Neutrino Day: Getting the public excited about dark matter

In South Dakota’s Black Hills, near the town of Deadwood and about a mile underground in an old gold mine, a physics lab plumbs the secrets of the universe. The researchers at Sanford Underground Research Facility (SURF) seek exotic phenomena, such as miniscule particles that pass right through our planet and a hypothetical form of matter that has mass and gravity, but is otherwise undetectable. Cosmic rays would crowd its sensitive instruments with junk data, so the facility is buried deep underground.

Ultimately, though, such a seemingly remote spot is a great place to look at some of the harder-to-detect building blocks of the universe.

“Basically what we see in the universe makes up about 5 percent of the universe,” says Dr. Patrick Treuthardt, assistant director of the Astronomy and Astrophysics lab at the N.C. Museum of Natural Sciences. Dark matter is invisible – at least to us – and neutrinos are tiny and lightweight.

On Saturday, SURF celebrates Neutrino Day – and this year, the annual event expands out of the Black Hills. One Neutrino Day event is at the N.C. Museum of Natural Sciences and features talks by Treuthardt and Dr. Matthew Green, assistant professor of physics at N.C. State University and Oak Ridge National Lab, and a live video feed to SURF itself, where researchers in that South Dakota lab will be taking audience questions.

It’s a glimpse into a state-of-the-art facility and a chance to talk with people on the cutting edge of physics research – some of whom live and work locally.

“Every year the Sanford Underground Research Facility hosts Neutrino Day, which is to bring the public in to educate them about the science that’s being done underground in the mine,” Green says. “Typically, it’s difficult to drum up that kind of public interest for physics experiments, and it’s nice to be able to really connect with the public.”

What are neutrinos?

Green will talk about neutrinos – what they are, namely, but also his work with them. They’re incredibly small – electrons and neutrons dwarf them – yet they have mass, unlike photons (that is, the waves or particles that make up light). Neutrinos pass through solid matter without stopping – they’re passing through you right now – and one source is the sun.

The technology to detect neutrinos has existed since the 1960s, Green says, with this year being the 50th anniversary of the first experiment at the Homestake Mine, where the SURF lab is located. Detecting them typically requires a large source like a nuclear reactor, Green says, or a sizable detector. One facility inside a mountain in Japan, he says, is the size of an office building.

All this gadgetry in all these buried labs is so that researchers like Green can get at the secrets these tiny particles keep. Why are neutrinos so lightweight, for instance?

“We have some ideas, and actually the experiment that we are building underground in South Dakota seeks to try and address that,” he says. “We’re trying to determine if neutrinos are their own anti-particles. If they are, that suggests a mechanism for how the neutrinos acquired masses that are so small compared to everything else.”

Next-generation research

This is only one of many experiments in the works at SURF. Another, Green says, involves directing a neutrino beam from the Fermilab in Batavia, Ill., to pass through the Earth and intersect with liquid argon in the South Dakota facility. Green’s not sure of the timeline on this experiment, but it’s one of many next-generation physics experiments for which SURF is the ideal lab.

For Green’s studies of the tiny, Treuthardt studies matter that’s often observed on a massive scale. His work is in galaxy morphology and dynamics – in short, the study of how galaxies are shaped and how they came to be that way. In looking at a galaxy, he says, you can determine its mass by observing how it rotates. When that’s compared to how much light it generates, there’s a gap – there aren’t enough stars visible to account for the galaxy’s mass. Something else is there.

Aside from giving galaxies much of their mass, dark matter is also what binds them together in clusters. The very shape of the universe, as current thought is concerned, stems from massive filaments of dark matter. It’s invisible, but so is much of the universe.

“That’s why we call it dark, because it doesn’t give off any radiation, and the reason we call it matter is because it has mass,” Treuthardt says. “That’s basically all we know about it.”

This story was originally published July 9, 2015 at 9:00 AM with the headline "Neutrino Day: Getting the public excited about dark matter."