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  • richardmitnick 9:38 am on October 22, 2017 Permalink | Reply
    Tags: , LUX Dark Matter Experiment, New Life Found That Lives Off Electricity, , , The electricity-eating microbes that the researchers were hunting for belong to a larger class of organisms that scientists are only beginning to understand   

    From Quanta: “New Life Found That Lives Off Electricity” 

    Quanta Magazine
    Quanta Magazine

    June 21, 2016 [Just found in social media. Where has it been?]
    Emily Singer

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    Yamini Jangir and Moh El-Naggar

    Last year, biophysicist Moh El-Naggar and his graduate student Yamini Jangir plunged beneath South Dakota’s Black Hills into an old gold mine that is now more famous as a home to a dark matter detector.

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    A bottom-up view inside the Large Underground Xenon dark matter experiment, which is located a mile beneath the surface in the Black Hills of South Dakota. LUX Dark Matter.

    Unlike most scientists who make pilgrimages to the Black Hills these days, El-Naggar and Jangir weren’t there to hunt for subatomic particles. They came in search of life.

    In the darkness found a mile underground, the pair traversed the mine’s network of passages in search of a rusty metal pipe. They siphoned some of the pipe’s ancient water, directed it into a vessel, and inserted a variety of electrodes. They hoped the current would lure their prey, a little-studied microbe that can live off pure electricity.

    The electricity-eating microbes that the researchers were hunting for belong to a larger class of organisms that scientists are only beginning to understand. They inhabit largely uncharted worlds: the bubbling cauldrons of deep sea vents; mineral-rich veins deep beneath the planet’s surface; ocean sediments just a few inches below the deep seafloor. The microbes represent a segment of life that has been largely ignored, in part because their strange habitats make them incredibly difficult to grow in the lab.

    Yet early surveys suggest a potential microbial bounty. A recent sampling of microbes collected from the seafloor near Catalina Island, off the coast of Southern California, uncovered a surprising variety of microbes that consume or shed electrons by eating or breathing minerals or metals. El-Naggar’s team is still analyzing their gold mine data, but he says that their initial results echo the Catalina findings. Thus far, whenever scientists search for these electron eaters in the right locations — places that have lots of minerals but not a lot of oxygen — they find them.

    As the tally of electron eaters grows, scientists are beginning to figure out just how they work. How does a microbe consume electrons out of a piece of metal, or deposit them back into the environment when it is finished with them? A study published last year revealed the way that one of these microbes catches and consumes its electrical prey. And not-yet-published work suggests that some metal eaters transport electrons directly across their membranes — a feat once thought impossible.

    The Rock Eaters

    Though eating electricity seems bizarre, the flow of current is central to life. All organisms require a source of electrons to make and store energy. They must also be able to shed electrons once their job is done. In describing this bare-bones view of life, Nobel Prize-winning physiologist Albert Szent-Györgyi once said, “Life is nothing but an electron looking for a place to rest.”

    Humans and many other organisms get electrons from food and expel them with our breath. The microbes that El-Naggar and others are trying to grow belong to a group called lithoautotrophs, or rock eaters, which harvest energy from inorganic substances such as iron, sulfur or manganese. Under the right conditions, they can survive solely on electricity.

    The microbes’ apparent ability to ingest electrons — known as direct electron transfer — is particularly intriguing because it seems to defy the basic rules of biophysics. The fatty membranes that enclose cells act as an insulator, creating an electrically neutral zone once thought impossible for an electron to cross. “No one wanted to believe that a bacterium would take an electron from inside of the cell and move it to the outside,” said Kenneth Nealson, a geobiologist at the University of Southern California, in a lecture to the Society for Applied Microbiology in London last year.


    Ken Nealson – Environmental Microbiology Annual Lecture 2015: Extracellular electron transport (EET): opening new windows of metabolic opportunity for microbes.
    For more information about Environmental Microbiology
    visit http://goo.gl/7ZJOc6 For more information about Environmental Microbiology Reports
    visit http://goo.gl/NBdORV

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    Lucy Reading-Ikkanda/Quanta Magazine

    In the 1980s, Nealson and others discovered a surprising group of bacteria that can expel electrons directly onto solid minerals. It took until 2006 to discover the molecular mechanism behind this feat: A trio of specialized proteins [PubMed] sits in the cell membrane, forming a conductive bridge that transfers electrons to the outside of cell. (Scientists still debate whether the electrons traverse the entire distance of the membrane unescorted.)

    Inspired by the electron-donators, scientists began to wonder whether microbes could also do the reverse and directly ingest electrons as a source of energy. Researchers focused their search on a group of microbes called methanogens, which are known for making methane. Most methanogens aren’t strict metal eaters. But in 2009, Bruce Logan, an environmental engineer at Pennsylvania State University, and collaborators showed for the first time that a methanogen could survive using only energy from an electrode [PubMed]. The researchers proposed that the microbes were directly sucking up electrons, perhaps via a molecular bridge similar to the ones the electron-producers use to shuttle electrons across the cell wall. But they lacked direct proof.

    Then last year, Alfred Spormann, a microbiologist at Stanford University, and collaborators poked a hole in Logan’s theory. They uncovered a way [PubMed] that these organisms can survive on electrodes without eating naked electrons.

    The microbe Spormann studied, Methanococcus maripaludis, excretes an enzyme that sits on the electrode’s surface. The enzyme pairs an electron from the electrode with a proton from water to create a hydrogen atom, which is a well-established food source among methanogens. “Rather than having a conductive pathway, they use an enzyme,” said Daniel Bond, a microbiologist at the University of Minnesota Twin Cities. “They don’t need to build a bridge out of conductive materials.”

    Though the microbes aren’t eating naked electrons, the results are surprising in their own right. Most enzymes work best inside the cell and rapidly degrade outside. “What’s unique is how stable the enzymes are when they [gather on] the surface of the electrode,” Spormann said. Past experiments suggest these enzymes are active outside the cell for only a few hours, “but we showed they are active for six weeks.”

    Spormann and others still believe that methanogens and other microbes can directly suck up electricity, however. “This is an alternative mechanism to direct electron transfer, it doesn’t mean direct electron transfer can’t exist,” said Largus Angenent, an environmental engineer at Cornell University, and president of the International Society for Microbial Electrochemistry and Technology. Spormann said his team has already found a microbe capable of taking in naked electrons. But they haven’t yet published the details.

    Microbes on Mars

    Only a tiny fraction — perhaps 2 percent — of all the planet’s microorganisms can be grown in the lab. Scientists hope that these new approaches — growing microbes on electrodes rather than in traditional culture systems — will provide a way to study many of the microbes that have been so far impossible to cultivate.

    “Using electrodes as proxies for minerals has helped us open and expand this field,” said Annette Rowe, a postdoctoral researcher at USC working with El-Naggar. “Now we have a way to grow the bacteria and monitor their respiration and really have a look at their physiology.”

    Rowe has already had some success.

    In 2013, she went on a microbe prospecting trip to the iron-rich sediments that surround California’s Catalina Island. She identified at least 30 new varieties [PubMed]of electric microbes in a study published last year. “They are from very diverse groups of microbes that are quite common in marine systems,” Rowe said. Before her experiment, no one knew these microbes could take up electrons from an inorganic substrate, she said. “That’s something we weren’t expecting.”

    Just as fishermen use different lures to attract different fish, Rowe set the electrodes to different voltages to draw out a rich diversity of microbes. She knew when she had a catch because the current changed — metal eaters generate a negative current, as the microbes suck electrons from the negative electrode.

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    Yamini Jangir, then a graduate student in Moh El-Naggar’s lab at the University of Southern California, collects water from a pipe at the Sanford Underground Research Facility nearly a mile underground. Connie A. Walter and Matt Kapust

    SURF-Sanford Underground Research Facility


    SURF Above Ground

    SURF Out with the Old


    SURF An Empty Slate


    SURF Carving New Space


    SURF Shotcreting


    SURF Bolting and Wire Mesh


    SURF Outfitting Begins


    SURF circular wooden frame was built to form a concrete ring to hold the 72,000-gallon (272,549 liters) water tank that would house the LUX dark matter detector


    SURF LUX water tank was transported in pieces and welded together in the Davis Cavern


    SURF Ground Support


    SURF Dedicated to Science


    SURF Building a Ship in a Bottle


    SURF Tight Spaces


    SURF Ready for Science


    SURF Entrance Before Outfitting


    SURF Entrance After Outfitting


    SURF Common Corridior


    SURF Davis


    SURF Davis A World Class Site


    SURF Davis a Lab Site


    SURF DUNE LBNF Caverns at Sanford Lab


    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford


    U Washington LUX Xenon experiment at SURF


    SURF Before Majorana


    U Washington Majorana Demonstrator Experiment at SURF

    The different varieties of bacteria that Rowe collected thrive under different electrical conditions, suggesting they employ different strategies for eating electrons. “Each bacteria had a different energy level where electron uptake would happen,” Rowe said. “We think that is indicative of different pathways.”

    Rowe is now searching new environments for additional microbes, focusing on fluids from a deep spring with low acidity. She’s also helping with El-Naggar’s gold mine expedition. “We are trying to understand how life works under these conditions,” said El-Naggar. “We now know that life goes far deeper than we thought, and there’s a lot more than we thought, but we don’t have a good idea for how they are surviving.”

    El-Naggar emphasizes that the field is still in its infancy, likening the current state to the early days of neuroscience, when researchers poked at frogs with electrodes to make their muscles twitch. “It took a long time for the basic mechanistic stuff to come out,” he said. “It’s only been 30 years since we discovered that microbes can interact with solid surfaces.”

    Given the bounty from these early experiments, it seems that scientists have only scratched the surface of the microbial diversity that thrives beneath the planet’s shallow exterior. The results could give clues to the origins of life on Earth and beyond. One theory for the emergence of life suggests it originated on mineral surfaces, which could have concentrated biological molecules and catalyzed reactions. New research could fill in one of the theory’s gaps — a mechanism for transporting electrons from mineral surfaces into cells.

    Moreover, subsurface metal eaters may provide a blueprint for life on other worlds, where alien microbes might be hidden beneath the planet’s shallow exterior. “For me, one of the most exciting possibilities is finding life-forms that might survive in extreme environments like Mars,” said El-Naggar, whose gold mine experiment is funded by NASA’s Astrobiology Institute. Mars, for example, is iron-rich and has water flowing beneath its surface. “If you have a system that can pick up electrons from iron and have some water, then you have all the ingredients for a conceivable metabolism,” said El-Naggar. Perhaps a former mine a mile underneath South Dakota won’t be the most surprising place that researchers find electron-eating life.

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

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  • richardmitnick 11:39 am on June 30, 2017 Permalink | Reply
    Tags: , , , LUX Dark Matter Experiment,   

    From aeon: “In the dark” 

    1

    aeon

    6.29.17
    Alexander B Fry

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    Photomultiplier array at LUX, SURF, South Dakota. Photo courtesy of Luxdarkmatter.org

    Dark matter is the commonest, most elusive stuff there is. Can we grasp this great unsolved problem in physics?

    Lux Dark Matter Experiment

    SURF building in Lead SD USA

    LUX Xenon experiment at SURF, Lead, SD, USA


    I’m sitting at my desk at the University of Washington trying to conserve energy. It isn’t me who’s losing it; it’s my computer simulations. Actually, colleagues down the hall might say I was losing it as well. When I tell people I’m working on speculative theories about dark matter, they start to speculate about me. I don’t think everyone who works in the building even believes in it.

    In presentations, I point out how many cosmological puzzles it helps to solve. Occam’s Razor is my silver bullet: the fact that just one posit can explain so much. Then I talk about the things that standard dark matter doesn’t fix. There don’t seem to be enough satellite galaxies around our Milky Way. The inner shapes of small galaxies are inconsistent. I invoke Occam’s Razor again and argue that you can resolve these issues by adding a weak self-interaction to standard dark matter, a feeble scattering pattern when its particles collide. Then someone will ask me if I really believe in all this stuff. Tough question.

    The world we see is an illusion, albeit a highly persistent one. We have gradually got used to the idea that nature’s true reality is one of uncertain quantum fields; that what we see is not necessarily what is. Dark matter is a profound extension of this concept. It appears that the majority of matter in the universe has been hidden from us. That puts physicists and the general public alike in an uneasy place. Physicists worry that they can’t point to an unequivocal confirmed prediction or a positive detection of the stuff itself. The wider audience finds it hard to accept something that is necessarily so shadowy and elusive. The situation, in fact, bears an ominous resemblance to the aether controversy of more than a century ago.

    In the late-1800s, scientists were puzzled at how electromagnetic waves (for instance, light) could pass through vacuums. Just as the most familiar sort of waves are constrained to water — it’s the water that does the waving — it seemed obvious that there had to be some medium in which electromagnetic waves were ripples. Hence the notion of ‘aether’, an imperceptible field that was thought to permeate all of space.

    The American scientists Albert Michelson and Edward Morley carried out the most famous experiment to probe the existence of aether in 1887. If light needed a medium to propagate, they reasoned, then the Earth ought to be moving through this same medium. They set up an ingenious apparatus to test the idea: a rigid optics table floating on a cushioning vat of liquid mercury such that the table could rotate in any direction. The plan was to compare the wavelengths of light beams travelling in different relative directions, as the apparatus rotated or as the Earth swung around the sun. As our planet travelled along its orbit in an opposite direction to the background aether, light beams should be impeded, compressing their wavelength. Six months later, the direction of the impedance should reverse and the wavelength would expand. But to the surprise of many, the wavelengths were the same no matter what direction the beams travelled in. There was no sign of the expected medium. Aether appeared to be a mistake.

    This didn’t rule out its existence in every physicist’s opinion. Disagreement about the question rumbled on until at least some of the aether proponents died. Morley himself didn’t believe his own results. Only with perfect hindsight is the Michelson-Morley experiment seen as evidence for the absence of aether and, as it turned out, confirmation of Albert Einstein’s more radical theory of relativity.

    Dark matter, dark energy, dark money, dark markets, dark biomass, dark lexicon, dark genome: scientists seem to add dark to any influential phenomenon that is poorly understood and somehow obscured from direct perception. The darkness, in other words, is metaphorical. At first, however, it was intended quite literally. In the 1930s, the Swiss astronomer Fritz Zwicky observed a cluster of galaxies, all gravitationally bound to each other and orbiting one another much too fast. Only the gravitational pull of a very large, unseen mass seemed capable of explaining why they did not simply spin apart. Zwicky postulated the presence of some kind of ‘dark’ matter in the most casual sense possible: he just thought there was something he couldn’t see. But astronomers have continued to find the signature of unseen mass throughout the cosmos. For example, the stars of galaxies also rotate too fast. In fact, it looks as if dark matter is the commonest form of matter in our universe.

    It is also the most elusive. It does not interact strongly with itself or with the regular matter found in stars, planets or us. Its presence is inferred purely through its gravitational effects, and gravity, vexingly, is the weakest of the fundamental forces. But gravity is the only significant long-range force, which is why dark matter dominates the universe’s architecture at the largest scales.

    In the past half-century, we have developed a standard model of cosmology that describes our observed universe quite well.

    The standard cosmology model, ΛCDM model Cosmic pie chart after Planck Big Bang and inflation

    In the beginning, a hot Big Bang caused a rapid expansion of space and sowed the seeds for fluctuations in the density of matter throughout the universe. Over the next 13.7 billion years, those density patterns were scaled up thanks to the relentless force of gravity, ultimately forming the cosmic scaffolding of dark matter whose gravitational pull suspends the luminous galaxies we can see.

    This standard model of cosmology is supported by a lot of data, including the pervasive radiation field of the universe, the distribution of galaxies in the sky, and colliding clusters of galaxies. These robust observations combine expertise and independent analysis from many fields of astronomy. All are in strong agreement with a cosmological model that includes dark matter. Astrophysicists who try to trifle with the fundamentals of dark matter tend to find themselves cut off from the mainstream. It isn’t that anybody thinks it makes for an especially beautiful theory; it’s just that no other consistent, predictively successful alternative exists. But none of this explains what dark matter actually is. That really is a great, unsolved problem in physics.

    So the hunt is on. Particle accelerators sift through data, detectors wait patiently underground, and telescopes strain upwards. The current generation of experiments has already placed strong constraints on viable theories. Optimistically, the nature of dark matter could be understood within a few decades. Pessimistically, it might never be understood.

    We are in an era of discovery. A body of well-confirmed theory governs the assortment of fundamental particles that we have already observed. The same theory allows the existence of other, hitherto undetected particles. A few decades ago, theorists realised that a so-called Weakly Interacting Massive Particle (WIMP) might exist. This generic particle would have all the right characteristics to be dark matter, and it would be able to hide right under our noses. If dark matter is indeed a WIMP, it would interact so feebly with regular matter that we would have been able to detect it only with the generation of dark matter experiments that are just now coming on stream. The most promising might be the Large Underground Xenon (LUX) experiment in South Dakota, the biggest dark matter detector in the world. The facility opened in a former gold mine this February and is receptive to the most elusive of subatomic particles. And yet, despite LUX’s exquisite sensitivity, the hunt for dark matter itself has been something of a waiting game. So far, the only particles to turn up in the detector’s trap are bits of cosmic noise: nothing more than a nuisance.

    The past success of standard paradigms in theoretical physics leads us to hunt for a single generic dark matter particle — the dark matter. Arguably, though, we have little justification for supposing that there is anything to be found at all; as the English physicist John D Barrow said in 1994: ‘There is no reason that the universe should be designed for our convenience.’ With that caveat in mind, it appears the possibilities are as follows. Either dark matter exists or it doesn’t. If it exists, then either we can detect it or we can’t. If it doesn’t exist, either we can show that it doesn’t exist or we can’t. The observations that led astronomers to posit dark matter in the first place seem too robust to dismiss, so the most common argument for non-existence is to say there must be something wrong with our understanding of gravity – that it must not behave as Einstein predicted. That would be a drastic change in our understanding of physics, so not many people want to go there. On the other hand, if dark matter exists and we can’t detect it, that would put us in a very inconvenient position indeed.

    But we are living through a golden age of cosmology. In the past two decades, we have discovered so much: we have measured variations in the relic radiation of the Big Bang, learnt that the universe’s expansion is accelerating, glimpsed black holes and spotted the brightest explosions ever in the universe. In the next decades, we are likely to observe the first stars in the universe, map nearly the entire distribution of matter, and hear the cataclysmic merging of black holes through gravitational waves. Even among these riches, dark matter offers a uniquely inviting prospect, sitting at a confluence of new observations, theory, technology and (we hope) new funding.

    The various proposals to get its measure tend to fall into one of three categories: artificial creation (in a particle accelerator), indirect detection, and direct detection. The last, in which researchers attempt to catch WIMPs in the wild, is where the excitement is. The underground LUX detector is one of the first in a new generation of ultra-sensitive experiments. It counts on the WIMP interacting with the nucleus of a regular atom. These experiments generally consist of a very pure detector target, such as pristine elemental Germanium or Xenon, cooled to extremely low temperatures and shielded from outside particles. The problem is that stray particles tend to sneak in anyway. Interloper interactions are carefully monitored. Noise reduction, shielding and careful statistics are the only way to confirm real dark-matter interaction events from false alarms.

    Theorists have considered a lot of possibilities for how the real thing might work with the standard WIMP. Actually, the first generation of experiments has already ruled out the so-called z-boson scattering interaction. What is left is Higgs boson-mediated scattering, which would involve the same particle that the Large Hadron Collider discovered in Geneva in November last year.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event


    Higgs Always the last place your look.

    That implies a very weak interaction, but it would be perfectly matched to the current sensitivity threshold of the new generation of experiments.

    Then again, science is less about saying what is than what is not, and non-detections have placed relatively interesting constraints on dark matter. They have also, in a development that is strikingly reminiscent of the aether controversy, thrown out some anomalies that need to be cleared up. Using a different detector target to LUX, the Italian DAMA (short for ‘DArk MAtter’) experiment claims to have found an annual modulation of their dark matter signal.

    DAMA-LIBRA at Gran Sasso

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

    Detractors dispute whether they really have any signal at all. Just like with the aether, we expected to see this kind of yearly variation, as the Earth orbits the Sun, sometimes moving with the larger galactic rotation and sometimes against it. The DAMA collaboration measured such an annual modulation. Other competing projects (XENON, CDMS, Edelweiss and ZEPLIN, for example) didn’t, but these experiments cannot be compared directly, so we should probably reserve judgment.

    XENON1T at Gran Sasso

    LBNL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    Edelweiss Dark Matter Experiment, located at the Modane Underground Laboratory in France

    Lux Zeplin project at SURF

    Nature can be cruel. Physicists could take non-detection as a hint to give up, but there is always the teasing possibility that we just need a better experiment. Or perhaps dark matter will reveal itself to be almost as complex as regular matter. Previous experiments imposed quite strict limitations on just how much complexity we can expect — there’s no prospect of dark-matter people, or even dark-matter chemistry, really — but it could still come in multiple varieties. We might find a kind of particle that explains only a fraction of the expected total mass of dark matter.

    In a sense, this has already occurred. Neutrinos are elusive but widespread (60 billion of them pass through an area the size of your pinky every second). They hardly ever interact with regular matter, and until 1998 we thought they were entirely massless. In fact, neutrinos make up a tiny fraction of the mass budget of the universe, and they do act like an odd kind of dark matter. They aren’t ‘the’ dark matter, but perhaps there is no single type of dark matter to find.

    To say that we are in an era of discovery is really just to say that we are in an era of intense interest. Physicists say we would have achieved something if we determine that dark matter is not a WIMP. Would that not be a discovery? At the same time, the field is burgeoning with ideas and rival theories. Some are exploring the idea that dark matter has interactions, but we will never be privy to them. In this scenario, dark matter would have an interaction at the smallest of scales which would leave standard cosmology unchanged. It might even have an exotic universe of its own: a dark sector. This possibility is at once terrifying and entrancing to physicists. We could posit an intricate dark matter realm that will always escape our scrutiny, save for its interaction with our own world through gravity. The dark sector would be akin to a parallel universe.

    It is rather easy to tinker with the basic idea of dark matter when you make all of your modifications very feeble. And so this is what all dark matter theorists are doing. I have run with the idea that dark matter might have self-interactions and worked that into supercomputer simulations of galaxies. On the largest scales, where cosmology has made firm predictions, this modification does nothing, but on small scales, where the theory of dark matter shows signs of faltering, it helps with several issues. The simulations are pretty to look at and they make acceptable predictions. There are too many free parameters, though — what scientists call fine-tuning — such that the results can seem tailored to fit the observations. That’s why I reserve judgement, and you would be well advised to do the same.

    We will probably never know for certain whether dark matter has self-interactions. At best, we might put an upper limit on how strong such interactions could be. So, when people ask me if I think self-interacting dark matter is the correct theory, I say no. I am constraining what is possible, not asserting what is. But this is kind of disappointing, isn’t it? Surely cosmology should hold some deep truth that we can hope to grasp.

    One day, perhaps, LUX or one of its competitors might discover just what they are looking for. Or maybe on some unassuming supercomputer, I will uncover a hidden truth about dark matter. Regardless, such a discovery will feel removed from us, mediated as it will be through several layers of ghosts in machines. The dark matter universe is part of our universe, but it will never feel like our universe.

    Nature plays an epistemological trick on us all. The things we observe each have one kind of existence, but the things we cannot observe could have limitless kinds of existence. A good theory should be just complex enough. Dark matter is the simplest solution to a complicated problem, not a complicated solution to simple problem. Yet there is no guarantee that it will ever be illuminated. And whether or not astrophysicists find it in a conceptual sense, we will never grasp it in our hands. It will remain out of touch. To live in a universe that is largely inaccessible is to live in a realm of endless possibilities, for better or worse.

    See the full article here .

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  • richardmitnick 3:50 pm on May 16, 2017 Permalink | Reply
    Tags: , Blind studies, , , , LUX Dark Matter Experiment, , , ,   

    From Symmetry: “The facts and nothing but the facts” 

    Symmetry Mag

    Symmetry

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    Artwork by Corinne Mucha

    05/16/17
    Manuel Gnida

    At a recent workshop on blind analysis, researchers discussed how to keep their expectations out of their results.

    Scientific experiments are designed to determine facts about our world. But in complicated analyses, there’s a risk that researchers will unintentionally skew their results to match what they were expecting to find. To reduce or eliminate this potential bias, scientists apply a method known as “blind analysis.”

    Blind studies are probably best known from their use in clinical drug trials, in which patients are kept in the dark about—or blind to—whether they’re receiving an actual drug or a placebo. This approach helps researchers judge whether their results stem from the treatment itself or from the patients’ belief that they are receiving it.

    Particle physicists and astrophysicists do blind studies, too. The approach is particularly valuable when scientists search for extremely small effects hidden among background noise that point to the existence of something new, not accounted for in the current model. Examples include the much-publicized discoveries of the Higgs boson by experiments at CERN’s Large Hadron Collider and of gravitational waves by the Advanced LIGO detector.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    “Scientific analyses are iterative processes, in which we make a series of small adjustments to theoretical models until the models accurately describe the experimental data,” says Elisabeth Krause, a postdoc at the Kavli Institute for Particle Astrophysics and Cosmology, which is jointly operated by Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. “At each step of an analysis, there is the danger that prior knowledge guides the way we make adjustments. Blind analyses help us make independent and better decisions.”

    Krause was the main organizer of a recent workshop at KIPAC that looked into how blind analyses could be incorporated into next-generation astronomical surveys that aim to determine more precisely than ever what the universe is made of and how its components have driven cosmic evolution.

    Black boxes and salt

    One outcome of the workshop was a finding that there is no one-size-fits-all approach, says KIPAC postdoc Kyle Story, one of the event organizers. “Blind analyses need to be designed individually for each experiment.”

    The way the blinding is done needs to leave researchers with enough information to allow a meaningful analysis, and it depends on the type of data coming out of a specific experiment.

    A common approach is to base the analysis on only some of the data, excluding the part in which an anomaly is thought to be hiding. The excluded data is said to be in a “black box” or “hidden signal box.”

    Take the search for the Higgs boson. Using data collected with the Large Hadron Collider until the end of 2011, researchers saw hints of a bump as a potential sign of a new particle with a mass of about 125 gigaelectronvolts. So when they looked at new data, they deliberately quarantined the mass range around this bump and focused on the remaining data instead.

    They used that data to make sure they were working with a sufficiently accurate model. Then they “opened the box” and applied that same model to the untouched region. The bump turned out to be the long-sought Higgs particle.

    That worked well for the Higgs researchers. However, as scientists involved with the Large Underground Xenon experiment reported at the workshop, the “black box” method of blind analysis can cause problems if the data you’re expressly not looking at contains rare events crucial to figuring out your model in the first place.

    LUX has recently completed one of the world’s most sensitive searches for WIMPs—hypothetical particles of dark matter, an invisible form of matter that is five times more prevalent than regular matter.

    LUX/Dark matter experiment at SURF

    LUX scientists have done a lot of work to guard LUX against background particles—building the detector in a cleanroom, filling it with thoroughly purified liquid, surrounding it with shielding and installing it under a mile of rock. But a few stray particles make it through nonetheless, and the scientists need to look at all of their data to find and eliminate them.

    For that reason, LUX researchers chose a different blinding approach for their analyses. Instead of using a “black box,” they use a process called “salting.”

    LUX scientists not involved in the most recent LUX analysis added fake events to the data—simulated signals that just look like real ones. Just like the patients in a blind drug trial, the LUX scientists didn’t know whether they were analyzing real or placebo data. Once they completed their analysis, the scientists that did the “salting” revealed which events were false.

    A similar technique was used by LIGO scientists, who eventually made the first detection of extremely tiny ripples in space-time called gravitational waves.

    High-stakes astronomical surveys

    The Blind Analysis workshop at KIPAC focused on future sky surveys that will make unprecedented measurements of dark energy and the Cosmic Microwave Background—observations that will help cosmologists better understand the evolution of our universe.

    CMB per ESA/Planck

    ESA/Planck

    Dark energy is thought to be a force that is causing the universe to expand faster and faster as time goes by. The CMB is a faint microwave glow spread out over the entire sky. It is the oldest light in the universe, left over from the time the cosmos was only 380,000 years old.

    To shed light on the mysterious properties of dark energy, the Dark Energy Science Collaboration is preparing to use data from the Large Synoptic Survey Telescope, which is under construction in Chile. With its unique 3.2-gigapixel camera, LSST will image billions of galaxies, the distribution of which is thought to be strongly influenced by dark energy.


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam


    LSST Camera, built at SLAC



    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    “Blinding will help us look at the properties of galaxies picked for this analysis independent of the well-known cosmological implications of preceding studies,” DESC member Krause says. One way the collaboration plans on blinding its members to this prior knowledge is to distort the images of galaxies before they enter the analysis pipeline.

    Not everyone in the scientific community is convinced that blinding is necessary. Blind analyses are more complicated to design than non-blind analyses and take more time to complete. Some scientists participating in blind analyses inevitably spend time looking at fake data, which can feel like a waste.

    Yet others strongly advocate for going blind. KIPAC researcher Aaron Roodman, a particle-physicist-turned-astrophysicist, has been using blinding methods for the past 20 years.

    “Blind analyses have already become pretty standard in the particle physics world,” he says. “They’ll be also crucial for taking bias out of next-generation cosmological surveys, particularly when the stakes are high. We’ll only build one LSST, for example, to provide us with unprecedented views of the sky.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • 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” 

    1
    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.

    1
    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.

    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 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

    1
    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.

    2
    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.

    3
    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.

    4
    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.

    6
    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.”

    7
    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.

    1
    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.”

    9
    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.”

    9
    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

    1
    Rapid City Journal

    6.20.16
    Tom Griffith

    1
    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 .

    Please help promote STEM in your local schools.
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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 .

    Please help promote STEM in your local schools.

    STEM Icon

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    LLNL Campus

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

     
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