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  • richardmitnick 8:39 am on March 21, 2019 Permalink | Reply
    Tags: "Superconducting nanowires could be used to detect dark matter", A promising new sensor based on tiny superconducting wires, , Dark Matter Detection, , , The team’s prototype already shows the potential of this approach, Yonit Hochberg at Hebrew University of Jerusalem in Israel and a few colleagues   

    From M.I.T. Technology Review: “Superconducting nanowires could be used to detect dark matter” 

    MIT Technology Review
    From M.I.T. Technology Review

    1

    March 20, 2019
    No writer credit or image credits

    One of the great scientific searches of our time is the hunt for dark matter. Physicists believe this stuff fills the universe and think they can see evidence of it in the way galaxies rotate. Indeed, galaxies spin so quickly that they ought to fly apart unless some hidden mass is generating enough gravitational force to hold them together.

    That evidence has set physicists scrabbling to find dark matter on Earth. They’ve constructed dozens of observatories, most of them in underground caverns deep beneath the surface, where background noise is low. At stake is scientific fame and fortune, with the group that finds dark matter likely to be richly rewarded.

    But so far physicists have found precisely nothing. If it is out there, dark matter is very well hidden. Or physicists have been looking in the wrong place. One possibility is that dark matter particles are too small for current experiments to see. So physicists desperately want better, more sensitive ways to detect these things.

    2

    Enter Yonit Hochberg at Hebrew University of Jerusalem in Israel and a few colleagues, who have developed a promising new sensor based on tiny superconducting wires. The team’s prototype already shows the potential of this approach.

    The principle behind the new device is straightforward. Cool certain metals below a critical temperature and they conduct with no resistance. But as soon as their temperature rises above this threshold, the superconducting behavior disappears.

    Physicists know that dark matter particles cannot interact strongly with visible matter; otherwise they would have already seen them. But dark matter particles can collide head-on with ordinary particles.

    These collisions are rare because ordinary matter is mostly empty space, so dark matter particles can pass straight through. But when they do collide with an atomic nucleus or electron in a lattice, for example, the collision causes the lattice to vibrate, thereby raising its temperature.

    It is this rise in temperature that superconducting nanowires are good at revealing. The heating causes a small portion of the wire to stop superconducting, and this in turn creates a voltage pulse that is easy to measure. What’s more, such a device produces few, if any, false positives.

    Hochberg and Co have put their idea through its paces by building a prototype. This device consists of set of tungsten silicide nanowires just 140 nanometers wide (a human hair is about 100,000 nanometers wide) and 400 micrometers long. The entire apparatus sits just a few millidegrees above absolute zero, so that the tungsten silicide wires become superconductors.

    The team then looked for the voltage pulses that might reveal a dark matter collision. With appropriate shielding in place, they found no pulses during the 10,000-second duration of their measurements.

    That places important constraints on the type of dark matter that could be present and its density. It also places constraints on other types of particles that physicists speculate might exist.

    One of these is the “dark photon”—essentially the dark matter equivalent of the ordinary photon. If they exist, then the new sensor did not detect a single one. “The results from this device already place meaningful bounds on dark matter-electron interactions, including the strongest terrestrial bounds on sub-eV dark photon absorption to date,” say Hochberg and Co.

    That’s impressive work, given that the mass of the nanowires is just a few nanograms. The next stage is to fabricate them on a larger scale. Hochberg and co say that the technology is relatively mature, so this should be possible on a short time scale. Indeed, they estimate that an academic lab could churn out a thousand 200-nanometer detectors with a total mass of 1.3 grams in just a year. “An industrial effort could realize many times that number,” they point out.

    So a kilogram-scale detector could be feasible in the not too distant future. Such a machine would rival those already in operation in the search for dark matter, but it would look at different energies in a different way.

    So it may be that one day, superconducting nanowires will discover dark matter—if it exists at all.

    Science paper:
    Detecting Dark Matter with Superconducting Nanowires
    https://arxiv.org/pdf/1903.05101.pdf

    See the full article here .


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  • richardmitnick 12:06 pm on February 26, 2019 Permalink | Reply
    Tags: , Dark Matter Detection, LBNL LZ- LUX-ZEPLIN experiment at SURF, , The LZ collaboration will circulate liquid xenon through the test cryostat to ensure the system will work properly when the experiment begins operations next year   

    From Sanford Underground Research Facility: “LZ begins new phase: testing the xenon circulation system” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    February 25, 2019
    Constance Walter

    Test will ensure critical element of the next-generation dark matter experiment will operate as needed.

    1
    David Woodward, a researcher on the LZ experiment, works on the test cryostat. Photo by Claudio Pascoal da Silva

    In preparation to test the xenon circulation system for the LUX-ZEPLIN (LZ) dark matter experiment, David Woodward carefully positioned a tower holding a stainless-steel test cryostat. The LZ collaboration will circulate liquid xenon through the test cryostat to ensure the system will work properly when the experiment begins operations next year.

    LBNL LZ project at SURF, Lead, SD, USA

    “We aren’t looking for dark matter with this test. But we do want to make sure all of our systems work the way they are supposed to,” said Woodward, a post doc at Penn State University.

    The circulation system is, perhaps, the most critical component of the LUX-ZEPLIN dark matter experiment. LZ will use 10 tons of liquid xenon to look for WIMPs—weakly interacting massive particles—and that xenon must meet very high radio-purity standards to eliminate background noise. To achieve and maintain this level of radiopurity, the xenon must be continuously removed, purified and reintroduced to the LZ detector, or circulated, during operation.

    The circulation system sits outside the water tank, which will house LZ. It’s a complicated system comprised of thousands of components: circulation compressors, tubing, wiring, sensors, all of which will connect to the actual experiment. The inner cryostat will hold the xenon, which will be fed into the experiment through an opening at the bottom of the water tank then continuously circulated.

    The test cryostat is designed very much like the real inner cryostat. It is the same height and has many of the same components; however, it is not as big around.

    “One of the goals of the test is to make sure we can circulate the xenon at the correct rate,” Woodward said. “That’s definitely possible even with a test device that isn’t exactly the same size as the actual device. It helps us understand whether the flow will work correctly—to make sure we can get the xenon to circulate all the way to the top of the actual cryostat,” Woodward added.

    The tower holding the test cryostat was positioned precisely to ensure the xenon transfer lines, which have a fixed length, will reach the real LZ cryostat once the experiment is actually running. The collaboration will monitor the system; however, there are some things they won’t be able to know, unless they can physically look inside the test cryostat. To do that, they added a glass view port on the top of the device.

    Why do they need a viewport?

    “The xenon has to stay at a certain temperature to remain liquid (minus 169.2 degrees F),” Woodward said. “If it doesn’t stay cold enough, it can revert back to gas. Gas creates bubbles, so if that happened, we could see the bubbles. But, really, we don’t want to see anything—we want this test to be boring and just see a nice flow of the liquid xenon. But if something did happen, we could see it.”

    The team will test the circulation system for several months, or as long as possible, Woodward said, to ensure it is working correctly. Then the test cryostat will be unhooked and removed. By end of summer this year, the actual cryostat will be installed, with operation of the experiment expected to begin in early 2020.

    “This test is very important to our experiment, a very important check for the next phase,” Woodward added.

    Facts and figures

    The test cryostat is made of stainless steel, whereas the one that will be used in the experiment is made of titanium. Although it is as tall as the actual cryostat, it is much smaller in diameter. “We are not looking to collect physics data with the test vessel, so we don’t need the volume,” said Woodward.

    In building the test vessel, the team followed fairly closely the cleanliness protocols for the actual vessel that will be used. It’s important that we have the purest materials possible to minimize radioactive backgrounds in the actual experiment. “We don’t want this test to dirty the real circulation system, so we had to construct it inside the surface clean room then seal it up before bringing it underground,” Woodward said.

    The test cryostat arrived from Penn State where it was initially assembled inside a cleanroom. At Sanford Lab, the test cryostat was cleaned and prepared for use underground. Now, it is underground where it is being used to test the circulation system. “That’s how we’ll know if the system is working.”

    By the numbers:

    100 inches: The height of the inner cryostat
    10 feet: The height of the outer cryostat
    10 tons: The amount of liquid xenon that will be used inside the inner cryostat
    70 kg: The amount of liquid xenon used to test the circulation system

    See the full article here .


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    About us.
    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

    LBNL LZ project will replace LUX at SURF [see below]

    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.

    LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

    In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

    SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
    “LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
    We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

    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

    U Washington Majorana Demonstrator Experiment at SURF

    The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

    LBNL LZ project at SURF, Lead, SD, USA

    CASPAR at SURF


    CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

    The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”

     
  • richardmitnick 11:38 am on January 13, 2017 Permalink | Reply
    Tags: , , Dark Matter Detection, , Physicist Peter Graham, ,   

    From Stanford: “Stanford physicist suggests looking for dark matter in unusual places” 

    Stanford University Name
    Stanford University

    January 12, 2017
    Amy Adams

    Most experiments searching for mysterious dark matter require massive colliders, but Stanford physicist Peter Graham advocates a different, less costly approach.

    1
    Physicist Peter Graham recently received a Breakthrough New Horizons Prize for his novel approach to particle physics. (Image credit: L.A. Cicero)

    For decades, particle physics has been the domain of massive colliders that whip particles around at high speeds and smash them into one another while teams of thousands observe the results. These kinds of experiments have produced great insights into forces and particles that make up the physical world.

    But Stanford physicist Peter Graham is advocating a much different approach – one that could be faster and cheaper than massive colliders, and that may be able to detect previously elusive forms of physics like dark matter.

    Graham pointed out that colliders cost tens of billions of dollars and come along so rarely that there might only be one new collider built in his lifetime. His approach evokes a time when physics could be carried out on a tabletop by one or two people and produce results in just a few years.

    “It’s going back to that in some ways, but using very different types of technologies and different approaches,” said Graham, who is an assistant professor of physics. “It’s a new direction for looking for the most basic laws of nature.”

    Graham, who is also a collaborator with the elementary particle physics division at SLAC National Accelerator Laboratory, recently received a Breakthrough New Horizons in Physics Prize for his novel direction, which he hopes more people will join. He spoke with Stanford Report about why physics needs new types of experiments, what dark matter might be and how he hopes to detect it.

    You’ve said that your experiments explore new physics. What does that mean?

    The standard model of particle physics is everything we’ve discovered. It explains almost every experiment ever done over gigantic scales, from nuclei to galaxies.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    There’s really just a very few things it doesn’t explain, which we call new physics. We know there is stuff out there beyond what we’ve seen, like dark matter, and new fundamental laws. Those are the things we are trying to discover.

    Dark matter is one form of new physics you might be able to detect. Can you explain what dark matter is and why physicists believe it exists?

    Initially, people realized that there’s much more gravity pulling in on galaxies than they could account for. Either the laws of gravity were wrong, which was possible, or there was something else that we don’t know about pulling on the galaxies. Either way, you can’t explain it with what we know.

    There’s now a lot of evidence that our understanding of gravity isn’t wrong, and instead there’s some new kind of stuff that physicists have named dark matter. It’s been a major goal in physics to understand dark matter and come up with new types of experiments to try to detect it. But you have to have some guesses about what it might be if you are going to find it. It’s a universal point in science that you have to have some idea what you are looking for in order to know how to go about looking for it.

    What are some of the theories about what dark matter might be?

    There is a lot of evidence for two candidates, called WIMPs and axions. You can look for WIMPs [weakly interacting massive particles] with more traditional techniques, like the giant colliders, and that attracted a lot of attention.

    There was just one experiment looking for axions and it only looked at part of the possible axion spectrum. It was a scary scenario that axions might be the dark matter and there might be no way to detect them. Axions are very difficult to search for because they don’t interact much with our experiments.

    Dark matter could also be some crazy new kind of particle, or a combination of WIMPs and axions, or even collections of black holes. We don’t know.

    What motivated you to think about alternate ways of exploring new physics?

    Part of the motivation is that the big colliders are important but they are also getting expensive to build. In addition, we are realizing that some new theories about dark matter really couldn’t be discovered at colliders.

    My work has been to take techniques from other fields of physics and use them in particle physics. The Breakthrough Prize is really nice because it brings a stamp of approval and could really help us get this new experimental direction going.

    Can you give me an example of one type of experiment you’ve designed?

    People had thought about one approach to detect axion dark matter and it did a good job for higher mass axions, but could not possibly see lower mass axions. We came up with a new technique to detect low mass axions. It involved combining NMR [nuclear magnetic resonance], which is commonly used in medical applications, and magnetometry, which is a very precise tool for measuring magnetic fields. We use NMR to amplify the axion signal so that the magnetometer can pick it up.

    We’ve already started building this experiment, and it could generate results in a few years. It’s very exciting because these kinds of experiments can produce results on short time scales.

    Why is it important to explore these new frontiers in physics?

    Humanity has always stared up at the stars and wondered why we are here. These kinds of questions, like the nature of dark matter, tell us about the birth of the universe, why the whole universe is here.

    But a part of it for me is also that I want to be making some contribution. One example of how basic physics helps people came from quantum mechanics. I’m sure at the time they thought it was a pure physics exercise and had no relation to human health. Well, we learned quantum mechanics and now we have MRI machines and PET scans. I would say that’s a really important lesson. Humans are creative and we do find ways to use new information.

    See the full article here .

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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 4:08 pm on September 26, 2016 Permalink | Reply
    Tags: Dark Matter Detection, , ,   

    From SURF: “Construction of World’s Most Sensitive Dark Matter Detector Moves Forward” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    September 26, 2016
    Constance Walter

    A next-generation dark matter detector that will be at least 100 times more sensitive than its predecessor, has cleared another approval milestone and is on schedule to begin its deep-underground hunt for theoretical particles known as WIMPs, or weakly interacting massive particles, in 2020.

    1
    TestStand-Prototype: Tomasz Biesiadzinski (left, SLAC) and Jeremy Mock (State University of New York/Berkeley Lab) install a miniversion of the future LUX-ZEPLIN (LZ) dark matter detector at a test stand at SLAC. The white container is a prototype of the detector’s core, also known as a time projection chamber (TPC). For the dark matter hunt, LZ’s TPC will be filled with liquid xenon. (Credit: SLAC National Accelerator Laboratory)

    2
    LZ-TestStand: SLAC’s Thomas “TJ” Whitis at the test stand for the LZ experiment at SLAC. The TPC prototype is installed inside the cylinder on the left. (Credit: SLAC National Accelerator Laboratory)

    3
    LZ-KrRemoval: SLAC’s Christina Ignarra (left) and Wing To are working on a system to remove krypton from commercially available xenon. (Credit: SLAC National Accelerator Laboratory)

    WIMPs are among the top prospects for explaining dark matter, the unseen stuff that we have observed only through gravitational effects.

    Last month, LZ received an important U.S. Department of Energy approval (known as Critical Decision 2 and 3b) for the project’s overall scope, cost and schedule. The latest approval step sets in motion the build-out of major components and the preparation of its mile-deep lair at the Sanford Underground Research Facility (SURF) in Lead, S.D.

    The experiment is designed to tease out dark matter signals from within a chamber filled with 10 metric tons of purified liquid xenon, one of the rarest elements on Earth. The project is supported by a collaboration of more than 30 institutions and about 200 scientists worldwide.

    “The nature of the dark matter, which comprises 85 percent of all matter in the universe, is one of the most perplexing mysteries in all of contemporary science,” said Harry Nelson, LZ spokesperson and a physics professor at University of California, Santa Barbara. “Just as science has elucidated the nature of familiar matter—from the periodic table of elements to subatomic particles, including the recently discovered Higgs boson—the LZ project will lead science in testing one of the most attractive hypotheses for the nature of the dark matter.”

    LZ is named for the merger of two dark matter detection experiments: the Large Underground Xenon experiment (LUX) and the U.K.-based ZonEd Proportional scintillation in Liquid Nobel gases experiment (ZEPLIN). LUX, a smaller liquid xenon-based underground experiment at SURF will be dismantled to make way for the new project.

    4
    A cutaway rendering of the LUX-ZEPLIN (LZ) detector that will be installed nearly a mile deep near Lead, S.D. The central chamber will be filled with 10 metric tons of purified liquid xenon that produces flashes of light and electrical pulses in particle interactions. An array of detectors, known as photomultiplier tubes, at the top and bottom of the liquid xenon tank are designed to pick up these particle signals. (Credit: Matt Hoff/Berkeley Lab)

    “Liquid Xenon has turned out to be a nearly magical substance for WIMP detection, as demonstrated by the sensitivities achieved by ZEPLIN and LUX,“ said Professor Henrique Araujo from Imperial College London, who leads the project in the U.K.

    The SURF site shields the experiment from many particle types that are constantly showering down on the Earth’s surface and would obscure the signals LZ is seeking.

    “Nobody looking for dark matter interactions with matter has so far convincingly seen anything, anywhere, which makes LZ more important than ever,” said Murdock “Gil” Gilchriese, LZ project director and Berkeley Lab physicist.

    Dan McKinsey, a Lawrence Berkeley National Laboratory (Berkeley Lab) faculty senior scientist and UC Berkeley Physics professor who is a part of the LZ collaboration, said, “A major reason for LZ is surprises: We’re really pushing way into the low-energy, low-background parameter space where no one has ever looked, and this is where surprises could await. That’s where new things get discovered. While we are looking for dark matter, we may see something else that has a rare interaction with matter at low energies.”

    Some previous and planned experiments that also use liquid xenon as the medium for dark-matter detection are helping to set the stage for LZ.

    Experiments seeking traces of dark matter have grown increasingly sensitive in a short time, Gilchriese said, noting, “It’s really like Moore’s law,” an observation about regular, exponential growth in computing power through the increasing concentration of transistors on a computer chip over time. “The technologies used in liquid xenon detectors have been demonstrated around the world.”

    The entire supply of xenon for the project is already under contract, Gilchriese said, and the state of South Dakota aided in the purchase of this supply. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry.

    Before the xenon is delivered in gas form in tanks to South Dakota, it will be purified at SLAC National Accelerator Laboratory.

    “Having focused on design and prototyping for some time now, it’s very exciting to be moving forward toward building the LZ detector and the production-scale purification systems that will process its xenon,” said Dan Akerib, who co-leads SLAC’s LZ team. “The goal is to limit contamination from another element, krypton, to just one-tenth of a part per trillion.”

    Liquid xenon was selected because it can be ultra-purified, including the removal of most traces of radioactivity that could interfere with particle signals, and because it produces light and electrical pulses when it interacts with particles.

    Engineers at Fermi National Accelerator Laboratory and the University of Wisconsin’s Physical Sciences Laboratory are working together to make sure that none of that expensive xenon is lost should there be a power outage or extended down time.

    “The xenon in LZ is precious both scientifically and financially, so it’s very important that we have the same amount of xenon at the end of the experiment as at the beginning,” said Hugh Lippincott of Fermilab, the current physics coordinator of the collaboration. “We’re excited to be part of this next generation of direct dark matter experiments.”

    LZ is designed so that a dark matter particle would produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank, will carry the telltale fingerprint of the particles that created them.

    The tubes are currently being manufactured by a company in Japan and will be tested by collaboration members. Progress is also continuing on the construction of ultrapure titanium sheets in Italy that will be formed, fitted and welded together to create a double-walled vessel that will hold the liquid xenon.

    In recent weeks, researchers used LUX, which will soon be dismantled, as a test bed for prototype LZ electronics. They tested new approaches in monitoring and measuring particle signals, which will help them in fine-tuning the LZ detector.

    “We have learned a ton of stuff from LUX,” McKinsey said. “We are mixing in some different forms of elements that we can remove really well or that decay to stable isotopes—to measure all of the responses of the liquid xenon detector. We are making sure our errors are small when we actually do the LZ experiment.”

    Other work is focused on precisely measuring the slightest contribution to background noise in the detector posed by all of the components that will surround the liquid xenon, to help predict what the detector will see once it’s turned on. A high-voltage system is being tested at Berkeley Lab that will generate an electric field within the detector to guide the flow of electrons produced in particle interactions to the top of the liquid xenon chamber.

    “At SLAC, we’ve set up an entire platform where the LZ collaboration is testing detector prototypes and is performing all kinds of system tests,” said Tom Shutt, co-leader of the national lab’s LZ group and LUX co-founder.

    In the next year there will be lot of work at SURF to disassemble LUX and prepare the underground site for LZ assembly and installation. Much of the onsite assembly for LZ will take place in 2018-2019 at SURF.

    Kevin Lesko, a senior physicist at Berkeley Lab and head of Berkeley Lab’s SURF operations office, said that LZ will benefit from previous work at the SURF site to prepare for new and larger experiments. “Back in 2009, we sized the water tank and other infrastructure to support next-generation experiments,” he said.

    Strong scientific teams from the U.K., Portugal, Russia, and South Korea are making crucial physical and intellectual contributions to the LZ project. For more information about the LZ collaboration, visit: http://lz.lbl.gov/collaboration/.

    LZ is supported by the U.S. Department of Energy’s Office of High Energy Physics, the U.K. Science & Technology Facilities Council, the Portuguese Foundation for Science and Technology, and the South Dakota Science and Technology Authority (SDSTA), which developed the Sanford Underground Research Facility (SURF). SURF is operated by the SDSTA under a contract with the Lawrence Berkeley National Laboratory for the Department of Energy’s Office of High Energy Physics.

    See the full article here .

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    About us.
    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

     
  • richardmitnick 8:27 pm on June 27, 2016 Permalink | Reply
    Tags: , , Dark Matter Detection, ,   

    From particlebites: “The Fermi LAT Data Depicting Dark Matter Detection” 

    particlebites bloc

    particlebites

    June 27, 2016
    Chris Karwin

    The center of the galaxy is brighter than astrophysicists expected. Could this be the result of the self-annihilation of dark matter? Chris Karwin, a graduate student from the University of California, Irvine presents the Fermi collaboration’s analysis.

    Presenting: Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center
    Authors: The Fermi-LAT Collaboration (ParticleBites blogger is a co-author)
    Reference: 1511.02938, Astrophys.J. 819 (2016) no.1, 44

    NASA/Fermi Telescope
    NASA/Fermi

    Introduction

    Like other telescopes, the Fermi Gamma-Ray Space Telescope is a satellite that scans the sky collecting light. Unlike many telescopes, it searches for very high energy light: gamma-rays. The satellite’s main component is the Large Area Telescope (LAT).

    NASA/Fermi LAT
    NASA/Fermi LAT

    When this detector is hit with a high-energy gamma-ray, it measures the the energy and the direction in the sky from where it originated. The data provided by the LAT is an all-sky photon counts map:

    1
    All-sky counts map of gamma-rays. The color scale correspond to the number of detected photons. Image from NASA

    In 2009, researchers noticed that there appeared to be an excess of gamma-rays coming from the galactic center. This excess is found by making a model of the known astrophysical gamma-ray sources and then comparing it to the data.

    What makes the excess so interesting is that its features seem consistent with predictions from models of dark matter annihilation. Dark matter theory and simulations predict:

    The distribution of dark matter in space. The gamma rays coming from dark matter annihilation should follow this distribution, or spatial morphology.
    The particles to which dark matter directly annihilates. This gives a prediction for the expected energy spectrum of the gamma-rays.

    Although a dark matter interpretation of the excess is a very exciting scenario that would tell us new things about particle physics, there are also other possible astrophysical explanations. For example, many physicists argue that the excess may be due to an unresolved population of milli-second pulsars. Another possible explanation is that it is simply due to the mis-modeling of the background. Regardless of the physical interpretation, the primary objective of the Fermi analysis is to characterize the excess.

    The main systematic uncertainty of the experiment is our limited understanding of the backgrounds: the gamma rays produced by known astrophysical sources. In order to include this uncertainty in the analysis, four different background models are constructed. Although these models are methodically chosen so as to account for our lack of understanding, it should be noted that they do not necessarily span the entire range of possible error. For each of the background models, a gamma-ray excess is found. With the objective of characterizing the excess, additional components are then added to the model. Among the different components tested, it is found that the fit is most improved when dark matter is added. This is an indication that the signal may be coming from dark matter annihilation.
    Analysis

    This analysis is interested in the gamma rays coming from the galactic center. However, when looking towards the galactic center the telescope detects all of the gamma-rays coming from both the foreground and the background. The main challenge is to accurately model the gamma-rays coming from known astrophysical sources.

    2
    Schematic of the experiment. We are interested in gamma-rays coming from the galactic center, represented by the red circle. However, the LAT detects all of the gamma-rays coming from the foreground and background, represented by the blue region. The main challenge is to accurately model the gamma-rays coming from known astrophysical sources. Image adapted from Universe Today.

    An overview of the analysis chain is as follows. The model of the observed region comes from performing a likelihood fit of the parameters for the known astrophysical sources. A likelihood fit is a statistical procedure that calculates the probability of observing the data given a set of parameters. In general there are two types of sources:

    1. Point sources such as known pulsars
    2. Diffuse sources due to the interaction of cosmic rays with the interstellar gas and radiation field

    Parameters for these two types of sources are fit at the same time. One of the main uncertainties in the background is the cosmic ray source distribution. This is the number of cosmic ray sources as a function of distance from the center of the galaxy. It is believed that cosmic rays come from supernovae. However, the source distribution of supernova remnants is not well determined. Therefore, other tracers must be used. In this context a tracer refers to a measurement that can be made to infer the distribution of supernova remnants. This analysis uses both the distribution of OB stars and the distribution of pulsars as tracers. The former refers to OB associations, which are regions of O-type and B-type stars. These hot massive stars are progenitors of supernovae. In contrast to these progenitors, the distribution of pulsars is also used since pulsars are the end state of supernovae. These two extremes serve to encompass the uncertainty in the cosmic ray source distribution, although, as mentioned earlier, this uncertainty is by no means bracketing. Two of the four background model variants come from these distributions.

    3
    An overview of the analysis chain. In general there are two types of sources: point sources and diffuse source. The diffuse sources are due to the interaction of cosmic rays with interstellar gas and radiation fields. Spectral parameters for the diffuse sources are fit concurrently with the point sources using a likelihood fit. The question mark represents the possibility of an additional component possibly missing from the model, such as dark matter.

    The information pertaining to the cosmic rays, gas, and radiation fields is input into a propagation code called GALPROP. This produces an all-sky gamma-ray intensity map for each of the physical processes that produce gamma-rays. These processes include the production of neutral pions due to the interaction of cosmic ray protons with the interstellar gas, which quickly decay into gamma-rays, cosmic ray electrons up-scattering low-energy photons of the radiation field via inverse Compton, and cosmic ray electrons interacting with the gas producing gamma-rays via Bremsstrahlung radiation.

    4
    Residual map for one of the background models. Image from 1511.02938

    The maps of all the processes are then tuned to the data. In general, tuning is a procedure by which the background models are optimized for the particular data set being used. This is done using a likelihood analysis. There are two different tuning procedures used for this analysis. One tunes the normalization of the maps, and the other tunes both the normalization and the extra degrees of freedom related to the gas emission interior to the solar circle. These two tuning procedures, performed for the the two cosmic ray source models, make up the four different background models.

    Point source models are then determined for each background model, and the spectral parameters for both diffuse sources and point sources are simultaneously fit using a likelihood analysis.

    Results and Conclusion

    6
    Best fit dark matter spectra for the four different background models. Image: 1511.02938

    In the plot of the best fit dark matter spectra for the four background models, the hatching of each curve corresponds to the statistical uncertainty of the fit. The systematic uncertainty can be interpreted as the region enclosed by the four curves. Results from other analyses of the galactic center are overlaid on the plot. This result shows that the galactic center analysis performed by the Fermi collaboration allows a broad range of possible dark matter spectra.

    The Fermi analysis has shown that within systematic uncertainties a gamma-ray excess coming from the galactic center is detected. In order to try to explain this excess additional components were added to the model. Among the additional components tested it was found that the fit is most improved with that addition of a dark matter component. However, this does not establish that a dark matter signal has been detected. There is still a good chance that the excess can be due to something else, such as an unresolved population of millisecond pulsars or mis-modeling of the background. Further work must be done to better understand the background and better characterize the excess. Nevertheless, it remains an exciting prospect that the gamma-ray excess could be a signal of dark matter.

    See the full article here .

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