Clues to the origin of matter

A third type of neutrino oscillation may explain why all the antimatter in the universe has disappeared.

Scientists in the UK and Japan believe they have witnessed previously unseen behaviour in subatomic particles, which could explain why the universe contains very little antimatter.

There are three types of neutrinos: the electron neutrino which pairs with electrons and two more paired with the electron’s heavier cousin the muon and tau leptons. Neutrinos have the ability to spontaneously transform into each other – a process known as neutrino oscillation.

Two types of oscillation have been confirmed but researchers working on the T2K neutrino experiment believe they have observed indications of a third type. They say their result is not statistically significant to confirm new physics, but there is a strong indication.

“People sometimes thinks that scientific discoveries are like light switches that click from ‘off’ to ‘on’, but in reality it goes from ‘maybe’ to ‘probably’ to ‘almost certainly’ as you get more data,” said Professor Dave Wark from Imperial College London.

“Right now we’re somewhere between ‘probably’ and ‘almost certainty’.”

Scientists fired a beam of neutrons from the J-PARC lab at Tokai Village on the Eastern Coast of Japan, and detected them at the Super-Kamiokande neutrino detector 295km away in the mountains of the north-west.

They were looking to see if the neutrinos at the end of the beam matched those emitted at the start – they expected to see an average of between one and two oscillations, but found six electron neutrinos in the beam of muon neutrinos. This indicated a third type of oscillation, and researchers believe they have now observed neutrinos oscillating in every way they expect possible.

The results mean that it is possible that neutrinos oscillate in a different way to their antimatter particles – antimatter neutrinos – if proven true; it might explain how antimatter has disappeared from the universe.