Physicists from the MicroBooNE (Micro Booster Neutrino) collaboration have ruled out the existence of a single sterile neutrino with a 95% probability.
Using data from the MicroBooNE detector, physicists report one of the first searches for sterile neutrinos using two accelerator neutrino beams. Image credit: Gemini AI.
Neutrinos are tiny subatomic particles that have little or no interaction with matter. They can pass through planets without stopping.
The Standard Model of particle physics states that there are three types of neutrinos: electron, muon, and tau.
These particles can change from one type to another, a process called oscillations.
But in past experiments, researchers saw neutrinos that appeared to change in ways that were inconsistent with the Standard Model.
To explain this, scientists have proposed a fourth type: the sterile neutrino. Unlike the others, it will be even more difficult to detect since it will not interact with matter at all except through gravity.
“The existence of three different varieties of neutrinos 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 steering group, and colleagues.
“Quantum mechanical interference may allow neutrinos from one original flavor to be detected later as another flavor. This process is called neutrino oscillation.”
“Several anomalous observations inconsistent with this three-color picture have given rise to the hypothesis that there is an additional state of neutrinos that does not interact directly with matter, called the 'sterile' neutrino.”
In their experiments, MicroBooNE physicists observed neutrinos from two different beams and measured how they oscillated.
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 the strange behavior of neutrinos.
“This result is a turning point,” Dr. Mastbaum said.
“This result will spark innovative ideas in neutrino research that will help us understand what's really going on.”
“We can rule out a major suspect, but that doesn't quite solve the mystery.”
“The standard model doesn't explain everything, including dark matter, dark energy or gravity, so scientists are looking for clues 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).
“Through careful modeling and clever analysis approaches, the MicroBooNE team squeezed an incredible amount of information out of this detector,” said Dr. Mastbaum.
“In next-generation experiments like DUNE, we are already using these techniques to address even more fundamental questions about the nature of matter and the existence of the universe.”
teams results were published in the magazine Nature.
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MicroBooNE collaboration. 2025. Search for light sterile neutrinos with two neutrino beams on MicroBooNE. Nature 648, 64–69; two: 10.1038/s41586-025-09757-7
