June 15, 2011 The international T2K collaboration has announced that it has observed an indication of a new type of neutrino transformation or oscillation from a muon neutrino to an electron neutrino. Boston University Professor of Physics Edward Kearns is among the team of researchers responsible for this discovery.
Evidence of this new type of neutrino oscillation may lead the way to new studies of a matter/ anti-matter 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 CP violation in neutrinos will be a major scientific quest in the coming years.
"Even though we have studied neutrino oscillations for years, there is still a great thrill in seeing these six events. The neutrino beam technique that we use is working beautifully and the interpretation is simple and direct. I can hardly wait to collect more data. It has been a privilege for all of us at Boston University to participate in this series of experiments in Japan, and we greatly appreciate the efforts at J-PARC and KEK to restart the T2K beam," says Kearns.
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.
Further steps towards this goal will continue to require global scientific collaborations, like T2K, to overcome the significant technical challenges in this search. 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 superconducting corrector magnets, proton beam monitor electronics, the second neutrino horn and a GPS time synchronization system for the T2K neutrino beamline; and a pi-zero detector and a side muon range detector (partial detector) in the T2K near detector complex.
They are also 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.
More details on this measurement have been provided in a press report at: http://jnusrv01.kek.jp/public/t2k/
For more details, visit: http://physics.bu.edu/sites/neutrino/?p=97
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- The T2K Collaboration. Indication of Electron Neutrino Appearance from an Accelerator-produced O-axis Muon Neutrino Beam. Physical Review Letters, 2011; (submitted)
- The T2K Collaboration. The T2K Experiment. arXiv.org, 2011; [link]
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