💥 Physicists eliminate a major theory about neutrinos

Why do neutrinos, these elementary particles, sometimes seem to act in such a puzzling way? For decades, physicists have been faced with this puzzle, observing behaviors that do not fit with established theories.

One idea has long circulated to explain these anomalies: the existence of a sterile neutrino, a fourth variety that would hardly interact with matter. This hypothetical particle, if real, would escape direct detection and modify the oscillations of known neutrinos, offering a clue beyond the Standard Model (see below).


To test this hypothesis, the MicroBooNE experiment at Fermilab was implemented. It uses two neutrino beams and a very sensitive liquid argon detector, allowing it to track changes in neutrino type over a long period. Data accumulated over ten years were carefully analyzed.

The results, presented in Nature, clearly show the absence of a sterile neutrino. With a confidence level of 95%, researchers can rule out this possibility, redirecting efforts toward other explanations for the strange behaviors of neutrinos.

These methodological advances are essential for future experiments, such as DUNE. They will allow addressing deeper questions about the nature of matter and the foundations of the Universe, using proven approaches.

Thus, although a major lead has been eliminated, neutrino research continues. Scientists are now exploring other ideas to unravel the mysteries of these particles, with more powerful instruments and a refined understanding.

Neutrino oscillations

Neutrinos are very light subatomic particles that exist in three types: electron, muon, and tau. One of their remarkable properties is oscillation, where a neutrino can change type as it travels. This phenomenon was discovered in the late 20th century and showed that neutrinos have mass, contrary to what the Standard Model initially predicted.

Oscillation occurs because the mass states and flavor states of neutrinos are not aligned. Simply put, a neutrino produced as an electron can transform into a muon or tau over long distances. This ability to mutate would explain why detectors sometimes capture fewer neutrinos than expected.

Measuring oscillations is fundamental for testing particle physics theories. Understanding oscillations also helps explain cosmic phenomena, such as neutrino production in the Sun or supernovae. This opens windows into stellar evolution and the large-scale structure of the Universe.

The Standard Model and its limitations

The Standard Model is the fundamental theory that describes elementary particles and their interactions, except for gravity. It includes quarks, leptons such as neutrinos, and force bosons such as the photon. This framework has allowed the prediction and confirmation of many phenomena with great accuracy.

However, the Standard Model has significant gaps. It does not explain dark matter, that invisible substance influencing the rotation of galaxies. Furthermore, dark energy, responsible for the acceleration of the Universe's expansion, remains outside its predictions. Gravity itself is not satisfactorily integrated.

Neutrino research is one of the paths to go beyond this model. By studying their abnormal properties, physicists hope to find clues to new physics. The absence of a sterile neutrino, as shown by MicroBooNE, eliminates a popular extension but encourages exploring other theories.

Other leads include supersymmetry or extra dimensions. Future experiments will be able to test these ideas and perhaps revolutionize our understanding of reality.