Scientists look for the most elusive particles in the universe in underground laboratories, such as this one adjacent to an old iron mine in northern Minnesota. The Soudan Laboratory is studying neutrinos with the hexagonal detector at left, which is more than two stories tall. A mural depicts the effort to solve some of the most important mysteries in physics. Detectors in an adjacent cavern are searching for particles of dark matter, which makes up about five-sixths of all matter. [Damond Benningfield]
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A half-mile below the hills of northern Minnesota, visitors to the Soudan Mine State Park face a choice. Turn left, and they can climb aboard carts like those in “Temple of Doom” to explore an abandoned iron mine. Turn right, though, and they enter a laboratory where scientists are studying some of the most important topics in modern physics.
Miners began hauling out iron ore in the 1880s. The mine was shut down in 1962, and it’s been a state park ever since.
In recent decades, though, scientists dug two new tunnels off the mine’s lowest level. One of the tunnels hosts an experiment that studies neutrinos — phantom-like particles produced in the hearts of stars. The other hosts two experiments that are trying to find particles of dark matter — matter that produces no detectable energy, but that exerts a gravitational pull on the normal matter around it.
Several dark matter experiments are operating around the world, and all of them are deep underground. That’s because interactions between dark matter and normal matter are extremely rare, if they happen at all. At the surface, the signal of such an interaction would be drowned out by cosmic rays — heavy particles from deep space — as well as the radioactive decay of elements on Earth’s surface and other events.
The rock above the Soudan laboratory blocks most of these other signals. That should make it easier to detect the “fingerprint” of dark matter. More about that tomorrow.
Script by Damond Benningfield, Copyright 2014