A cryogenic RICH detector demonstrator for SiPM operation with flex-PCB readout

Silicon photomultiplier (SiPM) arrays are strong photodetector candidates for future RICH detectors owing to their excellent single-photon detection efficiency, time resolution and fine granularity. The main challenge in operating SiPM arrays is the dark-count rate (DCR), especially after irradiation damage. Operation at cryogenic temperature effectively mitigates the DCR. The design and integration of a cryostat in a RICH detector pose a technical challenge. A modular cryostat demonstrator is under development at CERN to characterise SiPM arrays at liquid-nitrogen temperatures ( ∼ 80 K) under different experimental conditions. The design of the demonstrator addresses key technical aspects such as the coupling of SiPM arrays to a cold block, the operation of multi-channel readout electronics in vacuum and the transmission of the SiPM analogue signals over distances of several centimetres. This demonstrator will provide valuable insights for the scalability of the system to large photodetector areas. A flex-PCB solution transmits the analogue signals from the cryogenically cooled SiPM arrays to the readout electronics at room temperature. A prototype of the flex-PCB was designed and produced to evaluate the effect of 15 cm-long high-density traces on signal integrity and time resolution. The results demonstrate that signal integrity is preserved and a single-photon time resolution of σ = 103 ± 5 ps was measured using a picosecond-pulsed laser setup at room temperature.