The floors are steel grids or ultra-smooth surfaces of burnt-orange epoxy-resin over concrete. The ceilings are acoustic tile or overhead conduits packaged in shiny foil. The walls are ho-hum cinder block—except when they suddenly bulge into Gaudiesque undulating freeforms, the shotcreted natural rock face intruding into the architectural tedium. It's the Davis Campus on the 4,850-foot level of the Sanford Underground Research Facility in what was formerly the Homestake gold mine in Lead, S.D. The mine was repurposed for science, and the Davis Campus officially opened during a dedication ceremony on May 30, 2012.
Deep underground is the only place to do the kind of leading-edge physics experiments. The Large Underground Xenon experiment, or LUX, is searching for dark matter, while the Majorana experiment is looking to see if neutrinos are their own antiparticles. Majorana will do this by detecting something never before observed: neutrinoless double-beta decay. Both LUX and Majorana require the absolute minimum of background interference. The Davis Campus, nearly a mile underground, is more than a million times quieter than a surface facility.
“The 4,850 feet of rock screens out most cosmic rays, and the surrounding rock is lower in radioactivity by a factor of 10 or more than other underground locations, including even those deeper than the Davis Campus,” said Kevin Lesko of Lawrence Berkeley National Laboratory’s Nuclear Science Division. Lesko is Principal Investigator for the Sanford Lab, whose operations are funded by DOE through Berkeley Lab.
Majorana's goal is to prove that background noise at the Davis Campus is indeed “quiet” enough to be worth the expense of searching here for neutrinoless double-beta decay, a process with an estimated half-life longer than a trillion times the age of the universe. In its search for dark matter, LUX scientists hope to find WIMPs, or weakly interacting massive particles. To date, LUX is the most sensitive dark matter detector in the world. The next generation dark matter detector, LUX-Zeplin (LZ) is expected to be 100 times more sensitive.
Quiet was the reason Ray Davis came from Brookhaven Lab in the mid-1960s, while Homestake was still a working gold mine, to look for neutrinos from the sun. He found only a third the number he expected, and the result was modern neutrino science, including the revelation that neutrinos have mass and come in flavors that oscillate among themselves. Three decades later he was recognized by a Nobel Prize.
Davis died in 2006. His widow, Anna, along with a son and daughter-in-law, helped dedicate the Davis Campus, bringing along an official replica of his Nobel Prize medal. (The original is in a bank vault.) Sanford Lab officials presented her with a fragment of the Davis neutrino experiment, which was torn down to prepare the cavern for LUX. The 25-ton water tank that shields LUX now stands in the same space excavated for Davis.
The official opening of the underground campus covered a wide spectrum of significance, with different meanings for different visitors. Notables included South Dakota Gov. Dennis Daugaard, former Gov. (now U.S. Senator) Mike Rounds and philanthropist T. Dennis Sanford. The Department of Energy was represented by James Siegrist, Associate Director of Science for High Energy Physics in the Office of Science. James Symons, Berkeley Lab’s Associate Director of General Sciences, Lesko and many other scientists from the national laboratories, including Fermilab’s Deputy Director Young-Kee Kim, also were present.
For the state, the dedication was a vindication that more than $40 million of public investment and $70 million in private support, as well as the gift of the Homestake mine itself, was not in vain. The National Science Foundations in December 2010 decided to stop funding what was to have been the Deep Underground Science and Engineering Laboratory (DUSEL). DOE, until then a junior partner in DUSEL planning but the sponsor of major experiments to come, found itself facing an important decision—whether to continue the project. In July 2011, DOE did decide to fund the continued operation of the Sanford Lab and its existing experiments, and to pursue options for future experiments. One of them, the Long Baseline Neutrino Facility and associated Deep Underground Neutrino Experimnet (LBNF/DUNE), will fire neutrinos from Fermilab in Batavia, Ill., to a detector on the 4850 Level at Sanford Lab, a distance of 800 miles.
This article was written by Paul Preuss, a science writer at Berkeley Lab, and Bill Harlan, the former Communications Director for Sanford Lab. It was updated in November 2015 to reflect the progress made since 2012.