Optical crosstalk between SiPMs in dual-ended readout.

Gamma-ray detection performance in scintillation crystals can be improved by coupling multiple photodetectors around the sensitive volume. Greater light collection leads to improved time and energy resolution. However, neighboring detector noise, both uncorrelated and correlated, can produce optical photons that may deteriorate their performance. We studied the impact of external optical crosstalk in a dual-ended readout setup using AFBR-S4N44P014M silicon photomultipliers (SiPMs) from Broadcom coupled to 20 mm thick bismuth germanate (BGO) crystal, with and without scintillation light. SiPMs were biased individually. The behavior of crosstalk was analytically modeled. The dark count rate increased up to 50 % when both SiPMs were biased with respect to only one active SiPM. At the same time, the crosstalk probability increased more than 2-fold at high overvoltages due to detection and re-emission of avalanche photons, limiting the operational range and causing an up to 5-fold increase in the total number of detected photons. Energy resolution in BGO was impacted, and the coincidence time resolution distribution shape between two BGO detectors was significantly altered- both in a non-intuitively manner. Experimental results validate the analytical model which rely on a single constant to predict dark count rate, crosstalk and light output enhancement. Crosstalk in multi-SiPM configurations, especially at high overvoltage, significantly impacts performance. Deep understanding of the effects of excess noise in SiPM is crucial for an optimal overall gamma detector operation. Findings extend to applications in high-energy physics, time-of-flight positron emission tomography using dual-ended or monolithic crystals, and cryogenic SiPM experiments in neutrino/dark matter studies.