A "landmark discovery" about neutrinos -- one of the universe's most puzzling fundamental particles -- has been announced by more than 90 American and Japanese scientists, including University of Hawaii-Manoa physicists. UH plays role in
‘landmark’ physics findA team of American and Japanese experts
learn that neutrinos can change identitiesBy Helen Altonn
haltonn@starbulletin.comUH physicist John Learned, one of the principal investigators of experiments at KamLAND, an underground neutrino detector in central Japan, said the results are "completely unheralded by the theories."
In the KamLAND experiment, the scientists found anti-neutrinos from nearby nuclear reactors "disappearing," confirming that they have mass and can oscillate or change identities back and forth as they travel through space.
Although neutrinos have the smallest mass of any elementary particles, they could affect how much matter is in the universe and help resolve a question of whether the universe will expand forever or collapse on itself, scientists believe.
Learned said the discovery has "tremendous scientific implications, ranging from elementary particle physics to cosmology, through the tiniest scales up to the greatest scales of cosmology, the big bang, the fate of stars and, most particularly, the origin of mass in the universe."
Learned said physicists now think neutrinos account for about as much mass as all the visible stars in the sky.
"On the other hand, the astronomers are still finding that all the regular matter that we know of is a tiny fraction compared to the dark matter and dark energy."
It is believed neutrinos may be part of a mechanism that allowed a little more matter to be generated than antimatter in the big bang -- the cosmic explosion believed to have created the universe 10 billion to 20 billion years ago, Learned said.
If matter and antimatter had been the same, they would have been annihilated and nothing would be left, he said.
"All of these questions about neutrino mass and mixing are important for the big bang, for supernovae and to remind people we're all just made of leftover junk from recycled matter from stars that have blown up."
The KamLAND group said its results "make the case for neutrino oscillation and mass seemingly inescapable" and that the Standard Model of Particle Physics used since the 1970s needs updating.
The results also "point the way to the first direct measurements of the total radioactivity of the earth," the researchers said.
Neutrinos are elementary particles of different "flavors," or types -- the muon, electron and tao.
A Japanese-American team, including UH physicists, discovered in 1998 that muon neutrinos are oscillating in mass.
The discovery shattered the standard theory of particle physics.
"This is kind of like the other bookend of the observations of neutrinos," Learned said of the KamLAND experiment. "These two bookends and a bunch of other in-between experiments all come together as a consistent picture that neutrinos have mass, that they have this peculiar property of changing their stripes as they fly along and, moreover, that they change their stripes as much as they're allowed to by quantum mechanics."
Besides Learned, UH participants include Peter Gorham, Gene Guillian, Jelena Maricic, Shigenobu Matsuno and Sandip Pakvasa. Stephen Olsen is principal investigator of a U.S. Department of Energy grant supporting work of the high-energy physics group at Manoa.
Physicist Atsuto Suzuki of the Research Center for Neutrino Science at Tohuku University heads the international collaboration.
UH physicists are involved in three research projects in Japan, and "it's experimentalist heaven," Learned said.
"We're feeling like the paddlers paddling off over the horizon in search of new lands. We don't know where this is leading. There is no grand unified theory to give us guidance, and indeed, what theory there is has pointed us in the wrong direction."
KamLAND
Dept. of Physics and Astronomy
Research Center for Neutrino Science
