|
|
|
NEWS SEARCH
|
|
|
|
|
Neutrinos exhibit multiple personalities
6 December 2002
By Bob Sanders, Media Relations
BERKELEY -
Neutrinos
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
measurable, mass.
"Our results
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).
The
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.
Because
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
large.
Additional
information:
|
|
