Scientists Takaaki Kajita and Arthur McDonald Win Nobel Prize for Neutrino Research

The Nobel Prize for physics was awarded to scientists Takaaki Kajita and Arthur McDonald for their research regarding the neutrino oscillations, leading to the discovery that the particles have mass.

APS News Writer Emily Conover covered the news in the story below:

The Nobel Prize in physics was awarded today for the discovery of neutrino oscillations, an observation that revealed the unusual behavior of these misfit particles, and indicated that neutrinos have mass. The prize honored two scientists who were instrumental in making the discovery: Takaaki Kajita of the University of Tokyo, for his work on the Super-Kamiokande experiment, and Arthur McDonald of Queen’s University, Kingston, Canada, for his work on the Sudbury Neutrino Observatory (SNO) experiment.
Neutrinos, which are produced in a variety of nuclear reactions and were once thought to be massless, come in three types — electron, muon, and tau. But we now know that these identities, known as “flavors,” are not fixed. In a series of large-scale particle physics experiments performed deep underground, scientists showed that neutrinos oscillate from one flavor to another.

In 1998, the Super-Kamiokande experiment saw evidence of oscillation in muon neutrinos that are produced when cosmic rays interact with the Earth’s atmosphere. Physicists measured the number of muon neutrinos coming from directly overhead, and compared that to the number from below, which traversed a longer path — through the Earth — to reach the detector. They saw fewer muon neutrinos from below than expected, indicating that the neutrinos changed flavor during their long journey.

SNO clinched the case for oscillation in electron neutrinos produced by the sun. They observed the expected total number of neutrinos, but fewer electron neutrinos than predicted, indicating a flavor change. The prize honors the leaders of the two collaborations, who worked with their many colleagues to secure the results. On the phone during a press conference announcing the prize, McDonald emphasized the contributions of his collaborators, saying, “There’s great camaraderie associated with this work, even though it took many years working to try to accomplish it.”

APS President Sam Aronson said of the prize, “APS congratulates Takaaki Kajita and Arthur McDonald on the Nobel Committee’s recognition of their important work on the behavior of neutrinos, and in particular the ability of the particles to change form, which indicates that neutrinos have mass. The discovery has major bearing on the structure of the universe as well as the physics of the nucleus.”

Takaaki Kajita (left) and Arthur McDonald

Takaaki Kajita (left) and Arthur McDonald

McDonald, an APS fellow, previously won the APS Tom W. Bonner Prize in Nuclear Physics in 2003. Kajita received the APS W.K.H. Panofsky Prize in Experimental Particle Physics in 2002.

A number of key papers from their groups were published in the APS journal Physical Review Letters and are free to read:

Gray Arrow Evidence for Oscillation of Atmospheric Neutrinos
Gray Arrow Measurement of the Rate of νe + d → p + p +e Interactions Produced by 8B Solar Neutrinos at the Sudbury Neutrino Observatory
Gray Arrow Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory
Gray Arrow Physics offers a Landmark Focus article by PRL Editor Robert Garisto. Neutrinos Have Mass


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