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Deep in the Earth, a search for neutrinos

A historic gold and silver mine in South Dakota’s Black Hills has been selected as the site for an underground laboratory complex that could become the largest and deepest in the world.
/ Source: contributor

A historic gold and silver mine in South Dakota’s Black Hills has been selected as the site for an underground laboratory complex that could become the largest and deepest in the world. The Homestake mine near Lead, S.D., the oldest mine in the Western Hemisphere, won out over three other sites in a bid to develop an underground lab that may help illuminate both a tiny particle known as a neutrino and some of the universe’s biggest mysteries.

Yesterday’s announcement was greeted enthusiastically by South Dakota officials and residents who have celebrated an annual Neutrino Day for the past six years and even created a Miss Neutrino persona in an effort to renovate the shuttered mine and revitalize the state’s economy.

“This is great news for science and of course for the children of South Dakota and the region,” said Gov. Mike Rounds in a statement.

The scientific sweepstakes, sponsored by the National Science Foundation and potentially worth hundreds of millions of dollars, also had been watched closely by researchers eager for a national underground facility to become a reality after years of political wrangling and often tortuous rounds of bidding. Besides the Homestake site, research groups had proposed building the lab in an active molybdenum mine in Colorado, in an iron mine-turned laboratory in northern Minnesota and in an old railway tunnel beneath a Washington State ski resort.

“We’re very, very pleased with the result,” said Kevin Lesko, a neutrino physicist who led the Homestake effort. “Then comes the reality that we’ve got a lot of work ahead of us.”

Lesko, who holds joint appointments at the University of California at Berkeley and Lawrence Berkeley National Laboratory, said his consortium will use the awarded grant money of up to $15 million over three years to proceed with a conceptual design of the laboratory. Eventual construction and experiments valued up to $500 million, however, will hinge on approval of the final design and authorization by the National Science Board and Congress.

Pier Oddone, director of Fermilab in Chicago, welcomed the move toward a new underground laboratory and the range of experiments it would enable, though he said physicists and other scientists must keep pushing until the lab is constructed.

“It’s great that this is being considered,” Oddone said. “Of course, there is a long ways yet for this to go.”

Critics had raised concerns over the mine’s infrastructure and flooding in its lower reaches. But the science foundation’s 22-member panel of experts was unanimous in its opinion that the Homestake site offered the greatest potential for developing an extensive underground laboratory. If built as envisioned, the space would be the largest and deepest of its kind in the world, with major research campuses positioned 0.9 miles and 1.4 miles underground and scientific access to a depth of more than 1.5 miles.

The deep underground space, physicists said, will provide a thick rock shield against the trillions of cosmic rays constantly raining down on the planet, allowing researchers to tune out the background and focus on rarer but far more informative neutrino particles. Some of these ghostly specks, much smaller in size than an atom, may hold the secrets to understanding how the universe is stitched together, what makes up the peculiar substance known as dark matter  and where the universe’s supply of antimatter is really stored.

Among the many potential experiments bandied about by scientists, neutrino beams could be generated in Chicago’s Fermilab and aimed toward underground detectors in the Homestake mine. Initial physics experiments aimed at understanding dark matter could begin in a year or so, and other fields such as microbiology, geology and engineering also stand to benefit from the new space.

Shuttered in 2002, the mine first caught the attention of scientists four decades earlier when physicist Raymond Davis of Brookhaven National Laboratory used a 100,000-gallon tank of dry cleaning solvent to detect neutrino particles nearly one mile beneath Homestake’s surface. The pioneering experiments demonstrated that the ethereal neutrino specks capable of zipping through any surface virtually unhindered are produced in the thermonuclear reactions that fuel the sun, earning Davis a share of the Nobel Prize in Physics just weeks after the mine auctioned off much of its heavy machinery.

By then, the residents of Lead had already celebrated their second annual Neutrino Day, a hopeful acknowledgment of scouting missions to Homestake that sought to convert the leaky 19th century mine into a sleek 21st century scientific powerhouse. The movement energized much of the state, garnering $46 million in state-controlled funds and $70 million in donations from S.D. philanthropist T. Denny Sanford, for whom the new laboratory will be named.

The conversion project has likewise sparked the imagination of the local community. A costumed chamber of commerce board member known as Miss Neutrino has regularly appeared during Neutrino Day festivities and a former miner recently designed a whimsical T-shirt proclaiming Lead the “Neutrino Capital of the World.”

Karen Everett, executive director of the Historic Deadwood Lead Arts Council that sponsored the T-shirt design competition, said she can confirm that the local community’s knowledge of particle physics is now “definitely” better than average.

Beyond the potential windfall for the local and state economies, researchers may have the most to gain. Although American scientists have played key roles in conducting experiments within deep underground laboratories in countries such as Canada, Italy and Japan, “this is going to be the first opportunity to really have a domestic program,” Lesko said. “And that gives the U.S. scientists an opportunity to really lead in the field of underground research.”