Characterization of Avalanche Photodiodes for the CMS Electromagnetic Calorimeter

The CMS Electromagnetic Calorimeter (ECAL) is crucial for precision measurements of the energies of electrons and photons. The ECAL is a homogeneous detector made up of 61,200 crystals in the central barrel region and 15,000 crystals in the endcaps. Avalanche Photodiodes (APDs) serve as the photodetectors for the ECAL barrel, converting scintillation light from lead tungstate crystals into electrical signals. In preparation for High Luminosity (HL) LHC, the APDs (both irradiated and non-irradiated) have been characterized in terms of their gain and dark current properties.