counters Down to Liquid Helium Temperatures

We are investigating the possibility of using Silicon Avalanche Photo Detectors (APD), both in proportional and in Geiger mode, to readout inorganic scintillators operated at cryogenic temperatures. Such detectors, that need to operate close to liquid helium (LHe) temperatures and in a magnetic field of a few Tesla, have been proposed by our group as a way to build an active polarized target to be used for neutrino physics, for the search of axions and CP violation, as suggested by some theoretical papers. In the present work we investigate in some details the performance of Hamamatsu Multi-Pixel Photon Counters (MPPCs) down to LHe temperature to verify the temperature range of usability of these devices.