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Scientists search for understanding of dark matter

January 20, 2014 at 7:00 PM EST
At the bottom of a nickel mine near Sudbury, Ontario, scientists at one of the world's most sophisticated particle physics observatories are investigating one of the biggest mysteries of the cosmos: What is dark matter? Science correspondent Miles O'Brien helps to shed some light on the research at SNOLAB.
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GWEN IFILL: Basic research, the less glamorous side of science, is often the most important, leading to sometimes unanticipated discoveries that pay off years later.

Tonight, we begin a series of occasional reports on air and online exploring that work.

NewsHour science correspondent Miles O’Brien starts with a report on one project trying to answer a huge question about the cosmos.

MILES O’BRIEN: It’s a long ride down to pay dirt at the Creighton nickel mine in Sudbury, Ontario, the perfect place to find precious metal and, hopefully, a priceless answer to one of the biggest mysteries of the universe; 6,800 feet below the surface, at the end of a long, dusty, dark tunnel, sits a hermetically sealed warren, brimming with intent technicians working on odd-looking scientific instruments.

Welcome to SNOLAB, one of the most sophisticated particle physics observatories in the world, nestled deep underground to filter out the background radiation all around us at the surface. This is where one of the great unanswered questions in the realm of basic research may soon be answered: What exactly is dark matter?

NIGEL SMITH, SNOLAB: This is one of the longstanding contemporary problems in particle — particle astrophysics is, what the hell is this stuff? You know, it’s just — 24 percent of the mass of the universe, we don’t know what it is.

MILES O’BRIEN: While most of us marvel at the stunning beauty of the planets, stars, nebulas and galaxies, particle physicists are fixated on the seemingly empty space in between.

NIGEL SMITH: There has to be more out there than meets the eye. There has to be a significant fraction of the galaxy and a significant fraction of the universe is in a form that we don’t yet understand.

MILES O’BRIEN: So, how can they be so certain? Well, without it, what you see is not what you would get.

At the edge of the Milky Way, stars move faster than they would if they were simply being tugged by the mass of the visible objects at the center of the galaxy. It is likely something else is pulling them along. Scientists may not understand what dark matter is, but they know enough about what it does to map it. And they also are pretty sure what it is made of. They are called WIMPs, generically, so, weakly interacting massive particles.

Yes, WIMPs, they are the current best theory of what dark matter might be. They superseded an earlier idea called massive astrophysical compact halo objects, or MACHOs.

MILES O’BRIEN: The WIMP is winning?

NIGEL SMITH: Everything points towards the WIMP solution being the appropriate solution. So there are many projects that are focused on trying to understand the WIMP and discover the WIMP in reality.

MILES O’BRIEN: And scientists are hunting in the blind, and it is a constant challenge to know how and where to look for the answer. But they think they have a good idea of how to find some WIMPs.

IAN LAWSON, SNOLAB: It’s very critical that we actually maintain a constant temperature for the experiment.

MILES O’BRIEN: Ian Lawson works on an experiment at SNOLAB called PICASSO. It uses superheated freon droplets to try and detect dark matter. When ionizing subatomic particles collide with the freon droplet in just the right way, it creates a gas bubble.

IAN LAWSON: There actually is like a little bubble right in there that hasn’t been compressed yet.

MILES O’BRIEN: Not the dark matter bubble, of course. The bubbles that have appeared so far are created by a neutron radiation source used regularly to calibrate and test the instruments.

What would the dark matter bubble look like?

IAN LAWSON: The dark matter bubble looks very, very similar to a neutron bubble.

MILES O’BRIEN: You think? But we haven’t seen one, right?

IAN LAWSON: We haven’t seen one, but that’s what we think.

MILES O’BRIEN: Is there some disappointment that you haven’t seen it yet?

IAN LAWSON: Not a disappointment that we haven’t seen it, but it just means that we have to make our detectors more and more sensitive.

MILES O’BRIEN: That’s what Chris Jillings and his team are working on in another vein of this mine of the mind.

The experiment they are building is called DEAP. In this case, the target medium for detecting the ghostly dark matter particles will be liquefied argon. The hope is a WIMP will act like a cue ball, striking an argon nucleus in just the right way.

CHRIS JILLINGS, SNOLAB: The argon nucleus would recoil through the liquid argon, and a little bit of interesting chemistry would happen. The energy will temporarily make some molecules, which will decay and emit a flash of light. So the irony is, although we don’t — dark matter doesn’t interact with light in any way, once it hits the argon nucleus, what we will detect is a tiny flash of light.

MILES O’BRIEN: This device, a photomultiplier, is designed to see and record those tiny flashes with an array of extremely sensitive lenses and sensors.

In order to give the detectors a fighting chance of success, workers here keep SNOLAB squeaky clean to remove as much background radiation as they can. Everything that comes into the lab is thoroughly wiped down, everything, and everyone as well — no exceptions for visiting reporters. I had to remove the clothes I wore in the dirty part of the mine, take a thorough shower, and then change into clean room clothing that stays in the lab.

SNOLAB has some deep roots in the hunt for the tiniest particles that make up our universe. The predecessor organization here, the Sudbury Neutrino Observatory, in the 1990s made some very significant scientific finds in the hunt for neutrinos, tiny particles which are emitted from the fusion reaction on our sun.

For many years, physicists hoped neutrinos were the answer to the dark matter mystery, but the speedy, wispy particles only constitute 1 percent of the missing puzzle piece.

SNOLAB physicist Christine Kraus is pretty sure this time they are homing in on the right answer.

CHRISTINE KRAUS, SNOLAB: I think that we will see something very exciting, exciting within the next five to 10 years, hopefully the next five years. So, I think the next generation of experiments has a very good shot at finding dark matter.

MILES O’BRIEN: This is Nobel kind of work, isn’t it?

CHRISTINE KRAUS: If dark matter would be discovered, I think that would be — would be a Nobel Prize, yes.

MILES O’BRIEN: Legendary physicist Stephen Hawking came to visit SNOLAB in September of 2012. But make no mistake. This observatory is not the pre-anointed victor. The race for this Nobel is under way, underground, at competing facilities in the U.S., Europe, Russia, and Japan.

This is big, basic research, without a clear application in mind, or even conceivable. But it is completely worthwhile, according to Nigel Smith.

NIGEL SMITH: The things that we developed to observe dark matter, the things that we developed to observe these neutrinos, they will have spin-out. They will have spin-out in technology and the knowledge that is developed to understand the systems that we are building. So, you never quite know where knowledge is going to take you.

MILES O’BRIEN: Physicist Clarence Virtue believes scientists here are leaving a legacy of knowledge for future generations. He heads up an experiment designed to catch neutrinos emitted by an exploding giant star, a supernova.

CLARENCE VIRTUE, Laurentian University: We’re building an ever more complete picture of what the universe is, how it came about, where it’s going.

MILES O’BRIEN: So dark matter matters?

CLARENCE VIRTUE: Absolutely. It’s a piece of a real puzzle. It’s rather annoying to particle physicists that it is so important and yet we know next to nothing about it.

MILES O’BRIEN: Apparently, when particle physicists get annoyed, they don’t mess around. They have dug themselves some deep holes, and the only way out may be to shed some light on some particles that don’t reflect it, and yet may enlighten us all.