University of Rochester

Indications of New Type of Neutrino Oscillation at the T2KExperiment

June 15, 2011

University physicists helped design equipment in multi-nation project

The international T2K collaboration, which includes scientists from the University of Rochester, announced today that they have observed an indication of a new type of neutrino transformation or oscillation from a muon neutrino to an electron neutrino. Neutrinos come in three types, or "flavors"; electron, muon, and tau.

In the T2K experiment in Japan, a muon neutrino beam was produced in the Japan Proton Accelerator Research Complex, called J-PARC, located in Tokai village, Ibaraki prefecture, on the east coast of Japan, and was aimed at the gigantic Super-Kamiokande underground detector in Kamioka, near the west coast of Japan, 295 km (185 miles) away from Tokai. An analysis of the detected neutrino-induced events in the Super-Kamiokande detector indicates that a very small number of muon neutrinos traveling from Tokai to Kamioka (T2K) transformed themselves into electron neutrinos.

Evidence of this new type of neutrino oscillation may lead the way to new studies of a matter-antimatter asymmetry called charge-parity (CP) violation. This phenomenon has been observed in quarks (for which Nobel prizes were awarded in 1980 and 2008), but never in neutrinos. CP violation in the early Universe may be the reason that the observable universe today is dominated by matter and no significant anti-matter. If the T2K result does indicate this third oscillation, then a search for this CP violation in neutrinos will be a major scientific quest in the coming years. Further steps towards this goal will continue to require global scientific collaborations, like T2K, to overcome the significant technical challenges in this search.

The University of Rochester was involved in the international collaboration from the beginning, helping to design and construct the detectors and neutrino source. The local team consists of physicists Kevin McFarland and Steven Manly, senior scientist Howard Budd, postdoctoral researcher Philip Rodrigues, and graduate student Melanie Day.

"This finding suggests that there may be differences between matter and anti-matter neutrinos," said McFarland. "Ultimately, those differences could lead to a better understanding of the process by which anti-matter disappeared from the universe after the Big Bang."

The T2K experiment utilizes the J-PARC complex that accelerates protons onto a target to produce an intense secondary particle beam that is focused by special magnets called neutrino horns. The focused particle beam decays into a beam of neutrinos, which is monitored by a neutrino detector 280 meters from the target. This beam of neutrinos travels 295 km underground to be detected in the Super-Kamiokande detector.

The work of the T2K experiment is located in Japan and primarily supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology. However, the experiment was constructed and is operated by an international collaboration, which consists of about 500 physicists from 59 institutions in 12 countries [Japan, US, UK, Italy, Canada, Korea, Switzerland, Spain, Germany, France, Poland, and Russia]. The data collected by the experiment is also analyzed by the collaboration. The US T2K collaborating team of approximately 70 members [Boston University, Brookhaven National Lab, UC Irvine, University of Colorado, Colorado State University, Duke University, Louisiana State University, Stony Brook University, University of Pittsburgh, University of Rochester, and University of Washington (Seattle)] is funded by the US Department of Energy, Office of Science. The US groups have built super-conducting corrector magnets, proton beam monitor electronics, the 2nd neutrino horn and GPS time synchronization system for the T2K neutrino beam line; and a pi-zero detector and a side muon range detector (partial detector) in the T2K near detector complex, and are part of the team that built, upgraded and operates the Super-Kamiokande detector.

The March 2011 earthquake in eastern Japan caused damage to the accelerator complex at JPARC, and the data-taking run of the T2K experiment was abruptly discontinued. Fortunately, however, no scientists working on T2K or technical staff supporting their work were injured in the earthquake or its aftermath. The T2K experiment will be ready to take data when J-PARC resumes its operation, which is planned to occur at the end of 2011.

"The efforts of our Japanese colleagues after the earthquake were inspiring," said McFarland. "It is a truly great nation that can face a disaster of such magnitude, and still continue the pursuit of scientific truths with such vigor."

More details on this measurement have been provided in a press report at http://jnusrv01.kek.jp/public/t2k/.




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