Hampton Roads physicists chase 'ghostly' neutrinos

Tamara Dietrich
Contact Reportertdietrich@dailypress.com
Hampton Roads physicists chase "ghostly" neutrinos, which open up new frontiers of research

In the time it took you to read this, thousands of billions of neutrinos streamed through your body at nearly the speed of light, and you never even noticed.

The second most-abundant particle in the universe behind photons, neutrinos are elusive to the point of ghostly, and so little understood that until recently they were considered devoid of mass.

This week, Nobel Prizes went to two physicists for their work begun around the turn of this century proving that neutrinos do have mass, after all — a finding that sent ripples through the Standard Model of physics, the complex theory that explains how the cosmos works.

"The discovery," the Nobel committee said in its announcement, "has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe."

But the news comes as no surprise to physicist Robert McKeown, deputy director for science at Jefferson Lab, a national laboratory in Newport News, and the Governor's Distinguished CEBAF Professor at the College of William and Mary in Williamsburg.

For, around the same time that new Nobel laureates Arthur B. McDonald of Canada and Takaaki Kajita of Japan were demonstrating in separate experiments that neutrinos could oscillate and change identities, proving they must have at least some mass, McKeown was part of yet another experiment called KamLAND in Japan. operating in the same mine as Kajita, and reporting similar results.

"So we were very close to the same discovery," McKeown said. "But in our case, we could actually see the neutrinos oscillate as a function of distance and could see the neutrinos oscillate away and come back."

But, while the three experiments may have been conducted around the same time, this week the awards committee only favored McDonald's and Kajita's work.

McKeown takes a philosophical stance.

"Nobel Prize decisions are sometimes difficult to understand," McKeown said. "I think maybe a three-way prize might have made sense. But obviously the Nobel committee saw it differently. I'm just happy to see a Nobel Prize for neutrinos, because we've known that this was extremely important physics discoveries for more than 10 years now."

The prize was appropriate, he said, "even though we were close."

Shy shapeshifters

Neutrinos are forged in various ways: by stars, by nuclear reactor decay or by reactions between cosmic radiation and the Earth's atmosphere. They come in three "flavors" known as electron, muon and tau.

Because they're so elusive, they're hard to detect, much less study. In fact, they were only first theorized in the 1930s and not detected until the 1950s.

"Neutrinos are quite hard to discover," said Michael Kordosky, associate professor of physics at the College of William and Mary in Williamsburg. "They were the last major kind of particle type that was postulated in what we now call the Standard Model."

It was the neutrino results of the early 2000s that drew him to physics in the first place, Kordosky said, and he's now involved in an experiment called MINOS that's considered a definitive cross-check or proving ground to confirm that atmospheric neutrinos do oscillate, or morph from one flavor to another.

In MINOS, or Main Injector Neutrino Oscillation Search, the Fermilab outside Chicago shoots an underground neutrino beam 450 miles way to a detector located half a mile down in a old iron mine in Minnesota. Neutrinos that travel long distances are more likely to oscillate.

When the detector picks up a flash of light, it indicates a neutrino. But those flashes aren't common.

"They're hard to see," Kordosky said. "They just are so shy, they don't want to interact with anything.

"Our neutrino beam creates about 10 to the 13 neutrinos each second — so that is 10,000 billion neutrinos per second. Not all of the beam hits that detector, but it will see something like one neutrino interaction per day."

Only a handful of facilities in the world are capable of this level of neutrino research, said McKeown. Some are conducted in abandoned mines or excavations deep underground to avoid cosmic rays, like the Gran Sasso lab in Italy that was built in conjunction with a roadway as it was carved through a mountain. Their detectors are sometimes submerged in huge water tanks to shield against the radioactive decay of surrounding rock.

Such facilities are time-consuming, vastly expensive undertakings that can require about a decade to pull together from conception to first data-taking, Kordosky said.

What it means

Other than revealing that they're misfits of the Standard Model, neutrinos are now giving physicists fresh lines of research.

"It's already changed physics," Kordosky said. "It's the first bit of the Standard Model as it was originally written down that doesn't work.

"We're looking and trying to figure out what's the rest of the story. That's our job. That's why we got into it. That's why our students are interested in it. And it's exploring the universe in its most fundamental kind of form."

For physicists, said McKeown, punching holes in the Standard Model like this only opens up a world of possibilities.

"There's evidence astronomically for something called dark matter, and also dark energy, and these are things that are not in the Standard Model," McKeown said. "And we now also have these unusual properties of neutrinos which were not in the Standard Model, so we're starting to see evidence that there really is new physics.

"So it's very exciting. It means there's a whole new frontier to explore to try to figure out what is causing all these anomalous properties of the universe."

Dietrich can be reached by phone at 757-247-7892.

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