Bold claim first: solar ghost particles can sculpt matter in surprising, measurable ways deep underground. Neutrino Alchemy: Sun’s Ghost Particles Transform Atoms, Now Seen in Action.
Researchers buried thousands of meters beneath the surface have finally witnessed solar neutrinos converting carbon-13 into nitrogen-13. This is the first verified instance of this rare, neutrino-driven nuclear reaction, revealing that these nearly massless, chargeless particles can quietly reshape matter far from the Sun, right here on Earth’s dark, subterranean stage.
Physicist Christine Kraus of SNOLAB in Canada explains that the study leverages the natural abundance of carbon-13 inside the experiment’s liquid scintillator to detect a very specific interaction. To our knowledge, this marks the lowest-energy observation of neutrino interactions on carbon-13 nuclei to date and provides the first direct cross-section measurement for this reaction ending in the ground state of nitrogen-13.
Neutrinos are among the cosmos’s most common inhabitants. They spring from high-energy events like supernovae and the fusion processes powering stars, so they’re everywhere. Yet they carry no electric charge, have vanishingly small mass, and interact only rarely with other matter. Countless neutrinos stream through our bodies and through Earth every moment, which is why they’re nicknamed ghost particles.
Most of the time, neutrinos pass through unimpeded. On the rare occasion they collide with a nucleus, they produce a fleeting flash of light and a spray of secondary particles. At Earth’s surface, however, background noise from cosmic rays and radiation makes such signals extremely difficult to discern.
That’s why some of the most sensitive neutrino detectors sit deep underground, where the Earth itself acts as a shield. Giant chambers lined with photodetectors and filled with a liquid scintillator amplify the faint signals from rare neutrino interactions, all hidden in near-total darkness.
Solar neutrinos, emitted from the Sun’s core, continuously traverse our planet. Their energies form a relatively narrow band that helps distinguish them from higher-energy atmospheric or astrophysical neutrinos. At SNOLAB’s SNO+ detector, located about 2 kilometers underground, the majority of detected events within this energy window originate from the Sun.
Led by Gulliver Milton of the University of Oxford, the team analyzed SNO+ data gathered between May 4, 2022, and June 29, 2023, hunting for a telltale signature of a neutrino interacting with carbon-13 in the scintillator fluid.
What happens in the interaction is twofold. When a solar electron neutrino strikes a carbon-13 nucleus, an electron is produced as the nucleus absorbs the neutrino. Carbon-13 contains 6 protons and 7 neutrons. The weak force driven by the neutrino converts one neutron into a proton, transforming the atom into nitrogen-13 and emitting an electron.
This nitrogen-13 now has 7 protons and 6 neutrons and is unstable, with a half-life of about 10 minutes. It decays by emitting a positron, a positively charged electron.
The whole process yields a characteristic delayed coincidence: an initial electron signal, followed roughly 10 minutes later by a positron. This two-step glow serves as the unmistakable signature of a neutrino converting carbon-13 into nitrogen-13.
From 231 days of data, the researchers identified 60 candidate events. After applying a statistical model, they estimated about 5.6 neutrino-induced carbon-13 to nitrogen-13 conversions, fairly close to the 4.7 events they expected to see.
“Capturing this interaction is an extraordinary achievement,” Milton notes. “Despite the rarity of carbon-13, we observed its interaction with neutrinos born in the Sun’s core and traveling vast distances to reach our detector.”
The finding matters because it confirms theoretical predictions and provides a fresh measurement of the probability for this specific low-energy neutrino–carbon reaction. This establishes a new benchmark for nuclear physics that will inform future work.
As Steven Biller of the University of Oxford puts it, solar neutrinos have long been a curiosity, and measurements from the predecessor SNO experiment helped earn the 2015 Nobel Prize in Physics. It’s remarkable that our understanding of solar neutrinos has advanced to the point where we can use them as a laboratory to study rare atomic processes.
The research is published in Physical Review Letters.
