* Japanese, Canadian researchers showed neutrinos have mass
* Paves way to better understanding of evolution of universe
(Adds comment from Kajita, further reaction)
By Simon Johnson and Ben Hirschler
STOCKHOLM/LONDON, Oct 6 (Reuters) - A Japanese and a
Canadian scientist won the 2015 Nobel Prize for Physics on
Tuesday for discovering that elusive subatomic particles called
neutrinos have mass, opening a new window onto the fundamental
nature of the universe.
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 "flavours", 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 travelling 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 honour. 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.
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 honour 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. ID:nL8N1251OJ
($1 = 8.3151 Swedish crowns)
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Graphic on Nobel laureates http://graphics.thomsonreuters.com/15/nobels/index.html
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