Physicists with the MicroBooNE (Micro Booster Neutrino) Collaboration have ruled out the existence of a single sterile neutrino with 95% certainty.
Using data from the MicroBooNE detector, physicists report one of the first searches for a sterile neutrino using two accelerator neutrino beams. Image credit: Gemini AI.
Neutrinos are tiny subatomic particles that barely interact with matter. They can pass through planets without stopping.
The Standard Model of particle physics states there are three types of neutrinos: electron, muon and tau.
These particles can change from one type to another, a process called oscillation.
But in past experiments, researchers saw neutrinos that appeared to change in ways that didn’t fit the Standard Model.
To explain this, scientists proposed a fourth type: the sterile neutrino. Unlike the others, it would be even more difficult to detect because it wouldn’t interact with matter at all, except through gravity.
“The existence of three distinct neutrino flavors is a central tenet of the Standard Model of particle physics,” said Dr. Andrew Mastbaum, a physicist at Rutgers University and a member of the MicroBooNE leadership team, and colleagues.
“Quantum-mechanical interference can allow a neutrino of one initial flavor to be detected sometime later as a different flavor, a process called neutrino oscillation.”
“Several anomalous observations inconsistent with this three-flavor picture have motivated the hypothesis that an additional neutrino state exists, which does not interact directly with matter, termed as ‘sterile’ neutrino.”
In their experiments, the MicroBooNE physicists observed neutrinos from two different beams and measured how they oscillate.
After ten years of data collection and analysis, they found no sign of sterile neutrinos, closing the door on one of the most popular explanations for strange neutrino behavior.
“This result is a turning point,” Dr. Mastbaum said.
“This result will spark innovative ideas across neutrino research to understand what is really going on.”
“We can rule out a great suspect, but that doesn’t quite solve a mystery.”
“The Standard Model doesn’t explain everything, including dark matter, dark energy or gravity, so scientists are searching for clues that point beyond the model,” he added.
“Eliminating one possibility helps focus the search on other ideas that could lead to breakthroughs in understanding the Universe.”
The new result will also help future experiments, including the Deep Underground Neutrino Experiment (DUNE).
“With careful modeling and clever analysis approaches, the MicroBooNE team has squeezed an incredible amount of information out of this detector,” Dr. Mastbaum said.
“With the next generation of experiments, such as DUNE, we are already using these techniques to address even more fundamental questions about the nature of matter and the existence of the Universe.”
The team’s results were published in the journal Nature.
_____
MicroBooNE Collaboration. 2025. Search for light sterile neutrinos with two neutrino beams at MicroBooNE. Nature 648, 64-69; doi: 10.1038/s41586-025-09757-7