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  • richardmitnick 10:02 am on September 8, 2016 Permalink | Reply
    Tags: , , , LUX Dark Matter Experiment,   

    From Don Lincoln for CNN: “Something is wrong with dark matter” 

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    CNN

    September 7, 2016

    FNAL Don Lincoln
    Don Lincoln

    Dr. Don Lincoln is a senior physicist at Fermilab and does research using the Large Hadron Collider. He has written numerous books and produces a series of science education videos. He is the author of The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Things That Will Blow Your Mind. Follow him on Facebook. The opinions expressed in this commentary are solely those of the author.

    Nearly a mile under the Black Hills of South Dakota sits a canister of the atomic element xenon, chilled cold enough to turn it to liquid. The canister is the Large Underground Xenon, or LUX, detector — the most sensitive dark matter detector in the world.

    SURF logo
    Sanford Underground levels
    Sanford Underground Research Facility
    LUX Dark matter Experiment at SURF
    LUX Dark matter Experiment at SURF

    But the results of a new analysis by the LUX Collaboration has left scientists perplexed about a substance that has guided the formation of the stars and galaxies since the cosmos began: dark matter.

    Since the 1930s, scientists have known that there was something unexplained about the heavens. Swiss astronomer Fritz Zwicky studied the Coma Cluster, a group of about a thousand galaxies, held together by their mutual gravitational interactions.

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    A map of the Coma cluster. http://www.atlasoftheuniverse.com

    There was only one problem: The galaxies were moving so fast that gravity shouldn’t have been able to hold them together. The cluster should have been ripped apart. In the 1970s, astronomers Vera Rubin and her collaborator Kenneth Ford studied the rotation rates of individual galaxies and came to the same conclusion. There appeared to be no way the observed matter contained in galaxies would generate enough gravity to keep the stars locked in their stately orbits.

    These observations, combined with many other independent lines of evidence, led scientists to consider several possible explanations. These explanations included the possibility that Newton’s familiar laws of motion might be wrong, or that our understanding of gravity needed to be modified. Both these proposals, though, have been largely ruled out.

    Another idea was that there was somehow invisible matter that was generating more gravity. Initial ideas centered on the possibility of black holes, brown dwarf stars or rogue planets roaming the cosmos, but those explanations have also been dismissed. Using a ruthless process of elimination worthy of Sherlock Holmes, astronomers have come to believe the explanation for all of the gravitational anomalies is that there must be some sort of new and undiscovered type of matter in the universe, which Zwicky in 1933 named “dunkle materie,” or dark matter.

    For decades, scientists have tried to work out the properties of dark matter and, while we don’t know everything, we know a lot. From astronomical observations, we know there is five times more dark matter in the universe than all the “billions and billions” of stars and galaxies mentioned in Carl Sagan’s oft-quoted phrase. We also know that dark matter cannot have electrical charge, otherwise it would interact with light and we would have seen it. In fact, by a process of elimination, we know that dark matter is not any known form of matter. It is something new. Of this, scientists are sure.

    However, scientists are less sure about the details.

    For decades now, the most popular theoretical idea was that dark matter was a WIMP, short for weakly interacting massive particle. A WIMP would have a mass in the range of 10 to perhaps 100 times heavier than the familiar proton. It was a particle like a heavy neutron (but definitely not a neutron), massive, electrically neutral, and stable on time scales long compared to the lifetime of the universe.
    The WIMP was popular for two main reasons.

    First, when cosmologists modeled the Big Bang and included WIMPs in the calculation, the WIMPs actively participated in the earliest phases of the birth of the universe but, as the universe expanded and cooled, the space between them grew large enough that they stopped interacting with one another. When scientists calculated how much mass should be tied up in the relic WIMPs, they found it was five times as much mass as ordinary matter, exactly the amount of dark matter seen by astronomers.

    The second reason for the popularity of the WIMP idea is that it explained a mystery in particle physics. The recently discovered Higgs boson has a mass of about 130 times that of the proton. Theoretical considerations predicted a much larger mass, but if a WIMP exists, it is easy to reconcile the prediction and measurement. These two reasons account for the popularity of the WIMP idea and are called “the WIMP miracle.”

    The LUX measurement is simply the most recent and most powerful of a long line of searches for dark matter. They found no evidence for the existence of dark matter and were able to rule out a significant range of possible WIMP properties and masses.

    Now this doesn’t mean the WIMP idea is dead or that dark matter has been disproven. There remain WIMP masses that haven’t been ruled out, and there exist other possible dark matter candidates, including objects called sterile neutrinos, which are possible cousins of the well-known neutrinos generated in nuclear reactors and in the sun. Another recurring proposed dark matter particle is the axion, suggested in the 1970s to explain mysteries in the asymmetry of subatomic processes. (Although neither sterile neutrinos, nor axions, have been observed).

    Nobody knows what the final answer will be. That’s why we do research. But there is no question that there is a mystery in the cosmos. Galaxies don’t act as we expect. The LUX measurement is a powerful new bit of information for astronomers to consider and has added to the general confusion, forcing scientists to take another look at ideas other than WIMPs.

    All this reminds me of the old Buffalo Springfield song: “There’s something happening here. What it is ain’t exactly clear …”

    See the full article here .

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  • richardmitnick 1:43 pm on July 26, 2016 Permalink | Reply
    Tags: , LUX Dark Matter Experiment, , ,   

    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.

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    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.

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    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.

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    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 Dark Matter Experiment, ,   

    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 .

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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 2:11 pm on July 21, 2016 Permalink | Reply
    Tags: , Dark Matter May Be Completely Invisible Concludes World's Most Sensitive Search, LUX Dark Matter Experiment   

    From Ethan Siegel: “Dark Matter May Be Completely Invisible, Concludes World’s Most Sensitive Search” 

    From Ethan Siegel

    Jul 21, 2016

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    The LUX underground detector, installed and in the tank. Image credit: C.H. Faham and the LUX collaboration.

    Dark matter is the most elusive substance ever detected in the Universe, and even at that, it’s only been detected indirectly. We know it interacts gravitationally, but it’s so sparse and diffuse that Earth-based experiments don’t stand a chance at seeing that interaction. Instead, if we want to see this new form of matter directly, we have to hope that there’s an additional interaction: a way for dark matter to scatter off of normal matter, and produce a recoil due to a collision. In an announcement earlier today, the LUX Collaboration — running the Large Underground Xenon experiment — performed the longest, deepest, most sensitive search for dark matter ever, using 370 kilograms of liquid xenon with the detector running for a total of 20 months. The final result? Not a single dark matter collision was observed.

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    The exclusion bounds on dark matter-neutron scattering released today, July 21, 2016, by the LUX collaboration. Image credit: C. Nehrkorn, W. To, S. Haselschwardt, retrieved from A. Manalaysay’s talk.

    A huge variety of astrophysical observations point to the existence of dark matter, and point to its presence in a massive halo surrounding every large galaxy ever observed. Dark matter is required to reproduce our observations of everything from galaxy rotation curves to the gravitational bending of light around clusters; from the large-scale filamentary structure of the Universe to the tiny fluctuations in the cosmic microwave background; from the correlations of galaxies 500 million light years apart to the existence of the tiniest mini-galaxies of all. Most spectacularly, we observe dark matter separating from normal matter when two massive galaxy clusters collide. Without dark matter, the explanations for these phenomena all fall apart; we know it must be real.

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    Four colliding galaxy clusters, showing the separation between X-rays (pink) and gravitation (blue). Images credit: X-ray: NASA/CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A. Mahdavi et al. (top left); X-ray: NASA/CXC/UCDavis/W.Dawson et al.; Optical: NASA/ STScI/UCDavis/ W.Dawson et al. (top right); ESA/XMM-Newton/F. Gastaldello (INAF/ IASF, Milano, Italy)/CFHTLS (bottom left); X-ray: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University) (bottom right).

    But if it’s real, we really want to be able to detect it directly, under laboratory conditions. To do that, we need to know something about the particle nature of dark matter itself, because we need for it to interact with normal matter: with the particles in the Standard Model, the ones we know how to detect here on Earth.

    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.

    So what are the possibilities for that interaction? It could occur through any number of pathways, with a wide variety of masses allowed for the dark matter. The most common models, though, all have a few features in common:

    They all have dark matter not interacting through the strong nuclear or the electromagnetic interaction.
    They all have dark matter in a mass range that’s heavier than the mass of an electron, and lower than the maximum energy of the LHC.
    And they all have dark matter interacting through either the weak nuclear interaction or a new force that’s weaker than that, but stronger than the gravitational interaction.

    If you’re willing to make those assumptions, a general experimental design emerges: take a tremendously large collection of atoms and look for the disturbance a passing, colliding dark matter particle would cause.

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    The LUX underground laboratory. Image credit: C.H. Faham and the LUX Collaboration.

    Outdoing previous experiments like CDMS and its successors, Edelweiss, PandaX and Xenon, the LUX collaboration has collected more data at a greater sensitivity than any experiment before it.

    XENON1T at Gran Sasso
    XENON1T at Gran Sasso

    With a sensitivity range that sets the record from just about a fifth of a proton’s mass (~0.2 GeV/c2) to about ten times the mass of the heaviest known particle, the top quark (more than 1,000 GeV/c2), LUX has pushed the interaction limits not only lower than ever before, but significantly lower than the experiment was even designed to push them.

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    A diagram of the LUX detector. Image credit: LUX Collaboration, diagram by David Taylor, James White and Carlos Faham.

    According to Rick Gaitskell, co-spokesperson of LUX:

    “With this final result from the 2014-2016 search, the scientists of the LUX Collaboration have pushed the sensitivity of the instrument to a final performance level that is 4 times better than the original project goals. 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.”

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    The effected expect of background in the LUX detectors, including how radioactive material abundances have decayed over time. The signals seen by LUX are consistent with background alone. Image credit: D.S. Akerib et al., Astropart.Phys. 62 (2015) 33, 1403.1299.

    The LUX results rule out all the touted detections from experiments like DAMA, LIBRA and CoGeNT; it rules out most models of dark matter from supersymmetry and extra-dimensions. It means that many ongoing dark matter experiments are destined to find absolutely nothing at all. By filling an ultra-sensitive detector with more than a third of a tonne of liquid xenon, a single collision between a dark matter particle and a xenon nucleus would produce a recoil visible by the photodetectors surrounding it.

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    The photomultiplier tubes installed on the bottom of the LUX detector. Image credit: C.H. Faham and the LUX Collaboration.

    By burying the detector more than a mile underground, shielded by rock, and surrounding it inside a 72,000-gallon, high-purity water tank, it’s protected from cosmic rays, solar events, terrestrial radiation and other sources of contamination. When all the anticipated backgrounds are accounted for — including natural radioactivity, muons and cosmic neutrinos — the LUX collaboration concludes that a total of zero significant events were observed over the 20 month time period the experiment ran, from 2014-2016. According to co-spokesperson Dan McKinsey:

    “As the charge and light signal response of the LUX experiment varied slightly over the dark matter search period, our calibrations allowed us to consistently reject radioactive backgrounds, maintain a well-defined dark matter signature for which to search and compensate for a small static charge buildup on the Teflon inner detector walls.”

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    After everything was modeled and backgrounds were fully accounted for, only three events remained, all of which could be explained by external factors rather than dark matter. Image credit: A. Manalaysay, slide #42 of his IDM2016 talk.

    By running a whole slew of new background rejection and calibration techniques, LUX became sensitive to events that would have a fantastically tiny rate. As LUX project scientist Aaron Manalaysay detailed:

    “These careful background-reduction techniques and precision calibrations and modeling, have enabled us to probe dark matter candidates that would produce signals of only a few events per century in a kilogram of xenon.”

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    Results released and published earlier this year from the LUX collaboration, excluding dark matter at a specific sensitivity. New results are up to four times better. Images credit: D. S. Akerib et al. (LUX Collaboration); Phys. Rev. Lett. 116, 161301 and 161302.

    The null detection is incredible, with a fantastic slew of implications:

    Dark matter is most likely not made up, 100%, of the most commonly thought-of WIMP candidates.
    It is highly unlikely that whatever dark matter is, in light of the LUX results, will be produced at the LHC.
    And it is quite likely that dark matter lies outside of the standard mass range, either much lower (as with axions or sterile neutrinos) or much higher (as with WIMPzillas).

    Sanford Underground levels
    Sanford Underground levels

    SURF logo
    SURF, home of the LUX collaboration

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 6:36 pm on June 20, 2016 Permalink | Reply
    Tags: , LUX Dark Matter Experiment, ,   

    From Rapid City Journal via SURF: “Xenon central to next-gen dark matter experiment” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

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    Rapid City Journal

    6.20.16
    Tom Griffith

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    LUX researchers spell out the experiment’s name, like cheerleaders, inside a 72,000 gallon water tank. The detector is the cylindrical titanium tank behind them. The tank is now filled with water, and the detector is operating. Credit: Matt Kapust

    If you happen to have some extra xenon lying around – say about 1.8 million liters – officials at the Sanford Underground Research Facility would like to talk to you.

    That’s the amount of the colorless, odorless element that makes up only 0.0000087 percent of the Earth’s atmosphere that scientists say will be needed for the deep underground laboratory’s $50 million to $60 million LUX-ZEPLIN experiment, so the Sanford Lab is going to start stockpiling it soon.

    At its annual meeting Thursday, the South Dakota Science and Technology Authority unanimously approved a loan from the University of South Dakota Foundation and authorization for its executive director to procure up to 500,000 liters of xenon.

    “The SDSTA truly appreciates the USD Foundation’s investment in the LUX-ZEPLIN experiment,” said Mike Headley, the Science Authority’s executive director. “Their investment along with similar investments by the South Dakota State University Foundation and the South Dakota Community Foundation, along with tremendous support from Gov. Daugaard, will help keep the U.S. in a leadership role in the global search for dark matter.”

    Two years ago, xenon was priced at nearly $25 per liter, meaning the necessary gaseous element of atomic number 54, obtained through the distillation of liquid air, would have set the Science Authority back a cool $45 million. Fortunately, the price has dropped significantly since then.

    “We will pay $5.50 per liter and this is not a discount; it’s the current market price,” said Sanford Lab spokeswoman Constance Walter. “Basically, the increased use of LED lights in vehicles, etc., has decreased the demand for xenon lighting. So, the price has dropped dramatically from a couple of years ago when they were in excess of $20 per liter.”

    Headley said late Thursday that the Science Authority had secured the first 500,000 liters at a cost of $6.25 per liter and the remaining 1.3 million liters would cost $5.50 per liter. Consequently, even with the price reduction, the xenon will likely cost the Science Authority nearly $10.3 million.

    Initially, the Science Authority will purchase 1.5 million liters, or about 80 percent of the 1.8 million liters the experiment will require, Walters said. The xenon will be delivered over the next two-plus years and when it is purchased, it will first go to the U.S. Department of Energy’s SLAC National Accelerator Laboratory in Menlo Park, Calif., where it will be purified. Then it will be shipped to the Sanford Lab to be placed in the detector sometime in 2018, she explained.

    Discovered in 1898 by Sir William Ramsay, a Scottish chemist, and Morris M. Travers, an English chemist, shortly after their discovery of the elements krypton and neon, xenon was used in the Sanford Lab’s original Large Underground Xenon experiment known as LUX.

    In October 2013, more than 100 science enthusiasts and government officials gathered at the Sanford Lab to receive initial findings of the LUX, while hundreds more from around the world joined via webcam. In that complex three-month trial involving particle physics, scientists sought to detect mysterious dark matter particles previously observed only through their gravitational effects on galaxies.

    Nearly a mile deep in the bedrock of the Black Hills and shielded from vast amounts of cosmic radiation that constantly bombard the earth’s atmosphere, the LUX was comprised of a phone booth-sized titanium tank filled with nearly a third of a metric-ton (370 kilograms) of liquid xenon cooled to minus 150 degrees, scientists explained. The detector was further buffered from background radiation by its immersion in a 72,000-gallon tank of ultra-pure water.

    Now, scientists around the globe are awaiting the start-up of the much larger 60-ton particle detector known as the LUX-ZEPLIN or LZ, which will be approximately 30 times larger (10 metric tons or 10,000 kilograms of xenon) and 100 times more sensitive than the LUX.

    And, it’s going to take quite a bit of xenon to make that happen.

    __________________________________________________________________________________________

    Xenon Q, xenon A

    LEAD | With the help of a few friends, the South Dakota Science and Technology Authority will spend more than $10 million on xenon this year, a hefty amount for a gaseous element that a non-scientist knows so little about.

    So, we asked Sanford Underground Research Facility scientist Markus Horn, who worked on the LUX and is now collaborating on the LUX LZ, the next-generation dark matter experiment, what makes xenon critical to its success.

    Q: How is xenon extracted from the earth’s atmosphere?

    A: Xenon is a trace gas in the atmosphere and is extracted as a by-product at the separation of air into oxygen and nitrogen.

    Q: Why is xenon worth so much money?

    A: It’s rare in the Earth’s atmosphere; only about 1 part in 20 million.

    Q: Why is xenon critical to the LUX LZ? Succinctly, what does it do?

    A: Xenon has unique properties for dark matter research. To name a few:

    • It emits light at 175nm (UV light, sort of easy detectable with our PMTs);

    • It is heavy, 135 times mass of proton, which is around the theoretically most favorable mass of the WIMP particle (billiard-ball-nuclear recoil is largest, hence easier to detect);

    • It liquifies easily at moderate temperature of -100 Celsius;

    • It is radio-pure;, does not have any natural radioactive isotopes;

    • It has a high scintillation yield (emits a lot of light, so to say), very low energy threshold can be achieved (as we do in LUX);

    • It is self-shielding (easily said, because it’s heavy, it shields itself, so the inner part of the detector is even quieter);

    • It is a liquid noble gas detectors are easy to scale, LUX to LZ, etc.

    Q: Why does it have to be so cold (-150 degrees)?

    A: As with any material, it can be in different states (gas, liquid, solid). Depending on the element, this happens at different temperatures and pressures. Xenon is a gas at room temperature and atmospheric pressure, you need to compress it or cool it to approx -100C to force it into a liquid. I guess that’s simple chemistry.

    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 5:44 pm on May 2, 2016 Permalink | Reply
    Tags: , , LUX Dark Matter Experiment,   

    From Surf: “Notes from the underground – LUX celebrates 300 live days” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    Monday, May 2, 2016
    Constance Walter, Communications Director, SURF

    Amid streamers, a piñata and paper unicorns, LUX researchers celebrated the 300-live-day run of their dark matter detector.

    LUX Dark matter
    LUX Dark matter
    LUX Dark matter experiment
    Lux Dark Matter 2
    Lux Dark Matter 2

    “I would describe the mood as exciting, joyous and electric,” said Mark Hanhardt, Sanford Lab support scientist. Why unicorns? For LUX researchers, they symbolize thesearch for the elusive WIMP, or weakly interacting massive particle, the leading contender in the dark matter search.

    But don’t kid yourselves, in the search for dark matter, these researchers remain focused and motivated.

    LUX consists of one third-of-a-ton of liquid xenon inside a titanium vessel.

    Researchers hope to identify the very rare occasions when a dark matter particle collides with a xenon atom inside the detector. When that happens, the xenon atom will recoil and emit a tiny flash of light, which will be detected by sensitive light detectors.

    In October 2013, after a 90-live-day run, LUX announced it was the most sensitive dark matter detector in the world. “LUX was so much larger than existing detectors that within a few weeks of starting its first run in 2013, it had surpassed all previous direct detection experiments,” said Richard Gaitskell, co-spokesperson for LUX.
    And the trend continues. In December, LUX released a reanalysis of the 2013 data, which discussed new calibration techniques that allowed for even greater sensitivity. Those techniques, which included the use of tritiated methane, krypton-83 and a neutron generator, were used in the most recent run; however, results willnot be available before the end of 2016.

    The 300-day run began in November 2014 and the detector has been in WIMP search mode or calibration mode since. But it has not been without its challenges, Gaitskell said. “During any dark matter search, we must ensure the detector is taking data in a completely stable mode in which the operating conditions are clearly understood,” he said. “This means we monitor the detector health continually and occasionally we have to react to any apparent issues that have developed.”

    At regular intervals throughout the new run, calibrations were carried out for two weeks every four months to ensure a high level of accuracy in measuring responses to backgrounds and potential dark matter signals, he added.

    After 19 months, the run officially ended today at 1 p.m. “That’s a long time to to operate a detector without a significant break,” said Simon Fiorucci, LUX science operationsmanager. “But it was critical to demonstrate our ability to do so as we prepare to run LZ for more than three years.”

    Later this year, LUX will be decommissioned to make way for a new, much larger xenon detector, known as LUX-ZEPLIN, or LZ. This second generation dark matter detector will have a 10-ton liquid xenon target and be up to 100 times more sensitive.

    LUX Xenon experiment at SURF
    LUX Xenon experiment at SURF

    “The tremendous success of LUX paved the way for LZ,” said Murdock Gilchriese, LBNL (Lawrence Berkeley National Laboratory) operations manager for LUX and LZ project director. LZ will be located inside the same 72,000-gallon water tank that currently shields LUX.

    “Sanford Lab will continue to play a global role in the search for dark matter,” said Jaret Heise, science director at Sanford Lab. “We’re looking
    forward to working with the expanded collaboration, which will include 31 institutions and about 200 scientists.”

    In the meantime, LUX researchers are continuing their work, including testing several new calibration techniques that will be used in LZ. The team has come a long way and made significant progress. “We are all proud to have made it this far,” Fiorucci said.

    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. 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 1:33 pm on December 29, 2015 Permalink | Reply
    Tags: , , , LUX Dark Matter Experiment   

    From LLNL: “New results from experimental facility deepen understanding of dark matter” 


    Lawrence Livermore National Laboratory

    Dec. 29, 2015
    Stephen Wampler
    wampler1@llnl.gov
    925-423-3107

    1
    Photomultiplier tubes can pick up the tiniest bursts of lights when a particle interacts with xenon atoms as part of the Large Underground Xenon (LUX) dark matter experiment at the Sanford Underground Research Facility (SURF). Photo courtesy of SURF.

    The Large Underground Xenon (LUX) dark matter experiment, which operates nearly a mile underground at the Sanford Underground Research Facility (SURF)in the Black Hills of South Dakota, has already proven itself to be the most sensitive dark matter detector in the world. Now, a new set of calibration techniques employed by LUX scientists has further improved its sensitivity.

    LUX researchers, including several from Lawrence Livermore National Laboratory’s (LLNL) Rare Event Detection Group, are looking for WIMPs, weakly interacting massive particles, which are among the leading candidates for dark matter.

    LLNL is one of the founding members of the LUX experiment, and LLNL researchers have participated in LUX and its predecessor experiment (XENON-10) since 2004.

    “It is vital that we continue to push the capabilities of our detector in the search for the elusive dark matter particles,” said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for the LUX experiment. “We have improved the sensitivity of LUX by more than a factor of 20 for low-mass dark matter particles, significantly enhancing our ability to look for WIMPs.”

    The new research is described in a paper submitted to Physical Review Letters and posted to ArXiv. The work re-examines data collected during LUX’s first experimental run in 2013, and helps to rule out the possibility of dark matter detections at low-mass ranges where other experiments had previously reported potential detections.

    “The latest LUX science results are a re-analysis of data obtained over three months in 2013,” said LLNL principal investigator and physicist Adam Bernstein. “The first analysis of that data was published in 2014, and since then we have expanded our understanding of the detector response through a combination of low-energy nuclear recoil measurements, low-energy electron recoil measurements and an improved understanding of our background in the low-energy recoil regime where dark matter interactions are likely to appear.

    “This combination of improvements enabled us to increase our sensitivity to low-mass WIMPs by upward of two orders of magnitude. LUX is currently in a longer science run lasting 300 live days, scheduled for completion by this July,” Bernstein added.

    Dark matter is thought to be the dominant form of matter in the universe. Scientists are confident in its existence because its gravitational effects can be seen in the rotation of galaxies and in the way light bends as it travels through the universe. Because WIMPs are thought to interact with other matter only on very rare occasions, they have yet to be detected directly.

    “We have looked for dark matter particles during the experiment’s first three-month run, but are exploiting new calibration techniques that do a better job of pinning down how they would appear to our detector,” said Alastair Currie of Imperial College London. “These calibrations have deepened our understanding of the response of xenon to dark matter, and to backgrounds. This allows us to search, with improved confidence, for particles that we hadn’t previously known would be visible to LUX.”

    Bernstein and other LLNL researchers have taken part in initial science planning and experimental design for LUX. Physicist Peter Sorensen, formerly with LLNL and now at Lawrence Berkeley National Laboratory, spent many months with on-site assembly and commissioning, and has made key contributions to the study of the low-mass WIMP signal.

    Physicist Kareem Kazkaz, who works in the LLNL Rare Event Detection Group, created the LUXSim simulation framework, which has been used throughout the collaboration to understand detector response and increase the team’s understanding of signal backgrounds and how the liquid xenon medium responds to incident radiation.

    More recently, LLNL graduate scholar Brian Lenardo has served as the deputy science coordination manager and has been an integral member of the team studying the light and charge yield of nuclear recoils within the active volume. Joining LLNL in September, postdoctoral fellow Jingke Xu has organized a sub-group focused on events at the single electron quantum limit of detector sensitivity.

    LUX consists of a third of a ton of liquid xenon surrounded with sensitive light detectors. It is designed to identify the very rare occasions when a dark matter particle collides with a xenon atom inside the detector. When a collision happens, the xenon atom will recoil and emit a small burst of light, which is detected by LUX’s light sensors. The detector’s location at Sanford Lab beneath a mile of rock helps to shield it from cosmic rays and other radiation that would interfere with the dark matter signal.

    So far, LUX hasn’t detected a dark matter signal, but its exquisite sensitivity has allowed scientists to all but rule out dark matter particles over a wide range of masses that current theories allow. These new calibrations increase that sensitivity even further.

    One calibration technique used neutrons as stand-ins for dark matter particles. Bouncing neutrons off the xenon atoms allows scientists to quantify how the LUX detector responds to the recoil process.

    “It is like a giant game of pool with a neutron as the cue ball and the xenon atoms as the stripes and solids,” Gaitskell said. “We can track the neutron to deduce the details of the xenon recoil, and calibrate the response of LUX better than anything previously possible.”

    The nature of the interaction between neutrons and xenon atoms is thought to be very similar to the interaction between dark matter and xenon. “It’s just that dark matter particles interact very much more weakly — about a million-million-million-million times more weakly,” Gaitskell said.

    The neutron experiments help to calibrate the detector for interactions with the xenon nucleus. But LUX scientists also have calibrated the detector’s response to the deposition of small amounts of energy by struck atomic electrons. That’s done by injecting tritiated methane – a radioactive gas – into the detector.

    “In a typical science run, most of what LUX sees are background electron recoil events,” said Carter Hall of the University of Maryland. “Tritiated methane is a convenient source of similar events, and we’ve now studied hundreds of thousands of its decays in LUX. This gives us confidence that we won’t mistake these garden variety events for dark matter.”

    Another radioactive gas, krypton, was injected to help scientists distinguish between signals produced by ambient radioactivity and a potential dark matter signal.

    “The krypton mixes uniformly in the liquid xenon and emits radiation with a known, specific energy, but then quickly decays away to a stable, nonradioactive Isotope, ” said Dan McKinsey, a University of California Berkeley physics professor and co-spokesperson for LUX, who also is an affiliate of Lawrence Berkeley National Laboratory. “By measuring the light and charge produced by these krypton events throughout the liquid xenon, we can flat-field the detector’s response, allowing better separation of dark matter events from natural radioactivity.”

    LUX improvements coupled to the advanced computer simulations at Lawrence Berkeley National Laboratory’s National Energy Research Scientific Computing Center and Brown University’s Center for Computation and Visualization have allowed scientists to test additional particle models of dark matter that can be excluded from the search. “And so the search continues,” McKinsey said.

    4
    Edison Cray XC30 at NERSC

    “LUX is once again in search mode at Sanford Lab. The latest run began in late 2014 and is expected to continue until June 2016. This run will represent an increase in exposure of more than four times compared to the previous 2013 run. We will be very excited to see if any dark matter particles have shown themselves in the new data.”

    The LUX scientific collaboration, which is supported by the DOE and National Science Foundation, includes 19 research universities and national laboratories in the United States, the United Kingdom and Portugal.

    “The global search for dark matter aims to answer one of the biggest questions about the makeup of our universe. We’re proud to support the LUX collaboration and congratulate them on achieving an even greater level of sensitivity,” said Mike Headley, executive director of the SDSTA.

    See the full article here .

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    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
    Administration
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    NNSA

     
  • richardmitnick 1:10 pm on December 14, 2015 Permalink | Reply
    Tags: , , , LUX Dark Matter Experiment   

    From LBL: “New Results from World’s Most Sensitive Dark Matter Detector” 

    Berkeley Logo

    Berkeley Lab

    December 14, 2015
    Glenn Roberts Jr. 510-486-5582

    Berkeley Lab Scientists Participate in Mile-deep Experiment in Former South Dakota Gold Mine

    The Large Underground Xenon (LUX) dark matter experiment, which operates nearly a mile underground at the Sanford Underground Research Facility (SURF) in the Black Hills of South Dakota, has already proven itself to be the most sensitive detector in the hunt for dark matter, the unseen stuff believed to account for most of the matter in the universe. Now, a new set of calibration techniques employed by LUX scientists has again dramatically improved the detector’s sensitivity.

    1
    A view inside the LUX detector. (Photo by Matthew Kapust/Sanford Underground Research Facility)

    Researchers with LUX are looking for WIMPs, or weakly interacting massive particles, which are among the leading candidates for dark matter. “We have improved the sensitivity of LUX by more than a factor of 20 for low-mass dark matter particles, significantly enhancing our ability to look for WIMPs,” said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for the LUX experiment. “It is vital that we continue to push the capabilities of our detector in the search for the elusive dark matter particles,” Gaitskell said.

    LUX improvements, coupled to advanced computer simulations at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory’s (Berkeley Lab) National Energy Research Scientific Computing Center (NERSC) and Brown University’s Center for Computation and Visualization (CCV), have allowed scientists to test additional particle models of dark matter that now can be excluded from the search. NERSC also stores large volumes of LUX data—measured in trillions of bytes, or terabytes—and Berkeley Lab has a growing role in the LUX collaboration.

    Scientists are confident that dark matter exists because the effects of its gravity can be seen in the rotation of galaxies and in the way light bends as it travels through the universe. Because WIMPs are thought to interact with other matter only on very rare occasions, they have yet to be detected directly.

    2
    The LUX dark matter detector is seen here during the assembly process in a surface laboratory in South Dakota. (Photo by Matthew Kapust/Sanford Underground Research Facility)

    “We have looked for dark matter particles during the experiment’s first three-month run, but are exploiting new calibration techniques better pinning down how they would appear to our detector,” said Alastair Currie of Imperial College London, a LUX researcher.

    “These calibrations have deepened our understanding of the response of xenon to dark matter, and to backgrounds. This allows us to search, with improved confidence, for particles that we hadn’t previously known would be visible to LUX.”

    The new research is described in a paper submitted to Physical Review Letters. The work reexamines data collected during LUX’s first three-month run in 2013 and helps to rule out the possibility of dark matter detections at low-mass ranges where other experiments had previously reported potential detections.

    3
    A view of the LUX detector during installation. (Photo by Matthew Kapust/Sanford Underground Research Facility)

    LUX consists of one-third ton of liquid xenon surrounded with sensitive light detectors. It is designed to identify the very rare occasions when a dark matter particle collides with a xenon atom inside the detector. When a collision happens, a xenon atom will recoil and emit a tiny flash of light, which is detected by LUX’s light sensors. The detector’s location at Sanford Lab beneath a mile of rock helps to shield it from cosmic rays and other radiation that would interfere with a dark matter signal.

    So far LUX hasn’t detected a dark matter signal, but its exquisite sensitivity has allowed scientists to all but rule out vast mass ranges where dark matter particles might exist. These new calibrations increase that sensitivity even further.

    One calibration technique used neutrons as stand-ins for dark matter particles. Bouncing neutrons off the xenon atoms allows scientists to quantify how the LUX detector responds to the recoiling process.

    “It is like a giant game of pool with a neutron as the cue ball and the xenon atoms as the stripes and solids,” Gaitskell said. “We can track the neutron to deduce the details of the xenon recoil, and calibrate the response of LUX better than anything previously possible.”

    The nature of the interaction between neutrons and xenon atoms is thought to be very similar to the interaction between dark matter and xenon. “It’s just that dark matter particles interact very much more weakly—about a million-million-million-million times more weakly,” Gaitskell said.

    The neutron experiments help to calibrate the detector for interactions with the xenon nucleus. But LUX scientists have also calibrated the detector’s response to the deposition of small amounts of energy by struck atomic electrons. That’s done by injecting tritiated methane—a radioactive gas—into the detector.

    “In a typical science run, most of what LUX sees are background electron recoil events,” said Carter Hall a University of Maryland professor. “Tritiated methane is a convenient source of similar events, and we’ve now studied hundreds of thousands of its decays in LUX. This gives us confidence that we won’t mistake these garden-variety events for dark matter.”

    Another radioactive gas, krypton, was injected to help scientists distinguish between signals produced by ambient radioactivity and a potential dark matter signal.

    “The krypton mixes uniformly in the liquid xenon and emits radiation with a known, specific energy, but then quickly decays away to a stable, non-radioactive form,” said Dan McKinsey, a UC Berkeley physics professor and co-spokesperson for LUX who is also an affiliate with Berkeley Lab. By precisely measuring the light and charge produced by this interaction, researchers can effectively filter out background events from their search.

    “And so the search continues,” McKinsey said. “LUX is once again in dark matter detection mode at Sanford Lab. The latest run began in late 2014 and is expected to continue until June 2016. This run will represent an increase in exposure of more than four times compared to our previous 2013 run. We will be very excited to see if any dark matter particles have shown themselves in the new data.”

    McKinsey, formerly at Yale University, joined UC Berkeley and Berkeley Lab in July, accompanied by members of his research team.

    The Sanford Lab is a South Dakota-owned facility. Homestake Mining Co. donated its gold mine in Lead to the South Dakota Science and Technology Authority (SDSTA), which reopened the facility in 2007 with $40 million in funding from the South Dakota State Legislature and a $70 million donation from philanthropist T. Denny Sanford. The U.S. Department of Energy (DOE) supports Sanford Lab’s operations.

    Kevin Lesko, who oversees SURF operations and leads the Dark Matter Research Group at Berkeley Lab, said, “It’s good to see that the experiments installed in SURF continue to produce world-leading results.”

    The LUX scientific collaboration, which is supported by the DOE and National Science Foundation (NSF), includes 19 research universities and national laboratories in the United States, the United Kingdom and Portugal.

    “The global search for dark matter aims to answer one of the biggest questions about the makeup of our universe. We’re proud to support the LUX collaboration and congratulate them on achieving an even greater level of sensitivity,” said Mike Headley, Executive Director of the SDSTA.

    Planning for the next-generation dark matter experiment at Sanford Lab is already under way. In late 2016 LUX will be decommissioned to make way for a new, much larger xenon detector, known as the LUX-ZEPLIN (LZ) experiment.

    LZ project
    LZ schematic

    LZ would have a 10-ton liquid xenon target, which will fit inside the same 72,000-gallon tank of pure water used by LUX. Berkeley Lab scientists will have major leadership roles in the LZ collaboration.

    “The innovations of the LUX experiment form the foundation for the LZ experiment, which is planned to achieve over 100 times the sensitivity of LUX. The LZ experiment is so sensitive that it should begin to detect a type of neutrino originating in the Sun that even Ray Davis’ Nobel Prize-winning experiment at the Homestake mine was unable to detect,” according to Harry Nelson of UC Santa Barbara, spokesperson for LZ.

    LUX is supported by the DOE Office of Science. NERSC is a DOE Office of Science User Facility.

    A version of this release and additional materials are available on the Sanford Lab site.

    See the full article here .

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  • richardmitnick 12:55 pm on December 8, 2015 Permalink | Reply
    Tags: , , LUX Dark Matter Experiment,   

    From SURF: “4850 Feet Below: The Hunt for Dark Matter” 

    SURF logo

    Sanford Underground levels

    Sanford Underground Research facility

    Oct 5, 2015
    Deep in an abandoned gold mine in rural South Dakota, a team of physicists are hunting for astrophysical treasure. Their rare and elusive quarry is dark matter, a theoretical particle which has never been seen or directly detected. Yet its gravitational effect on distant galaxies hints at its existence and provides ample evidence to fuel the experiments and aspirations of scientists at the Sanford Underground Research Facility. Insulated by 4,850 feet of rock, the researchers have constructed the world’s most sensitive particle detector, known as the Large Underground Xenon Experiment, or “LUX.

    LUX Dark matter
    Lux Dark Matter 2
    LUX

    Their goal is to use this complex device to capture an epiphanous event: the interaction between dark matter and atoms inside a chilled tank of liquid xenon. If they’re successful, the researchers may not only solve some of the biggest mysteries in astrophysics but affirm their faith in the nature of dark matter.

    “4850 Feet Below” was produced with generous support from the John Templeton Foundation.

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

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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. 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) [being replaced by DUNE]—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 [DUNE] will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

     
  • richardmitnick 12:23 pm on October 13, 2015 Permalink | Reply
    Tags: , , LUX Dark Matter Experiment,   

    From Symmetry: “Xenon, xenon everywhere” 

    Symmetry

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    October 13, 2015
    Glenn Roberts Jr.

    It’s in the air we breathe, but it’s not so easy to get ahold of 10 metric tons of xenon in its liquid form.

    So, you want to buy some xenon to try to detect dark matter deep underground. Not a problem. There’s a market for that, with a few large-scale suppliers.

    Wait, what’s that you say? You need 10 metric tons of incredibly pure, liquid xenon for the LUX-ZEPLIN dark matter experiment? That’s a bit trickier.

    LUX Dark matter
    LUX-ZEPLIN dark matter experiment

    Looking for large amounts of xenon is a bit like searching for dark matter: It’s all around us, but it’s colorless, odorless and hard to separate from everything else. Xenon is in the air that we breathe, but it’s also one of the rarest elements on Earth.

    There is about 1 part xenon in every 11.5 million parts of air. The global industry that extracts liquid xenon produces a total of about 40 tons of xenon per year, so 10 tons is a very tall order.

    “Buying several tons per year won’t perturb the market too much,” says Thomas Shutt, a SLAC physicist who, along with physicist Daniel Akerib, left Case Western Reserve University in Ohio last year to join SLAC National Accelerator Laboratory. “If you buy 10 tons in a year that’s a quarter of the market.”

    Akerib and Shutt are heading up SLAC’s effort in the planned LUX-ZEPLIN, or LZ, experiment, one of the largest-scale efforts to find dark matter particles. Like its smaller predecessor experiment, called LUX (for Large Underground Xenon), LZ will be filled with supercooled liquid xenon.

    Xenon, like several other rare gases, can emit flashes of light and electrons when its atoms are hit by other particles. The LZ detector will sit 1 mile underground in a South Dakota mine [SURF], shielded from most other particles, and wait to see signals from dark matter particles.

    Sanford Underground Research Facility Interior
    Sanford Underground levels
    Sanford Underground Research Facility [SURF], in South Dakota

    “Xenon has really good stopping power,” Akerib says. Its liquid form is so dense that aluminum can float on it. It is particularly sensitive to passing particles.

    Xenon is used in more than just dark matter experiments. It is also in demand as a component in halogen lights such as the bluish headlights in some vehicles, in the bulbs for other specialized lighting such as flash lamps that drive lasers, and as a propellant for satellites and other spacecraft. It is also used in semiconductor manufacturing and medical imaging, and it has been used as an anesthetic.

    Xenon is a by-product of the steel-making process, which uses liquid oxygen to wash away contaminants on the surface of molten iron. Russia, South Africa and Saudi Arabia are among the major producers of xenon. Russia became a major player in this market during the era of the Soviet Union, when steel-making was largely centralized.

    Industrially produced xenon isn’t nearly pure enough for the exacting requirements of LZ, though.

    Shutt says extracting its own xenon from air was not an option. “If we had to start from scratch in refining xenon, it would be vastly more expensive,” he says.

    The LZ team plans to acquire xenon over the next 3 to 4 years.

    There is no expiration date on xenon, Shutt said; it just needs to be tightly contained so no venting occurs. “The xenon we use we can put back on the market or put to other scientific uses after the LZ experiment is complete,” he says. “It’s around forever.”

    To ensure that the dark matter detector is ultrasensitive, the LZ team is building a purification system at SLAC National Accelerator Laboratory to remove krypton, another rare gas that can get mixed in with liquid xenon. LUX started with xenon that had 100 parts of krypton per billion and purified it down to four parts per trillion, and LZ needs xenon purified to a standard of 0.015 parts krypton per trillion—a factor of 300 purer.

    Shutt jokes that, while LZ is all about particle physics, “we have become armchair chemical engineers” in the process of putting the experiment together.

    The current plan is to purify the xenon in 2018, and to run each batch through the purification process twice. The process is expected to take several months in total. LZ is scheduled to start running in 2019.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
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