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  • richardmitnick 10:23 pm on October 30, 2018 Permalink | Reply
    Tags: Fritz Zwiky and Vera Rubin, , , , WIMPS   

    From Sanford Underground Research Facility: “Five years later, the hunt continues” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    October 29, 2018
    Erin Broberg

    Second-generation dark matter detector prepares to continue the search for WIMPs.

    The LZ cryostat undergoes leak tests in the Surface Lab cleanroom. Matthew Kapust

    Five years ago, lead scientists for the Large Underground Xenon (LUX) experiment presented the first scientific results to come from the 4850 Level of Sanford Lab since Ray Davis’ Nobel-winning research in the 1960s. And the results were big.

    After a run of just over three months operating a mile underground, LUX had proven itself the most sensitive dark matter detector in the world.

    “LUX is blazing the path to illuminate the nature of dark matter,” said Brown University physicist Rick Gaitskell, co-spokesperson for LUX with physicist Dan McKinsey of Yale University, at the time.

    Dark matter, so far observed only by its gravitational effects on galaxies and clusters of galaxies, is the predominant form of matter in the universe—making up more than 80 percent of all matter.

    Women in STEM – Vera Rubin
    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    Weakly interacting massive particles, or WIMPs—so-called because they rarely interact with ordinary matter except through gravity—are the leading theoretical candidates for dark matter. The mass of WIMPs is unknown, but theories and results from other experiments suggest a number of possibilities.

    LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

    U Washington Large Underground Xenon at SURF, Lead, SD, USA

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

    In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

    LBNL LZ project at SURF, Lead, SD, USA

    LZ Dark Matter Experiment at SURF lab

    SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.

    “LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”

    This month, we celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment. The following are just a few of the steps being taken by the LZ collaboration to make an experiment 30 times bigger and 100 times more sensitive—all in the pursuit of WIMPs.

    Renovating the Davis Cavern

    To make room for this scaled-up experiment, renovations had to occur inside the Davis Cavern.

    “Planning for this renovation started several years ago—even before LUX was built,” said John Keefner, underground operations engineer. “We had to refit the cavern and existing infrastructure to allow for the installation of LZ.”

    The Davis Cavern renovation project included removing an existing cleanroom, tearing down a wall between two former low-background counting rooms, installing a new hoist system, building a work deck and preparing the water tank itself to accommodate the larger cryostat.

    Reducing radon

    In addition to hosting the experiment nearly a mile underground to escape cosmic radiation, additional protections had to be put in place, including a radon-reduction system that was installed to further ensure the experiment remains free of backgrounds that could interfere with the results.

    Radon, a naturally occurring radioactive gas, significantly increases background noise in sensitive physics projects. The radon reduction system pressurizes, dehumidifies and cools air to minus 60 degrees Celsius before sending it through two columns, each filled with 1600 kg of activated charcoal, which remove the radon. The pressure is released, warmed and humidified before flowing into the cleanroom.

    “Our detectors need very low levels of radon,” said Dr. Richard Schnee, who is head of the physics department at SD Mines and a collaborator with LZ. Schnee heads up the SD Mines team that designed a radon reduction system that will be used underground. While the radon levels at the 4850 Level are safe for humans, they are too high for sensitive experiments like LZ, which go deep underground to escape cosmic radiation, Schnee explained. “We will take regular air from the facility and the systems will reduce the levels by 1,000 times or more.”


    The arrival of the LZ cryostats at Sanford Lab in May 2018 marked a significant milestone in the LZ project, as the cryostat was several years in the making and is a key component in the experiment.

    The cryostat works in a similar way to a big thermos flask and keeps the detector at freezing temperatures. This is crucial because the detector uses xenon, which at room temperature is a gas. For the experiment to work, the xenon must be kept in a liquid state, which is only achievable at about minus 148 degrees Fahrenheit.

    After being delivered to the surface facility at Sanford Lab, the outer cryostat vessel of the cryostat chamber spent five weeks being fully assembled and leak-checked in the Assembly Lab clean room. It has now been disassembled and packaged for transportation from the surface to the underground location on the 4850 Level. The inner cryostat vessel also passed its leak test.

    Water tank passivation

    To ensure unwanted particles are not misread as dark matter signals, LZ’s liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals.

    “The LUX water tank needed a number of ports added or modified to support the LZ infrastructure. We also added the capability to install small hoisting equipment on the ceiling of the tank,” said Simon Fiorucci, a physicist with Lawrence Berkeley National Laboratory, who oversaw LUX operations at Sanford Lab and will serve in a similar role for LZ.

    Once these steps were completed, the entire inside of the tank had to be re-passivated to prevent rusting during its many years of service ahead. Finally, the tank was filled to the brim and monitored for a week to ensure there were no leaks.

    Acrylic tanks

    Additionally, LZ will include a component not present in LUX—nine acrylic tanks, filled with a liquid scintillator, will form a veto system around the experiment, allowing researchers to better recognize a WIMP if they see one.

    The acrylic tanks, or more precisely the liquid scintillator inside the tanks, are crucial in bringing the experiment to a new level of sensitivity—100 times greater than LUX—by identifying neutrons, which can mimic dark matter signals.

    “Recent dark matter searches have found that neutrons can be a pernicious background,” said Carter Hall, former LZ spokesperson and professor of physics at the University of Maryland. “The acrylic tanks and their liquid scintillator payload will provide a powerful neutron rejection signal so LZ is not fooled.”

    These are just a few of the many steps being taken to ensure that LZ once again scours the universe with pristine accuracy.

    “We want to do again what we did five years ago—create the most sensitive dark matter detector in the world,” said Dr. Markus Horn, research scientist at Sanford Lab and a member of the LZ collaboration.

    See the full article here .

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    Stem Education Coalition

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

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

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

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

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

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

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

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

    Fermilab LBNE

    U Washington Majorana Demonstrator Experiment at SURF

    The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

  • richardmitnick 4:11 pm on October 16, 2018 Permalink | Reply
    Tags: , , , Fermilab’s Aaron Chou is leading a multi-institutional consortium to apply the techniques of quantum metrology to the problem of detecting axion dark matter, Finding an axion is a delicate endeavor even compared to other searches for dark matter, HAYSTAC axion experiment at Yale, , , , , , The qubit advantage at FNAL, WIMPS   

    From Symmetry: “Looking for dark matter using quantum technology” 

    Symmetry Mag
    From Symmetry

    Jim Daley

    Photo by Reidar Hahn, Fermilab

    For decades, physicists have been searching for dark matter, which doesn’t emit light but appears to make up the vast majority of matter in the universe. Several theoretical particles have been proposed as dark matter candidates, including weakly interacting massive particles—called WIMPs—and axions.

    Fermilab’s Aaron Chou is leading a multi-institutional consortium to apply the techniques of quantum metrology to the problem of detecting axion dark matter. The project, which brings together scientists at Fermilab, the National Institute of Standards and Technology, the University of Chicago, University of Colorado and Yale University, was recently awarded $2.1 million over two years through the Department of Energy’s Quantum Information Science-Enabled Discovery (QuantISED) program, which seeks to advance science through quantum-based technologies.

    If the scientists succeed, the discovery could solve several cosmological mysteries at once.

    “It’d be the first time that anybody had found any direct evidence of the existence of dark matter,” says Fermilab’s Daniel Bowring, whose work on this effort is supported by a DOE Office of Science Early Career Research Award. “Right now, we’re inferring the existence of dark matter from the behavior of astrophysical bodies. There’s very good evidence for the existence of dark matter based on those observations, but nobody’s found a particle yet.”

    The axion search

    Finding an axion would also resolve a discrepancy in particle physics called the strong CP problem. Particles and antiparticles are “symmetrical” to one another: They exhibit mirror-image behavior in terms of electrical charge and other properties.

    The strong force—one of the four fundamental forces of nature—obeys CP symmetry. But there’s no reason, at least in the Standard Model of physics, why it should. The axion was first proposed to explain why it does.

    Finding an axion is a delicate endeavor, even compared to other searches for dark matter. An axion’s mass is vanishingly low—somewhere between a millionth and a thousandth of an electronvolt. By comparison, the mass of a WIMP is expected to be between a trillion and quadrillion times more massive—in the range of a billion electronvolts—which means they’re heavy enough that they could occasionally produce a signal by bumping into the nuclei of other atoms. To look for WIMPs, scientists fill detectors with liquid xenon (for example, in the LUX-ZEPLIN dark matter experiment at Sanford Underground Research Facility in South Dakota) or germanium crystals (in the SuperCDMS Soudan experiment in Minnesota [not current, now at SNOLAB a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario]) and look for indications of such a collision.

    LBNL Lux Zeplin project at SURF

    UC Santa Barbara postdoctoral scientist Sally Shaw stands with one of the four large acrylic tanks fabricated for the LZ dark matter experiment’s outer detector.

    LZ Dark Matter Experiment at SURF lab

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

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

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    “You can’t do that with axions because they’re so light,” Bowring says. “So the way that we look for axions is fundamentally different from the way we look for more massive particles.”

    When an axion encounters a strong magnetic field, it should—at least in theory—produce a single microwave-frequency photon, a particle of light. By detecting that photon, scientists should be able to confirm the existence of axions. The Axion Dark Matter eXperiment, ADMX, at the University of Washington and the HAYSTAC experiment at Yale are attempting to do just that.

    ADMX Axion Dark Matter Experiment at the University of Washington

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

    U Washington ADMX

    Yale HAYSTAC axion dark matter experiment

    Yale Haloscope Sensitive To Axion CDM -HAYSTAC Experiment a microwave cavity search for cold dark matter (CDM)

    Those experiments use a strong superconducting magnet to convert axions into photons in a microwave cavity. The cavity can be tuned to different resonant frequencies to boost the interaction between the photon field and the axions. A microwave receiver then detects the signal of photons resulting from the interaction. The signal is fed through an amplifier, and scientists look for that amplified signal.

    “But there is a fundamental quantum limit to how good an amplifier can be,” Bowring says.

    Photons are ubiquitous, which introduces a high degree of noise that must be filtered from the signal detected in the microwave cavity. And at higher resonant frequencies, the signal-to-noise ratio gets progressively worse.

    Both Bowring and Chou are exploring how to use technology developed for quantum computing and information processing to get around this problem. Instead of amplifying the signal and sorting it from the noise, they aim to develop new kinds of axion detectors that will count photons very precisely—with qubits.

    Aaron Chou works on an FNAL experiment that uses qubits to look for direct evidence of dark matter in the form of axions. Photo by Reidar Hahn, Fermilab

    The qubit advantage

    In a quantum computer, information is stored in qubits, or quantum bits.

    Quantum computing – IBM

    A qubit can be constructed from a single subatomic particle, like an electron or a photon, or from engineered metamaterials such as superconducting artificial atoms. The computer’s design takes advantage of the particles’ two-state quantum systems, such as an electron’s spin (up or down) or a photon’s polarization (vertical or horizontal). And unlike classical computer bits, which have one of only two states (one or zero), qubits can also exist in a quantum superposition, a kind of addition of the particle’s two quantum states. This feature has myriad potential applications in quantum computing that physicists are just starting to explore.

    In the search for axions, Bowring and Chou are using qubits. For a traditional antenna-based detector to notice a photon produced by an axion, it must absorb the photon, destroying it in the process. A qubit, on the other hand, can interact with the photon many times without annihilating it. Because of this, the qubit-based detector will give the scientists a much higher chance of spotting dark matter.

    “The reason we want to use quantum technology is that the quantum computing community has already had to develop these devices that can manipulate a single microwave photon,” Chou says. “We’re kind of doing the same thing, except a single photon of information that’s stored inside this container is not something that somebody put in there as part of the computation. It’s something that the dark matter put in there.”

    Light reflection

    Using a qubit to detect an axion-produced photon brings its own set of challenges to the project. In many quantum computers, qubits are stored in cavities made of superconducting materials. The superconductor has highly reflective walls that effectively trap a photon long enough to perform computations with it. But you can’t use a superconductor around high-powered magnets like the ones used in Bowring and Chou’s experiments.

    “The superconductor is just ruined by magnets,” Chou says. Currently, they’re using copper as an ersatz reflector.

    “But the problem is, at these frequencies the copper will store a single photon for only 10,000 bounces instead of, say, a billion bounces off the mirrors,” he says. “So we don’t get to keep these photons around for quite as long before they get absorbed.”

    And that means that they don’t stick around long enough to be picked up as a signal. So the researchers are developing another, better photon container.

    “We’re trying to make a cavity out of very low-loss crystals,” Chou says.

    Think of a windowpane. As light hits it, some photons will bounce off it, and others will pass through. Place another piece of glass behind the first. Some of the photons that passed through the first will bounce off the second, and others will pass through both pieces of glass. Add a third layer of glass, and a fourth, and so on.

    “Even though each individual layer is not that reflective by itself, the sum of the reflections from all the layers gives you a pretty good reflection in the end,” Chou says. “We want to make a material that traps light for a long time.”

    Bowring sees the use of quantum computing technology in the search for dark matter as an opportunity to reach across the boundaries that often keep different disciplines apart.

    “You might ask why Fermilab would want to get involved in quantum technology if it’s a particle physics laboratory,” he says. “The answer is, at least in part, that quantum technology lets us do particle physics better. It makes sense to lower those barriers.”

    See the full article here .


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    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 4:47 pm on September 24, 2018 Permalink | Reply
    Tags: A New Single-Photon Sensor for Quantum Imaging, , Berkeley Quantum, Figuring out how to extend the search for dark matter particles, From Quantum Gravity to Quantum Technology, , , News Center A Quantum Leap Toward Expanding the Search for Dark Matter, , , U.S. Department of Energy’s Office of High Energy Physics, University of Massachusetts Amherst, WIMPS   

    From Lawrence Berkeley National Lab: “News Center A Quantum Leap Toward Expanding the Search for Dark Matter” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    September 24, 2018
    Glenn Roberts Jr.
    (510) 486-5582

    A visualization of a massive galaxy cluster that shows dark matter density (purple filaments) overlaid with the gas velocity field. (Credit: Illustris Collaboration)

    Figuring out how to extend the search for dark matter particles – dark matter describes the stuff that makes up an estimated 85 percent of the total mass of the universe yet so far has only been measured by its gravitational effects – is a bit like building a better mousetrap…that is, a mousetrap for a mouse you’ve never seen, will never see directly, may be joined by an odd assortment of other mice, or may not be a mouse after all.

    Now, through a new research program supported by the U.S. Department of Energy’s Office of High Energy Physics (HEP), a consortium of researchers from the DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), UC Berkeley, and the University of Massachusetts Amherst will develop sensors that enlist the seemingly weird properties of quantum physics to probe for dark matter particles in new ways, with increased sensitivity, and in uncharted regions. Maurice Garcia-Sciveres, a Berkeley Lab physicist, is leading this Quantum Sensors HEP-Quantum Information Science (QIS) Consortium.

    Quantum technologies are emerging as promising alternatives to the more conventional “mousetraps” that researchers have previously used to track down elusive particles. And the DOE, through the same HEP office, is also supporting a collection of other research efforts led by Berkeley Lab scientists that tap into quantum theory, properties, and technologies in the QIS field.

    These efforts include:

    Unraveling the Quantum Structure of Quantum Chromodynamics in Parton Shower Monte Carlo Generators – This effort will develop computer programs that test the interactions between fundamental particles in extreme detail. Current computer simulations are limited by classical algorithms, though quantum algorithms could more accurately model these interactions and could provide a better way to compare with and understand particle events measured at CERN’s Large Hadron Collider, the world’s most powerful particle collider. Berkeley Lab’s Christian Bauer, a senior research scientist, will lead this effort.
    Quantum Pattern Recognition (QPR) for High-Energy Physics –Increasingly powerful particle accelerators require vastly faster computer algorithms to monitor and sort through billions of particle events per second, and this effort will develop and study the potential of quantum-based algorithms for pattern recognition to reconstruct charged particles. Such algorithms have the potential for significant speed improvements and increased precision. Led by Berkeley Lab physicist and Divisional Fellow Heather Gray, this effort will involve high-energy physics and high-performance computing expertise in Berkeley Lab’s Physics Division and at the Lab’s National Energy Research Scientific Computing Center, a DOE Office of Science User Facility, and also at UC Berkeley.
    Skipper-CCD, a New Single-Photon Sensor for Quantum Imaging – For the past six years, Berkeley Lab and Fermi National Accelerator Laboratory (Fermilab) have been collaborating in the development of a detector for astrophysics experiments that can detect the smallest individual unit of light, known as a photon. This Skipper-CCD detector was successfully demonstrated in the summer of 2017 with an incredibly low noise that allowed the detection of even individual electrons. As a next step, this Fermilab-led effort will seek to image pairs of photons that exist in a state of quantum entanglement, meaning their properties are inherently related – even over long distances – such that the measurement of one of the particles necessarily defines the properties of the other. Steve Holland, a senior scientist and engineer at Berkeley Lab who is a pioneer in the development of high-performance silicon detectors for a range of uses, is leading Berkeley Lab’s participation in this project.
    Geometry and Flow of Quantum Information: From Quantum Gravity to Quantum Technology –This effort will develop quantum algorithms and simulations for properties, including error correction and information scrambling, that are relevant to black hole theories and to quantum computing involving highly connected arrays of superconducting qubits – the basic units of a quantum computer. Researchers will also compare these with more classical methods. UC Berkeley is heading up this research program, and Irfan Siddiqi, a scientist in Berkeley Lab’s Materials Sciences Division and founding director of the Center for Quantum Coherent Science at UC Berkeley, is leading Berkeley Lab’s involvement.
    Siddiqi is also leading a separate research program, Field Programmable Gate Array-based Quantum Control for High-Energy Physics Simulations with Qutrits, that will develop specialized tools and logic families for high-energy-physics-focused quantum computing. This effort involves Berkeley Lab’s Accelerator Technology and Applied Physics Division.

    These projects are also part of Berkeley Quantum, a partnership that harnesses the expertise and facilities of Berkeley Lab and UC Berkeley to advance U.S. quantum capabilities by conducting basic research, fabricating and testing quantum-based devices and technologies, and educating the next generation of researchers.

    Also, across several of its offices, the DOE has announced support for a wave of other R&D efforts (see a related news release) that will foster collaborative innovation in quantum information science at Berkeley Lab, at other national labs, and at partner institutions.

    At Berkeley Lab, the largest HEP-funded QIS-related undertaking will include a multidisciplinary team in the development and demonstration of quantum sensors to look for very-low-mass dark matter particles – so-called “light dark matter” – by instrumenting two different detectors.

    One of these detectors will use liquid helium at a very low temperature where otherwise familiar phenomena such as heat and thermal conductivity display quantum behavior. The other detector will use specially fabricated crystals of gallium arsenide (see a related article), also chilled to cryogenic temperatures. The ideas for how these experiments can search for very light dark matter sprang from theory work at Berkeley Lab.

    “There’s a lot of unexplored territory in low-mass dark matter,” said Natalie Roe, director of the Physics Division at Berkeley Lab and the principal investigator for the Lab’s HEP-related quantum efforts. “We have all the pieces to pull this together: in theory, experiments, and detectors.”

    This image of the Andromeda Galaxy, taken from a 1970 study by astronomers Vera Rubin and W. Kent Ford Jr., shows points (dots) that were tracked at different distances from the galaxy center. The selected points unexpectedly were found to rotate at a similar rate, which provides evidence for the existence of dark matter. (Credit: Vera Rubin, W. Kent Ford Jr.)

    Garcia-Sciveres, who is leading the effort in applying quantum sensors to the low-mass dark matter search, noted that other major efforts – such as the Berkeley Lab-led LUX-ZEPLIN (LZ) experiment that is taking shape in South Dakota – will help root out whether dark matter particles known as WIMPs (weakly interacting massive particles) exist with masses comparable to that of atoms. But LZ and similar experiments are not designed to detect dark matter particles of much lower masses.

    LBNL Lux Zeplin project at SURF

    “The traditional WIMP dark matter experiments haven’t found anything yet,” he said. “And there is a lot of theoretical work on models that favor particles of a lower mass than experiments like LZ can measure,” he added. “This has motivated people to really look hard at how you can detect very-low-mass particles. It’s not so easy. It’s a very small signal that has to be detected without any background noise.”

    Researchers hope to develop quantum sensors that are better at filtering out the noise of unwanted signals. While a traditional WIMP experiment is designed to sense the recoil of an entire atomic nucleus after it is “kicked” by a dark matter particle, very-low-mass dark matter particles will bounce right off nuclei without affecting them, like a flea bouncing off an elephant.

    The goal of the new effort is to sense the low-mass particles via their energy transfer in the form of very feeble quantum vibrations, which go by names like “phonons” or “rotons,” for example, Garcia-Sciveres said.

    “You would never be able to tell that an invisible flea hits an elephant by watching the elephant. But what if every time an invisible flea hits an elephant at one end of the herd, a visible flea is flung away from an elephant at the other end of the herd?” he said.

    “You could use these sensors to watch for such slight signals in a very cold crystal or superfluid helium, where an incoming dark matter particle is like the invisible flea, and the outgoing visible flea is a quantum vibration that must be detected.”

    The particle physics community has held some workshops to brainstorm the possibilities for low-mass dark matter detection. “This is a new regime. This is an area where there aren’t even any measurements yet. There is a promise that QIS techniques can help give us more sensitivity to the small signals we’re looking for,” Garcia-Sciveres added. “Let’s see if that’s true.”

    The demonstration detectors will each have about 1 cubic centimeter of detector material. Dan McKinsey, a Berkeley Lab faculty senior scientist and UC Berkeley physics professor who is responsible for the development of the liquid helium detector, said that the detectors will be constructed on the UC Berkeley campus. Both are designed to be sensitive to particles with a mass lighter than protons – the positively charged particles that reside in atomic nuclei.

    A schematic for low-mass dark matter particle detection in a planned superfluid helium (He) experiment. (Credit: Berkeley Lab)

    The superfluid helium detector will make use of a process called “quantum evaporation,” in which rotons and phonons cause individual helium atoms to be evaporated from the surface of superfluid helium.

    Kathryn Zurek, a Berkeley Lab physicist and pioneering theorist in the search for very-low-mass dark matter particles who is working on the quantum sensor project, said the technology to detect such “whispers” of dark matter didn’t exist just a decade ago but “has made major gains in the last few years.” She also noted, “There had been a fair amount of skepticism about how realistic it would be to look for this light-mass dark matter, but the community has moved more broadly in that direction.”

    There are many synergies in the expertise and capabilities that have developed both at Berkeley Lab and on the UC Berkeley campus that make it a good time – and the right place – to develop and apply quantum technologies to the hunt for dark matter, Zurek said.

    Theories developed at Berkeley Lab suggest that certain exotic materials exhibit quantum states or “modes” that low-mass dark matter particles can couple with, which would make the particles detectable – like the “visible flea” referenced above.

    “These ideas are the motivation for building these experiments to search for light dark matter,” Zurek said. “This is a broad and multipronged approached, and the idea is that it will be a stepping stone to a larger effort.”

    The new project will draw from a deep experience in building other types of particle detectors, and R&D in ultrasensitive sensors that operate at the threshold where an electrically conducting material becomes a superconductor – the “tipping point” that is sensitive to the slightest fluctuations. Versions of these sensors are already used to search for slight temperature variations in the relic microwave light that spans the universe.

    At the end of the three-year demonstration, researchers could perhaps turn their sights to more exotic types of detector materials in larger volumes.

    “I’m excited to see this program move forward, and I think it will become a significant research direction in the Physics Division at Berkeley Lab,” she said, adding that the program could also demonstrate ultrasensitive detectors that have applications in other fields of science.

    More info:

    Read a news release that summarizes all of the Berkeley Lab quantum information science awards announced Sept. 24
    Berkeley Lab to Build an Advanced Quantum Computing Testbed
    About Berkeley Quantum

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal

  • richardmitnick 5:14 pm on September 20, 2018 Permalink | Reply
    Tags: An ultrasensitive microphone for dark matter, , Dark Matter hunt, , Searching for much lighter dark matter candidates, , SuperCDMS experiment, , The predecessor of SuperCDMS SNOLAB—the SuperCDMS Soudan experiment housed in the Soudan mine in Minnesota—required the charge from 70 electron-hole pairs to make a detection. SuperCDMS SNOLAB wil, WIMPS   

    From Symmetry: “Dark matter vibes” 

    Symmetry Mag
    From Symmetry

    Manuel Gnida

    Dawn Harmer, SLAC

    SuperCDMS physicists are testing a way to amp up dark matter vibrations to help them search for lighter particles.

    A dark matter experiment scheduled to go online at the Canadian underground laboratory SNOLAB in the early 2020s will conduct one of the most sensitive searches ever for hypothetical particles known as weakly interacting massive particles, or WIMPs.

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    Scientists consider WIMPs strong dark matter candidates. But what if dark matter turns out to be something else? After all, despite an intense hunt with increasingly sophisticated detectors, scientists have yet to directly detect dark matter.

    That’s why researchers on the SuperCDMS dark matter experiment at SNOLAB are looking for ways to broaden their search. And they found one: They have tested a prototype detector that would allow their experiment to search for much lighter dark matter candidates as well.

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

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

    LBNL Super CDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    “This development is exciting because it gives us access to a new sector of particle masses where alternatives to WIMPs could be hiding,” says Priscilla Cushman from the University of Minnesota, spokesperson for the SuperCDMS collaboration. “It also demonstrates the flexibility of our detector technology, now reaching energy thresholds and resolutions that weren’t possible a few years ago.”

    The collaboration published the results of the first low-mass dark matter search with the new technology in Physical Review Letters. Some scientists on the team also described the prototype in an earlier paper in Applied Physics Letters.

    An ultrasensitive mic for dark matter

    The core of the SuperCDMS experiment is made of very sensitive detectors on the top and bottom of hockey puck-shaped silicon and germanium crystals. The detectors are able to observe very small vibrations caused by dark matter particles rushing through the crystals. The challenge in using this technology to find light dark matter particles is that, the lighter the particle, the smaller the vibrations.

    “To pick those vibrations up, you need an extraordinary ‘microphone’,” says Matt Pyle from the University of California, who contributed to both papers. “Our goal is to build microphones—detectors—that are sensitive enough to detect signals of very light particles. Our technology is at the leading edge of what’s currently possible.”

    The vibrations caused by a dark matter interaction can also dislodge negatively charged electrons in the crystal. This leaves positively charged spots, or holes, at the locations where the electrons once were. If an electric field is applied, the pairs of electrons and holes traverse the crystal in opposite directions, and the detector can measure their charge.

    One way of making the experiment more sensitive is to increase the efficiency with which it measures the charge of the electron-hole pairs. This approach has been the major factor in improving sensitivity until now. The predecessor of SuperCDMS SNOLAB—the SuperCDMS Soudan experiment, housed in the Soudan mine in Minnesota—required the charge from 70 electron-hole pairs to make a detection. SuperCDMS SNOLAB will require just half as much.

    “But that’s not the type of improvement we did here,” says Roger Romani, a recent undergraduate student in Blas Cabrera’s group at Stanford University and lead author of the Applied Physics Letters paper. The team found a different way to make the experiment even more sensitive.

    “In our approach, we counted the number of electron-hole pairs by looking at the vibrations they caused when traveling through our detector crystal,” he says.

    To do so, Cabrera’s team, joined by Pyle and Santa Clara University’s Betty Young, applied a high voltage that pushed the electron-hole pairs through the crystal. The acceleration led to the production of more vibrations, on top of those created without voltage.

    “As a result, our prototype is sensitive to a single electron-hole pair,” says Francisco Ponce, a postdoctoral researcher on Cabrera’s team. “Being able to measure a smaller charge gives us a higher resolution in our experiment and lets us detect particles with smaller mass.”

    This refrigeration unit in the Cabrera lab at Stanford keeps the experiment’s detector crystals at nearly absolute zero temperature. Dawn Harmer, SLAC

    First search for light dark matter

    The SuperCDMS collaboration has used the prototype detector for a first light dark matter search, and the outcome is promising.

    “The experiment demonstrates that we’re sensitive to a mass range in which we had no sensitivity at all before,” says Cabrera, former SuperCDMS SNOLAB project director from the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of the Department of Energy’s SLAC National Accelerator Laboratory and Stanford.

    Noah Kurinsky, a recent PhD student in Cabrera’s group, says, “Although the technology is in the early stages of its development, we’re able to set limits on the properties of light dark matter and are already competitive to other experiments that operate in the same mass range.”

    The result is even more compelling considering the experimental circumstances: Located in Cabrera’s lab in a basement at Stanford, the experiment wasn’t shielded from the unwanted cosmic-ray background (SuperCDMS SNOLAB will operate 6800 feet underground); it used a very small prototype crystal, limiting the size of the signal (SuperCDMS Soudan’s crystals were 1500 times heavier); and it ran for a relatively short time, limiting the amount of data for the analysis (XENON10 had 20,000 times more exposure).

    Eventually, the researchers want to scale up the size of their crystal and use it in a future generation of SuperCDMS SNOLAB. However, much more R&D work needs to be done before that can happen.

    At the moment, they’re working on improving the quality of the crystal and on better understanding its fundamental physics: for instance, how to deal with a quantum mechanical effect that randomly creates electron-hole pairs for no apparent reason and can cause a background signal that looks exactly like a signal from dark matter.

    The team is hopeful that their efforts will lead to new detector designs that continue to make SuperCDMS SNOLAB more powerful, Pyle says: “Then, we’ll have an even better shot at studying unknown dark matter territory.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.

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

    From NOVA: “Does Dark Matter Ever Die?” 


    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.

    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?

    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.

    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 .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

  • 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.

    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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    Stem Education Coalition

    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

    • 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.


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

        Thanks for reading and commenting. It is much appreciated.


        • 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.


  • 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

    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).


    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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    Symmetry is a joint Fermilab/SLAC publication.

  • 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

    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


    See the full article here .

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    CERN CMS New

    CERN LHCb New II


    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” 


    31. August 2017


    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.

    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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    Triumf Campus
    Triumf Campus
    World Class Science at Triumf Lab, British Columbia, Canada
    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?

    Associate Members:
    University of Calgary, McMaster University, University of Northern British Columbia, University of Regina, Saint Mary’s University, University of Winnipeg, How bad is that !!

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

    From aeon: “In the dark” 



    Alexander B Fry

    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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