Note to Reporters: Photos of the CSU team and the Japanese facility are available with the news release at http://news.colostate.edu. Copies of the U.S. and Japanese press releases are also available.
Four Colorado State University physics faculty members have been instrumental in an international experiment that combines a new particle accelerator and neutrino detector on the east coast of Japan with a 10-story water tank detector in a mine near Japan’s western coast.
This experiment indicates for the first time that certain subatomic particles called muon neutrinos can transform themselves into another type, called electron neutrinos. Ultimately, this character-changing behavior, unusual even for subatomic particles, could help scientists answer the fundamental question of why our observable universe evolved from the Big Bang into matter and very little anti-matter that exists today.
On Wednesday, more than 500 physicists from 12 countries announced the first major results from the experiment. At CSU, Professors Bruce Berger, Norman Buchanan, Robert Wilson, Walter Toki and engineer David Warner helped design, build, and install the “pi-zero” detector for the experiment and participated in recording and interpreting the data it has collected.
Neutrinos are sometimes known as “ghost particles” for their ability to pass through matter unhindered. Scientists built the facility in Japan so that they could create enough of these neutrinos to detect the very rare interactions that occur and track the transformation of neutrinos from one type into another as they travel nearly at the speed of light.
Neutrinos come in three types or “flavors:” electron, muon, and tau. The electron neutrinos are produced in the sun, in the Earth’s atmosphere and in nuclear reactors; muon neutrinos are just created in the earth’s atmosphere and in laboratory accelerators, which is what the scientists built on Japan’s eastern coast.
“It is truly an exciting time when the newly built T2K experiment works and finds an indication of the neutrino oscillation effect it was designed and constructed to find,” said Toki, leader of the CSU team who was the first from the university to join the T2K project in 2006. “We could have been very unlucky if nature was ornery with no effect to be found or if the Japan earthquake happened earlier before our experiment had enough time to detect the effect.”
The manmade particles were created in the particle accelerator laboratory located in Tokai village on the east coast of Japan about 90 miles north of Tokyo. The neutrinos traveled nearly 200 miles through the Earth’s crust on their way to the deep underground Super-Kamiokande detector – a 13 million-gallon tank of water lined with 11,000 ultra-sensitive light sensors.
The detector in the mine captures light at the single-photon level – one-billion-billionth of the intensity of sunlight – and converts that light into a measurable electrical signal. When a neutrino passes through the detector, it may interact with a water molecule and create another particle – an electron or muon – that emits light as it travels through water. The Super-Kamiokande detector acts like a giant underwater camera with 11,000 20-inch pixels to capture as much of the emitted light as possible. By comparison, a typical digital camera may contain millions of pixels but they are only one-tenth of a hair’s width across.
The CSU group is a key part of a group of U.S. universities that helped build the 10-ton “pi-zero” detector that probes the neutrinos as they exit the accelerator.
“This new result is very exciting,” Berger said. “The search for evidence of the third neutrino oscillation has been one of the top priorities in neutrino physics in the last decade. If we can confirm our results with more data, it will be a milestone towards measuring CP violation in neutrinos and trying to understand why the universe is primarily made of matter with little antimatter.”
Major parts of the detector were designed, built, and tested at the CSU by the group before being shipped to other U.S. universities and ultimately Japan. The CSU T2K research group currently includes four faculty, four postdoctoral researchers, and eight graduate students. Four undergraduate students have also been involved.
“It’s truly rewarding to see indications of this illusive type of neutrino oscillation at such an early stage of the experiment,” Buchanan said. “With so much data still to be collected, T2K is poised to provide significant insight into muon neutrino to electron neutrino oscillations, and neutrino physics in general.”
Added Wilson, “although it is just the first indication of electron-neutrino appearance, if future data provides confirmation it will be considered a major discovery and provide impetus for future larger scale neutrino projects in the U.S.”
The entire T2K experiment is an international collaboration of 12 countries: Japan, United States, United Kingdom, Italy, Canada, Korea, Switzerland, Spain, Germany, France, Poland and Russia. In addition to CSU, U.S. participants include CU-Boulder, Boston University, Brookhaven National Lab, University of California-Irvine, Duke University, Louisiana State University, Stony Brook University, University of Pittsburgh, University of Rochester, and University of Washington-Seattle. The 70-member team is funded by the U.S. Department of Energy, Office of Science.
Timeline of Colorado State University participation in T2K:
January 2006: CSU group joins the T2K collaboration.
January 2007: CSU obtains funding from the U.S. Department of Energy to design and construct parts of the pi-zero detector at CSU.
March 2009: Final assembly of the detector – including CSU’s portion – occurs at Stony Brook University.
April 2009: Completed pi-zero detector is shipped to Japan.
April-September 2009: Installation occurs in Japan.
January 24, 2010: First neutrinos, created by the particle accelerator, are seen in the pi-zero detector.
February 24, 2010: First neutrino, created from the particle accelerator in Tokai, is detected 200 miles away in the Super-Kamiokande detector in the Kamioka mine.
March 11, 2011: Japan earthquake stalls experiment, which is expected to be reactivated by the end of 2011.