• Kyodo


Through experiments in Japan, a team of physicists has detected the possibility that a neutrino particle and its corresponding antiparticle may be slightly asymmetric, a finding that could shed light on the birth of the universe.

The Japanese-led team presented the discovery from a probe using the Super-Kamiokande neutrino observatory in Gifu Prefecture at an academic conference in Chicago on Saturday.

Subatomic particles such as electrons and protons have corresponding antimatter particles. If the two collide, they annihilate one another and produce energy.

It remains a mystery why the universe is composed almost entirely of matter even though equal amounts of matter and antimatter are thought to have been produced when the universe came into being in the big bang.

The study may provide a clue to understanding this fundamental mystery.

The scientists, who include researchers from Japan’s High Energy Accelerator Research Organization, generated neutrinos and antineutrinos at the Japan Proton Accelerator Research Complex (J-PARC) northeast of Tokyo.

They discharged 100 trillion neutrinos and as many antineutrinos per second from the J-PARC complex toward the Super-Kamiokande facility 295 kilometers (183 miles) away.

Neutrinos, which have almost no mass, pass easily through matter. During flight, they oscillate between three forms: electron, muon and tau neutrinos.

At Super-Kamiokande, the researchers examined particles that transformed from muon neutrinos to electron neutrinos, and found there were 32 such neutrinos but only four such antineutrinos.

This asymmetry is believed to explain why more matter than antimatter remains in the universe.

More verification is required, they said, as the difference was not detected in all the cases examined.

“We were able to reach the first starting point. We hope to gather more data to enhance the credibility” of our finding, said Tsuyoshi Nakaya, the Kyoto University professor who led the experiment.

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