Neutrinos exhibit multiple personalities
6 December 2002
By Bob Sanders, Media Relations
have always seemed weird, zipping around at nearly the speed
of light and passing through matter as if it were not even there.
Now they're getting weirder. Results of a Japan-based experiment
confirm previous suspicions that neutrinos change their identities
as they wing through space, and that they have a small, but
make the case for neutrino oscillation and mass seemingly inescapable,"
said Stuart Freedman, a co-spokesperson for the U.S. team that
announced the results Friday, Dec. 6. Freedman is a nuclear
physicist and professor of physics at UC Berkeley with a joint
appointment at the Lawrence Berkeley National Laboratory (LBNL).
results come from an experiment called KamLAND, or 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. The largest low-energy anti-neutrino detector
ever built, KamLAND looked for neutrinos' mirror-image particles,
called anti-neutrinos, emanating from 51 nuclear reactors in
Japan plus 18 reactors in South Korea. During 145 days of operation,
KamLAND detected slightly less than 2/3 of the anti-neutrinos
predicted to come from these reactors.
of this discrepancy, the Standard Model of physics that predicted
the expected anti-neutrino flux is in need of updating, the
92-member research team conclude. The necessary revisions must
account for the fact that anti-neutrinos, and thus neutrinos,
change flavor with time, oscillating among the three known types,
electron, muon and tau. This means, too, that neutrinos have
a slight mass, though the team was not able to estimate how