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【Shanghai Daily】Progress cited in search for elusive particle

March 09, 2012      Author: Liang Yiwen

The Daya Bay Reactor Neutrino Experiment site in south China Guangdong Province plays a pivotal role in the study of neutrinos. A team of Chinese and American physicists, trying to explain the predominance of matter over antimatter in the universe, have confirmed and measured a third type of neutrino oscillation, said Wang Yifang, a co-spokesperson for the experiment and head of the Institute of High Energy Physics of the Chinese Academy of Sciences, at a press conference yesterday in Beijing.

THE first results of a search for the last, most elusive piece of a longstanding physics puzzle were reported yesterday by the Daya Bay Reactor Neutrino Experiment, a multinational collaboration operating in the south of China.

The question scientists seek to answer: Why do neutrinos appear to vanish as they travel? The answer opens a gateway to a new understanding of fundamental physics and may eventually solve the riddle of why there is far more ordinary matter than antimatter in the universe today.

Based on data collected from nuclear reactors, multinational scientists have been able to confirm and measure a third type of neutrino oscillation, said Wang Yifang, a spokesperson for the experiment and head of the Institute of High Energy Physics of the Chinese Academy of Sciences.

Neutrinos, the wispy particles that flooded the universe in the earliest moments after the Big Bang, are continually produced in the hearts of stars and other nuclear reactions. They travel at close to the speed of light and pass mostly unhindered through everything from planets to people, responding only to the weak nuclear force and very weakly, to gravity. The challenge of capturing these elusive particles has made neutrinos a mystery to scientists for decades.

The three basic neutrino "flavors" - electron, muon and tau neutrinos - mix together and oscillate. This activity is extremely difficult to detect.

Two types of oscillation -solar and atmospheric neutrino oscillation - have been confirmed previously and helped the discoverer win the Nobel Prize in Physics, while the third type of oscillation was not detected until the Daya Bay experiment.

Starting in 2011, scientists in the Daya Bay collaboration observed tens of thousands of interactions of electron antineutrinos, caught by six massive detectors buried in the mountains adjacent to the powerful nuclear reactors of the China Guangdong Nuclear Power Group. These reactors produce millions of quadrillions of elusive electron antineutrinos every second.

The copious data revealed for the first time the strong signal of the effect that the scientists were searching for, a so called "mixing angle" named theta one-three, which expresses how electron neutrinos and their antineutrino counterparts mix and change into the other flavors.

"People's improved knowledge about neutrinos can help solve the mystery of why antimatter disappears," said Liu Jianglai, a researcher of Shanghai Jiao Tong University, who participated in the experiment.

On a practical level, neutrinos could one day be applied to detect nuclear weapons carried by terrorists, scientists said. They could also provide an advanced spaceship using antimatter as power, something akin to the Enterprise of "Star Trek" fame, they said.

 


Source: Shanghai Daily