Duke physicists share prize for discovery of the top quark

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Below is a press release issued by Lawrence Berkeley National Laboratory on the start of the next phase of work for the LUX-ZEPLIN project. A Fermilab group led by Hugh Lippincott, currently a Fermilab scientist who will join the University of California, Santa Barbara, in the fall, and Eric Dahl, a joint appointee and associate professor at Northwestern University, is responsible for implementing key parts of the critical systems that handle the xenon in the LUX-ZEPLIN detector. These include the heat exchange system that allows the entire 10-ton xenon target to be purified every 2.3 days, as well as the controls system that safeguards the greater than $10 million xenon payload in emergency scenarios. View the original Berkeley Lab press release on their news site.

Major deliveries in June set the stage for the next phase of work on LUX-ZEPLIN project

Most of the remaining components needed to fully assemble an underground dark matter-search experiment called LUX-ZEPLIN (LZ) arrived at the project’s South Dakota home during a rush of deliveries in June.

When complete, LZ will be the largest, most sensitive U.S.-based experiment yet that is designed to directly detect dark matter particles. Scientists around the world have been trying for decades to solve the mystery of dark matter, which makes up about 85% of all matter in the universe though we have so far detected it only indirectly through observed gravitational effects.

The bulk of the digital components for LZ’s electronics system, which is designed to transmit and record signals from ever-slight particle interactions in LZ’s core detector vessel, were among the new arrivals at the Sanford Underground Research Facility (SURF). SURF, a former gold mine now dedicated to a broad spectrum of scientific research, was also home to a predecessor search experiment called LUX.

A final set of snugly fitting acrylic vessels, which will be filled with a special liquid designed to identify false dark matter signals in LZ’s inner detector also arrived at SURF in June.

Also, the last two of four intricately woven wire grids that are essential to maintain a constant electric field and extract signals from the experiment’s inner detector, also called the time projection chamber, arrived in June (see related article).

“LZ achieved major milestones in June. It was the busiest single month for delivering things to SURF — it was the peak,” said LZ Project Director Murdock Gilchriese of the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Berkeley Lab is the lead institution for the LZ project, which is supported by an international collaboration that numbers about 37 participating institutions and about 250 researchers and technical support crew members.

“A few months from now all of the action on LZ is going to be at SURF — we are already getting close to having everything there,” Gilchriese said.

“We’ve been collectively preparing for these deliveries for some time and everything has gone very well,” said Mike Headley, executive director at SURF. “It’s been exciting to see the experiment assembly work progress, and we look forward to lowering the assembled detector a mile underground for installation.”

All of these components will be transported down a shaft and installed in a nearly mile-deep research cavern. The rock above provides a natural shield against much of the constant bombardment of particles raining down on the planet’s surface that produce unwanted “noise.”

LZ components have also been painstakingly tested and selected to ensure that the materials they are made of do not themselves interfere with particle signals that researchers are trying to tease out.

LZ is particularly focused on finding a type of theoretical particle called a weakly interacting massive particle or WIMP by triggering a unique sequence of light and electrical signals in a tank filled with 10 metric tons of highly purified liquid xenon, which is among Earth’s rarest elements. The properties of xenon atoms allow them to produce light in certain particle interactions.

Proof of dark matter particles would fundamentally change our understanding of the makeup of the universe, as our current Standard Model of physics does not account for their existence.

Assembly of the liquid-xenon time projection chamber for LZ is now about 80% complete, Gilchriese said. When fully assembled later this month, this inner detector will contain about 500 photomultiplier tubes, which are designed to amplify and transmit signals produced within the chamber.

Once assembled, the time projection chamber will be lowered carefully into a custom titanium vessel already at SURF. Before it is filled with xenon, this chamber will be lowered to a depth of about 4,850 feet. It will be carried in a specially designed frame that is designed to minimize vibrations and then floated into the experimental cavern across a temporarily assembled metal runway on air-pumped pucks known as air skates.

Finally, it will be lowered into a larger outer titanium vessel, already long underground, to form the final vacuum-insulated cryostat needed to house the liquid xenon.

That daylong journey, planned in September, will be a nail-biting experience for the entire project team, noted Berkeley Lab’s Simon Fiorucci, LZ deputy project manager.

“It will certainly be the most stressful — this is the thing that really cannot fail. Once we’re done with this, a lot of our risk disappears, and a lot of our planning becomes easier,” he said, adding, “This will be the biggest milestone that’s left besides having liquid xenon in the detector.”

Project crews will soon begin testing the xenon circulation system, already installed underground, that will continually circulate xenon through the inner detector, further purify it, and reliquefy it. Fiorucci said researchers will use about 250 pounds of xenon for these early tests.

Work is also nearing completion on LZ’s cryogenic cooling system that is required to convert xenon gas to its liquid form.

LZ digital electronics, which will ultimately connect to the arrays of photomultiplier tubes and enable the readout of signals from particle interactions, were designed, developed, delivered and installed by University of Rochester researchers and technical staff at SURF in June.

“All of our electronics have been designed specifically for LZ with the goal of maximizing our sensitivity for the smallest possible signals,” said Frank Wolfs, a professor of physics and astronomy at the University of Rochester who is overseeing the university’s efforts.

He noted that more than 28 miles of coaxial cable will connect the photomultiplier tubes and their amplifying electronics — which are undergoing tests at UC Davis — to the digitizing electronics. “The successful installation of the digital electronics and the online network and computing infrastructure in June makes us eager to see the first signals emerge from LZ,” Wolfs added.

Also in June, LZ participants exercised high-speed data connections from the site of the experiment to the surface level at SURF and then to Berkeley Lab. Data captured by the detectors’ electronics will ultimately be transferred to LZ’s primary data center, the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab via the Energy Sciences Network (ESnet), a high-speed nationwide data network based at Berkeley Lab.

The production of the custom acrylic tanks (see related article), which will contain a fluid known as a liquid scintillator, was overseen by LZ participants at University of California, Santa Barbara.

“The last five tanks, delivered in June, were fabricated using a novel acrylic molding process to closely fit around the cryostat vessel,” said Harry Nelson, professor of physics at UC Santa Barbara.

“The partnership between LZ and SURF is tremendous as evidenced by the success of the assembly work to date,” Headley said. “We’re proud to be a part of the LZ team and host this world-leading experiment in South Dakota.”

NERSC and ESnet are DOE Office of Science User Facilities.

Major support for LZ comes from the DOE Office of Science, the South Dakota Science and Technology Authority, the U.K.’s Science & Technology Facilities Council, and by collaboration members in the U.S., U.K., South Korea, and Portugal.

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DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

Founded in 1931 on the belief that the biggest scientific challenges are best addressed by teams, Lawrence Berkeley National Laboratory and its scientists have been recognized with 13 Nobel Prizes. Today, Berkeley Lab researchers develop sustainable energy and environmental solutions, create useful new materials, advance the frontiers of computing, and probe the mysteries of life, matter, and the universe. Scientists from around the world rely on the Lab’s facilities for their own discovery science. Berkeley Lab is a multiprogram national laboratory, managed by the University of California for the U.S. Department of Energy’s Office of Science.

The Sanford Underground Research Facility’s mission is to enable compelling underground, interdisciplinary research in a safe work environment and to inspire our next generation through science, technology, engineering, and math education. For more information, please visit the Sanford Lab website at http://www.sanfordlab.org.

Below is a press release issued by Lawrence Berkeley National Laboratory announcing the completion of three sky surveys that will prepare the way for the Dark Energy Spectroscopic Instrument. DESI seeks to further our cosmic understanding by creating the largest 3-D map of galaxies to date. The U.S. Department of Energy’s Fermi National Accelerator Laboratory is a key player in the construction of this instrument, drawing on more than 25 years of experience with the Sloan Digital Sky Survey and the Dark Energy Survey.

Researchers will pick 35 million galaxies and quasars to target during DESI’s five-year mission

It took three sky surveys — conducted at telescopes in two continents, covering one-third of the visible sky, and requiring almost 1,000 observing nights – to prepare for a new project that will create the largest 3-D map of the universe’s galaxies and glean new insights about the universe’s accelerating expansion.

This Dark Energy Spectroscopic Instrument (DESI) project will explore this expansion, driven by a mysterious property known as dark energy, in great detail. It could also make unexpected discoveries during its five-year mission.

The surveys, which wrapped up in March, have amassed images of more than 1 billion galaxies and are essential in selecting celestial objects to target with DESI, now under construction in Arizona.

The latest batch of imaging data from these surveys, known as DR8, was publicly released July 8, and an online Sky Viewer tool provides a virtual tour of this data. A final data release from the DESI imaging surveys is planned later this year.

Scientists will select about 33 million galaxies and 2.4 million quasars from the larger set of objects imaged in the three surveys. Quasars are the brightest objects in the universe and are believed to contain supermassive black holes. DESI will target these selected objects for several measurements after its start, which is expected in February 2020.

DESI will measure each target across a range of different wavelengths of light, known as spectrum, from the selected set of galaxies repeatedly over the course of its mission. These measurements will provide details about their distance and acceleration away from Earth.

A collection of 5,000 swiveling robots, each carrying a fiber-optic cable, will point at sets of preselected sky objects to gather their light (see a related video) so it can be split into different colors and analyzed using a series of devices called spectrographs.

Three surveys, 980 nights

“Typically, when you apply for time on a telescope you get up to five nights,” said David Schlegel, a DESI project scientist at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution in the DESI collaboration. “These three imaging surveys totaled 980 nights, which is a pretty big number.”

The three imaging surveys for DESI include:

• The Mayall z-band Legacy Survey (MzLS), carried out at the Mayall Telescope at the National Science Foundation’s Kitt Peak National Observatory near Tucson, Arizona, over 401 nights. DESI is now under installation at the Mayall Telescope.
• The Dark Energy Camera Legacy Survey (DECaLS) at the Victor Blanco Telescope at NSF’s Cerro Tololo Inter-American Observatory in Chile, which lasted 204 nights.
• The Beijing-Arizona Sky Survey (BASS), which used the Steward Observatory’s Bok telescope at Kitt Peak National Observatory and lasted 375 nights.

On-site survey crews – typically two DESI project researchers per observing night for each of the surveys – served in a sort of “lifeguard” role, Schlegel said. “When something went wrong they were there to fix it – to keep eyes on the sky,” and researchers working remotely also aided in troubleshooting.

On the final night of the final survey …

In early March, Eva-Maria Mueller, a postdoctoral researcher at the U.K.’s University of Portsmouth, and Robert Blum, former deputy director at the National Optical Astronomy Observatory (NOAO), which manages the survey sites, were on duty with a small team in the control room of the NSF’s Victor Blanco Telescope on a mile-high Chilean mountain for the final night of DECaLS survey imaging.

Seated several stories beneath the telescope, Mueller and Blum viewed images in real time to verify the telescope’s position and focus. Mueller, who was participating in a five-night shift that was her first observing stint for the DESI surveys, said, “This was always kind of a childhood dream.”

Blum, who had logged many evenings at the Blanco telescope for DECaLS, said, “It’s really exciting to think about finishing this phase.” He noted that this final night was focused on “cleaning up little holes” in the previous imaging. Blum is now serving in a new role as acting operations director for the Large Synoptic Survey Telescope under installation in Chile.

New software designed for the DESI surveys and precise positioning equipment on the telescopes has helped to automate the image-taking process, setting the exposure time and filters and compensating for atmospheric distortions and other factors that can affect the imaging quality, Blum noted. During a productive evening, it was common to produce about 150 to 200 images for the DECaLS survey.

Cool cosmic cartography experiment

The data from the surveys was routed to supercomputers at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), which will be the major storehouse for DESI data.

More than 100 researchers participated in night shifts to conduct the surveys, said Arjun Dey, the NOAO project scientist for DESI. Dey served as a lead scientist for the MzLS survey and a co-lead scientist on the DECaLS survey with Schlegel.

“We are building a detailed map of the universe and measuring its expansion history over the last 10 to 12 billion years,” Dey said. “The DESI experiment represents the most detailed – and definitely the coolest – cosmic cartography experiment undertaken to date. Although the imaging was carried out for the DESI project, the data are publicly available so everyone can enjoy the sky and explore the cosmos.”

BASS survey supported by global team

Xiaohui Fan, a University of Arizona astronomy professor who was a co-lead on the BASS survey conducted at Kitt Peak’s Bok Telescope, coordinated viewing time by an international group that included co-leads Professor Zhou Xu and Associate Professor Zou Hu, other scientists from the National Astronomical Observatories of China (NAOC), and researchers from the University of Arizona and from across the DESI collaboration.

BASS produced about 100,000 images during its four-year run. It scanned a section of sky about 13 times larger than the Big Dipper, part of the Ursa Major constellation.

“This is a good example of how a collaboration is done,” Fan said. “Through this international partnership we were bringing in people from around the world. This is a nice preview of what observing with DESI will be like.”

Fan noted the DESI team’s swift response in updating the telescope’s hardware and software during the course of the survey.

“It improved a lot in terms of automated controls and focusing and data reduction,” he said. Most of the BASS survey imaging concluded in February, with some final images taken in March.

Next steps toward DESI’s completion

All of the images gathered will be processed by a mathematical code, called Tractor, that helps to identify all of the galaxies surveyed and measure their brightness.

With the initial testing of the massive corrector barrel, which houses DESI’s package of six large mirrors, in early April, the next major milestone for the project will be the delivery, installation, and testing of its focal plane, which caps the telescope and houses the robotic positioners.

Dey, who participated in formative discussions about the need for an experiment like DESI almost 20 years ago, said, “It’s pretty amazing that our small and dedicated team was able to pull off such a large survey in such a short time. We are excited to be turning to the next phase of this project!”

NERSC is a DOE Office of Science User Facility.

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DESI is supported by the U.S. Department of Energy’s Office of Science; the U.S. National Science Foundation, Division of Astronomical Sciences under contract to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain; the French Alternative Energies and Atomic Energy Commission (CEA); and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. View the full list of DESI collaborating institutions, and learn more about DESI here: desi.lbl.gov.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

The National Optical Astronomy Observatory (NOAO) is the national center for ground-based nighttime astronomy in the United States and is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation Division of Astronomical Sciences.

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.

The Heising-Simons Foundation is a family foundation based in Los Altos, California. The Foundation works with its many partners to advance sustainable solutions in climate and clean energy, enable groundbreaking research in science, enhance the education of our youngest learners, and support human rights for all people.

The Gordon and Betty Moore Foundation fosters path-breaking scientific discovery, environmental conservation, patient care improvements and preservation of the special character of the Bay Area. Visit moore.org and follow @MooreFound.

The Science and Technology Facilities Council (STFC) of the United Kingdom coordinates research on some of the most significant challenges facing society, such as future energy needs, monitoring and understanding climate change, and global security. It offers grants and support in particle physics, astronomy and nuclear physics; visit https://stfc.ukri.org/.

Established in 1958 and aiming at the forefront of astronomical science, the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) conducts cutting-edge astronomical studies, operates major national facilities and develops state-of the-art technological innovations.