Assistant physics professor Wenqin Xu has been leading the university collaboration on the experiment called the Majorana Demonstrator which has shown the ability to shield a sensitive, scalable 44-kilogram germanium detector array from background radioactivity in order to study neutrinoless double-beta decay. The University of South Dakota is a collaborating institution of this experiment led by the Department of Energy’s Oak Ridge National Laboratory.

“Over the last several years, USD faculty members and students have contributed to both the experiment construction and the data analysis of the Majorana Demonstrator,” said Xu. “USD has become an important player in the current and next generation germanium-based experiments.”

The experiment, located 4,850 feet underground at the Sanford Underground Research Facility in Lead, South Dakota, completed construction in 2016 and will continue taking data for several years.

In a 2015 report by the U.S. Nuclear Science Advisory Committee to the Department of Energy and the National Science Foundation, a U.S.-led ton-scale experiment to detect neutrinoless double-beta decay was deemed a top priority of the nuclear physics community in order to understand key neutrino properties and how matter was created after the Big Bang. Nearly a dozen experiments have sought neutrinoless double-beta decay, and many future experiments have been proposed. One of their keys to success depends on avoiding background that could mimic the signal of neutrinoless double-beta decay.

Avoiding background that could mimic the signal of neutrinoless double-beta decay was the key accomplishment of the Majorana Demonstrator.

Burying the experiment under nearly a mile of rock was the first of many steps collaborators took to reduce interference from background sources. Other steps included a cryostat made of the world’s purest copper and a complex six-layer shield to eliminate interference from cosmic rays, radon, dust, fingerprints and naturally occurring radioactive isotopes.

This accomplishment is critical to developing a much larger future experiment—with approximately a ton of detectors—to study the nature of neutrinos. These electrically neutral particles interact only weakly with matter, making their detection exceedingly difficult.

Researchers from the University of South Dakota were involved in many aspects of the experiment, from the conceptual design to the apparatus construction, from the experimental commissioning to the data analysis, which led to the published results.

“We are thankful that the current and former group members have received support from the National Science Foundation, the Department of Energy, as well as the State of South Dakota and USD,” said Xu. “I am particularly pleased to see multiple USD students, including undergraduate students, have gained substantial research experience by working on this experiment at the frontier of nuclear science.”

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