Coherent scattering of neutrinos on atomic nuclei (CEvNS) is an interaction of major relevance for fundamental research. The CONUS+ experiment aims to detect this interaction at nuclear power plants. Neutrinos can interact with matter in two ways: either on electrons in the atomic shell or on protons/neutrons in the nucleus. In the latter case, there is the possibility for the neutrino to 'coherently' scatter on the nucleus as a whole increasing the probability for the scattering process. Coherence requires that the neutrino has a long enough wavelength which translates into low energies. Since neutrinos only interact weakly with matter, the devices for neutrino detection are typically very large up to masses of kilo-tons. However, for the (CEvNS) channel a few kg are already sufficient to measure the elusive neutrinos using dedicated detectors with very low energy threshold!

The CEvNS detection requires a strong neutrino flux. The CONUS+ experiment is therefore operated close to the nuclear reactor at the Leibstadt power plant in Switzerland at a distance of 21 m to the core. An extremely high flux of 14 trillions of neutrinos per second and cm2 is available for the measurement. The CONUS+ experiment uses high-purity germanium semiconductor detectors sensitive to ionizing radiation. Several layers of shielding material with a total mass of 10 tons protect the detectors against external radioactivity. The  shielding design is based on the world-leading expertise established at MPIK over many decades. In January 2025 results from the first run of CONUS+ were published. A 3.7σ excess for the rare neutrino interaction process was found after 9 months of data acquisition. After the first data taking period, three new detectors with 2.4 times more mass were installed in November 2024 to enhance event rates and sensitivity.