Scientists at the Tokai-to-Kamioka (T2K) experiment in Japan have tracked the experiment's first neutrino, a small step towards finding out why we live in a matter-dominated Universe.

Neutrinos are particles that are extremely hard to detect because they interact very weakly with other matter. They may pass through the entire planet losing far less intensity than light passing through a window. They are electrically neutral and are also very fast, travelling at nearly the speed of light. Scientists have identified three types of neutrinos – the electron neutrino, the muon neutrino and the tau neutrino.

According to the Standard Model of physics, it was thought that neutrinos have to be massless. It was also believed that these three kinds didn't change from one form to another. However, observations of the neutrinos originating from the Sun showed far fewer neutrinos than predicted. To explain this and other anomalies, the Standard Model had to be revised and neutrinos are now thought to have mass. Part of this revision comes in the form of the proposed neutrino oscillations that might be responsible for converting one type of neutrino to another. The fewer detections of solar neutrinos might be explained if the expected neutrinos changed to another type that weren't detected.

The T2K experiment will produce muon neutrinos, and the objective will be to study what fraction of these get converted into electron neutrinos before they reach the detector. T2K is an international collaboration based in Japan, with 508 scientists from Canada, France, Germany, Japan, Italy, Poland, Russia, South Korea, the UK and the USA. It consists of a neutrino source at the J-PARC laboratory in Tokai, the Super-Kamiokande detector in Kamioka and some near detectors 280 metres from the source. The particle accelerators at J-PARC bombard protons on a target producing the neutrinos that then travel towards the detector which is located 1,000 metres underground.

The first confirmed detection of a neutrino came ten months after the first neutrino beam was produced, and travelled 295 kilometres from the source to the detector. It is the first step in the experiment that the team of scientists from 12 countries hope will answer some of the questions concerning these mysterious particles, and hopefully tell us more about the imbalance in matter and anti-matter in the Universe. Specifically, the team hopes to find out more about neutrino oscillations, a phenomenon that might explain why some types of neutrinos appear to vanish. So far, no one has observed these oscillations.

Some of the funding for this project has come from the UK's Science and Technology Facilities Council (SFTC). Professor Dave Wark of Imperial College London and the SFTC's Rutherford Appleton Laboratory says, “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 greatest mysteries in fundamental physics – why is there more matter than anti-matter in the Universe?”

The hunt for the answer has just begun. Scientists expect the initial results in a few months, although we may have to wait many years for the definitive answers.

For more information about the TK2 experiment, visit the official website at: http://jnusrv01.kek.jp/public/t2k/

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