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  • richardmitnick 11:15 am on October 8, 2015 Permalink | Reply
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    From FNAL: “Dan Bauer leads SuperCDMS as new spokesperson” 

    FNAL II photo

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

    Oct. 8, 2015
    Leah Hesla

    Temp 1
    Dan Bauer

    The Cryogenic Dark Matter Search has gone through a number of major changes over the years. In 2002, operations moved from Stanford University to the Soudan Mine in Minnesota. In 2010, the CDMS collaboration installed more advanced germanium detectors and renamed itself SuperCDMS.

    And in 2019, the experiment will begin a new phase in the underground Canadian laboratory SNOLAB.


    Fermilab scientist Dan Bauer will lead the SuperCDMS collaboration through this upcoming transition as its recently elected spokesperson. He began his three-year term in May, taking over from Blas Cabrera of Stanford University. Prior to his role as spokesperson, Bauer served CDMS and SuperCDMS as project manager and project scientist for 13 years.

    SuperCDMS is one of several experiments around the world that is on the hunt for dark matter, hypothesized invisible stuff that holds galaxies together. SuperCDMS’ goal is to detect it in the form of WIMPs: weakly interacting massive particles. The experiment will focus particularly on light WIMPS, with masses less than 10 times the mass of the proton.

    Bauer’s main goal is to make sure the move to SNOLAB, whose cleaner environment and greater depth beneath ground will help reduce backgrounds in the experiment, goes off smoothly.

    It’s not a matter of popping the experiment on a truck and sending it on its way to Ontario. One major piece of the transition is building a considerably larger, more complicated cryogenic system to lower the sensors’ temperature from 50 millikelvin, their temperature in Soudan, to a mere 15 millikelvin. Colder sensors and improved shielding will allow the detectors to be more sensitive to potential dark matter interactions.

    “We’ve been doing a lot of physics at Soudan, and switching to a new site is always a challenge,” Bauer said. “We want to be set up to do the best possible experiment at SNOLAB.”

    Bauer is working to add new institutions to the collaboration, including SNOLAB. He is also in discussions with members of two similar experiments in Europe (Edelweiss and CRESST) to bring their detectors to SuperCDMS SNOLAB.

    Edelweiss experiment

    CRESST experiment

    The SuperCDMS collaboration currently has members from 21 institutions, including SLAC National Accelerator Laboratory (the project managing institution), Pacific Northwest National Laboratory, U.S. and Canadian universities, a group in the UK, and NISER in India.

    “I’m looking forward to building a new experiment — that’s always fun,” Bauer said. “Seeing dark matter particles for the first time would be fantastic.”

    See the full article here .

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    Fermilab Campus

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

  • richardmitnick 5:42 pm on September 28, 2015 Permalink | Reply
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    From AAAS: “X-ray signal from outer space points to dark matter” 



    25 September 2015
    Edwin Cartlidge

    Data from the European Space Agency’s XMM-Newton x-ray satellite contain a possible signal of dark matter.

    For years, high-energy radiation from space has been teasing scientists with inconclusive hints of dark matter. But a definitive answer may be at hand. A team of physicists says that certain galactic x-rays could be a sign of decaying dark matter, and that an upcoming satellite mission should prove or disprove their claim.

    Dark matter makes up about 80% of matter in the universe, but no one knows exactly what it is. Most theorists suspect it consists of so-called weakly interacting massive particles (WIMPs)—undiscovered subatomic particles that give off so little light that we can’t see them, though they still interact with other matter through gravity and the weak nuclear force. But laboratory experiments haven’t spotted them, and the most likely evidence from space—gamma rays that putative WIMPs would give off while annihilating one another in the centers of galaxies—are swamped by cascades of gamma rays from other sources such as hot gas.

    Particle physicist Alexey Boyarsky of Leiden University in the Netherlands and colleagues went after a different quarry. They scoured data from the European Space Agency’s XMM-Newton orbiting x-ray observatory, for signs of particles weighing a few thousand electron-volts—a millionth as massive as WIMPs. In theory, particles like that—if they exist—should decay inside galactic centers and other objects in space to produce x-rays with a certain energy. The group started its search in 2005 and for years remained empty-handed. But they finally got lucky: Last year they reported finding a peak at 3.5 thousand electron-volts (keV) in the x-ray energy spectrum from both the Milky Way’s nearest neighbor, the Andromeda Galaxy, and the Perseus galaxy cluster. At the same time, another group—physicist Esra Bulbul of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and colleagues—reported finding an emission line at about 3.5 keV in the combined spectra from 73 galaxy clusters.

    Now, in a paper accepted for publication in Physical Review Letters, Boyarsky’s group reports a similar peak in x-rays from the core of the Milky Way. The intensity of the peak lies in the right range to be produced by dark matter reactions, the researchers say: higher than a lower limit inferred from the galaxy cluster data, but lower than a ceiling calculated from studies of the Milky Way’s less dense outer regions. “We can’t prove that dark matter is coming from the center of the Milky Way because we don’t know the physics around the galactic center well enough,” Boyarsky says. “But the signal passes a very nontrivial consistency check.”

    Other researchers, however, dispute the signal’s dark matter origin. Physicists Tesla Jeltema and Stefano Profumo at the University of California, Santa Cruz, have analyzed the x-rays given off by ordinary atoms inside the Milky Way, Andromeda, and the relevant galaxy clusters. They conclude that the 3.5-keV line could easily come from hot, glowing potassium and other elements blasted into space by stars.

    Meanwhile, physicist Ondrej Urban of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University in Palo Alto, California, and colleagues say data from the NASA/Japanese space agency (JAXA) Suzaku x-ray satellite show no real evidence of dark matter–like emission at 3.5 keV in the spectra of four galaxy clusters, including Perseus.

    JAXA Suzaku satellite
    JAXA Suzaku

    Boyarsky says more data are needed to settle the question. He and his colleagues have booked observing time on XMM-Newton to study the x-ray spectrum of a dwarf galaxy thought to harbor lots of dark matter but few chemical elements. “If we see the signal there, it would be very hard to interpret it in terms of normal astrophysics,” he says. “That would constitute very solid proof of dark matter.” He says he hopes to have results by early next year.

    The ultimate test could also start next year, when JAXA is scheduled launch a new x-ray satellite called ASTRO-H.

    JAXA ASTRO-H - Copy

    ASTRO-H will be able to plot the shape of the 3.5-keV peak in much more detail than current satellites can, says Jonathan Feng, a particle theorist at the University of California, Irvine. A relatively broad line, he explains, would imply that the x-rays are due to dark matter, whereas a narrower line would point to normal atoms as the source. “The 3.5-keV x-ray signal has a real chance of being definitively confirmed as dark matter in a few years, unlike other putative signals currently on the market.”

    If dark matter is the cause, physicists will still need to pin down its identity. Feng says the energy and intensity of the 3.5-keV line are “just as would be expected” from sterile neutrinos: hypothetical ultraelusive cousins of ordinary neutrinos that would give off x-rays when decaying into normal neutrinos.

    Cosmologist Kevork Abazajian, also at the University of California, Irvine, agrees that sterile neutrinos are the most likely candidate, in part because they arise in natural explanations for the existence of neutrino mass. But other hypothetical particles could also produce the signal, he adds. Ground-based measurements of β-decay—the same radioactive process that gave physicists their first hints that neutrinos exist—could settle whether keV-scale sterile neutrinos are also part of nature’s lineup, Abazajian suggests.

    See the full article here .

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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  • richardmitnick 3:10 pm on September 25, 2015 Permalink | Reply
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    From LLNL: “‘Stealth dark matter’ theory may explain universe’s missing mass” 

    Lawrence Livermore National Laboratory

    Sep. 24, 2015

    Anne M Stark

    This 3D map illustrates the large-scale distribution of dark matter, reconstructed from measurements of weak gravitational lensing by using the Hubble Space Telescope.

    Lawrence Livermore National Laboratory (LLNL) scientists have come up with a new theory that may identify why dark matter has evaded direct detection in Earth-based experiments.

    A group of national particle physicists known as the Lattice Strong Dynamics Collaboration, led by a Lawrence Livermore National Laboratory team, has combined theoretical and computational physics techniques and used the Laboratory’s massively parallel 2-petaflop Vulcan supercomputer to devise a new model of dark matter. It identifies it as naturally “stealthy” ( like its namesake aircraft, difficult to detect) today, but would have been easy to see via interactions with ordinary matter in the extremely high-temperature plasma conditions that pervaded the early universe.

    “These interactions in the early universe are important because ordinary and dark matter abundances today are strikingly similar in size, suggesting this occurred because of a balancing act performed between the two before the universe cooled,” said Pavlos Vranas of LLNL, and one of the authors of the paper, Direct Detection of Stealth Dark Matter Through Electromagnetic Polarizability. (The paper appears in an upcoming edition of the journal Physical Review Letters and is an “Editor’s Choice.”

    Dark matter makes up 83 percent of all matter in the universe and does not interact directly with electromagnetic or strong and weak nuclear forces. Light does not bounce off of it, and ordinary matter goes through it with only the feeblest of interactions. Essentially invisible, it has been termed dark matter, yet its interactions with gravity produce striking effects on the movement of galaxies and galactic clusters, leaving little doubt of its existence.

    Lawrence Livermore scientists have devised a new model of dark matter. It identifies it as naturally “stealthy” today, but would have been easy to see via interactions with ordinary matter in the extremely high-temperature plasma conditions that pervaded the early universe.

    The key to stealth dark matter’s split personality is its compositeness and the miracle of confinement. Like quarks in a neutron, at high temperatures these electrically charged constituents interact with nearly everything. But at lower temperatures they bind together to form an electrically neutral composite particle. Unlike a neutron, which is bound by the ordinary strong interaction of quantum chromodynamics (QCD), the stealthy neutron would have to be bound by a new and yet-unobserved strong interaction, a dark form of QCD.

    “It is remarkable that a dark matter candidate just several hundred times heavier than the proton could be a composite of electrically charged constituents and yet have evaded direct detection so far,” Vranas said.

    Similar to protons, stealth dark matter is stable and does not decay over cosmic times. However, like QCD, it produces a large number of other nuclear particles that decay shortly after their creation. These particles can have net electric charge but would have decayed away a long time ago. In a particle collider with sufficiently high energy (such as the Large Hadron Collider in Switzerland), these particles can be produced again for the first time since the early universe. They could generate unique signatures in the particle detectors because they could be electrically charged.

    “Underground direct detection experiments or experiments at the Large Hadron Collider may soon find evidence of (or rule out) this new stealth dark matter theory,” Vranas said.

    The LLNL lattice team authors are Evan Berkowitz, Michael Buchoff, Enrico Rinaldi, Christopher Schroeder and Pavlos Vranas, who is the lead of the team. The Laboratory Directed Research and Development, the LLNL Grand Challenge computation programs, the DOE Office of Science High Energy Theory and the High Energy Physics Lattice SciDAC program supported this research. Other collaborators include researchers from Yale University, Boston University, Institute for Nuclear Theory, Argonne Leadership Computing Facility, University of California, Davis, University of Oregon, University of Colorado, Brookhaven National Laboratory and Syracuse University.

    See the full article here .

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    Operated by Lawrence Livermore National Security, LLC, for the Department of Energy’s National Nuclear Security
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  • richardmitnick 6:19 pm on September 21, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter   

    From COSMOS: :Ghost traps: the hunt for dark matter” 

    Cosmos Magazine bloc


    21 Sep 2015
    Robin McKie

    If you were designing a villain’s lair for a James Bond movie, you would be hard pushed to create one as spectacular as Italy’s Gran Sasso Laboratory.

    Gran Sasso

    To reach it, you follow the A24 motorway west towards Rome as it plunges through a 10-kilometre tunnel drilled below the Gran Sasso National Park, a mountain range that is home to bears, wildcats, wolves, chamois and thousands of summer tourists.

    Half way along, an unsigned tunnel branches to the right. Travel 100 metres along this passageway and you reach a four-metre high, solid stainless steel door topped with barbed wire. As it swings open, a labyrinth of tunnels, uniformed guards and glittering racks of equipment appear before you. All the scene lacks is the appearance of a mysterious figure, clutching a white Persian cat, to let you know: “We’ve been expecting you, Mr Bond.”

    You won’t find a Bond villain down here. But you will find physicists, burrowed under the mountains in their hunt for dark matter. This elusive material makes up 85% of the matter in the Universe. We know it must be out there – without it galaxies would fly apart and we would not exist. But so far what it’s made of remains a mystery; we’ve been unable to detect the stuff.

    That is about to change. Researchers working in several scientific arenas – including Gran Sasso – are now confident that within the next two or three years they will make the breakthrough that will reveal the truth about dark matter.

    “There are two ways we’re likely to succeed,” says Chamkaur Ghag, who leads the “direct” dark matter search at University College London. Direct searches involve placing detectors deep underground at places such as Gran Sasso. Here 1,400 metres of rock shelters the detectors from the cacophony of particles pelting the Earth’s surface. If the physicists pick up any hint of a signal way down there, “we will know we have hit pay dirt”, Ghag says.

    In the tunnels under Gran Sasso mountain lie several traps for dark matter.Credit: Franco Fasciolo

    The other method of revealing dark matter is more dramatic. Scientists believe they should soon be able to make the invisible material inside the world’s most powerful atom-smasher, the Large Hadron Collider at the European Organisation for Nuclear Research (CERN), near Geneva.

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

    The collider recently reopened with double the power it employed during its successful hunt for the Higgs boson. Since matter and energy are interchangeable, at these massive energies particles can be created.

    More power means a greater chance of creating more massive particles – possibly dark ones. It also creates more interactions so if the creation of dark matter is extremely rare, the chances of picking it up are greater.

    “I would have thought that if dark matter exists we will be well placed to make it at CERN in the very near future,” says John Ellis, one of the organisation’s key theoretical physicists. The dark matter will be detected at CERN by its absence – the energy and mass that is missing after physicists account for all the particles in the debris of smashed protons.

    Who is likely to get there first? Will it be the subterranean teams manning underground detectors in their lairs, or will it be the collider physicists smashing protons into each other?

    “It’s going to be a very close call,” admits Ghag, who previously worked on the Xenon100 and DarkSide-50 projects at Gran Sasso and now works at a similar facility called SURF (the Sanford Underground Research Facility) in the US.

    Sanford Underground levels

    “But even if CERN gets there before us, we would still need to confirm with direct detection that the particle they make is entirely responsible for all dark matter,” he says. The CERN result – which will narrow down the energy and mass of the dark particle – would “indicate we are on the right track and are closing in on our target”, he says.

    The story of dark matter goes back to the first half of the 20th century when astronomers realised galaxies were spinning so fast that they should have flung themselves apart.

    Think of a stone tied to a piece of string. If the string is too weak, when you whizz it round your head it will snap and your stone will hurtle into the distance. And so it is with galaxies. A galaxy needs a great deal of mass to generate a gravitational field powerful enough to hold on to its rapidly rotating stars. In 1932, Dutch astronomer Jan Oort [of Oort Cloud fame] pointed his optical telescope at the Milky Way and from its luminosity and redshift (a way of measuring how fast stars are receding), estimated the mass and rotation speed of the stars. He concluded there were too few stars to glue the spinning galaxy together.

    A year later, Fritz Zwicky at the California Institute of Technology reported a similar conundrum while observing a large group of galaxies known as the Coma Cluster. At their speed of rotation, the outer galaxies ought to have been flung out. Oort and Zwicky referred to the missing galactic material as “dark matter”.

    The idea that some exotic form of invisible matter existed was hotly contested. Surely it could be explained by the inability of light telescopes to detect faint galactic objects. There was no shortage of mundane candidates: tiny stars, large dark neutron stars, brown dwarfs (small failed stars) or clouds of diffuse gas.

    But the idea of dark matter refused to go away. In the 1970s Vera Rubin and colleagues at the Carnegie Institution of Washington made more rigorous measurements of the rotation speeds and matter content of a number of galaxies. In every galaxy measured, there were far too few stars to account for the speed of the galaxy’s rotation. Something else was generating a powerful gravitational field that held each galaxy together.

    In subsequent decades, astrophysicists have eliminated virtually all the mundane candidates for dark matter. Spinning neutron stars were detected by their radio waves. Infrared detectors picked up dim stars and brown dwarfs. And space-based telescopes such as NASA’s Chandra X-ray Observatory measured the vast mass of gas clouds, such as the one that engulfs our Milky Way and weighs as much as all the stars inside. Yet when all the dim and ethereal matter is added up, it is still not enough to glue galaxies together.

    “We’ve spent more than 30 years trying to pin down objects that might account for dark matter, and have had no success,” says astrophysicist Gerry Gilmore of Cambridge University.

    Other evidence for dark matter comes from gravitational lensing. Sometimes, as a galaxy spins through an apparently empty stretch of space, multiple images appear – as if it were passing behind a warped lens. The lens in this case is inferred to be dark matter: its gravity is warping the fabric of space.

    But the strongest evidence for dark matter “is that we’re here at all”, says Alan Duffy, a theoretical physicist at Melbourne’s Swinburne University of Technology. His supercomputer-based models of the formation of the Universe show that the plasma created by the Big Bang was too hot and too smoothly distributed to have collapsed into galaxies 13 billion years later.

    But dark matter is not subject to the same frenetic interactions. It would have settled down early on, forming “wells” that ordinary detectable matter – also known as baryonic matter – could fall into.

    Having ruled out baryonic matter as the source of the missing mass, the only remaining option was that dark matter is composed of an exotic subatomic particle. It is also abundant: five times more plentiful than the baryonic matter scattered throughout the Universe.

    Physicists took to calling these numerous but mysterious bits of matter weakly interacting massive particles – or WIMPS.

    So how are we to detect a WIMP? Via one of the fundamental forces. There are four: gravity; the electromagnetic force; the strong nuclear force that glues the nuclei of atoms together; and the weak nuclear force that transforms particles from one type to another and drives radioactive decay.

    Scientists have ruled out the idea that dark matter interacts in any way with either electromagnetism or the strong nuclear force. “If it did we would have seen the results – bursts of light or radiation,” says Ghag. These would be produced whenever dark matter and regular matter particles collide.

    We know dark matter does interact with gravity. But gravity exerts a virtually undetectable force at subatomic scales. For an electron and proton, the gravitational force is 39 orders of magnitude weaker than the electromagnetic force – so gravity is not a helpful way to detect a dark matter particle.

    That means all our hopes are pinned on the last remaining force, the weak force. “And that is what we really mean when we call them weakly interacting massive particles – it’s because they may interact with the weak force,” says Ghag.

    Space must be saturated with WIMPS. Katherine Freese, a theoretical physicist at Michigan University and author of The Cosmic Cocktail: Three Parts Dark Matter, believes billions of these particles must pass through the human body every second – rather like neutrinos. Indeed neutrinos seem to fit the bill for dark matter since they have mass but only interact via the weak force. But they cannot account for dark matter. Although they are the most abundant particle in the cosmos – with one billion cosmic neutrinos for every atom – their mass is less than a billionth the mass of a proton. They are far too light to account for the missing mass in the Universe.

    Hunting for WIMPS has been “like searching for a particular kind of fish in the ocean”, says the slim, amiable Ghag, with his typical rapid-fire verbal delivery. “At first, you put on goggles and dive down just below the surface to see if you can see it. If that does not work, you try scuba gear and go deeper. Then you try a submarine until, eventually, you find it.” Or so he hopes.

    Hence the detectors installed under Gran Sasso and at several other underground laboratories have been built thousands of feet below the surface, usually in old mines. These include the Stawell gold mine near the Grampians National Park in Victoria, Australia; the old Homestake gold mine in South Dakota; and the Boulby salt mine in north England.

    The subterranean locations are important. The Earth’s surface is bombarded by sub-atomic particles called muons. These energetic, charged particles are the byproducts of high-energy cosmic rays which slam into our atmosphere so hard they smash oxygen, nitrogen and other atmospheric gases into showers of subatomic particles. “Muons light up our detectors like Christmas trees,” says Ghag. “They are so numerous they would blind us to anything else.”

    Down in Gran Sasso, shielded by 1,400 metres of rock, muon levels are one million times lower than at the surface. More of them are filtered out by placing the particle detectors in huge vats containing thousands of cubic metres of pure water. Inside the tank, a huge sphere containing a device called a scintillator is used to cut out any stray particles that make it through the water jacket. “We are putting one device inside another like a set of Russian dolls to get rid of every possible spurious signal,” says Frank Calaprice of Princeton University, who co-leads the DarkSide-50 experiment at Gran Sasso.

    Gran Sasso Darkside 50
    Gran Sasso DarkSide 50

    The last Russian doll is a stainless steel sphere containing argon or xenon liquid, with some gas on top. If a WIMP passing through hits an argon or xenon atom directly, the weak nuclear interaction between atom and particle might bump out an electron or spit out a photon. The characteristics of that signal will tell scientists if a muon has slipped through the screens or whether they have actually detected a WIMP.

    To date, despite some tantalising signals at detectors such as DAMA, physicists are yet to be convinced that any WIMP has announced its existence.

    DAMA-LIBRA at Gran Sasso
    DAMA at Gran Sasso

    While researchers are continually refining the sensitivities of their machines, it is possible that we will never catch a WIMP. Sadly (for all the billions spent on the detectors) it may be that dark matter does not interact via any of the known forces other than gravity. “One way or other, we are going to find out very soon if that is the case,” says Ghag.

    The Large Hadron Collider under Geneva was shut down for two years and upgraded to increase its energy by 60%. Scientists hope some of this energy will be converted into dark matter.Credit: Claudia Marcelloni De Oliveira / CERN

    Gran Sasso’s detectors might never trap a WIMP. But scientists at CERN are confident they can create dark matter.

    For a start, their base of operations utterly dwarfs those at Gran Sasso or South Dakota’s Homestake mine. CERN is a sprawling suburb of Geneva stacked with laboratories, dormitories, restaurants and control rooms all built over a giant circular tunnel, 27 kilometres in circumference, that makes up the Large Hadron Collider.

    The collider is roughly the size of the London Underground’s Circle Line, and has been constructed with nanometre precision. Its magnets – which guide beams of protons round its tunnel – are chilled to within two degrees above absolute zero (a temperature at which electricity flows without resistance), making the collider the coldest place on Earth. At the same time, the tube that carries those beams of protons has been sucked of virtually every atom or molecule, creating a vacuum that is purer than that found in space.

    Three years ago, CERN scientists used their astonishingly powerful and precise instrument to discover the Higgs boson. Then they shut down for two years to upgrade the machine. The LHC “is almost like a new machine now”, says CERN’s Frederick Bordry, director of accelerators and technology.

    When it discovered the Higgs, the LHC could generate energy bursts of up to eight trillion electron volts (8 TeV). Now, it can produce collisions with energies of up to 13 TeV.

    The more energy, the more likely this matter-energy soup will create new massive particles. Just as two protons collided with enough energy to form the Higgs boson – with far more than twice the mass-energy of two protons – the hope is the higher energy will create a massive dark matter particle.

    “When we batter the beams of protons into each other, we will make particles of a mass we think could be similar to those that we think account for dark matter,” says John Ellis, one of CERN’s key theorists.

    Ellis has been hunting for dark matter all his working life, albeit indirectly at first. He is an amiable, slightly shambolic figure with a massive white beard, who has been compared to Santa Claus, Dumbledore and Gandalf.

    A Cambridge University graduate, Ellis began his research on supersymmetry in the early 1970s.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Supersymmetry predicts that versions of the particles that make up normal matter possess mirror, or “supersymmetrical”, versions. Thus there could be supersymmetrical quarks – or squarks – out there. Or supersymmetrical electrons – selectrons. Ellis’s field became embroiled in the hunt for dark matter when physicists realised some types of supersymmetrical particles and WIMPS could be one and the same.

    If the Large Hadron Collider wins the battle to find these elusive entities, it will be a fitting tribute to Ellis who has directed much of CERN’s research effort over the past couple of decades. These efforts have revealed the nature of the Standard Model of Matter, which could finally be completed by incorporating the ideas of supersymmetry.

    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.


    Most CERN physicists believe supersymmetrical particles – and therefore, WIMPS – are likely to lie within the range of the upgraded collider. As Dave Charlton, head of the collider’s ATLAS detector, puts it: “The supersymmetry particles that we think we will soon be producing provide a perfectly natural explanation for dark matter – in the form of WIMPS.” He predicts that “the next couple of years promise to be extremely interesting”.

    ATLAS in the LHC at CERN

    Because dark matter rarely interacts with regular matter, it won’t appear directly in the collider’s detectors, Ellis explains. “If WIMPS are created … they will escape through the collider’s detectors unnoticed.” But when they go, they will carry away energy and momentum with them. “We will be to able to infer their existence from the amount of energy and momentum missing after a collision.”

    But there’s no guarantee says Duffy. “The collider might not be capable of producing a dark matter particle, regardless of the energies it reaches. And if it does, it has to make enough to notice that some matter is missing.”

    So who will be the first to snare these ghostly particles? Duffy has no qualms about backing the physicists at Gran Sasso. “It’s a race. But just like the tortoise and the hare, I’d rather go with the slower, surer runner.”

    Anthony Calvert is a Sydney-based illustrator.

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  • richardmitnick 8:19 am on September 20, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, Swinburne U   

    From Swinburne: “How we plan to bring dark matter to light” 

    Swinburne U bloc

    Swinburne University

    17 Sep 2015
    Alan Duffy, Swinburne University of Technology
    Elisabetta Barberio, University of Melbourne

    Long before we had the atomic theory of matter, scientists knew the air was real, even though it was invisible. This was because we could see its action as the wind caressed the leaves in trees.

    Likewise we see the influence of another invisible force in the wider cosmos in the movement of stars within galaxies. But we don’t yet know what this mysterious dark matter is made of.

    Now a new generation of detectors – including one we’re building in a gold mine in Victoria – is giving us hope that we might finally shed some light on dark matter.

    Glow in the dark

    Some models predict that whatever particle makes up dark matter is also its own antiparticle. This leads to the fascinating prediction that if two dark matter particles interact they annihilate into a shower of either exotic particles or radiation.

    If it annihilates into particles, then space-based detectors, such as the Alpha Magnetic Spectrometer (AMS) on the International Space Station, might detect unusual numbers of, say, positrons.

    The Alpha Magnetic Spectrometer mounted on the International Space Station could help detect the signs of dark matter. NASA

    If it annihiliates into radiation (or if the positrons themselves annihilate), then the radiation will be in the form of highly energetic gamma-rays, which could be detected by NASA’s Fermi Gamma-ray Space Telescope orbiting above the Earth.

    NASA Fermi Telescope
    NASA’s Fermi Gamma-ray Space Telescope

    If so, the signal will be strongest where the density of dark matter is highest. This could be near the centre of our galaxy, where it is pulled close by the enormous gravity of the densely-packed stars and supermassive black hole.

    Unfortunately, black holes and nearby exploding stars can all produce similar signals to annihilating dark matter. This makes it hard to discriminate any dark matter signal from black hole or supernovae noise.

    However, if we were to find a clump of dark matter that was glowing brightly in gamma-rays, and there were barely any stars within, then we could be far more confident that we were seeing signs of dark matter.

    Fortunately, there are such objects orbiting the Milky Way, known as an ultra-faint dwarf spheroidal galaxies. But, unfortunately, there appears to be no confirmed detection of gamma-rays from these objects, although there are hints there might be something interesting going on within.

    To confirm the nature of dark matter there is no substitute for direct detection in the lab. It might be possible to produce dark matter during collisions in the Large Hadron Collider at CERN, in which case it would fly through the detectors without ever setting them off.

    Its presence would be revealed in the same way as a dodgy accountant: we measure all the energy that goes into a collision, and we measure all the energy that comes out. If it doesn’t add up, we know that some energy has escaped in the form of dark matter.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    The Large Hadron Collider might be able to create dark matter particles. CERN

    Digging for dark gold

    There is another option, and that is to try to detect the naturally occurring dark matter of our galaxy that the Earth ploughs through each year. This relies on the ghost-like dark matter colliding with the nucleus of an atom in a head-on collision.

    Indeed, in the time it’s taken you to read this article, it’s likely that you’ve had an atom knocked away by a dark matter particle. It’s unlikely that you felt it, though, as humans make for bad detectors. But we’re building a better one.

    With an international consortium of universities, research agencies and industry we are constructing the Stawell Underground Physics Laboratory (SUPL) a kilometre underground at a gold mine in Stawell, Victoria. This will house the world’s first dark matter detector in the southern hemisphere, known as SABRE.

    We use the layers of rock above to block radiation from space that would otherwise overwhelm our sensitive detector. This ensures that only the ghostly dark matter is able to pass through the solid rock, and will occasionally collide with the detector.

    Some of the lead scientists of the SABRE experiment in the Stallwell gold mine. In the background is the radiation testing facility. Carl Knox (Swinburne University), Author provided

    The SABRE experiment consists of an ultra-pure sodium iodide crystal doped with thallium that has extraordinarily low levels of radiation (we don’t want to see our own radioactive “glow” after all). This unique crystal, created by Princeton’s Professor Frank Calaprice, will occasionally be struck by a dark matter particle, causing the nucleus of an atom to recoil away like a game of billiards. The atom will be energetically excited during the collision and eventually release this energy as a high energy gamma-ray.

    The sodium iodide crystal itself is a natural scintillator, taking this gamma-ray and producing a flash of optical light that the sensitive cameras around the crystal can detect. So, in hunting for ghosts, we look for faint flashes of light in the dark.

    We hope that, in time, we might finally shed some light on dark matter, and gain an insight into this mysterious substance that makes up five times more of the mass of the universe than what we can see.

    See the full article here .

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    Swinburne U Campus

    Swinburne is a large and culturally diverse organisation. A desire to innovate and bring about positive change motivates our students and staff. The result is in an institution that grows and evolves each year.

  • richardmitnick 3:34 pm on September 18, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter   

    From CERN: “CAST explores the dark side of the universe” 

    CERN New Masthead

    18 Sep 2015
    Corinne Pralavorio

    CERN CAST Axion Solar Telescope
    CAST – CERN Axion Solar Telescope

    Over the next 10 days, CERN’s Axion Solar Telescope (CAST) will receive the Sun’s rays. The Sun’s course is visible from the window in the CAST experimental hall just twice a year, in March and September. The scientists will take advantage of these few days to improve the alignment of the detector with respect to the position of the Sun to within a thousandth of a radian.

    Outside of this alignment operation, CAST tracks the Sun but does not see it. The astroparticle experiment is searching for solar axions, hypothetical particles that are thought to interact so weakly with ordinary matter that they pass through walls unimpeded. It is in order to catch these elusive particles that the CAST detector tracks the movement of the Sun for an hour and a half at dawn and an hour and a half at dusk.

    Axions were postulated to solve the problem of a discrepancy between the theory of the infinitely small and what is actually observed. They were named after a brand of washing powder because their existence may allow the theory to be “cleaned up”. If they exist, axions could also be good candidates for the universe’s dark matter. Dark matter is thought to represent 80% of the matter of the universe, but its nature remains unknown.

    After 12 years of research, CAST has not (yet) detected solar axions, but has established the most restrictive limit on their interaction strength. The experiment has therefore become a global reference on the subject.

    For two years, the collaboration, which involves around 70 researchers from 20 or so institutes, has also been searching for another type of hypothetical particle: chameleons. These were postulated to solve the problem of dark energy. Dark energy, which, as its name suggests, remains mysterious and undetectable, is thought to represent around 70% of the Universe’s energy and to cause the acceleration of the expansion observed in the cosmos. Theories have postulated that this dark energy may be due to a fifth force and that chameleon particles could prove the existence of this force. They were named after the reptile because they are thought to interact differently according to the density of material encountered.

    If chameleons exist, they could, like axions, be also produced by the Sun and be detected by CAST. The collaboration has therefore installed two new detectors at the end of its magnet. It is also preparing to install an innovative sensor with an ultra-thin membrane, capable of detecting a displacement of around 10-15 metres – the size of the nucleus of an atom!

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier



    CERN CMS New

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    LHC particles

    Quantum Diaries

  • richardmitnick 11:28 am on September 18, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter,   

    From phys.org: “Dark matter hiding in stars may cause observable oscillations” 


    September 18, 2015
    Lisa Zyga

    This sequence shows snapshots of a star’s density when two dark matter cores collide, where the x-axis is the plane of collision (only half the space is shown, but the remaining space can be obtained by symmetry). Although the final configuration is more compact and massive than the original, the star does not collapse into a black hole because it ejects some of its mass, slowing down its growth so that it remains stable. Credit: Brito, et al. ©2015 American Physical Society

    Dark matter has never been seen directly, but scientists know that something massive is out there due to its gravitational effects on visible matter. One explanation for how such a large amount of mass appears to be right in front of our eyes yet completely invisible by conventional means is that the dark matter is hiding in the centers of stars.

    In a new study, physicists have investigated the possibility that large amounts of hidden mass inside stars might be composed of extremely lightweight hypothetical particles called axions, which are a primary dark matter candidate. The scientists, Richard Brito at the University of Lisbon in Portugal; Vitor Cardoso at the University of Lisbon and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada; and Hirotada Okawa at Kyoto University and Waseda University, both in Japan, have published their paper on dark matter in stars in a recent issue of Physical Review Letters.

    “Our work studies how dark matter piles up inside stars if the dark matter is composed of massive bosonic particles (axions are an example of such particles),” Brito told Phys.org. “Our results show that dark matter accretion by stars does not lead to gravitational collapse; instead it may give rise to characteristic vibrations in stars.”

    The researchers theoretically showed that, if numerous axions were to pile up inside normal stars, then the dark matter core would oscillate. The oscillating core would in turn cause the star’s fluid to oscillate in tune with it at a specific frequency related to the star’s mass, or at multiples of this frequency. For a typical axion mass, the oscillating stars would emit microwave radiation and might have observable effects.

    “What oscillates is the fluid density and its pressure, but it’s probably correct as well to say that the entire star is oscillating,” Brito explained. “These are like sound waves propagating through the fluid, with a very specific frequency. Oscillations of this kind could, for example, lead to variations in the luminosity or in the temperature of the star, and these are quantities that we can measure directly.

    “In fact, there is already a whole branch of physics called asteroseismology, which studies the internal structure of stars by observing their oscillation modes. This is very much like the way scientists study the internal structure of the Earth by looking at seismic waves. It is possible that the oscillations of a star driven by a dark matter core could also be observed using similar methods. Given the very specific frequencies at which these stars would vibrate, this could be a smoking gun for the presence of dark matter. Asteroseismology is still in its infancy but it will, almost certainly, become a very precise way of observing stars in the future.”

    In previous research on dark matter stars, it has often been assumed that stars accreting dark matter will continue to grow until they become so dense that they collapse into black holes. However, in the new study the physicists’ simulations showed that these stars actually appear to be stable and do not become black holes. Their stability arises from a self-regulatory mechanism called gravitational cooling in which the stars eject mass to slow down and stop their growth before they approach the critical Chandrasekhar limit, the point at which they collapse into black holes.

    As the scientists explain, the finding that dark matter stars are stable makes a surprising contribution to the research in this area.

    “Although it was known for some time that dark matter can be accreted by stars and form dark matter cores at their center, those studies were all phenomenological,” Brito said. “In addition, basically all these studies suggested that, if enough dark matter is accreted by a star, it will eventually trigger gravitational collapse and a black hole would form, eventually eating all the star.

    “We set about checking these claims, using a rigorous fully relativistic framework, i.e., solving the full [Albert] Einstein’s equations. This is important if we want to understand how the dark matter core behaves for large densities. Well, it turns out that our results show that black hole formation can, in principle, be avoided by ejecting excessive mass: the dark matter core starts ‘repelling’ itself when it is too massive and compact, and is unable to grow past a certain threshold. This is, as far as we know, something that was ignored in previous works.

    “The above results are quite generic. Because any self-gravitating massive bosonic field can form compact structures, any such putative dark matter component would lead to the kind of effects we discuss in our paper. In this sense it proposes another way to search for these kinds of particles that can be complementary to observations coming from cosmology, for example. Given the lack of information that we have about the nature of dark matter, we think that it might be worth the effort to further develop this subject.”

    The scientists hope that the results here may help guide future research by suggesting where to look for dark matter and what methods to use to detect it.

    “We don’t know much about dark matter,” Brito said. “The only thing we do know is that all kinds of matter (be it regular matter or dark, invisible matter) fall in the same way in gravitational fields. This is Einstein’s equivalence principle in action. Thus, dark matter also falls in the usual way. It seems therefore appropriate to look for effects of dark matter in regions where gravity is strong, like neutron stars, black holes, etc. We are now trying to understand how dark matter behaves generically in regions of strong gravity.

    “At this precise moment, we are working on a long version of this letter. We want to understand in depth how the dark matter core grows for different kind of scenarios, and how viscosity in the star’s material affects the development of the accretion process.”

    See the full article here .

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    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

  • richardmitnick 11:25 am on September 17, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, ,   

    From Symmetry: “Hitting the neutrino floor” 


    September 17, 2015
    Laura Dattaro

    Artwork by Sandbox Studio, Chicago with Ana Kova

    Dark matter experiments are becoming so sensitive, even the ghostliest of particles will soon get in the way.

    The scientist who first detected the neutrino called the strange new particle “the most tiny quantity of reality ever imagined by a human being.” They are so absurdly small and interact with other matter so weakly that about 100 trillion of them pass unnoticed through your body every second, most of them streaming down on us from the sun.

    And yet, new experiments to hunt for dark matter are becoming so sensitive that these ephemeral particles will soon show up as background. It’s a phenomenon some physicists are calling the “neutrino floor,” and we may reach it in as little as five years.

    The neutrino floor applies only to direct detection experiments, which search for the scattering of a dark matter particle off of a nucleus. Many of these experiments look for WIMPs, or weakly interacting massive particles. If dark matter is indeed made of WIMPs, it will interact in the detector in nearly the same way as solar neutrinos.

    We don’t know what dark matter is made of. Experiments around the world are working toward detecting a wide range of particles.

    “What’s amazing is now the experimenters are trying to measure dark matter interactions that are at the same strength or even smaller than the strength of neutrino interactions,” says Thomas Rizzo, a theoretical physicist at SLAC National Accelerator Laboratory. “Neutrinos hardly interact at all, and yet we’re trying to measure something even weaker than that in the hunt for dark matter.”

    This isn’t the first time the hunt for dark matter has been linked to the detection of solar neutrinos. In the 1980s, physicists stumped by what appeared to be missing solar neutrinos envisioned massive detectors that could fix the discrepancy. They eventually solved the solar neutrino problem using different methods (discovering that the neutrinos weren’t missing; they were just changing as they traveled to the Earth), and instead put the technology to work hunting dark matter.

    In recent years, as the dark matter program has grown in size and scope, scientists realized the neutrino floor was no longer an abstract problem for future researchers to handle. In 2009, Louis Strigari, an astrophysicist at Texas A&M University, published the first specific predictions of when detectors would reach the floor. His work was widely discussed at a 2013 planning meeting for the US particle physics community, turning the neutrino floor into an active dilemma for dark matter physicists.

    “At some point these things are going to appear,” Strigari says, “and the question is, how big do these detectors have to be in order for the solar neutrinos to show up?”

    Strigari predicts that the first experiment to hit the floor will be the SuperCDMS experiment, which will hunt for WIMPs from SNOLAB in the Vale Inco Mine in Canada.

    LBL SuperCDMS
    LBL SuperCDMS


    While hitting the floor complicates some aspects of the dark matter hunt, Rupak Mahapatra, a principal investigator for SuperCDMS at Texas A&M, says he hopes they reach it sooner rather than later—a know-thy-enemy kind of thing.

    “It is extremely important to know the neutrino floor very precisely,” Mahapatra says. “Once you hit it first, that’s a benchmark. You understand what exactly that number should be, and it helps you build a next-generation experiment.”

    Much of the work of untangling a dark matter signal from neutrino background will come during data analysis. One strategy involves taking advantage of the natural ebbs and flows in the amount of dark matter and neutrinos hitting Earth. Dark matter’s natural flux, which arises from the motion of the sun through the Milky Way, peaks in June and reaches its lowest point in December. Solar neutrinos, on the other hand, peak in January, when the Earth is closest to the sun.

    “That could help you disentangle how much is signal and how much is background,” Rizzo says.

    There’s also the possibility that dark matter is not, in fact, a WIMP. Another potentially viable candidate is the axion, a hypothetical particle that solves a lingering mystery of the strong nuclear force. While WIMP and neutrino interactions look very similar, axion interactions would appear differently in a detector, making the neutrino floor a non-issue.

    But that doesn’t mean physicists can abandon the WIMP search in favor of axions, says JoAnne Hewett, a theoretical physicist at SLAC. “WIMPs are still favored for many reasons. The neutrino floor just makes it more difficult to detect. It doesn’t make it less likely to exist.”

    Physicists are confident that they’ll eventually be able to separate a dark matter signal from neutrino noise. Next-generation experiments might even be able to distinguish the direction a particle is coming from when it hits the detector, something the detectors being built today just can’t do. If an interaction seemed to come from the direction of the sun, that would be a clear indication that it was likely a solar neutrino.

    “There’s certainly avenues to go here,” Strigari says. “It’s not game over, we don’t think, for dark matter direct detection.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:31 pm on September 16, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, MiniCLEAN,   

    From Symmetry: “A light in the dark” 


    September 16, 2015
    Diana Kwon

    Courtesy of the MiniCLEAN collaboration

    Getting to an experimental cavern 6800 feet below the surface in Sudbury, Ontario, requires an unusual commute. The Cage, an elevator that takes people into the SNOLAB facility, descends twice every morning at 6 a.m. and 8 a.m. Before entering the lab, individuals shower and change so they don’t contaminate the experimental areas.


    A thick layer of natural rock shields the clean laboratory where air quality, humidity and temperature are highly regulated. These conditions allow scientists to carry out extremely sensitive searches for elusive particles such as dark matter and neutrinos.

    The Cage returns to the surface at 3:45 p.m. each day. During the winter months, researchers go underground before the sun rises and emerge as it sets. Steve Linden, a postdoctoral researcher from Boston University, makes the trek every morning to work on MiniCLEAN, which scientists will use to test a novel technique for directly detecting dark matter.

    “It’s a long day,” Linden says.

    Scientists and engineers have spent the past eight years designing and building the MiniCLEAN detector. Today that task is complete; they have begun commissioning and cooling the detector to fill it with liquid argon to start its search for dark matter.

    Though dark matter is much more abundant than the visible matter that makes up planets, stars and everything we can see, no one has ever identified it. Dark matter particles are chargeless, don’t absorb or emit light, and interact very weakly with matter, making them incredibly difficult to detect.

    Spotting the WIMPs

    MiniCLEAN (CLEAN stands for Cryogenic Low-Energy Astrophysics with Nobles) aims to detect weakly interacting massive particles, or WIMPs, the current favorite dark matter candidate. Scientists will search for these rare particles by observing their interactions with atoms in the detector.

    To make this possible, the detector will be filled with over 500 kilograms of very cold, dense, ultra-pure materials—argon at first, and later neon. If a WIMP passes through and collides with an atom’s nucleus, it will produce a pulse of light with a unique signature. Scientists can collect and analyze this light to determine whether what they saw was a dark matter particle or some other background event.

    The use of both argon and neon will allow MiniCLEAN to double-check any possible signals. Argon is more sensitive than neon, so a true dark matter signal would disappear when liquid argon is replaced with liquid neon. Only an intrinsic background signal from the detector would persist. Scientists would like to eventually scale this experiment up to a larger version called CLEAN.

    Overcoming obstacles

    MiniCLEAN is a small experiment, with about 15 members in the collaboration and the project lead at Pacific Northwest National Laboratory.. While working on this experiment underground with few hands to spare, the team has run into some unexpected roadblocks.

    MiniCLEAN detector

    One such obstacle appeared while transporting the inner vessel, a detector component that will contain the liquid argon or neon.

    “Last November, as we finished assembling the inner vessel and were getting ready to move it to where it needed to end up, we realized it wouldn’t fit between the doors into the hallway we had to wheel it down,” Linden explains.

    When this happened, the team was faced with two options: somehow reduce the size of the vessel, or cut away a part of the door—not a simple thing to do in a clean lab. Fortunately, temporarily replacing some of the vessel’s parts reduced the size enough to make it fit. They got it through the doorway with about an eighth of an inch clearance on each side.

    “What gives me the energy to persist on this project is that the CLEAN approach is unique, and there isn’t another approach to dark matter that is like it,” says Pacific Northwest National Laboratory scientist Andrew Hime, MiniCLEAN spokesperson and principal investigator. “It’s been eight years since we starting pushing hard on this program, and finally getting real data from the detector will be a breath of fresh air.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:04 pm on September 10, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, , XMASS   

    From Symmetry: “XMASS continues dark matter debate” 


    September 10, 2015
    Kathryn Jepsen

    Courtesy of Kamioka Observatory, ICRR, The University of Tokyo

    XMASS is the latest of multiple experiments to contradict a previous dark matter discovery claim, but the conversation isn’t over yet.

    Since 1998, scientists on the DAMA-LIBRA experiment at Gran Sasso National Laboratory in Italy have claimed the discovery of an increasingly statistically significant sign of dark matter.

    DAMA-LIBRA at Gran Sasso

    This week, the XMASS experiment in Japan joined the LUX, Xenon100 and CDMS experiments in reporting results that seem to contradict that claim.

    LUX Dark matter

    XENON Dark Matter Experiment


    Scientists look for dark matter in many ways. Both this result from the XMASS experiment and the results from DAMA-LIBRA look for something called annual modulation, a sign that the Earth is constantly moving through a halo of dark matter particles.

    As the sun rotates around the center of the Milky Way, the Earth moves around the sun, completing one revolution per year. During the first half of the year, the Earth moves in the same direction as the sun; during the second half, the Earth completes its circle, moving in the opposite direction.

    When the sun and Earth are moving in the same direction, the Earth should move through slightly more dark matter than when the sun and Earth are moving in opposite directions. So scientists should see a few more dark matter particles hit their detectors during that part of the year.

    Experiments other than DAMA-LIBRA have seen hints of an annual modulation, but only the CoGeNT experiment has ever provided support for DAMA-LIBRA’s claim that this modulation comes from dark matter.

    CoGeNT experiment

    The effect could be caused by other annual changes. Pressure and temperature could affect an experiment. Atmospheric changes with the seasons could affect the number of cosmic rays that reach the experiment. Background radiation from radon gas has been known to change seasonally for underground experiments because of its interaction with the water table in the rock, says Fermilab scientist Dan Bauer of the CDMS experiment.

    “Nobody’s been able to put their finger on what’s causing the DAMA modulation,” he says. “We can’t find the smoking gun.”

    The XMASS experiment in Kamioka, Japan, looks for signs that dark matter particles have bounced off the nuclei in their 832-kilogram container of liquid Xenon. The experiment has sensitivity to two types of possible dark matter interactions, says scientist Yoichiro Suzuki, principal investigator for XMASS at the Tokyo-based Kavli Institute for the Physics and Mathematics of the Universe, in an email.

    After taking data for about 16 months, the XMASS experiment disagreed with the DAMA-LIBRA claim, if one assumes dark matter particles scatter like billiard balls when they collide with nuclei. XMASS did find a low level of annual modulation, though, and that could be a hint of dark matter interacting with normal matter in a different way.

    However, XMASS scientists deduced from their signal some characteristics that the dark matter particles causing the modulation would need to have: their masses and their rates of interaction with normal matter. And experiments that search for dark matter directly have already ruled out those masses and interaction rates.

    But scientists still don’t know for sure what dark matter particles are like. Until they do, or until they identify the source of the annual modulation signals, they might have a hard time dissuading scientists on DAMA-LIBRA.

    The XMASS experiment continues to take data, Suzuki says. XMASS scientists hope eventually to build a 5-ton version of the experiment.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

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