The Sanford Underground Research Facility (SURF) houses world-leading physics experiments that could give us a better understanding of the universe. Located at the former Homestake Gold Mine in Lead, S.D., SURF provides significant depth and rock stability—a near-perfect environment for experiments that need to escape cosmic radiation that can interfere with the detection of rare physics events. Until its closure in 2002, Homestake was the largest and deepest gold mine in North America, producing approximately 41 million ounces of gold in its 126-year lifetime.
When the Homestake Mine closed in 2002, the National Science Foundation (NSF) had already considered the facility as a possible future sight for the United States’ Deep Underground Science and Engineering Laboratory (DUSEL). Barrick Gold Corporation agreed to keep the pumps running while discussions about the facility's future as a research facility were underway. However, soaring costs caused the company to turn off the pumps just one year later.
The first two major physics experiments located on the 4850 Level were the Large Underground Xenon (LUX) experiment and the Majorana Demonstrator Project. Majorana was housed in a new transition cavern. LUX was housed in the renovated Davis Cavern, where Ray Davis ran his Nobel Prize-winning solar neutrino experiment for nearly three decades.
In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive dark matter detector in the world. Further analysis confirmed that result in 2016, the same year the experiment was decommissioned.
The Majorana Demonstrator is searching for a rare type of radioactive decay called neutrinoless double-beta decay, which requires extreme quiet. If this phenomenon were detected, it could confirm that neutrinos are their own antiparticles and provide clues as to why matter prevailed over antimatter. In a study published in 2018, Physical Review Letters, the Majorana collaboration showed they can shield a sensitive, scalable, 44-kilogram germanium detector array from background radioactivity.
Beginning in 2015, other projects and experiments began moving to the 4850 Level, including CASPAR, a low-compact accelerator that seeks to learn how elements heavier than iron were formed in collapsing stars.
Future experiments include the second generation dark matter experiment, LUX-ZEPLIN (LZ), and the Long-Baseline Neutrino Facility and associated Deep Underground Neutrino Experiment (LBNF/DUNE). LZ is currently being installed in the Davis Cavern and is expected to be operational by 2020. In 2017, the LBNF/DUNE collaboration held a groundbreaking on the 4850 Level of Sanford Lab to mark the start of pre-excavation.
