The CRAB (Calibrated nuclear Recoils for Accurate Bolometry) project aims to precisely measure the response of cryogenic detectors to sub-keV nuclear recoils, which are central to cryogenic coherent elastic neutrino–nucleus scattering (CEνNS) and light dark-matter searches. The technique is based on thermal-neutron capture within the detector material, creating a nuclear recoil of well-defined energy accompanied by γ emission detected in coincidence – we do see single atom recoils! The main setup, installed at the TRIGA Mark-II reactor in Vienna, delivers a clean, low-intensity thermal-neutron beam to cryogenic detectors operated in a dilution refrigerator, surrounded by a crown of BaF₂ γ-detectors for gamma tagging. A complementary test setup also exists at TU Munich, providing flexibility for detector characterization and development.

At MPIK, our group is involved in the data analysis from CaWO₄ (calcium tungstate) and Al₂O₃ (sapphire) detectors. We develop a dedicated software framework CryoLab, designed for full waveform reconstruction, noise analysis, pulse-shape analysis and comparison to thermal model, and the identification of capture-induced events – the so-called CRAB peaks! Current studies include the characterization of TES-based sensors and the connection to crystal-lattice defect formation, which affect the partition of energy and hence the energy reconstruction accuracy. We recently submitted our discovery of the CRAB single atom recoil peak in sapphire.