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A study of the detector response of PbF 2 crystals and three different types of lead glass blocks to electrons from a 14-MeV beam of the Mainz Microtron MAMI is presented. For the first time, signal height, signal width, and homogeneity of the response of these Cherenkov radiators were determined for energies between 10 and 14 MeV. To complement the beam tests, optical properties of the materials, in particular measured transmittances in the near UV and visible spectrum, were studied. The measured detector responses were also compared to Monte Carlo simulations of energy-loss, light production, transport, and detection. These Cherenkov radiators are considered as active material of a low-energy calorimeter for the detection of light dark matter particles recoiling off electrons behind the beam-dump of the Mainz Energy Recovering Superconducting Accelerator MESA. [ABSTRACT FROM AUTHOR]

At the Institute for Nuclear Physics in Mainz the new electron accelerator MESA will go into operation within the next years. The high-power beam dump of the P2 experiment is ideally suited for a parasitic dark sector experiment — DarkMESA. In the first stage 1,000 high density Cherenkov radiators from a previous experiment will be used. The experiment is studied with a simulation based on MadGraph and Geant4. The simulation includes an optical photon study, where the response of possible calorimeter materials – PbF 2 , BGO, the Pb glasses SF5, SF6 and SF57HTultra from Schott – was investigated. The simulation outcomes are compared with the results of prototypes tested at the Mainz Microtron (MAMI) with 6 to 14 MeV electrons. The exclusion limits for PbF 2 are shown, together with the limits obtained incrementally adding Pb glass blocks in two successive phases. The current development status of a prototype detector will be described, including a concept for a cosmics veto system. [ABSTRACT FROM AUTHOR]