UK particle physicists working on the T2K (Tokai-to-Kamioka) neutrino experiment in Japan celebrated as the experiment detected its first neutrinos - fundamental particles which are amongst the least understood in the Universe.

T2K - an international experiment led by Japan and part funded by the UK's Science and Technology Facilities Council (STFC) - will probe the strange properties of the enigmatic neutrino to unprecedented precision, by firing the most intense neutrino beam ever designed from the east coast of Japan, all the way under the country, to a detector near Japan's west coast.

Neutrino oscillations are one of the frontiers of current particle physics and the T2K project will move us one step closer to understanding the role of the neutrino in the early Universe and may even shed light on the mystery of why there is more matter than anti-matter in the universe.

Professor Dave Wark of Imperial College London and the STFC Rutherford Appleton Laboratory, the International Co-Spokesperson of T2K, said "It was extremely satisfying to see the first events in the detector. It has been the result of a lot of hard work by a large number of people, and I think we will have a sake or two to celebrate and then send a bottle along to CERN as I hear they are going to need quite a few bottles pretty soon as well."

Neutrinos interact only weakly with matter, and thus pass effortlessly through the Earth (and mostly through the detectors!).

Neutrinos exist in three types, called electron, muon, and tau; linked by particle interactions to their more familiar charged cousins like the electron. Measurements over the last few decades have shown that neutrinos possess the strange property of neutrino oscillations, whereby one type of neutrino will turn into another as they propagate through space.

Neutrino oscillations, which require neutrinos to have mass and therefore were not allowed in our previous theoretical understanding of particle physics, probe new physical laws and are thus of great interest in the study of the fundamental constituents of matter.

Among the international team of around 400 physicists from 12 countries, UK scientists have made a significant contribution to the experiment. With 9 UK institutions involved, the UK has produced vital hardware for both the accelerator and detectors.

The UK is also playing a leading role in the analysis software for the experiment and will be fully involved in the most exciting bit - using the data to explore the properties of neutrinos. This is expected to begin in January 2010, when the experiment is scheduled to begin production running.

"Within a year T2K should have sensitivity to neutrino properties beyond any existing experiment, and the search for the unknown will begin," said Professor Wark.

Professor Keith Mason, CEO of the Science and Technology Facility Council (STFC), said, "We're very excited to be a part of the T2K project. Neutrinos are incredibly difficult to detect but with the skilful engineering that has gone into this experiment we will soon be able to learn much more about these elusive particles, further understand their role in the formation on the Universe and improve our model of particle physics."