Speaker
Description
The NUCLEUS experiment aims to measure CE$\nu$NS of reactor antineutrinos on tungsten nuclei. To do so, NUCLEUS deploys gram-scale CaWO$_\text{4}$ crystals as cryogenic calorimeters with an ultra-low nuclear recoil energy threshold of O(10) eV. The detectors are instrumented with Transition Edge Sensors (TESs), operated at ~10 mK, to read out the phonon signal directly.
The experiment is currently undergoing commissioning at its final site, the nuclear power plant of Chooz, where it will be located at respectively 72 and 102 meters from two 4.25 GW$_\text{th}$ reactor cores, which provide a ~$10^{12}$ $\nu$/cm$^2$/s electron antineutrino flux.
In the upcoming run, the detector array features four CaWO$_\text{4}$ crystals, each simultaneously read out with two TESs, for a total target mass of ~7 grams. Achieving a low nuclear recoil energy threshold with these detectors is critical for NUCLEUS, as it has a significant impact on the capability of the experiment to detect CE$\nu$NS and study the process at very low momentum transfer. To assess the performance of the array in a controlled environment, a 3-week data-taking campaign was carried out at the Cryolab of the Technical University of Munich in December 2025/January 2026 before the deployment of the detectors at Chooz.
In this poster, I will show the first results of the analysis of data acquired during this run, focusing on detector stability and performance, in particular at very low energies, and presenting implications for the Low Energy Excess.