In a remarkable stride forward in neutrino physics, researchers at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg have successfully detected antineutrinos stemming from a nuclear reactor using a compact detector weighing just 3 kilograms. This groundbreaking result stems from the advanced CONUS+ experiment deployed at the Leibstadt nuclear power plant (KKL) in Switzerland. The achievement is particularly notable, given the elusive nature of neutrinos—elementary particles that scarcely interact with matter and pass through the Earth in extraordinary numbers every second without leaving a trace.
Neutrinos, among the most abundant particles in the universe, have mystified physicists since their existence was hypothesized nearly a century ago. These particles’ ghostly nature demands experimental setups of colossal scale and complexity to capture even a handful of interactions. In contrast to these massive detectors, CONUS+ demonstrates pioneering sensitivity and precision with a detector volume diminutive enough to fit on a tabletop. The experiment leverages germanium semiconductor detectors, which, after notable improvements, have reached a mass of 3 kilograms and exceptional sensitivity, enabling a novel observation.
What sets the CONUS+ experiment apart is its ability to directly observe a phenomenon first predicted in the 1970s—Coherent Elastic Neutrino-Nucleus Scattering (CEvNS). In CEvNS, rather than neutrinos interacting with individual protons or neutrons within the nucleus, they scatter coherently with the entire atomic nucleus as a whole. This coherence markedly amplifies the probability of interaction, albeit the nuclear recoils remain minuscule, making detection a formidable challenge. To illustrate, this recoil can be likened to the subtle movement of a large vehicle upon being gently bounced by a small ball, symbolizing the tiny energy transfer during neutrino scattering.
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The CONUS+ apparatus is strategically situated just 20.7 meters from the core of the Leibstadt reactor, where an immense flux of neutrinos, amounting to over 10 trillion per square centimeter per second, permeates the environment. This proximity ensures a dense field of low-energy neutrinos, ideal for triggering CEvNS events. Spanning approximately 119 days of data collection between late 2023 and mid-2024, the experiment meticulously recorded neutrino interactions amidst significant background noise, eventually identifying an excess of 395 ± 106 neutrino-induced signals after rigorous background subtraction.
These results harmonize remarkably well with theoretical predictions, affirming not only the experiment’s sensitivity but also bolstering confidence in the existing theoretical framework describing neutrino interactions. Dr. Christian Buck, one of the study’s principal investigators, underscores the significance by noting that CONUS+ has verified its capability to detect antineutrino scatters off entire atomic nuclei with unprecedented precision. This milestone opens the door for the development of compact, potentially mobile neutrino detectors capable of real-time monitoring of nuclear reactors’ operational status, such as heat output and isotope composition.
Historically, the first empirical confirmation of CEvNS came relatively recently, in 2017, through the COHERENT experiment, which utilized a particle accelerator as a neutrino source. The CONUS+ experiment advances this frontier by achieving the first observation of CEvNS at full coherence from a nuclear reactor’s lower-energy neutrino flux. This accomplishment reflects substantial enhancements in detector technology, notably the increased mass and improved noise suppression capabilities of germanium detectors, alongside the advantageous experimental environment afforded by the KKL facility.
Beyond applied monitoring, the CEvNS measurement probes fundamental aspects of particle physics within the Standard Model—the bedrock theory explaining the universe’s known particles and forces. Unlike many neutrino experiments, CEvNS facilitates interaction measurements less influenced by complex nuclear physics uncertainties, refining the experimental sensitivity to potential new physics phenomena that lie beyond the Standard Model. The CONUS+ collaboration anticipates that these capabilities will catalyze further exploratory studies aiming to uncover subtle signs of physics yet unseen.
In anticipation of enhancing these scientific vistas, the CONUS+ experiment underwent an equipment upgrade in autumn 2024, incorporating larger and more sensitive detectors to augment measurement precision and data quality. These improvements promise to yield even more compelling results and facilitate more exacting tests of theoretical models. Project initiator Prof. Lindner emphatically states that the methodologies refined in CONUS+ have enormous potential to initiate transformative discoveries in neutrino science, heralding a fresh era of research on these enigmatic particles.
From a technical perspective, the germanium semiconductor detectors employed in CONUS+ operate by discerning the faint nuclear recoil energies deposited during neutrino interactions. Achieving the necessary low background conditions to isolate these rare events requires meticulous shielding from cosmic rays and ambient radioactivity. The deployment in Leibstadt benefits from such stringent background control, enabling detection thresholds sufficiently low to register the subtle signals attributed to CEvNS.
Moreover, the CONUS+ experiment’s compactness and proximity to the reactor core allow for high-statistics data acquisition without necessitating extensive infrastructure. This practical advantage suggests that CEvNS detection technology could revolutionize nuclear safeguards and reactor monitoring. Real-time neutrino flux measurements could become an invaluable non-invasive tool for confirming reactor status and fuel composition, augmenting current verification techniques with unparalleled fidelity.
The success of CONUS+ also reinvigorates interest in low-energy neutrino physics, an area that has traditionally grappled with low interaction rates and formidable experimental complexity. As low-threshold detectors evolve, future deployments may extend beyond reactors to applications in geophysics, astrophysics, and even neutrino-based communication technologies, illustrating the broad scientific impact anticipated from these advances.
In summary, the CONUS+ experiment breaks new ground by successfully detecting coherent elastic scattering of reactor antineutrinos using a remarkably small germanium detector. This result not only validates decades-old theoretical predictions but also accelerates the path toward practical applications and novel physics discovery. As the experiment progresses with enhanced sensitivity, it promises to deepen our understanding of neutrino properties, strengthen nuclear monitoring capabilities, and potentially unveil new physics phenomena lurking within the neutrino sector.
Subject of Research: Not applicable
Article Title: Direct observation of coherent elastic antineutrino–nucleus scattering
News Publication Date: 30-Jul-2025
Web References: http://dx.doi.org/10.1038/s41586-025-09322-2
References: Article published in Nature, DOI: 10.1038/s41586-025-09322-2
Image Credits: MPIK
Keywords
Neutrinos, Antineutrinos, Coherent Elastic Neutrino-Nucleus Scattering, CEvNS, CONUS+, Germanium Detectors, Nuclear Reactor Neutrinos, Particle Physics, Standard Model, Neutrino Detection, Nuclear Monitoring, Experimental Physics
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