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  • richardmitnick 4:14 pm on August 10, 2016 Permalink | Reply
    Tags: , , Dark Matter, ,   

    From Symmetry: “Dark matter hopes dwindle with X-ray signal” 

    Symmetry Mag

    Symmetry

    08/10/16
    Manuel Gnida

    A previously detected, anomalously large X-ray signal is absent in new Hitomi satellite data, setting tighter limits for a dark matter interpretation.

    1
    Hitomi collaboration; NASA/CXC; Greg Stewart

    In the final data sent by the Hitomi spacecraft, a surprisingly large X-ray signal previously seen emanating from the Perseus galaxy cluster did not appear.

    JAXA/Hitomi telescope
    JAXA/Hitomi telescope

    This casts a shadow over previous speculation that the anomalously bright signal might have come from dark matter.

    “We would have been able to see this signal much clearer with Hitomi than with other satellites,” says Norbert Werner from the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    “However, there is no unidentified X-ray line at the high flux level found in earlier studies.”

    Werner and his colleagues from the Hitomi collaboration report their findings in a paper submitted to The Astrophysical Journal Letters.

    The mysterious signal was first discovered with lower flux in 2014 when researchers looked at the superposition of X-ray emissions from 73 galaxy clusters recorded with the European XMM-Newton satellite.

    ESA/XMM Newton
    ESA/XMM Newton

    These stacked data increase the sensitivity to signals that are too weak to be detected in individual clusters.

    The scientists found an unexplained X-ray line at an energy of about 3500 electronvolts (3.5 keV), says Esra Bulbul from the MIT Kavli Institute for Astrophysics and Space Research, the lead author of the 2014 study and a co-author of the Hitomi paper.

    “After careful analysis we concluded that it wasn’t caused by the instrument itself and that it was unlikely to be caused by any known astrophysical processes,” she says. “So we asked ourselves ‘What else could its origin be?’”

    One interpretation of the so-called 3.5-keV line was that it could be caused by hypothetical dark matter particles called sterile neutrinos decaying in space.

    Yet, there was something bizarre about the 3.5-keV line. Bulbul and her colleagues found it again in data taken with NASA’s Chandra X-ray Observatory from just the Perseus cluster.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    But in the Chandra data, the individual signal was inexplicably strong—about 30 times stronger than it should have been according to the stacked data.

    Adding to the controversy was the fact that some groups saw the X-ray line in Perseus and other objects using XMM-Newton, Chandra and the Japanese Suzaku satellite, while others using the same instruments reported no detection.

    Astrophysicists highly anticipated the launch of the Hitomi satellite, which carried an instrument—the soft X-ray spectrometer (SXS)—with a spectral resolution 20 times better than the ones aboard previous missions. The SXS would be able to record much sharper signals that would be easier to identify.

    Hitomi recorded the X-ray spectrum of the Perseus galaxy cluster with the protective filter still attached to its soft X-ray spectrometer.
    Hitomi collaboration

    The new data were collected during Hitomi’s first month in space, just before the satellite was lost due to a series of malfunctions. Unfortunately during that time, the SXS was still covered with a protective filter, which absorbed most of the X-ray photons with energies below 5 keV.

    “This limited our ability to take enough data of the 3.5-keV line,” Werner says. “The signal might very well still exist at the much lower flux level observed in the stacked data.”

    Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its X-ray signal is not anomalously strong. A signal 30 times stronger than expected would have made it through the filter.

    The Hitomi results rule out that the anomalously bright signal in the Perseus cluster was a telltale sign of decaying dark matter particles. But they leave unanswered the question of what exactly scientists detected in the past.

    “It’s really unfortunate that we lost Hitomi,” Bulbul says. “We’ll continue our observations with the other X-ray satellites, but it looks like we won’t be able to solve this issue until another mission goes up.”

    Chances are this might happen in a few years. According to a recent report, the Japan Aerospace Exploration Agency and NASA have begun talks about launching a replacement satellite.

    3
    Hitomi recorded the X-ray spectrum of the Perseus galaxy cluster with the protective filter still attached to its soft X-ray spectrometer.
    Hitomi collaboration

    The new data were collected during Hitomi’s first month in space, just before the satellite was lost due to a series of malfunctions. Unfortunately during that time, the SXS was still covered with a protective filter, which absorbed most of the X-ray photons with energies below 5 keV.

    “This limited our ability to take enough data of the 3.5-keV line,” Werner says. “The signal might very well still exist at the much lower flux level observed in the stacked data.”

    Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its X-ray signal is not anomalously strong. A signal 30 times stronger than expected would have made it through the filter.

    The Hitomi results rule out that the anomalously bright signal in the Perseus cluster was a telltale sign of decaying dark matter particles. But they leave unanswered the question of what exactly scientists detected in the past.

    “It’s really unfortunate that we lost Hitomi,” Bulbul says. “We’ll continue our observations with the other X-ray satellites, but it looks like we won’t be able to solve this issue until another mission goes up.”

    Chances are this might happen in a few years. According to a recent report, the Japan Aerospace Exploration Agency and NASA have begun talks about launching a replacement satellite.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:23 am on August 3, 2016 Permalink | Reply
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    From SLAC: “Physicist Trio Amplifies SLAC Research on Mysterious Forms of Matter” 


    SLAC Lab

    August 2, 2016

    1
    Left: This image shows the remnant of Supernova 1987A, a star explosion detected in 1987, in three different wavelengths (radio, red; visible, green; X-ray, blue). Neutrinos released by supernovae and detected on Earth help researchers understand how stars die. Right: This artist’s impression shows the Milky Way galaxy inside a halo of dark matter (blue), an invisible substance that makes up 85 percent of all matter in the universe. Researchers search for unknown particles and forces related to dark matter. (ALMA/A. Angelich/NASA/ESA, ESO/L. Calçada)

    Elusive Neutrinos and Hypothetical ‘Dark Sector’ Particles Could Hold Answers to Cosmic Mysteries

    All material things appear to be made of elementary particles that are held together by fundamental forces. But what are their exact properties? How do they affect how our universe looks and changes? And are there particles and forces that we don’t know of yet?

    Questions with cosmic implications like these drive many of the scientific efforts at the Department of Energy’s SLAC National Accelerator Laboratory. Three distinguished particle physicists have joined the lab over the past months to pursue research on two particularly mysterious forms of matter: neutrinos and dark matter.

    Neutrinos, which are abundantly produced in nuclear reactions, are among the most common types of particles in the universe. Although they were discovered 60 years ago, their basic properties puzzle scientists to this date.

    Alexander Friedland, a senior staff scientist in SLAC’s Elementary Particle Physics Theory Group, works on techniques that pave the way for future analyses of neutrino bursts from supernovae. Studying the details of these powerful star explosions helps scientists understand how dying stars spit out chemical elements into deep space.

    Natalia Toro and Philip Schuster, associate professors of particle physics and astrophysics at SLAC, look for something even more enigmatic. They develop ideas for experiments that search for hidden particles and forces linked to dark matter, an invisible form of matter that is five times more prevalent than ordinary matter.

    “Alex, Natalia and Philip are significant additions to the SLAC family, whose outstanding expertise tremendously strengthens our research in areas of national priority,” says JoAnne Hewett, head of the lab’s Elementary Particle Physics Division. Neutrino physics and dark matter research are among the five science drivers for U.S. particle physics identified in 2014 by the Particle Physics Project Prioritization Panel. Neutrino research also ranked high in the 2015 long-range plan for nuclear science issued by the Nuclear Science Advisory Committee.

    Neutrinos from Across the Country and from Across the Galaxy

    One of the major neutrino projects with SLAC involvement is the international Deep Underground Neutrino Experiment (DUNE) at the planned Long-Baseline Neutrino Facility (LBNF) – the world’s flagship neutrino experiment for the coming decade and beyond.

    FNAL LBNF/DUNE from FNAL to SURF
    FNAL LBNF/DUNE from FNAL to SURF

    Researchers will send a neutrino beam produced at Fermi National Accelerator Laboratory in Illinois to the Sanford Underground Facility in South Dakota.

    SURF logo

    After travelling 800 miles through the Earth, some of these neutrinos will be detected by the DUNE Far Detector, which will eventually consist of four 10,000-ton modules of liquid argon located 4,850 feet underground.

    FNAL DUNE Argon tank at SURF
    FNAL DUNE Argon tank at SURF

    The ultrasensitive neutrino “eye” will measure how the three known types of neutrinos, called flavors, and their antiparticles morph from one into another during their underground journey. This study will provide crucial insights into the relative masses of neutrino flavors and the possibility that antineutrinos behave differently than neutrinos, which could potentially help explain why the universe is made of matter rather than antimatter. The experiment will also follow up on hints that there may be more than three neutrino flavors in nature.

    “To help DUNE reach its full potential, my work addresses a number of fundamental questions,” says Friedland, SLAC’s first neutrino theorist, who joined the lab in the summer of 2015. “How can additional neutrinos be incorporated into our theories? Are there also additional forces? Is there a link between neutrinos and dark matter? How do neutrinos interact with atomic nuclei in the detector material?”

    In addition to neutrinos from Fermilab, DUNE will also be able to detect very brief neutrino bursts from supernovae – powerful explosions of massive stars with cores that can no longer resist gravity and collapse to form dense neutron stars.

    “Such a burst should be an exquisite probe of neutrino properties,” Friedland says. “Our goal is to understand how to read the signal and optimize our detector for it.”

    Supernova explosions are important events in the universe. They inject chemical elements, synthesized inside stars over their lifetimes, into space, including crucial elements of life. Friedland hopes that DUNE’s data will reveal never-before-seen details in the related neutrino bursts that could open a window into the processes inside dying stars.

    “Our calculations show that those neutrino signals have a certain time structure that is linked to what’s going on in the star,” he says. “Measuring these minute details could help us understand the different stages of a supernova, from the collapse of the star’s core to the outward propagation of powerful shock waves.”

    Such detailed analysis can only be done by looking at neutrinos. Unlike other particles, which frequently interact with their surroundings on their way out of the star and therefore carry the imprint of this complicated environment, neutrinos stream out nearly undisturbed and deliver direct information about the processes in which they were set free.

    “Supernovae go off without warning, and detectable ones don’t occur very often,” says Friedland, who co-leads the DUNE supernova working group. “Although the next supernova neutrino burst may be a decade or more away, what will be seen then is affected by crucial decisions about the detector design made now. My job is to make sure that we’ll be prepared.”

    SLAC provides a unique environment for the pursuit of this line of research, according to Friedland. “The lab is building a strong neutrino program, with experimentalists and theorists working closely together,” he says. “It also unites a number of disciplines under one roof that stimulate and complement each other, from particle physics to astrophysics to computing.”

    Before coming to SLAC, Friedland was at Los Alamos National Laboratory, first as a Richard P. Feynman Fellow and then as a staff scientist. He received his doctorate in physics from the University of California, Berkeley in 2000 and pursued postdoctoral research at the Institute for Advanced Study in Princeton, New Jersey from 2000 to 2002. In addition to neutrinos, Friedland’s studies look into unknown ultraweak forces in nature, extra dimensions beyond space and time and the effect of postulated particles on the evolution of stars.

    Searching for ‘Light Dark Matter’

    Another burning question researchers around the world are yearning to answer is: What is dark matter? With 85 percent of all matter in the universe being dark, this invisible substance has tremendous influence on how the cosmos evolves. Although scientists know that dark matter exists because it gravitationally pulls on ordinary matter, they have yet to find out what it is made of.

    At SLAC, Natalia Toro and Philip Schuster search for entire dark sectors of hypothetical particles and forces that could be linked to dark matter.

    “We work on a number of small-scale experiments that have a real shot at discovering what dark matter is or what it isn’t,” Schuster says. “Unlike most dark matter searches, which focus on rather massive particles, we look for much lighter ones, in a mass range that is surprisingly unexplored.”

    The researchers participate in two experiments that hunt for light dark matter at the Thomas Jefferson National Accelerator Facility in Virginia: the Heavy Photon Search (HPS), for which the scientists developed the theoretical framework, and the A Prime Experiment (APEX), which they co-lead. Both experiments hope to catch a glimpse of dark photons – hypothetical carriers of a new force – that could potentially be produced when powerful electron beams slam into a target. Toro and Schuster are also members of a collaboration that proposed a third experiment at Jefferson Lab to search for dark matter, the Beam Dump Experiment (BDX).

    Similar searches could also be done at SLAC once the upgrade to the lab’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, is complete.

    SLAC LCLS-II line
    SLAC LCLS-II

    The future LCLS-II will produce X-rays from a rapid sequence of electron bunches – up to a million per second – that will fly through the facility’s linear particle accelerator.

    “We’re developing ideas for an experiment that would use the dark current of LCLS-II’s electron beam,” Toro says. “This is a small number of unused electrons in between the main bunches that we could extract and shoot into targets for light dark matter searches.”

    A proposal based on this concept is the Light Dark Matter Experiment (LDMX), whose young collaboration is led by researchers from the University of California, Santa Barbara, the University of Minnesota and SLAC.

    At the moment, the parasitic use of LCLS-II is only an idea, but Toro and Schuster have already teamed up with members of SLAC’s Accelerator Directorate to think about how these experiments could be designed and, most importantly, operated without interfering with X-ray laser operations. Together they are exploring the possibility for a future facility for Dark Sector Experiments at LCLS-II (DASEL).

    “The lab has a unique culture of vibrant collaborations,” Toro says. “It creates an ideal environment to follow through with our projects from beginning to end. Here we can establish the theoretical foundation, work on the engineering aspects and turn them into successful experiments, all in one place.”

    See the full article here .

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

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

    From Sky & Telescope: “No Dark Matter from LUX Experiment” 

    SKY&Telescope bloc

    Sky & Telescope

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

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

    SURF logo

    Sanford Underground levels
    Sanford Underground levels

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

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

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

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

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

    A Physicist’s Gold Mine

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

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

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

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

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

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

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

    Not All That’s Gold Glitters

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

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

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

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

    Lux Zeplin project
    Lux Zeplin project at SURF

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

    See the full article here (More …)

     
  • richardmitnick 6:57 pm on July 25, 2016 Permalink | Reply
    Tags: , Dark Matter, , ,   

    From SURF: “LUX exceeds sensitivity goals” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    7.25.16
    Connie Walker

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

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

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

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

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

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

    Lux Zeplin project
    Lux Zeplin project

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

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

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

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

    The tests will run through January.

    See the full article here .

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

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

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

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

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

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

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

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

    Fermilab LBNE
    LBNE

     
  • richardmitnick 6:51 am on July 16, 2016 Permalink | Reply
    Tags: , , Dark Matter,   

    From FNAL: “Clearest Picture Yet of Dark Matter Points the Way to Better Understanding of Dark Energy – January 9, 2012” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    July 15, 2016
    No writer credit

    Scientists at Fermilab and Berkeley Lab build the biggest map of dark matter yet, using methods that will improve ground-based surveys

    Two teams of physicists at the U.S. Department of Energy’s Fermilab and Lawrence Berkeley National Laboratory (Berkeley Lab) have independently made the largest direct measurements of the invisible scaffolding of the universe, building maps of dark matter using new methods that, in turn, will remove key hurdles for understanding dark energy with ground-based telescopes.

    The teams’ measurements look for tiny distortions in the images of distant galaxies, called “cosmic shear,” caused by the gravitational influence of massive, invisible dark matter structures in the foreground. Accurately mapping out these dark-matter structures and their evolution over time is likely to be the most sensitive of the few tools available to physicists in their ongoing effort to understand the mysterious space-stretching effects of dark energy.

    1
    Teams from Fermilab and Berkeley Lab used galaxies from wide-ranging SDSS Stripe 82, a tiny detail of which is shown here, to plot new maps of dark matter based on the largest direct measurements of cosmic shear to date. Credit: SDSS.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    Both teams depended upon extensive databases of cosmic images collected by the Sloan Digital Sky Survey (SDSS), which were compiled in large part with the help of Berkeley Lab and Fermilab.

    Berkeley Logo

    “These results are very encouraging for future large sky surveys. The images produced lead to a picture of the galaxies in the universe that is about six times fainter, or further back in time, than is available from single images,” says Huan Lin, a Fermilab physicist and member of the SDSS and the Dark Energy Survey (DES).

    2
    Layering photos of one area of sky taken at various time periods, a process called coaddition, can increase the sensitivity of the images six fold by removing errors and enhancing faint light signals. The image on the left show a single picture of galaxies from the SDSS Stripe 82 area of sky. The image on the right shows the same area with the layered effect, increasing the number of visible, distant galaxies. Credit: SDSS.

    Several large astronomical surveys, such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the HyperSuprimeCam survey, will try to measure cosmic shear in the coming years.

    Dark Energy Icon

    LSST

    2

    Weak lensing distortions are so subtle, however, that the same atmospheric effects that cause stars to twinkle at night pose a formidable challenge for cosmic shear measurements. Until now, no ground-based cosmic-shear measurement has been able to completely and provably separate weak lensing effects from the atmospheric distortions.

    “The community has been building towards cosmic shear measurements for a number of years now,” says Huff, an astronomer at Berkeley Lab, “but there’s also been some skepticism as to whether they can be done accurately enough to constrain dark energy. Showing that we can achieve the required accuracy with these pathfinding studies is important for the next generation of large surveys.”

    To construct dark matter maps, the Berkeley Lab and Fermilab teams used images of galaxies collected between 2000 and 2009 by SDSS surveys I and II, using the 2.5-meter SLOAN telescope at Apache Point Observatory in New Mexico. The galaxies lie within a continuous ribbon of sky known as SDSS Stripe 82, lying along the celestial equator and encompassing 275 square degrees. The galaxy images were captured in multiple passes over many years.

    The two teams layered snapshots of a given area taken at different times, a process called coaddition, to remove errors caused by the atmospheric effects and to enhance very faint signals coming from distant parts of the universe. The teams used different techniques to model and control for the atmospheric variations and to measure the lensing signal, and have performed an exhaustive series of tests to prove that these models work.

    Gravity tends to pull matter together into dense concentrations, but dark energy acts as a repulsive force that slows down the collapse. Thus the clumpiness of the dark matter maps provides a measurement of the amount of dark energy in the universe.

    3
    Constrains on cosmological parameters from SDSS Stripe 82 cosmic shear at the 1- and 2-sigma level. Also shown are the constraints from WMAP. The innermost region is the combined constrain from both WMAP and Stripe 82. Credit: SDSS.

    When they compared their final results before the AAS meeting, both teams found somewhat less structure than would have been expected from other measurements such as the Wilkinson Microwave Anisotropy Probe (WMAP), but, says Berkeley Lab’s Huff, “the results are not yet different enough from previous experiments to ring any alarm bells.”

    Meanwhile, says Lin, “Our image-correction processes should prove a valuable tool for the next generation of weak-lensing surveys.”

    See the full article here .

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 12:00 pm on July 12, 2016 Permalink | Reply
    Tags: , Dark Matter, , PICO group   

    From FNAL: “Dark matter search with bubble chambers” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    July 7, 2016
    Chanpreet Amole

    Astrophysical observations, from galactic to cosmological scale, hint at a significant amount of invisible matter in the universe. The nature of the constituent particle of this invisible, or dark, matter is unlike any of the particles described by the Standard Model of particle physics. Since almost three-quarters of the total matter content of the universe is estimated to be dark, the search for its constituent particle is thrilling, especially since it calls for an extension or modification to our current understanding of particle physics.

    1
    This shows the first event observed in the PICO-2L detector captured by one of its two cameras. Only neutrons can cause multiple bubble nucleations, like the one seen in the image above, due to the detector’s excellent sensitivity to nuclear recoils. No image credit.

    While the weakly interacting massive particle (WIMP) is the favorite candidate for dark matter particles, model-free theoretical descriptions of its interaction demand a broad experimental search. Hence, various collaborative efforts to directly detect interactions between these hypothesized WIMPs and the atomic nucleons (protons and neutrons) are under way with a variety of technologies and target nuclei. Direct detection of this particle involves identifying the small amount of energy deposited in the detector material as a WIMP collides (undergoes a nuclear recoil) with a nucleus in the detector material.

    2
    This is an electronic image of a typical microscopic quartz particulate found during the investigation of the active mass of the PICO-2L detector after its first run. The image was taken using an EDS-SEM (scanning electron microscopy with X-ray microanalysis). Such particulate contamination was thought to be the cause for the anomalous background, and a profound effort went into its elimination (and suppression of its production) for the follow up PICO-2L WIMP-search run.

    Since these highly sensitive nuclear recoil detectors aim to identify a rare WIMP interaction, the detection technology needs to be practically free of any backgrounds. Although they find refuge from the abundant cosmic rays in underground laboratories, these detectors are nevertheless prone to backgrounds from neutrons, radioactive decays that emit helium nuclei (alpha decays) and electron scatterings. Enclosed within a large mass of water, which provides shielding from the locally produced neutrons in the underground laboratory, various detector technologies use specialized techniques to distinguish the alpha decays and electron scatterings from the expected WIMP-nuclear recoil signals.

    Superheated detectors, such as bubble chambers, offer a unique advantage as they are insensitive to electron scatterings even when the detector sensitivity is tuned to low-energy nuclear recoils (on the order of few thousand electronvolts, or keV). Due to this reason among others, the PICO collaboration has rejuvenated and augmented the bubble chamber technology for WIMP detection. A combination of optical, acoustic and pressure sensors is used to identify the candidate nuclear recoils in the bulk of the active mass of the detector. So far, the collaboration has operated a 2-liter (PICO-2L) and a 30-liter (PICO-60) bubble chamber detector in the Sudbury Neutrino Observatory underground laboratory (SNOLAB) in Sudbury, Ontario, Canada.

    When the PICO group deployed their first bubble chamber detector in the beginning of 2014 with 2 liters of superheated fluorocarbon fluid in SNOLAB, it performed as well as expected, except for an unknown background signal that was observed during this experimental run.

    2

    This signal was consistent with neither the known backgrounds nor WIMP signal and had characteristics that hinted at particulate contamination as the cause. The discovery of micron sized quartz and stainless steel particulates in the detector’s active fluid fortified this hypothesis. The first WIMP search with the PICO-2L, even with the unknown background, provided the world’s leading sensitivity to WIMP-proton spin-dependent interactions.

    A profound effort was made to mitigate the particulate contamination, especially that of natural quartz. The 2-liter detector was redeployed in early 2015 with an ultraclean bubble chamber jar, along with various technical improvements and advancements. The modifications were such that the initial state of the bubble chamber was significantly cleaner, and the mechanisms of particulate generation during the experimental run were suppressed.

    The effects were apparent right away. The observed events had a remarkably different spatial distribution from that of the first run. The data of the WIMP search during this second run showed an absence of the unknown background signal, and only one candidate nuclear recoil was observed, consistent with the expected neutron background. Since contamination control was the key to these results, much of the credit for this success is attributed to the work accomplished at Fermilab in the development of cleaning and fluid handling techniques.

    3
    This shows the acoustic power (AP) distributions (in log scale) of the events originating within the PICO-2L detector during the second experimental run. The nuclear-recoil calibration data obtained by using a neutron source (AmBe) is shown in black and WIMP-search data in red. For nuclear recoils, the signal region is indicated between the dashed blue lines. In both the calibration and WIMP search data, the three peaks at higher AP are from events produced by alpha decays within the detector. Only one candidate nuclear-recoil event was observed during this run, consistent with the expected neutron background.

    The results from the second PICO-2L run are highlighted in the journal Physical Review D as an editor’s suggestion. These results present the strongest exclusion limits on the spin-dependent dark matter scatterings for WIMP masses less than 50 GeV/c2. For higher WIMP masses, the recent results from the PICO-60 experiment, also published in Physical Review D, provide the leading exclusion limits.

    Now, with the absence of the unknown background and a low background signal, the collaboration is focusing on the larger bubble chamber detectors in their search for WIMP interactions. PICO-60 detector has been redeployed with its own ultraclean bubble chamber vessel in SNOLAB with 40 liters of active mass.

    SNOLAB
    SNOLAB, Sudbury, Ontario, Canada.
    SNOLAB, Sudbury, Ontario, Canada

    Currently, in its initial tests and calibrations stage, it is well on the path to initiate a new WIMP search run this summer.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 12:18 pm on June 29, 2016 Permalink | Reply
    Tags: , Dark Matter,   

    From PI: “What We Know (And What We Don’t) About Dark Matter” 

    Perimeter Institute
    Perimeter Institute

    June 29, 2016

    Eamon O’Flynn
    Manager, Media Relations
    eoflynn@perimeterinstitute.ca
    (519) 569-7600 x5071

    Some of the most abundant stuff in the universe is also the most mysterious, but we may not be in the dark for long.

    The concept of dark matter is a mind-bender.

    It proposes that all the stuff we’re familiar with in the universe – planets, stars, galaxies, hippopotamuses – represent just a smidgen of what’s really out there, and that the universe is mostly populated by something else that we don’t yet understand.

    The existence of this abundant-but-elusive stuff is inferred by the gravitational sway it seems to exert on what we can see, and on the large-scale structure of the universe.

    So what is it? Well, we’re still largely in the dark, but much research aims to shed light on the matter.

    Here’s a look at what we know, and what we don’t, about one of the greatest mysteries in modern physics.

    1

    2
    Check out Perimeter Institute’s educational resource, The Mystery of Dark Matter.

    3
    Watch an excerpt about Fritz Zwicky from a Perimeter Institute Public Lecture by Katherine Freese.

    4

    5
    Weakly interacting massive particles (WIMPs) are a leading candidate for dark matter. Wimpzillas are, as the name implies, supermassive WIMPs. Other candidates include robust associations of massive baryonic objects (RAMBOs), gravitinos, and massive astrophysical compact halo objects (MACHOs). Less catchy, but equally intriguing, are the axion and the Kaluza-Klein particle.

    6

    7
    Watch a public lecture by Perimeter researcher Kendrick Smith about what we have learned from the CMB.

    9

    10

    11

    12

    12

    16
    Check out this Business Insider article on the physics of Super Mario World.

    17

    17

    19

    Watch “The Dark Side of the Universe,” a Perimeter Institute Public Lecture by Katherine Freese, delivered March 2, 2016.

    Access mp4 video here .

    See the full article here .

    Please help promote STEM in your local schools.

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    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

     
  • richardmitnick 1:40 pm on June 24, 2016 Permalink | Reply
    Tags: , , Dark Matter, , Is dark matter required for life to exist? Yes.   

    From Ethan Siegel: “Is dark matter required for life to exist?” 

    Ethan Siegel

    6.24.16

    1
    Image credit: The Marenostrum Numerical Cosmology Project, with acknowledgment to Arman Khalatian and Klaus Dolag.

    We need it for the large-scale structure of the Universe for certain, but the smallest, human-like scales need it, too.

    “The privilege of a lifetime is being who you are.” –Joseph Campbell

    Dark matter is the most mysterious, non-interacting substance in the Universe. Its gravitational effects are necessary to explain the rotation of galaxies, the motions of clusters, and the largest scale-structure in the entire Universe. But on smaller scales, it’s too sparse and diffuse to impact the motion of the Solar System, the matter here on Earth, or the origin and evolution of humans in any meaningful way. Yet the gravity that dark matter provides is an absolute necessity for allowing our galaxy to hold onto the raw ingredients that made life like us and planets like Earth possible at all. Without dark matter, the Universe would likely have no signs of life at all.

    2
    Image credit: M. Cappellari and the Sloan Digital Sky Survey.

    Stars make up 100% of the light we observe in the Universe, but only 2% of the mass. When we look at the motions of galaxies, clusters and more, we find that the amount of gravitational mass outweighs the stellar mass by a factor of fifty. You might think, however, that other types of normal matter could account for this difference. After all, we’ve discovered lots of other types of matter in the Universe besides stars, including:

    stellar remnants like white dwarfs, neutron stars and black holes,
    asteroids, planets and other objects with masses too low (like brown dwarfs) to become stars,
    neutral gas both within galaxies and in the space between them,
    light-blocking dust and nebulous regions,
    and ionized plasma, found mostly in the intergalactic medium.

    All of these forms of normal matter — or matter originally made of the same things we are: protons, neutrons and electrons — do in fact contribute to what’s there, with gas and plasma in particular each contributing more than the sum total of all the stars in the Universe. But even adding all these components together only gets us up to about 15-to-17% of the total amount of matter we need to explain gravitation. For the rest of the motions that we see, we need a new form of matter that isn’t just different from protons, neutrons and electrons, but that doesn’t match up with any of the known particles in the Standard Model. We need some type of dark matter.

    3
    Images credit: X-ray: NASA/ CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A.Mahdavi et al. (top left); X-ray: NASA/CXC/UCDavis/W.Dawson et al.; Optical: NASA/STScI/UCDavis/ W.Dawson et al. (top right); ESA/XMM-Newton/F. Gastaldello (INAF/IASF, Milano, Italy)/CFHTLS (bottom left); X-ray: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University) (bottom right). These colliding galaxy clusters show a clear separation between the normal matter (in pink) and the gravitational effects (in blue).

    A minority group of scientists favor not adding some unseen source of mass, but to rather modify the laws of gravitation instead. These models all have difficulties, including the inability to reproduce the full suite of observations, including individual galaxies moving within clusters, the cosmic microwave background, galaxy cluster collisions (above) the grand cosmic web or the patterns observed in the large-scale structure of the Universe. But there’s an important piece of evidence that points to the existence of dark matter that you might not expect: our very existence.

    4
    The Grand Canyon’s 23rd Annual Star Party in 2013. Image credit: NPS photo by Michael Quinn, under a cc by 2.0 generic license.

    It might surprise you to learn that we don’t just need dark matter to explain astrophysical phenomena like galactic rotation, cluster motions and collisions, but to explain the origin of life itself!

    To understand why, all you need to remember is that the Universe began from a hot, dense state — the hot Big Bang — where everything started off as a mostly uniform sea of individual, free, high-energy particles. As the Universe expands and cools, we can form protons, neutrons, and the lightest nuclei (hydrogen, deuterium, helium and a trace amount of lithium), but nothing else. It isn’t until tens or even hundreds of millions of years later that matter will collapse into dense enough regions to form stars and what will eventually become galaxies.

    All of this will happen just fine, albeit differently in detail, whether there were plenty of dark matter or none at all. But in order to make the elements necessary for life in great abundance — elements like carbon, oxygen, nitrogen, phosphorous and sulphur — they need to be forged in the cores of the most massive stars in the Universe. They do us no good in there, though; in order to enable the creation of rocky planets, organic molecules and (eventually) life, they need to eject those heavier atoms back into the interstellar medium, where they can be recycled into future generations of stars. To do that, we need a supernova explosion.

    5
    Image credit: NASA / JPL-Caltech / O. Krause et al., combining Hubble (visible), Spitzer (IR) and Chandra (X-ray) data.

    But we’ve observed these explosions in great detail, and in particular, we know how quickly this material gets ejected from the stars in their death throes: on the order of a thousand kilometers per second. (The Cas A supernova remnant has ejecta leaving it between a whopping 5,000 and 14,500 km/s!) While this may not sound like that big a number, especially compared to the speed of light, remember that our own star orbits the Milky Way at only some 220 km/s. In fact, if the Sun were to move even three times as fast as that, we’d find ourselves — today — escaping well beyond our galaxy’s gravitational pull.

    A supernova remnant might see the fastest of its ejecta leave the luminous, star-based part of the galaxy, but combined with the intense gravitational pull of a diffuse, extended halo of dark matter, we’ll keep most of that mass inside our own galaxy. Over time, it will fall back towards the normal-matter-rich regions, form neutral, molecular clouds, and participate in subsequent generations of stars, planets, and more interesting,organic molecular combinations.

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    Image credit: ESO/L. Calçada, of the illustration of the dark matter halo surrounding the luminous disk of our galaxy.

    But without the additional gravitation of a massive dark matter halo surrounding a galaxy, the overwhelming amount of material ejected from a supernova would escape from galaxies forever. It would wind up floating freely in the intergalactic medium, never to become incorporated into future generations of star systems. In a Universe without dark matter, we’d still have stars and galaxies, but the only planets would be gas giant worlds, with no rocky ones, no liquid water, and insufficient ingredients for life as we know it. Without the copious amounts of heavy elements provided by generations of massive stars, molecule-based life like us would never have come to be.

    7
    The Cigar Galaxy, Messier 82, and its supergalactic winds that would drive all this matter out of the galaxy itself, were it not for dark matter. Image credit: NASA, ESA, The Hubble Heritage Team, (STScI / AURA); Acknowledgement: M. Mountain (STScI), P. Puxley (NSF), J. Gallagher (U. Wisconsin).

    It’s only the presence of these massive dark matter halos, surrounding our galaxies, that allow the carbon-based life that took hold on Earth — or a planet like Earth, for that matter — to even be a possibility within our Universe. As we’ve come to understand what makes up our Universe and how it came to be the way it is, we’re left with one inescapable conclusion: dark matter is absolutely necessary for the origin of life. Without it, the chemistry that underlies it all — the heavy, complex elements, the ingredients necessary for biology in the first place, and the rocky planets that life takes hold on — could never have occurred at all.

    See the full article here .

    Please help promote STEM in your local schools.

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

     
  • richardmitnick 2:11 pm on June 18, 2016 Permalink | Reply
    Tags: , Dark Matter, , Johns Hopkins Henry A. Rowland Department of Physics and Astronomy   

    From Hopkins: “Did Gravitational Wave Detector Find Dark Matter?” 

    Johns Hopkins
    Johns Hopkins University

    June 15, 2016
    Arthur Hirsch
    Office: 443-997-9909
    Cell: 443-462-8702
    ahirsch6@jhu.edu

    Johns Hopkins scientists offer hypothesis to solve long-standing mystery in physics

    1
    This image depicts two black holes just moments before they collided and merged with each other, releasing energy in the form of gravitational waves. On 26 December 2015, after travelling for 1.4 billion years, the waves reached Earth and set off the twin LIGO detectors. This marks the second time that LIGO has detected gravitational waves, providing further confirmation of Einstein’s general theory of relativity and securing the future of gravitational wave astronomy as a fundamentally new way to observe the universe. The black holes were 14 and 8 times the mass of the Sun (L-R), and merged to form a new black hole 21 times the mass of the Sun. An additional Sun’s worth of mass was transformed and released in the form of gravitational energy. Image credit: Numerical Simulations: S. Ossokine and A. Buonanno, Max Planck Institute for Gravitational Physics, and the Simulating eXtreme Spacetime (SXS) project. Scientific Visualisation: T. Dietrich and R. Haas, Max Planck Institute for Gravitational Physics. Credit here is http://astronomynow.com/2016/06/16/did-gravitational-wave-detector-find-dark-matter/

    When an astronomical observatory in the United States this winter detected a whisper of two black holes colliding in deep space, scientists celebrated a successful effort to confirm Albert Einstein’s prediction of gravitational waves.

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    A team of Johns Hopkins University astrophysicists wondered about something else: Had the experiment found the “dark matter” that makes up most of the mass of the universe?

    The eight scientists from the Johns Hopkins Henry A. Rowland Department of Physics and Astronomy had already started making calculations when the discovery by the Laser Interferometer Gravitational-Wave Observatory (LIGO) was announced in February. Their results, published recently in Physical Review Letters, unfold as a hypothesis suggesting a solution for an abiding mystery in astrophysics.

    “We consider the possibility that the black hole binary detected by LIGO may be a signature of dark matter,” wrote the scientists in their summary, referring to the black hole pair as a “binary.” What follows are five pages of annotated mathematical equations showing how the researchers considered the mass of the two objects LIGO detected as a point of departure, suggesting that these objects could be part of the mysterious substance known to make up about 85 percent of the mass of the universe.

    A matter of scientific speculation since the 1930s, dark matter has recently been studied with greater precision; more evidence has emerged since the 1970s, albeit always indirectly. While dark matter itself cannot yet be detected, its gravitational effects can be. For example, dark matter is believed to explain inconsistencies in the rotation of visible matter in galaxies.

    The Johns Hopkins team, led by postdoctoral fellow Simeon Bird, was struck by the mass of the black holes detected by LIGO, an observatory that consists of two expansive L-shaped detection systems anchored to the ground. One is in Louisiana and the other in Washington State.

    Black hole masses are measured in terms of multiples of our sun. The colliding objects that generated a gravity wave detected by LIGO – a joint project of the California Institute of Technology and the Massachusetts Institute of Technology — were 36 and 29 solar masses. Those are too large to fit predictions of the size of most stellar black holes, the ultra-dense structures that form when stars collapse. But they are also too small to fit the predictions of the size of supermassive black holes at the center of galaxies.

    The two LIGO-detected objects do, however, fit within the expected range of mass of “primordial” black holes.

    Primordial black holes are believed to have formed not from stars but from the collapse of large expanses of gas during the birth of the universe. While their existence has not been established with certainty, primordial black holes have in the past been suggested as a possible solution to the dark matter mystery. Because there’s so little evidence of them, though, the primordial black hole-dark matter hypothesis has not gained a large following among scientists.

    The LIGO findings, however, raise the prospect anew, especially as the objects detected in that experiment conform to the mass predicted for dark matter. Predictions made by scientists in the past held that conditions at the birth of the universe would produce lots of these primordial black holes distributed roughly evenly in the universe, clustering in halos around galaxies. All this would make them good candidates for dark matter.

    The Johns Hopkins team calculated how often these primordial black holes would form binary pairs, and eventually collide. Taking into account the size and elongated shape believed to characterize primordial black hole binary orbits, the team came up with a collision rate that conforms to the LIGO findings.

    “We are not proposing this is the dark matter,” said one of the authors, Marc Kamionkowski, the William R. Kenan, Jr. Professor in the Department of Physics and Astronomy. “We’re not going to bet the house. It’s a plausibility argument.”

    More observations from LIGO and other evidence will be needed to support this hypothesis, including further detections like the one announced in February. That could suggest greater abundance of objects of that signature mass.

    “If you have a lot of 30-mass events, that begs an explanation,” said co-author Ely D. Kovetz, a postdoctoral fellow in physics and astronomy. “That the discovery of gravitational waves could be connected to dark matter” is creating lots of excitement among astrophysicists, he said.

    “It’s got a lot of potential,” Kamionkowski said.

    See the full article here .

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    Johns Hopkins Campus

    The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

    The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

    What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

     
  • richardmitnick 5:54 am on June 7, 2016 Permalink | Reply
    Tags: , Dark Matter, LUX innovates calibration techniques,   

    From SURF: “Deep Thoughts – LUX innovates calibration techniques” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    6.6.16
    Constance Walker

    LUX Dark matter Experiment at SURF
    LUX Xenon experiment at SURF

    Over the past two-and-a-half years, the Large Underground Xenon (LUX) experiment hit significant milestones. In October 2013, it was named the most sensi¬tive dark matter detector in the world after a 90-live-day run. In May 2016, it celebrated 300 live days. But late last year, LUX announced it had further improved the calibrations of the detector compared to the initial runs and showed the experiment to be more sensitive by a factor of 20 for low mass WIMPs.

    To reach this level of sensitivity, the collaboration developed and employed several calibration techniques: krypton-83, tritiated methane and neutrons from a deuterium-deuterium accelerator. Each calibration method is unique and could go a long way in discovering the elusive WIMP, or weakly interacting massive particle, the leading contender in the dark matter search.

    Tritiated Methane

    In 2008, Tom Shutt, of SLAC Accelerator Lab and then co-spokesperon of LUX, sketched out an idea for using tritium to create fake dark matter particles. “We need to have a very good understanding of different backgrounds for better control of the experiment,” Shutt said. Tritium seemed the perfect candidate. But it took some convincing, Shutt said.

    A radioactive isotope of hydrogen, tritium contains one proton and two neutrons. As it decays, it emits an electron, giving a signal similar to dark matter. But hydrogen is “sticky,” making it hard to remove from the xenon. Carter Hall, a professor at the University of Maryland, was asked to help.

    “If we can’t remove it, it just becomes another background that interferes with the experiment,” Hall said. After care¬ful study, he determined that putting tritium together with methane and utilizing LUX’s purification system, would eliminate the problem. “Tritiated methane passed all the tests,” Hall said. “We’ve studied hundreds of thousands of its decays in LUX. This gives us confidence that we won’t mistake these garden-variety events for dark matter.”

    Hall initially tested the process in a prototype before injecting tritiated methane directly into LUX. “It was risky. It had never been done before,” Hall said. “But we reviewed all the evidence from all the tests and ultimately were satisfied that the risk was small.”

    Neutron generation

    LUX consists of one third-of-a-ton of liquid xenon sur¬rounded by sensitive light detectors inside a titanium vessel housed within a 72,000-gallon tank of deionized water. It is designed to identify the very rare occasions when a dark matter particle collides with a xenon atom. When a colli¬sion happens, the xenon atom recoils and emits a tiny flash of light, which is detected by the light sensors. Neutrons are great stand-ins for dark matter but they create a lot of background noise.

    As neutrons bounce off the xenon atoms, scientists can quantify how the detector responds to the recoiling process. The neutrons are fired into the detector using the generator, a small particle accelerator that sits outside the water tank. The deuterium-deuterium generator was developed by Rick Gaitskell, Brown University professor and co-spokesperson of LUX.
    “We use the water as a shield because it is good at stop¬ping neutrons from entering the detector and creating constant background noise,” Gaitskell said. The collabora¬tion needed a clever, but simple delivery method to get the neutrons through the water to the detector: a plastic tube that sits at the bottom of the water tank filled with air.

    “When we want neutron calibration, we position it in the middle of the tank and shoot the neutrons directly into the detector,” said Harry Nelson, UC-Santa Barbara and a member of the LUX collaboration who oversaw the design.

    Krypton-83

    Another radioactive gas, krypton, was injected to help scientists distinguish between signals produced by ambient radioactivity and a potential dark matter signal.
    “The krypton mixes uniformly in the liquid xenon and emits radiation with a known, specific energy, but then quickly decays away to a stable, non-radioactive isotope,” said Dan McKinsey, University of California Berkeley phys¬ics professor and co-spokesperson for LUX.
    As yet, LUX hasn’t detected a dark matter signal. However, the new calibration techniques give it an exqui¬site sensitivity that allows scientists to all but rule out vast mass ranges where dark matter particles might exist.

    Received via email .

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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

     
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