Silicon photomultipliers for MAGIC/CTA

So far the current ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs) have an energy threshold in the range of 30 to 50 GeV (H.E.S.S.-II and MAGIC-II), which is combined with a rather poor hadron background suppression at energies close to the threshold. Going for larger mirror dishes for telescopes would lower the energy threshold of IACTs and may improve the background reduction. However, the very large telescopes may become prohibitively expensive. A cost effective way of providing/improving the sensitivity at lower energies is to use novel photo sensors with superior photon detection efficiency (PDE). Currently the best superbialkali photomultipliers (PMTs) have a PDE of about 30-33%, whereas the SiPMs (MPPC,GAPD) from few manufacturers show a photon detection efficiency of about 40-45%. Using these can lower the energy threshold of the instrument and may improve the background rejection. 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 the overview of our setup and measurements of comparison between superbialkali PMTs and the SiPMs.