Neutrinos are extremely elusive elementary nuclear particles. Sixty billion of them stream from the sun through every square centimeter of Earth every second, which is transparent to them. They were detected decades after the first theoretical prediction of their existence. The experiments used to detect are usually extremely because of the very weak interaction of neutrinos with matter.
Researchers at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg have now succeeded in detecting antineutrinos from the reactor of a nuclear power plant using the CONUS+ experiment. CONUS+ has with a detector mass of just one and one third pounds. The new research work is published in the journal Nature.
The CONUS experiment was originally based at the Brokdorf nuclear power plant. In the summer of 2023, it was relocated to the Leibstadt nuclear power plant (KKL) in Switzerland in the summer of 2023. Improvements to the one-pound germanium semiconductor detectors, as well as the excellent measurement conditions at KKL, made it possible for the first time to measure what is known as Coherent Elastic Neutrino-Nucleus Scattering (CEvNS).
In this new process, neutrinos do not scatter off the individual components of the atomic nuclei in the detector, but rather scatter coherently off the entire nucleus. This significantly increases the probability of a very small but observable recoil of nuclear. This recoil caused by neutrino scattering is comparable to the effect of a ping-pong ball bouncing off a car. The new detector registers the changing motion of the nucleus.
In the case of CONUS+ experiment, the scattering partners are the atomic nuclei of the germanium. Detecting this effect requires low-energy neutrinos, such as those produced in large numbers in nuclear reactors.
The effect was predicted as early as 1974. However, it was first confirmed in 2017 by the COHERENT experiment at a particle accelerator. For the first time, the CONUS+ experiment has now successfully observed the effect at full coherence and lower energies in a nuclear reactor. The compact CONUS+ setup is located twenty-two yards from the reactor core. At this location, more than ten trillion neutrinos flow through every square centimeter of surface every second.
After approximately one hundred and nineteen days of measurement between autumn 2023 and summer 2024, the researchers were able to extract an excess of three hundred and ninety-five ± one hundred and six neutrino signals from the CONUS+ data, after subtracting all background and interfering signals. This value is in very close agreement with theoretical calculations, within the measurement uncertainty.
Dr. Christian Buck is one of the authors of the study. He explained, “We have thus successfully confirmed the sensitivity of the CONUS+ experiment and its ability to detect antineutrino scattering from atomic nuclei.” He also emphasizes the potential development of small, mobile neutrino detectors to monitor reactor heat output or isotope concentration as potential future applications of the CEvNS technique presented here.
The CEvNS measurement provides unique insights into fundamental physical processes within the Standard Model of particle physics which is the current theory describing the structure of our universe. Compared to other experiments, the measurements with the CONUS+ apparatus allow for a reduced dependence on nuclear physics aspects, thereby improving the sensitivity to new physics beyond the Standard Model. CONUS+ was equipped with improved and larger detectors in autumn 2024. With the increased measurement accuracy, even better results are expected.
Professor Manfred Lindner is the initiator of the project and also an author of the study. He said, “The techniques and methods used in CONUS+ have excellent potential for fundamental new discoveries. Groundbreaking CONUS+ results could mark the starting point for a new field in neutrino research.”