Oscillating Neutrinos: The 2015 Physics Nobel Prize

On the 6th October 2015 researchers Takaaki Kajita (University of Tokyo) and Arthur McDonald (Queen’s University, Canada) won the 2015 physics Nobel prize for there career long research into the unusual behavior of the fundamental Leptonic particle the Neutrino. The standard model of particle physics predicts the existence of three flavours of Leptons the electron, the muon and the tauon. Each of these particles have a corresponding neutrino ,which have been known to exist from the early analysis of decaying radioactive material in Nuclear power plants.

Since the discovery of these sub-atomic particles one thing that has become obvious is that they have a tiny mass. In fact for a long time many scientists believed that the particle could even be massless in existence, as would be predicted from the Standard model.

At the turn of the millennium, under a mountain in Japan, Kajita was using the Super-Kamiokande detector to hunt for neutrinos. This detector is located 1km underground and contains 50,000 tonnes of ultra-pure water in which the rare interactions of neutrinos are recorded. Meanwhile McDonald and his research team were using a similar detector (Sudbury Neutrino Observatory) in Canada to also hunt for these elusive particles.

Once these experiments had managed to detect a statistically significant number of interactions it became apparent that there was a strange effect at work. Kajita’s team were finding that neutrinos from the Earth’s atmosphere appeared to switch their identities on the way to the detector. Also McDonald’s team were observing that a particular species of neutrinos from Sun had a population deficit of ~2/3rds.

The reason for this mysterious activity is the new physics that neutrinos can readily oscillate between flavours. This discovery is a great breakthrough and a thoroughly deserved Nobel winner. Not only is it an interesting and fundamental physics process in it’s own right but it has further implications. The process of flavour oscillation requires that the neutrinos must have varying mass eigenstates, implying that neutrinos do indeed have masses. This has been observed but also is not inline with what would be expected from the standard model and therefore a review of the fundamental laws of particle physics is required.

Evidence of deviations from the standard model pave the path for further discoveries such as a potential further fundamental particle (or group of particles) which would constitute the missing mass in the Universe, dark matter.


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