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  • richardmitnick 9:03 pm on February 1, 2016 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, XENON1T   

    From SA: “Last Call: Will WIMPs Show Their Faces in the Latest Dark Matter Experiment” 

    Scientific American

    Scientific American

    February 1, 2016
    Clara Moskowitz

    Gran Sasso XENON1T
    XENON1T at Gran Sasso

    It’s now or never for physicists’ favorite explanation of dark matter, the invisible material that seems to pervade the universe. The largest, most sensitive search yet for the particles many physicists think make up dark matter—weakly interacting massive particles (WIMPs)—will begin in March at the XENON1T experiment at the Gran Sasso National Laboratory in Italy.

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO
    Gran Sasso

    The project is the latest in a line of detectors that date back as early as the 1980s but have all failed so far to find dark matter. If the elusive particles go unfound in the next few years at XENON1T, physicists may have to abandon the leading theory and search for more exotic explanations. “Our best models are within reach of XENON1T,” says Rafael Lang, a physicist at Purdue University who works on the experiment. “If we don’t see it, that means our ideas are completely wrong, and we really have to go back to the drawing board.”

    WIMPs are a prediction of superstring theory. This extension of the Standard Model of particle physics proposes the existence of partner particles for all the known fundamental bits of matter in the universe.

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

    WIMPs would be the lightest of these partners, and physicists favor them because the theory naturally predicts just about the amount of dark matter that experts know must exist because of its gravitational pull. (Dark matter represents an estimated 84 percent of all matter in the cosmos.) Many versions of WIMPs have already been ruled out because previous searches for them turned up nothing, but investigators are still hopeful that one of the remaining possibilities will show up.

    Buried in a cave 1,400 meters underground, XENON1T houses a large cylindrical vat filled with 3,500 kilograms of liquid xenon. The substance naturally gives off light when its atoms are disturbed; scientists are aiming to catch the rare occasion when a dark matter particle collides with a xenon nucleus, an impact that should leave a unique energy signal. Although dark matter is thought to be ubiquitous—roughly 100,000 dark particles fly through every square centimeter of space each second—it almost never interacts with regular matter and generally makes its presence known only through gravity. After the planned two-year search at XENON1T, the detection of just 10 particles that appear to match dark matter’s predicted properties would be enough to claim a discovery.

    The $15-million project, sponsored by a collaboration among 10 different countries, follows a previous iteration of the experiment that was 25 times smaller. The new XENON’s larger collecting volume, as well as improved shielding to block other particles that might masquerade as dark matter, should allow it to surpass the earlier experiment’s level of sensitivity within two days of turning on. It should also overtake the current leading dark matter experiment, the 370-kilogram Large Underground Xenon experiment (LUX) in South Dakota, within weeks.

    Lux Dark Matter 2
    LUX Dark Matter Experiment

    “I would not at all be surprised if XENON1T were able to make a discovery that had just barely escaped the generations of experiments that came before it,” says Tim Tait, a theorist at the University of California, Irvine, who is not involved in the experiments.

    Meanwhile WIMPs could also show up any day now at the Large Hadron Collider near Geneva, where protons crash into one another at near the speed of light to give rise to new particles.

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

    The accelerator began a second run last year at almost twice the energy with which it turned on in 2009 and now should be powerful enough to create roughly the same range of WIMPs that might be detectable at XENON1T.

    And if in the next few years, neither of them sees a hint of the particles, the time may come for theorists to move on to another explanation for dark matter. “On one hand, we know it exists, but on the other hand, we know very little about it, so it’s very easy to theorize about possibilities,” Tait says. “If we don’t see it, that tells us the dark matter has turned out to be more weird and wonderful than we had originally guessed it might be.”

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  • richardmitnick 3:56 pm on January 19, 2016 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter, , ,   

    From Symmetry: “A speed trap for dark matter” 

    Symmetry

    01/19/16
    Manuel Gnida

    Analyzing the motion of X-ray sources could help researchers identify dark matter signals.

    Temp 1
    ASTRO-H, an X-ray satellite of the Japan Aerospace Exploration Agency

    Dark matter or not dark matter? That is the question when it comes to the origin of intriguing X-ray signals scientists have found coming from space.

    In a theory paper published today in Physical Review Letters, scientists have suggested a surprisingly simple way of finding the answer: by setting up a speed trap for the enigmatic particles.

    Eighty-five percent of all matter in the universe is dark: It doesn’t emit light, nor does it interact much with regular matter other than through gravity.

    The nature of dark matter remains one of the biggest mysteries of modern physics. Most researchers believe that the invisible substance is made of fundamental particles, but so far they’ve evaded detection. One way scientists hope to prove their particle assumption is by searching the sky for energetic light that would emerge when dark matter particles decayed or annihilated each other in space.

    Over the past couple of years, several groups analyzing data from two X-ray satellites—the European Space Agency’s XMM-Newton and NASA’s Chandra X-ray space observatories—reported the detection of faint X-rays with a well-defined energy of 3500 electronvolts (3.5 keV).

    ESA XMM Newton
    ESA/XMM-Newton

    NASA Chandra Telescope
    NASA/Chandra

    The signal emanated from the center of the Milky Way; its nearest neighbor galaxy, Andromeda; and a number of galaxy clusters.

    1
    Andromeda Galaxy. Adam Evans

    Some scientists believe it might be a telltale sign of decaying dark matter particles called sterile neutrinos—hypothetical heavier siblings of the known neutrinos produced in fusion reactions in the sun, radioactive decays and other nuclear processes. However, other researchers argue that there could be more mundane astrophysical origins such as hot gases.

    There might be a straightforward way of distinguishing between the two possibilities, suggest researchers from Ohio State University and the Kavli Institute for Particle Astrophysics and Cosmology [KIPAC], a joint institute of Stanford University and SLAC National Accelerator Laboratory.

    It involves taking a closer look at the Doppler shifts of the X-ray signal. The Doppler effect is the shift of a signal to higher or lower frequencies depending on the relative velocity between the signal source and its observer. It’s used, for instance, in roadside speed traps by the police, but it could also help astrophysicists “catch” dark matter particles.

    “On average, dark matter moves differently than gas,” says study co-author Ranjan Laha from KIPAC. “Dark matter has random motion, whereas gas rotates with the galaxies to which it is confined. By measuring the Doppler shifts in different directions, we can in principle tell whether a signal—X-rays or any other frequency—stems from decaying dark matter particles or not.”

    Researchers would even know if the signal were caused by the observation instrument itself because then the Doppler shift would be zero for all directions

    Although a promising approach, it can’t just yet be applied to the 3.5-keV X-rays because the associated Doppler shifts are very small. Current instruments either don’t have enough energy resolution for the analysis or they don’t operate in the right energy range.

    However, this situation may change very soon with ASTRO-H, an X-ray satellite of the Japan Aerospace Exploration Agency, whose launch is planned for early this year. As the researchers show in their paper, it will have just the right specifications to return a verdict on the mystery X-ray line. Dark matter had better watch its speed.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 9:33 pm on January 14, 2016 Permalink | Reply
    Tags: , , , Dark Energy/Dark Matter, ,   

    From Symmetry: “Exploring the dark universe with supercomputers” 

    Symmetry

    Temp 1

    01/14/16
    Katie Elyce Jones

    Next-generation telescopic surveys will work hand-in-hand with supercomputers to study the nature of dark energy.

    The 2020s could see a rapid expansion in dark energy research.

    For starters, two powerful new instruments will scan the night sky for distant galaxies. The Dark Energy Spectroscopic Instrument, or DESI, will measure the distances to about 35 million cosmic objects, and the Large Synoptic Survey Telescope, or LSST, will capture high-resolution videos of nearly 40 billion galaxies.

    DESI Dark Energy Spectroscopic Instrument
    LBL DESI

    LSST Exterior
    LSST Telescope
    LSST Camera
    LSST, the building that will house it in Chile, and the camera, being built at SLAC

    Both projects will probe how dark energy—the phenomenon that scientists think is causing the universe to expand at an accelerating rate—has shaped the structure of the universe over time.

    But scientists use more than telescopes to search for clues about the nature of dark energy. Increasingly, dark energy research is taking place not only at mountaintop observatories with panoramic views but also in the chilly, humming rooms that house state-of-the-art supercomputers.

    The central question in dark energy research is whether it exists as a cosmological constant—a repulsive force that counteracts gravity, as Albert Einstein suggested a century ago—or if there are factors influencing the acceleration rate that scientists can’t see. Alternatively, Einstein’s theory of gravity [General Relativity] could be wrong.

    “When we analyze observations of the universe, we don’t know what the underlying model is because we don’t know the fundamental nature of dark energy,” says Katrin Heitmann, a senior physicist at Argonne National Laboratory. “But with computer simulations, we know what model we’re putting in, so we can investigate the effects it would have on the observational data.”

    Temp 2
    A simulation shows how matter is distributed in the universe over time. Katrin Heitmann, et al., Argonne National Laboratory

    Growing a universe

    Heitmann and her Argonne colleagues use their cosmology code, called HACC, on supercomputers to simulate the structure and evolution of the universe. The supercomputers needed for these simulations are built from hundreds of thousands of connected processors and typically crunch well over a quadrillion calculations per second.

    The Argonne team recently finished a high-resolution simulation of the universe expanding and changing over 13 billion years, most of its lifetime. Now the data from their simulations is being used to develop processing and analysis tools for the LSST, and packets of data are being released to the research community so cosmologists without access to a supercomputer can make use of the results for a wide range of studies.

    Risa Wechsler, a scientist at SLAC National Accelerator Laboratory and Stanford University professor, is the co-spokesperson of the DESI experiment. Wechsler is producing simulations that are being used to interpret measurements from the ongoing Dark Energy Survey, as well as to develop analysis tools for future experiments like DESI and LSST.

    Dark Energy Survey
    Dark Energy Camera
    CTIO Victor M Blanco 4m Telescope
    DES, The DECam camera, built at FNAL, and the Victor M Blanco 4 meter telescope in Chile that houses the camera.

    “By testing our current predictions against existing data from the Dark Energy Survey, we are learning where the models need to be improved for the future,” Wechsler says. “Simulations are our key predictive tool. In cosmological simulations, we start out with an early universe that has tiny fluctuations, or changes in density, and gravity allows those fluctuations to grow over time. The growth of structure becomes more and more complicated and is impossible to calculate with pen and paper. You need supercomputers.”

    Supercomputers have become extremely valuable for studying dark energy because—unlike dark matter, which scientists might be able to create in particle accelerators—dark energy can only be observed at the galactic scale.

    “With dark energy, we can only see its effect between galaxies,” says Peter Nugent, division deputy for scientific engagement at the Computational Cosmology Center at Lawrence Berkeley National Laboratory.

    Trial and error bars

    “There are two kinds of errors in cosmology,” Heitmann says. “Statistical errors, meaning we cannot collect enough data, and systematic errors, meaning that there is something in the data that we don’t understand.”

    Computer modeling can help reduce both.

    DESI will collect about 10 times more data than its predecessor, the Baryon Oscillation Spectroscopic Survey, and LSST will generate 30 laptops’ worth of data each night. But even these enormous data sets do not fully eliminate statistical error.

    LBL BOSS
    LBL BOSS telescope

    Simulation can support observational evidence by modeling similar conditions to see if the same results appear consistently.

    “We’re basically creating the same size data set as the entire observational set, then we’re creating it again and again—producing up to 10 to 100 times more data than the observational sets,” Nugent says.

    Processing such large amounts of data requires sophisticated analyses. Simulations make this possible.

    To program the tools that will compare observational and simulated data, researchers first have to model what the sky will look like through the lens of the telescope. In the case of LSST, this is done before the telescope is even built.

    After populating a simulated universe with galaxies that are similar in distribution and brightness to real galaxies, scientists modify the results to account for the telescope’s optics, Earth’s atmosphere, and other limiting factors. By simulating the end product, they can efficiently process and analyze the observational data.

    Simulations are also an ideal way to tackle many sources of systematic error in dark energy research. By all appearances, dark energy acts as a repulsive force. But if other, inconsistent properties of dark energy emerge in new data or observations, different theories and a way of validating them will be needed.

    “If you want to look at theories beyond the cosmological constant, you can make predictions through simulation,” Heitmann says.

    A conventional way to test new scientific theories is to introduce change into a system and compare it to a control. But in the case of cosmology, we are stuck in our universe, and the only way scientists may be able to uncover the nature of dark energy—at least in the foreseeable future—is by unleashing alternative theories in a virtual universe.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:31 pm on January 14, 2016 Permalink | Reply
    Tags: , , , Dark Energy/Dark Matter,   

    From BNL: “New Theory of Secondary Inflation Expands Options for Avoiding an Excess of Dark Matter” 

    Brookhaven Lab

    January 14, 2016
    Chelsea Whyte, (631) 344-8671
    Peter Genzer, (631) 344-3174

    Physicists suggest a smaller secondary inflationary period in the moments after the Big Bang could account for the abundance of the mysterious matter.

    Temp 1
    No image credit found

    Standard cosmology—that is, the Big Bang theory with its early period of exponential growth known as inflation—is the prevailing scientific model for our universe, in which the entirety of space and time ballooned out from a very hot, very dense point into a homogeneous and ever-expanding vastness. This theory accounts for many of the physical phenomena we observe. But what if that’s not all there was to it?

    A new theory from physicists at the U.S. Department of Energy’s Brookhaven National Laboratory, Fermi National Accelerator Laboratory, and Stony Brook University, which will publish online on January 18 in Physical Review Letters, suggests a shorter secondary inflationary period that could account for the amount of dark matter estimated to exist throughout the cosmos.

    Temp 2
    Brookhaven Lab physicist Hooman Davoudiasl published a theory that suggests a shorter secondary inflationary period that could account for the amount of dark matter estimated to exist throughout the cosmos.

    “In general, a fundamental theory of nature can explain certain phenomena, but it may not always end up giving you the right amount of dark matter,” said Hooman Davoudiasl, group leader in the High-Energy Theory Group at Brookhaven National Laboratory and an author on the paper. “If you come up with too little dark matter, you can suggest another source, but having too much is a problem.”

    Measuring the amount of dark matter in the universe is no easy task. It is dark after all, so it doesn’t interact in any significant way with ordinary matter. Nonetheless, gravitational effects of dark matter give scientists a good idea of how much of it is out there. The best estimates indicate that it makes up about a quarter of the mass-energy budget of the universe, while ordinary matter—which makes up the stars, our planet, and us—comprises just 5 percent. Dark matter is the dominant form of substance in the universe, which leads physicists to devise theories and experiments to explore its properties and understand how it originated.

    Some theories that elegantly explain perplexing oddities in physics—for example, the inordinate weakness of gravity compared to other fundamental interactions such as the electromagnetic, strong nuclear, and weak nuclear forces—cannot be fully accepted because they predict more dark matter than empirical observations can support.

    This new theory solves that problem. Davoudiasl and his colleagues add a step to the commonly accepted events at the inception of space and time.

    In standard cosmology, the exponential expansion of the universe called cosmic inflation began perhaps as early as 10-35 seconds after the beginning of time—that’s a decimal point followed by 34 zeros before a 1. This explosive expansion of the entirety of space lasted mere fractions of a fraction of a second, eventually leading to a hot universe, followed by a cooling period that has continued until the present day. Then, when the universe was just seconds to minutes old – that is, cool enough – the formation of the lighter elements began. Between those milestones, there may have been other inflationary interludes, said Davoudiasl.

    “They wouldn’t have been as grand or as violent as the initial one, but they could account for a dilution of dark matter,” he said.

    In the beginning, when temperatures soared past billions of degrees in a relatively small volume of space, dark matter particles could run into each other and annihilate upon contact, transferring their energy into standard constituents of matter—particles like electrons and quarks. But as the universe continued to expand and cool, dark matter particles encountered one another far less often, and the annihilation rate couldn’t keep up with the expansion rate.

    “At this point, the abundance of dark matter is now baked in the cake,” said Davoudiasl. “Remember, dark matter interacts very weakly. So, a significant annihilation rate cannot persist at lower temperatures. Self-annihilation of dark matter becomes inefficient quite early, and the amount of dark matter particles is frozen.”

    However, the weaker the dark matter interactions, that is, the less efficient the annihilation, the higher the final abundance of dark matter particles would be. As experiments place ever more stringent constraints on the strength of dark matter interactions, there are some current theories that end up overestimating the quantity of dark matter in the universe. To bring theory into alignment with observations, Davoudiasl and his colleagues suggest that another inflationary period took place, powered by interactions in a “hidden sector” of physics. This second, milder, period of inflation, characterized by a rapid increase in volume, would dilute primordial particle abundances, potentially leaving the universe with the density of dark matter we observe today.

    “It’s definitely not the standard cosmology, but you have to accept that the universe may not be governed by things in the standard way that we thought,” he said. “But we didn’t need to construct something complicated. We show how a simple model can achieve this short amount of inflation in the early universe and account for the amount of dark matter we believe is out there.”

    Proving the theory is another thing entirely. Davoudiasl said there may be a way to look for at least the very feeblest of interactions between the hidden sector and ordinary matter.

    “If this secondary inflationary period happened, it could be characterized by energies within the reach of experiments at accelerators such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider [LHC],” he said.

    BNL RHIC Campus
    BNL RHIC
    RHIC with map

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN with map.

    Only time will tell if signs of a hidden sector show up in collisions within these colliders, or in other experimental facilities.

    Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 1:33 pm on December 29, 2015 Permalink | Reply
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    From LLNL: “New results from experimental facility deepen understanding of dark matter” 


    Lawrence Livermore National Laboratory

    Dec. 29, 2015
    Stephen Wampler
    wampler1@llnl.gov
    925-423-3107

    1
    Photomultiplier tubes can pick up the tiniest bursts of lights when a particle interacts with xenon atoms as part of the Large Underground Xenon (LUX) dark matter experiment at the Sanford Underground Research Facility (SURF). Photo courtesy of SURF.

    The Large Underground Xenon (LUX) dark matter experiment, which operates nearly a mile underground at the Sanford Underground Research Facility (SURF)in the Black Hills of South Dakota, has already proven itself to be the most sensitive dark matter detector in the world. Now, a new set of calibration techniques employed by LUX scientists has further improved its sensitivity.

    LUX researchers, including several from Lawrence Livermore National Laboratory’s (LLNL) Rare Event Detection Group, are looking for WIMPs, weakly interacting massive particles, which are among the leading candidates for dark matter.

    LLNL is one of the founding members of the LUX experiment, and LLNL researchers have participated in LUX and its predecessor experiment (XENON-10) since 2004.

    “It is vital that we continue to push the capabilities of our detector in the search for the elusive dark matter particles,” said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for the LUX experiment. “We have improved the sensitivity of LUX by more than a factor of 20 for low-mass dark matter particles, significantly enhancing our ability to look for WIMPs.”

    The new research is described in a paper submitted to Physical Review Letters and posted to ArXiv. The work re-examines data collected during LUX’s first experimental run in 2013, and helps to rule out the possibility of dark matter detections at low-mass ranges where other experiments had previously reported potential detections.

    “The latest LUX science results are a re-analysis of data obtained over three months in 2013,” said LLNL principal investigator and physicist Adam Bernstein. “The first analysis of that data was published in 2014, and since then we have expanded our understanding of the detector response through a combination of low-energy nuclear recoil measurements, low-energy electron recoil measurements and an improved understanding of our background in the low-energy recoil regime where dark matter interactions are likely to appear.

    “This combination of improvements enabled us to increase our sensitivity to low-mass WIMPs by upward of two orders of magnitude. LUX is currently in a longer science run lasting 300 live days, scheduled for completion by this July,” Bernstein added.

    Dark matter is thought to be the dominant form of matter in the universe. Scientists are confident in its existence because its gravitational effects can be seen in the rotation of galaxies and in the way light bends as it travels through the universe. Because WIMPs are thought to interact with other matter only on very rare occasions, they have yet to be detected directly.

    “We have looked for dark matter particles during the experiment’s first three-month run, but are exploiting new calibration techniques that do a better job of pinning down how they would appear to our detector,” said Alastair Currie of Imperial College London. “These calibrations have deepened our understanding of the response of xenon to dark matter, and to backgrounds. This allows us to search, with improved confidence, for particles that we hadn’t previously known would be visible to LUX.”

    Bernstein and other LLNL researchers have taken part in initial science planning and experimental design for LUX. Physicist Peter Sorensen, formerly with LLNL and now at Lawrence Berkeley National Laboratory, spent many months with on-site assembly and commissioning, and has made key contributions to the study of the low-mass WIMP signal.

    Physicist Kareem Kazkaz, who works in the LLNL Rare Event Detection Group, created the LUXSim simulation framework, which has been used throughout the collaboration to understand detector response and increase the team’s understanding of signal backgrounds and how the liquid xenon medium responds to incident radiation.

    More recently, LLNL graduate scholar Brian Lenardo has served as the deputy science coordination manager and has been an integral member of the team studying the light and charge yield of nuclear recoils within the active volume. Joining LLNL in September, postdoctoral fellow Jingke Xu has organized a sub-group focused on events at the single electron quantum limit of detector sensitivity.

    LUX consists of a third of a ton of liquid xenon surrounded with sensitive light detectors. It is designed to identify the very rare occasions when a dark matter particle collides with a xenon atom inside the detector. When a collision happens, the xenon atom will recoil and emit a small burst of light, which is detected by LUX’s light sensors. The detector’s location at Sanford Lab beneath a mile of rock helps to shield it from cosmic rays and other radiation that would interfere with the dark matter signal.

    So far, LUX hasn’t detected a dark matter signal, but its exquisite sensitivity has allowed scientists to all but rule out dark matter particles over a wide range of masses that current theories allow. These new calibrations increase that sensitivity even further.

    One calibration technique used neutrons as stand-ins for dark matter particles. Bouncing neutrons off the xenon atoms allows scientists to quantify how the LUX detector responds to the recoil process.

    “It is like a giant game of pool with a neutron as the cue ball and the xenon atoms as the stripes and solids,” Gaitskell said. “We can track the neutron to deduce the details of the xenon recoil, and calibrate the response of LUX better than anything previously possible.”

    The nature of the interaction between neutrons and xenon atoms is thought to be very similar to the interaction between dark matter and xenon. “It’s just that dark matter particles interact very much more weakly — about a million-million-million-million times more weakly,” Gaitskell said.

    The neutron experiments help to calibrate the detector for interactions with the xenon nucleus. But LUX scientists also have calibrated the detector’s response to the deposition of small amounts of energy by struck atomic electrons. That’s done by injecting tritiated methane – a radioactive gas – into the detector.

    “In a typical science run, most of what LUX sees are background electron recoil events,” said Carter Hall of the University of Maryland. “Tritiated methane is a convenient source of similar events, and we’ve now studied hundreds of thousands of its decays in LUX. This gives us confidence that we won’t mistake these garden variety events for dark matter.”

    Another radioactive gas, krypton, was injected to help scientists distinguish between signals produced by ambient radioactivity and a potential dark matter signal.

    “The krypton mixes uniformly in the liquid xenon and emits radiation with a known, specific energy, but then quickly decays away to a stable, nonradioactive Isotope, ” said Dan McKinsey, a University of California Berkeley physics professor and co-spokesperson for LUX, who also is an affiliate of Lawrence Berkeley National Laboratory. “By measuring the light and charge produced by these krypton events throughout the liquid xenon, we can flat-field the detector’s response, allowing better separation of dark matter events from natural radioactivity.”

    LUX improvements coupled to the advanced computer simulations at Lawrence Berkeley National Laboratory’s National Energy Research Scientific Computing Center and Brown University’s Center for Computation and Visualization have allowed scientists to test additional particle models of dark matter that can be excluded from the search. “And so the search continues,” McKinsey said.

    4
    Edison Cray XC30 at NERSC

    “LUX is once again in search mode at Sanford Lab. The latest run began in late 2014 and is expected to continue until June 2016. This run will represent an increase in exposure of more than four times compared to the previous 2013 run. We will be very excited to see if any dark matter particles have shown themselves in the new data.”

    The LUX scientific collaboration, which is supported by the DOE and National Science Foundation, includes 19 research universities and national laboratories in the United States, the United Kingdom and Portugal.

    “The global search for dark matter aims to answer one of the biggest questions about the makeup of our universe. We’re proud to support the LUX collaboration and congratulate them on achieving an even greater level of sensitivity,” said Mike Headley, executive director of the SDSTA.

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  • richardmitnick 9:50 am on December 17, 2015 Permalink | Reply
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    From ESA: “Euclid dark Universe mission ready to take shape” 

    ESASpaceForEuropeBanner
    European Space Agency

    17 December 2015
    Markus Bauer
    ESA Science and Robotic Exploration Communication Officer
    Email: markus.bauer@esa.int
    Tel: +31 71 565 6799

    Giuseppe Racca
    ESA Euclid Project Manager
    Email: giuseppe.racca@esa.int

    René Laureijs
    ESA Euclid Project Scientist
    Email: rene.laureijs@esa.int

    1
    Euclid

    Euclid, ESA’s Dark Universe mission, has passed its preliminary design review, providing confidence that the spacecraft and its payload can be built. It’s time to start ‘cutting metal’.

    “This is really a big step for the mission,” says Giuseppe Racca, Euclid’s project manager. “All the elements have been put together and evaluated. We now know that the mission is feasible and we can do the science.”

    First proposed to ESA in 2007, Euclid was selected as the second medium-class mission in the Cosmic Vision programme in October 2011. Italy’s Thales Alenia Space was chosen as the prime contractor in 2013.

    Since then, the mission’s design has been studied and refined. This has involved a wide range of detailed technical designs, in addition to building and testing key components.

    The outcome of Euclid’s recent review was positive, opening the door to the industrial contractors and external instrument teams building the spacecraft and payload for real. Airbus Defence & Space in France will deliver the complete payload module incorporating a 1.2 m-diameter telescope feeding the two science instruments being developed by the Euclid Consortium.

    “This is a major milestone for us. Everyone is now ready to start cutting metal,” says René Laureijs, Euclid’s project scientist.

    On the scientific side, this review checked that the mission can indeed deliver the required data. The combined performance of the spacecraft, telescope and instruments shows that the data returned over the six-year mission will achieve the objectives.

    Euclid is designed to give us important new insights into the ‘dark side’ of the Universe, namely dark matter and dark energy, both key components of the current model for the formation and evolution of the Universe.

    Observations made over recent decades reveal that less than 5% of the matter in the Universe is in the form of normal atoms, while a much larger amount of dark matter is inferred from measurements including the rotation speeds of galaxies. This matter acts through gravity, but is invisible.

    Dark energy, on the other hand, is invoked to explain the finding that the expansion of the Universe is accelerating.

    Although they are thought to make up the majority of the matter and energy in the Universe, dark matter and dark energy cannot be seen. Instead, their presence is inferred by the movement of galaxies, the shape of galaxies, their distribution in space, and the rate of the Universe’s expansion as traced by the galaxies.

    By mapping the shapes, positions and movements of two billion galaxies across more than a third of the sky, Euclid will provide astronomers with an unprecedented wealth of data to analyse.

    The unrivalled accuracy of its measurements will allow them to close in on the properties and behaviour of dark matter and dark energy. This, in turn, will put constraints on the theoretical properties of what these two unseen components of the Universe may be.

    With Euclid’s preliminary design review now safely passed, the next major milestone comes in two years at the critical design review.

    At this point, the major hardware components will have been built and tested. If all goes well, Euclid will then be assembled.

    After this, Euclid will be ready for launch in December 2020 on a Soyuz rocket from Europe’s Spaceport in Kourou, French Guiana.

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 1:10 pm on December 14, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, ,   

    From LBL: “New Results from World’s Most Sensitive Dark Matter Detector” 

    Berkeley Logo

    Berkeley Lab

    December 14, 2015
    Glenn Roberts Jr. 510-486-5582

    Berkeley Lab Scientists Participate in Mile-deep Experiment in Former South Dakota Gold Mine

    The Large Underground Xenon (LUX) dark matter experiment, which operates nearly a mile underground at the Sanford Underground Research Facility (SURF) in the Black Hills of South Dakota, has already proven itself to be the most sensitive detector in the hunt for dark matter, the unseen stuff believed to account for most of the matter in the universe. Now, a new set of calibration techniques employed by LUX scientists has again dramatically improved the detector’s sensitivity.

    1
    A view inside the LUX detector. (Photo by Matthew Kapust/Sanford Underground Research Facility)

    Researchers with LUX are looking for WIMPs, or weakly interacting massive particles, which are among the leading candidates for dark matter. “We have improved the sensitivity of LUX by more than a factor of 20 for low-mass dark matter particles, significantly enhancing our ability to look for WIMPs,” said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for the LUX experiment. “It is vital that we continue to push the capabilities of our detector in the search for the elusive dark matter particles,” Gaitskell said.

    LUX improvements, coupled to advanced computer simulations at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory’s (Berkeley Lab) National Energy Research Scientific Computing Center (NERSC) and Brown University’s Center for Computation and Visualization (CCV), have allowed scientists to test additional particle models of dark matter that now can be excluded from the search. NERSC also stores large volumes of LUX data—measured in trillions of bytes, or terabytes—and Berkeley Lab has a growing role in the LUX collaboration.

    Scientists are confident that dark matter exists because the effects of its gravity can be seen in the rotation of galaxies and in the way light bends as it travels through the universe. Because WIMPs are thought to interact with other matter only on very rare occasions, they have yet to be detected directly.

    2
    The LUX dark matter detector is seen here during the assembly process in a surface laboratory in South Dakota. (Photo by Matthew Kapust/Sanford Underground Research Facility)

    “We have looked for dark matter particles during the experiment’s first three-month run, but are exploiting new calibration techniques better pinning down how they would appear to our detector,” said Alastair Currie of Imperial College London, a LUX researcher.

    “These calibrations have deepened our understanding of the response of xenon to dark matter, and to backgrounds. This allows us to search, with improved confidence, for particles that we hadn’t previously known would be visible to LUX.”

    The new research is described in a paper submitted to Physical Review Letters. The work reexamines data collected during LUX’s first three-month run in 2013 and helps to rule out the possibility of dark matter detections at low-mass ranges where other experiments had previously reported potential detections.

    3
    A view of the LUX detector during installation. (Photo by Matthew Kapust/Sanford Underground Research Facility)

    LUX consists of one-third ton of liquid xenon surrounded with sensitive light detectors. It is designed to identify the very rare occasions when a dark matter particle collides with a xenon atom inside the detector. When a collision happens, a xenon atom will recoil and emit a tiny flash of light, which is detected by LUX’s light sensors. The detector’s location at Sanford Lab beneath a mile of rock helps to shield it from cosmic rays and other radiation that would interfere with a dark matter signal.

    So far LUX hasn’t detected a dark matter signal, but its exquisite sensitivity has allowed scientists to all but rule out vast mass ranges where dark matter particles might exist. These new calibrations increase that sensitivity even further.

    One calibration technique used neutrons as stand-ins for dark matter particles. Bouncing neutrons off the xenon atoms allows scientists to quantify how the LUX detector responds to the recoiling process.

    “It is like a giant game of pool with a neutron as the cue ball and the xenon atoms as the stripes and solids,” Gaitskell said. “We can track the neutron to deduce the details of the xenon recoil, and calibrate the response of LUX better than anything previously possible.”

    The nature of the interaction between neutrons and xenon atoms is thought to be very similar to the interaction between dark matter and xenon. “It’s just that dark matter particles interact very much more weakly—about a million-million-million-million times more weakly,” Gaitskell said.

    The neutron experiments help to calibrate the detector for interactions with the xenon nucleus. But LUX scientists have also calibrated the detector’s response to the deposition of small amounts of energy by struck atomic electrons. That’s done by injecting tritiated methane—a radioactive gas—into the detector.

    “In a typical science run, most of what LUX sees are background electron recoil events,” said Carter Hall a University of Maryland professor. “Tritiated methane is a convenient source of similar events, and we’ve now studied hundreds of thousands of its decays in LUX. This gives us confidence that we won’t mistake these garden-variety events for dark matter.”

    Another radioactive gas, krypton, was injected to help scientists distinguish between signals produced by ambient radioactivity and a potential dark matter signal.

    “The krypton mixes uniformly in the liquid xenon and emits radiation with a known, specific energy, but then quickly decays away to a stable, non-radioactive form,” said Dan McKinsey, a UC Berkeley physics professor and co-spokesperson for LUX who is also an affiliate with Berkeley Lab. By precisely measuring the light and charge produced by this interaction, researchers can effectively filter out background events from their search.

    “And so the search continues,” McKinsey said. “LUX is once again in dark matter detection mode at Sanford Lab. The latest run began in late 2014 and is expected to continue until June 2016. This run will represent an increase in exposure of more than four times compared to our previous 2013 run. We will be very excited to see if any dark matter particles have shown themselves in the new data.”

    McKinsey, formerly at Yale University, joined UC Berkeley and Berkeley Lab in July, accompanied by members of his research team.

    The Sanford Lab is a South Dakota-owned facility. Homestake Mining Co. donated its gold mine in Lead to the South Dakota Science and Technology Authority (SDSTA), which reopened the facility in 2007 with $40 million in funding from the South Dakota State Legislature and a $70 million donation from philanthropist T. Denny Sanford. The U.S. Department of Energy (DOE) supports Sanford Lab’s operations.

    Kevin Lesko, who oversees SURF operations and leads the Dark Matter Research Group at Berkeley Lab, said, “It’s good to see that the experiments installed in SURF continue to produce world-leading results.”

    The LUX scientific collaboration, which is supported by the DOE and National Science Foundation (NSF), includes 19 research universities and national laboratories in the United States, the United Kingdom and Portugal.

    “The global search for dark matter aims to answer one of the biggest questions about the makeup of our universe. We’re proud to support the LUX collaboration and congratulate them on achieving an even greater level of sensitivity,” said Mike Headley, Executive Director of the SDSTA.

    Planning for the next-generation dark matter experiment at Sanford Lab is already under way. In late 2016 LUX will be decommissioned to make way for a new, much larger xenon detector, known as the LUX-ZEPLIN (LZ) experiment.

    LZ project
    LZ schematic

    LZ would have a 10-ton liquid xenon target, which will fit inside the same 72,000-gallon tank of pure water used by LUX. Berkeley Lab scientists will have major leadership roles in the LZ collaboration.

    “The innovations of the LUX experiment form the foundation for the LZ experiment, which is planned to achieve over 100 times the sensitivity of LUX. The LZ experiment is so sensitive that it should begin to detect a type of neutrino originating in the Sun that even Ray Davis’ Nobel Prize-winning experiment at the Homestake mine was unable to detect,” according to Harry Nelson of UC Santa Barbara, spokesperson for LZ.

    LUX is supported by the DOE Office of Science. NERSC is a DOE Office of Science User Facility.

    A version of this release and additional materials are available on the Sanford Lab site.

    See the full article here .

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

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  • richardmitnick 12:55 pm on December 8, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, ,   

    From SURF: “4850 Feet Below: The Hunt for Dark Matter” 

    Sanford Underground Research facility

    Sanford Underground levels

    Sanford Underground Research facility

    Oct 5, 2015
    Deep in an abandoned gold mine in rural South Dakota, a team of physicists are hunting for astrophysical treasure. Their rare and elusive quarry is dark matter, a theoretical particle which has never been seen or directly detected. Yet its gravitational effect on distant galaxies hints at its existence and provides ample evidence to fuel the experiments and aspirations of scientists at the Sanford Underground Research Facility. Insulated by 4,850 feet of rock, the researchers have constructed the world’s most sensitive particle detector, known as the Large Underground Xenon Experiment, or “LUX.

    LUX Dark matter
    Lux Dark Matter 2
    LUX

    Their goal is to use this complex device to capture an epiphanous event: the interaction between dark matter and atoms inside a chilled tank of liquid xenon. If they’re successful, the researchers may not only solve some of the biggest mysteries in astrophysics but affirm their faith in the nature of dark matter.

    “4850 Feet Below” was produced with generous support from the John Templeton Foundation.

    See the full article here .

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

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

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

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

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

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s. 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) [being replaced by DUNE]—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 [DUNE] will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

     
  • richardmitnick 6:07 pm on December 7, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter,   

    From New Scientist: “Tiny dark matter stars would harbour particles that act as one” 

    NewScientist

    New Scientist

    7 December 2015
    Anna Nowogrodzki

    1
    (Image: NIST)

    “You will be assimilated.” In Star Trek, members of the strange and sinister race known as the Borg would utter this threat as if one. Their behaviour could be echoed in space if dark matter exists in a particular form: if so, it could create Borg-like stars in which every particle is in the same state at the same time.

    Dark matter accounts for 80 percent of the matter in the universe, but we can’t observe it directly and its constituents are a mystery.

    One theory is that dark matter could be made of particles called axions. Unlike protons, neutrons and electrons that make up ordinary matter, axions can share the same quantum energy state. They also attract each other gravitationally, so they clump together.

    Together, those two properties mean that the clumps would exist as a Bose-Einstein condensate (BEC) – a state of matter in which all the particles occupy the same quantum state, according to calculations by Chanda Prescod-Weinstein at the Massachusetts Institute of Technology and her colleagues.

    “They act like one super-atom together,” says Prescod-Weinstein. But those clumps are prone to fracturing, she adds. “The configuration the axions ‘want’ to settle into is not one giant BEC.” Rather, they break apart into smaller clumps, which the team calls Bose stars.
    Asteroid-sized

    These would have formed when the universe was a mere 47,000 years old and should survive to this day, she says. Such stars would be totally dark and relatively tiny, the size of the asteroid Ceres and about 20 times as dense.

    Dark matter is hard to study because it does not interact much with ordinary matter, but axion dark matter could theoretically be observed in the form of Bose stars, if they are orbiting a pulsar. Under the right conditions, the interaction between the pulsar and the axions could produce radiation we can pick up, says Prescod-Weinstein.

    This would be like a naturally occurring, space-based version of the Axion Dark Matter Experiment [ADMX] at the University of Washington in Seattle, which uses a large superconducting magnet to search for axions.

    U Washington ADMX
    ADMX

    “I’m sure that experimentalists would express some scepticism about that,” she says. “But I tend to be optimistic that the universe is weirder than we think it is.”

    “It’s a great paper, and we agree with their conclusions,” says Rohana Wijewardhana at the University of Cincinnati, Ohio, whose team has done similar calculations.

    Wijewardhana adds that if a Bose star crashed into Earth, we might be able to observe its effects. It’s not something we need worry about, either: because a Bose star would interact weakly with matter, we would only see small gravitational effects even if the entire thing passed right through Earth.

    Journal reference: Physical Review D, 10.1103/PhysRevD.92.103513

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  • richardmitnick 2:49 pm on December 1, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, ,   

    From Symmetry: “What could dark matter be?” 

    Symmetry

    12/01/15
    Laura Dattaro

    1
    Dark matter is an invisible material that emits or absorbs no light but betrays its presence by interacting gravitationally with visible matter. This image from Dark Universe shows the distribution of dark matter in the universe, as simulated with a novel, high-resolution algorithm at the Kavli Institute of Particle Astrophysics & Cosmology at Stanford University and SLAC National Accelerator Laboratory. Credit: © AMNH

    Although nearly a century has passed since an astronomer first used the term dark matter in the 1930s, the elusive substance still defies explanation. Physicists can measure its effects on the movements of galaxies and other celestial objects, but what it’s made of remains a mystery.

    In order to solve it, physicists have come up with myriad possibilities, plus a unique way to find each one. Some ideas for dark matter particles arose out of attempts to solve other problems in physics. Others are pushing the boundaries of what we understand dark matter to be.

    “You don’t know which experiment is going to ultimately show it,” says Neal Weiner, a New York University physics professor. “And if you don’t think of the right experiment, then you might not find it. It’s not just going to hit you in the face, because it’s dark matter.”

    2
    One image of WIMPS

    WIMPs

    The term WIMP encompasses many dark matter particles, some of which are discussed in this list.

    Short for weakly interacting massive particles, WIMPs would have about 1 to 1000 times the mass of a proton and would interact with one another only through the weak force , the force responsible for radioactive decay.

    If dark matter were a pop star, WIMPs would be Beyoncé. “WIMPs are the canonical candidate,” says Manoj Kaplinghat, a professor of physics and astronomy at the University of California, Irvine.

    But a recent surge in data has cast new doubt on their existence. Despite the fact that scientists are hunting for them in experiments in space and on Earth, including ones at the Large Hadron Collider, WIMPs have yet to show themselves, making the restrictions on their mass, interaction strength and other properties ever tighter.

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

    If WIMPs do fail to appear, the upshot will be a push for creative new solutions to the dark matter mystery—plus a chance to finally cross something off the list.

    “If we don’t see it, it will at least end up closing the chapter on a really dominant paradigm that’s been the guide in the field for many, many years,” says Mariangela Lisanti, a theoretical particle physicist at Princeton University.

    3
    Fermilab is running an experiment called MiniBooNE, whose detector is shown here, to verify the existence of a relatively low-mass ‘sterile’ neutrino (Image: FNAL)

    Sterile neutrinos

    Neutrinos are almost massless particles that shape-shift from one type to another and can stream right through an entire planet without hitting a thing. As strange as they are, they may have an even odder counterpart known as sterile neutrinos.

    These most elusive particles would be so unresponsive to their surroundings that it would take the entire age of the universe for just one to interact with another bit of matter.

    If sterile neutrinos are the stuff of dark matter, their reluctance to interact might seem to spell doom for physicists hoping to detect them. But in a poetic twist, it’s possible that they decay into something we can find quite easily: photons, or particles of light.

    “Photons, we’re pretty good at,” says Stefano Profumo, a physics professor at the University of California, Santa Cruz.

    Last year, physicists using space-based telescopes discovered a steady signal with the energy predicted for decaying sterile neutrinos streaming from the centers of galaxy clusters. But the signal could originate from a different source, such as potassium ions. (Profumo proposed this idea in a paper provocatively titled Dark matter searches going bananas.) A new Japanese telescope known as [JAXA]/ASTRO-H has much better energy resolution and may be able to put an end to the debate.

    JAXA ASTRO-H telescope
    JAXA/ASTRO-H

    4
    Image including neutralinos

    Neutralinos

    The canonical example of a WIMP, the neutralino, arises out of the theory of Supersymmetry. Supersymmetry posits that every known particle has a “super” partner and helps to fill some holes in the Standard Model, but its particles have stubbornly eluded observation.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    6
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Some of them, like the partners of the photon and the Z boson, have properties akin to dark matter. Dark matter could be a mix of these supersymmetric particles, and the one we’d be most likely to observe is known as the neutralino.

    Discovering a neutralino would help solve two massive physics problems—it would tell us the identity of dark matter and would give us proof of the existence of Supersymmetry. But it would also leave physicists with the conundrum of all those other missing supersymmetric particles.

    “If dark matter is a neutralino, it’s essentially telling us there’s a whole host of other new stuff that’s out there that’s just waiting to be discovered,” Lisanti says. “It opens up a floodgate of really, really interesting and very exciting work to be done.”

    Asymmetric dark matter

    In the beginning of the universe, matter and antimatter collided furiously, annihilating each other on contact until, somehow, only matter was left. But there’s nothing in the Standard Model of particle physics that says this must be so. Antimatter and matter should have existed in equal amounts, wiping each other out and leaving an empty universe.

    That’s clearly not the case, and physicists don’t yet know why. It’s possible the same principle applies to dark matter. In a twist on the standard neutralino theory, which includes the property that neutralinos are their own antiparticle, an idea known as asymmetric dark matter proposes that anti-dark matter particles were wiped out by their dark matter counterparts, leaving behind the dark matter we see today. Finding asymmetric dark matter could help answer not only the question of what dark matter is, but also why we’re here to look for it.

    5
    From Quantum Diaries, depiction of Axions.

    Axions

    As the search for WIMPs faces challenges, a particle known as the axion is generating new excitement.

    The axion itself is not new. Physicists first imagined its existence in the early 1980s, shortly after physicists Helen Quinn and Roberto Peccei published a landmark paper that helped to solve a problem with the strong nuclear force. While it’s been simmering in the background as a dark matter candidate for decades, experimentalists haven’t been able to search for it—until now.

    “We’re just recently getting to the stage of having experiments that are able to probe the most interesting regions of axion parameter space,” says physics professor Risa Wechsler of the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and SLAC National Accelerator Laboratory.

    The University of Washington’s Axion Dark Matter Experiment (ADMX) is on the hunt for axions, using a strong magnetic field to try to turn them into detectable photons.

    U Washington ADMX Axion Dark Matter Experiment
    ADMX

    At the same time, theorists are beginning to imagine new types of axions, along with novel ways to search for them.

    “There’s been a renaissance in axion theory, leading to a lot more excitement in axion experiments,” says UCI theoretical physicist Jonathan Feng.

    Mirror world dark matter

    Just like strange objects and creatures inhabited the world beyond Alice’s looking glass, dark matter might exist in an entirely separate world full of its own versions of all the elementary particles. These dark protons and neutrons would never interact with us, save through gravity, exerting a pull on matter in our world without leaving any other trace. “The only reason we know there’s something out there called dark matter is because of gravity,” Feng says. “This embodies that very beautifully.”

    Beautiful as it may be, the theory leaves little hope for ever detecting dark matter. But there are hints that dark photons might be able to morph into regular photons, similar to the way neutrinos oscillate among flavors. This has spawned active research into understanding and finding these mysterious particles.

    Extra dimensional dark matter

    If dark matter doesn’t exist in another world entirely, it might live in a fourth spatial dimension unseen by humans and our experiments. Such a dimension would be too small for us to observe a particle’s movements within it. Instead, we would see multiple particles with the same charge but different masses, an idea proposed by Theodor Kaluza and Oskar Klein in the 1920s. One of these particles could be the dark matter particle, a much more recent concept known as Kaluza-Klein dark matter. These particles wouldn’t shine or reflect any light, explaining why dark matter can’t be seen by anyone in our three dimensions.

    Confirming that dark matter exists in another dimension could also be seen as support for string theory, which requires extra dimensions to work.

    “You can go out there and map out the extra-dimensional world just like 500 years ago people mapped out the continents,” Feng says.

    SIMPs

    Though physicists have never detected dark matter, they have a pretty good idea of how much of it exists, based on observations of galaxies. But observations of the inner regions of galaxies don’t match up with some dark matter simulations, a puzzle physicists and astronomers are still working to solve.

    Those simulations often assume that dark matter doesn’t interact with itself, but there’s no reason to believe that has to be the case. That realization has led to the concept of strongly interacting massive particles, or SIMPs, the latest newcomer to the crowded field of dark matter candidates. Simulations run with SIMPs seem to eliminate the discrepancy in other models, Feng says, and could even explain the strange photon signal emanating from galaxy clusters, rather than sterile neutrinos.

    Composite dark matter

    Dark matter could be none of these candidates—or it could be more than one.

    “There is no reason for dark matter to be just one particle, not a single one,” Kaplinghat says. “We only assume it is for simplicity.”

    After all, visible matter is made up of a swarm of particles, each with their own properties and behaviors, each able to combine with others in countless ways. Why should dark matter be any different?

    Dark matter could have its own equivalents of quarks and gluons interacting to form dark baryons and other particles. There could be dark atoms, made of several particles linked together.

    Whatever the case, dark matter is likely to keep physicists probing the depths of the universe for decades, revealing new mysteries even as old ones are solved.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
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