From SURF: “Majorana Demonstrator: Preparing to scale up”

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Sanford Underground Research facility

September 11, 2017
Constance Walter

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John Wilkerson (left) and Cabot-Ann Christofferson work on the systems for the Majorana experiment, which sits inside a six-layered shield to block backgrounds. Photo by Matt Kapust

For years, the Majorana Demonstrator laboratories and machine shop bustled with activity. Dozens of collaboration members worked on various elements of the experiment— from electroforming copper to building a shield to machining every component for the detectors and cryostats. Today, nestled deep within its six-layered shield, Majorana quietly collects data with just a handful of team members to ensure things are working.

“We’ve made the transition from managing construction to overseeing an operation,” said Vince Guiseppe, assistant professor of physics at the University of South Carolina. “Since the winter, we’ve been running smoothly.”

The Majorana Demonstrator uses natural and enriched germanium crystals to look for neutrinoless double-beta decay. Such a discovery could determine whether the neutrino is its own antiparticle.

U Washington Majorana Demonstrator Experiment at SURF

But the project is, first and foremost, a demonstrator, a research and development project built on a small scale to determine whether a 1-ton version is feasible, said Steve Elliott of Los Alamos National Laboratory. “For it to be feasible, we have to show that backgrounds can be low enough to justify building such a next-generation experiment.”

Which Majorana has done, Guiseppe said. “We’ve only been running for about a year and we appear to be meeting those goals. Our backgrounds are excellent.”

Guiseppe recently became a co-spokesperson for the project, along with Jason Detwiler of the University of Washington. The two replace Elliott, who will become co-spokesperson for LEGEND, the recently formed collaboration that will develop a much larger next-generation neutrinoless double-beta decay experiment

The Large Enriched Germanium Experiment for Neutrinoless ββ Decay, or LEGEND, collaboration was formed a year ago and includes members of the Majorana Demonstrator collaboration, the GERDA (GERmanium Detector Array) collaboration, and other researchers in this field.

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The GERDA experiment has been proposed in 2004 as a new 76Ge double-beta decay experiment at LNGS. The GERDA installation is a facility with germanium detectors made out of isotopically enriched material. The detectors are operated inside a liquid argon shield. The experiment is located in Hall A of LNGS.

GERDA and Majorana are searching for the same thing, but they’ve used different technologies to reach their goals. For example, where Majorana used electroformed copper and built a complicated six-layered shield to keep backgrounds out, GERDA used commercial copper and shielded its detector inside a tank of liquid argon, which scintillates, or lights up, when backgrounds enter.

And both are seeing what they hoped to see: low backgrounds. “They’ve done a lot of nice things, we’ve done a lot of nice things and there are some things we both did very well.” Guiseppe said. “And we’ve both demonstrated we can get the backgrounds we want. LEGEND will take the best features of each experiment.”

The LEGEND collaboration wants to scale up to 1,000 kg of enriched germanium. By comparison, Majorana and GERDA each use approximately 30 kg in their experiments. But the plan is to start smaller, with a 200-kg experiment.

“LEGEND 200 will be the first incarnation and will be the roadmap to get to the ton-scale experiment,” Guiseppe said.

“The good news is we have a great collaboration with great people. We have a common vision and design and funding plans are moving forward. This is not something one of us can do alone. It’s important to have international partners.”

Although he’s looking to the future, Guiseppe remains focused on the here and now. “Both GERDA and Majorana have to complete their life cycles,” he said. “And there’s still a lot we can learn from running our current experiments.”

See the full article here .

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The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

Fermilab LBNE
LBNE