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  • richardmitnick 2:03 pm on September 16, 2016 Permalink | Reply
    Tags: , , , , Symmetry Magazine   

    From Symmetry: “The secret lives of long-lived particles” 

    Symmetry Mag

    Symmetry

    09/16/16
    Sarah Charley

    A theoretical species of particle might answer nearly every question about our cosmos—if scientists can find it.

    1
    ATLAS collaboration

    The universe is unbalanced.

    Gravity is tremendously weak. But the weak force, which allows particles to interact and transform, is enormously strong. The mass of the Higgs boson is suspiciously petite. And the catalog of the makeup of the cosmos? Ninety-six percent incomplete.

    Almost every observation of the subatomic universe can be explained by the Standard Model of particle physics—a robust theoretical framework bursting with verifiable predictions.

    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.
    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.

    But because of these unsolved puzzles, the math is awkward, incomplete and filled with restrictions.

    A few more particles would solve almost all of these frustrations. Supersymmetry (nicknamed SUSY for short) is a colossal model that introduces new particles into the Standard Model’s equations.

    Standard model of Supersymmetry DESY
    Standard model of Supersymmetry DESY

    It rounds out the math and ties up loose ends. The only problem is that after decades of searching, physicists have found none of these new friends.

    But maybe the reason physicists haven’t found SUSY (or other physics beyond the Standard Model) is because they’ve been looking through the wrong lens.

    “Beautiful sets of models keep getting ruled out,” says Jessie Shelton, a theorist at the University of Illinois, “so we’ve had to take a step back and consider a whole new dimension in our searches, which is the lifetime of these particles.”

    In the past, physicists assumed that new particles produced in particle collisions would decay immediately, almost precisely at their points of origin. Scientists can catch particles that behave this way—for example, Higgs bosons—in particle detectors built around particle collision points. But what if new particles had long lifetimes and traveled centimeters—even kilometers—before transforming into something physicists could detect?

    This is not unprecedented. Bottom quarks, for instance, can travel a few tenths of a millimeter before decaying into more stable particles. And muons can travel several kilometers (with the help of special relativity) before transforming into electrons and neutrinos. Many theorists are now predicting that there may be clandestine species of particles that behave in a similar fashion. The only catch is that these long-lived particles must rarely interact with ordinary matter, thus explaining why they’ve escaped detection for so long. One possible explanation for this aloof behavior is that long live particles dwell in a hidden sector of physics.

    “Hidden-sector particles are separated from ordinary matter by a quantum mechanical energy barrier—like two villages separated by a mountain range,” says Henry Lubatti from the University of Washington. “They can be right next to each other, but without a huge boost in energy to get over the peak, they’ll never be able to interact with each other.”

    High-energy collisions generated by the Large Hadron Collider could kick these hidden-sector particles over this energy barrier into our own regime. And if the LHC can produce them, scientists should be able to see the fingerprints of long-lived particles imprinted in their data.

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

    Long-lived particles jolted into our world by the LHC would most likely fly at close to the speed of light for between a few micrometers and a few hundred thousand kilometers before transforming into ordinary and measurable matter. This incredibly generous range makes it difficult for scientists to pin down where and how to look for them.

    But the lifetime of a subatomic particle is much like that of any living creature. Each type of particle has an average lifespan, but the exact lifetime of an individual particle varies. If these long-lived particles can travel thousands of kilometers before decaying, scientists are hoping that they’ll still be able to catch a few of the unlucky early-transformers before they leave the detector. Lubatti and his collaborators have also proposed a new LHC surface detector, which would extend their search range by many orders of magnitude.

    Because these long-lived particles themselves don’t interact with the detector, their signal would look like a stream of ordinary matter spontaneously appearing out of nowhere.

    “For instance, if a long lived particle decayed into quarks while inside the muon detector, it would mimic the appearance of several muons closely clustered together,” Lubatti says. “We are triggering on events like this in the ATLAS experiment.” After recording the events, scientists use custom algorithms to reconstruct the origins of these clustered particles to see if they could be the offspring of an invisible long-lived parent.

    If discovered, this new breed of matter could help answer several lingering questions in physics.

    “Long-lived particles are not a prediction of a single new theory, but rather a phenomenon that could fit into almost all of our frameworks for beyond-the-Standard-Model physics,” Shelton says.

    In addition to rounding out the Standard Model’s mathematics, inert long-lived particles could be cousins of dark matter—an invisible form of matter that only interacts with the visible cosmos through gravity. They could also help explain the origin of matter after the Big Bang.

    “So many of us have spent a lifetime studying such a tiny fraction of the universe,” Lubatti says. “We’ve understood a lot, but there’s still a lot we don’t understand—an enormous amount we don’t understand. This gives me and my colleagues pause.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:18 pm on September 12, 2016 Permalink | Reply
    Tags: , , CERN HIE-ISOLDE, First physics experiment at HIE-ISOLDE begins, , Symmetry Magazine   

    From CERN: “First physics experiment at HIE-ISOLDE begins” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    CERN ISOLDE New
    CERN ISOLDE

    1
    Miniball is one of two detection stations receiving beams from HIE-ISOLDE. It’s a very efficient gamma detector array, and will be permanently linked to the beams from HIE-ISOLDE (Image: CERN)

    This weekend the first physics experiment started running using radioactive beams from the newly upgraded HIE-ISOLDE facility. ISOLDE, the nuclear research facility at CERN, allows many different experiments to study the properties of atomic nuclei.

    The upgrade means the machine can now reach an energy of 5.5MeV per nucleon (MeV/u.), making ISOLDE the only facility in the world capable of investigating nuclei from the middle to heavy end of this energy range.

    The experiment is ready to go after the second of two cryomodules (containing the accelerating cavities)was installed – marking the end of the installation of phase one of HIE-ISOLDE.

    The HIE-ISOLDE (High Intensity Energy-ISOLDE) Project is a major upgrade of the ISOLDE facility, which will increase the energy, intensity and quality of the beams delivered to scientists.

    “It’s a major breakthrough. This is the result of eight years of development and manufacturing. This would not have been possible without the dedication of the technical staff at CERN. But what makes us most proud isn’t that we built a machine, but that we have attracted enthusiastic users to do forefront physics. We are looking forward to this exciting high intensity period,” says Yacine Kadi , leader of the HIE-ISOLDE project.

    2
    The tunnel at HIE-ISOLDE now contains two cryomodules – a unique set up that marks the end of phase one for the HIE-ISOLDE installation. By Spring 2018 the project will have four cryomodules installed and will be able to reach higher energy up to 10 MeV/u a broader range of nuclear physics (Image: Erwin Siesling/ CERN)

    This is the second physics run of the project (the first radioactive beam was run on 22 October 2015) but then the machine only had one cryomodule and was capable of running at an energy of just 4.3MeV/u.

    Now, with the second cryostat coupled on, the machine is capable of reaching up to 5.5 MeV/u and can investigate the structure of heavier isotopes.

    “It is a universal machine that can accelerate and investigate all nuclei from mass number 6 to mass 224 or more and at variable energies,” explains Maria Borge, leader of the ISOLDE group. “This year we’re investigating nuclei with mass number from 9 to 142 – these experiments can only be done at this moment at ISOLDE. At CERN.”

    HIE-ISOLDE will be capable of investigating nuclei of all masses when the additional two cryomodules are installed in 2018, as the machine will be able to accelerating them up to energies of 10MeV/u.

    The further upgrades mean that, while ISOLDE can currently collect information about the collective properties of isotopes, eventually researchers will be able to use the machine at higher intensities to investigate the properties of individual particles. This can be done at the moment for lower masses, but has never been done before for heavier isotopes.

    “The community has grown a lot recently, as people are attracted by the possibilities new higher energies bring. It’s a energy domain that’s not explored much, since no other facility in world can deliver pure beams at these energies,” Borge says.

    HIE-ISOLDE will run from now until mid-November. All but one of the seven different experiments planned during this time will use the Miniball detection station. The first experiment will investigate Tin, a special element with two double magic isotopes.


    Eight years since the start of the HIE-ISOLDE project, a new accelerator is in place taking nuclear physics at CERN to higher energies. The first physics run last year marked the start of the project, but after a new cryomodule was installed physicists are able to reach a greater energy of up to 5.5.MeV/u. With physicists setting their sights on even higher energies of 10 MeV/u in the future, they will continue to commission more HIE-ISOLDE accelerating cavities and beamlines in the years to come. (Video: Christoph Madsen/CERN)

    See the full article here.

    Please help promote STEM in your local schools.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 1:09 pm on September 9, 2016 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine   

    From Symmetry: “A tale of two black holes” 

    Symmetry Mag

    Symmetry

    09/09/16
    Liz Kruesi

    1
    LIGO

    The historic detection of gravitational waves announced earlier this year breathed new life into a theory that’s been around for decades: that black holes created in the first second of the universe might make up dark matter. It also inspired a new idea: that those so-called primordial black holes could be contributing to a diffuse background light.

    The connection between these perhaps seemingly disparate areas of astronomy were tied together neatly in a theory from Alexander Kashlinsky, an astrophysicist at NASA’s Goddard Spaceflight Center. And while it’s an unusual idea, as he says, it could be proven true in only a few years.

    Mapping the glow

    Kashlinsky’s focus has been on a residual infrared glow in the universe, the accumulated light of the earliest stars. Unfortunately, all the stars, galaxies and other bright objects in the sky—the known sources of light—oversaturate this diffuse glow. That means that Kashlinsky and his colleagues have to subtract them out of infrared images to find the light that’s left behind.

    They’ve been doing precisely that since 2005, using data from the Spitzer space telescope to arrive at the residual infrared glow: the cosmic infrared background (CIB).

    NASA/Spitzer Telescope
    “NASA/Spitzer Telescope

    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA)
    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA

    Other astronomers followed a similar process using Chandra X-ray Observatory data to map the cosmic X-ray background (CXB), the diffuse glow of hotter cosmic material and more energetic sources.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    Cosmic X-ray Background, imagine.gsfc.nasa.gov
    Cosmic X-ray Background, imagine.gsfc.nasa.gov

    In 2013, Kashlinsky and colleagues compared the CIB and CXB and found correlations between the patchy patterns in the two datasets, indicating that something is contributing to both types of background light. So what might be the culprit for both types of light?

    “The only sources that could be coherent across this wide range of wavelengths are black holes,” he says.

    To explain the correlation they found, roughly 1 in 5 of the sources had to be black holes that lived in the first few hundred million years of our universe. But that ratio is oddly large.

    “For comparison,” Kashlinsky says, “in the present populations, we have 1 in 1000 of the emitting sources that are black holes. At the peak of star formation, it’s 1 in 100.”

    He wasn’t sure how the universe could have ever had enough black holes to produce the patterns his team saw in the CIB and CXB. Then the Laser Interferometric Gravitational-wave Observatory (LIGO) discovered a pair of strange beasts: two roughly-30-solar-mass black holes merging and emitting gravitational waves.

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    A few months later, Kashlinsky saw a study led by Simeon Bird analyzing the possibility that the black holes LIGO had detected were primordial—formed in the universe’s first second. “And it just all came together,” Kashlinsky says.

    Gravitational secrets

    The crucial ripples in space-time picked up by the LIGO detector on September 14, 2015, came from the last dance of two black holes orbiting each other and colliding. One black hole was 36 times the sun’s mass, the other 29 times. Those black-hole weights aren’t easy to make.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    The majority of the universe’s black holes are less than about 15 solar masses and form as massive stars collapse at the end of their lives. A black hole weighing 30 solar masses would have to start from a star closer to 100 times our sun’s mass—and nature seems to have a hard time making stars that enormous. To compound the strangeness of the situation, the LIGO detection is from a pair of those black holes. Scientists weren’t expecting such a system, but the universe has a tendency to surprise us.

    Bird and his colleagues from Johns Hopkins University next looked at the possibility that those black holes formed not from massive stars but instead during the universe’s first fractions of a second. Astronomers haven’t yet seen what the cosmos looked like at that time, so they have to rely on theoretical models.

    In all of these models, the early universe exists with density variations. If there were regions of very high-contrasting density, those could have collapsed into black holes in the universe’s first second. If those black holes were at least as heavy as mountains when they formed, they’d stick around until today, dark and seemingly invisible and acting through the gravitational force. And because these primordial black holes formed from density perturbations, they wouldn’t be comprised of protons and neutrons, the particles that make up you, me, stars and, thus, the material that leads to normal black holes.

    All of those characteristics make primordial black holes a tempting candidate for the universe’s mysterious dark matter, which we believe makes up some 25 percent of the universe and reveals itself only through the gravitational force. This possible connection has been around since the 1970s, and astronomers have looked for hints of primordial black holes since. Even though they’ve slowly narrowed down the possibilities, there are a few remaining hiding spots—including the region where the black holes that LIGO detected fall, between about 20 and 1000 solar masses.

    Astronomers have been looking for explanations of what dark matter is for decades. The leading theory is that it’s a new type of particle, but searches keep coming up empty. On the other hand, we know black holes exist; they stem naturally from the theory of gravity.

    “They’re an aesthetically pleasing candidate because they don’t need any new physics,” Bird says.

    A glowing contribution

    Kashlinsky’s newest analysis took the idea of primordial black holes the size that LIGO detected and looked at what that population would do to the diffuse infrared light of the universe. He evolved a model of the early universe, looking at how the first black holes would congregate and grow into clumps. These black holes matched the residual glow of the CIB and, he found, “would be just right to explain the patchiness of infrared background by sources that we measured in the first couple hundred million years of the universe.”

    This theory fits nicely together, but it’s just one analysis of one possible model that came out of an observation of one astrophysical system. Researchers need several more pieces of evidence to say whether primordial black holes are in fact the dark matter. The good news is LIGO will soon begin another observing run that will be able to see black hole collisions even farther away from Earth and thus further back in time. The European gravitational wave observatory VIRGO will also come online in January, providing more data and working in tandem with LIGO.

    VIRGO Collaboration bloc
    VIRGO interferometer EGO Campus
    VIRGO interferometer EGO Campus, in Cascina, Italy

    More cases of gravitational waves from black holes around this 30-solar-masses range could add evidence that there is a population of primordial black holes. Bird and his colleague Ilias Cholis suggest looking for a more unique signal, though, in future gravitational-wave data. For two primordial black holes to become locked in a binary system and merge, they would likely be gravitationally captured during a glancing interaction, which could result in a signal with multiple frequencies or tones at any one moment.

    “This is a rare event, but it would be very characteristic of our scenario,” Cholis says. “In the next 5 to 10 years, we might see one.”

    This smoking-gun signature, as they call it, would be a strong piece of evidence that primordial black holes exist. And if such objects are floating around our universe, it might not be such a stretch to connect them to dark matter.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:34 pm on September 6, 2016 Permalink | Reply
    Tags: , Symmetry Magazine, Turning on the cosmic microphone   

    From Symmetry: “Turning on the cosmic microphone” 

    Symmetry Mag

    Symmetry

    09/06/16
    Diana Kwon

    1
    Listen to the sound of Gravitational Waves (LIGO)

    A new tool lets astronomers listen to the universe for the first time.

    When Galileo first introduced the telescope in the 1600s, astronomers gained the ability to view parts of the universe that were invisible to the naked eye. This led to centuries of discovery—as telescopes advanced, they exposed new planets, galaxies and even a glimpse of the very early universe.

    Last September, scientists gained yet another invaluable tool: the ability to hear the cosmos through gravitational waves.


    If I understand this correctly then what you see and hear is the real signal (played as audio), but in the second version the frequency is simply shifted up a notch to make it easier to hear.

    3 solar masses converted to gravitational radiation 1.3 billion years ago for us to make their sounds into ringtones🙂 fair enough…

    Gravitational waves has been detected!
    Courtesy of LIGO http://www.ligo.org/

    The LIGO collaboration just announced their detection of gravitational waves! This is truly a historic moment.

    Ripples in space-time

    Newton described gravity as a force. Thinking about gravity this way can explain most of the phenomena that happens here on Earth. For example, the force of gravity acting on an apple makes it fall from a tree onto an unsuspecting person sitting below it. However, to understand gravity on a cosmic scale, we need to turn to Einstein, who described gravity as the bending of space-time itself.

    Some physicists describe this process using a bowling ball and a blanket. Imagine space-time as a blanket. A bowling ball placed at the center of the blanket bends the fabric around it. The heavier an object is, the further it sinks. As you move the ball along the fabric, it produces ripples, much like a boat travelling through water.

    “The curvature is what makes the Earth orbit the sun—the sun is a bowling ball in a fabric and it’s that bending in the fabric that makes the Earth go around,” explains Gabriela González, the spokesperson for the Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration.

    3

    Everything with mass—planets, stars and people—pulls on the fabric of space-time and produces gravitational waves as they move through space. These are passing through us all time, but they are much too weak to detect.

    To find these elusive signals, physicists built LIGO, twin observatories in Louisiana and Washington.

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    At each L-shaped detector, a laser beam is split and sent down two four-kilometer arms. The beams reflect off the mirrors at each end and travel back to reunite. A passing gravitational wave slightly alters the relative lengths of the arms, shifting the path of the laser beam, creating a change that physicists can detect.

    Unlike telescopes, which are pointed toward very specific parts of the sky, detectors like LIGO scan a much larger area of the universe and hear sources from all directions. “Gravitational waves detectors are like microphones,” says Laura Nuttall, a postdoctoral researcher at Syracuse University.

    First detections

    On the morning of September 14, 2015, a gravitational wave from two black holes that collided 1.3 billion years ago passed through the two LIGO detectors, and an automatic alert system pinged LIGO scientists around the world. “It took us a good part of the day to convince ourselves that this was not a drill,” González says.

    Because LIGO was still preparing for an observing run—researchers were still running tests and diagnostics during the day—they needed to conduct a large number of checks and analyses to make sure the signal was real.

    Months later, once researchers had meticulously checked the data for errors or noise (such as lightning or earthquakes) the LIGO collaboration announced to the world that they had finally reached a long-anticipated goal: Almost 100 years after Einstein first predicted their existence, scientists had detected gravitational waves.

    A few months after the first signal arrived, LIGO detected yet another black hole collision. “Finding a second one proves that there’s a population of sources that will produce detectible gravitational waves,” Nuttall says. “We are actually an observatory now.”

    Cosmic microphones

    Many have dubbed the detection of gravitational waves as the dawn of the age of gravitational wave astronomy. Scientists expect to see hundreds, maybe even thousands, of these binary black holes in the years to come. Gravitational-wave detectors will also allow astronomers to look much more closely at other astronomical phenomena, such as neutron stars, supernovae and even the Big Bang.

    One important next step is to detect the optical counterparts—such as light from the surrounding matter or gamma ray bursts—of the sources of gravitational waves. To do this, astronomers need to point their telescopes to the area of the sky where the gravitational waves came from to find any detectable light.

    Currently, this feat is like finding a needle in a haystack. Because the field of view of gravitational wave detectors is much, much larger than telescopes, it is extremely difficult to connect the two. “Connecting gravitational waves with light for the first time will be such an important discovery that it’s definitely worth the effort,” says Edo Berger, an astronomy professor at Harvard University.

    LIGO is also one of several gravitational wave observatories. Other ground-based observatories, such as Virgo in Italy, KAGRA in Japan and the future LIGO India have similar sensitivities to LIGO. There are also other approaches that scientists are using—and plan to use in the future—to detect gravitational waves at completely different frequencies.

    The evolved Laser Interferometer Space Antenna (eLISA), for example, is a gravitational wave detector that physicists plan to build in space.

    ESA/eLISA
    ESA/eLISA

    Once complete, eLISA will be composed of three spacecraft that are over a million kilometers apart, making it sensitive to much lower gravitational wave frequencies, where scientists expect to detect supermassive black holes.

    Pulsar array timing is a completely different method of detection.

    Network of pulsars could be used to search for the ripples in space-time.  David Champion NASA JPL
    Network of pulsars could be used to search for the ripples in space-time. David Champion NASA JPL

    Pulsars are natural timekeepers, regularly emitting beams of electromagnetic radiation. Astronomers carefully measure the arrival time of the pulses to find discrepancies, because when a gravitational wave passes by, space-time warps, changing the distance between us and the pulsar, causing the pulses to arrive slightly earlier or later. This method is sensitive to even lower frequencies than eLISA.

    These and many other observatories will reveal a new view of the universe, helping scientists to study phenomena such as merging black holes, to test theories of gravity and possibly even to discover something completely unexpected, says Daniel Holz, a professor of physics and astronomy at the University of Chicago. “Usually in science you’re just pushing the boundaries a little bit, but in this case, we’re opening up a whole new frontier.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:35 pm on September 2, 2016 Permalink | Reply
    Tags: , , , Seach for neutrinoless double beta decay, Symmetry Magazine   

    From Symmetry: “CUORE almost ready for first cool-down” 

    Symmetry Mag

    Symmetry

    09/02/16
    Ricarda Laasch

    1
    CUORE collaboration

    The refrigerator that will become the coldest cubic meter in the universe is fully loaded and ready to go.

    Deep within a mountain in Italy, scientists have finished the assembly of an experiment more than one decade in the making. The detector of CUORE, short for Cryogenic Underground Observatory for Rare Events, is ready to be cooled down to its operating temperature for the first time.

    Ettore Fiorini, the founder of the collaboration, proposed the use of low temperature detectors to search for rare events in 1984 and started creating the first prototypes with his group in Milano. What began as a personal project involving a tiny crystal and a small commercial cooler has grown to a collaboration of 165 scientists loading almost one ton of crystals and several tons of refrigerator and shields.

    The CUORE experiment is looking for a rare process that would be evidence that almost massless particles called neutrinos are their own antiparticles, something that would give scientists a clue as to how our universe came to be.

    Oliviero Cremonesi, current spokesperson of the CUORE collaboration, joined the quest in 1988 and helped write the first proposal for the experiment. At first, funding agencies in Italy and the United States approved a smaller version: Cuoricino.

    “We had five exciting years of measurements from 2003 to 2008 on this machine, but we knew that we wanted to go bigger. So we kept working on CUORE,” Cremonesi says.

    In 2005 the collaboration got approval for the big detector, which they called CUORE. That started them on a whole new journey involving growing crystals in China, bringing them to Italy by boat, and negotiating with archeologists for the right to use 2000-year-old Roman lead as shielding material.

    “I imagine climbing Mount Everest is a little bit like this,” says Lindley Winslow, a professor at the Massachusetts Institute of Technology and group leader of the MIT activities on CUORE. “We can already see the top, but this last part is the hardest. The excitement is high, but also the fear that something goes wrong.”

    The CUORE detector, assembled between 2012 and 2014, consists of 19 fragile copper towers that each host 52 tellurium oxide crystals connected by wires and sensors to measure their temperature.

    For this final stage, scientists built a custom refrigerator from extremely pure materials. They shielded and housed it inside of a mountain at Gran Sasso, Italy.

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO
    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, Italy

    At the end of July, scientists began moving the detector to its new home. After a brief pause to ensure the site had not been affected by the 6.2-magnitude earthquake that hit central Italy on August 24, they finished the job on August 26.

    The towers now reside in the largest refrigerator used for a scientific purpose. By the end of October, they will be cooled below 10 millikelvin (negative 460 Fahrenheit), colder than outer space.

    Everything has to be this cold because the scientists are searching for minuscule temperature changes caused by an ultra-rare process. It is predicted to occur only once every trillion trillion years and is called neutrinoless double beta decay.

    During a normal beta decay, one atom changes from one chemical element into its daughter element and sends out one electron and one antineutrino. For the neutrinoless double beta decay, this would be different: The element would change into its granddaughter. Instead of one electron and one neutrino sharing the energy of the decay, only two electrons would leave, and an observer would see no neutrinos at all.

    This would only happen if neutrinos were their own antiparticles. In that case, the two neutrinos would cancel each other out, and it would seem like they never existed in the first place.

    If scientists measure this decay, it would change the current scientific thinking about the neutrino and give scientists clues about why there is so much more matter than anti-matter in the universe.

    “We are excited to start the cool-down, and if everything works according to plan, we can start measuring at the beginning of next year,” Winslow says.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:01 pm on September 1, 2016 Permalink | Reply
    Tags: , , , , Super light particles?, Symmetry Magazine   

    From Symmetry: “Universe steps on the gas” 

    Symmetry Mag

    Symmetry

    09/01/16
    Shannon Hall

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

    1
    Dark Energy Survey

    A puzzling mismatch is forcing astronomers to re-think how well they understand the expansion of the universe.

    Astronomers think the universe might be expanding faster than expected.

    If true, it could reveal an extra wrinkle in our understanding of the universe, says Nobel Laureate Adam Riess of the Space Telescope Science Institute and Johns Hopkins University. That wrinkle might point toward new particles or suggest that the strength of dark energy, the mysterious force accelerating the expansion of the universe, actually changes over time.

    The result appears in a study published in The Astrophysical Journal this July, in which Riess’s team measured the current expansion rate of the universe, also known as the Hubble constant, better than ever before.

    In theory, determining this expansion is relatively simple, as long as you know the distance to a galaxy and the rate at which it is moving away from us. But distance measurements are tricky in practice and require using objects of known brightness, so-called standard candles, to gauge their distances.

    The use of Type Ia supernovae—exploding stars that shine with the same intrinsic luminosity—as standard candles led to the discovery that the universe was accelerating in the first place and earned Riess, as well as Saul Perlmutter and Brian Schmidt, a Nobel Prize in 2011.

    The latest measurement builds on that work and indicates that the universe is expanding by 73.2 kilometers per second per megaparsec (a unit that equals 3.3 million light-years). Think about dividing the universe into grids that are each a megaparsec long. Every time you reach a new grid, the universe is expanding 73.2 kilometers per second faster than the grid before.

    Although the analysis pegs the Hubble constant to within experimental errors of just 2.4 percent, the latest result doesn’t match the expansion rate predicted from the universe’s trajectory. Here, astronomers measure the expansion rate from the radiation released 380,000 years after the Big Bang and then run that expansion forward in order to calculate what today’s expansion rate should be.

    It’s similar to throwing a ball in the air, Riess says. If you understand the state of the ball (how fast it’s traveling and where it is) and the physics (gravity and drag), then you should be able to precisely predict how fast that ball is traveling later on.

    “So in this case, instead of a ball, it’s the whole universe, and we think we should be able to predict how fast it’s expanding today,” Riess says. “But the caveat, I would say, is that most of the universe is in a dark form that we don’t understand.”

    The rates predicted from measurements made on the early universe with the Planck satellite are 9 percent smaller than the rates measured by Riess’ team—a puzzling mismatch that suggests the universe could be expanding faster than physicists think it should.

    David Kaplan, a theorist at Johns Hopkins University who was not involved with the study, is intrigued by the discrepancy because it could be easily explained with the addition of a new theory, or even a slight tweak to a current theory.

    “Sometimes there’s a weird discrepancy or signal and you think ‘holy cow, how am I ever going to explain that?’” Kaplan says. “You try to come up with some cockamamie theory. This, on the other hand, is something that lives in a regime where it’s really easy to explain it with new degrees of freedom.”

    Kaplan’s favorite explanation is that there’s an undiscovered particle, which would affect the expansion rate in the early universe. “If there are super light particles that haven’t been taken into account yet and they make up some smallish fraction of the universe, it seems that can explain the discrepancy relatively comfortably,” he says.

    But others disagree. “We understand so little about dark energy that it’s tempting to point to something there,” says David Spergel, an astronomer from Princeton University who was also not involved in the study. One explanation is that dark energy, the cause of the universe’s accelerating expansion, is growing stronger with time.

    “The idea is that if dark energy is constant, clusters of galaxies are moving apart from each other but the clusters of galaxies themselves will remain forever bound,” says Alex Filippenko, an astronomer at the University of California, Berkeley and a co-author on Riess’ paper. But if dark energy is growing in strength over time, then one day—far in the future—even clusters of galaxies will get ripped apart. And the trend doesn’t stop there, he says. Galaxies, clusters of stars, stars, planetary systems, planets, and then even atoms will be torn to shreds one by one.

    The implications could—literally—be Earth-shattering. But it’s also possible that one of the two measurements is wrong, so both teams are currently working toward even more precise measurements. The latest discrepancy is also relatively minor compared to past disagreements.

    “I’m old enough to remember when I was first a student and went to conferences and people argued over whether the Hubble constant was 50 or 100,” says Spergel. “We’re now in a situation where the low camp is arguing for 67 and the high camp is arguing for 73. So we’ve made progress! And that’s not to belittle this discrepancy. I think it’s really interesting. It could be the signature of new physics.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:34 pm on August 30, 2016 Permalink | Reply
    Tags: , , , , , Symmetry Magazine   

    From Symmetry: “Our galactic neighborhood” 

    Symmetry Mag

    Symmetry

    08/30/16
    Molly Olmstead

    What can our cosmic neighbors tell us about dark matter and the early universe?

    Milky Way NASA/JPL-Caltech /ESO R. Hurt
    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Imagine a mansion.

    Now picture that mansion at the heart of a neighborhood that stretches irregularly around it, featuring other houses of different sizes—but all considerably smaller. Cloak the neighborhood in darkness, and the houses appear as clusters of lights. Many of the clusters are bright and easy to see from the mansion, but some can just barely be distinguished from the darkness.

    This is our galactic neighborhood. The mansion is the Milky Way, our 100,000-light-years-across home in the universe. Stretching roughly a million light years from the center of the Milky Way, our galactic neighborhood is composed of galaxies, star clusters and large roving gas clouds that are gravitationally bound to us.

    The largest satellite galaxy, the Large Magellanic Cloud [LMC], is also one of the closest.

    2
    LMC

    It is visible to the naked eye from areas clear of light pollution in the Southern Hemisphere. If the Large Magellanic Cloud were around the size of the average American home—about 2,500 square feet—then by a conservative estimate the Milky Way mansion would occupy more than a full city block. On that scale, our most diminutive neighbors would occupy the same amount of space as a toaster.

    Our cosmic neighbors promise answers to questions about hidden matter and the ancient universe. Scientists are setting out to find them.

    What makes a neighbor

    If we are the mansion, the neighboring houses are dwarf galaxies. Scientists have identified about 50 possible galaxies orbiting the Milky Way and have confirmed the identities of roughly 30 of them. These galaxies range in size from several billion stars to only a few hundred. For perspective, the Milky Way contains somewhere between 100 billion to a trillion stars.

    Dwarf galaxies are the most dark-matter-dense objects known in the universe. In fact, they have far more dark matter than regular matter. Segue 1, our smallest confirmed neighbor, is made of 99.97 percent dark matter.

    Dark matter is key to galaxy formation. A galaxy forms when enough regular matter is attracted to a single area by the gravitational pull of a clump of dark matter.

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

    Projects such as the Dark Energy Survey, or DES, find these galaxies by snapping images of a segment of the sky with a powerful telescope camera. Scientists analyze the resulting images, looking for the pattern of color and brightness characteristic of galaxies.

    Dark Energy Icon
    Dark Energy Camera,  built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    Dark Energy Camera, built at FNAL; NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

    Scientists can find dark matter clumps by measuring the motion and chemical composition of stars. If a smaller galaxy seems to be behaving like a more massive galaxy, observers can conclude a considerable amount of dark matter must anchor the galaxy.

    “Essentially, they are nearby clouds of dark matter with just enough stars to detect them,” says Keith Bechtol, a postdoctoral researcher at the University of Wisconsin-Madison and a member of the Dark Energy Survey.

    Through these methods of identification (and thanks to the new capabilities of digital cameras), the Sloan Digital Sky Survey kicked off the modern hunt for dwarf galaxies in the early 2000s.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    The survey, which looked at the northern part of the sky, more than doubled the number of known satellite dwarf galaxies from 11 to 26 galaxies between 2005 and 2010.

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

    Now DES, along with some other surveys, is leading the search. In the last few years DES and its Dark Energy Camera, which maps the southern part of the sky, brought the total to 50 probable galaxies.

    Dark matter mysteries

    Dwarf galaxies serve as ideal tools for studying dark matter. While scientists haven’t yet directly discovered dark matter, in studying dwarf galaxies they’ve been able to draw more and more conclusions about how it behaves and, therefore, what it could be.

    “Dwarf galaxies tell us about the small-scale structure of how dark matter clumps,” says Alex Drlica-Wagner of Fermi National Accelerator Laboratory, one of the leaders of the DES analysis. “They are excellent probes for cosmology at the smallest scales.”

    Dwarf galaxies also present useful targets for gamma-ray telescopes, which could tell us more about how dark matter particles behave.

    NASA/Fermi Telescope
    NASA/Fermi Gamma-ray Telescope

    ESA/Integral
    ESA/Integral Gamma-ray telescope

    Some models posit that dark matter is its own antiparticle. If that were so, it could annihilate when it meets other dark matter particles, releasing gamma rays. Scientists are looking for those gamma rays.

    But while studying these neighbors provides clues about the nature of dark matter, they also raise more and more questions. The prevailing cosmological theory of dark matter has accurately described much of what scientists observe in the universe. But when scientists looked to our neighbors, some of the predictions didn’t hold up.

    The number of galaxies appears to be lower than expected from calculations, for example, and those that are around seem to be too small. While some of the solutions to these problems may lie in the capabilities of the telescopes or the simulations themselves, we may also need to reconsider the way we think dark matter interacts.

    The elements of the neighborhood

    Dwarf galaxies don’t just tell us about dark matter: They also present a window into the ancient past. Most dwarf galaxies’ stars formed more than 10 billion years ago, not long after the Big Bang. Our current understanding of galaxy formation, according to Bechtol, is that after small galaxies formed, some of them merged over billions of years into larger galaxies.

    If we didn’t have these ancient neighbors, we’d have to peer all the way across the universe to see far enough back in time to glimpse galaxies that formed soon after the big bang. While the Milky Way and other large galaxies bustle with activity and new star formation, the satellite galaxies remain mostly static—snapshots of galaxies soon after their birth.

    “They’ve mostly been sitting there, waiting for us to study them,” says Josh Simon, an astronomer at the Carnegie Institution for Science.

    The abundance of certain elements in stars in dwarf galaxies can tell scientists about the conditions and mechanisms that produce them. Scientists can also look to the elements to learn about even older stars.

    The first generation of stars are thought to have looked very different than those formed afterward. When they exploded as supernovae, they released new elements that would later appear in stars of the next generation, some of which are found in our neighboring galaxies.

    “They do give us the most direct fingerprint we can get as to what those first stars might have been like,” Simon says.

    Scientists have learned a lot about our satellites in just the past few years, but there’s always more to learn. DES will begin its fourth year of data collection in August. Several other surveys are also underway. And the Large Synoptic Survey Telescope, an ambitious international project currently under construction in Chile, will begin operating fully in 2022.

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST/Camera, built at SLAC; SST telescope, currently under construction at Cerro Pachón Chile

    LSST will create a more detailed map than any of the previous surveys’ combined.

    From NatGeo, Inside the Milky Way, possibly the best science video ever made.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:26 pm on August 24, 2016 Permalink | Reply
    Tags: , , Symmetry Magazine, The $100 muon detector   

    From Symmetry: “The $100 muon detector” 

    Symmetry Mag

    Symmetry

    08/19/16
    By Laura Dattaro

    1
    Spencer Axani

    A doctoral student and his adviser designed a tabletop particle detector they hope to make accessible to budding young engineering physicists.

    When Spencer Axani was an undergraduate physics student, his background in engineering led him to a creative pipe dream: a pocket-sized device that could count short-lived particles called muons all day.

    Muons, heavier versions of electrons, are around us all the time, a byproduct of the cosmic rays that shoot out from supernovae and other high-energy events in space. When particles from those rays hit Earth’s atmosphere, they often decay into muons.

    Muons are abundant on the surface of the Earth, but in Axani’s University of Alberta underground office, shielded by the floors above, they might be few and far between. A pocket detector would be the perfect gadget for measuring the difference.

    Now a doctoral student at Massachusetts Institute of Technology, Axani has nearly made this device a reality. Along with an undergraduate student and Axani’s adviser, Janet Conrad, he’s developed a detector that sits on a desk and tallies the muons that pass by. The best part? The whole system can be built by students for under $100.

    “Compared to most detectors, it’s by far the cheapest and smallest I’ve found,” Axani says. “If you make 100,000 of these, it starts becoming a very large detector. Instrumenting airplanes and ships would let you start measuring cosmic ray rates around the world.”

    Particle physicists deal with cosmic rays all of the time, says Conrad, a physics professor at MIT. “Sometimes we love them, and sometimes we hate them. We love them if we can use them for calibration of our detectors, and we hate them if they provide a background for what it is that we are trying to do.”

    Conrad used small muon detectors similar to the one Axani dreamed about when leading a neutrino experiment at Fermi National Accelerator Laboratory called MiniBooNE. When a professor at the University of Alberta proposed adding mini-muon detectors to another neutrino experiment, Axani was ready to pitch in.

    FNAL/MiniBooNE
    FNAL/MiniBooNE

    The idea was to create muon detectors to add to IceCube, a neutrino detector built into the ice in Antarctica. They would be inserted into IceCube’s proposed low-energy upgrade, known as PINGU (Precision IceCube Next Generation Upgrade).

    U Wisconsin ICECUBE neutrino detector at the South Pole
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector at the South Pole

    IceCube PINGU
    IceCube PINGU

    First, they needed a prototype. Axani got to work and quickly devised a rough detector housed in PVC pipe. “It looked pretty lab,” Axani said. It also gave off a terrible smell, the result of using a liquid called toluene as a scintillator, a material that gives off light when hit by a charged particle.

    Over the next few months, Axani refined the device, switching to an odorless plastic scintillator and employing silicon photomultipliers (SiPM), which amplify the light from the scintillator into a signal that can be read. Adding some electronics allowed him to build a readout screen that ticks off the amount of energy from muon interactions and registers the time of the event.

    Sitting in Axani’s office, the counter shows a rate of one muon every few seconds, which is what they expected from the size of the detector. Though it’s fairly constant, even minor changes like increased humidity or heavy rain can alter it.

    Conrad and Axani have taken the detector down into the Boston subway, using the changes in the muon count to calculate the depth of the train tunnels. They’ve also brought it into the caverns of Fermilab’s neutrino experiments to measure the muon flux more than 300 feet underground.

    Axani wants to take it to higher elevations—say, in an airplane at 30,000 feet above sea level—where muon counts should be higher, since the particles have had less time to decay after their creation in the atmosphere.

    Fermilab physicist Herman White suggested taking one of the the tiny detectors on a ship to study muon counts at sea. Mapping out the muon rate around the globe at sea has never been achieved. Liquid scintillator can be harmful to marine life, and the high voltage and power consumption of the large devices present a safety hazard.

    While awaiting review of the PINGU upgrade, both Conrad and Axani see value in their project as an educational tool. With a low cost and simple instructions, the muon counter they created can be assembled by undergraduates and high school students, who would learn about machining, circuits, and particle physics along the way—no previous experience required.

    “The idea was, students building the detectors would develop skills typically taught in undergraduate lab classes,” Spencer says. “In return, they would end up with a device useful for all sorts of physics measurements.”

    Conrad has first-hand knowledge of how hands-on experience like this can teach students new skills. As an undergraduate at Swarthmore College, she took a course that taught all the basic abilities needed for a career in experimental physics: using a machine shop, soldering, building circuits. As a final project, she constructed a statue that she’s held on to ever since.

    Creating the statue helped Conrad cement the lessons she learned in the class, but the product was abstract, not a functioning tool that could be used to do real science.

    “We built a bunch of things that were fun, but they weren’t actually useful in any way,” Conrad says. “This [muon detector] takes you through all of the exercises that we did and more, and then produces something at the end that you would then do physics with.”

    Axani and Conrad published instructions for building the detector on the open-source physics publishing site arXiv, and have been reworking the project with the aim of making it accessible to high-school students. No math more advanced than division and multiplication is needed, Axani says. And the parts don’t need to be new, meaning students could potentially take advantage of leftovers from experiments at places like Fermilab.

    “This should be for students to build,” Axani says. “It’s a good project for creative people who want to make their own measurements.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:51 pm on August 23, 2016 Permalink | Reply
    Tags: , , , , Symmetry Magazine   

    From Symmetry: “Five facts about the Big Bang” 

    Symmetry Mag

    Symmetry

    08/23/16
    Matthew R. Francis

    1
    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

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

    It’s the cornerstone of cosmology, but what is it all about?

    Astronomers Edwin Hubble and Milton Humason in the early 20th century discovered that galaxies are moving away from the Milky Way. More to the point: Every galaxy is moving away from every other galaxy on average, which means the whole universe is expanding. In the past, then, the whole cosmos must have been much smaller, hotter and denser.

    That description, known as the Big Bang model, has stood up against new discoveries and competing theories for the better part of a century. So what is this “Big Bang” thing all about?

    The Big Bang happened everywhere at once.

    The universe has no center or edge, and every part of the cosmos is expanding. That means if we run the clock backward, we can figure out exactly when everything was packed together—13.8 billion years ago. Because every place we can map in the universe today occupied the same place 13.8 billion years ago, there wasn’t a location for the Big Bang: Instead, it happened everywhere simultaneously.

    The Big Bang may not describe the actual beginning of everything.

    “Big Bang” broadly refers to the theory of cosmic expansion and the hot early universe. However, sometimes even scientists will use the term to describe a moment in time—when everything was packed into a single point. The problem is that we don’t have either observations or theory that describes that moment, which is properly (if clumsily) called the “initial singularity.”

    The initial singularity is the starting point for the universe we observe, but there might have been something that came before.

    The difficulty is that the very hot early cosmos and the rapid expansion called “inflation” that likely happened right after the singularity wiped out most—if not all—of the information about any history that preceded the Big Bang. Physicists keep thinking of new ways to check for signs of an earlier universe, and though we haven’t seen any of them so far, we can’t rule it out yet.

    The Big Bang theory explains where all the hydrogen and helium in the universe came from.

    In the 1940s, Ralph Alpher and George Gamow calculated that the early universe was hot and dense enough to make virtually all the helium, lithium and deuterium (hydrogen with a neutron attached) present in the cosmos today; later research showed where the primordial hydrogen came from. This is known as “Big Bang nucleosynthesis,” and it stands as one of the most successful predictions of the theory. The heavier elements (such as oxygen, iron and uranium) were formed in stars and supernova explosions.

    The best evidence for the Big Bang is in the form of microwaves. Early on, the whole universe was dense enough to be completely opaque. But at a time roughly 380,000 years after the Big Bang, expansion spread everything out enough to make the universe transparent.

    The light released from this transition, known as the cosmic microwave background (CMB), still exists.

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    It was first observed in the 1960s by Arno Penzias and Robert Wilson.

    Big Ear, Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA
    Big Ear, Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA

    That discovery cemented the Big Bang theory as the best description of the universe; since then, observatories such WMAP and Planck have used the CMB to tell us a lot about the total structure and content of the cosmos.

    One of the first people to think scientifically about the origin of the universe was a Catholic priest.

    In addition to his religious training and work, Georges Lemaître was a physicist who studied the general theory of relativity and worked out some of the conditions of the early cosmos in the 1920s and ’30s.

    4

    His preferred metaphors for the origin of the universe were “cosmic egg” and “primeval atom,” but they never caught on, which is too bad, because …

    It seems nobody likes the name “Big Bang.”

    Until the 1960s, the idea of a universe with a beginning was controversial among physicists. The name “Big Bang” was actually coined by astronomer Fred Hoyle, who was the leading proponent of an alternative theory, where universe continues forever without a beginning.

    His shorthand for the theory caught on, and now we’re kind of stuck with it. Calvin and Hobbes’ attempt to get us to adopt “horrendous space kablooie” has failed so far.

    The Big Bang is the cornerstone of cosmology, but it’s not the whole story. Scientists keep refining the theory of the universe, motivated by our observation of all the weird stuff out there. Dark matter (which holds galaxies together) and dark energy (which makes the expansion of the universe accelerate) are the biggest mysteries that aren’t described by the Big Bang theory by itself.

    Our view of the universe, like the cosmos itself, keeps evolving as we discover more and more new things. But rather than fading away, our best explanation for why things are the way they are has remained—the fire at the beginning of the universe.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:14 pm on August 10, 2016 Permalink | Reply
    Tags: , , , , Symmetry Magazine   

    From Symmetry: “Dark matter hopes dwindle with X-ray signal” 

    Symmetry Mag

    Symmetry

    08/10/16
    Manuel Gnida

    A previously detected, anomalously large X-ray signal is absent in new Hitomi satellite data, setting tighter limits for a dark matter interpretation.

    1
    Hitomi collaboration; NASA/CXC; Greg Stewart

    In the final data sent by the Hitomi spacecraft, a surprisingly large X-ray signal previously seen emanating from the Perseus galaxy cluster did not appear.

    JAXA/Hitomi telescope
    JAXA/Hitomi telescope

    This casts a shadow over previous speculation that the anomalously bright signal might have come from dark matter.

    “We would have been able to see this signal much clearer with Hitomi than with other satellites,” says Norbert Werner from the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    “However, there is no unidentified X-ray line at the high flux level found in earlier studies.”

    Werner and his colleagues from the Hitomi collaboration report their findings in a paper submitted to The Astrophysical Journal Letters.

    The mysterious signal was first discovered with lower flux in 2014 when researchers looked at the superposition of X-ray emissions from 73 galaxy clusters recorded with the European XMM-Newton satellite.

    ESA/XMM Newton
    ESA/XMM Newton

    These stacked data increase the sensitivity to signals that are too weak to be detected in individual clusters.

    The scientists found an unexplained X-ray line at an energy of about 3500 electronvolts (3.5 keV), says Esra Bulbul from the MIT Kavli Institute for Astrophysics and Space Research, the lead author of the 2014 study and a co-author of the Hitomi paper.

    “After careful analysis we concluded that it wasn’t caused by the instrument itself and that it was unlikely to be caused by any known astrophysical processes,” she says. “So we asked ourselves ‘What else could its origin be?’”

    One interpretation of the so-called 3.5-keV line was that it could be caused by hypothetical dark matter particles called sterile neutrinos decaying in space.

    Yet, there was something bizarre about the 3.5-keV line. Bulbul and her colleagues found it again in data taken with NASA’s Chandra X-ray Observatory from just the Perseus cluster.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    But in the Chandra data, the individual signal was inexplicably strong—about 30 times stronger than it should have been according to the stacked data.

    Adding to the controversy was the fact that some groups saw the X-ray line in Perseus and other objects using XMM-Newton, Chandra and the Japanese Suzaku satellite, while others using the same instruments reported no detection.

    Astrophysicists highly anticipated the launch of the Hitomi satellite, which carried an instrument—the soft X-ray spectrometer (SXS)—with a spectral resolution 20 times better than the ones aboard previous missions. The SXS would be able to record much sharper signals that would be easier to identify.

    Hitomi recorded the X-ray spectrum of the Perseus galaxy cluster with the protective filter still attached to its soft X-ray spectrometer.
    Hitomi collaboration

    The new data were collected during Hitomi’s first month in space, just before the satellite was lost due to a series of malfunctions. Unfortunately during that time, the SXS was still covered with a protective filter, which absorbed most of the X-ray photons with energies below 5 keV.

    “This limited our ability to take enough data of the 3.5-keV line,” Werner says. “The signal might very well still exist at the much lower flux level observed in the stacked data.”

    Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its X-ray signal is not anomalously strong. A signal 30 times stronger than expected would have made it through the filter.

    The Hitomi results rule out that the anomalously bright signal in the Perseus cluster was a telltale sign of decaying dark matter particles. But they leave unanswered the question of what exactly scientists detected in the past.

    “It’s really unfortunate that we lost Hitomi,” Bulbul says. “We’ll continue our observations with the other X-ray satellites, but it looks like we won’t be able to solve this issue until another mission goes up.”

    Chances are this might happen in a few years. According to a recent report, the Japan Aerospace Exploration Agency and NASA have begun talks about launching a replacement satellite.

    3
    Hitomi recorded the X-ray spectrum of the Perseus galaxy cluster with the protective filter still attached to its soft X-ray spectrometer.
    Hitomi collaboration

    The new data were collected during Hitomi’s first month in space, just before the satellite was lost due to a series of malfunctions. Unfortunately during that time, the SXS was still covered with a protective filter, which absorbed most of the X-ray photons with energies below 5 keV.

    “This limited our ability to take enough data of the 3.5-keV line,” Werner says. “The signal might very well still exist at the much lower flux level observed in the stacked data.”

    Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its X-ray signal is not anomalously strong. A signal 30 times stronger than expected would have made it through the filter.

    The Hitomi results rule out that the anomalously bright signal in the Perseus cluster was a telltale sign of decaying dark matter particles. But they leave unanswered the question of what exactly scientists detected in the past.

    “It’s really unfortunate that we lost Hitomi,” Bulbul says. “We’ll continue our observations with the other X-ray satellites, but it looks like we won’t be able to solve this issue until another mission goes up.”

    Chances are this might happen in a few years. According to a recent report, the Japan Aerospace Exploration Agency and NASA have begun talks about launching a replacement satellite.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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