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  • richardmitnick 7:02 am on September 9, 2014 Permalink | Reply
    Tags: , , , , Dark Energy/Dark Matter,   

    From The Royal Astronomical Society: “Interactive dark matter could explain Milky Way’s missing satellite galaxies” 

    Royal Astronomical Society

    Royal Astronomical Society

    Tuesday, 09 September 2014
    Media contacts

    Durham University Media Relations Team
    Tel: +44 (0)191 334 6075
    media.relations@durham.ac.uk

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307 x214
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contacts

    All the contacts are available for interview on Monday 8 and Tuesday 9 September.

    Professor Carlton Baugh
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 43542
    c.m.baugh@durham.ac.uk

    Ryan Wilkinson
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 45753
    ryan.wilkinson@durham.ac.uk

    Jascha Schewtschenko
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 43710
    j.a.schewtschenko@durham.ac.uk

    Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.

    This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.

    sim
    The simulated distribution of dark matter in a Milky Way-like galaxy for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilised. Credit: Durham University. Now cosmologists and particle physicists at the Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.

    Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.

    Scientists think clumps of dark matter – or haloes – that emerged from the early Universe, trapped the intergalactic gas needed to form stars and galaxies. Scattering the dark matter particles wipes out the structures that can trap gas, stopping more galaxies from forming around the Milky Way and reducing the number that should exist.

    Lead author Dr Celine Boehm, in the Institute for Particle Physics Phenomenology at Durham University, said: “We don’t know how strong these interactions should be, so this is where our simulations come in.”

    “By tuning the strength of the scattering of particles, we change the number of small galaxies, which lets us learn more about the physics of dark matter and how it might interact with other particles in the Universe.”

    “This is an example of how a cosmological measurement, in this case the number of galaxies orbiting the Milky Way, is affected by the microscopic scales of particle physics.”

    There are several theories about why there are not more galaxies orbiting the Milky Way, which include the idea that heat from the Universe’s first stars sterilised the gas needed to form stars. The researchers say their current findings offer an alternative theory and could provide a novel technique to probe interactions between other particles and cold dark matter.

    two
    Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way. Credit: Durham University.

    Co-author Professor Carlton Baugh said: “Astronomers have long since reached the conclusion that most of the matter in the Universe consists of elementary particles known as dark matter.”

    “This model can explain how most of the Universe looks, except in our own backyard where it fails miserably.”

    “The model predicts that there should be many more small satellite galaxies around our Milky Way than we can observe.”

    “However, by using computer simulations to allow the dark matter to become a little more interactive with the rest of the material in the Universe, such as photons, we can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us compared with what we originally thought.”

    The calculations were carried out using the COSMA supercomputer at Durham University, which is part of the UK-wide DiRAC super-computing framework.

    The work was funded by the Science and Technology Facilities Council and the European Union.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 2:32 pm on August 26, 2014 Permalink | Reply
    Tags: , , , CERN CAST, , Dark Energy/Dark Matter, International Axion Observatory (IAXO)   

    From CERN Courier: “IAXO: the International Axion Observatory” 

    CERN Courier

    Aug 26, 2014

    Igor G Irastorza, Universidad de Zaragoza, Michael Pivovaroff, Lawrence Livermore National Laboratory, and Herman Ten Kate, CERN, on behalf of the IAXO collaboration.

    A large superconducting magnet could open a new window on the dark universe.

    The recent discovery of a Higgs boson at CERN appears to represent the summit in the successful experimental verification of the Standard Model of particle physics.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    However, although essentially all of the data from particle accelerators are so far in perfect agreement with the model’s predictions, a number of important theoretical and observational considerations point to the necessity of physics beyond the Standard Model. An especially powerful argument comes from cosmology. The currently accepted cosmological model invokes two exotic ingredients – dark matter and dark energy – which pervade the universe. In particular, the observational evidence for dark matter (via its gravitational effects on visible matter) is now overwhelming, even though the particle-physics nature of both dark matter and dark energy remains a mystery.

    At the same time, the theoretical foundations of the Standard Model have shortcomings that prompt theorists to propose and explore hypothetical ways to extend it. Supersymmetry is one such hypothesis, which also naturally provides particles as candidates for dark matter, known as weakly interacting massive particles (WIMPs).

    Supersymmetry standard model

    Other extensions to the Standard Model predict particles that could lie hidden at the low-energy frontier, of which the axion is the prototype. The fact that supersymmetry has not yet been observed at the LHC, and that no clear signal of WIMPs has appeared in dark-matter experiments, has increased the community’s interest in searching for axions. However, there are independent and powerful motivations for axions, and dark matter composed of both WIMPs and axions is viable, implying that they should not be considered as alternative, exclusive solutions to the same problem.

    Axions appear in Standard Model extensions that include the Peccei–Quinn mechanism, which provides the most promising solution so far to one of the problems of the Standard Model: why do strong interactions seem not to violate charge–parity symmetry, while according to QCD, the standard theory of strong interactions, they should do? Unlike many particles predicted by theories that go beyond the Standard Model, axions should be light, and it might seem that they should have been detected already. Nevertheless, they could exist and remain unnoticed because they naturally couple only weakly with Standard Model particles.

    A generic property of axions is that they couple with photons in a way that axion–photon conversion (and vice versa) can occur in the presence of strong magnetic or electric fields. This phenomenon is the basis of axion production in the stars, as well as of most strategies for detecting axions. Magnets are therefore at the core of any axion experiment, as is the case for axion helioscopes, which look for axions from the Sun. This is the strategy followed by the CERN Axion Solar Telescope (CAST), which uses a decommissioned LHC test magnet (CERN Courier April 2010 p22). After more than a decade of searching for solar axions, CAST has put the strongest limits yet on axion–photon coupling across a range of axion masses, surpassing previous astrophysical limits for the first time and probing relevant axion models of sub-electron-volt mass. However, to improve these results and go deep into unexplored axion parameter space requires a completely new experiment.

    CERN CAST Axion Solar Telescope
    CERN CAST

    The International Axion Observatory (IAXO) aims for a signal-to-noise ratio 105 better than CAST. Such an improvement is possible only by building a large magnet, together with optics and detectors that optimize the axion helioscope’s figure of merit, while building on experience and concepts of the pioneering CAST project.

    cast
    Schematic view of IAXO

    The central component of IAXO is a superconducting toroid magnet. The detector relies on a high magnetic field distributed across a large volume to convert solar axions to detectable X-ray photons. The magnet’s figure of merit is proportional to the square of the product of magnetic field and length, multiplied by the cross-sectional area filled with the magnetic field. This consideration leads to a 25-m-long and 5.2-m-diameter toroid assembled from eight coils, generating 2.5 T in eight bores of 600 mm diameter, thereby having a figure of merit that is 300 times better than the CAST magnet. The toroid’s stored energy is 500 MJ.

    The design is inspired by the barrel and endcap toroids of the ATLAS experiment at the LHC, which has the largest superconducting toroids ever built and currently in operation at CERN. The superconductor used is a NbTi/Cu-based Rutherford cable co-extruded with aluminum – a successful technology common to most modern detector magnets. The IAXO detector needs to track the Sun for the longest possible period, so to allow rotation around the two axes, the 250-tonne magnet is supported at its centre of mass by a system used for large telescopes (figure 1). The necessary services for vacuum, helium supply, current and controls rotate together with the magnet.

    Each of the eight magnet bores will be equipped with X-ray focusing optics that rely on the fact that at X-ray energies the index of refraction is less than unity for most materials. By working at shallow (or grazing) incident angles, it is possible to make mirrors with high reflectivity. Mirrors are commonly used at synchrotrons and free-electron lasers to condition or focus the intense X-ray beams for user experiments, but IAXO requires optics with much larger apertures. For nearly 50 years, the X-ray astronomy and astrophysics community has been building telescopes following the design principle of Hans Wolter, employing two conic-shaped mirrors to provide true-imaging optics. This class of optics allows “nesting” – that is, placing concentric co-focal X-ray mirrors inside one another to achieve high throughput.

    The IAXO collaboration envisions using optics similar to those used on NASA’s NuSTAR – an X-ray astrophysics satellite with two focusing telescopes that operate in the 3–79 keV band. NuSTAR’s optics consist of thousands of thermally formed glass substrates deposited with multilayer coatings to enhance the reflectivity above 10 keV (figure 2). For IAXO, the multilayer coatings will be designed to match the softer 1–10 keV solar-axion spectrum.

    NASA NuSTAR
    NASA/Nu-STAR

    At the focal plane in each of the optics, IAXO will have small time-projection chambers read by pixelized planes of Micromegas. These detectors (figure 2) have been developed extensively within the CAST collaboration and show promise for detecting X-rays with a record background level of 10–8–10–7 counts/keV/cm2/s. This is achieved by the use of radiopure detector components, appropriate shielding, and offline discrimination algorithms on the 3D event topology in the gas registered by the pixelized read-out.

    Beyond the baseline described above, additional enhancements are being considered to explore extensions of the physics case for IAXO. Because a high magnetic field in a large volume is an essential component in any axion experiment, IAXO could evolve into a generic “axion facility” and facilitate various detection techniques. Most intriguing is the possibility of hosting microwave cavities and antennas to search for dark-matter axions in mass ranges that are complementary to those in previous searches.

    The growing IAXO collaboration has recently finished the conceptual design of the experiment, and last year a Letter of Intent was submitted to the SPS and PS Experiments Committee of CERN. The committee acknowledged the physics goals of IAXO and recommended proceeding with the next stage – the creation of the Technical Design Report. These are the first steps towards the realization of the most ambitious axion experiment so far.

    After more than three decades, the axion hypothesis remains one of the most compelling portals to new physics beyond the Standard Model, and must be considered seriously. IAXO will use CERN’s expertise efficiently to venture deep into unexplored axion parameter space. Complementing the successful high-energy frontier at the LHC, the IAXO facility would open a new window on the dark universe.

    See the full article here.

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  • richardmitnick 3:41 pm on August 18, 2014 Permalink | Reply
    Tags: , , , , , Dark Energy/Dark Matter   

    From Symmetry: “Dark Energy Survey kicks off second season” 

    Symmetry

    August 18, 2014
    No Writer Credit

    On August 15, with its successful first season behind it, the Dark Energy Survey collaboration began its second year of mapping the southern sky in unprecedented detail. Using the Dark Energy Camera, a 570-megapixel imaging device built by the collaboration and mounted on the Victor M. Blanco Telescope in Chile, the survey’s five-year mission is to unravel the fundamental mystery of dark energy and its impact on our universe.

    CTIO Victor M Blanco 4m Telescope
    Victor M Blanco 4m Telescope

    Dark Energy Camera
    Dark Energy Camera

    Along the way, the survey will take some of the most breathtaking pictures of the cosmos ever captured. The survey team has announced two ways the public can see the images from the first year.

    Today, the Dark Energy Survey relaunched its photo blog, Dark Energy Detectives. Once every two weeks during the survey’s second season, a new image or video will be posted to http://www.darkenergydetectives.org with an explanation provided by a scientist. During its first year, Dark Energy Detectives drew thousands of readers and followers, including more than 46,000 followers on its Tumblr site.

    Starting on September 1, the one-year anniversary of the start of the survey, the data collected by DES in its first season will become freely available to researchers worldwide. The data will be hosted by the National Optical Astronomy Observatory. The Blanco Telescope is hosted at the National Science Foundation’s Cerro Tololo Inter-American Observatory, the southern branch of NOAO.

    In addition, the hundreds of thousands of individual images of the sky taken during the first season are being analyzed by thousands of computers at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Fermi National Accelerator Laboratory and Lawrence Berkeley National Laboratory. The processed data will also be released in coming months.

    Scientists on the survey will use these images to unravel the secrets of dark energy, the mysterious substance that makes up 70 percent of the mass and energy of the universe. Scientists have theorized that dark energy works in opposition to gravity and is responsible for the accelerating expansion of the universe.

    “The first season was a resounding success, and we’ve already captured reams of data that will improve our understanding of the cosmos,” says DES Director Josh Frieman of Fermilab and the University of Chicago. “We’re very excited to get the second season under way and continue to probe the mystery of dark energy.”

    While results on the survey’s probe of dark energy are still more than a year away, a number of scientific results have already been published based on data collected with the Dark Energy Camera.

    The first scientific paper based on Dark Energy Survey data was published in May by a team led by Ohio State University’s Peter Melchior. Using data that the survey team acquired while putting the Dark Energy Camera through its paces, they used a technique called gravitational lensing to determine the masses of clusters of galaxies.

    In June, Dark Energy Survey researchers from the University of Portsmouth and their colleagues discovered a rare superluminous supernova in a galaxy 7.8 billion light years away. A group of students from the University of Michigan discovered five new objects in the Kuiper Belt, a region in the outer reaches of our solar system, including one that takes over a thousand years to orbit the Sun.

    kuiper
    Kuiper Belt

    In February, Dark Energy Survey scientists used the camera to track a potentially hazardous asteroid that approached Earth. The data was used to show that the newly discovered Apollo-class asteroid 2014 BE63 would pose no risk.

    Several more results are expected in the coming months, says Gary Bernstein of the University of Pennsylvania, project scientist for the Dark Energy Survey.

    The Dark Energy Camera was built and tested at Fermilab. The camera can see light from more than 100,000 galaxies up to 8 billion light-years away in each crystal-clear digital snapshot.

    “The Dark Energy Camera has proven to be a tremendous tool, not only for the Dark Energy Survey, but also for other important observations conducted year-round,” says Tom Diehl of Fermilab, operations scientist for the Dark Energy Survey. “The data collected during the survey’s first year—and its next four—will greatly improve our understanding of the way our universe works.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 4:30 pm on August 14, 2014 Permalink | Reply
    Tags: , , , , Dark Energy/Dark Matter,   

    From SPACE.com: ” Could Mystery Signal be First Detection of Dark Matter?” 

    space-dot-com logo

    SPACE.com

    August 14, 2014
    Ian O’Neill

    Through the analysis of light from distant galactic clusters, astronomers have detected a mysterious signal that they’re having a hard time explaining. Although the signal is weak, could it be the much sought-after direct evidence for dark matter?

    Dark matter pervades the entire universe and makes up for the bulk of its mass, but what is it? We know it’s out there and oodles of indirect evidence for its presence, but seeing a direct signal has so far proven elusive.

    When observing a galactic cluster, for example, we can gauge how much mass it contains by how much light is bent around the cluster. The greater the effect on passing light beams, the greater the space-time warping, the greater the cluster’s mass. When astronomers estimate the cluster’s mass, they tally up all the visible matter (i.e. stars), but the amount of visible mass comes way short of the cluster’s space-time-warping mass. There’s therefore mass locked up in “invisible” matter called, simply, “dark matter.”

    The bulk of dark matter is thought to be composed of non-baryonic matter. As opposed to baryonic matter — matter that we know and love like protons, neutrons and all the quarks in between — non-baryonic matter does not interact with electromagnetic radiation. In other words, we can’t directly see it. It does, however, interact gravitationally with normal matter, hence why we can see its gravitational effects on galactic clusters.

    But in a newly published study, astronomers analyzing X-ray radiation from distant galactic clusters have spotted a signal, with a specific energy, that doesn’t seem to be associated with any known element or chemical reaction.

    Galactic Clusters = Dark Matter Hunting Grounds

    Galaxies can become gravitationally bound, creating clusters of galaxies. Our Milky Way, for example, is one member of the aptly-named “Local Group” of galaxies, which also includes the neighboring heavyweight Andromeda. Though the Local Group contains around three dozen other galaxies, as far as galactic clusters go, it’s actually quite dinky. Many clusters contain thousands of galaxies that have immense gravitational dominance over their surroundings.

    Local Group
    Local Group

    ANALYSIS: Is Earth Surrounded by Dark Matter?

    It is therefore believed that these massive gravitational islands “pool” dark matter, causing the clusters to pack on the pounds, making them prime focal points for the search for direct evidence of dark matter.

    In these clusters, the space between the galaxies is not empty, it’s actually filled with hot gases that have accumulated from billions of years of supernova explosions. These gases generate X-rays that can be readily studied by space-based X-ray telescopes. The elements oxygen, neon, magnesium, silicon, sulfur, argon, calcium, iron, nickel, chromium and manganese have all been identified via their X-ray signals, but Harvard-Smithsonian Center for Astrophysics astronomers have found an X-ray signal detected by the European XMM-Newton space observatory that doesn’t fit in.

    ESA XMM Newton
    ESA/XMM-Newton

    Although more work is needed to tease the signal from the background noise, after analysis of 73 clusters, the same signal keeps appearing in observational data. A few of the clusters have also been studied by NASA’s Chandra X-ray observatory, which has also identified the signal at varying strengths. One explanation could be that they have detected the specific X-ray emission from the decay of the hypothesized “sterile neutrino” — a type of non-baryonic particle that could be a significant dark matter candidate.

    NASA Chandra Telescope
    NASA/Chandra

    The researchers urge caution over the detection of this X-ray signal — that is centered around an energy of 3.56 keV — however. Although the signal has been detected across a large sample of clusters and it appears to be real, its statistical significance is well below the threshold that can be considered to be a “discovery.” Better resolution of this emission line is required, something that may be attainable with the launch of the Japanese Astro-H X-ray observatory in 2015.

    The jury may still be out as to whether this mystery X-ray signal is indeed caused by the decay process of sterile neutrinos, but it’s exciting to think that we may be on the verge of finally uncovering a direct dark matter signal at last.

    See the full article here.

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  • richardmitnick 8:39 am on August 11, 2014 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter,   

    From Brookhaven Lab: “Dark Interactions Workshop Brings Global Physicists to Brookhaven” 

    Brookhaven Lab

    August 11, 2014
    Chelsea Whyte

    people
    Nearly 80 physicists — representing experiments from laboratories including Thomas Jefferson National Accelrator Facility, the Large Hadron Collider, the Mainz Microtron, SLAC National Accelerator Laboratory, KEK, and universities involved in other dark particle detector experiments — attended the Dark Interactions Workshop at Brookhaven National Laboratory in June 2014.

    For three days in June, physicists from around the world came together at the U.S. Department of Energy’s Brookhaven National Laboratory for the inaugural physics workshop “Dark Interactions: Perspectives from Theory and Experiment,” chaired by Brookhaven physicist Ketevi Assamagan. He jointly organized the workshop with Brookhaven physicist Hooman Davoudiasl and Stony Brook University assistant professor of physics Rouven Essig.

    The goal of the workshop was to review and discuss the theoretical context as well as the status and future of the searches for dark sector particles, such as dark vector bosons, and the implications for dark matter.

    “We hope to continue this meeting in the years to come. We gain a lot by sharing ideas between theorists and experimentalists,” Assamagan said. Nearly 80 physicists attended the workshop to hear presentations that covered a range of topics on the frontier of new physics: the theories and experiments trying to track down dark matter, the mysterious substance that neither emits nor absorbs light, but is theorized to comprise nearly 27% of the cosmos.

    So far, despite the tremendous amount of evidence for the existence of dark matter, nobody knows its identity; but if anyone is going to devise a way to determine its makeup, it could be one of the physicists in attendance at the workshop. Over the course of several days, they discussed theoretical motivations for the search for dark matter, and several experiments already looking for the mystery matter, including:

    The DarkLight, HPS, and APEX experiments at Thomas Jefferson National Accelerator Facility;
    The CMS, ATLAS, ALICE and LHCb experiments at the Large Hadron Collider in Geneva, Switzerland;
    The A1 collaboration at the Mainz Microtron;
    Dark photon and low-mass Higgs searches at the BaBar detector at the SLAC National Accelerator Laboratory;
    The Belle Collaboration at KEK
    The PHENIX experiment at Brookhaven National Laboratory
    The Muon g-2 experiment [at Fermilab]
    The Axion Dark Matter Experiment at the University of Washington
    LHC experiments, namely ATLAS, CMS, ALICE and LHCb also contribute to the searches for Dark Matter. Ketevi Assamagan (BNL) and Oliver Keith Baker (Yale University) are working on some of the ATLAS analyses that may provide clues into the nature of Dark Matter.

    “It’s hard to believe dark matter is an idea that’s 80 years old,” said Professor David Brown of the University of Louisville. “Of course, we still don’t know what dark matter is. But colliders let us search for dark particles.”

    “Understanding the nature of dark matter poses one of the most urgent problems for our fundamental description of the Universe,” Davoudiasl said. “Interactive meetings, like DI2014, allow us to share various points of view on the scope of theoretical and experimental opportunities, as well as challenges, that lie ahead in the quest to uncover the properties of dark matter.”

    The attendees shared results from experiments all over the world, with tantalizing hints at the nature of dark matter. And as they continue this search, coordination across disciplines and national borders remains key to collaboration.

    “An enormous amount of progress has been made over the last few years in the search for dark matter and dark forces,” Essig said. “All of us hope that the current generation of experiments will be successful at finding new physics.”

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

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  • richardmitnick 4:31 pm on August 4, 2014 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, ,   

    From Sanford Underground Research Facility: “DOE, NSF to fund LUX-ZEPLIN (LZ) experiment at Sanford Lab” 

    Sanford Underground Research facility

    Sanford Underground levels

    Sanford Underground Research facility
    August 4, 2014
    Constance Walter

    LUX-ZEPLIN (LZ), a second generation dark matter experiment, got a big boost when the Department of Energy and National Science Foundation selected it as one of three experiments that will be funded in the next-generation dark matter search. LZ will build on the Large Underground Xenon (LUX) experiment, which has been operating at the 4850 Level of the Sanford Underground Research Facility since 2012, and on the ZEPLIN dark matter program in the United Kingdom, which pioneered the use of these types of detectors underground.

    “We emerged from a very intense competition,” said Daniel McKinsey, professor of physics at Yale and a spokesperson for LUX. “We have the most sensitive detector in the world, with LUX. LZ will be hundreds of times more sensitive. It’s gratifying to see that our approach is being validated.”

    Construction on the supersized detector is scheduled to begin in 2016, with a commissioning date of 2018. Plans for LZ have been in the works for several years.

    “This is great news for the future of Dark Matter exploration and the Sanford Lab,” said Mike Headley, Executive Director of the South Dakota Science and Technology Authority. “The LZ experiment will play a key role in the future of the lab and we’re pleased that the DOE selected the experiment. It certainly will extend the state’s investment in this world-class facility.”

    Rick Gaitskell, Hazard Professor of Physics at Brown, is a founding member of LZ and also co-spokesperson for the LUX experiment.

    “The go-ahead from DOE and NSF is a major event,” Gaitskell said. “The LZ experiment will continue the liquid xenon direct dark matter search program at Sanford Lab, which we started with the operation of LUX in 2013. LUX will run until 2016 when we will replace it with LZ, which can provide a further improvement in sensitivity of two orders of magnitude due to its significant increase in size.”

    Even if LUX makes a dark matter detection before LZ is up and running, LZ will still be necessary to confirm the detection and fully characterize the nature of WIMPS, Gaitskell said.

    “This green light is a clear indication of the value the agencies see, not only in all the preparatory work that has gone into LZ, but also in the existing accomplishment of LUX and Sanford Lab these past few years,” said Simon Fiorucci, a research scientist at Brown who is the science coordinator for LUX and simulations coordinator for LZ. “LZ will be timed so that it is ready to start operations when LUX delivers its final results and reaches the limits of its technology. It will be a very natural transition.”

    Harry Nelson, professor of physics at the University of California, Santa Barbara and spokesperson for the LZ Collaboration, said, “We still have a lot of work to do. Basically, we got the green light to go the next green light, then the next green light.” Still, he continued, “Everyone is excited.”

    See the full article here.

    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

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  • richardmitnick 12:06 pm on July 29, 2014 Permalink | Reply
    Tags: , , , , , Dark Energy/Dark Matter   

    From ARS Technica: “Dark matter makes up 80% of the Universe—but where is it all?” 

    Ars Technica
    ARS Technica

    July 27 2014
    Matthew Francis

    It’s in the room with you now. It’s more subtle than the surveillance state, more transparent than air, more pervasive than light. We may not be aware of the dark matter around us (at least without the ingestion of strong hallucinogens), but it’s there nevertheless.

    dm
    Composite image of X-ray (pink) and weak gravitational lensing (blue) of the famous Bullet Cluster of galaxies.
    X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.

    Although we can’t see dark matter, we know a bit about how much there is and where it’s located. Measurement of the cosmic microwave background shows that 80 percent of the total mass of the Universe is made of dark matter, but this can’t tell us exactly where that matter is distributed. From theoretical considerations, we expect some regions—the cosmic voids—to have little or none of the stuff, while the central regions of galaxies have high density. As with so many things involving dark matter, though, it’s hard to pin down the details.

    Cosmic Background Radiation Planck
    CMB per ESA/Planck

    ESA Herschel
    ESA/Planck

    Unlike ordinary matter, we can’t see where dark matter is by using the light it emits or absorbs. Astronomers can only map dark matter’s distribution using its gravitational effects. That’s especially complicated in the denser parts of galaxies, where the chaotic stew of gas, stars, and other forms of ordinary matter can mask or mimic the presence of dark matter. Even in the galactic suburbs or intergalactic space, dark matter’s transparency to all forms of light makes it hard to locate with precision.

    Despite that difficulty, astronomers are making significant progress. While individual galaxies are messy, analyzing surveys of huge numbers of them can provide a gravitational map of the cosmos. Astronomers also hope to overcome the messiness of galaxies and estimate how much dark matter must be in the central regions using careful observation of the motion of stars and gas.

    There’s also been a tantalizing hint of dark matter particles themselves in the form of a signal that may come from their annihilation near the center of the Milky Way. If this is borne out by other observations, it could constrain dark matter’s properties while avoiding messy gravitational considerations. Adding it all up, it’s a promising time for mapping the location of dark matter, even as researchers still build particle detectors to identify what it is.

    A (very) brief history of dark matter

    In the 1930s, Fritz Zwicky measured the motion of galaxies within the Coma galaxy cluster. Based on simple gravitational calculations, he found that they shouldn’t move as they did unless the cluster contained a lot more mass than he could see. As it turned out, Zwicky’s estimates of how much matter there was were too large by a huge factor. Still, he was correct in the broader picture: more than 80 percent of a galaxy cluster’s mass isn’t in the form of atoms.

    Zwicky’s work didn’t get a lot of attention at the time, but Vera Rubin’s later observations of spiral galaxies were another matter. She found that the combined stars and gas had too little mass to explain the rotation rates she measured. Between Rubin’s work and subsequent measurements, astronomers established that every spiral galaxy is engulfed by a roughly spherical halo (as it is called) of matter—matter that’s transparent to every form of light.

    The Bullet Cluster

    That leads us to the “Bullet Cluster,” one of the most important systems in astronomy.

    bullt
    X-ray photo by Chandra X-ray Observatory of the Bullet Cluster (1E0657-56). Exposure time was 0.5 million seconds (~140 hours) and the scale is shown in megaparsecs. Redshift (z) = 0.3, meaning its light has wavelengths stretched by a factor of 1.3. Based on today’s theories this shows the cluster to be about 4 billion light years away. In this photograph, a rapidly moving galaxy cluster with a shock wave trailing behind it seems to have hit another cluster at high speed. The gases collide, and gravitational fields of the stars and galaxies interact. When the galaxies collided, based on black-body temperature readings, the temperature reached 160 million degrees and X-rays were emitted in great intensity, claiming title of the hottest known galactic cluster. Studies of the Bullet cluster, announced in August 2006, provide the best evidence to date for the existence of dark matter.

    First described in 2006, it’s actually a pair of galaxy clusters observed in the act of colliding. Researchers mapped it in visible and X-ray light, finding that it consists of two clumps of galaxies. But it’s the stuff they couldn’t image directly that ensured the Bullet Cluster is rightfully cited as one of the best pieces of evidence for dark matter’s existence (the title of the paper announcing the discovery even calls it “direct empirical proof”).

    Galaxy clusters are the biggest individual objects in the Universe. They can contain thousands of galaxies bound to each other by mutual gravity. However, the stuff within those galaxies—stars, gas, dust—is outweighed by an extremely hot, gaseous plasma between them, which shines brightly in X-rays. In the Bullet Cluster, the collision between the two clusters created a shock wave in the plasma (the shape of this shock wave gives the structure its name).

    More dramatically, though, the astronomers who described the cluster used gravitational lensing—the distortion of light from more distant galaxies by the mass within the cluster—to map the distribution of most of the material in the Bullet Cluster. That method is known as “weak gravitational lensing.” Unlike the sexier strong lensing, weak lensing doesn’t create multiple images of the more distant galaxies. Instead, it slightly warps the light from background objects in a small but measurable way, depending on the amount and concentration of mass in the “lens”—in this case, the cluster.

    Astronomers found the shocked plasma, which represents most of the mass of the Bullet Cluster, was almost entirely in the region between the two clusters, separated from the galaxies. However, the mass was largely concentrated around the galaxies themselves. This enabled a clear, independent measurement of the amount of dark matter, separate from the mass of the gas.

    The results also confirmed some predictions about the behavior of dark matter. Thanks to the shock of the collision, the plasma stayed in the region between the two clusters. Since the dark matter doesn’t interact much with either itself or normal matter, it passed right through the collision without any noticeable change.

    It’s a phenomenal discovery, but it’s only one galaxy cluster, and that ain’t enough. Science is inherently greedy for evidence (as it should be). A single example of anything tells us very little in a Universe full of possibilities. We want to know if dark matter always clusters around galaxies or if it can be more widely dispersed. We want to know where all the dark matter is, in all galaxy clusters and beyond, throughout the entire cosmos.

    A dark matter census

    Weak gravitational lensing provides a method to search for dark matter in other galaxy clusters, too, as well as even larger and smaller structures. Princeton University astronomers Neta Bahcall and Andrea Kulier took a weak lensing census of 132,473 galaxy groups and clusters, all within a well-defined patch of the sky but at a range of distances from the Milky Way. (“Groups” are smaller associations of galaxies; for example, the Milky Way is the second largest galaxy in the Local Group, after the Andromeda galaxy.) While individual galaxy clusters usually can’t tell us much, a large sample allowed the astronomers to treat the problem statistically—weak lensing effects that were too small to spot for a single cluster became obvious when looking at hundreds of thousands.

    For example, a typical quantity used in studying galaxies is the mass-to-light ratio. To measure this statistically, Bahcall and Kulier looked at the cumulative amount of light (mostly emitted by stars) and weak lensing (mostly from dark matter), starting from the centers of each cluster and working outward. They found something intriguing: the amount of mass and light increased in tandem and then leveled off together. That means neither the dark matter nor the light extends farther than the other: the stars inside these groups and clusters were a very good tracer for the dark matter. That’s surprising because stars are typically less than two percent of the mass in a cluster, with the balance of ordinary matter made up by gas and dust.

    As Kulier told Ars, “The total amount of dark matter in galaxy groups and clusters might be accounted for entirely by the amount of dark matter in the halos of their constituent galaxies.” That’s an average result, though; the details could look quite different. “This does not necessarily imply that the halos are still ‘attached’ to the galaxies,” Kulier said. In other words, when galaxies came together to form clusters, the stronger forces acting on galaxies and their stars could in principle separate them from their dark matter but leave everything inside the cluster thanks to mutual gravity.

    Kulier pointed out that these results provide strong support for the “hierarchical” model of structure formation: “smaller structures collapse earlier than larger ones, so that galaxies form first and then merge together to form larger structures like clusters.” The Bullet Cluster is an archetypical example of this, but things could be otherwise. For instance, dark matter could have ended up in the center of clusters, separate from the galaxies and their individual halos.

    But that’s not what astronomers see. In their analysis, Bahcall and Kulier also calculated that the total ratio of dark matter to ordinary matter in galaxy clusters matches that of the Universe as a whole. That’s another strong piece of evidence in favor of the standard model in cosmology: maybe most of the dark matter everywhere is in galactic halos.

    Every galaxy wears a halo

    halo
    Computer reconstruction of the location of mass in terms of how it affects the image of distant galaxies through weak lensing.
    S. Colombi (IAP), CFHT Team

    So what about the halos themselves and the galaxies that wear them? Historically, dark matter was first recognized for its role in spiral galaxies. However, it’s one thing to say that dark matter is present. It’s another to map out where it is—especially in the dense, star-choked inner parts of galaxies.

    Spiral galaxies consist of three basic parts: the disk, the bulge, and the halo. The disk is a thin region containing the spiral arms and most of the bright stars. The bulge is the central, densest part, with large populations of older stars and (at its very heart) a supermassive black hole. The halo is a more or less spherical region containing a smattering of stars; it envelops the other regions, extending several times beyond the limit of the disk. To provide an example, the Milky Way’s disk is about 100,000 light-years in diameter, but its halo is between 300,000 to 1 million light-years across.

    Because of the relative sizes of the different regions, most of a galaxy’s dark matter is in the halo. Relatively little is in the disk; Jo Bovy and Scott Tremaine showed that the disk and halo contain less than the equivalent mass of 100 Earths in a cube one light-year across. That may sound like a lot, but Earth isn’t that large, and a light-year defines a big volume. That amount isn’t enough to affect the Sun’s orbit around the galactic center strongly. (It’s still enough for a few particles to drift through detectors like LUX, though.)

    By contrast, the amount of dark matter increases toward the galaxy’s center, so the density should be much higher in the bulge than anywhere else. For that reason, a number of astronomers look to the central part of the Milky Way for indications of dark matter annihilation, which (under some models) would produce gamma rays. This would occur if dark matter particles are their own antimatter partners, so that their (very rare) collisions result in mutual destruction and some high-energy photons. This winter, a group of researchers announced a possible detection of excess gamma rays originating in the Milky Way’s core, based on data from the orbiting [NASA] Fermi gamma ray observatory.

    NASA Fermi Telescope
    NASA/Fermi

    However, the bulge also has the highest density of stars, making it a tangled mess. Many things in that region could produce an excess of gamma rays. As University of Melbourne cosmologist Katherine Mack told me, “The Galactic Center is a really messy place, and the analysis of the signal is complicated. It’ll take a lot to show that the signal has to be dark matter annihilation rather than some un-accounted-for astrophysical source.” We can’t rule out the possibility of dark matter annihilation, but it’s definitely too soon to break out the champagne.

    The difference between the ease of calculating an average density and detecting the presence of dark matter is illustrative of the general problem with mapping dark matter inside galaxies. It’s relatively simple to put limits on how much there is in the disk, since that’s a small fraction of the total volume of a galaxy. The tougher questions include how steeply the density falls off from the galactic center, how far the halo actually extends, and how lumpy the halo is.

    For instance, our galaxy’s halo is big enough to encompass its satellite galaxies, including the Magellanic Clouds and a host of smaller objects. But these galaxies also have their own halos in accordance with the hierarchical model. Because they’re denser dark matter lumps inside the Milky Way’s larger halo, the satellites’ halos create a substructure.

    Our dark matter models predict how much substructure should be present. However, dwarf galaxies are very faint, so astronomers have difficulty determining if there are enough of them to account for all the predicted substructure. This is known as the “missing satellite problem,” but many astronomers suspect the problem will evaporate as they get better at finding these faint objects.

    A hopeful conclusion

    So where is the dark matter? Based on both theory and observation, it looks like most of it is in galactic halos. Surveys using weak gravitational lensing are ongoing, with many more planned for the future. These surveys will show where most of the mass in the Universe is located in unprecedented detail.

    How dark matter is distributed within those halos is still a bit mysterious, but there are several hopeful approaches. By looking for “dark galaxies”—small satellites with few stars but high dark matter concentrations—astronomers can determine the substructure within larger halos. The [ESA]Gaia mission is working to produce a three-dimensional map of a billion stars and their motions, which will provide information about the structure of the Milky Way and its surrounding satellites. That in turn will allow researchers to work backward, determining the gravitational field dictating the motion of these stars. With that data in hand, we should have a good map of the dark matter in many regions that are currently difficult to study.

    Dark matter may be subtle and invisible, but we’re much closer than ever to knowing exactly where it hides.


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  • richardmitnick 8:58 pm on July 24, 2014 Permalink | Reply
    Tags: , , , , Dark Energy/Dark Matter,   

    From Symmetry: “How to weigh a galaxy cluster” 

    Symmetry

    July 24, 2014
    Glenn Roberts Jr.

    The study of galaxy clusters is bringing scientists closer to an understanding of the “dark” universe.

    Step on a scale and you’ll get a quick measure of your weight. Weighing galaxy clusters, groups of hundreds or thousands of galaxies bound together by gravity, isn’t so easy.

    But scientists have many ways to do it. This is fortunate for particle astrophysics; determining the mass of galaxy clusters led to the discovery of dark matter, and it’s key to the continuing study of the “dark” universe: dark matter and dark energy.

    “Galaxy cluster measurements are one of the most powerful probes of cosmology we have,” says Steve Allen, an associate professor of physics at SLAC National Accelerator Laboratory and Stanford University.

    When you weigh a galaxy cluster, what you see is not all that you get. Decades ago, when scientists first estimated the masses of galaxy clusters based on the motions of the galaxies within them, they realized that something strange was going on. The galaxies were moving faster than expected, which implied that the clusters were more massive than previously thought, based on the amout of light they emitted. The prevailing explanation today is that galaxy clusters contain vast amounts of dark matter.

    Measurements of the masses of galaxy clusters can tell scientists about the sizes and shapes of the dark matter “halos” enveloping them and can help them determine the effects of dark energy, which scientists think is driving the universe’s accelerating expansion.

    Today, researchers use a combination of simulations and space- and ground-based telescope observations to estimate the total masses of galaxy clusters.

    Redshift, blueshift: Just as an ambulance’s siren seems higher in pitch as it approaches and lower as it speeds into the distance, the light of objects traveling away from us is shifted to longer, “redder” wavelengths, and the light of those traveling toward us is shifted to shorter, “bluer” wavelengths. Measurements of these shifts in light coming from galaxies orbiting a galaxy cluster can tell scientists how much gravitational pull the cluster has, which is related to its mass.

    cluster
    Courtesy of NASA

    Gravitational lensing: Gravitational lensing, theorized by Albert Einstein, occurs when the light from a distant galaxy is bent by the gravitational pull of a massive object between it and the viewer. This bending distorts the image of the background galaxy (pictured above). Where the effects are strong, the process can cause dramatic distortions; multiple images of the galaxy can appear. Typically, however, the effects are subtle and require careful measurements to detect. The greater the lensing effect caused by a galaxy cluster, the larger the galaxy cluster’s mass.

    X-rays: Galaxy clusters are filled with superhot, 10- to 100-million-degree gas that shines brightly at X-ray wavelengths. Scientists use X-ray data from space telescopes to find and study massive galaxy clusters. They can use the measured properties of the gas to infer the clusters’ masses.

    The Sunyaev-Zel’dovich effect: The Sunyaev-Zel’dovich effect is a shift in the wavelength of the Cosmic Microwave Background—light left over from the big bang—that occurs when this light passes through the hot gas in a galaxy cluster. The size of the wavelength shift can tell scientists the mass of the galaxy cluster it passed through.

    Cosmic Background Radiation Planck
    CMB (ESA/Planck)

    “These methods are much more powerful in combination than alone,” says Aaron Roodman, a faculty member at the Kavli Institute for Particle Astrophysics and Cosmology at SLAC National Accelerator Laboratory.

    Forthcoming data from the Dark Energy Survey, the under-construction Large Synoptic Survey Telescope and Dark Energy Spectroscopic Instrument, improved Sunyaev-Zel’dovich effect measurements, and the soon-to-be-launched ASTRO-H and eRosita X-ray telescopes should further improve galaxy cluster mass estimates and advance cosmology. Computer simulations are also playing an important role in testing and improving mass estimates based on data from observations.

    LSST Telescope
    LSST

    DESI Dark Energy Spectroscopic Instrument
    DESI

    Astro H
    ASTRO-h

    eROSITA Max Planck
    eROSITA

    Even with an extensive toolkit, it remains a challenging business to weigh galaxy clusters, says Marc Kamionkowski, a theoretical physicist and professor of physics and astronomy at Johns Hopkins University. They are constantly changing; they continue to suck in matter; their dark matter halos can overlap; and no two are alike.

    “It’s like asking how many birds are in my backyard,” he says.

    Despite this, Allen says he sees no roadblocks toward pushing mass estimates to within a few percent accuracy.

    “We will be able to take full advantage of these amazing new data sets that are coming along,” he says. “We are going to see rapid advances.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 8:48 pm on July 11, 2014 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, ,   

    From Symmetry: “US reveals its next generation of dark matter experiments” 

    Symmetry

    July 11, 2014
    Kathryn Jepsen

    Together, the three experiments will search for a variety of types of dark matter particles.

    Two US federal funding agencies announced today which experiments they will support in the next generation of the search for dark matter.

    The Department of Energy and National Science Foundation will back the Super Cryogenic Dark Matter Search-SNOLAB, or SuperCDMS; the LUX-Zeplin experiment, or LZ; and the next iteration of the Axion Dark Matter eXperiment, ADMX-Gen2.

    cdmx
    CDMX detector

    LZ
    Lux-Zeplin

    ADMX
    ADMX

    “We wanted to pool limited resources to put together the most optimal unified national dark matter program we could create,” says Michael Salamon, who manages DOE’s dark matter program.

    Second-generation dark matter experiments are defined as experiments that will be at least 10 times as sensitive as the current crop of dark matter detectors.

    Program directors from the two federal funding agencies decided which experiments to pursue based on the advice of a panel of outside experts. Both agencies have committed to working to develop the new projects as expeditiously as possible, says Jim Whitmore, program director for particle astrophysics in the division of physics at NSF.

    Physicists have seen plenty of evidence of the existence of dark matter through its strong gravitational influence, but they do not know what it looks like as individual particles. That’s why the funding agencies put together a varied particle-hunting team.

    Both LZ and SuperCDMS will look for a type of dark matter particles called WIMPs, or weakly interacting massive particles. ADMX-Gen2 will search for a different kind of dark matter particles called axions.

    LZ is capable of identifying WIMPs with a wide range of masses, including those much heavier than any particle the Large Hadron Collider at CERN could produce. SuperCDMS will specialize in looking for light WIMPs with masses lower than 10 GeV. (And of course both LZ and SuperCDMS are willing to stretch their boundaries a bit if called upon to double-check one another’s results.)

    If a WIMP hits the LZ detector, a high-tech barrel of liquid xenon, it will produce quanta of light, called photons. If a WIMP hits the SuperCDMS detector, a collection of hockey-puck-sized integrated circuits made with silicon or germanium, it will produce quanta of sound, called phonons.

    “But if you detect just one kind of signal, light or sound, you can be fooled,” says LZ spokesperson Harry Nelson of the University of California, Santa Barbara. “A number of things can fake it.”

    SuperCDMS and LZ will be located underground—SuperCDMS at SNOLAB in Ontario, Canada, and LZ at the Sanford Underground Research Facility in South Dakota—to shield the detectors from some of the most common fakers: cosmic rays. But they will still need to deal with natural radiation from the decay of uranium and thorium in the rock around them: “One member of the decay chain, lead-210, has a half-life of 22 years,” says SuperCDMS spokesperson Blas Cabrera of Stanford University. “It’s a little hard to wait that one out.”

    To combat this, both experiments collect a second signal, in addition to light or sound—charge. The ratio of the two signals lets them know whether the light or sound came from a dark matter particle or something else.

    SuperCDMS will be especially skilled at this kind of differentiation, which is why the experiment should excel at searching for hard-to-hear low-mass particles.

    LZ’s strength, on the other hand, stems from its size.

    Dark matter particles are constantly flowing through the Earth, so their interaction points in a dark matter detector should be distributed evenly throughout. Quanta of radiation, however, can be stopped by much less significant barriers—alpha particles by a piece of paper, beta particles by a sandwich. Even gamma ray particles, which are harder to stop, cannot reach the center of LZ’s 7-ton detector. When a particle with the right characteristics interacts in the center of LZ, scientists will know to get excited.

    The ADMX detector, on the other hand, approaches the dark matter search with a more delicate touch. The dark matter axions ADMX scientists are looking for are too light for even SuperCDMS to find.

    If an axion passed through a magnetic field, it could convert into a photon. The ADMX team encourages this subtle transformation by placing their detector within a strong magnetic field, and then tries to detect the change.

    “It’s a lot like an AM radio,” says ADMX-Gen2 co-spokesperson Gray Rybka of the University of Washington in Seattle.

    The experiment slowly turns the dial, tuning itself to watch for one axion mass at a time. Its main background noise is heat.

    “The more noise there is, the harder it is to hear and the slower you have to tune,” Rybka says.

    In its current iteration, it would take around 100 years for the experiment to get through all of the possible channels. But with the addition of a super-cooling refrigerator, ADMX-Gen2 will be able to search all of its current channels, plus many more, in the span of just three years.

    With SuperCDMS, LZ and ADMX-Gen2 in the works, the next several years of the dark matter search could be some of its most interesting.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 12:12 pm on June 24, 2014 Permalink | Reply
    Tags: , , , , , Dark Energy/Dark Matter, , ,   

    From SLAC Lab: “SLAC, Stanford Scientists Play Key Roles in Confirming Cosmic Inflation” 


    SLAC Lab

    March 19, 2014
    Glennda Chui

    Chao-Lin Kuo and Kent Irwin Helped Develop Technology for Imaging Gravitational Waves

    Two scientists at Stanford University and SLAC National Accelerator Laboratory made key contributions to the discovery of the first direct evidence for cosmic inflation – the rapid expansion of the infant universe in the first trillionth of a trillionth of a trillionth of a second after the Big Bang.

    Chao-Lin Kuo is one of four co-leaders of the BICEP2 collaboration that announced the discovery on Monday. An assistant professor at SLAC and Stanford, he led the development of the BICEP2 detector and is building the BICEP3 follow-on experiment in his Stanford lab for deployment at the South Pole later this year.

    ck
    Chao-Lin Kuo at the South Pole research station where the BICEP2 experiment operated from 2010 to 2012. (Photo courtesy of Chao-Lin Kuo)

    BICEP 2
    BICEP With South Pole Telescope

    Kent Irwin invented the type of sensor used in BICEP2 as a graduate student at Stanford, adapted it for X-ray experiments and studies of the cosmos during a 20-year career at the National Institute for Standards and Technology, and returned to SLAC and Stanford as a professor in September to lead a major initiative in sensor development.

    ki
    Kent Irwin (Matt Beardsley/SLAC)

    Both are members of the Kavli Institute for Particle Physics and Astrophysics (KIPAC), which is jointly run by SLAC and Stanford.

    “It’s exciting that the same technology I developed as a grad student to search for tiny particles of dark matter is also being used to do research on the scale of the universe and to study the practical world of batteries, materials and biology in between,” Irwin said. His group is working toward installing a version of the BICEP2 sensors at SLAC’s X-ray light sources – Stanford Synchrotron Radiation Lightsource (SSRL) and Linac Coherent Light Source (LCLS) – as well as at a planned LCLS upgrade.

    Searching for Ripples in Space-time

    BICEP is a series of experiments that began operating at the South Pole in January 2006, taking advantage of the cold, clear, dry conditions to look for a faint, swirling polarization of light in the Cosmic Microwave Background (CMB) radiation. The light in the CMB dates back to 380,000 years after the Big Bang; before that, the early universe was opaque and no light could get through.

    Cosmic Background Radiation Planck
    CMB Planck

    But some theories predicted that gravitational waves – ripples in space-time – would have been released in the first tiny fraction of a second after the Big Bang, as the universe expanded exponentially in what is known as “cosmic inflation.” If that were the case, scientists might be able to detect the imprint of those waves in the form of a slight swirling pattern known as “B-mode polarization” in the CMB.

    On Monday, researchers from the BICEP2 experiment, which ran from January 2010 through December 2012, announced that they had found that smoking-gun signature, confirming the rapid inflation that had been theorized more than 30 years ago by Alan Guth and later modified by Andrei Linde, a Russian theorist who is now at Stanford.

    Building a Better Detector

    Kuo started working on BICEP1 as a postdoctoral researcher at Caltech in 2003. The circuitry in the experiment’s detectors was all made by hand. For the next-generation detector, BICEP2, the collaborating scientists wanted something that could be mass-produced in larger quantities, allowing them to pack more sensors into the array and collect data 10 times faster. So Kuo also started designing that technology, which used photolithography – a standard tool for making computer chips – to print sensors onto high-resolution circuit boards.

    sunset
    The sun sets behind BICEP2 (in the foreground) and the South Pole Telescope (in the background). (Steffen Richter, Harvard University)

    b2
    The BICEP2 detector shown in this electron-beam micrograph works by converting the light from the cosmic microwave background into heat. A titanium film tuned on its transition to a superconducting state makes a sensitive thermometer to measure this heat. The sensors are cooled to just 0.25 degrees above absolute zero to minimize thermal noise. (Anthony Turner, JPL)

    In 2008 Kuo arrived at SLAC and Stanford and began working on the next-generation experiment, BICEP3, for which he is principal investigator. Scheduled for deployment at the South Pole later this year, BICEP3 will look at a larger patch of the sky and collect data 10 times faster than its predecessor; it’s also more sensitive and more compact.

    SLAC took on a bigger role in this research in October 2013 by awarding up to $2 million in Laboratory Directed Research and Development funding over three years for the “KIPAC Initiative for Cosmic Inflation,” with Kuo as principal investigator. The grant establishes a large-scale Cosmic Microwave Background program at the lab, with part of the funding going toward BICEP3, and has a goal of establishing KIPAC as a premier institute for the study of cosmic inflation. There are also plans to establish a comprehensive development, integration, and testing center at SLAC for technologies to further explore the CMB, which holds clues not only to gravitational waves and cosmic inflation but also to dark matter, dark energy and the nature of the neutrino.

    A Fancy Thermometer for Tiny Signals

    Kent Irwin entered the picture in the early 1990s, while a graduate student in the laboratory of Stanford/SLAC Professor Blas Cabrera. There he invented the superconducting Transition Edge Sensor, or TES, for the Cryogenic Dark Matter Search, which is trying to detect incoming particles of dark matter in a former iron mine in Minnesota. When he moved to NIST, he and his team adapted the technology for other uses and also developed a very sensitive way to read out the signal from the sensors with devices known as SQUID multiplexers.

    Printing TES devices on circuit boards and using the SQUID multiplexers to read them out made it possible to create large TES arrays and greatly expanded their applications in astronomy, nuclear non-proliferation, materials analysis and homeland defense. It was also the key factor in allowing the BICEP team to expand the number of detectors in its experiments from 98 in BICEP1 to 500 in BICEP2, and opens the path to even larger arrays that will greatly increase the sensitivity of future experiments.

    A TES is “basically a very fancy thermometer,” Irwin says. “We’re measuring the power coming from the CMB.” The TES receives a microwave signal from an antenna and translates it into heat; the heat then warms a piece of metal that’s chilled to the point where it hovers on the edge of being superconducting – conducting electricity with 100 percent efficiency and no resistance. When a material is at this edge, a tiny bit of incoming heat causes a disproportionately large change in resistance, giving scientists a very sensitive way to measure small temperature changes. The TES devices for BICEP2 were built at NASA’s Jet Propulsion Laboratory, and Irwin’s team at NIST made the SQUID multiplexers.

    The Road Ahead

    Looking ahead, CMB researchers in the United States developed a roadmap leading to a fourth-generation experiment as part of last year’s Snowmass Summer Study, which lays out a long-term direction for the national high energy physics research program. That experiment would deploy hundreds of thousands of detector sensors and stare at a much broader swath of the cosmos at an estimated cost of roughly $100 million.

    “These are incredibly exciting times, with theory, technology and experiment working hand in hand to give us an increasingly clear picture of the very first moments of the universe,” said SLAC Lab Director Chi-Chang Kao. “I want to congratulate everyone in the many collaborating institutions who made this spectacular result possible. We at SLAC are looking forward to continuing to invest and work in this area as part of our robust cosmology program.”

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
    i1


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