Physicists Look for Dark Matter Underground
At 7:30 a.m. on a recent Tuesday, about a dozen scientists pulled on steel-toed boots and filed into a steel cage that once ferried hundreds of gold miners to work.
Their destination: a new laboratory 11 minutes and a mile beneath the earth’s surface that could deliver answers to some cosmic questions.
While scientists at CERN in Europe have been grabbing headlines recently by using an enormous accelerator in a hunt for the Higgs boson particle, the team here at the Sanford Underground Research Facility have lofty goals of their own but a very different approach.
They are betting on the power of the quiet, sheltered darkness of the former Homestake gold mine to, among other things, help find dark matter, the so-far invisible particles that are believed to make up as much as 25% of the universe’s mass.
The earth’s surface is bombarded with tiny particles that come from outer space, and they create a noisy setting for experiments. By placing the lab a mile underground, fewer particles reach the experiments, which allows scientists more control when trying to examine different particle interactions.
“We’re trying to chase particles that interact once a week, maybe once a month,” says Richard Gaitskell, a 47-year-old Brown University physicist, who is part of a team that is installing the most-sensitive dark-matter detector ever built in an experiment known as LUX.
Three years ago, the Sanford lab celebrated a reopening of the mine, which had been dormant since 2001. Initial plans called for an $875 million facility, but budget constraints scaled that back to about $120 million, of which $20 million goes to educational purposes. More than half of the funding came from Sioux Falls, S.D., banker T. Denny Sanford. The state and federal government paid for the remainder.
Now, the lab is considered a host space for experiments with their own funding source. They include the Majorana experiment, a $23 million effort to find a rare form of radioactivity to help explain the nature of matter and antimatter, which is being installed now. And one day, scientists hope to launch a $1.5 billion effort to shoot neutrinos, a type of particle, from an accelerator in Illinois through almost 1,000 miles of earth to see how they change before hitting a detector at the Sanford lab.