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!"

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 behavior.

"The first measurements of the flux of neutrinos coming from the thermonuclear reactions which power our Sun came as something of a shock because they were far lower than predicted", said Professor Wark.

A second anomaly was then clearly demonstrated by Super-Kamiokande, when it showed that the flux of different types of neutrino generated within our atmosphere by cosmic ray interactions was different depending on whether the neutrinos were coming from above or below (which should not have been possible given our understanding of particle physics).

Other experiments, such as KamLAND (also performed at Kamioka), the Canadian-American-UK SNO experiment, and the STFC-supported MINOS experiment, have conclusively demonstrated that these anomalies are caused by neutrino oscillations, whereby one type of neutrino turns into another.

UK scientists from 9 institutions, who are among the 508 physicists from 12 countries involved, have made a significant contribution to the experiment, producing 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 using the data to explore the properties of neutrinos.

Professor John Womersley, Director, Science Programmes at STFC said; "STFC is proud to be funding an experiment that could make such a significant contribution to our understanding of these elusive particles and indeed to what we know about the formation of the universe".

The first initial science results from this experiment are expected within a few months, but it will be several years before any definitive answers are found.