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Why the universe is made of matter rather than anti-matter

June 16, 2011 - Washington

Scientists have identified a unique ability of a particle, which may one day help explain why the universe is made of matter rather than anti-matter.

By shooting a beam of neutrinos through a small slice of the Earth under Japan, physicists say they've caught the particles changing their stripes in new ways.

The T2K experiment has been using the Japan Proton Accelerator Research Complex, or J-PARC, located on the east coast, to shoot a beam of muon neutrinos 185 miles, or 295 kilometers, underground toward the Super-Kamiokande, or Super-K, detector in Kamioka, near Japan's west coast.

The goal of the experiment, which is part of a new generation of neutrino-tracking facilities, is to observe the particles changing "flavors" from muon neutrinos to electron neutrinos on this brief journey.

Neutrinos are elementary particles that come in three flavors - muon, electron and tau. In past experiments, physicists have measured the change of muon neutrinos to tau neutrinos and electron neutrinos to muon neutrinos or tau neutrinos.

"But no one had seen muon neutrinos turn into electron neutrinos," said Chris Walter, a physicist at Duke who is part of the T2K collaboration, along with Duke physicist Kate Scholberg.

The T2K collaboration, a team of physicists from around the world, began observing the neutrinos for their transformations in January 2010.

The group measured the neutrinos, determining their flavor near the accelerator and then again at Super-K. So far, scientists caught 88 neutrinos with their detector.

Six of these likely began their lives as muon neutrinos and turned into electron neutrinos on their way to Super-K.

The preliminary findings were submitted to Physical Review Letters and announced at a press conference Wednesday in Japan.


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