U experiments at Duluth mine winding down

Soudan lab members say it will take several years to clear the mile-deep mine of equipment.

by Keaton Schmitt

In coming years, thousands of tons of complex machinery will be hauled from half a mile in the ground as experiments in a University of Minnesota physics lab close down.
For decades, the Soudan mine in northern Minnesota housed University physics experiments searching for answers to basic questions about the Universe. Within two to three years, all the major experiments will be decommissioned and moved out of the mine. 
One of the main experiments in the mine, the Cryogenic Dark Matter Search, was intended to detect dark matter and has operated for several years.
Dark matter is a type of matter theorized to exist that has gravity like regular matter, but thus far cannot be seen or detected, said Marvin Marshak, a University physics professor and founder and director of the Soudan lab.
“Most spiral galaxies shouldn’t exist. There’s not enough mass … to produce enough gravity to hold the galaxy together … and the usual assumption is that there’s more matter than you can see,” he said.
CDMS has collected data for 15 years, and gathering more data is no longer useful, Marshak said. 
“Basically, [the experiments] are done; the data that could be collected has been collected,” he said.
While the lab found no dark matter, no facility in the world has yet been able to find dark matter either — potentially due to interference from cosmic rays, he said.
An upgraded, more sensitive version of CDMS is planned to be built in a lab in Canada much deeper underground than Soudan, said Alec Habig, associate director of the Soudan lab. Researchers hope the added depth will reduce the cosmic ray interference.
The other primary lab experiment, the Main Injector Neutrino Oscillation Search, studied a beam of neutrinos, a type of fundamental particle shot from a lab near Chicago, Marshak said.
The differences between the neutrinos in Chicago and when they reach Soudan can tell researchers about its properties, Habig said.
Like CDMS, the MINOS detector has collected all the useful it data possibly can, said William Miller, a former director of the Soudan lab and current director of the NOvA lab.
“The MINOS detector has essentially come to the end of its life,” Miller said. “The next generation of experiments, they all need to get deeper to knock the background radiation levels down.”
It will take several years to clear the mine of experiment equipment, even after shutting down, said Habig. 
“It’ll take us several years of carefully moving all the electronics out and then moving them to the next place to use and then moving six thousand tons of steel out in small pieces,” he said.
While the experiments are closing down, the mine itself will stay open and will be available for any other experiments that need the space and can secure funding, Habig said.
The mine will also continue to host tours as the experiments shut down, he said.
“We still have a lot of cool things to see,” Habig said. “As we’re breaking things and moving them out, there might even be more things to see than if we have them all buttoned down and operating.”