University of Pittsburgh
March 29, 2006

Pitt, International Researchers Confirm Minuscule Particles Have Mass

MINOS experiment helps characterize mysterious neutrino

PITTSBURGH—Right now, as you read this, particles called neutrinos are zipping through your body. You just don't realize it because they're incredibly tiny. Produced by nuclear reactions in the sun and other stars, neutrinos are so small that scientists, until recently, thought they weighed nothing at all.

Today, an international collaboration including University of Pittsburgh researchers announced the results of the most complete experiment of its kind—the Main Injector Neutrino Oscillation Search (MINOS) experiment at the U.S. Department of Energy's (DOE) Fermi National Accelerator Laboratory (Fermilab). The researchers determined that neutrinos oscillate—change back and forth from one type to another. This provides further proof that neutrinos have mass, because only particles with mass oscillate.

"I wasn't 100 percent convinced that the oscillations were real until we saw these results," said Donna Naples, a Pitt associate professor of physics and astronomy and one of the experiment's principal investigators. Vittorio Paolone, associate professor of physics and astronomy at Pitt, also was involved in the study.

In the experiment, a beam of one kind of neutrinos was sent from the lab's site in Illinois to a detector in Minnesota. If some of the neutrinos didn't arrive in the same form as when they started, they would have had to change along the way. And that is exactly what the researchers observed.

These findings corroborate a recent Japanese study, and they verify that the signal recorded by the detector really is the result of neutrino oscillation. This experiment also offers a better measure of the mass of neutrinos.

The results of the experiment have important implications for cosmology. Because the neutrino doesn't decay like other particles, neutrinos produced in the early universe are still around. "When cosmologists model how the universe evolved into galaxies, they need to know how matter 'clumps' over time, and that depends on the mass of the neutrino," said Naples.

The MINOS experiment includes scientists, engineers, technical specialists, and students from 32 institutions in six countries. The DOE provides the major share of the funding, with additional funding from the U.S. National Science Foundation and from the United Kingdom's Particle Physics and Astronomy Research Council.

Fermilab, founded in 1967, is a DOE National Laboratory operated by Universities Research Association, Inc.