June 1, 2010 in Nation/World

Physicists confirm neutrinos have mass

Thomas H. Maugh Ii Los Angeles Times
 

LOS ANGELES – For the first time, physicists have confirmed that certain subatomic particles have mass and that they could account for a large proportion of matter in the universe, the so-called dark matter that astrophysicists know is there but that cannot be observed by conventional means.

The finding concerns the behavior of neutrinos, ghostlike particles that travel at the speed of light. In the new experiment, physicists captured a muon neutrino in the process of transforming into a tau neutrino.

Researchers had strongly believed that such transformations occur, but the research announced Monday marks the first time that the appearance of a tau neutrino has been directly observed. Physicists from CERN (the European Organization for Nuclear Research) in Geneva and the Italian National Institute of Nuclear Physics’ Gran Sasso National Laboratory were involved.

“This is an important step for neutrino physics,” CERN Director-General Rolf Heuer said in a statement. “We’re all looking forward to unveiling the new physics this result presages.”

The new finding is important because in the theories now used to explain the behavior of fundamental particles, called the Standard Model, neutrinos have no mass.

But if they have no mass, they cannot oscillate between muon and tau forms. The fact that they do oscillate indicates that they have mass.

The new discovery comes from researchers in an experiment known as OPERA, for Oscillation Project with Emulsion-tRacking Apparatus.

The project’s source of neutrinos is a proton accelerator at CERN in Geneva that slams protons into a graphite target, producing particles that quickly decay into muon neutrinos.


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