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  • richardmitnick 11:00 am on July 29, 2018 Permalink | Reply
    Tags: , Dynamical dark matter, , WIMPS   

    From NOVA: “Does Dark Matter Ever Die?” 

    PBS NOVA

    From NOVA

    30 May 2018 [Just found in social media]
    Kate Becker

    Dark matter is the unseen hand that fashions the universe. It decides where galaxies will form and where they won’t. Its gravity binds stars into galaxies and galaxies into galaxy clusters.

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

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    And when two galaxies merge, dark matter is there, sculpting the product of the merger. But as for what dark matter actually is? No one knows.

    Here’s the short list of what we do know about dark matter. Number one: There’s a lot of it, about five times more than “ordinary” matter. Two: It doesn’t give off, reflect, or absorb light, but it does exert gravity, which is what gives it a driver’s-seat role in the evolution of galaxies. Three: It’s stable, meaning that for almost 13.8 billion years—the current age of the universe—dark matter hasn’t decayed into anything else, at least not enough to matter much. In fact, the thinking goes, dark matter will still be around even when the universe is quintillions (that’s billions of billions) years old—maybe even forever.

    1
    Though invisible, dark matter exerts gravity just like other matter. No image credit.

    Theoretical physicists dreaming up new ideas about dark matter typically start with these three basic principles. But what if the third—the requirement that dark matter be stable over the cosmic long haul—is wrong? That’s the renegade idea behind a new dark matter proposal called “Dynamical Dark Matter.” Though it’s still on the fringe of dark matter physics (“It’s as far as you can get from the traditional approaches,” says physicist Keith Dienes of the University of Arizona, who first developed the idea with Lafayette College theorist Brooks Thomas), it’s been gaining traction and attracting collaborators from particle physics, astrophysics, and beyond.

    And dark matter is a field that could use some new ideas. While astronomers have been picking up dark matter’s fingerprints all over the universe for at least a century, physicists can’t seem to get a fix on a single dark matter particle. It’s not for lack of trying. Particle hunters have looked for signs of them in flurries of particles set loose by colliders like the Large Hadron Collider (LHC). They have buried germanium crystals and tanks of liquid xenon and argon deep underground—beneath mountains and in old gold mines—and looked for dark matter particles pinging off the atomic nuclei inside. The result: Nothing, at least not anything that physicists can agree on.

    DARWIN Dark Matter experiment. A design study for a next-generation, multi-ton dark matter detector in Europe at the University of Zurich

    Lux Dark Matter 2 at SURF, Lead, SD, USA

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    Lux Dark Matter 2 at SURF, Lead, SD, USA

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington

    Meanwhile, the astrophysical evidence for dark matter keeps building up. Take one universal mystery: Astronomers, after clocking how fast stars are circling around in galaxies, have found that stars skimming a galaxy’s perimeter are going just about as fast as closer-in stars. But based on everything we know about how gravity works, they should actually be going a lot slower—unless there is some invisible mass pulling on them. Then, there are galaxy clusters: Galaxies within them are jouncing around so quickly that they should fly apart, absent some invisible mass is holding them all together. Noticing a theme here? Even the cosmic microwave background radiation, the closest thing we have to a baby picture of the newborn universe, has patterns in it that can only really be explained by dark matter. So, if dark matter is so ubiquitous, why can’t we find it?

    3
    Gravity from Huchra’s Lens causes light from the quasar Einstein Cross to bend around it..No image credit.

    Some researchers are beginning to wonder if they’ve been searching for the wrong thing all along. Most (though not all) dark matter detectors are designed to find hypothetical particles called WIMPs—short for “weakly interacting massive particles.” WIMPs are an appealing dark matter candidate because they emerge naturally from a beyond-the-standard-model theory called supersymmetry, which posits that the all the fundamental subatomic particles have as-yet-undiscovered partners.

    As physicists worked out the properties of those still unseen particles, they noticed that one was a startlingly good match for dark matter. It would interact with other particles via gravity and something called the weak force, which only works when particles get within a proton’s-width of each other. Plus, it would be stable, and there could be just enough of it to account for the missing mass without upsetting with the evolution of the universe.

    The appeal of WIMPs is “almost aesthetic,” says Jason Kumar, a physicist at the University of Hawaii: it speaks to physicists’ love of all that is simple, symmetrical, and elegant. But, Kumar says, “It’s now becoming very hard to get these models to fit with the data we’re seeing.” That doesn’t mean that the WIMP model is wrong, but it does put researchers in the mood to consider ideas that, ten years ago, might have been brushed off as theoretical footnotes. Like, for instance, the idea that dark matter that isn’t stable after all.

    A Destabilizing Influence

    Dienes and Thomas were newcomers to dark matter when they first hatched the idea of Dynamical Dark Matter. They were so new to the field that, at first, they didn’t even worry about stability. Together, they began sketching a new kind of dark matter. First, they thought, what if dark matter weren’t just one kind of particle, but a whole bunch of different kinds? Second, what if those particles could decay? Some might disappear within seconds, but others could stick around for trillions of years. The trick would be getting the balance right, so that the bulk of the dark matter would linger until at least the present day.

    Dienes and Thomas called their new framework “Dynamical Dark Matter,” and started sharing it at talks and academic conferences. The reaction, according to Dienes: “A boatload of skepticism.”

    “People kept asking about stability,” Dienes remembers. “But we were not thinking about stability in the traditional way.”

    Why are physicists so sure that dark matter is stable, anyway? Galaxies from long ago—the ones astronomers see when they look billions of light years out into the universe—aren’t more weighed-down by dark matter than our nearby, present-day specimens, at least not at the level of precision that astronomers can measure. Plus, if dark matter decayed into lighter, detectable particles, the little shards would fly out into space with a lot of energy, which we would be able to measure on Earth. And if the decay started in the universe’s baby days, it would disrupt the formation of the elements, shifting the chemistry of the cosmos.

    3
    Galaxies far away from Earth aren’t any more massive than those nearby. No image credit.

    Dynamical Dark Matter resolves the stability problem through a balancing act. If most of dark matter is tied up in particles that live a long time—longer than the age of the universe—that leaves room for a small share of dark matter to be made up of particles that vanish quickly. “It’s a balancing between lifetimes and abundances,” Dienes says. “This balancing is the new underlying principle that replaces mere stability.”

    At first glance, this might sound contrived. Why should everything work out just so? But Dienes, Thomas, and their collaborators have discovered several scenarios that naturally produce just the right combination of particles. “It turns out there are a lot of interesting ways in which these things can come about,” Thomas says. Dynamical Dark Matter remains agnostic about what the dark matter particles are or how they came to be. “It’s not just a single model for dark matter, like a particle that’s a candidate,” he says. “It’s a whole new framework for thinking about what dark matter could be.”

    Dynamical Dark Matter is one of a growing number of “multi-component” dark matter models that welcome in multiple particles. “The key differentiator for Dynamical Dark Matter is that it’s not just a random collection of particles,” Kumar says. “There are just a couple of parameters that describe everything about it.”

    A Shrinking Slice of Pie

    Today, dark matter makes up about 85% of the “stuff” in the universe, out-massing regular matter by a factor of five to one. But if the Dynamical Dark Matter framework is right, one day, dark matter will fizzle out entirely. The process will start slowly. Then, as a larger share of dark matter hits its expiration date, the die-out will speed up until, ultimately, dark matter goes extinct.

    That won’t happen for a long, long time—long after dark energy, that other cosmic mystery force, stretches the universe to the brink of nothingness. (But that’s another story.) So one might ask: Who cares if a teeny weeny bit of dark matter goes “poof” if no one misses it?

    Scientists searching for dark matter particles do.

    That’s because, at dark matter detectors, Dynamical Dark Matter particles should leave a more complicated set of fingerprints than WIMPs. While WIMPs should make a relatively simple “clink” against the ordinary particles inside a detector, Dynamical Dark Matter (or any other brand of multiplex dark matter) would make a jumbled-up jangle. “If there is only one dark-matter particle, there is a well-known ‘shape’ for this recoil spectrum,” says Dienes, describing the detector read-out. “So seeing such a complex recoil spectrum would be a smoking gun of a multi-component dark-matter scenario such as Dynamical Dark Matter.”

    Particle collider experiments could also distinguish Dynamical Dark Matter from WIMPs. “Dynamical dark matter basically provides a very rich spectrum of very different types of collider signatures, some very different from conventional dark matter,” says Shufang Su, a physicist at the University of Arizona. With Dienes and Thomas, Su is trying to predict the traces Dynamical Dark Matter would leave in data from particle colliders like the LHC.

    Su was attracted to the dynamical dark matter model by the idea that dark matter could be a whole panoply of particles instead of just one, which would leave a distinctive signature on the visible particles produced in the LHC’s smash-ups. “These changes could be very dramatic and very different from what would occur if there is only a single dark matter species,” Su says. “If one dark matter particle leads to a single peak, Dynamical Dark Matter could lead to multiple peaks and perhaps even peculiar kinks.”

    Then there’s the decay factor. Depending on how long Dynamical Dark Matter particles live, some might fall apart almost as soon as they are created. Others might last long enough to travel some length of the detector, or escape entirely. “Even though it’s still dark matter, it could have a totally different signature,” Su says.

    While Su is thinking about how to detect Dynamical Dark Matter at colliders here on Earth, Kumar is thinking about whether it could explain something that has been puzzling astronomers: a mysterious excess of high-energy positrons in space. Dark matter researchers have suggested the positrons could be coming from WIMPs, which spit them out as they collide with and annihilate other WIMPs. The trouble, Kumar says, is that this process should only produce positrons up to a certain maximum energy before shutting down; so far, astronomers haven’t found such a cut-off. Dynamical dark matter just might be able to make positrons at the energy levels astronomers observe.

    Of course, Dynamical Dark Matter is just one of many alternatives to WIMPs. There are also SIMPS, RAMBOs, axions, sexaquarks—the list goes on. Until physicists make a clear-cut detection, theorists will have plenty of headroom to dream up new ideas.

    “The main message is that this is an interesting alternative. We are not claiming that it is necessarily better,” Dienes says. “The field is wide open, and data will eventually tell us.”

    See the full article here .

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  • richardmitnick 1:52 pm on May 14, 2018 Permalink | Reply
    Tags: Axion Cold Dark Matter experiment, , , , , , , Planckian interacting dark matter, Superfluid models of dark matter, WIMPS   

    From Physics- “Meetings: WIMP Alternatives Come Out of the Shadows” 

    Physics LogoAbout Physics

    Physics Logo 2

    From Physics

    May 14, 2018

    At an annual physics meeting in the Alps, WIMPs appeared to lose their foothold as the favored dark matter candidate, making room for a slew of new ideas.

    The Rencontres de Moriond (Moriond Conferences) have been a fixture of European high-energy physics for over half a century. These meetings—typically held at an Alpine ski resort—have been the site of many big announcements, such as the first public talk on the top quark discovery in 1995 and important Higgs updates in 2013. One day, perhaps, a dark matter detection will headline at Moriond. For now, physicists wait. But they’ve gotten a bit anxious, as their shoo-in candidate, the WIMP, has yet to make an appearance—despite several ongoing searches.

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    Lux Dark Matter 2 at SURF, Lead, SD, USA

    DARWIN Dark Matter experiment. A design study for a next-generation, multi-ton dark matter detector in Europe at the University of Zurich

    At this year’s Moriond, held this past March in La Thuile, Italy, some of the limelight passed to other dark matter candidates, such as axions, black holes, superfluids, and more.

    1
    T. Tait/University of California, Irvine

    WIMPs, or weakly interacting massive particles, have been a popular topic over the years at Moriond, according to meeting organizer Jacques Dumarchez from the Laboratory of Nuclear Physics and High Energy (LPNHE) in France. The reason for this enthusiasm is that WIMPs fall out of theory without much tweaking. Extensions of the standard model, like supersymmetry, predict a host of particles with weak interactions and a mass in the 1 to 100GeV∕c2 range. If WIMPs like this were created in the big bang, then, according to simple thermodynamic arguments, their density would match the expectations for dark matter based on astronomical observations. This seemingly effortless matching has been called the WIMP miracle.

    But these days, the miracle has less of a halo around it. At this year’s Moriond, updates from direct and indirect searches for WIMPs sounded almost apologetic. Alessandro Manfredini of the Weizmann Institute of Science in Israel told his listeners to “keep calm… and fingers crossed,” as he gave the latest news from Xenon 1T, a one-ton dark matter detector at Italy’s Gran Sasso laboratory. He showed that the experiment has now reached record-breaking sensitivity, so that if a 50GeV∕c2 WIMP exists, the next data release could reveal ten events. But, like other WIMP searches, the current results rule the particles out—by putting tighter limits on their properties—rather than rule them in. The hunt will continue for years to come, but the WIMP paradigm has “started to look less as the obvious solution to the dark matter problem,” Dumarchez said.

    XENON1T at Gran Sasso


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

    When did WIMP confidence start to deflate? Tim Tait from the University of California, Irvine, described the change as gradual. “It is hard to say exactly when it began, but I think it was becoming noticeable around 2014 or so,” Tait said. That’s when the null results from dark matter searches began closing the favored parameter space for the WIMP model. “Of course, there is still a good opportunity for those searches to discover WIMPs,” he said.

    At Moriond, Tait gave an overview of dark matter candidates, in which he discussed WIMPs but devoted much of his time to the dazzling variety of other dark matter theories. Chief among these is the axion.

    CERN CAST Axion Solar Telescope

    U Washington ADMX Axion Dark Matter Experiment

    AXION DME experiment at U Washington

    Like the WIMP, it is well-motivated from particle physics theory, as it may explain why strong interactions do not violate CP symmetry, while weak interactions do. The axion is also the target of several dedicated searches, such as ADMX. Other familiar “dark horse” candidates discussed at Moriond were neutrinos and black holes—with the latter seeing a boost in popularity after recent gravitational-wave observations.

    But at the conference, the doors seemed open to all comers, with several new dark matter ideas taking the stage. One of the talks was by Justin Khoury from the University of Pennsylvania in Philadelphia, who advocates a superfluid model of dark matter. The main assumption here is that dark matter has strong self-interactions that cause it to cool and condense in the centers of galaxies. The resulting superfluid could help explain certain anomalies in observed galactic velocity profiles.

    Martin Sloth from the University of Southern Denmark takes a very different approach. Rather than having strong interactions, his so-called Planckian interacting dark matter has zero interactions beyond gravity, but it makes up for its lack of interactions with an enormous mass (around 1028eV∕c2). At the opposite end of the mass spectrum is fuzzy dark matter, weighing in at 10−22eV∕c2. These ethereal particles could explain an apparent lack of small galaxies. But they could also run into constraints from observed absorption in the intergalactic medium, explained Eric Armengaud from France’s Atomic Energy Commission (CEA) in Saclay.

    Although WIMPs continue to be the odds-on favorite, the field has certainly expanded—with light and heavy masses, weak and strong interactions, and seemingly everything in between. Sloth compared the current situation without a WIMP detection to a Wimbledon tournament without Roger Federer: “Everybody is signing up, thinking that they now have a chance.”

    But can theorists make compelling arguments for these alternatives, as they did for WIMPs? David Kaplan from Johns Hopkins University, Maryland, believes that theoretical backing will not be a problem. In fact, he commented that the community has been too fixated on WIMPs (and the miracle) for the last 30 years. He warned his compatriots to not make the same mistake again: “I don’t want the next 30 years to be just axions.”

    See the full article here .

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    • mpc755 11:18 am on May 15, 2018 Permalink | Reply

      There is evidence of dark matter every time a double-slit experiment is performed, as it is the medium that waves.

      Like

      • richardmitnick 11:25 am on May 15, 2018 Permalink | Reply

        Thanks for reading and commenting. It is much appreciated.

        Like

        • mpc755 12:08 pm on May 15, 2018 Permalink

          Dark matter is a supersolid that fills ’empty’ space and is displaced by visible matter. What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the dark matter. The state of displacement of the dark matter is gravity.

          Dark matter ripples when galaxy clusters collide and waves in a double-slit experiment, relating general relativity and quantum mechanics.

          Thanks for the response.

          Like

  • richardmitnick 4:40 pm on May 6, 2018 Permalink | Reply
    Tags: , , , , LUX/Dark matter experiment at SURF, , , WIMPS   

    From Symmetry: “The origins of dark matter” 

    Symmetry Mag
    From Symmetry

    11/08/16 [Just brought forward in social media]
    Matthew R. Francis

    1
    Artwork by Sandbox Studio, Chicago with Corinne Mucha

    [Because this article is well over a year old, I have updated it with Dark Matter experiments and also included a section on the origins of Dark Matter research by Vera Rubin and Fritz Zicky.]

    Dark Matter Research

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    Milky Way Dark Matter Halo Credit ESO L. Calçada


    Dark matter halo. Image credit: Virgo consortium / A. Amblard / ESA

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

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

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LUX/Dark matter experiment at SURF

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

    Transitions are everywhere we look. Water freezes, melts, or boils; chemical bonds break and form to make new substances out of different arrangements of atoms. The universe itself went through major transitions in early times. New particles were created and destroyed continually until things cooled enough to let them survive. Those particles include ones we know about, such as the Higgs boson or the top quark. But they could also include dark matter, invisible particles which we presently know only because of their gravitational effects. In cosmic terms, dark matter particles could be a “thermal relic,” forged in the hot early universe and then left behind during the transitions to more moderate later eras. One of these transitions, known as “freeze-out,” changed the nature of the whole universe.

    The hot cosmic freezer

    On average, today’s universe is a pretty boring place. If you pick a random spot in the cosmos, it’s far more likely to be in intergalactic space than, say, the heart of a star or even inside an alien solar system. That spot is probably cold, dark and quiet. The same wasn’t true for a random spot shortly after the Big Bang. “The universe was so hot that particles were being produced from photons smashing into other photons, of photons hitting electrons, and electrons hitting positrons and producing these very heavy particles,” says Matthew Buckley of Rutgers University. The entire cosmos was a particle-smashing party, but parties aren’t meant to last. This one lasted only a trillionth of a second. After that came the cosmic freeze-out. During the freeze-out, the universe expanded and cooled enough for particles to collide far less frequently and catastrophically. “One of these massive particles floating through the universe is finding fewer and fewer antimatter versions of itself to collide with and annihilate,” Buckley says. “Eventually the universe would get large enough and cold enough that the rate of production and the rate of annihilation basically goes to zero, and you just a relic abundance, these few particles that are floating out there lonely in space.” Many physicists think dark matter is a thermal relic, created in huge numbers in before the cosmos was a half-second old and lingering today because it barely interacts with any other particle.

    A WIMPy miracle

    One reason to think of dark matter as a thermal relic is an interesting coincidence known as the “WIMP miracle.” WIMP stands for “weakly-interacting massive particle,” and WIMPs are the most widely accepted candidates for dark matter. Theory says WIMPs are likely heavier than protons and interact via the weak force, or at least interactions related to the weak force. The last bit is important, because freeze-out for a specific particle depends on what forces affect it and the mass of the particle. Thermal relics made by the weak force were born early in the universe’s history because particles need to be jammed in tight for the weak force, which only works across short distances, to be a factor.

    “If dark matter is a thermal relic, you can calculate how big the interaction [between dark matter particles] needs to be,” Buckley says. Both the primordial light known as the cosmic microwave background [CMB] and the behavior of galaxies tell us that most dark matter must be slow-moving (“cold” in the language of physics).

    COBE CMB


    NASA/COBE 1989 to 1993.


    Cosmic Microwave Background NASA/WMAP


    NASA/WMAP 2001 to 2010


    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    That means interactions between dark matter particles must be low in strength. “Through what is perhaps a very deep fact about the universe,” Buckley says, “that interaction turns out to be the strength of what we know as the weak nuclear force.” That’s the WIMP miracle: The numbers are perfect to make just the right amount of WIMPy matter. The big catch, though, is that experiments haven’t found any WIMPs yet.

    It’s too soon to say WIMPs don’t exist, but it does rule out some of the simpler theoretical predictions about them.

    Ultimately, the WIMP miracle could just be a coincidence. Instead of the weak force, dark matter could involve a new force of nature that doesn’t affect ordinary matter strongly enough to detect. In that scenario, says Jessie Shelton of the University of Illinois at Urbana-Champaign, “you could have thermal freeze-out, but the freeze-out is of dark matter to some other dark field instead of [something in] the Standard Model.” In that scenario, dark matter would still be a thermal relic but not a WIMP. For Shelton, Buckley, and many other physicists, the dark matter search is still full of possibilities. “We have really compelling reasons to look for thermal WIMPs,” Shelton says. “It’s worth remembering that this is only one tiny corner of a much broader space of possibilities.”

    Well, what about AXIONS?

    CERN CAST Axion Solar Telescope


    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington

    Origins of Dark Matter Research

    Vera Rubin measuring spectra (Emilio Segre Visual Archives AIP SPL)

    Vera Florence Cooper Rubin was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted angular motion of galaxies and the observed motion, by studying galactic rotation curves. This phenomenon became known as the galaxy rotation problem, and was evidence of the existence of dark matter. Although initially met with skepticism, Rubin’s results were confirmed over subsequent decades. Her legacy was described by The New York Times as “ushering in a Copernican-scale change” in cosmological theory.

    Fritz Zwicky, the Father of Dark Matter research.No image credit after long search

    Fritz Zwicky, a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and observational astronomy. In 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter, describing it as “dunkle Materie

    There was no Nobel award for either Rubin or Zwicky.

    See the full article here .

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  • richardmitnick 8:05 pm on September 25, 2017 Permalink | Reply
    Tags: , , , , , , , , , DM axions, , , , The origin of solar flares, WIMPS   

    From CERN Courier: “Study links solar activity to exotic dark matter” 


    CERN Courier

    1
    Solar-flare distributions

    The origin of solar flares, powerful bursts of radiation appearing as sudden flashes of light, has puzzled astrophysicists for more than a century. The temperature of the Sun’s corona, measuring several hundred times hotter than its surface, is also a long-standing enigma.

    A new study suggests that the solution to these solar mysteries is linked to a local action of dark matter (DM). If true, it would challenge the traditional picture of DM as being made of weakly interacting massive particles (WIMPs) or axions, and suggest that DM is not uniformly distributed in space, as is traditionally thought.

    The study is not based on new experimental data. Rather, lead author Sergio Bertolucci, a former CERN research director, and collaborators base their conclusions on freely available data recorded over a period of decades by geosynchronous satellites. The paper presents a statistical analysis of the occurrences of around 6500 solar flares in the period 1976–2015 and of the continuous solar emission in the extreme ultraviolet (EUV) in the period 1999–2015. The temporal distribution of these phenomena, finds the team, is correlated with the positions of the Earth and two of its neighbouring planets: Mercury and Venus. Statistically significant (above 5σ) excesses of the number of flares with respect to randomly distributed occurrences are observed when one or more of the three planets find themselves in a slice of the ecliptic plane with heliocentric longitudes of 230°–300°. Similar excesses are observed in the same range of longitudes when the solar irradiance in the EUV region is plotted as a function of the positions of the planets.

    These results suggest that active-Sun phenomena are not randomly distributed, but instead are modulated by the positions of the Earth, Venus and Mercury. One possible explanation, says the team, is the existence of a stream of massive DM particles with a preferred direction, coplanar to the ecliptic plane, that is gravitationally focused by the planets towards the Sun when one or more of the planets enter the stream. Such particles would need to have a wide velocity spectrum centred around 300 km s–1 and interact with ordinary matter much more strongly than typical DM candidates such as WIMPs. The non-relativistic velocities of such DM candidates make planetary gravitational lensing more efficient and can enhance the flux of the particles by up to a factor of 106, according to the team.

    Co-author Konstantin Zioutas, spokesperson for the CAST experiment at CERN, accepts that this interpretation of the solar and planetary data is speculative – particularly regarding the mechanism by which a temporarily increased influx of DM actually triggers solar activity.

    CERN CAST Axion Solar Telescope

    However, he says, the long persisting failure to detect the ubiquitous DM might be due to the widely assumed small cross-section of its constituents with ordinary matter, or to erroneous DM modelling. “Hence, the so-far-adopted direct-detection concepts can lead us towards a dead end, and we might find that we have overlooked a continuous communication between the dark and the visible sector.”

    Models of massive DM streaming particles that interact strongly with normal matter are few and far between, although the authors suggest that “antiquark nuggets” are best suited to explain their results. “In a few words, there is a large ‘hidden’ energy in the form of the nuggets,” says Ariel Zhitnitsky, who first proposed the quark-nugget dark-matter model in 2003. “In my model, this energy can be precisely released in the form of the EUV radiation when the anti-nuggets enter the solar corona and get easily annihilated by the light elements present in such a highly ionised environment.”

    The study calls for further investigation, says researchers. “It seems that the statistical analysis of the paper is accurate and the obtained results are rather intriguing,” says Rita Bernabei, spokesperson of the DAMA experiment, which for the first time in 1998 claimed to have detected dark matter in the form of WIMPs on the basis of an observed seasonal modulation of a signal in their scintillation detector.

    DAMA-LIBRA at Gran Sasso

    “However, the paper appears to be mostly hypothetical in terms of this new type of dark matter.”

    The team now plans to produce a full simulation of planetary lensing taking into account the simultaneous effect of all the planets in the solar system, and to extend the analysis to include sunspots, nano-flares and other solar observables. CAST, the axion solar telescope at CERN, will also dedicate a special data-taking period to the search for streaming DM axions.

    “If true, our findings will provide a totally different view about dark matter, with far-reaching implications in particle and astroparticle physics,” says Zioutas. “Perhaps the demystification of the Sun could lead to a dark-matter solution also.”

    Further reading

    S Bertolucci et al. 2017 Phys. Dark Universe 17 13. Elsevier

    http://www.elsevier.com/locate/dark

    See the full article here .

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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
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    CERN LHC particles

     
  • richardmitnick 4:11 pm on September 1, 2017 Permalink | Reply
    Tags: , , DEAP3600, , , , WIMPS   

    From TRIUMF: “New results surface from world’s most sensitive argon dark matter experiment” 

    TRIUMF

    31. August 2017

    1

    Argon in its natural form is a colourless, odorless, and non-flammable gas. It is also utterly unreactive – chemists and physicists have long wielded argon to formulate nonreactive and inert conditions. These qualities earned this noble gas its name, derived from the Greek word for ‘inactive.’

    What use, then, is a 3600-kilogram sphere of liquid argon, buried under two kilometers of Ontario bedrock?

    If you ask Dr. Pietro Giampa, a newly-joined TRIUMF scientist and recipient of the Otto Hausser Postdoctoral Fellowship, the simple answer (accompanied by a knowing smile) is: “Possibly changing our entire understanding of physics beyond the Standard Model, but also potentially the entire universe.” He delivers this response with the ease of repetition, a common trait among dark matter physicists. And while it may seem like a lofty claim, for Giampa and a dedicated team of particle physicists, astrophysicists, and astronomers at SNOLAB in Sudbury, ON, the proof may very well be in the depths of liquid argon.

    SNOLAB, Sudbury, Ontario, Canada.

    Deeper understanding

    The sphere of argon is a dark matter detector, and the central component of a state-of-the-art system called DEAP-3600: ‘Dark Matter Experiment using Argon Pulse-shape’ (with the argon weighing in at just over 3600 kilograms). Giampa and the DEAP-3600 team are working to characterize the fundamental properties of dark matter, a nebulous substance that makes up 23% of the mass of our universe and which we know next to nothing about.

    DEAP-3600 is in search of a host of particles widely considered the most viable candidates for dark matter: weakly interacting massive particles, or WIMPs. WIMPs behave similarly to the building-block particles of our universe like protons and neutrons, except that they don’t interact via any forces other than the electroweak and gravitational. This means that most WIMPs pass through our world without any interaction with atoms, subatomic particles, or nearly anything else.

    DEAP-3600 works by listening for collisions between dark matter and the nuclei of argon atoms. The impacts will be faint, and the apparatus can only listen in on one bandwidth at a time. Theoretical models beyond the Standard Model point to a WIMP of mass 100 gigaelectronvolts (GeV) or greater, a range DEAP is uniquely capable of investigating.

    Essentially, the detector provides a small sphere of space where collision events between WIMPs and the nuclei of argon atoms can be quietly recorded. Inactive argon, which undergoes no radioactive decay unless perturbed, is the perfect target for incoming dark matter particles; situating the argon sphere 2070 meters below Earth’s surface only heightens DEAP’s senses, eliminating the white noise of WIMP-like cosmic rays and muons. With a sufficiently large detector space and a sufficiently sensitive detection apparatus, there’s a chance that we’ll bear witness to the first WIMP ever observed as it glances off an argon atom.

    2
    DEAP-3600 takes a long, hard listen; silence.

    The DEAP team’s first results have surfaced: a new paper published by the group on August 1st, 2017 describes preliminary results from the experiment, and conclusions gleaned from just four and a half days of data-taking immediately following the completion of the detector system in August 2016. The paper details an extremely sensitive system, and a similarly sensitive, high-performance mathematical model for discriminating between the energy signals of WIMPs of different masses near the 100 GeV range.

    The experiment didn’t observe any dark matter-argon collisions during its initial monitoring period, but this absence of signal is itself a telling sign. While the number of potential WIMP-argon collisions is as large as the diversity of WIMP masses, it is finite – by ruling out different masses of WIMPs, Giampa and the DEAP team are honing in on the mass of the WIMP that may interact with an argon nucleus.

    Finding such a particle would be a boon for the field of particle physics. While WIMPS were chosen because they fit snugly into current theoretical models as potential dark matter particles, their discovery would have vast ramifications that extend beyond our current understanding of particle physics. Our entire concept of the universe would undergo a dramatic, tectonic shift.

    With this lofty goal as their north star, the DEAP team (including TRIUMF scientists Pierre-Andre Amadruz, Ben Smith, Thomas Lidner, and TRIUMF team leader Fabrice Retiere) will continue their search, re-calibrating and tuning into different bandwidths of potential collisions. Further data-taking has been ongoing since August 2016, and it’s possible that more results will surface soon.

    “We’re very excited to have proven the precision and sensitivity of the detector apparatus. While we’re but one of the many experiments around the world investigating the identity of dark matter, we can’t help but think that we are now one step closer to making this remarkable discovery.” – Dr. Pietro Giampa

    To keep tabs on the DEAP team or to learn more about the experiment, visit: http://deap3600.ca/

    See the full article here .

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    Canada’s national laboratory for particle and nuclear physics
    Member Universities:
    University of Alberta, University of British Columbia, Carleton University, University of Guelph, University of Manitoba, Université de Montréal, Simon Fraser University,
    Queen’s University, University of Toronto, University of Victoria, York University. Not too shabby, eh?

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  • richardmitnick 11:39 am on June 30, 2017 Permalink | Reply
    Tags: , , , , WIMPS   

    From aeon: “In the dark” 

    1

    aeon

    6.29.17
    Alexander B Fry

    1
    Photomultiplier array at LUX, SURF, South Dakota. Photo courtesy of Luxdarkmatter.org

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

    Lux Dark Matter Experiment

    SURF building in Lead SD USA

    LUX Xenon experiment at SURF, Lead, SD, USA


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event


    Higgs Always the last place your look.

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

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

    DAMA-LIBRA at Gran Sasso

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

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

    XENON1T at Gran Sasso

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

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

    Lux Zeplin project at SURF

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

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

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

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

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

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

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

    See the full article here .

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  • richardmitnick 5:00 pm on June 13, 2017 Permalink | Reply
    Tags: A different kind of dark matter could help to resolve an old celestial conundrum, , , , , , , Dark matter superfluid, Dark matter vortices, , Kent Ford, , , WIMPS   

    From Quanta: “Dark Matter Recipe Calls for One Part Superfluid” 

    Quanta Magazine
    Quanta Magazine

    June 13, 2017
    Jennifer Ouellette

    A different kind of dark matter could help to resolve an old celestial conundrum.

    1
    Markos Kay for Quanta Magazine

    For years, dark matter has been behaving badly. The term was first invoked nearly 80 years ago by the astronomer Fritz Zwicky, who realized that some unseen gravitational force was needed to stop individual galaxies from escaping giant galaxy clusters. Later, Vera Rubin and Kent Ford used unseen dark matter to explain why galaxies themselves don’t fly apart.

    Yet even though we use the term “dark matter” to describe these two situations, it’s not clear that the same kind of stuff is at work. The simplest and most popular model holds that dark matter is made of weakly interacting particles that move about slowly under the force of gravity. This so-called “cold” dark matter accurately describes large-scale structures like galaxy clusters. However, it doesn’t do a great job at predicting the rotation curves of individual galaxies. Dark matter seems to act differently at this scale.

    In the latest effort to resolve this conundrum, two physicists have proposed that dark matter is capable of changing phases at different size scales. Justin Khoury, a physicist at the University of Pennsylvania, and his former postdoc Lasha Berezhiani, who is now at Princeton University, say that in the cold, dense environment of the galactic halo, dark matter condenses into a superfluid — an exotic quantum state of matter that has zero viscosity. If dark matter forms a superfluid at the galactic scale, it could give rise to a new force that would account for the observations that don’t fit the cold dark matter model. Yet at the scale of galaxy clusters, the special conditions required for a superfluid state to form don’t exist; here, dark matter behaves like conventional cold dark matter.

    “It’s a neat idea,” said Tim Tait, a particle physicist at the University of California, Irvine. “You get to have two different kinds of dark matter described by one thing.” And that neat idea may soon be testable. Although other physicists have toyed with similar ideas, Khoury and Berezhiani are nearing the point where they can extract testable predictions that would allow astronomers to explore whether our galaxy is swimming in a superfluid sea.

    Impossible Superfluids

    Here on Earth, superfluids aren’t exactly commonplace. But physicists have been cooking them up in their labs since 1938. Cool down particles to sufficiently low temperatures and their quantum nature will start to emerge. Their matter waves will spread out and overlap with one other, eventually coordinating themselves to behave as if they were one big “superatom.” They will become coherent, much like the light particles in a laser all have the same energy and vibrate as one. These days even undergraduates create so-called Bose-Einstein condensates (BECs) in the lab, many of which can be classified as superfluids.

    Superfluids don’t exist in the everyday world — it’s too warm for the necessary quantum effects to hold sway. Because of that, “probably ten years ago, people would have balked at this idea and just said ‘this is impossible,’” said Tait. But recently, more physicists have warmed to the possibility of superfluid phases forming naturally in the extreme conditions of space. Superfluids may exist inside neutron stars, and some researchers have speculated that space-time itself may be a superfluid. So why shouldn’t dark matter have a superfluid phase, too?

    To make a superfluid out of a collection of particles, you need to do two things: Pack the particles together at very high densities and cool them down to extremely low temperatures. In the lab, physicists (or undergraduates) confine the particles in an electromagnetic trap, then zap them with lasers to remove the kinetic energy and lower the temperature to just above absolute zero.

    2
    Lucy Reading-Ikkanda/Quanta Magazine

    The dark matter particles that would make Khoury and Berezhiani’s idea work are emphatically not WIMP-like. WIMPs should be pretty massive as fundamental particles go — about as massive as 100 protons, give or take. For Khoury’s scenario to work, the dark matter particle would have to be a billion times less massive. Consequently, there should be billions of times as many of them zipping through the universe — enough to account for the observed effects of dark matter and to achieve the dense packing required for a superfluid to form. In addition, ordinary WIMPs don’t interact with one another. Dark matter superfluid particles would require strongly interacting particles.

    The closest candidate is the axion, a hypothetical ultralight particle with a mass that could be 10,000 trillion trillion times as small as the mass of the electron. According to Chanda Prescod-Weinstein, a theoretical physicist at the University of Washington, axions could theoretically condense into something like a Bose-Einstein condensate.

    But the standard axion doesn’t quite fit Khoury and Berezhiani’s needs. In their model, particles would need to experience a strong, repulsive interaction with one another. Typical axion models have interactions that are both weak and attractive. That said, “I think everyone thinks that dark matter probably does interact with itself at some level,” said Tait. It’s just a matter of determining whether that interaction is weak or strong.

    Cosmic Superfluid Searches

    The next step for Khoury and Berezhiani is to figure out how to test their model — to find a telltale signature that could distinguish this superfluid concept from ordinary cold dark matter. One possibility: dark matter vortices. In the lab, rotating superfluids give rise to swirling vortices that keep going without ever losing energy. Superfluid dark matter halos in a galaxy should rotate sufficiently fast to also produce arrays of vortices. If the vortices were massive enough, it would be possible to detect them directly.

    Inside galaxies, the role of the electromagnetic trap would be played by the galaxy’s gravitational pull, which could squeeze dark matter together enough to satisfy the density requirement. The temperature requirement is easier: Space, after all, is naturally cold.

    Outside of the “halos” found in the immediate vicinity of galaxies, the pull of gravity is weaker, and dark matter wouldn’t be packed together tightly enough to go into its superfluid state. It would act as dark matter ordinarily does, explaining what astronomers see at larger scales.

    But what’s so special about having dark matter be a superfluid? How can this special state change the way that dark matter appears to behave? A number of researchers over the years have played with similar ideas. But Khoury’s approach is unique because it shows how the superfluid could give rise to an extra force.

    In physics, if you disturb a field, you’ll often create a wave. Shake some electrons — for instance, in an antenna — and you’ll disturb an electric field and get radio waves. Wiggle the gravitational field with two colliding black holes and you’ll create gravitational waves. Likewise, if you poke a superfluid, you’ll produce phonons — sound waves in the superfluid itself. These phonons give rise to an extra force in addition to gravity, one that’s analogous to the electrostatic force between charged particles. “It’s nice because you have an additional force on top of gravity, but it really is intrinsically linked to dark matter,” said Khoury. “It’s a property of the dark matter medium that gives rise to this force.” The extra force would be enough to explain the puzzling behavior of dark matter inside galactic halos.

    A Different Dark Matter Particle

    Dark matter hunters have been at work for a long time. Their efforts have focused on so-called weakly interacting massive particles, or WIMPs. WIMPs have been popular because not only would the particles account for the majority of astrophysical observations, they pop out naturally from hypothesized extensions of the Standard Model of particle physics.

    Yet no one has ever seen a WIMP, and those hypothesized extensions of the Standard Model haven’t shown up in experiments either, much to physicists’ disappointment.

    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.

    With each new null result, the prospects dim even more, and physicists are increasingly considering other dark matter candidates. “At what point do we decide that we’ve been barking up the wrong tree?” said Stacy McGaugh, an astronomer at Case Western Reserve University.

    Unfortunately, this is unlikely to be the case: Khoury’s most recent computer simulations suggest that vortices in the dark matter superfluid would be “pretty flimsy,” he said, and unlikely to offer researchers clear-cut evidence that they exist. He speculates it might be possible to exploit the phenomenon of gravitational lensing to see if there are any scattering effects, similar to how a crystal will scatter X-ray light that passes through it.

    Gravitational Lensing NASA/ESA

    Astronomers could also search for indirect evidence that dark matter behaves like a superfluid. Here, they’d look to galactic mergers.

    The rate that galaxies collide with one another is influenced by something called dynamical friction. Imagine a massive body passing through a sea of particles. Many of the small particles will get pulled along by the massive body. And since the total momentum of the system can’t change, the massive body must slow down a bit to compensate.

    That’s what happens when two galaxies start to merge. If they get sufficiently close, their dark matter halos will start to pass through each other, and the rearrangement of the independently moving particles will give rise to dynamical friction, pulling the halos even closer. The effect helps galaxies to merge, and works to increase the rate of galactic mergers across the universe.

    But if the dark matter halo is in a superfluid phase, the particles move in sync. There would be no friction pulling the galaxies together, so it would be more difficult for them to merge. This should leave behind a telltale pattern: rippling interference patterns in how matter is distributed in the galaxies.

    Perfectly Reasonable Miracles

    While McGaugh is mostly positive about the notion of superfluid dark matter, he confesses to a niggling worry that in trying so hard to combine the best of both worlds, physicists might be creating what he terms a “Tycho Brahe solution.” The 16th-century Danish astronomer invented a hybrid cosmology in which the Earth was at the center of the universe but all the other planets orbited the sun. It attempted to split the difference between the ancient Ptolemaic system and the Copernican cosmology that would eventually replace it. “I worry a little that these kinds of efforts are in that vein, that maybe we’re missing something more fundamental,” said McGaugh. “But I still think we have to explore these ideas.”

    Tait admires this new superfluid model intellectually, but he would like to see the theory fleshed out more at the microscopic level, to a point where “we can really calculate everything and show why it all works out the way it’s supposed to. At some level, what we’re doing now is invoking a few miracles” in order to get everything to fit into place, he said. “Maybe they’re perfectly reasonable miracles, but I’m not fully convinced yet.”

    One potential sticking point is that Khoury and Berezhiani’s concept requires a very specific kind of particle that acts like a superfluid in just the right regime, because the kind of extra force produced in their model depends upon the specific properties of the superfluid. They are on the hunt for an existing superfluid — one created in the lab — with those desired properties. “If you could find such a system in nature, it would be amazing,” said Khoury, since this would essentially provide a useful analog for further exploration. “You could in principle simulate the properties of galaxies using cold atoms in the lab to mimic how superfluid dark matter behaves.”

    While researchers have been playing with superfluids for many decades, particle physicists are only just beginning to appreciate the usefulness of some of the ideas coming from subjects like condensed matter physics. Combining tools from those disciplines and applying it to gravitational physics might just resolve the longstanding dispute on dark matter — and who knows what other breakthroughs might await?

    “Do I need superfluid models? Physics isn’t really about what I need,” said Prescod-Weinstein. “It’s about what the universe may be doing. It may be naturally forming Bose-Einstein condensates, just like masers naturally form in the Orion nebula. Do I need lasers in space? No, but they’re pretty cool.”

    See the full article here .

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

     
  • richardmitnick 12:05 pm on May 23, 2017 Permalink | Reply
    Tags: , Bubble chamber, , FNAL PICO, , , WIMPS   

    From FNAL: “Sleuths use bubbles to look for WIMPs” 

    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.

    May 22, 2017
    Dan Garisto

    Invisible, imperceptible and yet far more common than ordinary matter, dark matter makes up an astounding 85 percent of the universe’s mass. Physicists are slowly but steadily tracking down the nature of this unidentified substance. The latest result from the PICO experiment places some of the best limits yet on the properties of certain types of dark matter.

    PICO searches for WIMPs (weakly interacting massive particles), a hypothesized type of dark matter particle that would interact only rarely, which makes them difficult to find.

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    FNAL PICO. 6,800 feet underground, PICO-60 is installed into its pressure vessel, which sits in a water tank. Photo: Dan Baxter

    In this extreme cosmic game of “Where’s Waldo?” the newest, most technologically complex detectors are usually considered the most promising. Many of these dark matter experiments rely on hundreds if not thousands of electrical channels and require racks of computer servers just to store the data they collect.

    But PICO relies on a simple phenomenon and a fairly low-key detector: bubbles, and a bubble chamber. At its core, PICO’s apparatus is simply a glass jar filled with fluid in which bubbles can form and be monitored by a video camera.

    Reinventing the bubble

    PICO had its beginnings in 2005 as a collaboration between the University of Chicago and the U.S. Department of Energy’s Fermilab. (The experiment started under a different name, COUPP, and later merged with the PICASSO experiment to form PICO.) In the experiment’s early days, much of Fermilab scientists’ work was devoted simply to developing bubble chamber technology. Because while the bubble chamber was hardly new — it was invented in 1952 — the technology had also been out of use for 20 years.

    Bubble chambers are designed to convert the energy deposited by a subatomic particle into a bubble that can be observed. In a liquid such as room temperature water, particle collisions do nothing noticeable. To achieve sensitivity to particles, the fluid inside bubble chambers is heated to just above its boiling point, so the slightest disruption could tip the fluid to a boiling state, creating a bubble.

    “You can actually watch the chamber and see the bubble form,” said Fermilab physicist Hugh Lippincott, a collaborator on PICO. In typical particle physics experiments, information about particle interactions is given solely through computer interfaces. In PICO, the interactions are visible to the naked eye as bubbles.

    “It’s great to press your face up against the glass and just … pop!” said Fermilab physicist Andrew Sonnenschein, also a collaborator on PICO.

    If WIMPs exist, they should occasionally interact with fluid in PICO’s bubble chamber, creating a certain number of bubbles every year.

    It was a return to old-school, low-tech particle physics when Fermilab collaborators began engineering the PICO bubble chamber, which is installed 2 kilometers underground at the Canadian laboratory SNOLAB.

    SNOLAB, Sudbury, Ontario, Canada.

    Bubble chambers of decades past had been used to track millions of charged particles such as protons and electrons, which would leave long, winding tracks in the fluid.

    “Old bubble chambers had a great run, but it ended in the ’80s,” Sonnenschein said. “They were too slow to keep up with experiments that had much larger data rates.”

    As a result, bubble chambers were phased out when modern particle colliders such as Fermilab’s Tevatron and CERN’s Large Hadron Collider took over. Using complex electronics, detectors at these colliders were able to collect millions of times more data than bubble chambers.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    In fact, bubble chambers had been out of commission for so long that PICO’s founders had to go back to the drawing board, return to some of the papers of the original bubble chamber pioneers, and effectively reinvent the technology for detecting dark matter.

    “After the early bubble chamber designers figured out how to make them work to track high-energy particles with trails of bubbles, the basic ingredients of the recipe didn’t change. We’re looking for low-energy particles that make only single bubbles, so many things are different,” Sonnenschein said.

    The new design to allow bubble chambers to detect dark matter still preserves many of the elements from older bubble chamber detectors.

    “The thing that makes PICO interesting is that we’re using a relatively simple detector design compared to the other dark matter experiments,” said Dan Baxter, a Northwestern University graduate student and Fermilab fellow who was PICO’s latest run coordinator.

    Unlike traditional charged-particle-detecting bubble chambers, PICO’s bubble chamber is designed to look for elusive, neutrally charged WIMPs that might take years to make an appearance.

    “It’s using it in a different way,” Lippincott said. “In the old days, you would never expect to use a bubble chamber by just letting it sit there without anything happening.”

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    PICO-60’s inner vessel is cleaned to remove even microscopic particles. Photo: Dan Baxter

    A WIMPy bubble

    The weak force that governs WIMPs lives up to its name. For comparison, it’s about 10,000 times weaker than the electromagnetic force. Particles that interact through the weak force, such as WIMPs and neutrinos, don’t interact often, making them hard to capture. But even a slow-moving WIMP can deposit enough energy to be visible in a detector.

    By carefully calibrating heat and pressure in PICO’s bubble chamber fluid, scientists were able to make the detector sensitive only to the interactions from massive particles like WIMPs. PICO researchers were able to avoid much of the standard background, such as signals from electrons and gamma rays, that plague other dark matter detectors.

    Mastering the technology to do this took years. Predecessors to PICO started off as little more than test tubes filled with a few teaspoons of liquid. Gradually, the vessels grew larger. Then researchers added sound monitoring to their detectors to capture the “pops” from bubbles created by WIMPs.

    “We see a sound chirp,” Sonnenschein said, referring to the bubbles popping. “It turns out that if you look at the frequency content of the sound chirp and the amplitude, you can tell the difference between different kinds of particle interactions.”

    If a WIMP created a bubble, PICO would be able to not only see evidence of dark matter, but hear it as well. Using this acoustic technology, researchers were able to effectively veto bubbles that could not have been created by WIMPs, allowing them to eliminate background.

    As it turns out, PICO did not see any bubbles from WIMPs, so they were able to place limits on both WIMP masses and the likelihood that they will interact with matter — two factors that influence the number of bubbles WIMPs produce.

    Placing limits on these factors — mass and interaction rate — can tell physicists where they should look next for dark matter.

    Where no bubble has gone before

    “We don’t know what dark matter is, and so there’s a lot of theories about what it could be and about how it could interact with normal matter,” Baxter said.

    The variety of theories calls for a variety of different experiments. Other experiments search for different sources of dark matter, such as particles called axions or sterile neutrinos. PICO’s search for WIMPs has a specific focus on so-called spin-dependent WIMPs.

    “We don’t know what the WIMPs are,” Lippincott said. “But broadly speaking their interactions with normal matter would fall into two categories: one that isn’t sensitive to the spin of the nucleus, and one that is.”

    Spin, like charge, is an intrinsic quantity carried by particles and atomic nuclei. PICO looks primarily for WIMP interactions that are sensitive to the spin of the nucleus. To boost their resolution of these interactions, the researchers use a fluid with a liquid containing fluorine, which has a relatively large nuclear spin. With this method, PICO increased their ability to see spin-sensitive WIMPs by a factor of 17.

    Essentially, PICO’s result is that these spin-sensitive WIMPs, if they exist, must interact extremely infrequently — otherwise PICO would have seen more bubbles.

    This result, which is by far the best yet for spin-sensitive WIMPs interacting with protons, does not rule out the existence of WIMPs. There are many other places left to still look for dark matter, but thanks to PICO, fewer places for it to hide.

    The PICO collaboration currently has a proposal in to the Canada Foundation for Innovation to build the next generation of PICO chamber, and physicists like Lippincott and Sonnenschein remain optimistic because of the technology’s potential to scale up.

    “They’re pretty cheap once the engineering is done, mainly because they’re very simple mechanically. The fiddly bits are not very fiddly,” Lippincott said. “There’s a good chance that bubble chambers will continue to play a role in the hunt for dark matter.”

    PICO comprises about 50 physicists at 20 institutions in the Canada, Europe, India, Mexico and the United States and receives support from the U.S. Department of Energy Office of Science and National Science Foundation.

    See the full article here .

    Please help promote STEM in your local schools.

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    FNAL Icon
    Fermilab Campus

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

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

    From Symmetry: “WIMPs in the dark matter wind” 

    Symmetry Mag

    Symmetry

    04/04/17
    Lori Ann White

    1
    No image credit found

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

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

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

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

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

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

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

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

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

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

    DAMA LIBRA Dark Matter Experiment

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

    CoGeNT experiment

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

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

    DEAP Dark Matter detector

    SNOLAB, Sudbury, Ontario, Canada.

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

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

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

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

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

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

    Or not.

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

    Even that, Monroe says, is progress.

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

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


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

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

    Nautilus

    Nautilus

    3.6.17
    Matthew Sedacca

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

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

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

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

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

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

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

    3
    COSINE-100 Dark Matter Experiment – Yale University

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

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

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

    What do the scientists behind DAMA claim to have discovered?

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

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

    7
    University of Wisconsin–Madison, DM-Ice collaborators

    So what is dark matter?

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

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

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

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

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

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

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

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

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

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

    What’s it like working in the South Pole?

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

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

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

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

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

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

    What’s the future for DM-Ice?

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

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
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