Neutrinos are tiny particles that pass through the planet's bulk like light through a windowpane. Every second, billions of them fly through your pinky fingernail, but catching even one is no easy feat. To do it, scientists dug a two-kilometer-deep mine in Canada and installed the SNO+ detector. The depth is needed to hide from cosmic rays, which create interference.
Inside the detector is a huge sphere filled with liquid scintillator. When a neutrino collides with an atom, a faint flash of light occurs, and instruments record it. Over 685 days of observations (from May 2022 to July 2025), scientists gathered enough flashes to measure how neutrinos change type in flight. It's like a traveler picking up an accent: you leave with one, and arrive with another. The researchers determined how quickly this transformation happens.
Additionally, SNO+ caught geoneutrinos, particles born from the decay of radioactive elements inside the Earth, for the first time in the Western Hemisphere. Their flux was 49 units (with an uncertainty of plus or minus 12–13). It's like hearing the faint hum of an engine buried deep underground: now we know that nuclear reactions really are happening inside our planet.
as written by the authors arXiv:2604.05746
SNO+ is a multipurpose liquid-scintillator neutrino detector located 2 km underground at SNOLAB, Canada. Three large nuclear reactors at baselines of 240-350 km allow a precise measurement of the neutrino oscillation parameter $$\Delta m^2_{21}$$ and, to a lesser extent, $$\theta_{12}$$. A spectral analysis is performed, simultaneously fitting $$\Delta m^2_{21}$$, $$\theta_{12}$$, the reactor antineutrino flux, background rates, and associated systematics. Using data collected between May 2022 and July 2025, corresponding to a livetime of 685 days, a value of $$\Delta m^2_{21} = (7.93^{+0.21}_{-0.24}) \times 10^{-5}$$ eV$$^2$$ is obtained. This result is compatible with other long-baseline reactor antineutrino measurements by KamLAND and JUNO. SNO+ has also made the first measurement of the geoneutrino flux in the Western Hemisphere, measuring $$49^{+13}_{-12}$$ TNU, in agreement with predictions from geological models.
Every second, about 60 billion neutrinos emitted by the Sun pass through each square centimeter of your body, but over a lifetime, only one or two of those neutrinos will actually stop in your body.