LUX dark-matter detector underground

Lead, S.D.?An experiment that soon could be the most sensitive instrument in the world looking for a mysterious substance called ?dark matter? has been lowered to a laboratory nearly a mile underground in the Black Hills of South Dakota. ?This was a huge team effort,? said Wendy Zawada, project engineer for the Sanford Underground Research Facility (Sanford Lab).

The Large Underground Xenon experiment, or LUX, arrived late Thursday afternoon at the Davis Campus?a group of laboratory spaces 4,850 feet deep in the former Homestake gold mine in Lead, S.D.  Deep labs protect sensitive experiments like LUX from the noise of cosmic radiation. The state of South Dakota, which constructed the Davis Campus, has converted Homestake into the Sanford Lab. A second experiment in the Davis Campus will look for a rare form of radioactive decay that could shed light on how the universe evolved. The Department of Energy, through Lawrence Berkeley National Laboratory, is supporting science operations at the Sanford Lab while studying how the lab might host other experiments.

Physicist Jeremy Mock of the University of California-Davis, who is a member of the LUX scientific collaboration, admitted he was nervous during the move. ?It?s a major milestone,? he said. And the 6,000-pound experiment is both complicated and delicate.

The LUX detector was built over the course of three years at the Sanford Lab, in a surface facility constructed to mimic the dimensions of the underground lab. The core of the detector is encased in a double-walled titanium ?cryostat??essentially a thermos 6-and-a-half feet tall by 3 feet in diameter. The big thermos keeps 770 pounds of liquid xenon chilled to minus 160 degrees F. If the experiment works, researchers will be able to detect rare collisions between xenon atoms and dark-matter particles, called ?weakly interacting massive particles,? or WIMPs. The second part of the detector, called the ?breakout cart,? is complicated set of pipes, conduits and valves that allow instruments inside detector to transmit data to the outside world. The detector and the breakout cart are connected through three thick, flexible umbilicals. Those umbilical connections had to be protected and maintained throughout the move.

On Wednesday, LUX was taken on a very slow ride by forklift from the surface lab to the top of the Yates Shaft?a distance of about 800 feet. By mid-day Thursday, the detector was ready for its ride down the Yates Shaft in an elevator car called a ?cage.? That trip normally takes scientists and technicians about 10 minutes, but LUX?s descent took two hours. The experiment had to be protected from even the slightest bumps and jiggles, and it was swathed in bubble-wrap, protective foam and plastic. On the 4850 Level, LUX was moved 500 feet to the Davis Campus on ?air bearings,? which lift heavy equipment on a thin cushion of compressed air.

The LUX scientists and a Sanford Lab team had practiced the move with steel and Styrofoam mockups before this week?s operation. ?We also had great contractors,? Zawada said. Donovan Construction of Spearfish, S.D., moved the detector on the surface. Feuillerat?s Welding and Machinery Moving of Rapid City provided the air bearings.

Now the LUX detector will be unwrapped, hooked up and tested before it is lowered into a 71,600-gallon water tank that will further protect it from traces of background radiation. LUX could be taking data by the end of the year, looking for a substance that, though it has never been detected, scientists believe is the most abundant form of matter in the universe.