Deep underground detector closes in on dark matter

May 3, 2004

GAINESVILLE, Fla. — A scientific team that includes a University of Florida physicist has used an “underground observatory” in a former iron mine to search with greater sensitivity than ever before for the universe’s most elusive component: dark matter.

Scientists with the Cryogenic Dark Matter Search project announced Monday they have collected the first data from the observatory, which consists of particle detectors buried nearly a half-mile beneath the Earth’s surface at the mine in Soudan, Minn. The data may shed light on the suspected existence of Weakly Interacting Massive Particles, or WIMPs, thought to be one of the most likely substances composing dark matter, the mysterious and so-far unobserved matter that may comprise as much as a third of the universe.

“What we’re announcing is that we have achieved the best sensitivity yet for detecting these WIMPs,” said UF Assistant Professor Laura Baudis.

The Cryogenic Dark Matter Search project includes 48 scientists from 13 institutions and is funded by the U.S. Department of Energy, the National Science Foundation and the member institutions. The UF group, which Baudis leads, is engaged in “detective work” to weed out interactions with the underground detectors that appear to be WIMPs but are really something else.

That’s not as straightforward as it sounds. The project is located underground because the Earth’s crust impedes cosmic rays, which would normally trip the detectors, creating so much interference that a WIMP could not register, Baudis said. While the Earth screens out the cosmic rays, the detectors are also vulnerable to other “background” particles, such as those generated by radioactive elements in the surrounding rocks or by common radon gas.

“The detectors measure the charge and the vibration of the particles, with the ratio of the two telling us if it’s a background particle or not,” she said. “But for some of the particles, the ratio is what we would expect for WIMPs. So our job is to pin down those false positives and think of strategies to prevent or reduce them from occurring.”

Baudis can be reached at lbaudis@ufl.edu, 352-392-9717.