spadRICH: Developing digital analog SiPMs as candidate photodetectors for future RICH detectors

In the next generation of experiments in high energy particle physics a large increase in beam interaction density will necessitate upgrades of particle detectors. Examples are the Ring imaging Cherenkov detectors (RICH) in the planned upgrades of the LHCb, Belle II and ALICE 3 experiments. The upgraded RICH detectors will need photodetectors capable of detecting rings of Cherenkov photons at high rates of true and background events as well as large background radiation. Silicon photomultipliers (SiPMs) are an attractive photodetector candidate, with the main remaining technological challenge being the resistance to neutron radiation damage — during the whole experiment run time, the photodetectors are expected to receive a fluence of a few 1013 1-MeV neutron equivalent/cm2. To achieve the targeted radiation tolerance, as well as other RICH detector requirements, dedicated developments and a combination of radiation damage reduction and mitigation techniques, such as cryogenic cooling, are needed. The spadRICH project is developing a CMOS single-photon avalanche diode (SPAD) based photodetector optimized for the application of the planned RICH detectors, with SPADs designed specifically for radiation hardness and cryogenic operation. In this work, we report on dark count rate measurements of SPADs designed by the AQUA Lab in 55 nm BCD technology and 110 nm CMOS image sensor technology, performed down to liquid nitrogen temperatures and for neutron irradiation up to 1012 1-MeV neutron equivalent/cm2.