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  • richardmitnick 11:41 am on November 18, 2016 Permalink | Reply
    Tags: , LUX-ZEPLIN, , ,   

    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

    LUX-ZEPLIN (LZ), 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.

    Lux Zeplin project at SURF
    Lux Zeplin project at SURF

    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.

    “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 .

    Please help promote STEM in your local schools.
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    Stem Education Coalition

    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 1:43 pm on July 26, 2016 Permalink | Reply
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    From Sky & Telescope: “No Dark Matter from LUX Experiment” 

    SKY&Telescope bloc

    Sky & Telescope

    An underground detector reports zero detections of weakly interacting massive particles (WIMPs), the top candidate for mysterious dark matter.

    1
    The Davis cavern, deep within what used to be the Homestake Mine, before the placement of the LUX experiment.

    SURF logo

    Sanford Underground levels
    Sanford Underground levels

    LUX/Dark matter experiment at SURF
    LUX/Dark matter experiment at SURF

    Founded in 1876, the town of Lead in South Dakota hummed along as a mining community for more than a century. Homestake Mine employed thousands in the largest, deepest, and most productive gold mine in the Western Hemisphere.

    Now scientists are using it to mine for gold of a darker kind.

    More than a mile underground, where miners once accessed precious ore, sits a 3-foot-tall, dodecagonal cylinder of liquid xenon. The 122 photomultiplier tubes at the container’s top and bottom await the glitter of light that would signal an elusive dark matter shooting through the cylinder and interacting with one of the xenon atoms.

    But after more than a year of data collecting, the Large Underground Xenon (LUX) experiment announced last week at the Identification of Dark Matter 2016 conference that they’re still coming up empty-handed.

    A Physicist’s Gold Mine

    Weakly interacting massive particles (WIMPs) are the top candidates for dark matter, the invisible stuff that makes up about 84% of the universe’s matter. By definition, dark matter doesn’t interact with light, nor does it interact via the strong force that holds nuclei together. And while we know it interacts with gravity, that interaction leaves only indirect evidence of its existence, such as its effect on galaxy rotation.

    3
    This bottom view shows the photomultiplier tube holders in the LUX experiment.

    But WIMP theory says dark matter particles should also interact via the weak force, a fundamental force that governs nature on a subatomic level — including the fusion within the Sun. So a WIMP particle should very rarely smash into a heavy nucleus, generating a flash of light. The chance for a direct hit is very, very low, but 350 kilograms (770 pounds) of liquid xenon in the LUX experiment should have good odds.

    After just three months of operation, in 2013 the LUX experiment had already reported a null result. At the time, the experiment had probed with a sensitivity 20 times that of previous experiments (check out the graph here to see how three months of LUX ruled out numerous WIMP scenarios).

    A new 332-day run began in September 2014, and the preliminary analysis announced last week probes four times deeper than the results before. Yet despite a longer run time, increased sensitivity, and better statistical analysis, the LUX team still hasn’t found any WIMPs.

    Simply put: either WIMPs don’t exist at all, or the WIMPs that do exist really, really don’t like interacting with normal matter.

    It’s also worth noting that LUX isn’t just looking for WIMPs. The WIMP scenario is the primary one it’s testing, and the one that last week’s announcement focused on. But more results are forthcoming about LUX results on dark matter alternatives, such as axions and axion-like particles.

    Not All That’s Gold Glitters

    The non-finding may not win any Nobel Prizes, but in a way it’s great news for physicists. Numerous experiments (such as CDMS II, CoGeNT, and CRESST) had found glimmers of WIMP detections, but none had found results statistically significant enough to be claimed as a real detection. The LUX results have been helpful in ruling out those hints of low-mass WIMPs.

    3
    For the technically minded, this is the result that was presented at the Identification of Dark Matter conference in Sheffield, UK. The plot shows the possibilities for dark matter in terms of its cross-section — the bigger the value, the more easily it interacts with normal matter — and its mass. (The mass is given in gigaelectron volts per speed of light squared, which translates to teeny tiny units of 1.9 x 10-27 kg.) LUX’s most recent results rule out any dark matter particles with mass and cross-section that place them above the solid black line. The upshot is that LUX, the most sensitive dark matter experiment to date, is narrowing the playing field, especially for low-mass WIMP scenarios.

    “It turns out there is no experiment we can think of so far that can eliminate the WIMP hypothesis entirely,” says Dan McKinsey (University of California, Berkeley). “But if we don’t detect WIMPs with the experiments planned in the next 15 years or so . . . physicists will likely conclude that dark matter isn’t made of WIMPs.”

    That’s why — despite not finding any WIMPs this time around — the LUX team continues to work on the next-gen experiment: LUX-ZEPLIN. Its 7 tons of liquid xenon should begin awaiting flashes from dark matter interactions by 2020.

    Lux Zeplin project
    Lux Zeplin project at SURF

    Three years of data from LUX-ZEPLIN will probe WIMP scenarios down to fundamental limits from the cosmic ray background. In other words, if LUX-ZEPLIN doesn’t detect WIMPs, they don’t exist — or they’re beyond our detection capabilities altogether.

    See the full article here (More …)

     
  • richardmitnick 6:57 pm on July 25, 2016 Permalink | Reply
    Tags: , , , LUX-ZEPLIN,   

    From SURF: “LUX exceeds sensitivity goals” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    7.25.16
    Connie Walker

    Last week, the Large Underground Xenon (LUX) collaboration announced a whole new level of sensitivity for its dark matter experiment. Although no dark matter particles were found, LUX’s sensitivity far exceeded the goals for the project. The results give researchers confidence that if a particle had interacted with the detector’s xenon target, they almost certainly would have seen it.

    “It would have been marvelous if the improved sensitivity had also delivered a clear dark matter signal. However, what we have observed is consistent with background alone,” said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for LUX.

    The new results allow scientists to eliminate many potential models for dark matter particles, offering critical guidance for the next generation of dark matter experiments. The final results were announced at the Identification of Dark Matter 2016 conference and signaled the completion of a 300-live-day search that ended in May.

    During a 20-month run, the LUX team incorporated unique calibration measures to search a wide swath of potential parameter space for dark matter particles called WIMPs, or weakly interacting massive particles.

    “These careful background-reduction techniques and precision calibrations and modeling, enabled us to probe dark matter candidates that would produce signals of only a few events per century in a kilogram of xenon,” said Aaron Manalaysay, the Analysis Working Group coordinator for LUX and a research scientist from UC Davis, who presented the new results in Sheffield, UK.

    With the completion of its final run, LUX is preparing for decommissioning this fall. But before that, the LUX team plans to use the detector to continue calibrating and testing backgrounds in preparation for the next generation dark matter detector, LUX-ZEPLIN (LZ).

    Lux Zeplin project
    Lux Zeplin project

    “The main driver behind this campaign of calibrations is to test new techniques or improve on existing techniques, which will be used for LZ,” said Simon Fiorucci, a physicist at Lawrence Berkeley National Laboratory and science coordination manager for the experiment. LUX has sufficient size, low-enough background and a known response that can tell researchers if the techniques will work.

    Fiorucci said some interesting science also can come out of some of these tests. For example, the neutron generator studies done in June and July could further improve understanding of the xenon response to WIMP interactions at extremely low energy. “This would be a boon to LZ, LUX and the entire field of dark matter,” he said.

    The LZ team also plans to measure the intrinsic radioactivity of a liquid scintillator mix that will be used with LZ and requires an extremely quiet environment. The scintillator will replace LUX inside the high-purity water tank.

    “This critical piece of information will tell LZ whether their background is good enough for the outer detector to perform as expected and, if not, where they should focus their efforts to make it so,” Fiorucci said.

    The tests will run through January.

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    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 4:48 pm on June 1, 2016 Permalink | Reply
    Tags: , , LUX-ZEPLIN,   

    From SLAC: “Prototype of LUX-ZEPLIN Dark Matter Detector Tested at SLAC” 


    SLAC Lab

    June 1, 2016

    Researchers Prepare to Build an Ultrasensitive ‘Eye’ for Elusive Form of Matter

    Prototyping of a new, ultrasensitive “eye” for dark matter is making rapid progress at the Department of Energy’s SLAC National Accelerator Laboratory: Researchers and engineers have installed a small-scale version of the future LUX-ZEPLIN (LZ) detector to test, develop and troubleshoot various aspects of its technology.

    1
    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. (SLAC National Accelerator Laboratory)

    2
    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. (SLAC National Accelerator Laboratory)

    When LZ goes online in early 2020 at the Sanford Underground Research Facility in South Dakota, hopes are that it will detect so-called weakly interacting massive particles, or WIMPs.

    SURF logo

    Many researchers believe that these hypothetical particles could make up the dark matter, the invisible substance that accounts for 85 percent of all matter in the universe.

    The detector’s core will be a 5-foot-tall container filled with 10 tons of liquid xenon. When particles pass through it and collide with a xenon atom, the xenon atom emits a flash of light and also releases electrons, which generate a second flash of light. These two consecutive light flashes could represent a characteristic WIMP signal, if all other possible origins have been ruled out.

    3
    The heart of the LZ detector will be a 5-foot-tall time projection chamber (TPC) filled with 10 tons of liquid xenon. Hopes are that hypothetical dark matter particles will produce flashes of light as they traverse the detector. (SLAC National Accelerator Laboratory)

    One particular challenge is to create a strong, stable electric field across the vessel to quickly pull all electrons to the top, where they can be detected. This requires applying high voltages over short distances at the bottom and top of the xenon container. However, it also produces unwanted stray light and can cause damaging electric sparks if not done properly.

    So the SLAC team is now carefully testing the design of the high-voltage system on a 20-inch-tall miniversion of the xenon vessel whose parts were manufactured by Lawrence Berkeley National Laboratory, which manages the LZ project.

    Berkeley Logo

    “We began testing the bottom part last year and have now assembled the entire prototype,” says Kimberly Palladino, an LZ scientist at SLAC and assistant professor at the University of Wisconsin, Madison. “Our goal is to reach high voltages of 100 kilovolts without sparking, demonstrate that the system runs stably over time, and reduce the stray emissions we’ve been observing.”

    4
    Bottom part of the TPC prototype. A high voltage will be applied to the metal grid to generate a strong electric field across the LZ detector. SLAC’s team is carefully testing the design to make sure the high-voltage system is stable and operates properly. (SLAC National Accelerator Laboratory)

    SLAC research associate Tomasz Biesiadzinski says, “In addition, we use our test stand to test all kinds of aspects of LZ, including the cooling system, xenon purification and circulation, control systems and sensors. Researchers from various groups around the world come here, too, to test the equipment they are developing for the experiment.”

    In parallel, SLAC’s team is working on a system to remove an isotope of the chemical element krypton that would cause unwanted signals in the LZ detector from commercially available xenon. The goal: Reach a level of 15 krypton atoms or less per one million billion xenon atoms. Once the design goal has been reached, the researchers will build a large-scale system to purify all 10 tons of xenon needed for the experiment.

    5
    SLAC’s Christina Ignarra (left) and Wing To are working on a system to remove krypton from commercially available xenon. (SLAC National Accelerator Laboratory)

    To learn more about the project, visit the website of SLAC’s LZ team, which is part of the lab’s Particle Astrophysics and Cosmology Division and SLAC’s/Stanford University’s Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). The team works closely with a number of LZ collaborators, including Berkeley Lab, Fermi National Accelerator Laboratory, Texas A&M University, University of Maryland, Oxford University and University of Wisconsin.

    See the full article here .

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 2:23 pm on November 8, 2014 Permalink | Reply
    Tags: , , , , LUX-ZEPLIN, ,   

    From Kavli: “New Dark Matter Experiments Prepare to Hunt the Unknown” 

    KavliFoundation

    The Kavli Foundation

    Kelen Tuttle (Fall 2014)

    Three astrophysicists – Enectali Figueroa-Feliciano, Harry Nelson and Gray Rybka – discuss preparations for three recently funded dark matter experiments, and the likelihood that one of them will strike gold.

    THIS MONTH, THREE NEW EXPERIMENTS take significant steps in the hunt for dark matter, the elusive substance that appears to make up more than a quarter of the universe, but interacts very rarely with the matter that makes up our world. The experiments – the Axion Dark Matter eXperiment Gen 2, LUX-ZEPLIN and the Super Cryogenic Dark Matter Search at SNOLAB – learned in July that each would receive much needed funding from the U.S. Department of Energy and the U.S. National Science Foundation. Each of these “second-generation” experiments will be at least 10 times more sensitive than today’s dark matter detectors, increasing the likelihood that they will see the small, rare interactions between dark matter and the regular matter we all interact with every day.

    As the experimental plans start to coalesce and detector equipment starts to arrive for ADMX Gen2, LZ and SuperCDMS SNOLAB, three scientists discuss the likelihood that these projects will at long last discover dark matter. The participants:

    ENECTALI FIGUEROA-FELICIANO – is a member of the SuperCDMS collaboration and an associate professor of physics at the MIT Kavli Institute for Astrophysics and Space Research.
    HARRY NELSON – is the science lead for the LUX-ZEPLIN experiment and is a professor of physics at the University of California, Santa Barbara.
    GRAY RYBKA – leads the ADMX Gen 2 experiment as a co-spokesperson and is a research assistant professor of physics at the University of Washington.

    THE KAVLI FOUNDATION: We know that dark matter is five times more prevalent than ordinary matter, and we’re able to infer that clumps of dark matter help hold together clusters of galaxies. So this substance is a huge part of what makes up our universe and an important part of why our universe looks the way it does. Why, then, haven’t we been able to observe it directly? What’s holding us back?

    HARRY NELSON: A big part of the challenge is that dark matter doesn’t interact with us very much. We know that dark matter is passing through our galaxy all the time, but it doesn’t disrupt the type of matter we’re made of.

    But more than that, dark matter doesn’t interact with itself very much either. The matter that we see around us every day interacts with itself: Atoms form molecules, the molecules form dirt, and the dirt forms planets. But that’s not the case with dark matter. Dark matter is widely dispersed, and doesn’t form dense objects like we’re used to. That, combined with the fact that it doesn’t interact with our type of matter very often, makes it hard to detect.

    ENECTALI FIGUEROA-FELICIANO: What Harry says is exactly right. In my mind, nature is being coy. There’s something we just don’t understand about the internal structure of how the universe works. When theorists write down all the ways dark matter might interact with our particles, they find, for the simplest models, that we should have seen it already. So even though we haven’t found it yet, there’s a message there, one that we’re trying to decode now.

    Gray RybkaGray Rybka leads the ADMX Gen 2 experiment as a co-spokesperson and is a research assistant professor of physics at the University of Washington.

    TKF: In fact, nature is being so coy that we don’t yet even know what dark matter particles look like. Gray, your experiment – ADMX – looks for a different particle altogether than the one that Tali and Harry look for. Why is that?

    gr
    GRAY RYBKA

    GRAY RYBKA: As you say, my project — the Axion Dark Matter eXperiment, or ADMX —searches for a theoretical type of dark matter particle called the axion, which is extremely lightweight with neither electric charge nor spin. Harry and Tali look for a different type of dark matter called the WIMP, for Weakly Interacting Massive Particle, which describes a number of theorized particles that interact with our world very weakly and very rarely.

    Both the WIMP and the axion are really good dark matter candidates. They’re especially great because they would explain both dark matter and other mysteries of physics at the same time. I suppose I like the axion because there aren’t a lot of experiments looking for it. If I’m going to gamble and spend a lot of time making an experiment to look for something, I don’t want to look for something that everyone else is looking for.

    We’ve been updating the ADMX experiment since 2010 and have demonstrated that we have the tools necessary to see axions if they are out there. ADMX is a scanning experiment, where we scan the various masses this axion could have, one at a time. How fast we scan depends on how cold we can make the experiment. With Gen2, we’re buying a very, very powerful refrigerator that will arrive next month. Once it arrives, we’ll be able to scan very, very quickly and we feel we’ll have a much better chance of finding axions – if they’re out there.
    “In my mind, nature is being coy. There’s something we just don’t understand about the internal structure of how the universe works… there’s a message there, one that we’re trying to decode now.” —Enectali Figueroa-Feliciano

    TKF: And, Harry, why do you bet on the WIMP?

    hn
    HARRY NELSON
    Harry Nelson leads the LUX-ZEPLIN experiment and is a professor of physics at the University of California, Santa Barbara. (Image: Sonia Fernandez/UCSB)

    NELSON: Even though I’m betting on WIMPs, I like axions too. I even wrote some papers on axions way back when. But these days, as Gray said, I look for WIMPs. My collaboration is currently operating the Large Underground Xenon, or LUX, experiment in the famous Black Hills of South Dakota, inside a mine that was the outgrowth of the 1876 gold rush that formed the city Deadwood. This month, we start our 12-month run with LUX. We’re also now carefully developing our plans to upgrade our detector to make it more than 100 times more sensitive for the new LUX-ZEPLIN project.

    But to tell you the truth, I actually have a little bit of the attitude that all of these possibilities are unlikely. I’m not saying that hunting for them is worthless; that’s not it at all. It’s just that nature doesn’t have to respect what physicists want. We desire to better understand our own strong interaction, the mechanism responsible for the strong nuclear force which holds the atomic nucleus together. The axion would help do that.

    The WIMP is great because it’s consistent with the physics of the Big Bang in a straightforward way. A lot of science is based on what’s called Occam’s razor: We make the simplest possible assumptions and then test them very well, and only give up simplicity if we absolutely need to. I’ve always felt that the WIMP is a tiny bit simpler than the axion. Both are unlikely, but are still the best candidates we can think of. It’s probably more likely that dark matter is somewhat different than either the WIMP or the axion, but we must start somewhere and the WIMP and axion are the best starting points we can imagine.

    TKF: If you think it’s unlikely that the WIMP is out there, why do you look for it?

    NELSON: The WIMP and axion have the absolute best theoretical motivations. And so it’s great that both WIMPs and axions have really strong experiments going after them.

    Tali Figueroa-Feliciano​Enectali (Tali) Figueroa-Feliciano is a member of the SuperCDMS collaboration and an associate professor of physics at the MIT Kavli Institute for Astrophysics and Space Research.

    ff
    ENECTALI (TALI) FIGUEROA-FELICIANO

    FIGUEROA-FELICIANO: As an experimentalist, I come at this from the point of view that theorists are very clever, and have come up with an incredible array of possible scenarios for what dark matter could be. And, as Harry said, we attempt to use Occam’s razor to try to weed out which of these things are more probable than the others. But that’s not an infallible way to go about it. Dark matter might not follow the simplest explanation possible. So we have to be a little agnostic about it.

    In a way it’s like looking for gold. Harry has his pan and he’s looking for gold in a deep pond, and we’re looking in a slightly shallower pond, and Gray’s a little upstream, looking in his own spot. We don’t know who’s going to find gold because we don’t know where it is.

    That said, I think it’s really important to stress how complementary these three searches are. Together, we look in a lot of the places where dark matter could be. But we certainly don’t cover all of the options. As Harry says, it could be that dark matter is there, but our three experiments will never see anything because we’re looking in the wrong place – it could be in another fork of the river, where we haven’t even started looking yet.

    RYBKA: I look at it a bit more optimistically. Although as Tali said all the experiments could be looking in entirely the wrong place, it’s also possible that they’ll all find dark matter. There’s nothing that would require dark matter to be made of just one type of particle except us hoping that it’s that simple. Dark matter could be one-third axions, one-third heavy WIMPs and one-third light WIMPs. That would be perfectly allowable from everything we’ve seen.

    FIGUEROA-FELICIANO: I agree. I should have said that the gold nugget we’re looking for is a very valuable one. So even though the search is hard, it’s worthwhile because we’re looking for a very valuable thing: to understand what dark matter is made of and to discover a new part of our universe. There’s a very beautiful prize at the end of this search, so it’s absolutely worthwhile.

    Dark matter in galaxy clusterThe inferred distribution of dark matter is superimposed in purple over this Hubble Space Telescope image of galaxy cluster Abell 1689. (Image: NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) & J-P. Kneib (LAM))

    TKF: Tali, tell us a little about the pond where you’re panning for that very valuable nugget of dark matter.

    FIGUEROA-FELICIANO: My experiment is currently running in Soudan, Minnesota, inside a mine that’s a bit over half a kilometer (at 2,341 feet) underground. This experiment, called SuperCDMS Soudan, was designed to demonstrate a new technology we’ve been developing that allows us to search for WIMPs that are on the lighter-mass side. It turns out that certain classes of WIMPs, ones that are lighter than Harry searches for, deposit very little energy into detectors. Our detectors are able to distinguish very small amounts of energy deposited in the detector from all the many different signals that we get from radioactive materials, cosmic rays, and all sorts of other things that stream though our detectors. Being able to make that separation is very important, both for SuperCDMS and for LZ.

    “There’s nothing that would require dark matter to be made of just one type of particle except us hoping that it’s that simple.” —Gray Rybka

    The next step for our experiment is called SuperCDMS SNOLAB. SNOLAB is a nickel mine in Canada that’s 2 kilometers (6,531 feet) deep. We’ve been approved to build a brand new experiment down there to search for these low-mass WIMPs. Also, if LUX or LZ sees a higher mass WIMP, we’ll be able to check that measurement. Right now, we’re in the process of finalizing the design and taking the first steps of putting this brand-new SNOLAB experiment together. We expect to have a first phase of detectors in the next couple of years.

    TKF: If one of your experiments finds evidence of dark matter, after the celebratory champagne, what would be the next steps?

    lux
    LUX physicist Jeremy Mock inspected the LUX detector before the large tank was filled with more than 70,000 gallons of ultra pure water. The water shields the detector from background radiation. (Image: Matt Kapust, Sanford Underground Research Facility)

    RYBKA: Bottle it and sell it, I guess! But really, I’d say that all of the experiments would need to keep going even after such a discovery, until someone could conclusively prove that the discovered dark matter makes up 100 percent of all the dark matter in the universe.

    NELSON: I would agree with that. We would also need to dig in and really try to understand what we discovered. There’s an old saying in particle physics that you haven’t discovered a particle until you know its mass, spin and parity, a property that’s important in the quantum-mechanical description of a physical system. To really discover dark matter, we’ll need to prove that it’s what we think it is, and we’ll need to learn its characteristics. After you discover a particle, everyone gets a lot smarter at what to do with it. This has been going on with the Higgs boson lately. Folks at the Large Hadron Collider are getting cleverer because now that they’ve seen the particle, they can focus on interrogating it.

    When we start to do that with dark matter, we’re going to see something new. That’s just how scientific progress works. Right now, we can’t see through the wall because we haven’t figured out what the wall is made of. But once we understand what’s in the wall – my analogy for dark matter – we’ll see through it and see to the next thing.

    FIGUEROA-FELICIANO: Let me add my two cents to that. There are three different things that I think would happen if one of our experiments saw convincing evidence for dark matter. First, we would want to confirm the discovery using a different technique. In other words, we will want as much confirmation as we can before we declare victory.

    ssds
    SuperCDMS experiment at the Soudan Underground Laboratory uses five towers like the one shown here to search for WIMP dark matter particles. (Image: SuperCDMS Soudan collaboration)

    Then, people will come up with 100 different ways to test the particle’s properties, as Harry described. After that, a phase of “dark matter astronomy” will help us learn the particle’s role in the universe. We’ll want to measure how fast it’s going, how much of it there is, how it behaves in a galaxy.

    TKF: There’s clearly a lot to be done once we find even just one type of dark matter particle. But it sounds like there could be a whole new zoo of dark particles. Do you think we’re going to need a “Dark Standard Model”?

    NELSON: I’ve often had the following thought: Here we are, in our measly 15 percent of the matter in the universe, wondering what dark matter is. If dark matter is as complex as we are, it might not even know that we exist. We’re just this minority 15 percent, but somehow we think we’re so important. But experiments undertaken by dark matter might not even know that we exist because we’re a much smaller perturbation on dark matter’s world than dark matter is on us.

    The dark matter sector may be as complex – or perhaps even five times as complex – as ours. Just as we’re made mostly of atoms made up of electrons and nuclei, maybe dark matter is too. In some of the searches for WIMPs, you have to be careful about that. It may be that the way these things interact with our matter is rather different than the simplest possible case that we’re looking for.
    “Here we are, in our measly 15 percent of the matter in the universe, wondering what dark matter is. If dark matter is as complex as we are, it might not even know that we exist.” —Harry Nelson

    two
    Gray Rybka (left) and Leslie Rosenberg examine ADMX’s primary components. (Image: Mary Levin / University of Washington)

    FIGUEROA-FELICIANO: Harry, if you were to apply Occam’s razor to our universe, how does it fare with the Standard Model?

    NELSON: Well, it doesn’t do very well. The Standard Model is a lot more complex than it needs to be. So maybe the same is true for dark matter. Maybe there are even dark photons out there. The idea is interesting. With ADMX, Gray is looking for a particle that has to do with the strong interaction. Tali and I are looking for a particle that has to do with the weak interaction. And searches for the dark photon look for a relationship between the electromagnetic interaction and the dark matter sector.

    The community really wants to figure out dark matter. There’s a feeling of urgency about it, and we’ll look for it in all the ways that we can.

    RYBKA: It’s true. With ADMX, we’re mostly focused on the axion, but we also look for dark photons at the lower masses. There are the dark matter candidates that people are really, really excited about, like axions and WIMPs. Those get experiments built that are dedicated to them. And then there are the ideas that might be good but don’t have quite as much motivation, like dark photons. People still look for ways to test those ideas, often with existing experiments.

    TKF: It’s clear there are a wide variety of places where we could find dark matter. We’re panning for this gold wherever we can, but we’re not entirely sure that it exists anywhere we’re looking. What’s it like searching for something that you might never find?

    FIGUEROA-FELICIANO: I think that the people who work on dark matter have a certain personality, a bit of a gambler’s streak. We go for the high stakes, putting all the chips in. There are other areas of physics where we would be sure to see something. Instead, we choose to look for something that we might not actually see. If we do see it, though, it’s a huge deal.

    We’re extremely lucky that we actually get paid to try to figure out what the universe is made of. That’s an incredibly wonderful thing.

    NELSON: Sometimes I think of what it must have been like to be Columbus and his crew, or the explorers who first went to the Earth’s poles. They were way out in the middle of the ocean, or in the ice, not quite sure what would come next. But they had set goals: India and China for Columbus, the poles for those explorers. We’re explorers too, we set goals for ourselves too, to seek certain pre-defined sensitivities to dark matter. We’re innovating with modern technology to reach our specific goals. And we may make it the New World or the North Pole, and that’s wonderfully exciting.

    See the full article, with other material, here.

    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

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