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October 06, 2015 | Uhuruspirit

The portraits of Nobel Physics Prize winners Takaaki Kajita (L) and Arthur B. McDonald are displayed on a screen during a press conference at the Swedish Academy of Sciences in Stockholm, on October 6, 2015 (AFP Photo/Jonathan Nackstrand)

Two physicists in Japan and Canada shared the 2015 Nobel Prize in Physics Tuesday for discoveries that subatomic particles known as neutrinos can change identities and have mass, offering new insights into the origin of the universe.

Arthur B McDonald of Queen's University in Ontario and Takaaki Kajita of the University of Tokyo were cited for resolving "a neutrino puzzle that physicists had wrestled with for decades."

"The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe," the Royal Swedish Academy of Sciences said.

Neutrinos are the most numerous particles in the cosmos after photons, but before McDonald's and Kajita's discoveries remained "all but hidden," the academy said.

Most neutrinos, which have no electrical charge, are created from nuclear reactions on the sun and continuously bombard our planet and stream through all matter, including human bodies, without being detected.

One of the quandaries surrounding neutrinos that had left physicists scratching their heads for decades was that measurements on Earth had discovered as little as one-third of the neutrinos that were actually thought to exist.

Kajita's and McDonald's work, however, solved the mystery with the discovery that many of the neutrinos had disguised themselves from researchers because they had changed identities.

The two laureates led research teams that tracked the neutrinos using huge water tanks, deep underground in mines, said Anne L'Huillier, chairwoman of the Nobel Committee for Physics.

Their experiments helped show that "neutrinos oscillate, they change identity," she told dpa.

The two physicists "solved the neutrino puzzle and opened a new realm in particle physics," the academy said of their findings.

About 15 years ago, Kajita found in his work at the Super-Kamiokande neutrino detector in Hida in central Japan that neutrinos from the atmosphere switch between two identities.

McDonald was leading a research group at the Sudbury Neutrino Observatory in Sudbury, Ontario, that, meanwhile, also discovered that neutrinos travelling from the sun were not disappearing en route to Earth but arrived with a different identity.

Their work also determined that neutrinos have a small mass, undermining the so-called Standard Model of particle physics, which sought to explain the inner workings of matter.

"Their discovery shows that the Standard Model has to be extended to really describe our universe correctly," L'Huillier said, adding "it changes the cosmological models," and how galaxies are formed.

Furthermore, it "has allowed to understand better how the sun is working, sending out light and heat," L'Huiller said.

Their work has set off a flurry of new experiments on neutrinos, including at the CERN particle physics research centre in Switzerland, that congratulated McDonald who worked there in 2004.

"It's very important for particle physics as a whole," CERN spokesman Arnaud Marsollier told dpa about this year's award.

McDonald said by telephone at the announcement that the subatomic particles help explain "how the universe has evolved."

"Neutrinos are among the fundamental particles we don't know how to subdivide any further," he told reporters at the Royal Swedish Academy of Sciences.

Knowledge of them sheds light on "how the universe has evolved, and knowing whether they are massive helps us unravel those mysteries as well," McDonald said, calling the news of his win a "a very daunting experience."

He also paid tribute to his many colleagues, noting that "there is great camaraderie associated with this work."

Kajita, director and professor at the Institute for Cosmic Ray Research at the University of Tokyo, told a news conference: "I'm very honoured and grateful. My mind has become a complete blank and I don't know what to say."

The Nobel Prize season kicked off Monday with the awarding of the medicine prize to William C Campbell, Satoshi Omura and Youyou Tu for developing treatments for devastating parasitic diseases that affect hundreds of millions of the world's poorest.

The recipients of prizes in the fields of chemistry, literature and peace will be announced later this week, and the prize in economics will be announced Monday.

With the exception of economics, the prizes were endowed by Swedish industrialist Alfred Nobel (1833-96), the inventor of dynamite.

This year the prizes are worth 8 million kronor (956,000 dollars).

The awards are to be presented on December 10, the anniversary of Nobel's death.

- dpa

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