Where did all the matter in the universe come from? This is one of the biggest mysteries in fundamental physics and exciting results released from the international T2K neutrino experiment in Japan could be an important step towards resolving this puzzle.
The T2K neutrino experiment has been conducted by a multinational team and the University of Liverpool’s Professor Christos Touramanis from the Department of Physics has project managed the UK team.
The intriguing results indicate a new property of the enigmatic particles known as neutrinos.
There are three types of neutrinos (called flavours) – one paired by particle interactions with the familiar electron (called the electron neutrino), and two more paired with the electron’s heavier cousins, the muon and tau leptons. Previous experiments around the world have shown that these different flavours of neutrinos can spontaneously change into each other, a phenomenon called “neutrino oscillation”.
Two types of oscillations have already been observed but in its first full period of operation, the T2K experiment has already seen evidence for a new type of oscillation (the appearance of electron neutrinos in a muon neutrino beam). This means that we have now observed that neutrinos can oscillate in every way possible.
This level of complexity opens the possibility that the oscillations of neutrinos and their anti-particles (called anti-neutrinos) could be different. And if the oscillations of neutrinos and anti-neutrinos are different, it would be an example of what physicists call CP violation. This could be the key to explaining why there is more matter than anti-matter in the universe (an excess which could not happen within the known laws of physics).
The experiment ran from January 2010 until 11 March this year, when it was dramatically interrupted by the Japanese earthquake. Fortunately, the multinational T2K team was unharmed and the highly sensitive detectors were largely undamaged. Six clean electron neutrino events are observed in the data from before the earthquake, while in the absence of oscillations there should only have been 1.5. Even though such an excess could only happen by chance about one time in a hundred, that is not good enough to confirm a new physics discovery, so this is called an ‘indication’.
Professor Christos Touramanis said: “We have examined the near detectors and turned some of them back on, and everything that we have tried works pretty well. So far it looks like our earthquake engineering was good enough, but we never wanted to see it tested so thoroughly”.
Prof Takashi Kobayashi from the KEK Laboratory in Japan and spokesperson for the T2K experiment added: “It shows the power of our experimental design that with only 2% of our design data we are already the most sensitive experiment in the world for looking for this new type of oscillation”.
STFC is the UK sponsor of particle physics and supports the UK universities involved in the T2K experiment.