Dark Energy Survey completes six-year mission

Scientists’ effort to map a portion of the sky in unprecedented detail is coming to an end, but their work to learn more about the expansion of the universe has just begun.

After scanning in depth about a quarter of the southern skies for six years and cataloguing hundreds of millions of distant galaxies, the Dark Energy Survey (DES) will finish taking data tomorrow, on Jan. 9.

The survey is an international collaboration that began mapping a 5,000-square-degree area of the sky on Aug. 31, 2013, in a quest to understand the nature of dark energy, the mysterious force that is accelerating the expansion of the universe. Using the Dark Energy Camera, a 520-megapixel digital camera funded by the U.S. Department of Energy Office of Science and mounted on the Blanco 4-meter telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile, scientists on DES took data on 758 nights over six years.

Over those nights, they recorded data from more than 300 million distant galaxies. More than 400 scientists from over 25 institutions around the world have been involved in the project, which is hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory. The collaboration has already produced about 200 academic papers, with more to come.

According to DES Director Rich Kron, a Fermilab and University of Chicago scientist, those results and the scientists who made them possible are where much of the real accomplishment of DES lies.

“First generations of students and postdoctoral researchers on DES are now becoming faculty at research institutions and are involved in upcoming sky surveys,” Kron said. “The number of publications and people involved are a true testament to this experiment. Helping to launch so many careers has always been part of the plan, and it’s been very successful.”

DES remains one of the most sensitive and comprehensive surveys of distant galaxies ever performed. The Dark Energy Camera is capable of seeing light from galaxies billions of light-years away and capturing it in unprecedented quality.

According to Alistair Walker of the National Optical Astronomy Observatory, a DES team member and the DECam instrument scientist, equipping the telescope with the Dark Energy Camera transformed it into a state-of-the-art survey machine.

“DECam was needed to carry out DES, but it also created a new tool for discovery, from the solar system to the distant universe,” Walker said. “For example, 12 new moons of Jupiter were recently discovered with DECam, and the detection of distant star-forming galaxies in the early universe, when the universe was only a few percent of its present age, has yielded new insights into the end of the cosmic dark ages.”

The survey generated 50 terabytes (that’s 50 million megabytes) of data over its six observation seasons. That data is stored and analyzed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign.

“Even after observations are ended, NCSA will continue to support the scientific productivity of the collaboration by making refined data releases and serving the data well into the 2020s,” said Don Petravick, senior project manager for the Dark Energy Survey at NCSA.

Now the job of analyzing that data takes center stage. DES has already released a full range of papers based on its first year of data, and scientists are now diving into the rich seam of catalogued images from the first several years of data, looking for clues to the nature of dark energy.

The first step in that process, according to Fermilab and University of Chicago scientist Josh Frieman, former director of DES, is to find the signal in all the noise.

“We’re trying to tease out the signal of dark energy against a background of all sorts of noncosmological stuff that gets imprinted on the data,” Frieman said. “It’s a massive ongoing effort from many different people around the world.”

The DES collaboration continues to release scientific results from their storehouse of data, and scientists will discuss recent results at a special session at the American Astronomical Society winter meeting in Seattle today, Jan. 8. Highlights from the previous years include:

• the most precise measurement of dark matter structure in the universe, which, when compared with cosmic microwave background results, allows scientists to trace the evolution of the cosmos.
• the discovery of many more dwarf satellite galaxies orbiting our Milky Way, which provide tests of theories of dark matter.
• the creation of the most accurate dark matter map of the universe.
• the spotting of the most distant supernova ever detected.
• the public release of the survey’s first three years of data, enabling astronomers around the world to make additional discoveries.

DES scientists also spotted the first visible counterpart of gravitational waves ever detected, a collision of two neutron stars that occurred 130 million years ago. DES was one of several sky surveys that detected this gravitational wave source, opening the door to a new kind of astronomy.

Recently DES issued its first cosmology results based on supernovae (207 of them taken from the first three years of DES data) using a method that provided the first evidence for cosmic acceleration 20 years ago. More comprehensive results on dark energy are expected within the next few years.

The task of amassing such a comprehensive survey was no small feat. Over the course of the survey, hundreds of scientists were called on to work the camera in nightly shifts supported by the staff of the observatory. To organize that effort, DES adopted some of the principles of high-energy physics experiments, in which everyone working on the experiment is involved in its operation in some way.

“This mode of operation also afforded DES an educational opportunity,” said Fermilab scientist Tom Diehl, who managed the DES operations. “Senior DES scientists were paired with inexperienced ones for training and, in time, would pass that knowledge on to more junior observers.”

The organizational structure of DES was also designed to give early-career scientists valuable opportunities for advancement, from workshops on writing research proposals to mentors who helped review and edit grant and job applications.

Antonella Palmese, a postdoctoral researcher associate at Fermilab, arrived at Cerro Tololo as a graduate student from University College London in 2015. She quickly came up to speed and returned in 2017 and 2018 as an experienced observer. She also served as a representative for early-career scientists, helping to assist those first making their mark with DES.

“Working with DES has put me in contact with many remarkable scientists from all over the world,” Palmese said. “It’s a special collaboration because you always feel like you are a necessary part of the experiment. There is always something useful you can do for the collaboration and for your own research.”

The Dark Energy Camera will remain mounted on the Blanco telescope at Cerro Tololo for another five to 10 years and will continue to be a useful instrument for scientific collaborations around the world. Cerro Tololo Inter-American Observatory Director Steve Heathcote foresees a bright future for DECam.

“Although the data-taking for DES is coming to an end, DECam will continue its exploration of the universe from the Blanco telescope and is expected remain a front-line ‘engine of discovery’ for many years,” Heathcote said.

The DES collaboration will now focus on generating new results from its six years of data, including new insights into dark energy. With one era at an end, the next era of the Dark Energy Survey is just beginning.

Follow the Dark Energy Survey online at www.darkenergysurvey.org and connect with the survey on Facebook at www.facebook.com/darkenergysurvey, on Twitter at www.twitter.com/theDESurvey and on Instagram at www.instagram.com/darkenergysurvey.

The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, U.S. National Science Foundation, Ministry of Science, Innovation and Universities of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, ETH Zurich for Switzerland, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and AstroParticle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and Ministério da Ciência e Tecnologia, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the Dark Energy Survey, the list of which can be found at www.darkenergysurvey.org/collaboration.

Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. NSF is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

NCSA at the University of Illinois at Urbana-Champaign provides supercomputing and advanced digital resources for the nation’s science enterprise. At NCSA, University of Illinois faculty, staff, students and collaborators from around the globe use advanced digital resources to address research grand challenges for the benefit of science and society. NCSA has been advancing one third of the Fortune 50® for more than 30 years by bringing industry, researchers and students together to solve grand challenges at rapid speed and scale. For more information, please visit www.ncsa.illinois.edu.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC, a joint partnership between the University of Chicago and the Universities Research Association Inc. Visit Fermilab’s website at www.fnal.gov and follow us on Twitter at @Fermilab.

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An international project to build the largest physics experiment ever constructed in the United States took a major step forward as a new phase of work has begun at the project’s South Dakota site.

The U.S. Department of Energy’s Fermi National Accelerator Laboratory has finalized an agreement with construction firm Kiewit-Alberici Joint Venture (KAJV) to start pre-excavation work for the Long-Baseline Neutrino Facility (LBNF), which will house the enormous particle detectors for the Deep Underground Neutrino Experiment (DUNE). The South Dakota portion of the facility will be built a mile beneath the surface at the Sanford Underground Research Facility in Lead, South Dakota.

The contract with KAJV covers the next two years and includes everything that will be needed to support the next phase of work — the fast, safe and continuous removal of approximately 800,000 tons of rock to create the large caverns that will house the massive DUNE detector modules.

“After years of design and planning, it’s gratifying to put boots on the ground and begin this pre-excavation work,” said Chris Mossey, Fermilab’s deputy director for the Long-Baseline Neutrino Facility. “Getting to this point has been the result of a lot of work from the entire LBNF/DUNE team and our partners at KAJV, Arup, Sanford Lab and DOE, and we’re all ready for this next phase of the project to begin.”

Included in the work is restoring and refurbishing rock-crushing equipment once used for the gold mine where Sanford Lab now resides and outfitting one of the mine shafts to carry loads of crushed rock. Much of the early pre-excavation work will take place underground at Sanford Lab or inside existing enclosures on site.

“Complicated tunneling, excavation and underground construction is what we do every day, but performing this work in support of a groundbreaking, international science experiment is a once-in-a-lifetime opportunity,” said Scott Lundgren, spokesperson for Kiewit/Alberici Joint Venture. “We are proud to be a part of this historic project and look forward to helping to make the vision for the LBNF become a reality.”

Fermilab and Sanford Lab will host an informational meeting in Lead, South Dakota, for local residents on Jan. 16, 2019, to answer questions about the construction of the project. The meeting will take place at 7 p.m. in the Education and Outreach Building at Sanford Lab. For more information, visit the event page.

DUNE, hosted by Fermilab, will be the world’s most advanced experiment dedicated to studying the properties of mysterious subatomic particles called neutrinos. Scientists are seeking to understand the role neutrinos played in the formation of our universe, and the DUNE detectors will enable them to study a beam of particles generated by an upgraded accelerator complex at Fermilab. The DUNE collaboration includes more than 1,000 scientists from more than 30 countries around the world. A large prototype detector for the experiment, constructed at the European research center CERN, successfully began recording particle tracks in September of this year.

For more information on LBNF/DUNE, see http://www.fnal.gov/dune.

Over the course of this year, the Fermilab Archives will present a rotating exhibit of the history of physics in print. The exhibit can be viewed in the glass display case in the Fermilab Art Gallery, which is located on the second floor of Fermilab’s Wilson Hall. The gallery is open to the public Monday through Friday, 8 a.m. to 4:30 p.m.

This display is part of a series of exhibits organized by Fermilab scientist Erik Ramberg and the Fermilab Archives. These exhibits will feature influential works in the history of physics loaned from Ramberg’s private collection. Each display will consist of several volumes illustrating a common theme in the evolution of physics and will rotate approximately once a month.

The first exhibit, currently showing, is titled “The Early Scientific Journals” and features works from the 17th and 18th centuries. It will be on display until February.

Today, the most common way for scientists to communicate new findings to their colleagues is by publishing articles in peer-reviewed scientific journals. The contemporary conventions of scientific publishing developed over the course of several centuries. They trace their origins back to 1665, when two groups began, nearly simultaneously, publishing periodicals devoted to science and society.

The first European journal was called Journal des Scavans and began publishing on Jan. 5, 1665. Two printings were produced in Paris and in Amsterdam. Following close behind, the secretary of The Royal Society of London for Improving Natural Knowledge published the first issue of Philosophical Transactions, England’s first scientific journal, on March 6, 1665.

The exhibit also includes examples of Acta Eruditorum and The Gentleman’s Magazine, which began publication in 1682 and 1731, respectively.

If you have questions, please contact archivist Valerie Higgins or scientist and collection curator Erik Ramberg.

A miniaturized technology originally developed for the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider in Geneva now is available for applications in maritime safety and homeland security.

This technology — silicon strip cosmic-muon detectors — has earned an R&D 100 Award for a team of scientists from the U.S. Department of Energy’s Fermi National Accelerator Laboratory — its 14th since 1980 — and its partners in the project, the Nevada National Security Site (NNSS) and the DOE’s Los Alamos National Laboratory.

The award-winning detectors were modified from silicon detector technology that high-energy physicists have used for years.

“It’s like a natural X-ray machine,” said Fermilab scientist Ron Lipton, who led the team that designed, mounted, assembled and tested the sensors. “It’s a synergistic use of what we’ve been doing already. We were able to use some of the engineering expertise here at the site to build these detectors.”

R&D 100 awards are presented annually by R&D Magazine in recognition of exceptional new products or processes that were developed during the previous year. An independent panel of judges selects the awardees based on the technical significance, uniqueness, and usefulness of projects and technology from across industry, government, and academia.

Cosmic-ray muons rain continuously upon Earth, produced when charged particles from deep space strike the upper atmosphere. Approximately 10,000 muons per minute per square meter arrive at sea level. This shower of subatomic particles passes unnoticed through all kinds of objects. Unlike X-rays, they even can traverse steel and other solid materials. And when captured by detectors placed behind or underneath an object, these muons can reveal what is inside.

Muons have been used to produce tomographic images of the interior of pyramids in Egypt and of nuclear reactors at Japan’s Fukushima Daiichi plant, which was heavily damaged by earthquakes and an ensuing tsunami in 2011. Radiation detectors and X-ray scanners are unable to penetrate materials concealed in concrete, lead and other materials, but muons can.

The technology may lend itself to additional applications that call for remote viewing of hazardous materials, Lipton said. These include verifying how much material is contained in concrete fuel casks, for example.

Leading the muon detector project was J. Andrew Green, principal scientist for the NNSS’ Remote Sensing Laboratory at Nellis Air Force Base in Nevada. Green had conducted research at Fermilab’s DZero experiment from 1997 to 2001 as a doctoral student at Iowa State University. During that period, Green met Lipton, Mike Utes, Cristian Gingu, Johnny B. Green and Paul Rubinov, who, along with William Cooper, composed the award-winning project team.

Andrew Green had worked with Utes and John Green on a key component of an upgrade to the DZero detector.

“From that experience, I knew who to call when I had my idea to build a silicon-based tracking system,” said Andrew Green, who later also worked as a postdoctoral scientist on the MiniBooNE neutrino experiment at Fermilab.

Green wrote the analysis software for reading the muon detector system’s data files, performing diagnostics and plotting muon signals in the detector in three dimensions.

“Even projects of this small scale require good software development to properly organize the large number of channels, data types and associated geometry,” he explained.

Fermilab’s cosmic-muon detector work is an outgrowth of its experience in building many tens of square yards of silicon sensors for the CMS experiment. The sensors the team developed for homeland security applications cover only a few square feet and are built in four planes that come in packages two inches thick.

They could potentially replace the bulky drift tube detectors in current use, which are two feet thick. The latter’s size and weight make them more difficult to ship and deploy. Their larger bulk is needed to boost the lower resolution of the muons passing through them as compared to the silicon strip technology, which can be used in thin layers. The conventional drift tube technology also presents potential hazards because it depends upon sets of cylindrical tubes that are filled with flammable gas and charged to high voltage to boost the signal.

Lipton, who specializes in silicon tracker detectors, led the construction of several silicon-based muon detectors for the DZero experiment, which finished data collection in 2011. He and his associates now are building a large-area silicon system for the Large Hadron Collider, which uses stacked planes of similar detectors in a somewhat different geometry.

“These are hundreds of square meters of material,” Lipton said. “They’re unprecedented in scale.”

Funding for silicon strip muon detectors for homeland security was provided by the National Nuclear Security Administration’s Laboratory-Directed Research and Development and Site-Directed Research and Development programs.