STOCKHOLM, Sweden, Oct. 6 (UPI) -- The 2015 Nobel Prize in Physics has been awarded to two scientists for their work on neutrino subatomic particles that led to the conclusion the elementary particle has mass.
Japanese scientist Takaaki Kajita and Canadian scientist Arthur B. McDonald will receive the prize "for the discovery of neutrino oscillations, which shows that neutrinos have mass," the Royal Swedish Academy of Sciences said in a statement released Tuesday.
Neutrinos are the second-most numerous elementary particles in the cosmos following photons, the particles of light. Many neutrinos are created in reactions between cosmic radiation on the Earth's atmosphere while others are created in nuclear reactions within the Sun.
"The Earth is constantly bombarded by them," the statement reads. "Thousands of billions of neutrinos are streaming through our bodies each second. Hardly anything can stop them passing; neutrinos are nature's most elusive elementary particles."
The scientists' work solved the neutrino puzzle. For decades prior to the discovery, researchers saw that nearly two-thirds of neutrinos were missing when measurements were performed on Earth when compared to theoretical calculations on the number of neutrinos that should have been hitting Earth.
In 1998, Kajita presented the discovery that neutrinos undergo a form of metamorphosis. Kajita's research group in Japan saw that neutrinos that were created in reactions between cosmic rays and the Earth's atmosphere changed identities on their way to Kajita's Super-Kamiokande detector in Japan.
Meanwhile, McDonald's research group in Canada was studying neutrinos created from nuclear reactions inside the Sun, and in 2001 McDonald's team at the Sudbury Neutrino Observatory proved that these neutrinos also switch identities.
"For particle physics this was a historic discovery," Royal Swedish Academy of Sciences said in a statement. "Its standard model of the innermost workings of matter had been incredibly successful, having resisted all experimental challenges for more than twenty years. However, as it requires neutrinos to be massless, the new observations had clearly showed that the standard model cannot be the complete theory of the fundamental constituents of the universe."
Kajita and McDonald will share the nearly $1 million prize for their work. Kajita is currently the director of the Institute for Cosmic Ray Research and a professor at the University of Tokyo in Kawisha.
McDonald, who received his doctorate in physics from the California Institute of Technology in 1969, was named professor emeritus at Queen's University in Kingston, Canada.
"The discovery rewarded with this year's Nobel Prize in Physics have yielded crucial insights into the all but hidden world of neutrinos," the statement adds. "Now the experiments continue and intense activity is underway worldwide in order to capture neutrinos and examine their properties."
"New discoveries about their deepest secrets are expected to change our current understanding of the history, structure and future fate of the universe," the statement concludes.