Results from T2K conclusively show muon neutrinos transform to electron neutrinos


Professor Christos Touramanis (right) with Japanese technicians installing one of the smaller modules of the detector made by the Liverpool team

The T2K experiment, which the University is a key partner in, has announced the definitive observation of muon neutrino to electron neutrino transformation.

In 2011, the collaboration announced the first indication of this process, a new type of neutrino oscillation.  Now, with 3.5 times more data this transformation is firmly established. The probability that random statistical fluctuations alone would produce the observed excess of electron neutrinos is less than one in a trillion.  Equivalently the new results exclude such possibility at 7.5 sigma level of significance.

Unique flavour

This T2Kobservation is the first of its kind in that an explicit appearance of a unique flavour of neutrino at a detection point is unequivocally observed from a different flavour of neutrino at its production point

The T2K experiment fires a muon neutrino beam produced at J-PARC on the east coast of Japan towards the 50,000 ton Super-Kamiokande underground detector in western Japan at a distance of 185 miles.

An analysis of Super-Kamiokande data finds 28 electron neutrinos when 4.6 are expected if neutrino flavour-mixing would not occur. The composition and properties of the original beam are measured by a suite of Near Detectors located at J-PARC.

”This is a great achievement. The Liverpool neutrino group is delivering its first major discovery only 10 years after it was set up”
Flavour-mixing opens up the possibility to search for CP Violation in neutrinos. This would be a matter-antimatter difference which could be related to the matter-dominance in our universe. The 500-strong T2K collaboration expects to collect 10 times more data in the coming years and part of that will be in anti-neutrino mode to search for CP Violation.

Scientists and engineers from the University play key roles in the T2K experiment. They designed and constructed a subsystem of the Near Detector (ECAL) which at 75 tones is the largest detector ever constructed in the West for an experiment in the Far East.  They also have responsibilities in running the experiment and analysing the data.

The T2K experiment was affected by the 9 Richter Japanese earthquake which struck in March 2011 and halted the experiment but it was able to re-start again by the end of the year.

New vistas

Professor Christos Touramanis, head of the neutrino group at the University of Liverpool, said: “This is a great achievement. The Liverpool neutrino group is delivering its first major discovery only 10 years after it was set up. This opens up new vistas into the mysteries of matter-antimatter. We are already working on these exciting opportunities in collaborations in USA and Europe.”

The T2K experiment was constructed and is operated by an international collaboration. The current T2K collaboration consists of over 400 physicists from 59 institutions in 11 countries [Canada, France, Germany, Italy, Japan, Poland, Russia, Switzerland, Spain, UK and US].

The announcement was made at the European Physical Society meeting in Stockholm.


Leave a comment