Dr Kirsty Duffy, Fellow in Physics at Queen’s and senior Physics Coordinator of the international MicroBooNE collaboration, has played a leading role in a breakthrough that rules out the existence of a long-hypothesised fourth neutrino.
Published this week in Nature, the findings narrow the search for new physics and close one of the most persistent puzzles in particle physics.
MicroBooNE, based at the US Department of Energy’s Fermilab, set out more than a decade ago to investigate anomalies that had hinted at the possible existence of a “sterile neutrino”, a new type of particle that, if discovered, would reshape our understanding of the universe.
The new analysis shows no evidence for such a particle at a 95% confidence level, eliminating the most widely discussed explanation for the anomalous behaviour seen in earlier experiments.
As Physics Coordinator, Dr Duffy holds the most senior physics leadership position in the collaboration. The decade-long sterile-neutrino analysis was conducted during her tenure and she developed the neutrino-interaction uncertainty model used in the analysis.
Dr Duffy said:
Neutrino physics has long been an area with fantastic potential for discovery science. Previous neutrino discoveries have turned our understanding of particle physics on its head, and various anomalous results from previous experiments have garnered a lot of interest within the community, as they could be interpreted as evidence for a new type of neutrino called a “sterile neutrino”. This is what MicroBooNE was built to investigate and it’s really exciting to publish the results of this over-a-decade-long search.
We see no disagreement with the Standard Model of Particle Physics, so we rule out the simple sterile neutrino explanation of previous anomalies at 95% statistical confidence level.
It’s also a huge demonstration of the power of liquid argon neutrino detectors to do precision measurements, which is what we’ll do with DUNE in the next decade. This is a huge step forward and means there’s even more exciting prospects to come from these experiments.
What MicroBooNE discovered
Neutrinos, sometimes dubbed “ghost particles”, are among the most abundant particles in the universe but interact so weakly with matter that trillions pass through our bodies every second.
The Standard Model describes three types (“flavours”) of neutrinos: electron, muon and tau. Some past experiments had observed behaviour that didn’t fit this framework, leading to speculation that a fourth, more elusive “sterile” neutrino might exist.
MicroBooNE provided the most sensitive test yet: it used a state-of-the-art liquid-argon detector, collected data over six years, and, crucially, analysed neutrinos from two different beams in the same detector – a major innovation that strengthened the test of the theory.
By combining these beams, the collaboration has now shown that the simplest sterile-neutrino model cannot explain previous anomalies.
Why this matters
Ruling out the simplest sterile-neutrino model sharpens the search for new physics, closes one of the most persistent questions raised by earlier experiments, and provides vital information for future international projects such as the Deep Underground Neutrino Experiment (DUNE), where Dr Duffy and Oxford researchers will again play a significant role.
Watch Dr Kirsty Duffy explain the result
A short explainer video from Dr Duffy:
