Characterization of New Hexagonal Large Area MPPCs

Abstract

Photomultipliers (PMTs) are the standard detector for construction of the current generation of imaging Atmospheric Cherenkov Telescopes (IACTs). Despite impressive improvements in Quantum Efficiency (QE) and reliability in the last years, these devices suffer from the limitation of being unable to operate in the partially illuminated sky (during full or partial moon periods) as the excess light leads to a significant increase in the rate of ageing of the devices themselves and consequently limit the camera life. Large area Multi-Pixel Photon Counters (MPPCs) - also known as Geiger-mode avalanche photodiodes (G-APDs) or Silicon Photomultipliers (SiPMs) - are a viable alternative and are commercially available from different producers in various types and dimensions. The maturity of this technology for application to Cherenkov Astronomy has already been demonstrated by the FACT telescope. The Small Size Telescopes (SSTs) of Cherenkov Telescope Array (CTA) observatory foresee the usage of MPPCs. One of the designs for a 4 m-diameter dish Davies-Cotton telescope engages custom designed large-area hexagonal MPPCs. This is the first time that an hexagonal device with area of $95~\hbox{mm}^{2}$ divided in 4 channels is made available. These photosensors, coupled with open non imaging light concentrators with a 24 degrees cut-off angle, offer a performing alternative to standard PMTs. In this paper we show the results of their characterization together with the comparison with other commercially available devices such as the Hamamatsu S10985-050C (2x2 array of $3~\hbox{mm} \times 3~\hbox{mm}$ MPPCs) and the SensL $\mu$ SB30035-X13-E15.