Effect of increased DCR on the detection of minimum-ionizing particles with SiPMs
Radiation damage to a Silicon Photomultiplier (SiPM), as it occurs during the lifetime of the planned CMS high-granularity calorimeter detector, increases the dark current and degrades the signal-to-noise separation for minimum-ionizing particles (MIPs) and their detection efficiency. To investigate these effects, a plastic scintillator tile air-coupled to a SiPM is used to detect MIPs from a 90Sr source, in a single-channel design similar to the tiles of the CMS high-granularity calorimeter upgrade. We compared the SiPM responses after actual radiation exposure with responses simulated in the laboratory by increasing the dark-count rate (DCR) through optical illumination with an LED light source. This optical method induces no structural damage or deep defects, thus isolating the effect of increased dark-count rate. Our results show that both radiation-induced damage and LED-induced dark-count rate increases lead to similar reductions in the MIP signal and the signal-to-noise ratio. This indicates that the primary factor for the performance degradation is the elevated dark-count rate itself, rather than additional defects in the silicon. The results demonstrate that the key effects of radiation damage on SiPMs can be effectively replicated using controlled optical illumination, providing a practical and easily accessible approach for evaluating and optimizing SiPM performance under radiation-like conditions in the laboratory.