Nobel Prize in Physics 2015 won by Kajita and McDonald
The Nobel Prize in Physics 2015 was awarded to Takaaki Kajita from Japan and Arthur McDonald from Canada for the discovery of neutrino oscillations, which shows that neutrinos have mass. Neutrinos were first considered to be massless. The award ceremony will be on 10 December, the anniversary of Nobel's death.
At the turn of the millennium, Takaaki Kajita and Arthur McDonald were both head of a research team of neutrino researchers. In 1998, Kajita presented the revolutionary discovery that neutrinos from the atmosphere oscillate: they switch identities on their way to the Super-Kamiokande detector in Japan. Meanwhile, the research group of McDonald of the Sudbury Neutrino Observatory (SNO) demonstrated that neutrinos from the sun can change 'flavour' as well. The fact that neutrinos oscillate, led to the conclusion that they must have some mass after all.
Solar neutrino problem
The research of Kajita and McDonald also solved a mystery from astrophysics. Most neutrinos that reach the earth are neutrinos from the sun. For decades however, astronomers measured far lower solar neutrino fluxes than predicted. Most particle physicists assumed the solar model had to be deficient. The research of Kajita and McDonald explained the gap between the measured and predicted solar neutrino fluxes. Some of the neutrinos start out as electron type neutrinos but oscillate into the muon or tau type neutrinos. The astronomers were only measuring electron neutrinos, which explained why a part of the neutrinos was missing.
"Wonderful news"
Frank Linde, chair of APPEC, the Astroparticle Physics European Consortium and former director of Nikhef, was one of the particle physicists who thought the astronomers were mistaken in their modelling: “Untill this proved they were right after all." He is thrilled that the Nobel Prize in Physics is awarded to neutrino research: "For me this discovery is exactly what makes experimental physics so interesting: sometimes you discover the completely unexpected and a long-standing mystery is solved! And as a bonus, a whole new field of research has opened up: the detailed study of neutrino oscillations.”
This year, FOM organised a Nobel Prize Poll in the run-up to the announcement. Nikhef researcher Kazuhiro Agatsuma has won by correctly predicting Kajita.
More information
Press release and background information of the Royal Swedish Academy of Science