Impulsive neutrinos change their flavor

U. COLORADO-BOULDER (US) — Neutrinos can spontaneously change flavors, a finding that may help explain why the universe is made up mostly of matter.

The new research is a significant step in discovering why matter trumped antimatter at the time of the big bang, helping to create virtually all the galaxies and stars in the universe.

The experiment, known as the Tokai to Kamioka experiment, or T2K, included shooting a beam of neutrinos underground from the Japan Proton Accelerator Research Complex, or J-PARC, on the country’s east coast to a detector near Japan’s west coast, a distance of about 185 miles.

Neutrinos are elementary particles that make up the fundamental building blocks of nature, generally travel at the speed of light, and can pass through ordinary matter, like Earth’s crust, with ease.

They come in three types: muon, electron, and tau.

Researchers discovered that muon neutrinos can spontaneously change their flavor to electron neutrinos, says Alysia Marino, assistant professor of physics at the University of Colorado-Boulder.

Scientists had previously measured the change of muon neutrinos to tau neutrinos and electron neutrinos to muon neutrinos or tau neutrinos, she says.

The shift of muon neutrinos to electron neutrinos detected in the new experiment is a new type of neutron oscillation that opens the way for new studies of a matter-antimatter symmetry called charge-parity, or CP violation, Marino says.

“This CP violation phenomenon has not yet been observed in a neutrino, but may be the reason that our universe today is made up mostly of matter and not antimatter.”

Scientists believe matter and antimatter were present in nearly equal proportions at the onset of the big bang.  Since matter and antimatter particles cancel each other out, it has been proposed that there must have been charge-parity violation in the early universe that produced slightly more matter than antimatter, which accounts for all the stars, galaxies, planets and life present today.

The project is a collaboration of roughly 500 scientists from 12 nations. Other participating U.S. institutions include Boston University, Brookhaven National Laboratory, the University of California-Irvine, Colorado State University, Duke University, Louisiana State University, Stony Brook University, the University of Pittsburgh, the University of Rochester, and the University of Washington.  The United States contingent is funded by the U.S. Department of Energy.

More data is required to confirm the new results.  The J-PARC accelerator is being repaired following damage from the Japan earthquake and is expected to be operational again by the end of the year.

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