Oxford Physicists Detect Solar 'Ghost Particles'

Physicists at the University of Oxford have achieved a significant breakthrough, recording the first observation of carbon-neutrino interactions, as announced by the University of Oxford on December 12, 2025. This landmark discovery, made using the SNO+ detector deep underground, marks a pivotal moment in particle physics.

The research team successfully observed solar neutrinos transforming carbon atoms into nitrogen, a reaction previously anticipated but never directly witnessed, according to a December 10, 2025 report by SciTechDaily. This achievement opens new frontiers in nuclear and particle physics, offering unprecedented insights into the universe's fundamental workings.

This novel method provides a new way to study rare atomic reactions using solar neutrinos, particles often dubbed "ghost particles" due to their elusive nature, EurekAlert! reported on December 10, 2025. Trillions of these neutrinos stream through our bodies every second, yet rarely interact with matter.

The breakthrough was led by researchers at Oxford, utilizing the SNO+ detector located two kilometers underground at SNOLAB in Sudbury, Canada, as detailed by the University of Oxford. This deep underground facility is crucial for shielding the experiment from cosmic rays and background radiation.

Lead author Gulliver Milton, a DPhil student at the University of Oxford's Department of Physics, stated that capturing this interaction is an extraordinary achievement, according to scitechdaily on December 10, 2025. He emphasized the rarity of the carbon isotope and the vast distances neutrinos travel from the Sun's core.

The findings, published in Physical Review Letters, lay the groundwork for future studies of similar low-energy neutrino interactions, the University of Oxford noted. This advancement is essential for a deeper understanding of stellar processes, nuclear fusion, and the evolution of the universe.

Co-author Professor Steven Biller of Oxford's Department of Physics highlighted that solar neutrinos can now be used as a "test beam" to study other rare atomic reactions, as reported by sciencedaily on December 12, 2025. This builds upon decades of solar neutrino measurements, including those from the SNO experiment.

• Neutrinos, often called "ghost particles," are among the most mysterious and abundant particles in the universe, originating from nuclear reactions like those in the Sun's core. Their detection is notoriously difficult because they rarely interact with other matter, as explained by SNOLAB in a December 14, 2025 release. This weak interaction means they can pass through vast amounts of material, including Earth, without leaving a trace.

• The SNO+ detector, an upgraded successor to the Nobel Prize-winning Sudbury Neutrino Observatory (SNO), played a critical role in this discovery. Located two kilometers underground in an active mine in Sudbury, Canada, its deep placement provides essential shielding from cosmic rays and background radiation that would otherwise obscure faint neutrino signals, according to the University of Oxford.

• The specific interaction observed involved a high-energy solar neutrino striking a carbon-13 nucleus, transforming it into radioactive nitrogen-13. This nitrogen-13 then decays approximately ten minutes later, a process identified using a "delayed coincidence" method, as detailed by Space Daily on December 11, 2025. This technique looks for two distinct flashes of light, allowing researchers to confidently distinguish real neutrino events from background noise.

• The data analyzed for this breakthrough was collected over a 231-day period, from May 4, 2022, to June 29, 2023. During this time, the SNO+ team identified 5.6 observed events, which is statistically consistent with the 4.7 events expected from solar neutrinos, confirming the validity of the observation, scitechdaily reported on December 10, 2025.

• This achievement builds upon the legacy of the original SNO experiment, which demonstrated that neutrinos oscillate between three types (electron, muon, and tau) on their journey from the Sun to Earth. This earlier work, led by Arthur B. McDonald, earned the 2015 Nobel Prize in Physics for solving the solar neutrino problem, according to SNOLAB staff scientist Dr. Christine Kraus in a December 14, 2025 statement.

• The SNO+ detector uses 780 tonnes of liquid scintillator within a 12-meter diameter acrylic sphere, monitored by nearly 10,000 photomultiplier tubes. This liquid scintillator, based on linear alkylbenzene, produces signals 50 times brighter than the heavy water used in the original SNO experiment, significantly enhancing its sensitivity to neutrino interactions, as described by Queen's University.

• The ability to precisely measure these rare interactions provides a new tool for probing the fundamental properties of neutrinos and their role in the universe. Researchers anticipate that this will lead to a better understanding of stellar evolution, element formation, and potentially new physics beyond the Standard Model, as noted by SciTechDaily on December 10, 2025.