MicroBooNE Results Add to the Mystery of Sterile Neutrinos

By Atif SuhailReviewed by Louis CastelJan 30 2026

The MicroBooNE experiment at Fermilab has spent years scrutinizing neutrino interactions and has not uncovered definitive evidence for sterile neutrinos, hypothetical particles once thought to be a natural explanation for puzzling anomalies in earlier neutrino data.¹

Image Credit: kakteen/Shutterstock.com

High-profile results released in December 2025, including a landmark Nature publication, show no statistically significant signals from sterile neutrino oscillations across multiple channels and neutrino beams. Rather than dispelling the short-baseline neutrino enigma stemming from LSND and MiniBooNE, these null findings intensify it, constraining models while opening doors to alternative interpretations.²

Background & Context

Sterile neutrinos are hypothetical neutral particles that, unlike ordinary neutrinos, do not interact via the weak nuclear force and couple at most through gravity and mixing with active flavours. They were introduced to extend the Standard Model, motivated by the fact that neutrinos have mass, by hints from oscillation data, and by the theoretical expectation that right-handed neutrinos should exist even if they are invisible to known forces.³

Because of these properties, sterile neutrinos are compelling dark matter candidates, can help explain how active neutrinos acquire mass, and might reconcile anomalies reported by accelerator, reactor, and radioactive-source experiments.³

The short-baseline anomaly largely traces back to two accelerator experiments: LSND at Los Alamos and MiniBooNE at Fermilab. LSND (1990s) observed a 3.8σ excess of electron antineutrinos in a muon antineutrino beam, while MiniBooNE (2002–2019) later reported a 4.8σ excess of low-energy electron-like events in both neutrino and antineutrino modes, together amounting to a 6.1σ deviation from three-flavor expectations.³

These excesses can be modeled as oscillations involving a fourth, mostly sterile neutrino with mass-squared splittings around the eV scale, but this interpretation conflicts with disappearance data and with cosmological bounds on the total neutrino mass.³

Against this backdrop, MicroBooNE was conceived as a next-generation, high-resolution test on the same beamline as MiniBooNE, specifically to interrogate those unexplained electron-like events.³

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The MicroBooNE Experiment

MicroBooNE uses a Liquid Argon Time Projection Chamber (LArTPC), in which neutrinos interact with argon nuclei, producing charged particles whose ionization tracks and scintillation light are recorded with fine granularity. In such a detector, an electric field drifts ionization electrons toward wire planes while photomultiplier tubes capture the prompt light, allowing three-dimensional reconstruction of interaction topologies and precise calorimetric measurements.^4-5

This technology represents a major step beyond MiniBooNE’s oil-Cherenkov design, which could not reliably distinguish electrons from photons, a crucial capability when trying to determine whether an excess is truly electron-like or due to misidentified gamma-induced showers.⁴

Situated in the Fermilab Booster Neutrino Beam at about 470 m from the target, roughly the same baseline as MiniBooNE, MicroBooNE is one of three LArTPCs in the Short-Baseline Neutrino (SBN) program alongside SBND (near) and ICARUS (far).⁴

It has been running since 2015, collecting accelerator neutrino data that both probe the sterile-neutrino hypothesis and serve as a technology pathfinder for larger liquid-argon detectors. The design explicitly targets detailed event classification (single electrons, single photons, e?e? pairs) to test the different ways MiniBooNE’s low-energy excess might arise.⁵

Key Findings

MicroBooNE has released several major analyses focused on the low-energy region where MiniBooNE saw its excess, including searches for single-electron charged-current events, single-photon final states, and e?e? topologies, as well as ν_μ disappearance channels.⁴

Using these complementary approaches, the collaboration examined whether the MiniBooNE excess could be explained by misreconstructed photons, by electron-neutrino appearance from oscillations, or by more exotic multi-body final states.⁴

The key outcome is that none of these analyses finds a statistically significant excess consistent with sterile-neutrino–induced ν_μ → ν_e oscillations; in particular, MicroBooNE excludes interpreting the MiniBooNE low-energy excess as simple ν_e appearance at more than 99% confidence level.⁴

These null results place strong constraints on the simplest 3+1 sterile neutrino models that were designed to fit LSND and MiniBooNE, since the same parameters that would generate the MiniBooNE excess would also have produced a clearly visible signature in MicroBooNE’s high-resolution LArTPC.⁴

However, the constraints do not completely rule out all sterile neutrino scenarios, and more complicated models, such as heavy decaying sterile neutrinos that mimic LSND and MiniBooNE via decay into an electron neutrino and a light scalar, remain viable and are being actively tested in other setups like the Deep Underground Neutrino Experiment (DUNE) near detector.⁶

The tension between MicroBooNE’s null result and MiniBooNE’s excess raises the possibility that some combination of unknown backgrounds, nuclear effects, or detector-specific systematics may be at play in the older experiment rather than a straightforward oscillation signal.⁶

Scientific Significance

For the Standard Model, MicroBooNE’s findings reinforce the robustness of the three-flavour oscillation framework, which already explains solar, atmospheric, reactor, and long-baseline accelerator data extremely well.⁷

They show that at least the most straightforward eV-scale sterile neutrino explanation of the LSND/MiniBooNE anomalies is disfavoured, tightening the allowed parameter space and constraining any extension that adds light sterile states mixing strongly with active flavours.⁷

At the same time, the persistence of the anomalies themselves pushes theorists toward more intricate possibilities, such as heavy decaying sterile neutrinos, secret interactions that alter early-universe constraints, or scenarios involving dark sectors and additional scalar fields.⁷

The heavy decaying sterile neutrino (HDSN) scenario discussed in recent theory work provides a concrete illustration of this shift. In that framework, a fourth, mostly sterile neutrino ν4 with keV–MeV mass mixes weakly with ν_μ and decays into ν_e plus a light scalar ?, producing electron-like signals without the strong disappearance and cosmological signatures that plague light eV-scale steriles.³

Industry and Technology Implications

MicroBooNE has been central to maturing LArTPC technology, which is now a key component of next-generation neutrino physics. The experiment has driven advances in cryogenic engineering, low-noise electronics, high-voltage systems, and photodetection, while also catalyzing sophisticated reconstruction software and pattern-recognition methods that rely on modern machine learning.⁸

Many of these developments have relevance beyond particle physics, for example in radiation monitoring, nuclear security, and potentially in medical imaging and proton-therapy beam diagnostics, where fine-grained tracking and calorimetry are valuable.⁸

The industrial ecosystem around liquid-argon detectors includes firms and laboratories involved in cryostats, purification systems, and photomultiplier or silicon-photomultiplier technologies, often in partnership with large experiments.⁸

MicroBooNE’s experience feeds directly into the design and optimization of the DUNE, whose far detectors in South Dakota will be massive LArTPCs aiming to measure CP violation and mass ordering, among other goals. The same near-detector complex examined in the HDSN study will also act as a precision instrument for cross-sections and fluxes, strengthening the physics reach of both DUNE and the broader neutrino community.^{6, 8}

What’s Next?

The full Short Baseline Neutrino Program at Fermilab, which includes SBND, MicroBooNE, and ICARUS, is designed to give a decisive test of short baseline anomalies by comparing spectra at multiple distances using the same beam and closely related detector technology.²

As SBND and ICARUS gather more data, combined analyses with MicroBooNE will improve sensitivity to both appearance and disappearance channels and allow more precise checks of backgrounds and detector effects, sharpening efforts to revisit the MiniBooNE excess with more powerful tools and to determine whether it is due to exotic physics, overlooked hadronic or nuclear processes, or limitations of the earlier Cherenkov detector.⁴

Internationally, complementary searches at CERN, other European laboratories, and J PARC’s JSNS squared experiment probe sterile neutrinos from different angles, while DUNE’s liquid argon near detector is expected to test or exclude broad classes of non-oscillation explanations for LSND and MiniBooNE, making MicroBooNE’s null result less an endpoint and more a turning point toward more discriminating experiments and more nuanced theoretical models.²

References and Further Readings

1. Microboone Finds No Evidence for a Sterile Neutrino. Fermilab: December 3, 2025. https://news.fnal.gov/2025/12/microboone-finds-no-evidence-for-a-sterile-neutrino/
2. Search for Light Sterile Neutrinos with Two Neutrino Beams at Microboone. Nature 2025, 648, 64-69.
3. Eberly, B.; Lincoln, D., Sterile Neutrinos: Are They Real? The Physics Teacher 2022, 60, 248-253.
4. Walsh, K. M. Two Beams, One Detector, Most Precise Search for 'Sterile' Neutrinos. https://www.bnl.gov/newsroom/news.php?a=222313.
5. Microboone Experiment’s First Results Show No Hint of a Sterile Neutrino. https://www.symmetrymagazine.org/article/microboone-experiments-first-results-show-no-hint-of-a-sterile-neutrino?language_content_entity=und.
6. Chatterjee, S. S.; Lavignac, S.; Miranda, O., Testing the Heavy Decaying Sterile Neutrino Hypothesis at the Dune near Detector. Journal of High Energy Physics 2025, 2025, 1-25.
7. Abratenko, P.; Alrashed, M.; An, R.; Anthony, J.; Asaadi, J.; Ashkenazi, A.; Balasubramanian, S.; Baller, B.; Barnes, C.; Barr, G., Search for Heavy Neutral Leptons Decaying into Muon-Pion Pairs in the Microboone Detector. Physical review D 2020, 101, 052001.
8. Lalnuntluanga, R.; Pradhan, R.; Giri, A., Probing Neutrino-Nucleus Interaction in Dune and Microboone. Nuclear Physics B 2024, 1008, 116703.

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