Towards SiPM camera for current and future generations of Cherenkov telescopes

So far the current ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs) have energy thresholds in the best case in the range of ~30 to 50 GeV (H.E.S.S. II and MAGIC telescopes). Lowest energy gamma-ray showers produce low light intensity images and cannot be efficiently separated from dominating images from hadronic background. A cost effective way of improving the telescope performance at lower energies is to use novel photosensors with superior photon detection efficiency (PDE). Currently the best commercially available superbialkali photomultipliers (PMTs) have a PDE of about 30-33%, whereas the silicon photomultipliers (SiPMs, also known as MPPC, GAPD) from some manufacturers show a photon detection efficiency of about 40-45%. Using these devices can lower the energy threshold of the instrument and may improve the background rejection due to intrinsic properties of SiPMs such as a superb single photoelectron resolution. Compared to PMTs, SiPMs are more compact, fast in response, operate at low voltage, and are insensitive to magnetic fields. SiPMs can be operated at high background illumination, which would allow to operate the IACT also during partial moonlight, dusk and dawn, hence increasing the instrument duty cycle. We are testing the SiPMs for Cherenkov telescopes such as MAGIC and CTA. Here we present an overview of our setup and first measurements, which we perform in two independent laboratories, in Munich, Germany and in Barcelona, Spain.