Japan’s Takaaki Kajita and American Arthur B. McDonald jointly won the 2015 Nobel Prize in Physics for their discovery of neutrino oscillations, which shows that neutrinos have mass.
Takaaki Kajita belongs to the University of Tokyo while McDonald is from Queen’s University, Canada.
Both the winners will share the 8 million Swedish kronor prize money with one half going to McDonand and the other half to Kajita. Each winner will also get a diploma and a gold medal at the annual award ceremony on 10 December 2015, the anniversary of the death of prize founder Alfred Nobel.
Takaaki Kajita presented the discovery that neutrinos from the atmosphere switch between two identities on their way to the Super-Kamiokande detector in Japan.
While, the research group in Canada led by Arthur B. McDonald demonstrated that the neutrinos from the Sun were not disappearing on their way to Earth. Instead they were captured with a different identity when arriving to the Sudbury Neutrino Observatory.
Their experiments demonstrated that neutrinos change identities. This metamorphosis requires that neutrinos have mass. The discovery has changed understanding of the innermost workings of matter and can prove crucial to view of the universe.
With this, a neutrino puzzle that physicists had wrestled with for decades, had been resolved. Compared to theoretical calculations of the number of neutrinos, up to two thirds of the neutrinos were missing in measurements performed on Earth. Now, these two experiments discovered that the neutrinos had changed identities.
The discovery led to the far-reaching conclusion that neutrinos, which for a long time were considered mass-less, must have some mass, however small.