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  • richardmitnick 12:39 pm on April 4, 2017 Permalink | Reply
    Tags: , , WIMPS   

    From Symmetry: “WIMPs in the dark matter wind” 

    Symmetry Mag

    Symmetry

    04/04/17
    Lori Ann White

    1
    No image credit found

    We know which way the dark matter wind should blow. Now we just have to find it.

    Picture yourself in a car, your hand surfing the breeze through the open window. Hold your palm perpendicular to the wind and you can feel its force. Now picture the car slowing, rolling up to a stop sign, and feel the force of the wind lessen until it—and the car—stop.

    This wind isn’t due to the weather. It arises because of your motion relative to air molecules. Simple enough to understand and known to kids, dogs and road-trippers the world over.

    This wind has an analogue in the rarefied world of particle astrophysics called the “dark matter wind,” and scientists are hoping it will someday become a valuable tool in their investigations into that elusive stuff that apparently makes up about 85 percent of the mass in the universe [don’t forget this is just the mass, saying nothing about dark energy which is about 75% of everything] .

    n the analogy above, the air molecules are dark matter particles called WIMPs, or weakly interacting massive particles. Our sun is the car, racing around the Milky Way at about 220 kilometers per second, with the Earth riding shotgun. Together, we move through a halo of dark matter that encompasses our galaxy. But our planet is a rowdy passenger; it moves from one side of the sun to the other in its orbit.

    When you add the Earth’s velocity of 30 kilometers per second to the sun’s, as happens when both are traveling in the same direction (toward the constellation Cygnus), then the dark matter wind feels stronger. More WIMPs are moving through the planet than if it were at rest, resulting in greater number of detections by experiments. Subtract that velocity when the Earth is on the other side of its orbit, and the wind feels weaker, resulting in fewer detections.

    Astrophysicists have been thinking about the dark matter wind for decades. Among the first, way back in 1986, were theorist David Spergel of Princeton and colleagues Katherine Freese of the University of Michigan and Andrzej K. Drukier (now in private industry, but still looking for WIMPs).

    “We looked at how the Earth’s motion around the sun should cause the number of dark matter particles detected to vary on a regular basis by about 10 percent a year,” Spergel says.

    At least that’s what should happen—if our galaxy really is embedded in a circular, basically homogeneous halo of dark matter, and if dark matter is really made up of WIMPs.

    The Italian experiment DAMA/NaI and its upgrade DAMA/Libra claim to have been seeing this seasonal modulation for decades, a claim that has yet to be conclusively supported by any other experiments.

    DAMA LIBRA Dark Matter Experiment

    CoGeNT, an experiment in the Soudan Underground Laboratory in South Dakota, seemed to back them up for a time, but now the signals are thought to be caused by other sources such as high-energy gamma rays hitting a layer of material just outside the germanium of the detector, resulting in a signal that looks much like a WIMP.

    CoGeNT experiment

    Actually confirming the existence of the dark matter wind is important for one simple reason: the pattern of modulation can’t be explained by anything but the presence of dark matter. It’s what’s called a “model-independent” phenomenon. No natural backgrounds—no cosmic rays, no solar neutrinos, no radioactive decays—would show a similar modulation. The dark matter wind could provide a way to continue exploring dark matter, even if the particles are light enough that experiments cannot distinguish them from almost massless particles called neutrinos, which are constantly streaming from the sun and other sources.

    “It’s a big, big prize to go after,” says Jocelyn Monroe, a physics professor at Royal Holloway University of London, who currently works on two dark matter detection experiments, DEAP-3600 at SNOLAB, in Canada, and DMTPC. “If you could correlate detections with the direction in which the planet is moving you would have unambiguous proof” of dark matter.

    DEAP Dark Matter detector

    SNOLAB, Sudbury, Ontario, Canada.

    At the same time Spergel and his colleagues were exploring the wind’s seasonal modulation, he also realized that this correlation could extend far beyond a twice-per-year variation in detection levels. The location of the Earth in its orbit would affect the direction in which nucleons, the particles that make up the nucleus of an atom, recoil when struck by WIMPs. A sensitive-enough detector should see not only the twice-yearly variations, but even daily variations, since the detector constantly changes its orientation to the dark matter wind as the Earth rotates.

    “I had initially thought that it wasn’t worth writing up the paper because no experiment had the sensitivity to detect the recoil direction,” he says. “However, I realized that if I pointed out the effect, clever experimentalists would eventually figure out a way to detect it.”

    Monroe, as the leader of the DMTPC collaboration, is a member of the clever experimentalist set. The DMTPC, or Dark Matter Time-Projection Chamber, is one of a small number of direct detection experiments that are designed to track the actual movements of recoiling atoms.

    Instead of semiconductor crystals or liquefied noble gases, these experiments use low-pressure gases as their target material. DMTPC, for example, uses carbon tetrafluoride. If a WIMP hits a molecule of carbon tetrafluoride, the low pressure in the chamber means that molecule has room to move—up to about 2 millimeters.

    “Making the detector is super hard,” Monroe says. “It has to map a 2-millimeter track in 3D.” Not to mention reducing the number of molecules in a detector chamber reduces the chances for a dark matter particle to hit one. According to Monroe, DMTPC will deal with that issue by fabricating an array of 1-cubic-meter-sized modules. The first module has already been constructed and a worldwide collaboration of scientists from five different directional dark matter experiments (including DMTPC) are working on the next step together: a much larger directional dark matter array called the CYGNUS (for CosmoloGY with NUclear recoilS) experiment.

    When and if such directional dark matter detectors raise their metaphorical fingers to test the direction of the dark matter wind, Monroe says they’ll be able to see far more than just seasonal variations in detections. Scientists will be able to see variations in atomic recoils not on a seasonal basis, but on a daily basis. Monroe envisions a sort of dark matter telescope with which to study the structure of the halo in our little corner of the Milky Way.

    Or not.

    There’s always a chance that this next generation of dark matter detectors, or the generation after, still won’t see anything.

    Even that, Monroe says, is progress.

    “If we’re still looking in 10 years we might be able to say it’s not WIMPs but something even more exotic As far as we can tell right now, dark matter has got to be something new out there.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:27 am on March 6, 2017 Permalink | Reply
    Tags: , COSINE-100 Dark Matter Experiment - Yale University, DAMA/LIBRA at Gran Sasso, , , Laboratori Nazionali del Gran Sasso in Italy, WIMPS, Women in STEM - "Meet the South Pole’s Dark Matter Detective" Reina Maruyama,   

    From Nautilus: Women in STEM – “Meet the South Pole’s Dark Matter Detective” Reina Maruyama 

    Nautilus

    Nautilus

    3.6.17
    Matthew Sedacca

    5
    Reina Maruyama wasn’t expecting her particle detector to work buried deep in ice. She was wrong.

    In the late 1990s, a team of physicists at the Laboratori Nazionali del Gran Sasso in Italy began collecting data for DAMA/LIBRA, an experiment investigating the presence of dark matter particles.

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

    DAMA/LIBRA at Gran Sasso
    DAMA/LIBRA at Gran Sasso

    The scientists used a scintillation detector to spot the weakly interactive massive particles, known as WIMPs, thought to constitute dark matter. They reported seeing an annual modulation in the number of “hits” that the detector receives. This was a potential sign that the Earth is moving through the galaxy’s supposed halo of dark matter—something that few, if any, researchers could claim.

    Reina Maruyama’s job, at a detector buried two-kilometers deep in the South Pole, is to determine whether or not these researchers’ findings are actually valid. Previously, Maruyama worked at the South Pole to detect neutrinos, the smallest known particle. But when it came to detecting dark matter, especially with using detectors buried under glacial ice, she was initially skeptical of the task. In those conditions, she “couldn’t imagine having it run and produce good physics data.”

    Contrary to Maruyama’s expectations, the detector’s first run went smoothly. Their most recent paper, published in Physical Review D earlier this year, affirmed the South Pole as a viable location for experiments detecting dark matter. The detector, despite the conditions, kept working. At the moment, however, “DM-Ice17,” as her operation is known, is on hiatus, with the team having relocated to Yangyang, South Korea, to focus on COSINE-100, another dark matter particle detector experiment, and continue the search for the modulation seen in DAMA/LIBRA.

    3
    COSINE-100 Dark Matter Experiment – Yale University

    3
    The shielding structure of COSINE-100 includes 3 cm of copper, 20 cm of lead, and 3 cm of 37 plastic scintillator panels for cosmic ray muon tagging. 18 5-inch PMTs are attached to the copper box to observe scintillation light from liquid scintillator, and each plastic scintillator has a 2-inch PMT attached on one side (top panels have a PMT on each side). http://cosine.yale.edu/about-us/cosine-100-experiment.

    3
    Dark Matter?Data visuals from COSINE-100, a dark matter experiment in Yangyang, South Korea. Reina Maruyama

    Nautilus sat down with Maruyama at Yale this past January to talk about the potential nature of dark matter, the variety of ways scientists use to search for it, and what it’s like working in the South Pole.

    What do the scientists behind DAMA claim to have discovered?

    What this experiment with DAMA has seen is that in June, the velocity is odd. The sun and Earth are going in the same direction; in December, the velocities are in opposite directions, at about a 10 percent difference. That means in June we expect this signature to occur more frequently than in December. DAMA claims to have seen this annual modulation signature. People started to think about: “Well what is it that DAMA is seeing? Could it be some sort of environmental effect?” We don’t know. They’ve looked at their data, and they’ve argued against every possibility that people have come up with. One thing that the dark matter community has asked them to do is actually release their data, but so far they have refused to do that.

    The original idea of DM-Ice was to go to the southern hemisphere where the seasonal variation is opposite in phase, so if we continue to see the signal, then it would be really hard to attribute that signal to something seasonal. If we don’t see anything, then there is something in their data that they don’t understand.

    7
    University of Wisconsin–Madison, DM-Ice collaborators

    So what is dark matter?

    We don’t know what it is. We know it exerts gravity. This is why we call it matter. We see evidence from it: in how stars move around in a galaxy, and galaxies around each other. When we look out at distant stars and galaxies, we can see light being bent around something that exerts gravity, even on photons, but we don’t see any light, x-rays, or clues of things existing.

    What we saw was that the speed of the rotating objects are much faster than what you would expect for something like that. So that seems to indicate there is more mass between these objects. You can do that by adding a clump of mass between. That’s what we see: not specific objects, but dark matter diffusely spread out all over, typically surrounding galaxies. There must be dark matter inside the orbit of our sun so that we can move at the speed that we are. That means we are going through this halo of dark matter, riding along with the sun and the earth.

    What can we do to prove that dark matter is causing these changes?

    Let’s just pick a volume, your coffee, right there. We are hypothesizing that if dark matter is WIMPs, then there’s a very small possibility that the WIMPs going at 300 kilometers per second could interact with the coffee nuclei. If that happens in our detectors, we can actually see a nucleus being kicked by a WIMP. That’s how a lot of particle detectors work: Either there are some energy transfers to the electrons, or there is some energy transfer into the nuclei, and then we detect the electrons or light emitted from that, or sound waves. If those occur at the right energy, with the right frequency, then we can say maybe we see dark matter in our detectors.

    When there is a knock into a nucleus you can actually collect two different kinds of signals: the charge and photon emissions. When nuclei get kicks, it transfers some of that energy into electrons, and then the electrons move around, and that process emits light, and in some of that, electrons can be collected, and that is a signal. You need some sort of mass, and you need to be able to tell if a nucleus got a kick. The most efficient way to do that is to have a detector that is also the target, where the nuclei is. You want some big volume to increase the likeliness this can occur. DAMA is using sodium iodide detectors. These are very sensitive experiments, and a lot of these can actually tell the difference between an initial electron kick versus an initial nuclear kick. The electron kicks actually occur much more often in these detectors, so you can reject those as background and just keep the nuclear kicks.

    Newer technologies are much more sensitive to nuclear kicks than sodium iodide. Every other experiment that has tried to look for a signature like this has not seen anything. They see nuclear kicks, but mostly attributable to neutrons. They cannot definitively say that this must be dark matter.

    4
    Gamma Ray Shield, or Bath tub?Maruyama said, “We put detectors inside when we need to shield them from gamma rays that are present in a typical room. The box is made of lead bricks.” NO image credit.

    How did you come up with the design for your experiments?

    With DM-Ice, we wanted to be as similar to DAMA as possible: We want sodium iodide, and we want it to be low-background. So we need shielding around it to block the detector from gamma rays and cosmic rays. The only thing that’s changing should be the dark matter. It turns out the South Pole is actually a pretty good environment. You have an entire continent of ice, which is very stable. Once you go two and a half kilometers into the ice, nothing is changing. Ice at the South Pole, it’s super clean.

    Then you need to start worrying about practical things like: Can you get there, and do you have infrastructure to run the experiment? Is it affordable, do you have the right people to do this with? That starts to narrow down the site and the environment. You end up with the a few places in the world you could do this, and then maybe you want to partner with somebody else so that you can afford a bigger detector, and more, better infrastructure that’s more stable. That is the thinking process. Then you have to convince your colleagues in the field that this is a really good idea and need to share a pot of resources available to all U.S. funds. That’s the thought-process behind the experiment.

    What’s it like working in the South Pole?

    First you have to get approved to go, but that’s pretty competitive. A lot of people want to go and so if you have a good reason to go, you go. Before you go, you need to get medical clearance. You get checked out. It’s a remote location. They want to make sure you’re not gonna get sick while you’re there. So you spend one or two nights in Christchurch, New Zealand. You meet a lot of other people who might be going with you: engineers, geologists, biologists, other scientists, firemen, cooks, and bus drivers; a lot of really engaged and very passionate people.

    When you get to the South Pole, you have take it slow, even though you’re excited and working, it’s 10,000 feet, so they ask you to take it easy your first few days. You enter through what looks like a restaurant-refrigerator door. Keep the cold out kind of thing. Very comfortable, get your own room, dormitory-style living. Water is very precious. All of the energy is provided by jet fuel. So airplanes fly in and siphon off the fuel except for what’s needed for to get back. And there’s a power station where they generate electricity. They get water by melting the ice, and it’s a very expensive process. You get like two-minute showers twice a week. It’s on the honor system. That’s what it’s like living in the station.

    What are some problems that you faced when working down there?

    It’s 24/7 sunlight. So the sun circles above your head. Because you’re there to get things done, it’s hard to know when to stop working. But before you know it, it’s two in the morning, and the sun’s bright and shining. So you have to make sure you get enough sleep and ready to work the next day. That was a challenge for me.

    So when you’re not on site what are you doing in terms of research?

    We might have a small-scale detector here and do stress tests on it. Physicists love to tinker: How we can improve these detectors? What if we changed the temperature a lot? How can we make this detector even quieter so that we can look for even smaller signals, or a signal that exists that looks even bigger? People like to say things like we’re looking for a needle in a haystack, so can we reduce the haystack? Can we change the color of the haystack so that the needle looks even more visible?

    What’s the future for DM-Ice?

    Right now there is no drilling happening at the South Pole. We’ll keep pushing to do that experiment. In the meantime, the detector is buried and frozen into the ice, so we might as well just keep it running. We’re focusing on the Korean effort. What we can do there is look for the signal. If we continue to see the same signal, we can try to look for other correlations and cross them off on our own. If we cannot find other causes for it, I think the case for DAMA becomes stronger. Then DAMA’s signal is not specific to DAMA.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 2:48 pm on February 18, 2017 Permalink | Reply
    Tags: , , , WIMPS   

    From Nautilus: “Dark Matter May Show Quantum Effects on a Galactic Scale” 

    Nautilus

    Nautilus

    2.18.17
    David “Doddy” Marsh

    This weird type of dark matter would also puff up galaxies and make stars age prematurely.

    1
    Microwave cavity in the ADMX axion detection experiment at the University of Washington. Credit: ADMX.

    U Washington ADMX
    U Washington ADMX

    An axion is a theoretical particle named after a laundry detergent. As particles go, it is a strange one. Its mass is tiny—somewhere between one trillionth the mass of the proton and one billion-trillion-trillionth. It is so lightweight, in fact, that it doesn’t even behave as a particle, but as a wave that could straddle a galaxy. It is also feeble—its influence extends over an almost absurdly short distance, a millionth of what the Large Hadron Collider is able to discern. These short distances stem from the possible relation between axions and very high energy physics, possibly even quantum gravity.

    When I first heard of the axion, I had no idea it would become my life’s work. I was a new grad student looking for a starter project, and I came across a paper with such a peculiar title that I couldn’t help but read it: “String Axiverse.” It was written by a group of people including John March-Russell, a theoretical physicist in my department at Oxford. Speaking to John and cosmologist Pedro Ferreira (who both later became my Ph.D. advisors), I realized that the axion was just what I wanted to work on: a fascinating theoretical construct, but with direct connection to the exciting modern progress in cosmology.

    An unknown particle that may exist in profusion: the axion is an ideal candidate for dark matter. But it is a very different beast than we’re used to thinking about, requiring us to go about the search for dark matter in a different way.

    The Nobelist Frank Wilczek gave the axion its name because it cleaned up a problem in the Standard Model of particle physics. In the 1970s, he and others puzzled over a mismatch between the two forces that govern atomic nuclei: the strong and weak nuclear forces. The strong force has a symmetry in its workings that the weak lacks, even though, a priori, there is no reason it should. Helen Quinn and Robert Peccei proposed that the force is not innately symmetrical, but develops this symmetry under the action of a new field akin to the Higgs field. The axion particle is a remnant of this field.

    To play its role, the axion must be extremely lightweight. For our current theories, that is awkward, because it creates an enormous gulf between this particle and all the others. But the low mass is entirely natural in string theory, our leading candidate for a unified theory of nature. String theory predicts there is not just one type of axion, but there are typically 30 or more different kinds, and it predicts that their masses are spread out over a wide range. Some therefore must be lightweight. String theory is often criticized for not making testable predictions, but that’s not quite right, because the theory does predict axions. Although I wouldn’t claim that discovering lots of axions would be evidence for string theory, I think it is fairly safe to say that, according to almost any theory other than string theory, it would be surprising if we discovered large numbers of them.

    ______________________________________________________________________
    If axion dark matter exists, it is completely invisible to a conventional experiment.
    ______________________________________________________________________

    Axions are like other candidates for dark matter in that they are dark—they have no electric charge and therefore do not emit or absorb light—and interact very weakly with ordinary matter. But there the resemblance stops. Compare it to the most commonly discussed type of dark matter, the WIMP, or weakly interacting massive particle.

    It is a so-called thermal relic, which, according to theory, is produced the same way as protons, neutrons, and atomic nuclei: from the collisions between particles in the hot, dense, early universe. Given the amount of missing mass that astronomers infer, this production mechanism for WIMPs sets their mass and interaction strength: 100 times the mass of the proton (hence “massive”) with an interaction strength roughly equal to the weak nuclear force (hence “weakly interacting”). These would be lumbering particles, and that is just what astronomers need to explain the distribution of galaxies. If they exist, we should be able to detect them in particle detectors similar to those we use to detect neutrinos, and we should even be able to produce them ourselves by mimicking those hot, dense conditions in the Large Hadron Collider.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Axions, in contrast, have a different origin story. Their production is determined not by the temperature of the plasma in the early universe, but gravitationally, by the expansion of space in the big bang. This production mechanism sets their mass and interaction strength, which are vastly different from those of WIMPs.

    Big Bang to today
    Big Bang to today. http://www.sun.org/encyclopedia/a-short-history-of-the-universe

    Axions would interact with ordinary matter to a limited degree, but only by a unique set of interactions. For this reason, if axion dark matter exists, it is completely invisible to a conventional experiment such a WIMP detector or even the Large Hadron Collider.

    The poster-child axion direct-detection experiment is ADMX, which operates at the University of Washington and relies on a concept invented by Pierre Sikivie in 1983. Though “dark”, axions do interact with electromagnetism in other ways and, in the presence of a magnetic field, can metamorphose into photons or vice versa. ADMX attempts to perform the metamorphosis inside a microwave radio-frequency cavity like those used in radar equipment and microwave relay stations. So far ADMX have observed nothing, but it is sensitive only to axions whose wavelengths are comparable to the size of the cavity, and it has still not completed its full search program. Proposed experiments such as MADMAX and CASPEr would probe a much wider range of wavelengths.

    In principle, axions might have shown up in experiments intended for other purposes. With colleagues at the University of Sussex, the Swiss Federal Institute of Technology, and the University of New South Wales, as well as two talented grad students, Nicholas Ayres and Michał Rawlik, I have been digging through the archives of the nEDM experiment, which ran for a number of years at the Institut Laue-Langevin in France and is now at the Paul Scherrer Institute in Switzerland. It has been measuring neutrons, which would oscillate in a particular way if a galactic axion wave happened to pass through it, and we are reanalyzing the data to look for this signal.

    ______________________________________________________________________________________

    In this field, there’s room for young theorists such as me to make headway.
    ______________________________________________________________________________________

    If axions exist, stars would produce them naturally. Some of the photons produced during nuclear fusion in the core could metamorphose into axions, and they would escape the star more readily than photons do. This would drain the star of energy and cause it to age faster. Astronomers have been combing through star clusters for stars that look older than they actually are, and they have found no evidence of extra cooling. This null result sets limits on how strongly axions can interact with the constituents of stars.

    With my colleagues Dan Grin and Renée Hložek, I have also been searching for axions in cosmological data. Their wavelike properties might give them away. Over distances smaller than the axion wavelength, multiple axion waves would overlap and interfere with one another, causing them to exert an outward pressure and puff up galaxies. And indeed astronomers do find that galaxies are less clumpy than WIMPs should cause them to be (although there are many possible explanations for this, not just axions). My colleagues and I have been exploring this idea further by combining galaxy data with cosmic microwave background radiation measurements, as well as conducting simulations of galaxy formation with axion dark matter.

    Finally, axions would alter what happened during cosmic inflation, the primeval period when the universe was expanding at a breakneck rate. Cosmologists generally think the inflationary process created a torrent of gravitational waves, but if dark matter is made of axions, it would have generated very few. So, the discovery of primordial gravitational waves could be taken as falsification of the axion idea, at least in a wide range of models. (If we ever detected both axion dark matter and these gravitational waves, then something would be wrong with standard inflationary theory.)

    Only a small band of devotees have given much thought to axions. That makes it a fun field to be working in. There’s room for young theorists such as me to make headway and feel like we’re adding to the understanding of the community, which is much harder to do in a more mature field such studying WIMPs.

    It should be said that there is room in the universe for both axions and WIMPs. Both have a firm grounding in fundamental physics and in cosmology, and both may exist out there. For me, one of the benefits of thinking about axions is that they force to think beyond WIMPs. If all we ever do is study and simulate WIMPs because it is relatively easy, as a community we run the risk of confirmation bias, where WIMPs always come up trumps because they are all we know. Thankfully, that doesn’t seem to be how the field of dark-matter research is going. People are exploring a huge range. Dark matter is out there and discovering it is just a matter of time. When we do discover it, whatever it is, it will revolutionize our ideas of particle physics and cosmology.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 10:02 pm on February 13, 2017 Permalink | Reply
    Tags: , , , LUX-ZEPLIN (LZ) dark matter-hunting experiment, , WIMPS   

    From LBNL: “Next-Gen Dark Matter Detector in a Race to Finish Line” 

    Berkeley Logo

    Berkeley Lab

    February 13, 2017
    Glenn Roberts Jr.
    geroberts@lbl.gov
    510-486-5582

    1
    Light-amplifying devices known as photomultiplier tubes (PMTs), developed for use in the LUX-ZEPLIN (LZ) dark matter-hunting experiment, are prepared for a test at Brown University. This test bed, dubbed PATRIC, will be used to test over 600 PMTs in conditions simulating the temperature and pressure of the liquid xenon that will be used for LZ. (Credit: Brown University)

    The race is on to build the most sensitive U.S.-based experiment designed to directly detect dark matter particles. Department of Energy officials have formally approved a key construction milestone that will propel the project toward its April 2020 goal for completion.

    The LUX-ZEPLIN (LZ) experiment, which will be built nearly a mile underground at the Sanford Underground Research Facility (SURF) in Lead, S.D., is considered one of the best bets yet to determine whether theorized dark matter particles known as WIMPs (weakly interacting massive particles) actually exist. There are other dark matter candidates, too, such as “axions” or “sterile neutrinos,” which other experiments are better suited to root out or rule out.

    SURF logo
    SURF – Sanford Underground Research Facility at Lead, SD, USA

    The fast-moving schedule for LZ will help the U.S. stay competitive with similar next-gen dark matter direct-detection experiments planned in Italy and China.

    2
    This image shows a cutaway rendering of the LUX-ZEPLIN (LZ) detector that will search for dark matter nearly a mile below ground. An array of detectors, known as photomultiplier tubes, at the top and bottom of the liquid xenon tank are designed to pick up particle signals. (Credit: Matt Hoff/Berkeley Lab)

    On Feb. 9, the project passed a DOE review and approval stage known as Critical Decision 3 (CD-3), which accepts the final design and formally launches construction.

    “We will try to go as fast as we can to have everything completed by April 2020,” said Murdock “Gil” Gilchriese, LZ project director and a physicist at the DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), the lead lab for the project. “We got a very strong endorsement to go fast and to be first.” The LZ collaboration now has about 220 participating scientists and engineers who represent 38 institutions around the globe.

    The nature of dark matter—which physicists describe as the invisible component or so-called “missing mass” in the universe that would explain the faster-than-expected spins of galaxies, and their motion in clusters observed across the universe—has eluded scientists since its existence was deduced through calculations by Swiss astronomer Fritz Zwicky in 1933.

    The quest to find out what dark matter is made of, or to learn whether it can be explained by tweaking the known laws of physics in new ways, is considered one of the most pressing questions in particle physics.

    Successive generations of experiments have evolved to provide extreme sensitivity in the search that will at least rule out some of the likely candidates and hiding spots for dark matter, or may lead to a discovery.

    3
    The underground home of LZ and its supporting systems are shown in this computerized rendering. (Credit: Matt Hoff/Berkeley Lab)

    LZ will be at least 50 times more sensitive to finding signals from dark matter particles than its predecessor, the Large Underground Xenon experiment (LUX), which was removed from SURF last year to make way for LZ. The new experiment will use 10 metric tons of ultra-purified liquid xenon, to tease out possible dark matter signals. Xenon, in its gas form, is one of the rarest elements in Earth’s atmosphere.

    “The science is highly compelling, so it’s being pursued by physicists all over the world,” said Carter Hall, the spokesperson for the LZ collaboration and an associate professor of physics at the University of Maryland. “It’s a friendly and healthy competition, with a major discovery possibly at stake.”

    4
    This chart shows the sensitivity limits (solid-line curves) of various experiments searching for signs of theoretical dark matter particles known as WIMPs, with LZ (green dashed line) set to expand the search range. (Credit: Snowmass report, 2013)

    A planned upgrade to the current XENON1T experiment at National Institute for Nuclear Physics’ Gran Sasso Laboratory (the XENONnT experiment) in Italy, and China’s plans to advance the work on PandaX-II, are also slated to be leading-edge underground experiments that will use liquid xenon as the medium to seek out a dark matter signal.

    11
    Assembly of the XENON1T TPC in the cleanroom. (Image: INFN)

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

    5
    PandaX-II

    Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders.

    Hall noted that while WIMPs are a primary target for LZ and its competitors, LZ’s explorations into uncharted territory could lead to a variety of surprising discoveries. “People are developing all sorts of models to explain dark matter,” he said. “LZ is optimized to observe a heavy WIMP, but it’s sensitive to some less-conventional scenarios as well. It can also search for other exotic particles and rare processes.”

    LZ is designed so that if a dark matter particle collides with a xenon atom, it will produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank—over four times more than were installed in LUX—will carry the telltale fingerprint of the particles that created them.

    6
    Inside LZ: When a theorized dark matter particle known as a WIMP collides with a xenon atom, the xenon atom emits a flash of light (gold) and electrons. The flash of light is detected at the top and bottom of the liquid xenon chamber. An electric field pushes the electrons to the top of the chamber, where they generate a second flash of light (red). (Credit: SLAC National Accelerator Laboratory)

    Daniel Akerib, Thomas Shutt, and Maria Elena Monzani are leading the LZ team at SLAC National Accelerator Laboratory. The SLAC effort includes a program to purify xenon for LZ by removing krypton, an element that is typically found in trace amounts with xenon after standard refinement processes. “We have already demonstrated the purification required for LZ and are now working on ways to further purify the xenon to extend the science reach of LZ,” Akerib said.

    SLAC and Berkeley Lab collaborators are also developing and testing hand-woven wire grids that draw out electrical signals produced by particle interactions in the liquid xenon tank. Full-size prototypes will be operated later this year at a SLAC test platform. “These tests are important to ensure that the grids don’t produce low-level electrical discharge when operated at high voltage, since the discharge could swamp a faint signal from dark matter,” said Shutt.

    7
    Assembly of the prototype for the LZ detector’s core, known as a time projection chamber (TPC). From left: Jeremy Mock (State University of New York/Berkeley Lab), Knut Skarpaas, and Robert Conley. (Credit: SLAC National Accelerator Laboratory)

    Hugh Lippincott, a Wilson Fellow at Fermi National Accelerator Laboratory (Fermilab) and the physics coordinator for the LZ collaboration, said, “Alongside the effort to get the detector built and taking data as fast as we can, we’re also building up our simulation and data analysis tools so that we can understand what we’ll see when the detector turns on. We want to be ready for physics as soon as the first flash of light appears in the xenon.” Fermilab is responsible for implementing key parts of the critical system that handles, purifies, and cools the xenon.

    All of the components for LZ are painstakingly measured for naturally occurring radiation levels to account for possible false signals coming from the components themselves. A dust-filtering cleanroom is being prepared for LZ’s assembly and a radon-reduction building is under construction at the South Dakota site—radon is a naturally occurring radioactive gas that could interfere with dark matter detection. These steps are necessary to remove background signals as much as possible.

    8
    A rendering of the Surface Assembly Laboratory in [at SURF] South Dakota where LZ components will be assembled before they are relocated underground. (Credit: LZ collaboration)

    The vessels that will surround the liquid xenon, which are the responsibility of the U.K. participants of the collaboration, are now being assembled in Italy. They will be built with the world’s most ultra-pure titanium to further reduce background noise.

    To ensure unwanted particles are not misread as dark matter signals, LZ’s liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals. Brookhaven National Laboratory is handling the production of another very pure liquid, known as a scintillator fluid, that will go into this tank.

    9
    A production prototype of highly purified, gadolinium-doped scintillator fluid, viewed under ultraviolet light. Scintillator fluid will surround LZ’s xenon tank and will help scientists veto the background “noise” of unwanted particle signals. (Credit: Brookhaven National Laboratory)

    The cleanrooms will be in place by June, Gilchriese said, and preparation of the cavern where LZ will be housed is underway at SURF. Onsite assembly and installation will begin in 2018, he added, and all of the xenon needed for the project has either already been delivered or is under contract. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry.

    “South Dakota is proud to host the LZ experiment at SURF and to contribute 80 percent of the xenon for LZ,” said Mike Headley, executive director of the South Dakota Science and Technology Authority (SDSTA) that oversees SURF. “Our facility work is underway and we’re on track to support LZ’s timeline.”

    UK scientists, who make up about one-quarter of the LZ collaboration, are contributing hardware for most subsystems. Henrique Araújo, from Imperial College London, said, “We are looking forward to seeing everything come together after a long period of design and planning.”

    10
    LZ participants conduct a quality-control inspection of photomultiplier tube bases that are being manufactured at Imperial College London. (Credit: Henrique Araújo /Imperial College London)

    Kelly Hanzel, LZ project manager and a Berkeley Lab mechanical engineer, added, “We have an excellent collaboration and team of engineers who are dedicated to the science and success of the project.” The latest approval milestone, she said, “is probably the most significant step so far,” as it provides for the purchase of most of the major components in LZ’s supporting systems.

    For more information about LZ and the LZ collaboration, visit: http://lz.lbl.gov/.

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

    Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders.

    See the full article here .

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    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 1:28 pm on November 28, 2016 Permalink | Reply
    Tags: Bolometers, , EDELWEISS experiment, IPNL, , , WIMPS   

    From IPNL: “First Results of the EDELWEISS III experiment” 

    ipnl-bloc

    Institut de Physique Nucleaire de Lyon

    13 May, 2016 [I just found these guys]
    Cazes Antoine

    1
    EDELWEISS bolometers before installation. No image credit

    The EDELWEISS experiment aims to detect WIMPs, a candidate for dark matter particles. It is located in the Modane Underground Laboratory. The experiment operates bolometers cooled to tens of Millikelvin where a WIMP might collide with a germanium nucleus and produce its recoil. This recoil is then measured by the resulting temperature rise (few microkelvin) and ionisation production (Germanium is a semiconductor material). This double measurment allow to identify nuclear recoils and thus eliminating much of the background due to gamma rays from natural radioactivity.

    For the third phase of the EDELWEISS experiment, the bolometers have been greatly improved and the cryostat was redesigned to reduce background noise and to accommodate a larger mass of detector. The experiment ran from July 2014 to April 2015. The data, equivalent to 582 kg.days were blindly analyzed and the background rejection was performed using a Boosted Decision Tree. This results in a lack of detection of WIMP and an improvement, by a factor varying between 12 to 41, compared to the previous limit EDELWEISS II: for a WIMP 5 GeV / c2, the collision cross sections WIMP -nucléon above 4.3×10-40 cm2 are excluded and those above 9.4×10-44 cm2 for WIMPs 20 GeV / c2.

    The EDELWEISS experiment is now working on a major R & D with the aim of lowering bolometers detection thresholds to explore collisions with low-mass WIMP (below 5 GeV / c2). This work is carried out in particular with the IOL cryostat installed IPNL.

    Science paper:
    Constraints on low-mass WIMPs from the EDELWEISS-III dark matter search

    See the full article here .

    ipnl-campus

     
  • richardmitnick 6:33 pm on October 17, 2016 Permalink | Reply
    Tags: , , , WIMPS   

    From SURF: “LUX: The end of an era” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    October 17, 2016
    Constance Walter

    1
    The top of the the LUX detector can be seeen emerging from the water tank. From Left Doug Tiedt, Wei Ji, and Ken Wilson work on the removal.
    Credit: Matthew Kapust

    Five years ago, the Large Underground Xenon (LUX) experiment began its long journey to the Davis Cavern on the 4850 Level of Sanford Lab. Results published in 2013 proved LUX to be the most sensitive dark matter experiment in the world. When LUX completed its 300-live-day run in May of this year, the world learned LUX was even more sensitive than previously determined.

    Earlier this month, the LUX collaboration began decommissioning the experiment. “It’s bittersweet, the end of an era, but it was time,” said Simon Fiorruci, a LUX collaborator from Lawrence Berkeley National Laboratory.

    “The detector delivered everything we promised in sensitivity and then went even further,” said Rick Gaitskell, physics professor at Brown University and a co-spokesperson for LUX. “So there is great pride, but also sadness to see an old friend being pensioned off. Of course, the success of LUX acted as an important pathfinder for the larger LZ experiment.”

    LZ (LUX-ZEPLIN), the second-generation dark matter detector, will hold 30 times more xenon and be 100 times more sensitive than LUX.

    Lux Zeplin project at SURF
    Lux Zeplin project at SURF

    It will continue the hunt for WIMPs, or weakly interacting massive particles. The top prospects for explaining dark matter are observed only through gravitational effects on galaxies.

    “The nature of dark matter, which comprises 85 percent of all matter in the universe, is one of the most perplexing mysteries in all of contemporary science,” said Harry Nelson, LZ spokesperson and a physics professor at University of California, Santa Barbara. “Just as science has elucidated the nature of familiar matter, LZ will lead science in testing one of the most attractive hypotheses for the nature of dark matter.”

    LZ recently received approval from the Department of Energy that set in motion the build-out of major components and the preparation of the Davis Cavern. But to make way for the new experiment, LUX must be completely uninstalled—with the exception of the water tank in which LZ will be housed.

    “Essentially, we have to do everything we did to build the LUX detector, but in reverse,” Gaitskell said.

    But decommissioning isn’t as simple as pulling the detector vessel out of the 72,000-gallon water tank in which it has resided for four years. The team first had to remove the 370 kg of xenon and prepare it for transport to SLAC National Accelerator Laboratory. Then they disabled the support system and disconnected thousands of cables. Next, the detector was removed from the water tank and readied for its trip to the surface. The vessel will be opened and the parts analyzed for possible use in LZ.

    “By March we should be removing the last table and chair and handing the space over to LZ,” Fiorruci said.

    Construction of LZ will begin in 2017. Operations are expected to begin in 2020.

    “And so, the process of build, operate, and deconstruct begins again,” Gaitskell said.

    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 4:08 pm on September 26, 2016 Permalink | Reply
    Tags: , , , WIMPS   

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

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    September 26, 2016
    Constance Walter

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

     
  • richardmitnick 1:43 pm on July 26, 2016 Permalink | Reply
    Tags: , , , , WIMPS   

    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 1:29 pm on November 11, 2015 Permalink | Reply
    Tags: , , WIMPS, XENON1T experiment   

    From Symmetry: “Dark matter’s newest pursuer” 

    Symmetry

    11/11/15
    Mike Ross

    Scientists have inaugurated the new XENON1T experiment at Gran Sasso National Laboratory in Italy.

    1

    Researchers at a laboratory deep underneath the tallest mountain in central Italy have inaugurated XENON1T, the world’s largest and most sensitive device designed to detect a popular dark matter candidate.

    Gran Sasso XENON1T
    XENON1T tank

    “We will be the biggest game in town,” says Columbia University physicist Elena Aprile, spokesperson for the XENON collaboration, which has over the past decade designed, built and operated a succession of ever-larger experiments that use liquid xenon to look for evidence of weakly interacting massive dark matter particles or WIMPs, at the Gran Sasso National Laboratory.

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO
    Gran Sasso National Laboratory

    Interactions with these dark matter particles are expected to be rare: Just one a year for every 1000 kilograms of xenon. As a result, larger experiments have a better chance of intercepting a WIMP as it passes through the Earth.

    XENON1T’s predecessors—XENON 10 (2006 to 2009) and XENON 100 (2010 to the present)—held 25 and 160 kilograms of xenon, respectively. The new XENON11 experiment’s detector measures 1 meter high and 1 meter in diameter and contains 3500 kilograms of liquid xenon, nearly 10 times as much as the next-biggest xenon-filled dark matter experiment, the Large Underground Xenon [LUX] experiment.

    LUX Dark matter
    LUX


    Looking for WIMPs

    Should a WIMP collide with a xenon atom, kicking its nucleus or knocking out one of its electrons, the result is a burst of fast ultraviolet light and a bunch of free electrons. Scientists built a strong electric field in the XENON1T detector to direct these freed particles to the top of the chamber, where they will create a second burst of light. The relative timing and brightness of the two flashes will help the scientists determine the type of particle that created them.

    “Since our detectors can detect even a single electron or photon, XENON1T will be sensitive to even the most feeble particle interactions,” says Rafael Lang, a Purdue University physicist on the XENON collaboration.

    Scientists cool the xenon to minus 163 degrees Fahrenheit to turn it into a liquid three times denser than water. One oddity of xenon is that its boiling temperature is only 7 degrees Fahrenheit above its melting temperature. So “we have to control our temperature and pressure precisely,” Aprile says.

    The experiment is shielded from other particles such as cosmic rays by separate layers of water, lead, polyethylene and copper—not to mention 1400 meters of Apennine rock that lie above the Gran Sasso lab’s underground tunnels.

    Keeping the xenon free of contaminants is essential to the detector’s sensitivity. Oxygen, for example, can trap electrons. And the decay of some radioactive krypton isotopes, which are difficult to separate from xenon, can obscure a WIMP signal. The XENON collaboration’s solution is to continuously circulate and filter 100 liters of xenon gas every minute from the top of the detector through a filtering system before chilling it and returning it to service.
    A matter of scale

    XENON researchers hope that their new experiment will finally be the one to see definitive evidence of WIMPs. But just in case, XENON1T was designed to accommodate a swift upgrade to 7000 kilograms of xenon in its next iteration. (At the same time, the LUX and UK-based Zeplin groups joined forces to design a similar-scale xenon detector, LZ.)

    “If we see nothing with XENON1T, it will still be worth it to move up to the 7000-kilogram device, since it will be relatively easy to do that,” Aprile says. “If we do see a few events with XENON1T—and we’re sure they are from the dark matter particle—then the best way to prove that it’s real is to confirm that result with a larger, more sensitive experiment.

    “In any case,” Aprile says, “we should know whether the WIMP is real or not before 2020.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:09 pm on July 15, 2015 Permalink | Reply
    Tags: , , , WIMPS   

    From Symmetry: “Miraculous WIMPs” 

    Symmetry

    July 15, 2015
    Manuel Gnida

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    What are WIMPs, and what makes them such popular dark matter candidates?

    Invisible dark matter accounts for 85 percent of all matter in the universe, affecting the motion of galaxies, bending the path of light and influencing the structure of the entire cosmos. Yet we don’t know much for certain about its nature.

    Most dark matter experiments are searching for a type of particles called WIMPs, or weakly interacting massive particles.

    “Weakly interacting” means that WIMPs barely ever “talk” to regular matter. They don’t often bump into other matter and also don’t emit light—properties that could explain why researchers haven’t been able to detect them yet.

    Created in the early universe, they would be heavy (“massive”) and slow-moving enough to gravitationally clump together and form structures observed in today’s universe.

    Scientists predict that dark matter is made of particles. But that assumption is based on what they know about the nature of regular matter, which makes up only about 4 percent of the universe.

    WIMPs advanced in popularity in the late 1970s and early 1980s when scientists realized that particles that naturally pop out in models of Supersymmetry could potentially explain the seemingly unrelated cosmic mystery of dark matter.

    Supersymmetry, developed to fill gaps in our understanding of known particles and forces, postulates that each fundamental particle has a yet-to-be-discovered superpartner. It turns out that the lightest one of the bunch has properties that make it a top contender for dark matter.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    “The lightest supersymmetric WIMP is stable and is not allowed to decay into other particles,” says theoretical physicist Tim Tait of the University of California, Irvine. “Once created in the big bang, many of these WIMPs would therefore still be around today and could have gone unnoticed because they rarely produce a detectable signal.”

    When researchers use the properties of the lightest supersymmetric particle to calculate how many of them would still be around today, they end up with a number that matches closely the amount of dark matter experimentally observed—a link referred to as the “WIMP miracle.” Many researchers believe it could be more than coincidence.

    “But WIMPs are also popular because we know how to look for them,” says dark matter hunter Thomas Shutt of Stanford University and SLAC National Accelerator Laboratory. “After years of developments, we finally know how to build detectors that have a chance of catching a glimpse of them.”

    2

    Shutt is co-founder of the LUX experiment and one of the key figures in the development of the next-generation LUX-ZEPLIN experiment. He is one member of the group of scientists trying to detect WIMPs as they traverse large, underground detectors.

    Lux Dark Matter 2
    LUX

    Lux Zeplin project
    LUX-ZEPLIN

    Other scientists hope to create them in powerful particle collisions at CERN’s Large Hadron Collider.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    “Most supersymmetric theories estimate the mass of the lightest WIMP to be somewhere above 100 gigaelectronvolts, which is well within LHC’s energy regime,” Tait says. “I myself and others are very excited about the recent LHC restart. There is a lot of hope to create dark matter in the lab.”

    3

    A third way of searching for WIMPs is to look for revealing signals reaching Earth from space. Although individual WIMPs are stable, they decay into other particles when two of them collide and annihilate each other. This process should leave behind detectable amounts of radiation. Researchers therefore point their instruments at astronomical objects rich in dark matter such as dwarf satellite galaxies orbiting our Milky Way or the center of the Milky Way itself.

    4

    “Dark matter interacts with regular matter through gravitation, impacting structure formation in the universe,” says Risa Wechsler, a researcher at Stanford and SLAC. “If dark matter is made of WIMPs, our predictions of the distribution of dark matter based on this assumption must also match our observations.”

    Wechsler and others calculate, for example, how many dwarf galaxies our Milky Way should have and participate in research efforts under way to determine if everything predicted can also be found experimentally.

    So how would researchers know for sure that dark matter is made of WIMPs? “We would need to see conclusive evidence for WIMPs in more than one experiment, ideally using all three ways of detection,” Wechsler says.

    In the light of today’s mature detection methods, dark matter hunters should be able to find WIMPs in the next five to 10 years, Shutt, Tait and Wechsler say. Time will tell if scientists have the right idea about the nature of dark matter.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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