June 17, 2011

UW part of physics collaboration that finds new type of neutrino conversion

News and Information

An international physics collaboration called T2K, which includes the University of Washington, has observed a previously unseen type of neutrino “oscillation,” or transformation, that could help explain the lack of antimatter in the observed universe.

Neutrinos are wispy subatomic particles that are electrically neutral and interact little with matter around them (millions pass through a human body each second). They come in three types, or “flavors” – electron, muon and tau. In the latest observation, a muon neutrino changed into an electron neutrino.

In the T2K experiment, a muon neutrino beam was produced in the Japan Proton Accelerator Research Complex in Tokai village on the east coast of Japan and was aimed at the giant Super-Kamiokande underground detector 185 miles away in Kamioka, near the west coast. Analysis showed a very small number of muon neutrinos traveling from Tokai to Kamioka (T2K) transformed into electron neutrinos. The result was announced June 15.

The discovery could lead to new studies of a matter-antimatter asymmetry called charge-parity violation, a phenomenon previously observed only in subatomic particles called quarks. Physicists believe charge-parity violations in the early universe could be the reason that the universe today is dominated by matter and no significant antimatter has been detected, said R. Jeffrey Wilkes, a UW physics professor who is part of the collaboration. Two UW doctoral students and three undergraduates also took part in the work.

“I am delighted that UW students were able to participate in the T2K effort leading to this important new physics result,” Wilkes said.

If the observation proves to be accurate, the search for charge-parity violations in neutrinos will be a major quest in the coming years, he said.

The T2K experiment is primarily supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology. The international collaboration that built and operates the experiment includes about 500 physicists from 59 institutions in 12 countries. The U.S. team includes about 70 researchers from 10 universities and the Brookhaven National Laboratory.

The collaboration noted that the magnitude 9.0 Japan earthquake in March damaged the accelerator complex and the T2K data run was abruptly halted. No scientists or support staff members were injured in the quake, and the experiment is expected to resume later this year.