Results of measurements of photodetectors for the ECAL0 calorimeter for the COMPASS-II experiment

Silicon Photomultipliers (SiPMs) are rapidly developing photosensitive devices which are already used as an alternative to photomultipliers (PMT) in the newly developed calorimeters for high-energy physics. Nevertheless, they do have some disadvantages, namely relatively high noise and limited dynamic range, which is caused by a fixed number of pixels. Two types of SiPMs with a very high pixel density have been measured in order to select photosensor for a new electromagnetic calorimeter being built for the COMPASS-II experiment in CERN. The two candidates were: Zecotek´s Micropixel Avalanche Photo Diode MAPD 3N and Hamamatsu Multi-pixel Photon Counter (MPPC) S12572-010P. This paper presents a dedicated measurement system designed to measure SiPM´s response to short light pulses, followed by measurements of the parameters of the above sensors at various temperatures and operating voltages. The results cover measurements of the gain, relative photon detection efficiency, correlated noise and dark rate. Furthermore, breakdown voltage and its dependency on temperature of both detectors is shown. The final results present the useful range of operating conditions and the comparison of signal to noise ratio of the two devices.