Japanese Detector Brings Neutrinos Into Sharper Focus

摘要

In 1998, the Super-Kamiokande Collaboration stunned the physics world with evidence that―contrary to long-standing prediction―neutrinos have mass. The group found that neutrinos generated in Earth's atmosphere were changing, or oscillating, into a "flavor" their Japan-based detector could not observe. By the laws of quantum mechanics, only particles with mass can oscillate. Now, with an additional 6 years' worth of data, the Super-K team has filled in the other half of the story: neutrinos' changing back. "You can actually see the oscillations," says Henry Sobel, a physicist at the University of California, Irvine, who is co-spokesperson for the U.S. side of the multicountry collaboration. The new results rule out some alternative theories of why the neutrinos were disappearing and sharpen up the numbers that govern how oscillations take place. Theorists need those numbers to construct comprehensive models of neutrino behavior. The results will be published in an upcoming issue of Physical Review Letters.