Radiation Damage of Optical Components In Scintillator Detectors: from ATLAS/LHC Tile Calorimeter To Future Experiments

Precision measurements at modern and future collider experiments rely on robust hadronic calorimeters. The ATLAS Tile Calorimeter (TileCal), a sampling hadronic calorimeter at the Large Hadron Collider (LHC), uses plastic scintillating tiles as an active medium to produce light when an ionizing particle passes through. This light is collected via wavelength-shifting fibres and read out by photomultiplier tubes (PMTs). TileCal has been in operation since the LHC started providing proton collisions in 2008, and has demonstrated excellent performance throughout all data-taking periods. The High Luminosity LHC (HL-LHC) phase will extend detector operation beyond its ori ginal design, increasing its radiation exposure. The scintillators degrade with radiation and cannot be replaced, so understanding and predicting their light output loss is important. Besides providing valuable guidelines for mitigation strategies for TileCal, this also offers important guidance for fu ture facilities such as the Future Circular Collider (FCC). To maintain good performance, TileCal has multiple calibration systems. In this work, the laser calibration constants were computed on a weekly basis during 2023 and 2024. In addition, a comparative study of the legacy and new PMT models for the upgrade was performed, revealing a good stable response in the new model. The laser and caesium system data are used to disentangle the individual responses of the optical compo nents, enabling a study of their relative light output evolution from 2018 to 2024. Extrapolations to the HL-LHC phase are presented considering dose and dose rate effects. Moreover, simulations of a high-granularity scintillator-based calorimeter following the TileCal design for the FCC-ee were performed. Studies covering various geometrical configurations, including different depths, seg mentation, granularity, and absorbers composition were carried out to evaluate energy resolution performance. Together, the results presented in this thesis provide a degradation model for TileCal and design guidance for scintillator-based calorimetry at future lepton colliders.