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  • richardmitnick 12:48 pm on January 22, 2019 Permalink | Reply
    Tags: Dark Matter, ,   

    From Sanford Underground Research Facility: “LZ gets an eye exam” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    January 18, 2019
    Erin Broberg

    1
    Brown University graduate student Will Taylor attaches data collection cables to a section of the PMT array. Matthew Kapust

    Lights out, windows darkened, doors closed. It’s not after hours at the Surface Assembly Lab (SAL), it’s just time for the first of LUX-ZEPLIN (LZ) dark matter detector’s on-site eye exam.

    LZ’s “eyes” are two massive arrays of photomultiplier tubes (PMTs), powerful light sensors that will detect any faint signals produced by dark matter particles when the experiment begins in 2020. The first of these arrays, which holds 241 PMTs, arrived at Sanford Underground Research Facility (Sanford Lab) in December. Now, researchers are testing the PMTs for the bottom array to make sure they are still in working condition after being transported from Brown University, where they were assembled.

    “These PMTs have already undergone rigorous testing, down to their individual components and this is the final test after transport to the site,” said Will Taylor, a graduate student at Brown University who has been working with the LZ collaboration since 2014.

    Once testing is completed, the bottom PMT array will be placed in the inner cryostat. The same process will be followed for the top array. The inner cryostat will be filled with xenon, both gaseous and liquid, and placed in the outer cryostat. Then, the entire detector will be submerged in the 72,000-gallon water tank in the Davis Campus on the 4850 Level of Sanford Lab.

    “As you can imagine,” Taylor said. “It will be impossible to change out a faulty PMT after the experiment is completely assembled. This is our last chance to ensure each PMT is working perfectly.”

    While researchers do expect a few PMTs to “blink out” over LZ’s five to six year lifetime, only the best of the best will make it into the detector. So, just how do researchers transform the SAL into an optometrist’s office?

    Royal treatment

    First, the array is placed in a special enclosure called the PALACE (PMT Array Lifting And Cleanliness Enclosure). There, the PMTs are shielded from light and dust. This enclosure also allows researchers access to the PMTs through a rotating window and to connect data collection systems to different sections of PMTs at a time.

    “We test by section, collecting data from 30 PMTs per day,” said Taylor. “Each individual PMT has a serial number and is tagged to its own data, so we know exactly what each PMT is ‘seeing.’”

    Going dark

    For the first test, researchers look at what is called the “dark rate” of each PMT. To perform this test, researchers seal up the PALACE, turn off the lights in the cleanroom and black out the windows. In this utter darkness, PMTs are monitored for “thermal noise.”

    “At a normal temperature, particles vibrate around inside the PMTs. When this happens, it is possible for electrons to ‘jump off’ and produce a signal that PMTs will detect,” Taylor explained. While most of this “thermal noise” will vanish once the experiment is cooled to liquid xenon temperature (-148 °F), researchers want to ensure the PMT’s dark rate is at the lowest threshold possible before being installed in LZ.

    “Typically, these false signals come from a single photoelectron,” Taylor said. “With the dark test, we can measure how many photoelectrons signals occur every second.”

    How much is too much noise? While a bit of noise (100-1000 events per second) is tolerable; rates closer to 10,000 events per second would be far too high, resulting in too many random signals that could overshadow WIMP signals during the experiment.

    “That’s why it is incredibly important to make sure each PMT has a low dark rate,” said Taylor.

    Lighting it up

    For the second test, called an “after-pulsing” test, researchers will flash a light, imperceptible to the human eye, at the PMTs. This test determines the health of each PMT’s internal vacuum. Why is this important?

    When light from a reaction inside the detector hits a photocathode of a PMT, an electron will be emitted. This single electron will be pulled through the PMT, hitting dynodes. Each time the electron hits an electrode, more electrons are emitted. This process continues, amplifying the original signal, turning the original electron into many, many, many electrons.

    “That’s how we get an electron signal strong enough to read out,” Taylor said. “For that to work, however, those electrons have to be able to bounce between those dynodes without interruption.”

    To decrease particle “traffic,” each PMT has a vacuum. The vacuum ensures there are no gas particles present to interfere with the amplification process. If a vacuum is faulty, gas particles may get in the way and hit an electron. This would cause the gas particle to bounce away and set off a second pulse of electrons, amplifying a signal of its own.

    “This is called an ‘after-pulse,’” Taylor said. “The after-pulse is indicative of how good the vacuum, and thus the PMT, really is.”

    Rather than depriving the PMTs of light as they did during the dark test, researchers now createa signal of their own to measure the after-pulse. To do this, an LED is affixed to the inside of the PALACE.

    “We flash the LED at a rate of 1 kilohertz for 30 seconds. That’s a total of 30,000 flashes of the LED,” Taylor said. While that might sound like a lot of light, it’s actually not even perceptible to the human eye. “Each flash lasts 10 nanoseconds and produces only 50-100 photons—so the human eye can’t detect it.”

    It is enough, however, for the PMT to detect it with a sizable initial pulse. Because researchers know exactly when the initial pulse was created, they can align their data to see when after-pulses occur and measure their strength.

    “This helps us see how healthy the vacuum is and determine if the PMT is fit for LZ,” Taylor said.

    20/20 vision

    After a week of testing, researchers have announced the bottom array has 20/20 vision.

    “Accepting the first of the two PMT arrays onsite, is one of many milestones toward the assembly and installation of the LZ experiment,” said Markus Horn, research support scientist at Sanford Lab and a member of the LZ collaboration. “While the detector assembly progresses at the Surface Lab, underground the installation of the xenon gas and Liquid Nitrogen cooling system begins. That would be the heart and the lung of LZ. But that’s another story!”

    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.
    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.

    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.

    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.

    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.”
    We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

    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
    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.

    LBNL LZ project at SURF, Lead, SD, USA

    CASPAR at SURF


    CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

    The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”

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  • richardmitnick 11:12 am on January 9, 2019 Permalink | Reply
    Tags: , , , , , Dark Matter, Galaxy clusters much more common than thought   

    From COSMOS Magazine: “Galaxy clusters much more common than thought” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    09 January 2019
    Andrew Masterson

    Data mining exercise reveals a whole new class of astronomical structure.

    1
    The MACS J0717 galaxy cluster, 5.6 billion light years from Earth, as seen by NASA’s Chandra X-ray Observatory.
    X-ray: NASA/CXC/SAO/van Weeren et al.; Optical: NASA/STScI; Radio: NSF/NRAO/VLA

    NASA/Chandra X-ray Telescope

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    A re-examination of data gathered a decade ago by astronomers using a 3.9-metre telescope [AAO Anglo Australian Telescope]located at the Siding Spring Observatory in the Australian state of New South Wales has revealed that the number of galaxy clusters in the universe has been underestimated by as much as a third.


    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    The finding is remarkable, because galaxy clusters – collections of individual galaxies bound together by gravity – are the largest structures in the universe and, by dint of containing billions or trillions of stars, relatively easy to see.

    The word “relatively”, in this case, is particularly apt, because stars, and whatever planets and other rocky bits and bobs accompany them, comprise only a very small fraction of any cluster’s mass.

    This was a discovery first made by American astronomer Fritz Zwicky in 1933, when he analysed the movements of stars within an enormous agglomeration called the COMA cluster and concluded that the mass of all the visible matter therein was insufficient to account for his findings. Something else – and something huge, at that – must have been in play.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

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

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    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

    Dark Matter Research

    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, Lead, SD, USA

    ADMX Axion Dark Matter Experiment, U Uashington

    And thus, the concept of dark matter entered the cosmological discourse.

    Current estimates suggest that in most galaxy clusters, the galaxies themselves – at least as defined by visible matter – comprise only 1% of the total mass. Hot gas clouds account for another 9%, and dark matter makes up the remaining 90%.

    The latest research, however, led by Luis Campusano from the Universidad de Chile, in Chile, suggests that in a substantial tranche of cases these percentages need to be revised, with the visible matter component declining even further.

    Campusano and colleagues revisited data gathered during a major galaxy redshift survey known as 2dFGRS, which was completed in 2003. The project looked at 191,440 galaxies.

    By carefully mining the information, and discarding some standard definitions, the astronomers identified 341 clusters – 87 of them previously unknown.

    The newly discovered groups, classified by the researchers as “late-type-rich clusters”, are described as being “high mass-to-light ratio systems”, which means that they contain fewer stars than other clusters. The stars are also less densely packed, meaning the galaxies contained in each cluster are less luminous than normal.

    Campusano and colleagues looked only at galaxies contained in the nearby universe – another highly relative term – but assume the results probably hold for the rest of the cosmos.

    The discovery – published in The Astrophysical Journal – seems likely to prompt a surge in newly focussed practical and theoretical astronomy. Not only are galaxy clusters about 33% more common than previously assumed, the astronomers report, but the newly defined “class of late-type-rich clusters is not predicted by current theory”.

    See the full article here .


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  • richardmitnick 11:31 am on January 8, 2019 Permalink | Reply
    Tags: , Antiuniverse, , , CPT symmetry, Dark Matter, Our universe has antimatter partner on the other side of the Big Bang say physicists, , , , The entity that respects the symmetry is a universe–antiuniverse pair   

    From physicsworld.com: “Our universe has antimatter partner on the other side of the Big Bang, say physicists” 

    physicsworld
    From physicsworld.com

    03 Jan 2019

    1
    (Courtesy: shutterstock/tomertu)

    Our universe could be the mirror image of an antimatter universe extending backwards in time before the Big Bang. So claim physicists in Canada, who have devised a new cosmological model positing the existence of an “antiuniverse” [Physical Review Letters] which, paired to our own, preserves a fundamental rule of physics called CPT symmetry. The researchers still need to work out many details of their theory, but they say it naturally explains the existence of dark matter.

    Standard cosmological models tell us that the universe – space, time and mass/energy – exploded into existence some 14 billion years ago and has since expanded and cooled, leading to the progressive formation of subatomic particles, atoms, stars and planets.

    However, Neil Turok of the Perimeter Institute for Theoretical Physics in Ontario reckons that these models’ reliance on ad-hoc parameters means they increasingly resemble Ptolemy’s description of the solar system. One such parameter, he says, is the brief period of rapid expansion known as inflation that can account for the universe’s large-scale uniformity. “There is this frame of mind that you explain a new phenomenon by inventing a new particle or field,” he says. “I think that may turn out to be misguided.”

    Instead, Turok and his Perimeter Institute colleague Latham Boyle set out to develop a model of the universe that can explain all observable phenomena based only on the known particles and fields. They asked themselves whether there is a natural way to extend the universe beyond the Big Bang – a singularity where general relativity breaks down – and then out the other side. “We found that there was,” he says.

    The answer was to assume that the universe as a whole obeys CPT symmetry. This fundamental principle requires that any physical process remains the same if time is reversed, space inverted and particles replaced by antiparticles. Turok says that this is not the case for the universe that we see around us, where time runs forward as space expands, and there’s more matter than antimatter.

    2
    In a CPT-symmetric universe, time would run backwards from the Big Bang and antimatter would dominate (L Boyle/Perimeter Institute of Theoretical Physics)

    Instead, says Turok, the entity that respects the symmetry is a universe–antiuniverse pair. The antiuniverse would stretch back in time from the Big Bang, getting bigger as it does so, and would be dominated by antimatter as well as having its spatial properties inverted compared to those in our universe – a situation analogous to the creation of electron–positron pairs in a vacuum, says Turok.

    Turok, who also collaborated with Kieran Finn of Manchester University in the UK, acknowledges that the model still needs plenty of work and is likely to have many detractors. Indeed, he says that he and his colleagues “had a protracted discussion” with the referees reviewing the paper for Physical Review Letters [link is above] – where it was eventually published – over the temperature fluctuations in the cosmic microwave background. “They said you have to explain the fluctuations and we said that is a work in progress. Eventually they gave in,” he says.

    In very broad terms, Turok says, the fluctuations are due to the quantum-mechanical nature of space–time near the Big Bang singularity. While the far future of our universe and the distant past of the antiuniverse would provide fixed (classical) points, all possible quantum-based permutations would exist in the middle. He and his colleagues counted the instances of each possible configuration of the CPT pair, and from that worked out which is most likely to exist. “It turns out that the most likely universe is one that looks similar to ours,” he says.

    Turok adds that quantum uncertainty means that universe and antiuniverse are not exact mirror images of one another – which sidesteps thorny problems such as free will.

    But problems aside, Turok says that the new model provides a natural candidate for dark matter. This candidate is an ultra-elusive, very massive particle called a “sterile” neutrino hypothesized to account for the finite (very small) mass of more common left-handed neutrinos. According to Turok, CPT symmetry can be used to work out the abundance of right-handed neutrinos in our universe from first principles. By factoring in the observed density of dark matter, he says that quantity yields a mass for the right-handed neutrino of about 5×108 GeV – some 500 million times the mass of the proton.

    Turok describes that mass as “tantalizingly” similar to the one derived from a couple of anomalous radio signals spotted by the Antarctic Impulsive Transient Antenna (ANITA). The balloon-borne experiment, which flies high over Antarctica, generally observes cosmic rays travelling down through the atmosphere. However, on two occasions ANITA appears to have detected particles travelling up through the Earth with masses between 2 and 10×108 GeV. Given that ordinary neutrinos would almost certainly interact before getting that far, Thomas Weiler of Vanderbilt University and colleagues recently proposed that the culprits were instead decaying right-handed neutrinos [Letters in High Energy Physics].

    Turok, however, points out a fly in the ointment – which is that the CPT symmetric model requires these neutrinos to be completely stable. But he remains cautiously optimistic. “It is possible to make these particles decay over the age of the universe but that takes a little adjustment of our model,” he says. “So we are still intrigued but I certainly wouldn’t say we are convinced at this stage.”

    See the full article here .


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    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

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  • richardmitnick 1:27 pm on December 19, 2018 Permalink | Reply
    Tags: , , Dark Matter, , ,   

    From WIRED: “Dark Matter Hunters Pivot After Years of Failed Searches” 

    Wired logo

    From WIRED

    12.19.18
    Sophia Chen

    1
    NASA Goddard

    Physicists are remarkably frank: they don’t know what dark matter is made of.

    “We’re all scratching our heads,” says physicist Reina Maruyama of Yale University.

    “The gut feeling is that 80 percent of it is one thing, and 20 percent of it is something else,” says physicist Gray Rybka of the University of Washington. Why does he think this? It’s not because of science. “It’s a folk wisdom,” he says.

    Peering through telescopes, researchers have found a deluge of evidence for dark matter. Galaxies, they’ve observed, rotate far faster than their visible mass allows. The established equations of gravity dictate that those galaxies should fall apart, like pieces of cake batter flinging off a spinning hand mixer. The prevailing thought is that some invisible material—dark matter—must be holding those galaxies together. Observations suggest that dark matter consists of diffuse material “sort of like a cotton ball,” says Maruyama, who co-leads a dark matter research collaboration called COSINE-100.

    2
    Jay Hyun Jo/DM-Ice/KIMS

    Here on Earth, though, clues are scant. Given the speed that galaxies rotate, dark matter should make up 85 percent of the matter in the universe, including on our provincial little home planet. But only one experiment, a detector in Italy named DAMA, has ever registered compelling evidence of the stuff on Earth.

    DAMA-LIBRA at Gran Sasso


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

    “There have been hints in other experiments, but DAMA is the only one with robust signals,” says Maruyama, who is unaffiliated with the experiment. For two decades, DAMA has consistently measured a varying signal that peaks in June and dips in December. The signal suggests that dark matter hits Earth at different rates corresponding to its location in its orbit, which matches theoretical predictions.

    But the search has yielded few other promising signals. This year, several detectors reported null findings. XENON1T, a collaboration whose detector is located in the same Italian lab as DAMA, announced they hadn’t found anything this May.

    XENON1T at Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

    Panda-X, a China-based experiment, published in July that they also hadn’t found anything.

    PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China

    Even DAMA’s results have been called into question: In December, Maruyama’s team published that their detector, a South-Korea based DAMA replica made of some 200 pounds of sodium iodide crystal, failed to reproduce its Italian predecessor’s results.

    These experiments are all designed to search for a specific dark matter candidate, a theorized class of particles known as Weakly Interacting Massive Particles, or WIMPs, that should be about a million times heavier than an electron. WIMPs have dominated dark matter research for years, and Miguel Zumalacárregui is tired of them. About a decade ago, when Zumalacárregui was still a PhD student, WIMP researchers were already promising an imminent discovery. “They’re just coming back empty-handed,” says Zumalacárregui, now an astrophysicist at the University of California, Berkeley.

    He’s not the only one with WIMP fatigue. “In some ways, I grew tired of WIMPs long ago,” says Rybka. Rybka is co-leading an experiment that is pursuing another dark matter candidate: a dainty particle called an axion, roughly a billion times lighter than an electron and much lighter than the WIMP. In April, the Axion Dark Matter Experiment collaboration announced that they’d finally tweaked their detector to be sensitive enough to detect axions.

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

    The detector acts sort of like an AM radio, says Rybka. A strong magnet inside the machine would convert incoming axions into radio waves, which the detector would then pick up. “Given that we don’t know the exact mass of the axion, we don’t know which frequency to tune to,” says Rybka. “So we slowly turn the knob while listening, and mostly we hear noise. But someday, hopefully, we’ll tune to the right frequency, and we’ll hear that pure tone.”

    He is betting on axions because they would also resolve a piece of another long-standing puzzle in physics: exactly how quarks bind together to form atomic nuclei. “It seems too good to just be a coincidence, that this theory from nuclear physics happens to make the right amount of dark matter,” says Rybka.

    As Rybka’s team sifts through earthly data for signs of axions, astrophysicists look to the skies for leads. In a paper published in October, Zumalacárregui and a colleague ruled out an old idea that dark matter was mostly made of black holes. They reached this conclusion by looking through two decades of supernovae observations. When a supernova passes behind a black hole, the black hole’s gravity bends the supernova’s light to make it appear brighter. The brighter the light, the more massive the black hole. So by tabulating the brightness of hundreds of supernovae, they calculated that black holes that are at least one-hundredth the size of the sun can account for up to 40 percent of dark matter, and no more.

    “We’re at a point where our best theories seem to be breaking,” says astrophysicist Jamie Farnes of Oxford University. “We clearly need some kind of new idea. There’s something key we’re missing about how the universe is working.”

    Farnes is trying to fill that void. In a paper published in December [Astronomy and Astrophysics], he proposed that dark matter could be a weird fluid that moves toward you if you try to push it away. He created a simplistic simulation of the universe containing this fluid and found that it could potentially also explain why the universe is expanding, another long-standing mystery in physics. He is careful to point out that his ideas are speculative, and it is still unclear whether they are consistent with prior telescope observations and dark matter experiments.

    WIMPs could still be dark matter as well, despite enthusiasm for new approaches. Maruyama’s Korean experiment has ruled out “the canonical, vanilla WIMP that most people talk about,” she says, but lesser-known WIMP cousins are still on the table.

    It’s important to remember, as physicists clutch onto their favorite theories—regardless of how refreshing they are—that they need corroborating data. “The universe doesn’t care what is beautiful or elegant,” says Farnes. Nor does it care about what’s trendy. Guys, the universe might be really uncool.

    See the full article here .

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  • richardmitnick 1:51 pm on December 18, 2018 Permalink | Reply
    Tags: Dark Matter, , ,   

    From Sanford Underground Research Facility: “LZ assembly begins — piecing together a 10-ton detector” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    December 17, 2018
    Erin Broberg

    With main components arriving, researchers have begun the meticulous work of piecing together LUX-ZEPLIN on the 4850 Level.

    1
    Inside the LZ water tank, assembly has begun on the Outer Cryostat Vessel. Photo by Matthew Kapust

    As they peer down into the LUX-ZEPLIN (LZ) water tank from the work deck above, researchers and engineers can finally see the assembly process in full swing. Science and Technology Facilities Council’s Pawel Majewski focuses on the cryostat installation. He recently returned to Sanford Underground Research Facility (Sanford Lab) after nearly half a year away and is thrilled with what he’s seeing.

    2
    The LZ experiment. LZ (LUX-ZEPLIN) will be 30 times larger and 100 times more sensitive than its predecessor, the Large Underground Xenon experiment.

    The race to build the most sensitive direct-detection dark matter experiment got a bit more competitive with the Department of Energy’s approval of a key construction milestone on Feb.9.

    LUX-ZEPLIN (LZ), a next-generation dark matter detector, will replace the Large Underground Xenon (LUX) experiment. The Critical Decision 3 (CD-3) approval puts LZ on track to begin its deep-underground hunt for theoretical particles known as WIMPs in 2020.

    “We got a strong endorsement to move forward quickly and to be the first to complete the next-generation dark matter detector,” said Murdock “Gil” Gilchriese, LZ project director and a physicist at Lawrence Berkeley National Laboratory, the lead lab for the project. The LZ collaboration includes approximately 220 participating scientists and engineers representing 38 institutions around the world.

    The fast-moving schedule allows the U.S. to remain competitive with similar next-generation dark matter experiments planned in Italy and China.

    WIMPs (weakly interacting massive particles) are among the top prospects for explaining dark matter, which has only been observed through its gravitational effects on galaxies and clusters of galaxies. Believed to make up nearly 80 percent of all the matter in the universe, this “missing mass” is considered to be one of the most pressing questions in particle physics.

    LZ will be at least 100 times more sensitive to finding signals from dark matter particles than its predecessor, the Large Underground Xenon experiment (LUX), which was decommissed last year to make way for LZ. The new experiment will use 10 metric tons of ultra-purified liquid xenon, to tease out possible dark matter signals. Xenon, in its gas form, is one of the rarest elements in Earth’s atmosphere.

    “The science is highly compelling, so it’s being pursued by physicists all over the world,” said Carter Hall, the spokesperson for the LZ collaboration and an associate professor of physics at the University of Maryland. “It’s a friendly and healthy competition, with a major discovery possibly at stake.”

    A planned upgrade to the current XENON1T experiment at National Institute for Nuclear Physics’ Gran Sasso Laboratory (the XENONnT experiment) in Italy, and China’s plans to advance the work on PandaX-II, are also slated to be leading-edge underground experiments that will use liquid xenon as the medium to seek out a dark matter signal.

    XENON1T at Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy


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

    PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China

    Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders.

    Hall noted that while WIMPs are a primary target for LZ and its competitors, LZ’s explorations into uncharted territory could lead to a variety of surprising discoveries. “People are developing all sorts of models to explain dark matter,” he said. “LZ is optimized to observe a heavy WIMP, but it’s sensitive to some less-conventional scenarios as well. It can also search for other exotic particles and rare processes.”

    LZ is designed so that if a dark matter particle collides with a xenon atom, it will produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank—over four times more than were installed in LUX—will carry the telltale fingerprint of the particles that created them.

    Daniel Akerib and Thomas Shutt are leading the LZ team at SLAC National Accelerator Laboratory, which includes an effort to purify xenon for LZ by removing krypton, an element that is typically found in trace amounts with xenon after standard refinement processes. “We have already demonstrated the purification required for LZ and are now working on ways to further purify the xenon to extend the science reach of LZ,” Akerib said.

    SLAC and Berkeley Lab collaborators are also developing and testing hand-woven wire grids that draw out electrical signals produced by particle interactions in the liquid xenon tank. Full-size prototypes will be operated later this year at a SLAC test platform. “These tests are important to ensure that the grids don’t produce low-level electrical discharge when operated at high voltage, since the discharge could swamp a faint signal from dark matter,” said Shutt.

    Hugh Lippincott, a Wilson Fellow at Fermi National Accelerator Laboratory (Fermilab) and the physics coordinator for the LZ collaboration, said, “Alongside the effort to get the detector built and taking data as fast as we can, we’re also building up our simulation and data analysis tools so that we can understand what we’ll see when the detector turns on. We want to be ready for physics as soon as the first flash of light appears in the xenon.” Fermilab is responsible for implementing key parts of the critical system that handles, purifies, and cools the xenon.

    All of the components for LZ are painstakingly measured for naturally occurring radiation levels to account for possible false signals coming from the components themselves. A dust-filtering cleanroom is being prepared for LZ’s assembly and a radon-reduction building is under construction at the South Dakota site—radon is a naturally occurring radioactive gas that could interfere with dark matter detection. These steps are necessary to remove background signals as much as possible.

    The vessels that will surround the liquid xenon, which are the responsibility of the U.K. participants of the collaboration, are now being assembled in Italy. They will be built with the world’s most ultra-pure titanium to further reduce background noise.

    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. Brookhaven National Laboratory is handling the production of another very pure liquid, known as a scintillator fluid, that will go into this tank

    The cleanrooms will be in place by June, Gilchriese said, and preparation of the cavern where LZ will be housed is underway at SURF. Onsite assembly and installation will begin in 2018, he added, and all of the xenon needed for the project has either already been delivered or is under contract. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry.

    “South Dakota is proud to host the LZ experiment at SURF and to contribute 80 percent of the xenon for LZ,” said Mike Headley, executive director of the South Dakota Science and Technology Authority (SDSTA) that oversees SURF. “Our facility work is underway and we’re on track to support LZ’s timeline.”

    UK scientists, who make up about one-quarter of the LZ collaboration, are contributing hardware for most subsystems. Henrique Araújo, from Imperial College London, said, “We are looking forward to seeing everything come together after a long period of design and planning.

    Kelly Hanzel, LZ project manager and a Berkeley Lab mechanical engineer, added, “We have an excellent collaboration and team of engineers who are dedicated to the science and success of the project.” The latest approval milestone, she said, “is probably the most significant step so far,” as it provides for the purchase of most of the major components in LZ’s supporting systems.

    See the full article here .


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    Please help promote STEM in your local schools.

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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.
    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.

    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.

    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.

    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.”
    We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

    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
    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.

    LBNL LZ project at SURF, Lead, SD, USA

    CASPAR at SURF


    CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

    The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”

     
  • richardmitnick 1:45 pm on December 17, 2018 Permalink | Reply
    Tags: , Dark Matter, , Lux Zeplin project, PMT's-photomultiplier tubes, ,   

    From Brown University: “Massive new dark matter detector gets its ‘eyes’” 

    Brown University
    From Brown University

    1
    The detector’s “eyes”
    Powerful light sensors assembled at Brown into two large arrays will keep watch on the LUX-ZEPLIN dark matter detector, looking for the tell-tale flashes of light that indicate interaction of a dark matter particle inside the detector. Credit: Nick Dentamaro

    LBNL Lux Zeplin project at SURF

    December 17, 2018
    Kevin Stacey

    Brown University researchers have assembled two massive arrays of photomultiplier tubes, powerful light sensors that will serve as the “eyes” for the LUX-ZEPLIN dark matter detector, which will start its search for dark matter particles in 2020.

    The LUX-ZEPLIN (LZ) dark matter detector, which will soon start its search for the elusive particles thought to account for a majority of matter in the universe, had the first of its “eyes” delivered late last week.

    The first of two large arrays of photomultiplier tubes (PMTs) — powerful light sensors that can detect the faintest of flashes — arrived last Thursday at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, where LZ is scheduled to begin its dark matter search in 2020. The second array will arrive in January. When the detector is completed and switched on, the PMT arrays will keep careful watch on LZ’s 10-ton tank of liquid xenon, looking for the telltale twin flashes of light produced if a dark matter particle bumps into a xenon atom inside the tank.

    The two arrays, each about 5 feet in diameter and holding a total of 494 PMTs, were shipped to South Dakota via truck from Providence, Rhode Island, where a team of researchers and technicians from Brown University spent the past six months painstakingly assembling them.

    “The delivery of these arrays is the pinnacle of an enormous assembly effort that we’ve executed here in our cleanroom at the Brown Department of Physics,” said Rick Gaitskell, a professor of physics at Brown University who oversaw the construction of the arrays. “For the last two years, we’ve been making sure that every piece that’s going into the devices is working as expected. Only by doing that can we be confident that everything will perform the way we want when the detector is switched on.”

    The Brown team has worked with researchers and engineers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and from Imperial College London to design, procure, test, and assemble all of the components of the array. Testing of the PMTs, which are manufactured by the Hamamatsu Corporation in Japan, was performed at Brown and at Imperial College “The PMTs have already qualified for significant air miles, even before they started their 2,000-mile journey by road from Rhode Island to South Dakota,” Gaitskell said.

    “The PMTs have already qualified for significant air miles, even before they started their 2,000-mile journey by road from Rhode Island to South Dakota,” Gaitskell said.

    Catching a WIMP

    Nobody knows exactly what dark matter is. Scientists can see the effects of its gravity in the rotation of galaxies and in the way light bends as it travels across the universe, but no one has directly detected a dark matter particle. The leading theoretical candidate for a dark matter particle is the WIMP, or weakly interacting massive particle. WIMPs can’t be seen because they don’t absorb, emit or reflect light. And they interact with normal matter only on very rare occasions, which is why they’re so hard to detect even when millions of them may be traveling through the Earth and everything on it each second.

    The LZ experiment, a collaboration of more than 250 scientists worldwide, aims to capture one of those fleetingly rare WIMP interactions, and thereby characterize the particles thought to make up more than 80 percent of the matter in the universe. The detector will be the most sensitive ever built, 50 times more sensitive than the LUX detector, which wrapped up its dark matter search at SURF in 2016.

    3
    This rendering shows a cutaway view of the LZ xenon tank (center), with PMT arrays at the top and bottom of the tank. (Credit: Greg Stewart/SLAC National Accelerator Laboratory)

    The PMT arrays are a critical part of the experiment. Each PMT is a six-inch-long cylinder that is roughly the diameter of a soda can. To form arrays large enough to monitor the entire LZ xenon target, hundreds of PMTs are assembled together within a circular titanium matrix. The array that will sit on top of the xenon target has 253 PMTs, while the lower array has 241.

    PMTs are designed to amplify weak light signals. When individual photons (particles of light) enter a PMT, they strike a photocathode. If the photon has sufficient energy, it causes the photocathode to eject one or more electrons. Those electrons strike then an electrode, which ejects more electrons. By cascading through a series of electrodes the original signal is amplified by over a factor of a million to create a detectable signal.

    LZ’s PMT arrays will need every bit of that sensitivity to catch the flashes associated with a WIMP interaction.

    “We could be looking for events emitting as few as 20 photons in a huge tank containing 10 tons of xenon, which is something that the human visual system wouldn’t be able to do,” Gaitskell said. “But it’s something these arrays can do, and we’ll need them to do it in order to see the signal from rare particle events.”

    The photons are produced by what’s known as a nuclear recoil event, which produces two distinct flashes. The first comes at the moment a WIMP bumps into a xenon nucleus. The second, which comes a few hundred microseconds afterward, is produced by the ricochet of the xenon atom that was struck. It bounces into the atoms surrounding it, which knocks a few electrons free. The electrons are then drifted by an electric field to the top of the tank, where they reach a thin layer of xenon gas that converts them into light.

    In order for those tiny flashes to be distinguishable from unwanted background events, the detector needs to be protected from cosmic rays and other kinds of radiation, which also cause liquid xenon to light up. That’s why the experiment takes place underground at SURF, a former gold mine, where the detector will be shielded by about a mile of rock to limit interference.

    A clean start

    The need to limit interference is also the reason that the Brown University team was obsessed with cleanliness while they assembled the arrays. The team’s main enemy was plain old dust.

    “When you’re dealing with an instrument that’s as sensitive as LZ, suddenly things you wouldn’t normally care about become very serious,” said Casey Rhyne, a Brown graduate student who had a leading role in building the arrays. “One of the biggest challenges we had to confront was minimizing ambient dust levels during assembly.”

    Each dust particle carries a minuscule amount of radioactive uranium and thorium decay products. The radiation is vanishingly small and poses no threat to people, but too many of those specks inside the LZ detector could be enough to interfere with a WIMP signal.

    4
    Much of the assembly work was done while the arrays sat inside PALACE, an ultraclean enclosure designed to keep the arrays dust-free. Nick Detamaro

    In fact, the dust budget for the LZ experiment calls for no more than one gram of dust in the entire 10-ton instrument. Because of all their nooks and crannies, the PMT arrays could be significant dust contributors if pains were not taken to keep them clean throughout construction.

    The Brown team performed most of its work in a “class 1,000” cleanroom, which allows no more than 1,000 microscopic dust particles per cubic foot of space. And within that cleanroom was an even more pristine space that the team dubbed “PALACE (PMT Array Lifting And Commissioning Enclosure).” PALACE was essentially an ultraclean exoskeleton where much of the actual array assembly took place. PALACE was a “class 10” space — no more than 10 dust particles bigger than one hundredth the width of a human hair per cubic foot.

    But the radiation concerns didn’t stop at dust. Before assembly of the arrays began, the team prescreened every part of every PMT tube to assess radiation levels.

    “We had Hamamatsu send us all of the materials that they were going to use for the PMT construction, and we put them in an underground germanium detector,” said Samuel Chan, a graduate student and PMT system team leader. “This detector is very good at detecting the radiation that the construction materials are emitting. If the intrinsic radiation levels were low enough in these materials, then we told Hamamatsu to go ahead and use them in the manufacture of these PMTs.”

    7
    A PMT is carefully inserted into the array inside PALACE. Nick Dentamaro

    The team is hopeful that all the work contributed over the past six months will pay dividends when LZ starts its WIMP search.

    “Getting everything right now will have a huge impact less than two years from now when we switch on the completed detector and we’re taking data,” Gaitskell said. “We’ll be able to see directly from that data how good of a job we and other people have done.”

    Given the major increase in dark matter search sensitivity that the LUX-ZEPLIN detector can deliver compared to previous experiments, the team hopes that this detector will finally identify and characterize the vast sea of stuff that surrounds us all. So far, the dark stuff has remained maddeningly elusive.

    See the full article here .

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    Welcome to Brown

    Brown U Robinson Hall
    Located in historic Providence, Rhode Island and founded in 1764, Brown University is the seventh-oldest college in the United States. Brown is an independent, coeducational Ivy League institution comprising undergraduate and graduate programs, plus the Alpert Medical School, School of Public Health, School of Engineering, and the School of Professional Studies.

    With its talented and motivated student body and accomplished faculty, Brown is a leading research university that maintains a particular commitment to exceptional undergraduate instruction.

    Brown’s vibrant, diverse community consists of 6,000 undergraduates, 2,000 graduate students, 400 medical school students, more than 5,000 summer, visiting and online students, and nearly 700 faculty members. Brown students come from all 50 states and more than 100 countries.

    Undergraduates pursue bachelor’s degrees in more than 70 concentrations, ranging from Egyptology to cognitive neuroscience. Anything’s possible at Brown—the university’s commitment to undergraduate freedom means students must take responsibility as architects of their courses of study.

     
  • richardmitnick 11:00 am on November 29, 2018 Permalink | Reply
    Tags: , , , , , Dark Matter, , ,   

    From NASA/ESA Hubble Telescope: “Hubble Uncovers Thousands of Globular Star Clusters Scattered Among Galaxies” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    From NASA/ESA Hubble Telescope

    Nov 29, 2018

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Juan Madrid
    Australian Telescope National Facility, Sydney, Australia
    jmadrid@astro.swin.edu.au

    1
    Survey will allow for mapping of dark matter in huge galaxy cluster

    Gazing across 300 million light-years into a monstrous city of galaxies, astronomers have used NASA’s Hubble Space Telescope to do a comprehensive census of some of its most diminutive members: a whopping 22,426 globular star clusters found to date.

    The survey, published in the November 9, 2018, issue of The Astrophysical Journal, will allow for astronomers to use the globular cluster field to map the distribution of matter and dark matter in the Coma galaxy cluster, which holds over 1,000 galaxies that are packed together.

    Because globular clusters are much smaller than entire galaxies – and much more abundant – they are a much better tracer of how the fabric of space is distorted by the Coma cluster’s gravity. In fact, the Coma cluster is one of the first places where observed gravitational anomalies were considered to be indicative of a lot of unseen mass in the universe – later to be called “dark matter.”

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

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

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    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

    Among the earliest homesteaders of the universe, globular star clusters are snow-globe-shaped islands of several hundred thousand ancient stars. They are integral to the birth and growth of a galaxy. About 150 globular clusters zip around our Milky Way galaxy, and, because they contain the oldest known stars in the universe, were present in the early formative years of our galaxy.

    Some of the Milky Way’s globular clusters are visible to the naked eye as fuzzy-looking “stars.” But at the distance of the Coma cluster, its globulars appear as dots of light even to Hubble’s super-sharp vision. The survey found the globular clusters scattered in the space between the galaxies. They have been orphaned from their home galaxy due to galaxy near-collisions inside the traffic-jammed cluster. Hubble revealed that some globular clusters line up along bridge-like patterns. This is telltale evidence for interactions between galaxies where they gravitationally tug on each other like pulling taffy.

    Astronomer Juan Madrid of the Australian Telescope National Facility in Sydney, Australia first thought about the distribution of globular clusters in Coma when he was examining Hubble images that show the globular clusters extending all the way to the edge of any given photograph of galaxies in the Coma cluster.

    He was looking forward to more data from one of the legacy surveys of Hubble that was designed to obtain data of the entire Coma cluster, called the Coma Cluster Treasury Survey. However, halfway through the program, in 2006, Hubble’s powerful Advanced Camera for Surveys (ACS) had an electronics failure. (The ACS was later repaired by astronauts during a 2009 Hubble servicing mission.)

    NASA Hubble Advanced Camera forSurveys

    To fill in the survey gaps, Madrid and his team painstakingly pulled numerous Hubble images of the galaxy cluster taken from different Hubble observing programs. These are stored in the Space Telescope Science Institute’s Mikulski Archive for Space Telescopes in Baltimore, Maryland. He assembled a mosaic of the central region of the cluster, working with students from the National Science Foundation’s Research Experience for Undergraduates program. “This program gives an opportunity to students enrolled in universities with little or no astronomy to gain experience in the field,” Madrid said.

    The team developed algorithms to sift through the Coma mosaic images that contain at least 100,000 potential sources. The program used globular clusters’ color (dominated by the glow of aging red stars) and spherical shape to eliminate extraneous objects – mostly background galaxies unassociated with the Coma cluster.

    Though Hubble has superb detectors with unmatched sensitivity and resolution, their main drawback is that they have tiny fields of view. “One of the cool aspects of our research is that it showcases the amazing science that will be possible with NASA’s planned Wide Field Infrared Survey Telescope (WFIRST) that will have a much larger field of view than Hubble,” said Madrid.

    NASA/WFIRST

    “We will be able to image entire galaxy clusters at once.”

    See the full article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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    AURA Icon

     
  • richardmitnick 1:39 pm on November 13, 2018 Permalink | Reply
    Tags: , , , , , Dark Matter, ,   

    From Symmetry: “Gravitational lenses” 

    Symmetry Mag
    From Symmetry

    11/13/18
    Jim Daley

    Gravitational Lensing NASA/ESA

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova [Could not pass this one up.]

    Predicted by Einstein and discovered in 1979, gravitational lensing helps astrophysicists understand the evolving shape of the universe.

    On March 29, 1979, high in the Quinlan Mountains in the Tohono O’odham Nation in southwestern Arizona, a team of astronomers at Kitt Peak National Observatory was scanning the night sky when they saw something curious in the constellation Ursa Major: two massive celestial objects called quasars with remarkably similar characteristics, burning unusually close to one another.

    Kitt Peak National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft)

    The astronomers—Dennis Walsh, Bob Carswell and Ray Weymann—looked again on subsequent nights and checked whether the sight was an anomaly caused by interference from a neighboring object. It wasn’t. Spectroscopic analysis confirmed the twin images were actually both light from a single quasar 8.7 billion light-years from Earth. It appeared to telescopes on Kitt Peak to be two bodies because its light was distorted by a massive galaxy between the quasar and Earth. The team had made the first discovery of a gravitational lens.

    Since then, gravitational lenses have given us remarkable images of the cosmos and granted cosmologists a powerful means to unravel its mysteries.

    “Lensing is one of the primary tools we use to learn about the evolution of the universe,” says Mandeep Gill, an astrophysicist at Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford. By observing the gravitational lensing and redshift of galaxy clusters, he explains, cosmologists can determine both the matter content of the universe and the speed at which the universe is expanding.

    Gravitational lensing was predicted by Einstein’s theory of general relativity. General relativity posited that massive objects like the sun actually bend the fabric of spacetime around them. Like a billiard ball sinking into a stretched-out rubber sheet, a massive object creates a depression around it; it’s called a “gravity well.” Light passing through a gravity well bends with its curves.

    When an object is really immense—such as a galaxy or galaxy cluster—it can bend the path of passing light dramatically. Astronomers call this “strong lensing.”

    Strong lensing can have remarkable effects. A distant light source arranged in a straight line with a massive body and Earth—a configuration called a syzygy—can appear as a halo around the lensing body, an effect known as an “Einstein ring.” And light from one quasar in the constellation Pegasus bends so much by the time it reaches Earth that it looks like four quasars instead. Astronomers call this phenomenon a “quad lens,” and they’ve named the quasar in Pegasus “the Einstein Cross.”

    Most gravitational lensing events are not so dramatic. Any mass will curve the spacetime around it, causing slight distortions to passing light. While this weak lensing is not apparent from a single observation, taking an average from many light sources allows observers to detect weak lensing effects as well.

    Weak gravitational lensing NASA/ESA Hubble

    The overall distribution of matter in the universe has a lensing effect on light from distant galaxies, a phenomenon known as “cosmic shear.”

    “A cosmic shear measurement is incredibly meticulous as the effect is so small, but it holds a wealth of information about how the structure in the universe has evolved with time,” says Alexandra Amon, an observational cosmologist at KIPAC who specializes in weak lensing.

    Strong and weak gravitational lensing are both important tools in the study of dark matter and dark energy, the invisible stuff that together make up 96 percent of the universe. There is not enough visible mass in the universe to cause all of the gravitational lensing that astronomers see; scientists think most of it is caused by invisible dark matter.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

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

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    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

    And how all of that matter moves and changes over time is thought to be affected by a mysterious “force” (scientists aren’t really sure what it is) pushing our universe to expand at an accelerating pace: dark energy.

    Studying gravitational lensing can help astrophysicists track the universe’s growth.

    “Strong gravitational lensing can give you a lot of cosmology—from time delays,” Gill says. “From a very far away quasar, you can get multiple images that have followed different light paths. Because they’ve followed different paths, they will get to you at different times. And that time delay depends on the geometry of the universe.”

    The Dark Energy Survey is one of several experiments using gravitational lensing to study dark matter and dark energy. DES scientists are using the Cerro Tololo Inter-American Observatory in Chile to perform a 5000-square-degree survey of the southern sky. Along with other measurements, DES is searching for weak lensing and cosmic shear effects of dark matter on distant objects.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    The Large Synoptic Survey Telescope, currently under construction in Chile, will also assess how dark matter is distributed in the universe by looking for gravitational lenses, among other things.

    “The LSST will see first light in the next couple of years,” Amon says. “As this telescope charts the southern sky every few nights, it’s going to bombard us with data—literally too much to handle—so a lot of the work right now is building pipelines that can analyze it.”

    Astronomers expect LSST to find 100 times more galaxy-scale strong gravitational lens systems than are currently known.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    “The ongoing lensing surveys—that is, the Kilo-Degree Survey, Hyper Suprime-Cam and Dark Energy Survey—are doing high-precision and high-quality analyses, but they are really training grounds compared to what we will be able to do with LSST,” Amon says. “We are stepping up from measuring the shapes of tens of millions of galaxies to a billion galaxies, building the largest, deepest map of the Southern sky over 10 years.”

    Surprisingly, these enormous studies of cosmic distortions may bring the make-up of our universe into focus.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:49 am on October 27, 2018 Permalink | Reply
    Tags: , Bose star, , Dark Matter, , Institute for Nuclear Physics of the Russian Academy of Sciences, , Russian physicists observe dark matter forming droplets   

    From EurekaAlert: “Russian physicists observe dark matter forming droplets” 

    eurekaalert-bloc

    From EurekaAlert

    22-Oct-2018

    Dmitry Levkov
    levkov@ms2.inr.ac.ru

    Researchers developed a mathematical model describing motion of dark matter particles inside the smallest galaxy halos.

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

    They observed that over time, the dark matter may form spherical droplets of quantum condensate. Previously this was considered impossible, as fluctuations of the gravity field produced by dark matter particles were ignored. The study is published in Physical Review Letters.

    Dark matter is a hypothetical form of matter that does not emit electromagnetic radiation.

    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

    This property hinders dark matter searches and makes it hard even to prove its existence. The speed of dark matter particles is low, which is why they are retained by galaxies. They interact with each other and with the ordinary matter so weakly that only their gravity field can be sensed, otherwise the dark matter does not manifest itself in any way. Each galaxy is surrounded by a dark matter shell (halo) of much larger size and mass.

    1
    Left image: initial moment, when the gas is mixed; right image: the moment shortly after the formation of a Bose star. The colour indicates density: white-blue-green-yellow, from sparse to dense. Credit Dmitry Levkov

    Most cosmologists believe that dark matter particles have large mass, hence their speed is high. Yet, back in the 1980s it was realized that under special conditions these particles may be produced in the early Universe with almost zero speed, regardless of their mass. They might also be very light. As a consequence, the distances at which the quantum nature of these particles becomes apparent can be huge. Instead of the nanometer scales that are usually required to observe quantum phenomena in laboratories, the “quantum” scale for such particles may be comparable to the size of the central part of our galaxy.

    The researchers observed that the dark matter particles, if they are bosons with sufficiently small mass, may form a Bose-Einstein condensate in the small galaxy halos or in even smaller substructures due to their gravitational interactions. Such substructures include halos of dwarf galaxies – systems of several billion stars bound together by gravitational forces, and miniclusters – very small systems formed only by dark matter. The Bose-Einstein condensate is a state of quantum particles in which they all occupy the lowest energy level, having the smallest energy. The Bose-Einstein condensate can be produced in the lab at low temperatures from ordinary atoms. This state of matter exhibits unique properties, such as superfluidity: the ability to pass through tiny cracks or capillaries without friction. Light dark matter in the galaxy has low speed and huge concentration. Under these conditions, it should eventually form a Bose-Einstein condensate. But in order for this to happen, dark matter particles must interact with each other, while as far as we know, they interact only gravitationally.

    “In our work, we simulated motion of a quantum gas of light gravitationally interacting dark matter particles. We started from a virialized state with maximal mixing, which is kind of opposite to the Bose-Einstein condensate. After a very long period, 100,000 times longer than the time needed for a particle to cross the simulation volume, the particles spontaneously formed a condensate, which immediately shaped itself into a spherical droplet, a Bose star, under the effect of gravity,” said one of the authors, Dmitry Levkov, Ph.D. in Physics, Senior Researcher at the Institute for Nuclear Research of the Russian Academy of Sciences.

    Dr. Levkov and his colleagues, Alexander Panin and Igor Tkachov from the Institute for Nuclear Physics of the Russian Academy of Sciences, concluded that Bose-Einstein condensate may form in the centres of halos of dwarf galaxies in a time smaller than the lifetime of the Universe. This means that Bose stars could populate them now.

    The authors were the first who saw the formation of the Bose-Einstein condensate from light dark matter in computer simulations. In previous numerical studies, the condensate was already present in the initial state, and Bose stars arose from it. According to one hypothesis, the Bose condensate could have formed in the early Universe long before the formation of galaxies or miniclusters, but reliable evidence for that is currently lacking. The authors demonstrated that the condensate is formed in the centres of small halos, and they plan to investigate condensation in the early Universe in further studies.

    The scientists pointed out that the Bose stars may produce Fast Radio Bursts that currently have no quantitative explanation. Light dark matter particles called “axions” interact with electromagnetic field very weakly and can decay into radiophotons. This effect is vanishingly small, but inside the Bose star it may be resonantly amplified like in a laser and could lead to giant radio bursts.

    “The next obvious step is to predict the number of the Bose stars in the Universe and calculate their mass in models with light dark matter,” concluded Dmitry Levkov.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    EurekAlert!, the premier online news source focusing on science, health, medicine and technology, is a free service for reporters worldwide.

    Since 1996, EurekAlert! has served as the leading destination for scientific organizations seeking to disseminate news to reporters and the public. Today, thousands of reporters around the globe rely on EurekAlert! as a source of ideas, background information, and advance word on breaking news stories.

    More than 1,000 peer-reviewed journals, universities, medical centers, government agencies and public relations firms have used EurekAlert! to distribute their news. EurekAlert! is an authoritative and comprehensive research news source for journalists all over the world.

     
  • richardmitnick 1:41 pm on October 25, 2018 Permalink | Reply
    Tags: , Dark Matter, ,   

    From Science Alert: “Dark Matter Could Be Forming Strange Cold ‘Stars’ Out There in The Universe” 

    ScienceAlert

    From Science Alert

    25 OCT 2018
    MIKE MCRAE

    3
    (pixelparticle/iStock)

    Deep inside the diffuse haze of gas and dust that surround the smallest galaxies, dark matter could be clumping into cold droplets called ‘Bose stars’.

    Of course, we don’t even know what the mysterious dark matter is, let alone have evidence of invisible ‘stars’. But if current assumptions pan out, a new mathematical model suggests dark matter might have some strange interactions.

    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

    The model was proposed by a team of Russian physicists who considered the way hypothetical particles of dark matter might aggregate in the smallest of galactic halos.

    “In our work, we simulated the motion of a quantum gas of light, gravitationally interacting dark matter particles,” says physicist Dmitry Levkov from the Institute for Nuclear Research of the Russian Academy of Sciences.

    Around 80 percent of the mass in the Universe is made of something we can’t seem to detect. Whatever it is, it doesn’t interact with normal matter through the usual channels, such as by exchanging photons via the electromagnetic field.

    The only sign of its presence is the added oomph it adds to the clumping of galaxies. Still, that’s no small thing – this unseen gravitational tax has already been mapped out in detail, providing us with key information on its nature.

    Thanks to its clear affinity for galaxies, we can assume the speed of the stuff making up dark matter isn’t fast enough to shoot off into the voids of space. It has to be relatively slow moving.

    One candidate for this sluggish dark matter is a hypothetical particle called an axion. They’re a type of boson – not unlike the photon – that was proposed as a solution for another perplexing paradox in quantum physics.

    6
    Dark Matter map by Chihway Chang of the Kavli Institute for Cosmological Physics, University of Chicago, DES collaboration

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

    Another option is fuzzy dark matter. It’s yet another type of boson, invented as a solution to a dilemma in astrophysics concerning the distribution of dark matter in galactic haloes.

    Neither of these bespoke bosons have been shown to exist. But if at least one of them turned out to be real, under some circumstances they could do some interesting things.

    The authors claim the model is the first to look at the kinetics of such a dark matter Bose-Einstein condensate actually forming.

    Bose-Einstein condensates are the Anonymous rallies of quantum particles. When the temperature drops to just above absolute zero, particles quit mixing and lose their individual identities to look eerily the same.

    Previous attempts have stuck to asking what happens when the bosons have already come together, such as in an infant Universe. In this case, they began with a jumble of interacting bosons.

    “We started from a virialised state with maximal mixing, which is kind of opposite to the Bose-Einstein condensate,” says Levkov.

    “After a very long period, 100,000 times longer than the time needed for a particle to cross the simulation volume, the particles spontaneously formed a condensate, which immediately shaped itself into a spherical droplet, a Bose star, under the effect of gravity.”

    In effect, a cloud of ‘dark’ bosons becomes the same particle. Not only that, the physicists have worked out this cloud can pull together under gravitational effects to form a globe – a Bose ‘star’.

    The conditions for these hypothetical objects would need to be fairly specific, such as concentrated in the middle of the relatively small halo surrounding a dwarf galaxy. And even then, while it should take place within the lifetime of the Universe, it would still be a slow process.

    These kinds of ‘what if?’ scenarios might sound a little sci-fi, but they help us improve boundaries on where to hunt for clues on this whole dark matter mystery.

    “The next obvious step is to predict the number of the Bose stars in the Universe and calculate their mass in models with light dark matter,” says Levkov.

    One day we will finally have a grasp on the fundamental nature of this ghostly mass. When we do, we’re almost certainly going to find some fascinating new structures hiding in plain view among the stars.

    This research was published in Physical Review Letters.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
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