The Tokai-to-Kamioka (T2K) neutrino experiment announced new results today which hint that muon neutrinos produced by a particle accelerator can transform into electron neutrinos as they travel across a long distance. The T2K experiment uses a beam of muon neutrinos produced at the J-PARC accelerator laboratory in eastern Japan. These neutrinos are beamed from J-PARC through the Honshu island of Japan to the Super-Kamiokande neutrino detector 295km away. Previous experiments have shown that muon neutrinos can transform into other kinds of neutrinos while in transit due to a phenomenon known as "neutrino oscillation". However, the very low rate at which they turn into electron neutrinos is an outstanding puzzle in particle physics that is the focus of a worldwide effort.

In data taken before the March 11 earthquake in Japan, T2K finds 6 candidate electron neutrino events. If muon neutrinos didn't change into electron neutrinos, then T2K should have only seen 1.5 events on average. The chance of seeing six or more events when only 1.5 are expected is less than one percent, suggesting that some of the muon neutrinos are indeed turning into electron neutrinos, although at a very low rate.

"This is the first time that an experiment looking for this effect has found a result not consistent with zero," said Prof. Scott Oser, spokesperson for the Canadian contingent of the T2K collaboration. "These results are very intriguing but not yet conclusive. Really we need more data to confirm that this effect is real and not just a statistical fluke. We're looking forward to the resumption of data-taking once the process of earthquake recovery is complete." T2K has submitted a publication describing the new results to the journal Physical Review Letters (see the draft).

UBC faculty members on the T2K experiment are Chris Hearty, Scott Oser, and Hirohisa Tanaka. UBC was instrumental in building two of T2K's near neutrino detectors and plays a key role in the data analysis.

See also the TRIUMF press release