Selection of photomultipliers for the Cherenkov Telescope Array facility

The future ground-based gamma-ray facility—Cherenkov Telescope Array (CTA)—is aiming for a sensitivity of 1 mCrab at energies above 20 GeV. This goal in sensitivity is aiming for an order of magnitude increase compared to currently operating instruments H.E.S.S., MAGIC, CANGAROO III and VERITAS. In order to provide high sensitivity and low energy threshold the photosensors should have highest possible photon detection efficiency (PDE), low after-pulsing rate and good single photoelectron resolution. Photosensors of Cherenkov telescopes are permanently exposed to the background light of the night sky, therefore a long life time and low fatigue are also necessary conditions. s photomultipliers (PMT) of 1–2 in. size from PHOTONIS and HAMAMATSU were tested in MPI for Physics in Munich. Comparative measurements of quantum efficiency, timing, after-pulsing and single photoelectron resolution will be presented here. An evaluation of Electron Tubes photomultipliers is ongoing