UA Professors Have Key Role in Disappearing Neutrino Research

TUSCALOOSA, Ala. – Results from the first six months of experiments at KamLAND, an underground neutrino detector in central Japan, show that anti-neutrinos emanating from nearby nuclear reactors are “disappearing,” which indicates they have mass and can oscillate, or change, from one type to another.

The University of Alabama has two faculty members, a post-doctoral research associate and several graduate students involved in the international project.

Neutrinos are subatomic particles that interact so rarely with other matter that one could pass untouched through a wall of lead stretching from the earth to the moon. They are produced during nuclear fusion, the reaction that lights the sun and other stars. Anti-neutrinos are created in fission reactions such as those that drive nuclear power plants.

It is hoped that this research will one day be able to help unlock the secrets about the fundamental nature of matter, how the sun works, the composition and evolution of the Earth, the process of star collapse and the origin and future of the universe.

In a paper for Physical Review Letters, the 92 physicists from Japan, the United States and China, who make up the KamLAND collaboration, report that during 145 days of operation, they recorded 54 electron anti-neutrino events in the energy range of one to 10 million electron volts, as opposed to the approximately 86 events predicted by the Standard Model under the assumption that no oscillations occur.

Anti-neutrinos are the anti-matter counterpart to neutrinos. These results, obtained using well-understood, man-made anti-neutrino sources, provide independent confirmation of earlier studies involving solar neutrinos and show that the Standard Model of Particle Physics, which has successfully explained fundamental physics since the 1970’s, is in need of updating.

The results also point the way to the first direct measurements of the total radioactivity of the earth.

University of Alabama researchers have been involved in the KamLAND project since the beginning of its construction in 1998.

“This research has put another piece of the puzzle in place,” said Dr. Jerrry Busenitz, professor of physics at The University of Alabama. “KamLAND has provided an important confirmation that neutrinos do in fact oscillate.”

“There have been a wide range of hypotheses on this subject, and neutrino research is scientifically popular right now,” said Dr. Andreas Piepke, professor of physics at The University of Alabama. “The results of our research are strong evidence that we are well on the way to a full understanding of neutrinos.”

KamLAND stands for Kamioka Liquid scintillator Anti-Neutrino Detector. Located in a mine cavern beneath the mountains of Japan’s main island of Honshu, near the city of Toyama, it is the largest low-energy anti-neutrino detector ever built. The detector consists of a 13 meter (43 feet) in diameter weather balloon filled with about a kiloton of liquid scintillator, a chemical soup that emits flashes of light when an incoming anti-neutrino collides with a proton.

These light flashes are detected by a surrounding array of 1,879 photomultiplier light sensors, which convert the flashes into electronic signals that computers can analyze. The photomultipliers are attached to the inner surface of an 18-meter in diameter stainless steel sphere and separated from the weather balloon by a buffering bath of inert oil and water, which helps suppress interference from background radiation.

The anti-neutrino events that were recorded in the KamLAND detector for this study stem from electron anti-neutrinos that originated from the 51 nuclear reactors in Japan plus 18 reactors in South Korea. Anti-neutrinos, like neutrinos, come in three different types or “flavors,” electron, muon and tau.

According to the predictions from the Standard Model, neutrinos/anti-neutrinos are without mass. Contrary to this, over the past years, neutrino experiments implied that the ghost-like snippets of matter do possess mass, enabling them to oscillate and change flavor over a distance. KamLAND’s results are compatible with earlier results and were obtained using a complementary approach.

Construction of the KamLAND detector began in 1998 and operations began in January of 2002.

Japan’s Ministry of Education, Science, Sports, and Culture provided more than $20 million of KamLAND’s construction costs. The U.S. Department of Energy’s Office of Science provided nearly $6 million.

The KamLAND experiments will continue for several more years, making refined measurements of reactor neutrinos that should shed more light on neutrino mass and flavor mixing. Since anti-neutrinos also are produced during the decay of radioactive uranium and thorium in the crust and mantle of the Earth, the KamLAND detector can also be used to measure our planet’s internal radioactivity.

KamLAND, with a more purified liquid scintillator, will also be used to study solar neutrinos in a new low energy regime. For now, the evidence of neutrino oscillations and flavor has been firmly established.

The KamLAND neutrino experiments are being conducted by an international collaboration largely comprised of scientists from Japan and the United States. The U.S. team at KamLAND includes researchers from The University of Alabama, the University of California Berkeley, Stanford University, the California Institute of Technology, Drexel University, the University of Hawaii, Louisiana State University, the University of New Mexico, the University of Tennessee, Duke University, the University of North Carolina and North Carolina State University.

The Japanese team at KamLAND is led by Atsuto Suzuki, a professor of physics at the Research Center for Neutrino Science at Tohuku University. Suzuki is the overall head of the international collaboration, which also includes, in addition to Tohuku University participants, researchers from the Institute of High Energy Physics in Beijing.

KamLAND Websites with additional images can be accessed at http://hep.stanford.edu/neutrino/KamLAND/KamLAND.html
The Japanese KamLAND Website can be accessed at: http://www.awa.tohoku.ac.jp/html/KamLAND/.