Nobel Prize for missing piece in neutrino mass puzzle

STOCKHOLM — Takaaki Kajita of Japan and Arthur McDonald of Canada won the Nobel Prize in physics on Tuesday for discovering that tiny particles called neutrinos change identities as they whiz through the universe, proving that they have mass.

By uncovering the "chameleon-like" nature of neutrinos, the laureates had solved a long-standing puzzle in particle physics that could alter our grasp of the cosmos, the Royal Swedish Academy of Sciences said.

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

Kajita, 56, is director of the Institute for Cosmic Ray Research and professor at the University of Tokyo. McDonald, 72, is a professor emeritus at Queen's University in Kingston, Canada.

Asked how he felt when he realized Tuesday that his work was suddenly going to receive the world's focus, McDonald said, "It's a very daunting experience, needless to say."

Kajita seemed flummoxed at a news conference organized by his university. "My mind has gone completely blank. I don't know what to say," he said after taking the stage.

After getting his composure back, he stressed that many people had contributed to his work, and that there was much work still to do.

"The universe where we live in is still full of unknowns. A major discovery cannot be achieved in a day or two. It takes a lot of people and a long time. I would like to see young people try to join our pursuit of mystery solving," he said.

Neutrinos are miniscule particles created in nuclear reactions, such as in the sun and the stars.

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