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  • richardmitnick 1:31 pm on March 28, 2017 Permalink | Reply
    Tags: , , Dark Matter, , , , SUPERRADIANCE   

    From PI via GIZMODO: “Mind-Blowing New Theory Connects Black Holes, Dark Matter, and Gravitational Waves” 

    Perimeter Institute
    Perimeter Institute

    GIZMODO

    3.28.17
    Ryan F. Mandelbaum

    The past few years have been incredible for physics discoveries. Scientists spotted the Higgs boson, a particle they’d been hunting for almost 50 years, in 2012, and gravitational waves, which were theorized 100 years ago, in 2016. This year, they’re slated to take a picture of a black hole. So, thought some theorists, why not combine all of the craziest physics ideas into one, a physics turducken? What if we, say, try to spot the dark matter radiating off of black holes through their gravitational waves?

    It’s really not that strange of an idea. Now that scientists have detected gravitational waves, ripples in spacetime spawned by the most violent physical events, they want to use their discovery to make real physics observations. They think they have a way to spot all-new particles that might make up dark matter, an unknown substance that accounts for over 80 percent of all of the gravity in the universe.

    The basic idea is that we’re trying to use black holes… the densest, most compact objects in the universe, to search for new kinds of particles,” Masha Baryakhtar, postdoctoral researcher at the Perimeter Institute for Theoretical Physics in Canada, told Gizmodo. Especially one particle: “The axion. People have been looking for it for 40 years.”

    Black holes are the universe’s sinkholes, so strong that light can’t escape their pull once it’s entered. They’ve got such powerful gravitational fields that they produce gravitational waves when they collide with each other. Dark matter might not be made from particles (specks of mass and energy), but if it was, we might observe it as axions, particles around one quintillion (a billion billion) times lighter than an electron, hanging around black holes. Now that you understand all the terms, here’s how the theory works.

    Baryakhtar and her teammates think that black holes are more than just bear traps for light, but nuclei at the center of a sort of gravitational atom. The axions would be the electrons, so to speak. If you already know about black holes, you know they have incredibly hot, high-energy discs of gas orbiting them, produced by the friction between particles accelerated by the black hole’s gravity. This theory ignores that stuff, since axions wouldn’t interact via friction.

    Keeping with the atom analogy, the axions can jump around the black hole, gaining and losing energy the same way that electrons do. But electrons interact via electromagnetism, so they let out electromagnetic waves, or light waves. Axions interact via gravity, so they let out gravitational waves. But like I said earlier, axions are tiny. Unlike a tiny atom, the black hole in these “gravity atoms” rotates, supercharging the space around it and coaxing it into producing more axions. Despite the axion’s tiny mass, this so-called superradiance process could generate 10^80 axions, the same number of atoms in the entire universe, around a single black hole. Are you still with me? Crazy spinning blob makes lots of crazy stuff.

    Craziest of all, we should be able to hear a gravitational wave hum from these axions moving around and releasing gravitational waves in our detectors, similar to the way you see spectral lines coming off of electrons in atoms in chemistry class. “You’d see this at a particular frequency which would be roughly twice the axion mass,” said Baryakhtar.

    There are giant gravitational wave detectors scattered around the world; presently there’s one called LIGO (Laser Interferometer Gravitational Wave Observatory) in Washington State, another LIGO in Louisiana, and one called Virgo in Italy that are sensitive enough to detect gravitational waves, and with upgrades, to detect axions and prove their theory right.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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



    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Scientists would essentially need to record data, play it back, and tune their analysis like a radio to pick up the signal at just the right frequency.

    There are other ways the team thinks it could spot this superradiance effect, by measuring the spins in sets of colliding black holes. If black holes really do produce axions, scientists would see very few quickly-spinning black holes in collisions, since the superradiance effects would slow down some of the colliding black holes and create a visible effect in the data, according to the research published this month in the journal Physical Review D. The black hole spins would have a specific pattern which we should be able to spot in the gravitational wave detector data.

    Other scientists were immediately excited about this paper. “I’m always super excited about new ways to detect my favorite pet particle, the axion! Also, SUPERRADIANCE!” Dr. Chanda Prescod-Weinstein, the University of Washington axion wrangler, told Gizmodo in an email. “It’s so cool, and I haven’t read a paper that talked about [superradiance] in years. So it was really fun to see superradiance and axions in one paper.”

    There are a few drawbacks, as there are with any theory. These theorized black hole atoms would have to produce axions of a certain mass, but that mass isn’t an ideal one for the axion to be a dark matter particle, said Prescod-Weinstein. Plus, the second detection idea, the one that looks at the spin rate of colliding black holes, might not work. “They say [in the paper] that they don’t take into account the potential influence of another black hole” in the colliding pair, Dr. Lionel London, a research associate at Cardiff University School of Physics and Astronomy specializing in gravitational wave modeling, told Gizmodo. “If this does turn out to be a significant effect and they’re not including it, this could cast doubt on their results.” But there’s hope. “There’s good reason to believe the effect of a companion [black hole] won’t be large.”

    When would we spot these kinds of events? As of now, the LIGO and Virgo gravitational wave detectors probably aren’t ready. “With the current sensitivity we’re on the edge” of detecting axions, said Baryakhtar. “But LIGO will continue improving their instruments and at design sensitivity we might be able to see as many as 1000s of these axion signals coming in,” she said. Thousands of hums from these black hole-atoms.

    So, if you’ve gotten all the way to this point of the story and still don’t understand what’s going on, a recap: We’ve got these gravitational wave detectors that cost hundreds of millions of dollars each, that are good at spotting really crazy things going on in the universe. Theorists have come up with an interesting way to use them to solve one of the most important interstellar mysteries: What the heck is dark matter? As with most new ideas in theoretical physics, this is something cool to think about and isn’t ready for the big time… yet.

    “I think that timescale is always a concern, but we’re just getting started with LIGO discoveries,” said Prescod-Weinstein. “So who knows what’s around the corner over the next 10 years.”

    See the full article here .

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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 7:56 am on March 28, 2017 Permalink | Reply
    Tags: , Dark Matter, LUX-ZEPLIN dark matter experiment, , , ,   

    From U Wisconsin via SURF : “Dark matter detection receives 10-ton upgrade” 

    SURF

    U Wisconsin

    University of Wisconsin

    1
    The LUX-ZEPLIN dark matter experiment will be located one mile underground at the Sanford Underground Research Facility in South Dakota, in a cavern within the former Homestake gold mine. Illustration: SLAC National Accelerator Laboratory


    Lux Zeplin project at SURF

    In an abandoned gold m­­­ine one mile beneath Lead, South Dakota, the cosmos quiets down enough to potentially hear the faint whispers of the universe’s most elusive material — dark matter.


    SURF bilding in Lead SD USA

    Shielded from the deluge of cosmic rays constantly showering the Earth’s surface, and scrubbed of noisy radioactive metals and gasses, the mine, scientists think, will be the ideal setting for the most sensitive dark matter experiment to date. Known as LUX-ZEPLIN, the experiment will launch in 2020 and will listen for a rare collision between a dark matter particle with 10 tons of liquid xenon.

    Ten University of Wisconsin–Madison scientists are involved in designing and testing the detector, and are part of a team of more than 200 researchers from 38 institutions in five countries working on the project. This month, the Department of Energy approved proceeding with the final stages of assembly and construction of LZ at the Sanford Underground Research Facility in South Dakota, with a total project cost of $55 million. Additional support comes from international collaborators in the United Kingdom, South Korea and Portugal, as well as the South Dakota Science and Technology Authority. The researchers’ goal is to take the experiment online as quickly as possible to compete in a global race to be the first to detect dark matter.

    3
    Scientists install a miniversion of the future LUX-ZEPLIN dark matter detector at a test stand. The white container is a prototype of the detector’s core. SLAC National Acceleratory Laboratory

    In the 1930s, as astronomers studied the rotation of distant galaxies, they noticed that there wasn’t enough matter — stars, planets, hot gas — to hold the galaxies together through gravity. There had to be some extra mass that helped bind all the visible material together, but it was invisible, missing.

    Dark matter, scientists believe, comprises that missing mass, contributing a powerful gravitational counterbalance that keeps galaxies from flying apart. Although dark matter has so far proven to be undetectable, there may be a lot of it — about five times more than regular matter.

    “Dark matter particles could be right here in the room streaming through your head, perhaps occasionally running into one of your atoms,” says Duncan Carlsmith, a professor of physics at UW–Madison.

    One proposed explanation for dark matter is weakly interacting massive particles, or WIMPs, particles that usually pass undetected through normal matter but which may, on occasion, bump into it. The LZ experiment, and similar projects in Italy and China, are designed to detect — or rule out — WIMPs in the search to explain this ghostly material.

    The detector is set up like an enormous bell capable of ringing in response to the lightest tap from a dark matter particle. Nestled within two outer chambers designed to detect and remove contaminating particles lies a chamber filled with 10 tons of liquid xenon. If a piece of dark matter runs into a xenon atom, the xenon will collide with its neighbors, producing a burst of ultraviolet light and releasing electrons.

    Moments later, the free electrons will excite the xenon gas at the top of the chamber and release a second, brighter burst of light. More than 500 photomultiplier tubes will watch for these signals, which together can discriminate between a contaminating particle and true dark matter collisions.

    Kimberly Palladino, an assistant professor of physics at UW–Madison, and graduate student Shaun Alsum were part of the research team for LUX, the predecessor to LZ, which set records searching for WIMPs. Building on their experience from the previous experiment, Palladino, Alsum, graduate student Jonathan Nikoleyczik and undergraduate researchers are conducting simulations of dark matter collisions and prototyping the particle detector to increase the sensitivity of LZ and more stringently discard signals produced by ordinary matter.

    3
    The heart of the LZ detector will be a 5-foot-tall chamber filled with 10 tons of liquid xenon. Hopes are that hypothetical dark matter particles will produce flashes of light as they traverse the detector. Illustration: SLAC National Accelerator Laboratory

    The LZ project is “doing science the way you want to do science,” says Palladino, explaining how the collaboration provides the time, funding and expertise needed to address fundamental questions about the nature of the universe.

    The success of LZ depends in part on excluding contaminating materials, including reactive chemicals and trace amounts of radioactive elements, from the xenon, which relies on engineering prowess provided by UW–Madison’s Physical Sciences Laboratory. Jeff Cherwinka, chief engineer of the LZ project and a PSL mechanical engineer, is overseeing assembly of the dark matter detector in a special facility scrubbed of radioactive radon and is designing a system to continuously remove gas that leaches out of the xenon chamber lining. Together with PSL engineer Terry Benson, Cherwinka is also designing the xenon storage system to prevent any radioactive elements from leaking in during transport and installation.

    “It’s one of the strengths of the university that we have the engineering and manufacturing expertise to contribute to these big-scale projects,” says Cherwinka. “It helps UW gain more stake in these projects.”

    Meanwhile, Carlsmith and Sridhara Dasu, also a UW–Madison professor of physics, are designing computational systems to manage and analyze the data coming out of the detector in order to be ready to listen for dark matter collisions as soon as LZ is turned on in 2020. Once operational, LZ will quickly approach the fundamental limit of its detection capacity, the background noise of particles streaming out of the sun.

    4
    Kimberly Palladino, an assistant professor of physics at UW–Madison, works to assemble a prototype of the dark matter detection chamber. SLAC National Accelerator Laboratory.

    “In a year, if there are no WIMPs, or if they interact too weakly, we’ll see nothing,” says Carlsmith. The experiment is expected to operate for at least five years to confirm any initial observations and set new limits on potential interactions between WIMPs and ordinary matter.

    Other experiments, including Wisconsin IceCube Particle Astrophysics Center projects IceCube, HAWC, and CTA, are searching for the signatures of dark matter annihilation events as independent and indirect methods to investigate the nature of dark matter. In addition, UW–Madison scientists are working at the Large Hadron Collider, searching for evidence that dark matter is produced during high energy particle collisions. This combination of efforts provides the best opportunity yet for uncovering more about the nature of dark matter, and with it the evolution and structure of our universe.

    See the full article here .

    Please help promote STEM in your local schools.

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    In achievement and prestige, the University of Wisconsin–Madison has long been recognized as one of America’s great universities. A public, land-grant institution, UW–Madison offers a complete spectrum of liberal arts studies, professional programs and student activities. Spanning 936 acres along the southern shore of Lake Mendota, the campus is located in the city of Madison.

     
  • richardmitnick 4:18 pm on March 17, 2017 Permalink | Reply
    Tags: , , , , Dark Matter,   

    From Symmetry: “Q&A: Dark matter next door?” 

    Symmetry Mag

    Symmetry

    03/17/17
    Manuel Gnida

    1
    NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

    Astrophysicists Eric Charles and Mattia Di Mauro discuss the surprising glow of our neighbor galaxy.

    [ApJ Volume 836, issue 2, Number 2, 2017] Astronomers recently discovered a stronger-than-expected glow of gamma rays at the center of the Andromeda galaxy, the nearest major galaxy to the Milky Way.


    Andromeda Galaxy Adam Evans

    The signal has fueled hopes that scientists are zeroing in on a sign of dark matter, which is five times more prevalent than normal matter but has never been detected directly.

    Researchers believe that gamma rays—a very energetic form of light—could be produced when hypothetical dark matter particles decay or collide and destroy each other. However, dark matter isn’t the only possible source of the gamma rays. A number of other cosmic processes are known to produce them.

    So what do Andromeda’s gamma rays really tell us about dark matter? To find out, Symmetry’s Manuel Gnida talked with Eric Charles and Mattia Di Mauro, two members of the Fermi-LAT collaboration—an international team of researchers that found the Andromeda gamma-ray signal using the Large Area Telescope [LAT], a sensitive “eye” for dark matter on NASA’s Fermi Gamma-ray Space Telescope.

    Both researchers are based at the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. The LAT was conceived of and assembled at SLAC, which also hosts its operations center.

    3
    KIPAC researchers Eric Charles and Mattia Di Mauro. Dawn Harmer, SLAC National Accelerator Laboratory

    S. Have you discovered dark matter?
    MD: No, we haven’t. In the study, the LAT team looked at the gamma-ray emissions of the Andromeda galaxy and found something unexpected, something we don’t fully understand yet. But there are other potential astrophysical explanations than dark matter.

    It’s also not the first time that the LAT collaboration has studied Andromeda with Fermi, but in the old data the galaxy only looked like a big blob. With more data and improved data processing, we have now obtained a much clearer picture of the galaxy’s gamma-ray glow and how it’s distributed.

    S.What’s so unusual about the results?
    EC: As a spiral galaxy, Andromeda is similar to the Milky Way. Therefore, we expected the emissions of both galaxies to look similar. What we discovered is that they are, in fact, quite different.

    In our galaxy, gamma rays come from all kinds of locations—from the center and the spiral arms in the outer regions. For Andromeda, on the other hand, the signal is concentrated at the center.

    S.Why do galaxies glow in gamma rays?
    EC: The answer depends on the type of galaxy. There are active galaxies called blazars. They emit gamma rays when matter in close orbit around supermassive black holes generates jets of plasma. And then there are “normal” galaxies like Andromeda and the Milky Way that produce gamma rays in other ways.

    When we look at the emissions of the Milky Way, the galaxy appears like a bright disk, with the somewhat brighter galactic center at the center of the disk. Most of this glow is diffuse and comes from the gas between the stars that lights up when it’s hit by cosmic rays—energetic particles spit out by star explosions or supernovae.

    Other gamma-ray sources are the remnants of such supernovae and pulsars—extremely dense, magnetized, rapidly rotating neutron stars. These sources show up as bright dots in the gamma-ray map of the Milky Way, except at the center where the density of gamma-ray sources is high and the diffuse glow of the Milky Way is brightest, which prevents the LAT from detecting individual sources.

    Andromeda is too far away to see individual gamma-ray sources, so it only has a diffuse glow in our images. But we expected to see most of the emissions to come from the disk as well. Its absence suggests that there is less interaction between gas and cosmic rays in our neighbor galaxy. Since this interaction is tied to the formation of stars, this also suggests that Andromeda had a different history of star formation than the Milky Way.

    3
    The sky in gamma rays with energies greater than 1 gigaelectronvolts, based on eight years of data from the LAT on NASA’s Fermi Gamma-ray Space Telescope. NASA/DOE/Fermi LAT Collaboration.


    NASA/Fermi LAT


    NASA/Fermi Telescope

    S. What does all this have to do with dark matter?
    MD: When we carefully analyze the gamma-ray emissions of the Milky Way and model all the gas and point-like sources to the best of our knowledge, then we’re left with an excess of gamma rays at the galactic center. Some people have argued this excess could be a telltale sign of dark matter particles.

    We know that the concentration of dark matter is largest at the galactic center, so if there were a dark matter signal, we would expect it to come from there. The localization of gamma-ray emissions at Andromeda’s center seems to have renewed the interest in the dark matter interpretation in the media.

    S.Is dark matter the most likely interpretation?
    EC: No, there are other explanations. There are so many gamma-ray sources at the galactic center that we can’t really see them individually. This means that their light merges into an extended, diffuse glow.

    In fact, two recent studies from the US and the Netherlands have suggested that this glow in the Milky Way could be due to unresolved point sources such as pulsars. The same interpretation could also be true for Andromeda’s signal.

    S.What would it take to know for certain?
    MD:To identify a dark matter signal, we would need to exclude all other possibilities. This is very difficult for a complex region like the galactic center, for which we don’t even know all the astrophysical processes. Of course, this also means that, for the same reason, we can’t completely rule out the dark matter interpretation.

    But what’s really important is that we would want to see the same signal in a few different places. However, we haven’t detected any gamma-ray excesses in other galaxies that are consistent with the ones in the Milky Way and Andromeda.

    This is particularly striking for dwarf galaxies, small companion galaxies of the Milky Way that only have few stars. These objects are only held together because they are dominated by dark matter. If the gamma-ray excess at the galactic center were due to dark matter, then we should have already seen similar signatures in the dwarf galaxies. But we don’t.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:52 pm on March 16, 2017 Permalink | Reply
    Tags: Dark Matter, , Nauilus, , , , Supersymetry   

    From Nautilus: “A Brief History of the Grand Unified Theory of Physics” 

    Nautilus

    Nautilus

    March 16, 2017
    Lawrence M. Krauss
    Paintings by Jonathan Feldschuh

    Particle physicists had two nightmares before the Higgs particle was discovered in 2012. The first was that the Large Hadron Collider (LHC) particle accelerator would see precisely nothing.


    CERN ATLAS Higgs Event

    CERN ATLAS detector


    CERN CMS Higgs Event


    CERN CMS detector




    LHC at CERN

    For if it did, it would likely be the last large accelerator ever built to probe the fundamental makeup of the cosmos. The second was that the LHC would discover the Higgs particle predicted by theoretical physicist Peter Higgs in 1964 … and nothing else.

    Each time we peel back one layer of reality, other layers beckon. So each important new development in science generally leaves us with more questions than answers. But it also usually leaves us with at least the outline of a road map to help us begin to seek answers to those questions. The successful discovery of the Higgs particle, and with it the validation of the existence of an invisible background Higgs field throughout space (in the quantum world, every particle like the Higgs is associated with a field), was a profound validation of the bold scientific developments of the 20th century.

    2
    Particles #22

    However, the words of Sheldon Glashow continue to ring true: The Higgs is like a toilet. It hides all the messy details we would rather not speak of. The Higgs field interacts with most elementary particles as they travel through space, producing a resistive force that slows their motion and makes them appear massive. Thus, the masses of elementary particles that we measure, and that make the world of our experience possible is something of an illusion—an accident of our particular experience.

    As elegant as this idea might be, it is essentially an ad hoc addition to the Standard Model of physics—which explains three of the four known forces of nature, and how these forces interact with matter.


    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    It is added to the theory to do what is required to accurately model the world of our experience. But it is not required by the theory. The universe could have happily existed with massless particles and a long-range weak force (which, along with the strong force, gravity, and electromagnetism, make up the four known forces). We would just not be here to ask about them. Moreover, the detailed physics of the Higgs is undetermined within the Standard Model alone. The Higgs could have been 20 times heavier, or 100 times lighter.

    Why, then, does the Higgs exist at all? And why does it have the mass it does? (Recognizing that whenever scientists ask “Why?” we really mean “How?”) If the Higgs did not exist, the world we see would not exist, but surely that is not an explanation. Or is it? Ultimately to understand the underlying physics behind the Higgs is to understand how we came to exist. When we ask, “Why are we here?,” at a fundamental level we may as well be asking, “Why is the Higgs here?” And the Standard Model gives no answer to this question.

    Some hints do exist, however, coming from a combination of theory and experiment. Shortly after the fundamental structure of the Standard Model became firmly established, in 1974, and well before the details were experimentally verified over the next decade, two different groups of physicists at Harvard, where both Sheldown Glashow and Steven Weinberg were working, noticed something interesting. Glashow, along with Howard Georgi, did what Glashow did best: They looked for patterns among the existing particles and forces and sought out new possibilities using the mathematics of group theory.

    In the Standard Model the weak and electromagnetic forces of nature are unified at a high-energy scale, into a single force that physicists call the “electroweak force.” This means that the mathematics governing the weak and electromagnetic forces are the same, both constrained by the same mathematical symmetry, and the two forces are different reflections of a single underlying theory. But the symmetry is “spontaneously broken” by the Higgs field, which interacts with the particles that convey the weak force, but not the particles that convey the electromagnetic force. This accident of nature causes these two forces to appear as two separate and distinct forces at scales we can measure—with the weak force being short-range and electromagnetism remaining long-range.

    Georgi and Glashow tried to extend this idea to include the strong force, and discovered that all of the known particles and the three non-gravitational forces could naturally fit within a single fundamental symmetry structure. They then speculated that this symmetry could spontaneously break at some ultrahigh energy scale (and short distance scale) far beyond the range of current experiments, leaving two separate and distinct unbroken symmetries left over—resulting in separate strong and electroweak forces. Subsequently, at a lower energy and larger distance scale, the electroweak symmetry would break, separating the electroweak force into the short-range weak and the long-range electromagnetic force.

    They called such a theory, modestly, a Grand Unified Theory (GUT).

    At around the same time, Weinberg and Georgi along with Helen Quinn noticed something interesting—following the work of Frank Wilczek, David Gross, and David Politzer. While the strong interaction got weaker at smaller distance scales, the electromagnetic and weak interactions got stronger.

    It didn’t take a rocket scientist to wonder whether the strength of the three different interactions might become identical at some small-distance scale. When they did the calculations, they found (with the accuracy with which the interactions were then measured) that such a unification looked possible, but only if the scale of unification was about 15 orders of magnitude in scale smaller than the size of the proton.

    This was good news if the unified theory was the one proposed by Howard Georgi and Glashow—because if all the particles we observe in nature got unified this way, then new particles (called gauge bosons) would exist that produce transitions between quarks (which make up protons and neutrons), and electrons and neutrinos. That would mean protons could decay into other lighter particles, which we could potentially observe. As Glashow put it, “Diamonds aren’t forever.”

    Even then it was known that protons must have an incredibly long lifetime. Not just because we still exist almost 14 billion years after the big bang, but because we all don’t die of cancer as children. If protons decayed with an average lifetime smaller than about a billion billion years, then enough protons would decay in our bodies during our childhood to produce enough radiation to kill us. Remember that in quantum mechanics, processes are probabilistic. If an average proton lives a billion billion years, and if one has a billion billion protons, then on average one will decay each year. There are a lot more than a billion billion protons in our bodies.

    However, with the incredibly small proposed distance scale and therefore the incredibly large mass scale associated with spontaneous symmetry breaking in Grand Unification, the new gauge bosons would get large masses. That would make the interactions they mediate be so short-range that they would be unbelievably weak on the scale of protons and neutrons today. As a result, while protons could decay, they might live, in this scenario, perhaps a million billion billion billion years before decaying. Still time to hold onto your growth stocks.

    With the results of Glashow and Georgi, and Georgi, Quinn, and Weinberg, the smell of grand synthesis was in the air. After the success of the electroweak theory, particle physicists were feeling ambitious and ready for further unification.

    How would one know if these ideas were correct, however? There was no way to build an accelerator to probe an energy scale a million billion times greater than the rest mass energy of protons. Such a machine would have to have a circumference of the moon’s orbit. Even if it was possible, considering the earlier debacle over the Superconducting Super Collider, no government would ever foot the bill.


    Superconducting Super Collider map, in the vicinity of Waxahachie, Texas.

    Happily, there was another way, using the kind of probability arguments I just presented that give limits to the proton lifetime. If the new Grand Unified Theory predicted a proton lifetime of, say, a thousand billion billion billion years, then if one could put a thousand billion billion billion protons in a single detector, on average one of them would decay each year.

    Where could one find so many protons? Simple: in about 3,000 tons of water.

    So all that was required was to get a tank of water, put it in the dark, make sure there were no radioactivity backgrounds, surround it with sensitive phototubes that can detect flashes of light in the detector, and then wait for a year to see a burst of light when a proton decayed. As daunting as this may seem, at least two large experiments were commissioned and built to do just this, one deep underground next to Lake Erie in a salt mine, and one in a mine near Kamioka, Japan. The mines were necessary to screen out incoming cosmic rays that would otherwise produce a background that would swamp any proton decay signal.

    Both experiments began taking data around 1982–83. Grand Unification seemed so compelling that the physics community was confident a signal would soon appear and Grand Unification would mean the culmination of a decade of amazing change and discovery in particle physics—not to mention another Nobel Prize for Glashow and maybe some others.

    Unfortunately, nature was not so kind in this instance. No signals were seen in the first year, the second, or the third. The simplest elegant model proposed by Glashow and Georgi was soon ruled out. But once the Grand Unification bug had caught on, it was not easy to let it go. Other proposals were made for unified theories that might cause proton decay to be suppressed beyond the limits of the ongoing experiments.

    On Feb. 23, 1987, however, another event occurred that demonstrates a maxim I have found is almost universal: Every time we open a new window on the universe, we are surprised. On that day a group of astronomers observed, in photographic plates obtained during the night, the closest exploding star (a supernova) seen in almost 400 years.

    3
    NASA is celebrating the 30th anniversary of SN 1987A by releasing new data.

    The star, about 160,000 light-years away, was in the Large Magellanic Cloud—a small satellite galaxy of the Milky Way observable in the southern hemisphere.


    Large Magellanic Cloud. Adrian Pingstone December 2003

    If our ideas about exploding stars are correct, most of the energy released should be in the form of neutrinos, despite that the visible light released is so great that supernovas are the brightest cosmic fireworks in the sky when they explode (at a rate of about one explosion per 100 years per galaxy). Rough estimates then suggested that the huge IMB (Irvine- Michigan-Brookhaven) and Kamiokande water detectors should see about 20 neutrino events.

    5
    Irvine- Michigan-Brookhaven detector


    Super Kamiokande detector

    When the IMB and Kamiokande experimentalists went back and reviewed their data for that day, lo and behold IMB displayed eight candidate events in a 10-second interval, and Kamiokande displayed 11 such events. In the world of neutrino physics, this was a flood of data. The field of neutrino astrophysics had suddenly reached maturity. These 19 events produced perhaps 1,900 papers by physicists, such as me, who realized that they provided an unprecedented window into the core of an exploding star, and a laboratory not just for astrophysics but also for the physics of neutrinos themselves.

    Spurred on by the realization that large proton-decay detectors might serve a dual purpose as new astrophysical neutrino detectors, several groups began to build a new generation of such dual-purpose detectors. The largest one in the world was again built in the Kamioka mine and was called Super-Kamiokande, and with good reason. This mammoth 50,000-ton tank of water, surrounded by 11,800 phototubes, was operated in a working mine, yet the experiment was maintained with the purity of a laboratory clean room. This was absolutely necessary because in a detector of this size one had to worry not only about external cosmic rays, but also about internal radioactive contaminants in the water that could swamp any signals being searched for.

    Meanwhile, interest in a related astrophysical neutrino signature also reached a new high during this period. The sun produces neutrinos due to the nuclear reactions in its core that power it, and over 20 years, using a huge underground detector, physicist Ray Davis had detected solar neutrinos, but had consistently found an event rate about a factor of three below what was predicted using the best models of the sun. A new type of solar neutrino detector was built inside a deep mine in Sudbury, Canada, which became known as the Sudbury Neutrino Observatory (SNO).


    SNOLAB, Sudbury, Ontario, Canada.

    Super-Kamiokande has now been operating almost continuously, through various upgrades, for more than 20 years. No proton-decay signals have been seen, and no new supernovas observed. However, the precision observations of neutrinos at this huge detector, combined with complementary observations at SNO, definitely established that the solar neutrino deficit observed by Ray Davis is real, and moreover that it is not due to astrophysical effects in the sun but rather due to the properties of neutrinos. The implication was that at least one of the three known types of neutrinos is not massless. Since the Standard Model does not accommodate neutrinos’ masses, this was the first definitive observation that some new physics, beyond the Standard Model and beyond the Higgs, must be operating in nature.

    Soon after this, observations of higher-energy neutrinos that regularly bombard Earth as high-energy cosmic-ray protons hit the atmosphere and produce a downward shower of particles, including neutrinos, demonstrated that yet a second neutrino has mass. This mass is somewhat larger, but still far smaller than the mass of the electron. For these results team leaders at SNO and Kamiokande were awarded the 2015 Nobel Prize in Physics—a week before I wrote the first draft of these words. To date these tantalizing hints of new physics are not explained by current theories.

    The absence of proton decay, while disappointing, turned out to be not totally unexpected. Since Grand Unification was first proposed, the physics landscape had shifted slightly. More precise measurements of the actual strengths of the three non-gravitational interactions—combined with more sophisticated calculations of the change in the strength of these interactions with distance—demonstrated that if the particles of the Standard Model are the only ones existing in nature, the strength of the three forces will not unify at a single scale. In order for Grand Unification to take place, some new physics at energy scales beyond those that have been observed thus far must exist. The presence of new particles would not only change the energy scale at which the three known interactions might unify, it would also tend to drive up the Grand Unification scale and thus suppress the rate of proton decay—leading to predicted lifetimes in excess of a million billion billion billion years.

    As these developments were taking place, theorists were driven by new mathematical tools to explore a possible new type of symmetry in nature, which became known as supersymmetry.


    Standard model of Supersymmetry DESY

    This fundamental symmetry is different from any previous known symmetry, in that it connects the two different types of particles in nature, fermions (particles with half-integer spins) and bosons (particles with integer spins). The upshot of this is that if this symmetry exists in nature, then for every known particle in the Standard Model at least one corresponding new elementary particle must exist. For every known boson there must exist a new fermion. For every known fermion there must exist a new boson.

    Since we haven’t seen these particles, this symmetry cannot be manifest in the world at the level we experience it, and it must be broken, meaning the new particles will all get masses that could be heavy enough so that they haven’t been seen in any accelerator constructed thus far.

    What could be so attractive about a symmetry that suddenly doubles all the particles in nature without any evidence of any of the new particles? In large part the seduction lay in the very fact of Grand Unification. Because if a Grand Unified theory exists at a mass scale of 15 to 16 orders of magnitude higher energy than the rest mass of the proton, this is also about 13 orders of magnitude higher than the scale of electroweak symmetry breaking. The big question is why and how such a huge difference in scales can exist for the fundamental laws of nature. In particular, if the Standard Model Higgs is the true last remnant of the Standard Model, then the question arises, Why is the energy scale of Higgs symmetry breaking 13 orders of magnitude smaller than the scale of symmetry breaking associated with whatever new field must be introduced to break the GUT symmetry into its separate component forces?

    ____________________________________________________________________________
    Following three years of LHC runs, there are no signs of supersymmetry whatsoever.
    ____________________________________________________________________________

    The problem is a little more severe than it appears. When one considers the effects of virtual particles (which appear and disappear on timescales so short that their existence can only be probed indirectly), including particles of arbitrarily large mass, such as the gauge particles of a presumed Grand Unified Theory, these tend to drive up the mass and symmetry-breaking scale of the Higgs so that it essentially becomes close to, or identical to, the heavy GUT scale. This generates a problem that has become known as the naturalness problem. It is technically unnatural to have a huge hierarchy between the scale at which the electroweak symmetry is broken by the Higgs particle and the scale at which the GUT symmetry is broken by whatever new heavy field scalar breaks that symmetry.

    The mathematical physicist Edward Witten argued in an influential paper in 1981 that supersymmetry had a special property. It could tame the effect that virtual particles of arbitrarily high mass and energy have on the properties of the world at the scales we can currently probe. Because virtual fermions and virtual bosons of the same mass produce quantum corrections that are identical except for a sign, if every boson is accompanied by a fermion of equal mass, then the quantum effects of the virtual particles will cancel out. This means that the effects of virtual particles of arbitrarily high mass and energy on the physical properties of the universe on scales we can measure would now be completely removed.

    If, however, supersymmetry is itself broken (as it must be or all the supersymmetric partners of ordinary matter would have the same mass as the observed particles and we would have observed them), then the quantum corrections will not quite cancel out. Instead they would yield contributions to masses that are the same order as the supersymmetry-breaking scale. If it was comparable to the scale of the electroweak symmetry breaking, then it would explain why the Higgs mass scale is what it is.

    And it also means we should expect to begin to observe a lot of new particles—the supersymmetric partners of ordinary matter—at the scale currently being probed at the LHC.

    This would solve the naturalness problem because it would protect the Higgs boson masses from possible quantum corrections that could drive them up to be as large as the energy scale associated with Grand Unification. Supersymmetry could allow a “natural” large hierarchy in energy (and mass) separating the electroweak scale from the Grand Unified scale.

    That supersymmetry could in principle solve the hierarchy problem, as it has become known, greatly increased its stock with physicists. It caused theorists to begin to explore realistic models that incorporated supersymmetry breaking and to explore the other physical consequences of this idea. When they did so, the stock price of supersymmetry went through the roof. For if one included the possibility of spontaneously broken supersymmetry into calculations of how the three non-gravitational forces change with distance, then suddenly the strength of the three forces would naturally converge at a single, very small-distance scale. Grand Unification became viable again!

    Models in which supersymmetry is broken have another attractive feature. It was pointed out, well before the top quark was discovered, that if the top quark was heavy, then through its interactions with other supersymmetric partners, it could produce quantum corrections to the Higgs particle properties that would cause the Higgs field to form a coherent background field throughout space at its currently measured energy scale if Grand Unification occurred at a much higher, superheavy scale. In short, the energy scale of electroweak symmetry breaking could be generated naturally within a theory in which Grand Unification occurs at a much higher energy scale. When the top quark was discovered and indeed was heavy, this added to the attractiveness of the possibility that supersymmetry breaking might be responsible for the observed energy scale of the weak interaction.

    _____________________________________________________________________
    In order for Grand Unification to take place, some new physics at energy scales beyond those that have been observed thus far must exist.
    _____________________________________________________________________

    All of this comes at a cost, however. For the theory to work, there must be two Higgs bosons, not just one. Moreover, one would expect to begin to see the new supersymmetric particles if one built an accelerator such as the LHC, which could probe for new physics near the electroweak scale. Finally, in what looked for a while like a rather damning constraint, the lightest Higgs in the theory could not be too heavy or the mechanism wouldn’t work.

    As searches for the Higgs continued without yielding any results, accelerators began to push closer and closer to the theoretical upper limit on the mass of the lightest Higgs boson in supersymmetric theories. The value was something like 135 times the mass of the proton, with details to some extent depending on the model. If the Higgs could have been ruled out up to that scale, it would have suggested all the hype about supersymmetry was just that.

    Well, things turned out differently. The Higgs that was observed at the LHC has a mass about 125 times the mass of the proton. Perhaps a grand synthesis was within reach.

    The answer at present is … not so clear. The signatures of new super- symmetric partners of ordinary particles should be so striking at the LHC, if they exist, that many of us thought that the LHC had a much greater chance of discovering supersymmetry than it did of discovering the Higgs. It didn’t turn out that way. Following three years of LHC runs, there are no signs of supersymmetry whatsoever. The situation is already beginning to look uncomfortable. The lower limits that can now be placed on the masses of supersymmetric partners of ordinary matter are getting higher. If they get too high, then the supersymmetry-breaking scale would no longer be close to the electroweak scale, and many of the attractive features of supersymmetry breaking for resolving the hierarchy problem would go away.

    But the situation is not yet hopeless, and the LHC has been turned on again, this time at higher energy. It could be that supersymmetric particles will soon be discovered.

    If they are, this will have another important consequence. One of the bigger mysteries in cosmology is the nature of the dark matter that appears to dominate the mass of all galaxies we can see.


    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    There is so much of it that it cannot be made of the same particles as normal matter. If it were, for example, the predictions of the abundance of light elements such as helium produced in the big bang would no longer agree with observation. Thus physicists are reasonably certain that the dark matter is made of a new type of elementary particle. But what type?

    Well, the lightest supersymmetric partner of ordinary matter is, in most models, absolutely stable and has many of the properties of neutrinos. It would be weakly interacting and electrically neutral, so that it wouldn’t absorb or emit light. Moreover, calculations that I and others performed more than 30 years ago showed that the remnant abundance today of the lightest supersymmetric particle left over after the big bang would naturally be in the range so that it could be the dark matter dominating the mass of galaxies.

    In that case our galaxy would have a halo of dark matter particles whizzing throughout it, including through the room in which you are reading this. As a number of us also realized some time ago, this means that if one designs sensitive detectors and puts them underground, not unlike, at least in spirit, the neutrino detectors that already exist underground, one might directly detect these dark matter particles. Around the world a half dozen beautiful experiments are now going on to do just that. So far nothing has been seen, however.

    So, we are in potentially the best of times or the worst of times. A race is going on between the detectors at the LHC and the underground direct dark matter detectors to see who might discover the nature of dark matter first. If either group reports a detection, it will herald the opening up of a whole new world of discovery, leading potentially to an understanding of Grand Unification itself. And if no discovery is made in the coming years, we might rule out the notion of a simple supersymmetric origin of dark matter—and in turn rule out the whole notion of supersymmetry as a solution of the hierarchy problem. In that case we would have to go back to the drawing board, except if we don’t see any new signals at the LHC, we will have little guidance about which direction to head in order to derive a model of nature that might actually be correct.

    Things got more interesting when the LHC reported a tantalizing possible signal due to a new particle about six times heavier than the Higgs particle. This particle did not have the characteristics one would expect for any supersymmetric partner of ordinary matter. In general the most exciting spurious hints of signals go away when more data are amassed, and about six months after this signal first appeared, after more data were amassed, it disappeared. If it had not, it could have changed everything about the way we think about Grand Unified Theories and electroweak symmetry, suggesting instead a new fundamental force and a new set of particles that feel this force. But while it generated many hopeful theoretical papers, nature seems to have chosen otherwise.

    The absence of clear experimental direction or confirmation of super- symmetry has thus far not bothered one group of theoretical physicists. The beautiful mathematical aspects of supersymmetry encouraged, in 1984, the resurrection of an idea that had been dormant since the 1960s when Yoichiro Nambu and others tried to understand the strong force as if it were a theory of quarks connected by string-like excitations. When supersymmetry was incorporated in a quantum theory of strings, to create what became known as superstring theory, some amazingly beautiful mathematical results began to emerge, including the possibility of unifying not just the three non-gravitational forces, but all four known forces in nature into a single consistent quantum field theory.

    However, the theory requires a host of new spacetime dimensions to exist, none of which has been, as yet, observed. Also, the theory makes no other predictions that are yet testable with currently conceived experiments. And the theory has recently gotten a lot more complicated so that it now seems that strings themselves are probably not even the central dynamical variables in the theory.

    None of this dampened the enthusiasm of a hard core of dedicated and highly talented physicists who have continued to work on superstring theory, now called M-theory, over the 30 years since its heyday in the mid-1980s. Great successes are periodically claimed, but so far M-theory lacks the key element that makes the Standard Model such a triumph of the scientific enterprise: the ability to make contact with the world we can measure, resolve otherwise inexplicable puzzles, and provide fundamental explanations of how our world has arisen as it has. This doesn’t mean M-theory isn’t right, but at this point it is mostly speculation, although well-meaning and well-motivated speculation.

    It is worth remembering that if the lessons of history are any guide, most forefront physical ideas are wrong. If they weren’t, anyone could do theoretical physics. It took several centuries or, if one counts back to the science of the Greeks, several millennia of hits and misses to come up with the Standard Model.

    So this is where we are. Are great new experimental insights just around the corner that may validate, or invalidate, some of the grander speculations of theoretical physicists? Or are we on the verge of a desert where nature will give us no hint of what direction to search in to probe deeper into the underlying nature of the cosmos? We’ll find out, and we will have to live with the new reality either way.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 3:15 pm on March 7, 2017 Permalink | Reply
    Tags: Dark Matter, Wimps axions and neutralinos, ,   

    From Yale: Women in STEM – “Yale-led team puts dark matter on the map” Priyamvada Natarajan 

    Yale University bloc

    Yale University

    March 1, 2017

    Jim Shelton
    james.shelton@yale.edu
    203-361-8332

    1
    Professor Priyamvada Natarajan

    2
    Detailed map of reconstructed dark matter clump distributions in a distant galaxy cluster, obtained from the Hubble Space Telescope Frontier Fields data. The unseen matter in this map is comprised of a smooth heap of dark matter on which clumps form. No image credit.

    A Yale-led team has produced one of the highest-resolution maps of dark matter ever created, offering a detailed case for the existence of cold dark matter — sluggish particles that comprise the bulk of matter in the universe.

    The dark matter map is derived from Hubble Space Telescope Frontier Fields data of a trio of galaxy clusters that act as cosmic magnifying glasses to peer into older, more distant parts of the universe, a phenomenon known as gravitational lensing.

    Yale astrophysicist Priyamvada Natarajan led an international team of researchers that analyzed the Hubble images. “With the data of these three lensing clusters we have successfully mapped the granularity of dark matter within the clusters in exquisite detail,” Natarajan said. “We have mapped all of the clumps of dark matter that the data permit us to detect, and have produced the most detailed topological map of the dark matter landscape to date.”

    Scientists believe dark matter — theorized, unseen particles that neither reflect nor absorb light, but are able to exert gravity — may comprise 80% of the matter in the universe. Dark matter may explain the very nature of how galaxies form and how the universe is structured. Experiments at Yale and elsewhere are attempting to identify the dark matter particle; the leading candidates include axions and neutralinos.

    “While we now have a precise cosmic inventory for the amount of dark matter and how it is distributed in the universe, the particle itself remains elusive,” Natarajan said.

    Dark matter particles are thought to provide the unseen mass that is responsible for gravitational lensing, by bending light from distant galaxies. This light bending produces systematic distortions in the shapes of galaxies viewed through the lens. Natarajan’s group decoded the distortions to create the new dark matter map.

    Significantly, the map closely matches computer simulations of dark matter theoretically predicted by the cold dark matter model; cold dark matter moves slowly compared to the speed of light, while hot dark matter moves faster. This agreement with the standard model is notable given that all of the evidence for dark matter thus far is indirect, said the researchers.

    The high-resolution simulations used in the study, known as the Illustris suite, mimic structure formation in the universe in the context of current accepted theory. A study detailing the findings appeared Feb. 28 in the journal Monthly Notices of the Royal Astronomical Society.

    Other Yale researchers involved in the study were graduate students Urmila Chadayammuri and Fangzhou Jiang, faculty member Frank van den Bosch, and former postdoctoral fellow Hakim Atek. Additional co-authors came from institutions worldwide: Mathilde Jauzac from the United Kingdom and South Africa; Johan Richard, Eric Jullo, and Marceau Limousin from France; Jean-Paul Kneib from Switzerland; Massimo Meneghetti from Italy; and Illustris simulators Annalisa Pillepich, Ana Coppa, Lars Hernquist, and Mark Vogelsberger from the United States.

    The research was supported in part by grants from the National Science Foundation, the Science and Technology Facilities Council, and NASA via the Space Telescope Institute HST Frontier Fields initiative.

    The study can be found online.

    See the full article here .

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    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

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

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

    Nautilus

    Nautilus

    3.6.17
    Matthew Sedacca

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

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

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

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

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

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

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

    3
    COSINE-100 Dark Matter Experiment – Yale University

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

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

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

    What do the scientists behind DAMA claim to have discovered?

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

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

    7
    University of Wisconsin–Madison, DM-Ice collaborators

    So what is dark matter?

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

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

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

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

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

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

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

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

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

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

    What’s it like working in the South Pole?

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

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

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

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

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

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

    What’s the future for DM-Ice?

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

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 10:10 am on March 2, 2017 Permalink | Reply
    Tags: , , , , Dark Matter,   

    From Science: “Scientists unveil the most detailed map of dark matter to date” 

    AAAS
    Science Magazine

    Mar. 1, 2017
    Adrian Cho

    1
    No image caption. No image credit.

    Using images from NASA’s orbiting Hubble Space Telescope, an international team of astronomers has deduced in unprecedented detail the distributions of dark matter [MNRAS]within three clusters of galaxies. They exploited the fact that the gravity of a cluster can distort the images of more-distant galaxies, magnifying them and even making their images multiply, in a process called strong gravitational lensing. Poring over images of a cluster, researchers identified multiple images of dozens of background galaxies. From the distribution and intensities of those images, they then deduced the distribution of dark matter in the cluster. For example, in galaxy MACSJ0416, above, the dark matter distribution consists of a pair of broad, overlapping blobs peppered with hundreds of denser knots enshrouding individual galaxies. The statistical properties of the distribution fit well the predictions of physicists’ favored model of “cold” dark matter, which assumes that dark matter consists of heavy, slow-moving particles that do not interact with one another.

    See the full article here .

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  • richardmitnick 10:11 am on March 1, 2017 Permalink | Reply
    Tags: , , , , Dark Matter, MOND - Modified Newtonian Dynamics, Mordehai Milgrom, ,   

    From Nautilus: “The Physicist Who Denies that Dark Matter Exists” 

    Nautilus

    Nautilus

    3.1.17
    Oded Carmeli

    1
    Mordehai Milgrom Credit: Weizmann Institute

    Maybe Newtonian physics doesn’t need dark matter to work, but Mordehai Milgrom instead.

    He is one of those dark matter people,” Mordehai Milgrom said about a colleague stopping by his office at the Weizmann Institute of Science. Milgrom introduced us, telling me that his friend is searching for evidence of dark matter in a project taking place just down the hall.

    “There are no ‘dark matter people’ and ‘MOND people,’” his colleague retorted.

    “I am ‘MOND people,’” Milgrom proudly proclaimed, referring to Modified Newtonian Dynamics, his theory that fixes Newtonian physics instead of postulating the existence of dark matter and dark energy—two things that, according to the standard model of cosmology, constitute 95.1% of the total mass-energy content of the universe.

    This friendly incident is indicative of (“Moti”) Milgrom’s calmly quixotic character. There is something almost misleading about the 70-year-old physicist wearing shorts in the hot Israeli summer, whose soft voice breaks whenever he gets excited. Nothing about his pleasant demeanor reveals that this man claims to be the third person to correct Newtonian physics: First Max Planck (with quantum theory), then Einstein (with relativity), now Milgrom.

    This year marks Milgrom’s 50th year at the Weizmann. I visited him there to learn more about how it feels to be a science maverick, what he appreciates about Thomas Kuhn’s The Structure of Scientific Revolutions, and why he thinks dark matter and dark energy don’t exist.

    What inspired you to dedicate your life to the motion of stars?

    I remember very vividly the way physics struck me. I was 16 and I thought: Here is a way to understand how things work, far beyond the understanding of my peers. I was drawn to the beauty of finding deeper reasons for events, to the aesthetics of discovering hidden symmetries. It wasn’t a long-term plan. It was a daily attraction. I simply loved physics, the same way other people love art or sports. I never dreamed of one day making a major discovery, like correcting Newton.

    I had a terrific physics teacher at school, but when you study textbook material, you’re studying done deals. You still don’t see the effort that goes into making breakthrough science, when things are unclear and advances are made intuitively and often go wrong. They don’t teach you that at school. They teach you that science always goes forward: You have a body of knowledge, and then someone discovers something and expands that body of knowledge. But it doesn’t really work that way. The progress of science is never linear.

    How did you get involved with the problem of dark matter?

    Toward the end of my Ph.D., the physics department here wanted to expand. So they asked three top Ph.D. students working on particle physics to choose a new field. We chose astrophysics, and the Weizmann Institute pulled some strings with institutions abroad so they would accept us as postdocs. And so I went to Cornell to fill my gaps in astrophysics.

    After a few years in high energy astrophysics, working on the physics of X-ray radiation in space, I decided to move to yet another field: The dynamics of galaxies. It was a few years after the first detailed measurements of the speed of stars orbiting spiral galaxies came in. And, well, there was a problem with the measurements.

    To understand this problem, one needs to wrap one’s head around some celestial rotations. Our planet orbits the sun, which, in turn, orbits the center of the Milky Way galaxy. Inside solar systems, the gravitational pull from the mass of the sun and the speed of the planets are in balance. By Newton’s laws, this is why Mercury, the innermost planet in our solar system, orbits the sun at over 100,000 miles per hour, while the outermost plant, Neptune, is crawling at just over 10,000 miles per hour.

    Now, you might assume that the same logic would apply to galaxies: The farther away the star is from the galaxy’s center, the slower it revolves around it; however, while at smaller radiuses the measurements were as predicted by Newtonian physics, farther stars proved to move much faster than predicted from the gravitational pull of the mass we see in these galaxies. The observed gap got a lot wider when, in the late 1970s, radio telescopes were able to detect and measure the cold gas clouds at the outskirts of galaxies. These clouds orbit the galactic center five times farther than the stars, and thus the anomaly grew to become a major scientific puzzle.

    One way to solve this puzzle is to simply add more matter. If there is too little visible mass at the center of galaxies to account for the speed of stars and gas, perhaps there is more matter than meets the eye, matter that we cannot see, dark matter.

    2
    MOND in the MakingMilgrom’s notes from 1981. On the left, each line represents the data from a separate galaxy. On the right is the MOND prediction, which is the line going through the data points.
    Mordehai Milgrom

    What made you first question the very existence of dark matter?

    What struck me was some regularity in the anomaly. The rotational velocities were not just larger than expected, they became constant with radius. Why? Sure, if there was dark matter, the speed of stars would be greater, but the rotation curves, meaning the rotational speed drawn as a function of the radius, could still go up and down depending on its distribution. But they didn’t. That really struck me as odd. So, in 1980, I went on my Sabbatical in the Institute for Advance Studies in Princeton with the following hunch: If the rotational speeds are constant, then perhaps we’re looking at a new law of nature. If Newtonian physics can’t predict the fixed curves, perhaps we should fix Newton, instead of making up a whole new class of matter just to fit our measurements.

    If you’re going to change the laws of nature that work so well in our own solar system, you need to find a property that differentiates solar systems from galaxies. So I made up a chart of different properties, such as size, mass, speed of rotation, etc. For each parameter, I put in the Earth, the solar system and some galaxies. For example, galaxies are bigger than solar systems, so perhaps Newton’s laws don’t work over large distances? But if this was the case, you would expect the rotation anomaly to grow bigger in bigger galaxies, while, in fact, it is not. So I crossed that one out and moved on to the next properties.

    I finally struck gold with acceleration: The pace at which the velocity of objects changes.

    We usually think of earthbound cars that accelerate in the same direction, but imagine a merry-go-round. You could be going in circles and still accelerate. Otherwise, you would simply fall off. The same goes for celestial merry-go-rounds. And it’s in acceleration that we find a big difference in scales, one that justifies modifying Newton: The normal acceleration for a star orbiting the center of a galaxy is about a hundred million times smaller than that of the Earth orbiting the sun.

    For those small accelerations, MOND introduces a new constant of nature, called a0. If you studied physics in high school, you probably remember Newton’s second law: force equals mass times acceleration, or F=ma. While this is a perfectly good tool when dealing with accelerations much greater than a0, such as those of the planets around our sun, I suggested that at significantly lower accelerations, lower even than that of our sun around the galactic center, force becomes proportional to the square of the acceleration, or F=ma2/a0.

    To put it in other words: According to Newton’s laws, the rotation speed of stars around galactic centers should decrease the farther the star is from the center of mass. If MOND is correct, it should reach a constant value, thus eliminating the need for dark matter.

    What did your colleagues at Princeton think about all this?

    I didn’t share these thoughts with my colleagues at Princeton. I was afraid to come across as, well, crazy. And then, in 1981, when I already had a clear idea of MOND, I didn’t want anyone to jump on my wagon, so to speak, which is even crazier when you think about it. Needless to say,” he laughs, “no one jumped on my wagon, even when I desperately wanted them to.

    Well, you were 35 and you proposed to fix Newton.

    Why not? What’s the big deal? If something doesn’t work, fix it. I wasn’t trying to be bold. I was very naïve at the time. I didn’t understand that scientists are just as swayed as other people by conventions and interests.

    Like Thomas Kuhn’s The Structure of Scientific Revolutions.

    I love that book. I read it several times. It showed me how my life’s story has happened to so many others scientists throughout history. Sure, it’s easy to make fun of people who once objected to what we now know is good science, but are we any different? Kuhn stresses that these objectors are usually good scientists with good reasons to object. It is just that the dissenters usually have a unique point of view of things that is not shared by most others. I laugh about it now, because MOND has made such progress, but there were times when I felt depressed and isolated.

    What’s it like being a science maverick?

    By and large, the last 35 years have been exciting and rewarding exactly because I have been advocating a maverick paradigm. I am a loner by nature, and despite the daunting and doubting times, I much prefer this to being carried with the general flow. I was quite confident in the basic validity of MOND from the very start, which helped me a lot in taking all this in stride, but there are two great advantages to the lingering opposition to MOND: Firstly, it gave me time to make more contributions to MOND than I would had the community jumped on the MOND wagon early on. Secondly, once MOND is accepted, the long and wide resistance to it will only have proven how nontrivial an idea it is.

    By the end of my sabbatical in Princeton, I had secretly written three papers introducing MOND to the world. Publishing them, however, was a whole different story. At first I sent my kernel paper to journals such as Nature and Astrophysical Journal Letters, and it got rejected almost off-hand. It took a long time until all three papers were published, side by side, in Astrophysical Journal.

    The first person to hear about MOND was my wife Yvonne. Frankly, tears come to my eyes when I say this. Yvonne is not a scientist, but she has been my greatest supporter.

    The first scientist to back MOND was another physics maverick: The late Professor Jacob Bekenstein, who was the first to suggest that black holes should have a well-defined entropy, later dubbed the Bekenstein-Hawking entropy. After I submitted the initial MOND trilogy, I sent the preprints to several astrophysicists, but Jacob was the first scientist I discussed MOND with. He was enthusiastic and encouraging from the very start.

    Slowly but surely, this tiny opposition to dark matter grew from just two physicists to several hundred proponents, or at least scientists who take MOND seriously. Dark matter is still the scientific consensus, but MOND is now a formidable opponent that proclaims the emperor has no clothes, that dark matter is our generation’s ether.

    So what happened? As far as dark matter is concerned, nothing really. A host of experiments searching for dark matter, including the Large Hadron Collider, many underground experiments and several space missions, have failed to directly observe its very existence. Meanwhile, MOND was able to accurately predict the rotation of more and more spiral galaxies—over 150 galaxies to date, to be precise.

    All of them? Some papers claim that MOND wasn’t able to predict the dynamics of certain galaxies.

    That’s true and it’s perfectly fine, because MOND’s predictions are based on measurements. Given the distribution of regular, visible matter alone, MOND can predict the dynamics of galaxies. But that prediction is based on our initial measurements. We measure the light coming in from a galaxy to calculate its mass, but we often don’t know the distance to that galaxy for sure, so we don’t know for certain just how massive that galaxy really is. And there are other variables, such as molecular gas, that we can’t observe at all. So yes, some galaxies don’t perfectly match MOND’s predictions, but all in all, it’s almost a miracle that we have enough data on galaxies to prove MOND right, over and over again.

    Your opponents say MOND’s greatest flaw is its incompatibility with relativistic physics.

    In 2004, Bekenstein proposed his TeVeS, or Relativistic Gravitational Theory for MOND. Since then, several different relativistic MOND formulations have been put forth, including one by me, called Bimetric MOND, or BIMOND.

    So, no, incorporating MOND into Einsteinian physics is no longer a challenge. I hear this statement still made, but only from people who parrot others, who themselves are not abreast with the developments of the last 10 years. There are several relativistic versions of MOND. What remains a challenge is demonstrating that MOND can account for the mass anomalies in cosmology.

    Another argument that cosmologists often make is that dark matter is needed not just for motion within galaxies, but on even larger scales. What does MOND have to say about that?

    According to the Big Bang theory, the universe began as a uniform singularity 13.8 billion years ago. And, just as in galaxies, observations made of the cosmic background radiation from the early universe suggest that the gravity of all the matter in the universe is simply not enough to form the different patterns we currently see, like galaxies and stars, in just 13.8 billion years. Once again, dark matter was called to the rescue: It does not emit radiation, but it does engage visible material with gravitation. And so, starting from the 1980s, the new cosmological dogma was that dark matter constituted a staggering 95 percent of all matter in the universe. That lasted, well, right until the bomb hit us in 1998.

    It turned out that the expansion of the universe is accelerating, not decelerating like all of us originally thought. Any form of genuine matter, dark or not, should have slowed down acceleration. And so a whole new type of entity was invented: Dark energy. Now the accepted cosmology is that the universe is made up of 70 percent dark energy, 25 percent dark matter, and 5 percent regular matter.

    But dark energy is just a quick fix, the same as dark matter is. And just as in galaxies, you can either invent a whole new type of energy and then spend years trying to understand its properties, or you can try fixing your theory.

    Among other things, MOND points to a very deep connection between structure and dynamics in galaxies and cosmology. This is not expected in accepted physics. Galaxies are tiny structures within the grand scale of the universe, and those structures can behave differently without contradicting the current cosmological consensus. However, MOND creates this connection, binding the two.

    This connection is surprising: For whatever reason, the MOND constant of a0 is close to the acceleration that characterizes the Universe itself. In fact, MOND’s constant equals the speed of light squared, divided by the radius of universe.

    So, indeed, to your question, the conundrum pointed to is valid at present. MOND doesn’t have a sufficient cosmology yet, but we’re working on it. And once we fully understand MOND, I believe we’ll also fully understand the expansion of the universe, and vice versa: A new cosmological theory would explain MOND. Wouldn’t that be amazing?

    What do you think about the proposed unified theories of physics, which merge MOND with quantum mechanics?

    These all hark back to my 1999 paper on ‘MOND as a vacuum effect’, where it was pointed out that the quantum vacuum in a universe such as ours may produce MOND behavior within galaxies, with the cosmological constant appearing in the guise of the MOND acceleration constant, a0. But I am greatly gratified to see these propositions put forth, especially because they are made by people outside the traditional MOND community. It is very important that researchers from other backgrounds become interested in MOND and bring new ideas to further our understanding of its origin.

    And what if you had a unified theory of physics that explains everything? What then?

    You know, I’m not a religious person, but I often think about our tiny blue dot, and the painstaking work we physicists do here. Who knows? Perhaps somewhere out there, in one of those galaxies I spent my life researching, there already is a known unified theory of physics, with a variation of MOND built into it. But then I think: So what? We still had fun doing the math. We still had the thrill of trying to wrap our heads around the universe, even if the universe never noticed it at all.

    See the full article here .

    Please help promote STEM in your local schools.

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

     
  • richardmitnick 3:28 pm on February 28, 2017 Permalink | Reply
    Tags: Dark Matter, , PICO collaboration,   

    From FNAL: “New world-leading limit on dark matter search from PICO experiment” 

    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.

    February 27, 2017
    Andre Salles
    Fermilab Office of Communication
    asalles@fnal.gov
    630-840-6733

    Editor’s note: The PICO-60 detector was originally called “COUPP-60,” with COUPP standing for “Chicagoland Observatory for Underground Particle Physics.” It was designed and built by Fermilab in collaboration with the University of Chicago and Indiana University, South Bend. Work began at Fermilab in 2005, and, after extensive testing, the detector was moved to SNOLAB in 2012.

    1
    A team of Fermilab scientists installs the PICO-60 dark matter detector at SNOLAB. Photo: Fermilab

    “We’ve been working on this for a long time,” said Fermilab’s project manager Andrew Sonnenschein of the below result. “This is by far our most satisfying result yet, because the techniques we used to reject background events from sources other than dark matter worked flawlessly. Bubble chambers are finally living up to their full potential as dark matter detectors. Now the dark matter just needs to show up.”

    Read the original SNOLAB press release on the SNOLAB website.

    The PICO Collaboration is excited to announce that the PICO-60 dark matter bubble chamber experiment has produced a new dark matter limit after analysis of data from the most recent run. This new result is a factor of 17 improvement in the limit for spin-dependent WIMP-proton cross-section over the already world-leading limits from PICO-2L run-2 and PICO-60 CF3I run-1 in 2016.

    The PICO-60 experiment is currently the world’s largest bubble chamber in operation; it is filled with 45 Liters of C3F8 (octafluoropropane) and is taking data in the ladder lab area of SNOLAB. The detector uses the target fluid in a superheated state such that a dark matter particle interaction with a fluorine nucleus causes the fluid to boil and creates a tell tale bubble in the chamber.

    The PICO experiment uses digital cameras to see the bubbles and acoustic pickups to improve the ability to distinguish between dark matter particles and other sources when analysing the data.

    The superheated detector technology has been at the forefront of spin-dependent (SD) searches, using various refrigerant targets including CF3I, C4F10 and C2ClF5, and two primary types of detectors: bubble chambers and droplet detectors. PICO is the leading experiment in the direct detection of dark matter for spin-dependent couplings and is developing a much larger version of the experiment with up to 500 kg of active mass.

    2
    Inside the PICO-60 detector, installed at SNOLAB in Sudbury, Ontario. Photo: SNOLAB

    About PICO

    17 participating institutions: University of Alberta; University of Chicago; Czech Technical University; Fermilab; Indiana University South Bend; Kavli Institute for Cosmological Physics; Laurentian University; Université de Montréal; Northeastern Illinois University (NEIU); Northwestern University; Universidad Nacional Autonoma de Mexico; Pacific Northwest National Laboratory; Queen’s University at Kingston; Saha Institute of Nuclear Physics, India; SNOLAB; Universitat Politecnica de Valencia; Virginia Tech.

    The PICO Collaboration (formed from the merger of two existing groups, PICASSO and COUPP) uses bubble chambers and superheated fluid to search for dark matter. The PICO-60 detector consists of a fused-silica jar sealed to flexible, stainless steel bellows, all immersed in a pressure vessel filled with hydraulic fluid. Eight lead zirconate (PZT) piezoelectric acoustic transducers mounted to the exterior of the bell jar record the acoustic emissions from bubble nucleation and four 2-megapixel resolution fast CMOS cameras are used to photograph the chamber. The PICO-60 detector was built at Fermilab in Batavia, IL and installed underground at SNOLAB in 2012.

    The PICO bubble chambers are made insensitive to electromagnetic interactions by tuning the operating temperatures of the experiment, while the alpha decays are discriminated from dark matter interactions by their sound signal, making these detectors very powerful tools in the search for dark matter.

    PICO is operating two detectors deep underground at SNOLAB: PICO-60, a bubble chamber with 52 kg of C3F8 and PICO-2L, another bubble chamber with 2.9 kg of C3F8.

    The paper is available on the arXiv.

    About SNOLAB

    SNOLAB is Canada’s leading edge astroparticle physics research facility located 2 km (6800 ft) underground in the Vale Creighton Mine. The SNOLAB facility was created by an expansion of the underground research areas next to the highly successful Sudbury Neutrino Observatory (SNO) experiment. The entire laboratory is operated as an ultra-clean space to limit local radioactivity. With greater depth and cleanliness than any other international laboratory, it has the lowest background from cosmic rays providing an ideal location for measurements of rare processes that would be otherwise unobservable.

    Learn more

    PICO website

    SNOLAB

    For more information, please contact:
    Samantha Kuula
    Communications officer, SNOLAB
    Phone: 705-692-7000 ext. 2222
    Email: Samantha.Kuula@snolab.ca
    Website: http://www.snolab.ca

    French language contact:
    Guillaume Giroux
    Postdoctoral fellow, Queen’s University
    Email: ggiroux@owl.phy.queensu.ca
    Phone: 613-533-6000 ext. 79203

    U.S. contact:
    Andrew Sonnenschein
    Project manager, PICO-60
    Fermi National Accelerator Laboratory
    Email: sonnensn@fnal.gov
    Phone: 630-840-2883

    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 2:37 pm on February 22, 2017 Permalink | Reply
    Tags: , , , Dark Matter,   

    From Fermi: “NASA’s Fermi Finds Possible Dark Matter Ties in Andromeda Galaxy” 

    NASA Fermi Banner


    Fermi

    Feb. 21, 2017
    Claire Saravia
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    NASA’s Fermi Gamma-ray Space Telescope has found a signal at the center of the neighboring Andromeda galaxy that could indicate the presence of the mysterious stuff known as dark matter. The gamma-ray signal is similar to one seen by Fermi at the center of our own Milky Way galaxy.

    1

    Gamma rays are the highest-energy form of light, produced by the universe’s most energetic phenomena. They’re common in galaxies like the Milky Way because cosmic rays, particles moving near the speed of light, produce gamma rays when they interact with interstellar gas clouds and starlight.

    Surprisingly, the latest Fermi data shows the gamma rays in Andromeda — also known as M31 — are confined to the galaxy’s center instead of spread throughout. To explain this unusual distribution, scientists are proposing that the emission may come from several undetermined sources. One of them could be dark matter, an unknown substance that makes up most of the universe.


    NASA’s Fermi telescope has detected a gamma-ray excess at the center of the Andromeda galaxy that’s similar to a signature Fermi previously detected at the center of our own Milky Way. Watch to learn more.
    Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger, producer

    2
    The gamma-ray excess (shown in yellow-white) at the heart of M31 hints at unexpected goings-on in the galaxy’s central region. Scientists think the signal could be produced by a variety of processes, including a population of pulsars or even dark matter.
    Credits: NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

    “We expect dark matter to accumulate in the innermost regions of the Milky Way and other galaxies, which is why finding such a compact signal is very exciting,” said lead scientist Pierrick Martin, an astrophysicist at the National Center for Scientific Research and the Research Institute in Astrophysics and Planetology in Toulouse, France. “M31 will be a key to understanding what this means for both Andromeda and the Milky Way.”

    A paper describing the results will appear in an upcoming issue of The Astrophysical Journal.

    Another possible source for this emission could be a rich concentration of pulsars in M31’s center. These spinning neutron stars weigh as much as twice the mass of the sun and are among the densest objects in the universe. One teaspoon of neutron star matter would weigh a billion tons on Earth. Some pulsars emit most of their energy in gamma rays. Because M31 is 2.5 million light-years away, it’s difficult to find individual pulsars. To test whether the gamma rays are coming from these objects, scientists can apply what they know about pulsars from observations in the Milky Way to new X-ray and radio observations of Andromeda.

    Now that Fermi has detected a similar gamma-ray signature in both M31 and the Milky Way, scientists can use this information to solve mysteries within both galaxies. For example, M31 emits few gamma rays from its large disk, where most stars form, indicating fewer cosmic rays roaming there. Because cosmic rays are usually thought to be related to star formation, the absence of gamma rays in the outer parts of M31 suggests either that the galaxy produces cosmic rays differently, or that they can escape the galaxy more rapidly. Studying Andromeda may help scientists understand the life cycle of cosmic rays and how it is connected to star formation.

    “We don’t fully understand the roles cosmic rays play in galaxies, or how they travel through them,” said Xian Hou, an astrophysicist at Yunnan Observatories, Chinese Academy of Sciences in Kunming, China, also a lead scientist in this work. “M31 lets us see how cosmic rays behave under conditions different from those in our own galaxy.”

    The similar discovery in both the Milky Way and M31 means scientists can use the galaxies as models for each other when making difficult observations. While Fermi can make more sensitive and detailed observations of the Milky Way’s center, its view is partially obscured by emission from the galaxy’s disk. But telescopes view Andromeda from an outside vantage point impossible to attain in the Milky Way.

    “Our galaxy is so similar to Andromeda, it really helps us to be able to study it, because we can learn more about our galaxy and its formation,” said co-author Regina Caputo, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s like living in a world where there’s no mirrors but you have a twin, and you can see everything physical about the twin.”

    While more observations are necessary to determine the source of the gamma-ray excess, the discovery provides an exciting starting point to learn more about both galaxies, and perhaps about the still elusive nature of dark matter.

    “We still have a lot to learn about the gamma-ray sky,” Caputo said. “The more information we have, the more information we can put into models of our own galaxy.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    For more information on Fermi, visit:

    http://www.nasa.gov/fermi

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

     
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