In DepthNobel Prizes

Neutrino oscillations honored

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Science  09 Oct 2015:
Vol. 350, Issue 6257, pp. 145
DOI: 10.1126/science.350.6257.145

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Takaaki Kajita of the University of Tokyo and Arthur McDonald of Queen's University in Kingston, Canada, won the Nobel Prize in physics for discovering a weird identity-shifting by ghostly particles called neutrinos. Neutrinos come in three flavors—electron, muon, and tau—and the new laureates showed that the types morph into one another. Kajita led researchers working with the Super-Kamiokande, a gargantuan neutrino detector in a zinc mine 250 kilometers northwest of Tokyo, to study muon neutrinos produced when cosmic rays strike the atmosphere. In 1998 they found that the number of muon neutrinos raining down from above differed from the number coming a much longer distance upward through Earth—evidence that the neutrinos were changing identity as they zipped along. McDonald and colleagues worked deep in a mine in Canada at the Sudbury Neutrino Observatory. They studied neutrinos from the sun, all of which start out as electron neutrinos, and showed that along the 150-million-kilometer trek to Earth, some of those neutrinos change into muon and tau neutrinos. The esoteric morphing proves neutrinos have mass, and physicists now study it in hopes of probing matters as fundamental as how the universe generated so much more matter than antimatter.

  • * With reporting by Daniel Clery and Dennis Normile.