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 Neutrinos are the second most bountiful particles after photons,
which carry light, with trillions of them streaming through our
bodies every second, but their true nature has been poorly
understood.
Takaaki Kajita and Arthur McDonald's breakthrough was the discovery
of a phenomenon called neutrino oscillation that has upended
scientific thinking and promises to change understanding about the
history and future fate of the cosmos.
“It is a discovery that will change the books in physics, so it is
really major discovery,” Barbro Asman, a Nobel committee member and
professor of physics at Stockholm University, told Reuters.
In awarding the prize, the Royal Swedish Academy of Sciences said
the finding had "changed our understanding of the innermost workings
of matter and can prove crucial to our view of the universe".
For many years, the central enigma with neutrinos was that up to
two-thirds fewer of them were detected on Earth than expected, based
on how many should be flooding through the cosmos from our Sun and
other stars or left over from the Big Bang.
 Around the turn of the millennium, Kajita and McDonald, using
different experiments, managed to explain this by showing that
neutrinos actually changed identities, or "flavors", and therefore
must have some mass, however small.
McDonald told a news conference in Stockholm by telephone that this
not only gave scientists a more complete understanding of the world
at a fundamental level but could also shed light on the science
behind fusion power, which causes stars to shine and could one day
be tapped as a source of electricity on Earth.
"Yes, there certainly was a Eureka moment in this experiment when we
were able to see that neutrinos appeared to change from one type to
the other in traveling from the Sun to the Earth," he said.
NEW PHYSICS
McDonald is professor emeritus at Queen’s University in Canada,
while Kajita is director of the Institute for Cosmic Ray Research at
the University of Tokyo.
“When I took the phone call and heard that they’d decided on the
prize, it was a huge honor. I’m still so shocked I don’t really know
what to say,” a grinning Kajita told a packed news conference in
Tokyo.
Kajita said his work was important because it showed there must be a
new kind of physics beyond the so-called Standard Model of
fundamental particles, which requires neutrinos to be massless.
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The final piece of the Standard Model was slotted into place in
2012, with the detection of the Higgs boson particle at CERN's Large
Hadron Collider outside Geneva. But it is now clear that the model
does not provide a complete picture of how the fundamental
constituents of the universe function.
While McDonald and Kajita have cracked a key part of the puzzle,
other questions remain, including the exact masses of neutrinos and
whether different types exist beyond the electron-neutrinos,
muon-neutrinos and tau-neutrinos identified so far.
Michael Turner, director of the Kavli Institute for Cosmological
Physics at the University of Chicago, who knows both laureates,
said, "neutrinos attract a special kind of person".
Unlike scientists who work on high-energy particle physics in
massive particle accelerators that produce trillions of events,
neutrino scientists search for elusive particles with detectors deep
in the ground, away from interference from cosmic and other
radiation.
The 8 million Swedish crown ($962,000) physics prize is the second
of this year's Nobels. Previous winners of the physics prize have
included Albert Einstein, Niels Bohr and Marie Curie.
The prizes were first awarded in 1901 to honor achievements in
science, literature and peace in accordance with the will of
dynamite inventor and business tycoon Alfred Nobel.
The prize for medicine was awarded on Monday to three scientists for
their work in developing drugs to fight parasitic diseases including
malaria and elephantiasis.
(Additional reporting by Sven Nordenstam, Elaine Lies and Julie
Steenhuysen; Editing by Alistair Scrutton and Alison Williams)
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