Sterile neutrino existence rejected

Scientists have dismissed the existence of sterile neutrinos after the analysis of hundreds and thousands of subatomic particles at the South Pole.

Neutrinos are one of the fundamental particles that make up the universe and exist in three different flavours — muon, electron and tau. Neutrinos intermittently change flavours as they travel. Electrically neutral, they can be created in a number of different ways, from nuclear reactions in stars to certain types of nuclear decay.

Some scientists also theorise there is another neutrino flavour — sterile. They believe it could have different properties compared to the other three flavours of neutrino and may help solve a wide number of particle physics questions.

Jason Koskinen, assistant professor at the University of Copenhagen and a co-author of the study, said: “One or more types of sterile neutrinos could help solve a number of mysteries, such as why there is more matter than antimatter in the universe. A sterile neutrino could provide an explanation for this imbalance, which currently cannot be explained by the three known neutrinos. A sterile neutrino with gravity could also shed light on the mysterious dark matter.”

Currently situated in the Antarctica, with more than 5,000 sensors bured under the ice, is a detector called IceCube. Although not its primary purpose, researchers realised they could use the detector to try and discover sterile neutrinos. The detector analysed neutrinos that had travelled through space before journeying 13,000km from the North to South Pole.

Koskinen, who is also team leader of the IceCube international research team on neutrino oscillations, said: “We know of three neutrino types and our international team of researchers has been looking for signals from a fourth neutrino type, the so-called sterile neutrinos. For years, there has been a global mystery about the existence of a sterile neutrino with a mass of about 1 eV. If it existed, it would produce a clear signal at a certain energy interval, but we have not seen a single signal that could come from such a sterile neutrino.”

However some scientists still harbour hope of finding sterile neutrinos, albeit at a much more specific energy range.

David Schmitz, an Assistant Professor of Physics from the University of Chicago, commenting on the research, said: “IceCube’s finding places strong limits on the possible existence of a sterile neutrino. In fact, a new analysis incorporating IceCube’s result with data from other experiments indicates that the value of the possible sterile-neutrino mass splitting is now limited to a small region around 1 to 2 eV².”

The study was published in Physical Review Letters.