19 July 2013 16:21

An international experiment investigating one of the biggest mysteries in fundamental physics – why the amount of matter greatly exceeds the amount of antimatter in the Universe - has made a leap forward. 

Lancaster University is one of eight UK partners involved in a global scientific collaboration called the T2K experiment based in Japan.

T2K studies a high intensity particle beam that travels deep underground from the east to the west coast of Japan. The beam is made up of neutrinos, which are among the fundamental constituents of the Universe. A ‘near’ detector positioned close to the source of the neutrino beam is used to investigate the initial composition of the beam, whilst a huge ‘far’ detector samples the beam about 185 miles downstream.

There are three types of neutrinos – the electron neutrino, the muon neutrino and the tau neutrino.  These different “flavours” of neutrinos can spontaneously change into each other, a phenomenon called neutrino oscillation. 

Now scientists have found final confirmation of a new type of neutrino oscillation from the muon type to the electron type. First observed in 2011 with marginal statistical significance, scientists have since collected 3.5 times more data and are now almost 100 per cent certain that they have witnessed the new oscillation.

This T2K observation is the first of its kind in that an explicit appearance of a unique flavour of neutrino at a detection point (the ‘far’ detector) is unequivocally observed from a different flavour of neutrino at its production point (the ‘near’ detector).

Professor Peter Ratoff from Lancaster University said: “This is an important step on the road to a much greater discovery – the reason why there is much more matter than antimatter in the Universe.  Neutrinos may have been instrumental soon after the Big Bang in facilitating a preference for the production of matter over antimatter without which the Universe as we know it would not exist.”

Measuring a difference in the rate of neutrino and antineutrino oscillations would provide evidence of charge parity (CP) violation in the behaviour of neutrinos. CP violation has thus far only been observed in quarks (for which Nobel prizes were awarded in 1980 and 2008).

CP violation by neutrinos in the very early Universe may be one of the key reasons that the observable Universe today is dominated by matter, with no significant amount of antimatter - which is one of the most profound mysteries in science.

Professor Ratoff said: “We have firmly established this form of neutrino oscillation, so a successful search for CP violation in neutrinos may become feasible in the coming years.”

T2K is led by Japan and partly funded by the UK’s Science and Technology Facilities Council (STFC). Part of the ‘near’ detector was built and calibrated at Lancaster by a large team of staff, technicians, PhD students and researchers managed by Dr Laura Kormos. Lancaster physicists are also involved in analysing the data collected with the ‘near’ detector.