The universe as we know it shouldn’t exist. Unlocking the reasons why may depend on once again striking gold in a mine buried a mile underground in rural South Dakota.
The largest U.S.-based particle physics experiment ever is now under construction in the old mine in Lead, S.D., breathing new life into the small town more than 140 years after the Black Hills gold rush drove its founding.
The international collaboration involving 1,000 scientists from more than 30 countries aims to answer the question: Are mysterious particles called neutrinos the reason we are here?
Scientists believe equal parts of matter and antimatter should have been created during the formation of the universe. But that didn’t happen, and no one knows why. Instead, the visible universe is dominated by matter. Neutrinos may be the reason why — physicists just need a bigger, well, everything to find out.
10 years, $1 billion, 870,000 tons of rock
Once complete, the Deep Underground Neutrino Experiment will beam the particles 800 miles through the earth from Fermi National Accelerator Laboratory outside Chicago to Lead’s Sanford Underground Research Facility.
Sanford Underground Research Facility, which opened in 2012 after it repurposed the gold mine for scientific research, has run experiments involving neutrinos and dark matter, but nothing even close to this scale.
To embark on its grand experiment, Sanford must first expand its footprint by carving out the Long-Baseline Neutrino Facility amid tunnels that once housed the deepest and most productive gold mine in the Western Hemisphere.
Over the next 10 years, workers will remove more than 870,000 tons of rock and install a four-story high, 70,000-ton neutrino detector, while the lab’s Illinois counterpart also undergoes significant renovations.
The project will cost more than $1 billion, but scientists hope the payoff from about 12 million neutrinos per second passing through the detector will be far larger, tantamount to striking gold on a universal scale.
“If history is our guide we may learn the answers to questions we don’t even know to ask right now,” says Bonnie Fleming, a physics professor at Yale and deputy research officer on neutrinos at Fermilab.
Intense beams, gigantic detectors
Neutrinos are tricky little things. The extremely tiny particles are among the most abundant in the universe. They don’t interact much with anything and travel close to the speed of light. In fact, three trillion neutrinos just flew through your body while you read the last two sentences — and that’s the big challenge for researchers.
“Maybe it makes you feel better that they only just pass through you, but if you’re actually trying to measure them it means that you need these really intense beams and gigantic detectors to be able to have just a couple interact and measure them,” Fleming says.
Experiments already underway on neutrinos lack the sensitivity and massive scale needed when you’re essentially “looking for a needle in the haystack,” Fleming says. “To do this kind of measurement you need all the right ingredients.”
Essentially, to measure the smallest things, everything must be bigger: Scientists require more neutrinos, larger detectors, more powerful beams, a greater distance to travel, and everything needs to be located deep underground to shield it from cosmic rays.
“Eventually you get to the scale where one organization, one science lab, one country can’t push the boundary to the next level,” says Chris Mossey, deputy director for the Long-Baseline Neutrino Facility.
That’s where the scientists from more than 160 institutions come in, including Europe’s CERN, home to the Large Hadron Collider, the world’s largest and most powerful particle accelerator.
Over the next decade, they will use cutting edge, state-of-the-art technology to build the detector and create data collection systems and algorithms that capture and analyze what’s happening inside. The complicated process involves a range of tasks, including creating electronics that can function in temperatures around-300 degrees Fahrenheit. The reason for the “world’s largest ice box,” as Mossey puts it, is liquid argon, which requires the chilly environment.
Liquid argon, a noble gas, is what neutrinos — and antineutrinos, their counterpart just like matter and antimatter — hit in the detector, allowing scientists to see what occurs on the rare occasion the mysterious particles interact with atoms. Differences in the numbers and properties of neutrinos versus antineutrinos would hint at why matter dominates antimatter in our universe and show if neutrinos played a role in its formation.
“If we don’t see a difference, there’s still a big mystery and a puzzle,” Fleming says. “If we do see something, it’s a big piece of the puzzle for why we exist.”
Renovating the mine, revitalizing the town
Before the first neutrino beam travels from Illinois to South Dakota, Lead’s decommissioned Homestake Gold Mine and some of its 370 miles of tunnels up to 8,100 feet below the surface will undergo major renovations.
Helping pave the way are former Homestake workers themselves: Half of Sanford’s current staff used to work in the mine, leaving the facility with an “incredible knowledge base” to repurpose it, says Mike Headley, executive director of the lab.
Workers will shore up shafts built in the 1930s to carry miners and equipment underground. To crush and move the rock, they will construct a 3,700-foot rock conveyer system. Then, they will install all the cutting-edge equipment that runs the experiment deep underground.
While many of the tools used for excavation to mine gold are the same as those used to sculpt the caverns that will house the neutrino detector, engineers must shift their focus to preserving the quality of the walls so they endure for decades.
“It’s like the difference between running a gravel quarry versus building a skyscraper. You want to get it right because you want the skyscraper to last forever,” says David Vardiman, one of Sanford Lab’s lead geotechnical engineers and a former Homestake engineer with 40 years in the mining business.
When Vardiman first arrived in Lead in the 1970s, “it was the place to live,” he says. The mine employed about 1,800 people back then, some the 6th generation in their family to work there.
The mine, which produced 41 million ounces of gold over 126 years, closed in 2002 when high production costs could no longer compete with the declining price of gold. Many citizens left town, says Vardiman, who took a severance package.
Today, change is brewing again for the 3,100 people living in the steep, rugged terrain of Lead, which receives more than 16 feet of snow on average each year and is known as a haven for outdoor sports year-round. The economic impact from Sanford Lab, the Homestake Visitor Center and now the neutrino experiment is revitalizing the community, spurring an uptick in sales tax revenue and opening of new businesses, from fast food and a brewery to a hardware store and pharmacy.
“We’re turning the corner from when the mine closed,” says Vardiman, who moved back to Lead for a fourth time when Sanford Lab offered him a job and is now a city commissioner. “We see a reawakening in our business district, more participation and development in the community than we have in the last 20 years.”
Sanford Lab’s staff of 125 will more than double during peak construction. Although the majority of the 1,000 scientists working on the experiment won’t live in Lead, they’ll stay there for about a couple weeks from time to time. Vardiman hopes that influx will spur the town’s economy even more and attract developers who want to build modern housing to entice new residents, he says. Negotiations for several new businesses, including a new motel, are already underway.
While the Department of Energy will fund the bulk of the construction aspect of the project, CERN and other international partners will shoulder most of the cost for building and designing the detector itself, Headley, the lab’s executive director says.
“It isn’t just some big federal government project that the federal government is providing all the resources,” he says. “Everyone’s got a little skin in the game.”
