Performance prospects for the CMS electromagnetic calorimeter barrel avalanche photodiodes for LHC phase I and phase II: Radiation hardness and longevity

The electromagnetic calorimeter of the Compact Muon Solenoid (CMS) experiment at the LHC is a hermetic, fine-grained, homogeneous calorimeter, comprising 75,848 lead tungstate scintillating crystals. Avalanche photodiodes produced by Hamamatsu are used as sensors for the electromagnetic barrel calorimeter. These devices were tested for radiation hardness assuming an integrated luminosity of 500 fb −1 , which corresponds to a neutron fluence of 2– 4×1013n/cm2 , depending on the detector location. Beginning in 2022, a new phase of the LHC is foreseen to exploit the full potential of the accelerator, which will deliver 3000 fb −1 of integrated luminosity. Irradiation studies up to a fluence of 1.5×1014n/cm2 have been performed to qualify the avalanche photodiodes for radiation hardness. We present measurements of gain, quantum efficiency and noise, and discuss the implications for the CMS electromagnetic barrel calorimeter performance.