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【Gifu】Behind the Nobel Prize: enormous experiments at Super-Kamiokande over decades2015.12.04

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The 2015 Nobel Prize in physics was jointly awarded to Takaaki Kajita of the University of Tokyo in Japan and Arthur B. McDonald of Queen’s University in Canada. They discovered that abundant subatomic particles known as neutrinos have a bit of mass. The two recipients are leaders of two major underground neutrino observatories on the other side of the planet. Kajita is one of the leaders of the Super-Kamiokande experiment in Japan.

Super-Kamiokande is a neutrino observatory located 1,000 m (3,300 ft) underground of Mt. Ikenoyama near the city of Hida in Gifu Prefecture. It consists of a cylindrical stainless steel tank that is 41.4 m tall and 39.3 m in diameter holding 50,000 tons of ultra-pure water. Neutrinos are one of nature’s basic building blocks which are constantly bombarding the Earth. They are some of the most abundant particles in the cosmos, and yet some of the most elusive. They have no charge and are so small that they were once thought to be massless. Kajita and McDonald’s work solved the long-standing solar neutrino problem, which was a major discrepancy between the predicted and measured solar neutrino fluxes. Specialized experiments involve huge detectors, and even those only collect a tiny fraction of the total neutrino flux passing through. Kajita and McDonald, in their separate experiments, each showed that neutrinos change between certain flavors – a process called neutrino oscillation.

Kajita expressed surprise at receiving the prize, saying that his head went totally blank. He praised his colleagues that they are the ones who deserve the honor. He also thanked his wife for her being patience with me, always doing research. Soon after the prize announcement, one of the first people, Kajita called was the 2002 Nobel physics winner Masatoshi Koshiba, his former mentor and a fellow neutrino researcher.

Both Kajita and McDonald will get a diploma and a gold medal at the prize ceremony on December 10th and the prize money will be equally split to the winners.

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