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Experiment a Top 10 Breakthrough in “Physics World”

T2kbeam 1
Chang Kee Jung
Professor Chang Kee Jung

Stony Brook University Physics Professor Chang Kee Jung, along with an international team of physicists working on the Tokai-to-Kamioka (T2K) collaboration, have been named seventh in a list of the top 10 breakthroughs of 2011, according to Physics World magazine for their experiment that appears to have measured, for the first time, muon neutrinos changing into electron neutrinos.

A neutrino (neutral subatomic particle), which exists in three types or flavors (muon, electron, and tau), can change or “oscillate” from one to another as they travel in space. They are very hard to detect because they interact weakly with matter. In the experiment the T2K team fired a beam of muon neutrinos 295 kilometers (183 miles) from the Japan Proton Accelerator Research Complex (J-PARC), located on the east coast of Japan in Tokai, underground to the Super-Kamiokande detector in Kamioka, near the west coast of Japan. The experiment revealed that six neutrinos had changed or oscillated into electron neutrinos. Data collection ran for 13 months until the March 2011 earthquake in eastern Japan caused damage to the accelerator complex at J-PARC.

“Even though our current result does not quite reach the level of statistical significance to claim an established discovery, we are heartened by the trust and support expressed by this recognition,” said Jung, who also serves as an international co-spokesperson for the T2K team. “The collaboration is making every effort to establish an unequivocal evidence of this new type of neutrino oscillation in the near future.”

The effect of this experiment could allow researchers to pinpoint the final undetermined neutrino “mixing angle,” as well as provide a clue toward solving the mystery of why matter, rather than antimatter, dominates the universe through 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.

“The result is not enough to claim a discovery, but it is important for not only T2K but also high-energy physics in general,” said Koichiro Nishikawa, former spokesperson for the T2K experiment currently based at the KEK particle physics lab in Tsukuba, Japan. “This result is also, except for one ‘tau event’ in the OPERA experiment at Gran Sasso in Italy, the first time that anyone has shown that neutrino oscillations occur as a change of flavor.”

The T2K Beam diagram illustrates the passage of the muon neutrino beam from J-PARC to the Super-Kamiokande detector 183 miles away.

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 from Boston University, Brookhaven National Laboratory, 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 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.

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