First Observation of a Nuclear Recoil Peak at 𝒪(100eV) with CRAB: A Potential New Calibration Standard for Cryogenic Detectors

Abstract

Any experiment aiming to measure rare events, like Coherent Elastic neutrino-Nucleus Scattering (CE ν NS) or hypothetical Dark Matter scattering, via nuclear recoils in cryogenic detectors relies crucially on a precise detector calibration at sub-keV energies. The Crab collaboration developed a new calibration technique based on the capture of thermal neutrons inside the target crystal. Together with the Nucleus experiment, first measurements with a moderated ²⁵²Cf neutron source and a cryogenic CaWO4 detector were taken. We observed for the first time the 112eV peak caused by the ¹⁸²W(n, γ ) ¹⁸³W capture reaction and subsequent nuclear recoils. Currently, Crab is preparing a precision measurement campaign based on a monochromatic flux of thermal neutrons from the 250-kW Triga-mark II nuclear reactor at TU Wien. In this contribution, we introduce the Crab technique, present the first measurement of the 112eV peak, report the preparations for the precision measurement campaign, and give an outlook on the impact on the field of cryogenic detectors.