First T2K Neutrino Event Seen at Super-Kamiokande

Interacting only weakly with matter, neutrinos can traverse the entire Earth with vastly less loss of intensity than light passing through a window. The very weakness of their interactions allows physicists to make what should be very accurate predictions of their behaviour.

UK particle physicists working on the multinational T2K project, which is designed to detect some of the least understood particles in the universe, have helped track their first neutrino which has travelled 185 miles (295 km) under Japan.

The detection of the neutrino as it passed from the East to the West of the country means the study of the mysterious phenomenon of neutrino oscillations, which it is hoped will shed more light on the role of the neutrino in the early universe, can now begin. It could even help answer questions about why there is more matter than anti-matter in the universe.

T2K (Tokai-to-Kamioka), an international experiment led by Japan and part-funded by the UK's Science and Technology Facilities Council (STFC), was built to help us understand with unprecedented precision more about the strange properties of the puzzling neutrino.

"Neutrinos are the elusive ghosts of particle physics," T2K spokesperson Takashi Kobayashi said. "They come in three types, called electron neutrinos, muon neutrinos, and tau neutrinos, which used to be thought to be unchanging. This is a big step forward, we've been working hard for more than 10 years to make this happen."

T2K's newly constructed neutrino beamline at the J-PARC facility in Tokai village (north of Tokyo) will now start to try to take measurements of the so-far unobserved neutrino oscillation which would cause a small fraction of the muon neutrinos produced there to become electron neutrinos by the time they reach the giant Super-Kamiokande underground detector on the other side of Japan.

"Observing the new type of oscillation would open up the prospect of comparing the oscillations of neutrinos and anti-neutrinos, which many theorists believe may be related to one of the great mysteries in fundamental physics - why is there more matter than anti-matter in the universe?"

Said Professor Dave Wark of Imperial College London and STFC's Rutherford Appleton Laboratory, who is the International Co-Spokesperson of the T2K experiment: "The observation of this first neutrino means that the hunt has just begun!"

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