Saturday, October 17, 2015

The Solar Neutrino Problem & The Standard Model

Particle Physics

Sudbury Neutrino Observatory is 2,100 metres (approx 6.800 feet) below the earth’s surface,
where the solar neutrino problem was solved.
K
ate Allen of The Toronto Star writes: “To solve this problem, McDonald and his
colleagues dreamt up SNO. Deep in an INCO mine (now owned by Vale), protected
from cosmic radiation constantly bombarding the earth’s surface, the scientists installed
a 12-metre-wide acrylic vessel filled with 1,000 tonnes of ultra-pure heavy water.
The vessel, surrounded by a geodesic sphere equipped with 9,456 light sensors.
The scientific facility measures 5,000 square metres (approx 54,000 square feet).
Photo Credit: SNOLAB
Source: Women In Science & Engineering, Sudbury

The co-winners of the 2015 Nobel Prize in Physics are not only deserving of the award, but also are increasing our understanding of our Sun. The prize was awarded to Takaaki Kajita for the SuperKamiokamde experiment in Japan and Arthur McDonald for the Sudbury Neutrino Observatory (SNO), in Canada, the Nobel Prize release says, “for the discovery of neutrino oscillations, which shows that neutrinos have mass.”

In particular, both research groups, working independently, solved the solar neutrino problem. The problem, simply stated, was that less solar neutrinos were detected than calculations suggested or predictions. When this happens, scientists look for reasons why the two differ. What they found is that the Standard Model of particle physics, which states neutrinos have no mass, is no longer true.

During their  journey from the Sun to Earth, neutrinos can change identity (in what are called neutrino oscillation), and come in three “flavours”— electron, tau and muon. In “Canadian physicist wins Nobel Prize for work on neutrinos,” (October 6, 2015), Kate Allen writes in The Toronto Star:
Canadian physicist Arthur B. McDonald has won the Nobel Prize for discoveries about the behaviour of a mysterious solar particle, teased from an experiment buried two kilometres below Sudbury.

The Queen’s University professor emeritus was honoured for co-discovering that elusive particles known as neutrinos can change their identity — or “oscillate” — as they travel from the sun. It proved that neutrinos must have mass, a finding that upset the Standard Model of particle physics and opened new avenues for research into the fundamental properties of the universe.

McDonald, 72, shares the prize with Takaaki Kajita, whose Japanese collaboration made the same discovery with slightly different methods.

To measure solar neutrinos, McDonald and a 130-person international team built a massive detector in an operational copper mine southwest of Sudbury. The location allowed the experiment to be highly sensitive but created enormous logistical challenges. Construction on the Sudbury Neutrino Observatory — SNO — began in 1990. The experiment collected its first data nine years later.

“I think we all knew that if we could manage to do it, it would be a very significant measurement. And that’s the way it turned out,” McDonald said Tuesday, 10 “crazy” hours after he was awakened by a telephone call from Sweden telling him he had won the prize in physics.
These experimented were confirmed at the Sudbury Neutrino Observatory in 2001. A bit about the observatory. Sudbury is a known mining city in northern Ontario, about 340 km (about 200 miles) northwest of Toronto; the SNO detector is situated deep in the ground of an INCO copper mine in Copper Cliff, which is a few miles outside Sudbury.

Now known as the SNOLAB, the facility used a geodesic sphere—it surrounds an acrylic container of 1,000 litres of heavy water (deuterium oxide) supplied by AECL—that contains almost 9,500 light sensors to detect neutrinos created by fusion reactions in the sun. When neutrinos hit the heavy water, an event that took place about 10 times a day, a flash of light resulted.

Here is an added note about the mass of neutrinos from the American Physical Society (Physics) news site in an article (“Neutrino Oscillations Nab Nobel Prize;” October 6, 2015), by Emily Conover:
The exact values of the neutrino masses are still unknown, but physicists do know that neutrino masses are oddly tiny — a millions times smaller than the electron mass. Some physicists believe there may be different physics underlying the masses of the neutrinos than of other particles. Massive neutrinos could also be a key to understanding the source of the matter-antimatter imbalance in our universe. And there may be other types of lurking, undetected neutrinos, known as "sterile" neutrinos.
So, the search for understanding neutrinos, and thus more about our universe, continues. For now, this ranks as one of the most important experiments of the 20th century. More tp follow.

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For more, go to [TorontoStar]

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