Radiation damage studies of silicon photomultipliers for the CMS HCAL phase I upgrade

Results from a study of the radiation hardness of silicon photomultipliers (SiPMs) are presented. Recently developed high density (>4500 cells/mm2) SiPMs from two manufacturers (Hamamatsu (Japan) and KETEK (Germany) were exposed to 62 MeV protons at fluences up to 1×1012 protons/cm2 at the UCL (Belgium) proton cyclotron (LIF irradiation facility). The measurements were carried out for the purpose of determining radiation hardness under the extreme conditions expected at the CERN Large Hadron Collider (LHC) and SLHC. The SiPMs were biased at operating voltage during the irradiation. An increase of the SiPM's dark currents and noise was observed during and after irradiation as expected for silicon devices. The SiPM's main parameters were measured before and after irradiation. The effects of the proton radiation on breakdown voltage, signal amplitude, dark current and noise for these devices are shown and discussed.