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  • richardmitnick 11:33 am on March 24, 2017 Permalink | Reply
    Tags: A new gem inside the CMS detector, , , , , , , , Symmetry Magazine   

    From Symmetry: “A new gem inside the CMS detector” 

    Symmetry Mag


    Sarah Charley

    Photo by Maximilien Brice, CERN

    This month scientists embedded sophisticated new instruments in the heart of a Large Hadron Collider experiment.

    Sometimes big questions require big tools. That’s why a global community of scientists designed and built gigantic detectors to monitor the high-energy particle collisions generated by CERN’s Large Hadron Collider in Geneva, Switzerland. From these collisions, scientists can retrace the footsteps of the Big Bang and search for new properties of nature.

    The CMS experiment is one such detector. In 2012, it co-discovered the elusive Higgs boson with its sister experiment, ATLAS. Now, scientists want CMS to push beyond the known laws of physics and search for new phenomena that could help answer fundamental questions about our universe. But to do this, the CMS detector needed an upgrade.

    “Just like any other electronic device, over time parts of our detector wear down,” says Steve Nahn, a researcher in the US Department of Energy’s Fermi National Accelerator Laboratory and the US project manager for the CMS detector upgrades. “We’ve been planning and designing this upgrade since shortly after our experiment first started collecting data in 2010.”

    The CMS detector is built like a giant onion. It contains layers of instruments that track the trajectory, energy and momentum of particles produced in the LHC’s collisions. The vast majority of the sensors in the massive detector are packed into its center, within what is called the pixel detector. The CMS pixel detector uses sensors like those inside digital cameras but with a lightning fast shutter speed: In three dimensions, they take 40 million pictures every second.

    For the last several years, scientists and engineers at Fermilab and 21 US universities have been assembling and testing a new pixel detector to replace the current one as part of the CMS upgrade, with funding provided by the Department of Energy Office of Science and National Science Foundation.

    Maral Alyari of SUNY Buffalo and Stephanie Timpone of Fermilab measure the thermal properties of a forward pixel detector disk at Fermilab. Almost all of the construction and testing of the forward pixel detectors occurred in the United States before the components were shipped to CERN for installation inside the CMS detector. Photo by Reidar Hahn, Fermilab

    Stephanie Timpone consults a cabling map while fellow engineers Greg Derylo and Otto Alvarez inspect a completed forward pixel disk. The cabling map guides their task of routing the the thin, flexible cables that connect the disk’s 672 silicon sensors to electronics boards. Maximilien Brice, CERN

    The CMS detector, located in a cavern 100 meters underground, is open for the pixel detector installation. Photo by Maximilien Brice, CERN

    Postdoctoral researcher Stefanos Leontsinis and colleague Roland Horisberger work with a mock-up of one side of the barrel pixel detector next to the LHC’s beampipe.
    Photo by Maximilien Brice, CERN

    Leontsinis watches the clearance as engineers slide the first part of the barrel pixel just millimeters from the LHC’s beampipe. Photo by Maximilien Brice, CERN

    Scientists and engineers lift and guide the components by hand as they prepare to insert them into the CMS detector. Photo by Maximilien Brice, CERN

    Scientists and engineers connect the cooling pipes of the forward pixel detector. The pixel detector is flushed with liquid carbon dioxide to keep the silicon sensors protected from the LHC’s high-energy collisions. Photo by Maximilien Brice, CERN

    The pixel detector consists of three sections: the innermost barrel section and two end caps called the forward pixel detectors. The tiered and can-like structure gives scientists a near-complete sphere of coverage around the collision point. Because the three pixel detectors fit on the beam pipe like three bulky bracelets, engineers designed each component as two half-moons, which latch together to form a ring around the beam pipe during the insertion process.

    Over time, scientists have increased the rate of particle collisions at the LHC. In 2016 alone, the LHC produced about as many collisions as it had in the three years of its first run together. To be able to differentiate between dozens of simultaneous collisions, CMS needed a brand new pixel detector.

    The upgrade packs even more sensors into the heart of the CMS detector. It’s as if CMS graduated from a 66-megapixel camera to a 124-megapixel camera.

    Each of the two forward pixel detectors is a mosaic of 672 silicon sensors, robust electronics and bundles of cables and optical fibers that feed electricity and instructions in and carry raw data out, according to Marco Verzocchi, a Fermilab researcher on the CMS experiment.

    The multipart, 6.5-meter-long pixel detector is as delicate as raw spaghetti. Installing the new components into a gap the size of a manhole required more than just finesse. It required months of planning and extreme coordination.

    “We practiced this installation on mock-ups of our detector many times,” says Greg Derylo, an engineer at Fermilab. “By the time we got to the actual installation, we knew exactly how we needed to slide this new component into the heart of CMS.”

    The most difficult part was maneuvering the delicate components around the pre-existing structures inside the CMS experiment.

    “In total, the full three-part pixel detector consists of six separate segments, which fit together like a three-dimensional cylindrical puzzle around the beam pipe,” says Stephanie Timpone, a Fermilab engineer. “Inserting the pieces in the right positions and right order without touching any of the pre-existing supports and protections was a well-choreographed dance.”

    For engineers like Timpone and Derylo, installing the pixel detector was the last step of a six-year process. But for the scientists working on the CMS experiment, it was just the beginning.

    “Now we have to make it work,” says Stefanos Leontsinis, a postdoctoral researcher at the University of Colorado, Boulder. “We’ll spend the next several weeks testing the components and preparing for the LHC restart.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 11:46 am on March 21, 2017 Permalink | Reply
    Tags: , , Hernán Quintana Godoy, Symmetry Magazine   

    From Symmetry: “High-energy visionary” 

    Symmetry Mag


    Oscar Miyamoto

    Meet Hernán Quintana Godoy, the scientist who made Chile central to international astronomy.


    Professor Hernán Quintana Godoy has a way of taking the long view, peering back into the past through distant stars while looking ahead to the future of astronomy in his home, Chile.

    For three decades, Quintana has helped shape the landscape of astronomy in Chile, host to some of the largest ground-based observatories in the world.


    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO/Cerro LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres


    Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile.

    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile



    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    Giant Magellan Telescope, Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile

    LSST telescope, currently under construction 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.

    In January he became the first recipient of the Education Prize of the American Astronomical Society from a country other than the United States or Canada.

    Long overdue.

    “Training the next generation of astronomers should not be limited to just a few countries,” says Keely Finkelstein, former chair of the AAS Education Prize Committee. “[Quintana] has been a tireless advocate for establishing excellent education and research programs in Chile.”

    Quintana earned his doctorate from the University of Cambridge in the United Kingdom in 1973. The same year, a military junta headed by General Augusto Pinochet took power in a coup d’état.

    Quintana came home and secured a teaching position at the University of Chile. At the time, Chilean researchers mainly focused on the fundamentals of astronomy—measuring the radiation from stars and calculating the coordinates of celestial objects. By contrast, Quintana’s dissertation on high-energy phenomena seemed downright radical.

    A year and a half after taking his new job, Quintana was granted a leave of absence to complete a post-doc abroad. Writing from the United States, Quintana published an article encouraging Chile to take better advantage of its existing international observatories. He urged the government to provide more funding and to create an environment that would encourage foreign-educated astronomers to return home to Chile after their postgraduate studies. The article did not go over well with the administration at his university.

    “I wrote it for a magazine that was clearly against Pinochet,” Quintana says. “The magazine cover was a black page with a big ‘NO’ in red” related to an upcoming referendum.

    UCh dissolved Quintana’s teaching position.

    Quintana became a wandering postdoc and research associate in Europe, the US and Canada. It wasn’t until 1981 that Quintana returned to teach at the Physics Institute at Pontifical Catholic University of Chile.

    He continued to push the envelope at PUC. He created elective courses on general astronomy, extragalactic astrophysics and cluster dynamics. He revived and directed a small astronomy group. He encouraged students to expand their horizons by hiring both Chilean and foreign teachers and sending students to study abroad.

    “Because of him I took advantage of most of the big observatories in Chile and had an international perspective of research from the very beginning of my career,” says Amelia Ramirez, who studied with Quintana in 1983. A specialist in interacting elliptical galaxies, she is now head of Research and Development in University of La Serena.

    In mid-1980s Quintana became the scriptwriter for a set of distance learning astronomy classes produced by the educational division of his university’s public TV channel, TELEDUC. He challenged his viewers to take on advanced topics—and they responded.

    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 4:18 pm on March 17, 2017 Permalink | Reply
    Tags: , , , , , Symmetry Magazine   

    From Symmetry: “Q&A: Dark matter next door?” 

    Symmetry Mag


    Manuel Gnida

    NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

    Astrophysicists Eric Charles and Mattia Di Mauro discuss the surprising glow of our neighbor galaxy.

    [ApJ Volume 836, issue 2, Number 2, 2017] Astronomers recently discovered a stronger-than-expected glow of gamma rays at the center of the Andromeda galaxy, the nearest major galaxy to the Milky Way.

    Andromeda Galaxy Adam Evans

    The signal has fueled hopes that scientists are zeroing in on a sign of dark matter, which is five times more prevalent than normal matter but has never been detected directly.

    Researchers believe that gamma rays—a very energetic form of light—could be produced when hypothetical dark matter particles decay or collide and destroy each other. However, dark matter isn’t the only possible source of the gamma rays. A number of other cosmic processes are known to produce them.

    So what do Andromeda’s gamma rays really tell us about dark matter? To find out, Symmetry’s Manuel Gnida talked with Eric Charles and Mattia Di Mauro, two members of the Fermi-LAT collaboration—an international team of researchers that found the Andromeda gamma-ray signal using the Large Area Telescope [LAT], a sensitive “eye” for dark matter on NASA’s Fermi Gamma-ray Space Telescope.

    Both researchers are based at the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. The LAT was conceived of and assembled at SLAC, which also hosts its operations center.

    KIPAC researchers Eric Charles and Mattia Di Mauro. Dawn Harmer, SLAC National Accelerator Laboratory

    S. Have you discovered dark matter?
    MD: No, we haven’t. In the study, the LAT team looked at the gamma-ray emissions of the Andromeda galaxy and found something unexpected, something we don’t fully understand yet. But there are other potential astrophysical explanations than dark matter.

    It’s also not the first time that the LAT collaboration has studied Andromeda with Fermi, but in the old data the galaxy only looked like a big blob. With more data and improved data processing, we have now obtained a much clearer picture of the galaxy’s gamma-ray glow and how it’s distributed.

    S.What’s so unusual about the results?
    EC: As a spiral galaxy, Andromeda is similar to the Milky Way. Therefore, we expected the emissions of both galaxies to look similar. What we discovered is that they are, in fact, quite different.

    In our galaxy, gamma rays come from all kinds of locations—from the center and the spiral arms in the outer regions. For Andromeda, on the other hand, the signal is concentrated at the center.

    S.Why do galaxies glow in gamma rays?
    EC: The answer depends on the type of galaxy. There are active galaxies called blazars. They emit gamma rays when matter in close orbit around supermassive black holes generates jets of plasma. And then there are “normal” galaxies like Andromeda and the Milky Way that produce gamma rays in other ways.

    When we look at the emissions of the Milky Way, the galaxy appears like a bright disk, with the somewhat brighter galactic center at the center of the disk. Most of this glow is diffuse and comes from the gas between the stars that lights up when it’s hit by cosmic rays—energetic particles spit out by star explosions or supernovae.

    Other gamma-ray sources are the remnants of such supernovae and pulsars—extremely dense, magnetized, rapidly rotating neutron stars. These sources show up as bright dots in the gamma-ray map of the Milky Way, except at the center where the density of gamma-ray sources is high and the diffuse glow of the Milky Way is brightest, which prevents the LAT from detecting individual sources.

    Andromeda is too far away to see individual gamma-ray sources, so it only has a diffuse glow in our images. But we expected to see most of the emissions to come from the disk as well. Its absence suggests that there is less interaction between gas and cosmic rays in our neighbor galaxy. Since this interaction is tied to the formation of stars, this also suggests that Andromeda had a different history of star formation than the Milky Way.

    The sky in gamma rays with energies greater than 1 gigaelectronvolts, based on eight years of data from the LAT on NASA’s Fermi Gamma-ray Space Telescope. NASA/DOE/Fermi LAT Collaboration.

    NASA/Fermi LAT

    NASA/Fermi Telescope

    S. What does all this have to do with dark matter?
    MD: When we carefully analyze the gamma-ray emissions of the Milky Way and model all the gas and point-like sources to the best of our knowledge, then we’re left with an excess of gamma rays at the galactic center. Some people have argued this excess could be a telltale sign of dark matter particles.

    We know that the concentration of dark matter is largest at the galactic center, so if there were a dark matter signal, we would expect it to come from there. The localization of gamma-ray emissions at Andromeda’s center seems to have renewed the interest in the dark matter interpretation in the media.

    S.Is dark matter the most likely interpretation?
    EC: No, there are other explanations. There are so many gamma-ray sources at the galactic center that we can’t really see them individually. This means that their light merges into an extended, diffuse glow.

    In fact, two recent studies from the US and the Netherlands have suggested that this glow in the Milky Way could be due to unresolved point sources such as pulsars. The same interpretation could also be true for Andromeda’s signal.

    S.What would it take to know for certain?
    MD:To identify a dark matter signal, we would need to exclude all other possibilities. This is very difficult for a complex region like the galactic center, for which we don’t even know all the astrophysical processes. Of course, this also means that, for the same reason, we can’t completely rule out the dark matter interpretation.

    But what’s really important is that we would want to see the same signal in a few different places. However, we haven’t detected any gamma-ray excesses in other galaxies that are consistent with the ones in the Milky Way and Andromeda.

    This is particularly striking for dwarf galaxies, small companion galaxies of the Milky Way that only have few stars. These objects are only held together because they are dominated by dark matter. If the gamma-ray excess at the galactic center were due to dark matter, then we should have already seen similar signatures in the dwarf galaxies. But we don’t.

    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 2:03 pm on March 14, 2017 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “The life of an accelerator” 

    Symmetry Mag


    Manuel Gnida


    Tens of thousands of accelerators exist around the world, producing powerful particle beams for the benefit of medical diagnostics, cancer therapy, industrial manufacturing, material analysis, national security, and nuclear as well as fundamental particle physics. Particle beams can also be used to produce powerful beams of X-rays.

    Many of these particle accelerators rely on artfully crafted components called cavities.

    The world’s longest linear accelerator (also known as a linac) sits at the Department of Energy’s SLAC National Accelerator Laboratory. It stretches two miles and accelerates bunches of electrons to very high energies.

    The SLAC linac has undergone changes in its 50 years of operation that illustrate the evolution of the science of accelerator cavities. That evolution continues and will determine what the linac does next.


    Robust copper

    An accelerator cavity is a mostly closed, hollow chamber with an opening on each side for particles to pass through. As a particle moves through the cavity, it picks up energy from an electromagnetic field stored inside. Many cavities can be lined up like beads on a string to generate higher and higher particle energies.

    When SLAC’s linac first started operations, each of its cavities was made exclusively from copper. Each tube-like cavity consisted of a 1-inch-long, 4-inch-wide cylinder with disks on either side. Technicians brazed together more than 80,000 cavities to form a straight particle racetrack.

    Scientists generate radiofrequency waves in an apparatus called a klystron that distributes them to the cavities. Each SLAC klystron serves a 10-foot section of the beam line. The arrival of the electron bunch inside the cavity is timed to match the peak in the accelerating electric field. When a particle arrives inside the cavity at the same time as the peak in the electric field, then that bunch is optimally accelerated.

    “Particles only gain energy if the variable electric field precisely matches the particle motion along the length of the accelerator,” says Sami Tantawi, an accelerator physicist at Stanford University and SLAC. “The copper must be very clean and the shape and size of each cavity must be machined very carefully for this to happen.”

    In its original form, SLAC’s linac boosted electrons and their antimatter siblings, positrons, to an energy of 50 billion electronvolts. Researchers used these beams of accelerated particles to study the inner structure of the proton, which led to the discovery of fundamental particles known as quarks.

    Today almost all accelerators in the world—including smaller systems for medical and industrial applications—are made of copper. Copper is a good electric conductor, which is important because the radiofrequency waves build up an accelerating field by creating electric currents in the cavity walls. Copper can be machined very smoothly and is cheaper than other options, such as silver.

    “Copper accelerators are very robust systems that produce high acceleration gradients of tens of millions of electronvolts per meter, which makes them very attractive for many applications,” says SLAC accelerator scientist Chris Adolphsen.

    Today, one-third of SLAC’s original copper linac is used to accelerate electrons for the Linac Coherent Light Source, a facility that turns energy from the electron beam into what is currently the world’s brightest X-ray laser light.

    Researchers continue to push the technology to higher and higher gradients—that is, larger and larger amounts of acceleration over a given distance.

    “Using sophisticated computer programs on powerful supercomputers, we were able to develop new cavity geometries that support almost 10 times larger gradients,” Tantawi says. “Mixing small amounts of silver into the copper further pushes the technology toward its natural limits.” Cooling the copper to very low temperatures helps as well. Tests at 45 Kelvin—negative 384 degrees Fahrenheit—have shown to increase acceleration gradients 20-fold compared to SLAC’s old linac.

    Copper accelerators have their limitations, though. SLAC’s historic linac produces 120 bunches of particles per second, and recent developments have led to copper structures capable of firing 80 times faster. But for applications that need much higher rates, Adolphsen says, “copper cavities don’t work because they would melt.”

    Chill niobium

    For this reason, crews at SLAC are in the process of replacing one-third of the original copper linac with cavities made of niobium.

    Niobium can support very large bunch rates, as long as it is cooled. At very low temperatures, it is what’s known as a superconductor.

    “Below the critical temperature of 9.2 Kelvin, the cavity walls conduct electricity without losses, and electromagnetic waves can travel up and down the cavity many, many times, like a pendulum that goes on swinging for a very long time,” says Anna Grassellino, an accelerator scientist at Fermi National Accelerator Laboratory. “That’s why niobium cavities can store electromagnetic energy very efficiently and can operate continuously.”

    You can find superconducting niobium cavities in modern particle accelerators such as the Large Hadron Collider at CERN and the CEBAF accelerator at Thomas Jefferson National Accelerator Facility. The European X-ray Free-Electron Laser in Germany, the European Spallation Source at CERN, and the Facility for Rare Isotope Beams at Michigan State University are all being built using niobium technology. Niobium cavities also appear in designs for the next-generation International Linear Collider.

    At SLAC, the niobium cavities will support LCLS-II, an X-ray laser that will produce up to a million ultrabright light flashes per second. The accelerator will have 280 cavities, each about three feet long with a 3-inch opening for the electron beam to fly through. Sets of eight cavities will be strung together into cryomodules that keep the cavities at a chilly 2 Kelvin, which is colder than interstellar space.

    Each niobium cavity is made by fusing together two halves stamped from a sheet of pure metal. The cavities are then cleaned very thoroughly because even the tiniest impurities would degrade their performance.

    The shape of the cavities is reminiscent of a stack of shiny donuts. This is to maximize the cavity volume for energy storage and to minimize its surface area to cut down on energy dissipation. The exact size and shape also depends on the type of accelerated particle.

    “We’ve come a long way since the first development of superconducting cavities decades ago,” Grassellino says. “Today’s niobium cavities produce acceleration gradients of up to about 50 million electronvolts per meter, and R&D work at Fermilab and elsewhere is further pushing the limits.”

    Hot plasma

    Over the past few years, SLAC accelerator scientists have been working on a way to push the limits of particle acceleration even further: accelerating particles using bubbles of ionized gas called plasma.

    Plasma wakefield acceleration is capable of creating acceleration gradients that are up to 1000 times larger than those of copper and niobium cavities, promising to drastically shrink the size of particle accelerators and make them much more powerful.

    “These plasma bubbles have certain properties that are very similar to conventional metal cavities,” says SLAC accelerator physicist Mark Hogan. “But because they don’t have a solid surface, they can support extremely high acceleration gradients without breaking down.”

    Hogan’s team at SLAC and collaborators from the University of California, Los Angeles, have been developing their plasma acceleration method at the Facility for Advanced Accelerator Experimental Tests, using an oven of hot lithium gas for the plasma and an electron beam from SLAC’s copper linac.

    Researchers create bubbles by sending either intense laser light or a high-energy beam of charged particles through plasma. They then send beams of particles through the bubbles to be accelerated.

    When, for example, an electron bunch enters a plasma, its negative charge expels plasma electrons from its flight path, creating a football-shaped cavity filled with positively charged lithium ions. The expelled electrons form a negatively charged sheath around the cavity.

    This plasma bubble, which is only a few hundred microns in size, travels at nearly the speed of light and is very short-lived. On the inside, it has an extremely strong electric field. A second electron bunch enters that field and experiences a tremendous energy gain. Recent data show possible energy boosts of billions of electronvolts in a plasma column of just a little over a meter.

    “In addition to much higher acceleration gradients, the plasma technique has another advantage,” says UCLA researcher Chris Clayton. “Copper and niobium cavities don’t keep particle beams tightly bundled and require the use of focusing magnets along the accelerator. Plasma cavities, on the other hand, also focus the beam.”

    Much more R&D work is needed before plasma wakefield accelerator technology can be turned into real applications. But it could represent the future of particle acceleration at SLAC and of accelerator science as a whole.

    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 8:51 pm on March 10, 2017 Permalink | Reply
    Tags: , , , , , , , , Symmetry Magazine, The strong force (strong interaction)   

    From Symmetry: “A strength test for the strong force [strong interaction]” 

    Symmetry Mag


    Sarah Charley

    Science Saturday

    New research could tell us about particle interactions in the early universe and even hint at new physics.

    Much of the matter in the universe is made up of tiny particles called quarks. Normally it’s impossible to see a quark on its own because they are always bound tightly together in groups. Quarks only separate in extreme conditions, such as immediately after the Big Bang or in the center of stars or during high-energy particle collisions generated in particle colliders.

    Scientists at Louisiana Tech University are working on a study of quarks and the force that binds them by analyzing data from the ATLAS experiment at the LHC. Their measurements could tell us more about the conditions of the early universe and could even hint at new, undiscovered principles of physics.

    ATLAS at the LHC

    The particles that stick quarks together are aptly named “gluons.” Gluons carry the strong force, one of four fundamental forces in the universe that govern how particles interact and behave. The strong force binds quarks into particles such as protons, neutrons and atomic nuclei.

    As its name suggests, the strong force [strong interaction] is the strongest—it’s 100 times stronger than the electromagnetic force (which binds electrons into atoms), 10,000 times stronger than the weak force (which governs radioactive decay), and a hundred million million million million million million (1039) times stronger than gravity (which attracts you to the Earth and the Earth to the sun).

    But this ratio shifts when the particles are pumped full of energy. Just as real glue loses its stickiness when overheated, the strong force carried by gluons becomes weaker at higher energies.

    “Particles play by an evolving set of rules,” says Markus Wobisch from Louisiana Tech University. “The strength of the forces and their influence within the subatomic world changes as the particles’ energies increase. This is a fundamental parameter in our understanding of matter, yet has not been fully investigated by scientists at high energies.”

    Characterizing the cohesiveness of the strong force is one of the key ingredients to understanding the formation of particles after the Big Bang and could even provide hints of new physics, such as hidden extra dimensions.

    “Extra dimensions could help explain why the fundamental forces vary dramatically in strength,” says Lee Sawyer, a professor at Louisiana Tech University. “For instance, some of the fundamental forces could only appear weak because they live in hidden extra dimensions and we can’t measure their full strength. If the strong force is weaker or stronger than expected at high energies, this tells us that there’s something missing from our basic model of the universe.”

    By studying the high-energy collisions produced by the LHC, the research team at Louisiana Tech University is characterizing how the strong force pulls energetic quarks into encumbered particles. The challenge they face is that quarks are rambunctious and caper around inside the particle detectors. This subatomic soirée involves hundreds of particles, often arising from about 20 proton-proton collisions happening simultaneously. It leaves a messy signal, which scientists must then reconstruct and categorize.

    Wobisch and his colleagues innovated a new method to study these rowdy groups of quarks called jets. By measuring the angles and orientations of the jets, he and his colleagues are learning important new information about what transpired during the collisions—more than what they can deduce by simple counting the jets.

    The average number of jets produced by proton-proton collisions directly corresponds to the strength of the strong force in the LHC’s energetic environment.

    “If the strong force is stronger than predicted, then we should see an increase in the number of proton-protons collisions that generate three jets. But if the strong force is actually weaker than predicted, then we’d expect to see relatively more collisions that produce only two jets. The ratio between these two possible outcomes is the key to understanding the strong force.”

    After turning on the LHC, scientists doubled their energy reach and have now determined the strength of the strong force up to 1.5 trillion electronvolts, which is roughly the average energy of every particle in the universe just after the Big Bang. Wobisch and his team are hoping to double this number again with more data.

    “So far, all our measurements confirm our predictions,” Wobisch says. “More data will help us look at the strong force at even higher energies, giving us a glimpse as to how the first particles formed and the microscopic structure of space-time.”

    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 2:46 pm on March 7, 2017 Permalink | Reply
    Tags: CERN Proto Dune, , , Researchers face engineering puzzle, , Symmetry Magazine, Transporting Argon   

    From Symmetry: “Researchers face engineering puzzle” 

    Symmetry Mag


    Daniel Garisto

    How do you transport 70,000 tons of liquid argon nearly a mile underground?

    FNAL DUNE Argon tank at SURF

    Nearly a mile below the surface of Lead, South Dakota, scientists are preparing for a physics experiment that will probe one of the deepest questions of the universe: Why is there more matter than antimatter?
    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA


    Surf-Dune/LBNF Caverns at Sanford Lab

    Because neutrinos interact with matter so rarely and so weakly, DUNE scientists need a lot of material to create a big enough target for the particles to run into. The most widely available (and cost effective) inert substance that can do the job is argon, a colorless, odorless element that makes up about 1 percent of the atmosphere.

    The researchers also need to place the detector full of argon far below Earth’s surface, where it will be protected from cosmic rays and other interference.

    “We have to transfer almost 70,000 tons of liquid argon underground,” says David Montanari, a Fermilab engineer in charge of the experiment’s cryogenics. “And at this point we have two options: We can either transfer it as a liquid or we can transfer it as a gas.”

    Either way, this move will be easier said than done.

    Liquid or gas?

    The argon will arrive at the lab in liquid form, carried inside of 20-ton tanker trucks. Montanari says the collaboration initially assumed that it would be easier to transport the argon down in its liquid form—until they ran into several speed bumps.

    Transporting liquid vertically is very different from transporting it horizontally for one important reason: pressure. The bottom of a mile-tall pipe full of liquid argon would have a pressure of about 3000 pounds per square inch—equivalent to 200 times the pressure at sea level. According to Montanari, to keep these dangerous pressures from occurring, multiple de-pressurizing stations would have to be installed throughout the pipe.

    Even with these depressurizing stations, safety would still be a concern. While argon is non-toxic, if released into the air it can reduce access to oxygen, much like carbon monoxide does in a fire. In the event of a leak, pressurized liquid argon would spill out and could potentially break its vacuum-sealed pipe, expanding rapidly to fill the mine as a gas. One liter of liquid argon would become about 800 liters of argon gas, or four bathtubs’ worth.

    Even without a leak, perhaps the most important challenge in transporting liquid argon is preventing it from evaporating into a gas along the way, according to Montanari.

    To remain a liquid, argon is kept below a brisk temperature of minus 180 degrees Celsius (minus 300 degrees Fahrenheit).

    “You need a vacuum-insulated pipe that is a mile long inside a mine shaft,” Montanari says. “Not exactly the most comfortable place to install a vacuum-insulated pipe.”

    To avoid these problems, the cryogenics team made the decision to send the argon down as gas instead.

    Routing the pipes containing liquid argon through a large bath of water will warm it up enough to turn it into gas, which will be able to travel down through a standard pipe. Re-condensers located underground act as massive air conditioners will then cool the gas until becomes a liquid again.

    “The big advantage is we no longer have vacuum insulated pipe,” Montanari says. “It is just straight piece of pipe.”

    Argon gas poses much less of a safety hazard because it is about 1000 times less dense than liquid argon. High pressures would be unlikely to build up and necessitate depressurizing stations, and if a leak occurred, it would not expand as much and cause the same kind of oxygen deficiency.

    The process of filling the detectors with argon will take place in four stages that will take almost two years, Montanari says. This is due to the amount of available cooling power for re-condensing the argon underground. There is also a limit to the amount of argon produced in the US every year, of which only so much can be acquired by the collaboration and transported to the site at a time.

    Illustration by Ana Kova

    Argon for answers

    Once filled, the liquid argon detectors will pick up light and electrons produced by neutrino interactions.

    Part of what makes neutrinos so fascinating to physicists is their habit of oscillating from one flavor—electron, muon or tau—to another. The parameters that govern this “flavor change” are tied directly to some of the most fundamental questions in physics, including why there is more matter than antimatter. With careful observation of neutrino oscillations, scientists in the DUNE collaboration hope to unravel these mysteries in the coming years.

    “At the time of the Big Bang, in theory, there should have been equal amounts of matter and antimatter in the universe,” says Eric James, DUNE’s technical coordinator. That matter and antimatter should have annihilated, leaving behind an empty universe. “But we became a matter-dominated universe.”

    James and other DUNE scientists will be looking to neutrinos for the mechanism behind this matter favoritism. Although the fruits of this labor won’t appear for several years, scientists are looking forward to being able to make use of the massive detectors, which are hundreds of times larger than current detectors that hold only a few hundred tons of liquid argon.

    Currently, DUNE scientists and engineers are working at CERN to construct Proto-DUNE, a miniature replica of the DUNE detector filled with only 300 tons of liquid argon that can be used to test the design and components.

    CERN Proto DUNE Maximillian Brice

    “Size is really important here,” James says. “A lot of what we’re doing now is figuring out how to take those original technologies which have already being developed… and taking it to this next level with bigger and bigger detectors.”

    To search for that answer, the Deep Underground Neutrino Experiment, or DUNE, will look at minuscule particles called neutrinos. A beam of neutrinos will travel 800 miles through the Earth from Fermi National Accelerator Laboratory to the Sanford Underground Research Facility, headed for massive underground detectors that can record traces of the elusive particles.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 2:42 pm on February 28, 2017 Permalink | Reply
    Tags: , , CERN Antimatter Factory, , , , Symmetry Magazine   

    From Symmetry: “How to build a universe” 

    Symmetry Mag


    Sarah Charley

    Our universe should be a formless fog of energy. Why isn’t it?

    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

    According to the known laws of physics, the universe we see today should be dark, empty and quiet. There should be no stars, no planets, no galaxies and no life—just energy and simple particles diffusing further and further into an expanding universe.

    And yet, here we are.

    Cosmologists calculate that roughly 13.8 billion years ago, our universe was a hunk of thick, hot energy with no boundaries and its own rules.

    CMB per ESA/Planck
    CMB per ESA/Planck

    But then, in less than a microsecond, it matured, and the fundamental laws and properties of matter arose from the pandemonium. How did our elegant and intricate universe emerge?

    The three conditions

    The question “How is it here?” alludes to a conundrum that arose during the development of quantum mechanics.

    In 1928 Paul Dirac combined quantum theory and special relativity to predict the energy of an electron moving near the speed of light. But his equations produced two equally favorable answers: one positive and one negative. Because energy itself cannot be negative, Dirac mused that perhaps the two answers represented the particle’s two possible electric charges. The idea of oppositely charged matter-antimatter pairs was born.

    Meanwhile, about six minutes away from Dirac’s office in Cambridge, physicist Patrick Blackett was studying the patterns etched in cloud chambers by cosmic rays. In 1933 he detected 14 tracks that showed a single particle of light colliding with an air molecule and bursting into two new particles. The spiral tracks of these new particles were mirror images of each other, indicating that they were oppositely charged. This was one of the first observations of what Dirac had predicted five years earlier—the birth of an electron-positron pair.

    Today it’s well known that matter and antimatter are the ultimate wonder twins. They’re spontaneously born from raw energy as a team of two and vanish in a silent poof of energy when they merge and annihilate. This appearing-disappearing act spawned one of the most fundamental mysteries in the universe: What is engraved in the laws of nature that saved us from the broth of appearing and annihilating particles of matter and antimatter?

    “We know this cosmic asymmetry must exist because here we are,” says Jessie Shelton, a theorist at the University of Illinois. “It’s a puzzling imbalance because theory requires three conditions—which all have to be true at once—to create this cosmic preference for matter.”

    In the 1960s physicist Andrei Sakharov proposed this set of three conditions that could explain the appearance of our matter-dominated universe. Scientists continue to look for evidence of these conditions today.

    1. Breaking the tether

    The first problem is that matter and antimatter always seem to be born together. Just as Blackett observed in the cloud chambers, uncharged energy transforms into evenly balanced matter-antimatter pairs. Charge is always conserved through any transition. For there to be an imbalance in the amounts of matter and antimatter, there needs to be a process that creates more of one than the other.

    “Sakharov’s first criterion essentially says that there must be some new process that converts antimatter into matter, or vice versa,” says Andrew Long, a postdoctoral researcher in cosmology at the University of Chicago. “This is one of the things experimentalists are looking for in the lab.”

    In the 1980s, scientists searched for evidence of Sakharov’s first condition by looking for signs of a proton decaying into a positron and two photons. They have yet to find evidence of this modern alchemy, but they continue to search.

    “We think that the early universe could have contained a heavy neutral particle that sometimes decayed into matter and sometimes decayed into antimatter, but not necessarily into both at the same time,” Long says.

    2. Picking a favorite

    Matter and antimatter cannot co-habitate; they always annihilate when they come into contact. But the creation of just a little more matter than antimatter after the Big Bang—about one part in 10 billion—would leave behind the ingredients needed to build the entire visible universe.

    How could this come about? Sakharov’s second criterion dictates that the matter-only process outlined in his first criterion must be more efficient than the opposing antimatter process. And specifically, “we need to see a favoritism for the right kinds of matter to agree with astronomical observations,” Shelton says.

    Observations of light left over from the early universe and measurements of the first lightweight elements produced after the Big Bang show that the discrepancy must exist in a class of particles called baryons: protons, antiprotons and other particles constructed from quarks.

    “These are snapshots of the early universe,” Shelton says. “From these snapshots, we can derive the density and temperature of the early universe and calculate the slight difference between the number of baryons and antibaryons.”

    But this slight difference presents a problem. While there are some tiny discrepancies between the behavior of particles and their antiparticle counterparts, these idiosyncrasies are still consistent with the Standard Model and are not enough to explain the origin of the cosmic imbalance nor the universe’s tenderness towards matter.

    3. Taking a one-way street

    In particle physics, any process that runs forward can just as easily run in reverse. A pair of photons can merge and morph into a particle and antiparticle pair. And just as easily, the particle and antiparticle pair can recombine into a pair of photons. This process happens all around us, continually. But because it is cyclical, there is no net gain or loss for a type of matter.

    If this were always true, our young universe could have been locked in an infinite loop of creation and destruction. Without something slamming the brakes on these cycles at least for a moment, matter could not have evolved into the complex structures we see today.

    “For every stitch that’s knit, there a simultaneous tug on the thread,” Long says. “We need a way to force the reaction to move forward and not simultaneously run in reverse at the same rate.”

    Many cosmologists suspect that the gradual expansion and cooling of the universe was enough to lock matter into being, like a supersaturated sweet tea whose sugar crystals drop to the bottom of the glass as it cools (or in the “freezing” interpretation, like a sweet tea that instantly freezes into ice, locking sugar crystals in place without giving them a chance to dissolve).

    Other cosmologists think that the plasma of the early universe may have contained bubbles that helped separate matter and antimatter (and then served as incubators for particles to acquire mass).

    Several experiments at CERN are looking for evidence that the universe meets Sakharov’s three conditions. For instance, several precision experiments at CERN’s Antimatter Factory are looking for minuscule differences between the intrinsic characteristics of protons and antiprotons.

    CERN’s Antimatter Factory

    The LHCb experiment at the Large Hadron Collider is examining the decay patterns of unstable matter and antimatter particles.


    Shelton and Long both hope that more research from experiments at the LHC will be the key to building a more complete picture of our early universe.

    LHC experiments could discover that the Higgs field served as the lock that halted the early universe’s perpetually evolving and devolving particle soup—especially if the field contained bubbles that froze faster than others, providing cosmic petri dishes in which matter and antimatter could evolve differently, Long says. “More measurements of the Higgs boson and the fundamental properties of matter and antimatter will help us develop better theories and a better understanding of what and where we come from.”

    What exactly transpired during the birth of our universe may always remain a bit of an enigma, but we continue to seek new pieces of this formidable puzzle.

    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 2:45 pm on February 23, 2017 Permalink | Reply
    Tags: , , Instrument finds new earthly purpose, NIST, , , Spectrometry, Symmetry Magazine,   

    From Symmetry: “Instrument finds new earthly purpose” 

    Symmetry Mag


    Amanda Solliday

    Nordlund and his colleagues—Sangjun Lee, a SLAC postdoctoral research fellow, and Jamie Titus, a Stanford University doctoral student (pictured above at SSRL, from left: Lee, Titus and Nordlund)—have already used the transition-edge-sensor spectrometer at SSRL to probe for nitrogen impurities in nanodiamonds and graphene, as well as closely examine the metal centers of proteins and bioenzymes, such as hemoglobin and photosystem II. The project at SLAC was developed with 
support by the Department of Energy’s Laboratory Directed Research and Development.
    Andy Freeberg, SLAC National Accelerator Laboratory

    Detectors long used to look at the cosmos are now part of X-ray experiments here on Earth.

    Modern cosmology experiments—such as the BICEP instruments and the in Antarctica—rely on superconducting photon detectors to capture signals from the early universe.

    BICEP 3 at the South Pole
    BICEP 3 at the South Pole

    Keck Array
    Keck Array at the South Pole

    These detectors, called transition edge sensors, are kept at temperatures near absolute zero, at only tenths of a Kelvin. At this temperature, the “transition” between superconducting and normal states, the sensors function like an extremely sensitive thermometer. They are able to detect heat from cosmic microwave background radiation, the glow emitted after the Big Bang, which is only slightly warmer at around 3 Kelvin.

    Scientists also have been experimenting with these same detectors to catch a different form of light, says Dan Swetz, a scientist at the National Institute of Standards and Technology. These sensors also happen to work quite well as extremely sensitive X-ray detectors.

    NIST scientists, including Swetz, design and build the thin, superconducting sensors and turn them into pixelated arrays smaller than a penny. They construct an entire X-ray spectrometer system around those arrays, including a cryocooler, a refrigerator that can keep the detectors near absolute zero temperatures.


    TES array and cover shown with penny coin for scale.
    Dan Schmidt, NIST

    Over the past several years, these X-ray spectrometers built at the NIST Boulder MicroFabrication Facility have been installed at three synchrotrons at US Department of Energy national laboratories: the National Synchrotron Light Source at Brookhaven National Laboratory, the Advanced Photon Source [APS] at Argonne National Laboratory and most recently at the Stanford Synchrotron Radiation Lightsource [SSRL] at SLAC National Accelerator Laboratory.

    BNL NSLS-II Interior
    BNL NSLS-II Interior

    ANL APS interior
    ANL APS interior


    Organizing the transition edge sensors into arrays made a more powerful detector. The prototype sensor—built in 1995—consisted of only one pixel.

    These early detectors had poor resolution, says physicist Kent Irwin of Stanford University and SLAC. He built the original single-pixel transition edge sensor as a postdoc. Like a camera, the detector can capture greater detail the more pixels it has.

    “It’s only now that we’re hitting hundreds of pixels that it’s really getting useful,” Irwin says. “As you keep increasing the pixel count, the science you can do just keeps multiplying. And you start to do things you didn’t even conceive of being possible before.”

    Each of the 240 pixels is designed to catch a single photon at a time. These detectors are efficient, says Irwin, collecting photons that may be missed with more conventional detectors.

    Spectroscopy experiments at synchrotrons examine subtle features of matter using X-rays. In these types of experiments, an X-ray beam is directed at a sample. Energy from the X-rays temporarily excites the electrons in the sample, and when the electrons return to their lower energy state, they release photons. The photons’ energy is distinctive for a given chemical element and contains detailed information about the electronic structure.

    As the transition edge sensor captures these photons, every individual pixel on the detector functions as a high-energy-resolution spectrometer, able to determine the energy of each photon collected.

    The researchers combine data from all the pixels and make note of the pattern of detected photons across the entire array and each of their energies. This energy spectrum reveals information about the molecule of interest.

    These spectrometers are 100 times more sensitive than standard spectrometers, says Dennis Nordlund, SLAC scientist and leader of the transition edge sensor project at SSRL. This allows a look at biological and chemical details at extremely low concentrations using soft (low-energy) X-rays.

    “These technology advances mean there are many things we can do now with spectroscopy that were previously out of reach,” Nordlund says. “With this type of sensitivity, this is when it gets really interesting for chemistry.”

    The early experiments at Brookhaven looked at bonding and the chemical structure of nitrogen-bearing explosives. With the spectrometer at Argonne, a research team recently took scattering measurements on high-temperature superconducting materials.

    “The instruments are very similar from a technical standpoint—same number of sensors, similar resolution and performance,” Swetz says. “But it’s interesting, the labs are all doing different science with the same basic equipment.”

    At NIST, Swetz says they’re working to pair these detectors with less intense light sources, which could enable researchers to do X-ray experiments in their personal labs.

    There are plans to build transition-edge-sensor spectrometers that will work in the higher energy hard X-ray region, which scientists at Argonne are working on for the next upgrade of Advanced Photon Source.

    To complement this, the SLAC and NIST collaboration is engineering spectrometers that will handle the high repetition rate of X-ray laser pulses such as LCLS-II, the next generation of the free-electron X-ray laser at SLAC. This will require faster readout systems. The goal is to create a transition-edge-sensor array with as many as 10,000 pixels that can capture more than 10,000 pulses per second.

    Irwin points out that the technology developed for synchrotrons, LCLS-II and future cosmic-microwave-background experiments provides shared benefit.

    “The information really keeps bouncing back and forth between X-ray science and cosmology,” Irwin says

    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 5:27 pm on February 21, 2017 Permalink | Reply
    Tags: A candidate for dark matter?, A mobile neutrino detector could be used to determine whether a nuclear reactor is in use, , Determine whether material from a reactor has been repurposed to produce nuclear weapons?, MiniCHANDLER is specifically designed to detect neutrinos' antimatter counterparts antineutrinos, MiniCHANDLER will make history as the first mobile neutrino detector in the US, , Symmetry Magazine, Virginia Tech   

    From Symmetry: “Mobile Neutrino Lab makes its debut” 

    Symmetry Mag


    Daniel Garisto

    The Mystery Machine for particles hits the road.

    It’s not as flashy as Scooby Doo’s Mystery Machine, but scientists at Virginia Tech hope that their new vehicle will help solve mysteries about a ghost-like phenomena: neutrinos.

    The Mobile Neutrino Lab is a trailer built to contain and transport a 176-pound neutrino detector named MiniCHANDLER (Carbon Hydrogen AntiNeutrino Detector with a Lithium Enhanced Raghavan-optical-lattice). When it begins operations in mid-April, MiniCHANDLER will make history as the first mobile neutrino detector in the US.

    “Our main purpose is just to see neutrinos and measure the signal to noise ratio,” says Jon Link, a member of the experiment and a professor of physics at Virginia Tech’s Center for Neutrino Physics. “We just want to prove the detector works.”

    Neutrinos are fundamental particles with no electric charge, a property that makes them difficult to detect. These elusive particles have confounded scientists on several fronts for more than 60 years. MiniCHANDLER is specifically designed to detect neutrinos’ antimatter counterparts, antineutrinos, produced in nuclear reactors, which are prolific sources of the tiny particles.

    Fission at the core of a nuclear reactor splits uranium atoms, whose products themselves undergo a process that emits an electron and electron antineutrino. Other, larger detectors such as Daya Bay have capitalized on this abundance to measure neutrino properties.

    MiniCHANDLER will serve as a prototype for future mobile neutrino experiments up to 1 ton in size.

    Link and his colleagues hope MiniCHANDLER and its future counterparts will find answers to questions about sterile neutrinos, an undiscovered, theoretical kind of neutrino and a candidate for dark matter. The detector could also have applications for national security by serving as a way to keep tabs on material inside of nuclear reactors.

    MiniCHANDLER echoes a similar mobile detector concept from a few years ago. In 2014, a Japanese team published results from another mobile neutrino detector, but their data did not meet the threshold for statistical significance. Detector operations were halted after all reactors in Japan were shut down for safety inspections.

    “We can monitor the status from outside of the reactor buildings thanks to [a] neutrino’s strong penetration power,” Shugo Oguri, a scientist who worked on the Japanese team, wrote in an email.

    Link and his colleagues believe their design is an improvement, and the hope is that MiniCHANDLER will be able to better reject background events and successfully detect neutrinos.

    Neutrinos, where are you?

    To detect neutrinos, which are abundant but interact very rarely with matter, physicists typically use huge structures such as Super-Kamiokande, a neutrino detector in Japan that contains 50,000 tons of ultra-pure water.

    Super-Kamiokande Detector, Japan
    Super-Kamiokande Detector, Japan

    Experiments are also often placed far underground to block out signals from other particles that are prevalent on Earth’s surface.

    With its small size and aboveground location, MiniCHANDLER subverts both of these norms.

    The detector uses solid scintillator technology, which will allow it to record about 100 antineutrino interactions per day. This interaction rate is less than the rate at large detectors, but MiniCHANDLER makes up for this with its precise tracking of antineutrinos.

    Small plastic cubes pinpoint where in MiniCHANDLER an antineutrino interacts by detecting light from the interaction. However, the same kind of light signal can also come from other passing particles like cosmic rays. To distinguish between the antineutrino and the riffraff, Link and his colleagues look for multiple signals to confirm the presence of an antineutrino.

    Those signs come from a process called inverse beta decay. Inverse beta decay occurs when an antineutrino collides with a proton, producing light (the first event) and also kicking a neutron out of the nucleus of the atom. These emitted neutrons are slower than the light and are picked up as a secondary signal to confirm the antineutrino interaction.

    “[MiniCHANDLER] is going to sit on the surface; it’s not shielded well at all. So it’s going to have a lot of background,” Link says. “Inverse beta decay gives you a way of rejecting the background by identifying the two-part event.”

    Monitoring the reactors

    Scientists could find use for a mobile neutrino detector beyond studying reactor neutrinos. They could also use the detector to measure properties of the nuclear reactor itself.

    A mobile neutrino detector could be used to determine whether a reactor is in use, Oguri says. “Detection unambiguously means the reactors are in operation—nobody can cheat the status.”

    The detector could also be used to determine whether material from a reactor has been repurposed to produce nuclear weapons. Plutonium, an element used in the process of making weapons-grade nuclear material, produces 60 percent fewer detectable neutrinos than uranium, the primary component in a reactor core.

    “We could potentially tell whether or not the reactor core has the right amount of plutonium in it,” Link says.

    Using a neutrino detector would be a non-invasive way to track the material; other methods of testing nuclear reactors can be time-consuming and disruptive to the reactor’s processes.

    But for now, Link just wants MiniCHANDLER to achieve a simple—yet groundbreaking—goal: Get the mobile neutrino lab running.

    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 3:01 pm on February 7, 2017 Permalink | Reply
    Tags: 21-centimeter cosmology, , , , , Symmetry Magazine, What ended the dark ages of the universe?   

    From Symmetry: “What ended the dark ages of the universe?” 

    Symmetry Mag

    Diana Kwon


    When we peer through our telescopes into the cosmos, we can see stars and galaxies reaching back billions of years. This is possible only because the intergalactic medium we’re looking through is transparent. This was not always the case.

    Around 380,000 years after the Big Bang came recombination, when the hot mass of particles that made up the universe cooled enough for electrons to pair with protons, forming neutral hydrogen. This brought on the dark ages, during which the neutral gas in the intergalactic medium absorbed most of the high-energy photons around it, making the universe opaque to these wavelengths of light.

    Then, a few hundred million years later, new sources of energetic photons appeared, stripping hydrogen atoms of their electrons and returning them to their ionized state, ultimately allowing light to easily travel through the intergalactic medium. After this era of reionization was complete, the universe was fully transparent once again.

    Physicists are using a variety of methods to search for the sources of reionization, and finding them will provide insight into the first galaxies, the structure of the early universe and possibly even the properties of dark matter.

    Energetic sources

    Current research suggests that most—if not all—of the ionizing photons came from the formation of the first stars and galaxies. “The reionization process is basically a competition between the rate at which stars produce ionizing radiation and the recombination rate in the intergalactic medium,” says Brant Robertson, a theoretical astrophysicist at the University of California, Santa Cruz.

    However, astronomers have yet to find these early galaxies, leaving room for other potential sources. The first stars alone may not have been enough. “There are undoubtedly other contributions, but we argue about how important those contributions are,” Robertson says.

    Active galactic nuclei, or AGN, could have been a source of reionization. AGN are luminous bodies, such as quasars, that are powered by black holes and release ultraviolet radiation and X-rays. However, scientists don’t yet know how abundant these objects were in the early universe.

    Another, more exotic possibility, is dark matter annihilation. In some models of dark matter, particles collide with each other, annihilating and producing matter and radiation. “If through this channel or something else we could find evidence for dark matter annihilation, that would be fantastically interesting, because it would immediately give you an estimate of the mass of the dark matter and how strongly it interacts with Standard Model particles,” says Tracy Slatyer, a particle physicist at MIT.

    Dark matter annihilation and AGN may have also indirectly aided reionization by providing extra heat to the universe.

    Probing the cosmic dawn

    To test their theories of the course of cosmic reionization, astronomers are probing this epoch in the history of the universe using various methods including telescope observations, something called “21-centimeter cosmology” and probing the cosmic microwave background.

    Astronomers have yet to find evidence of the most likely source of reionization—the earliest stars—but they’re looking.

    By assessing the luminosity of the first galaxies, physicists could estimate how many ionizing photons they could have released. “[To date] there haven’t been observations of the actual galaxies that are reionizing the universe—even Hubble can’t deliver any of those—but the hope is that the James Webb Space Telescope can,” says John Wise, an astrophysicist at Georgia Tech.

    Some of the most telling information will come from 21-centimeter cosmology, so called because it studies 21-centimeter radio waves. Neutral hydrogen gives off radio waves of this frequency, ionized hydrogen does not. Experiments such as the forthcoming Hydrogen Epoch of Reionization Array will detect neutral hydrogen using radio telescopes tuned to this frequency. This could provide clinching evidence about the sources of reionization.

    “The basic idea with 21-centimeter cosmology is to not look at the galaxies themselves, but to try to make direct measurements of the intergalactic medium—the hydrogen between the galaxies,” says Adrian Liu, a Hubble fellow at UC Berkeley. “This actually lets you, in principle, directly see reionization, [by seeing how] it affects the intergalactic medium.”

    By locating where the universe is ionized and where it is not, astronomers can create a map of how neutral hydrogen is distributed in the early universe. “If galaxies are doing it, then you would have ionized bubbles [around them]. If it is dark matter—dark matter is everywhere—so you’re ionizing everywhere, rather than having bubbles of ionizing gas,” says Steven Furlanetto, a theoretical astrophysicist at the University of California, Los Angeles.

    Physicists can also learn about sources of reionization by studying the cosmic microwave background, or CMB.

    When an atom is ionized, the electron that is released scatters and disrupts the CMB. Physicists can use this information to determine when reionization happened and put constraints on how many photons were needed to complete the process.

    For example, physicists reported last year that data released from the Planck satellite was able to lower its estimate of how much ionization was caused by sources other than galaxies. “Just because you could potentially explain it with star-forming galaxies, it doesn’t mean that something else isn’t lurking in the data,” Slatyer says. “We are hopefully going to get much better measurements of the reionization epoch using experiments like the 21-centimeter observations.”

    It is still too early to rule out alternative explanations for the sources of reionization, since astronomers are still at the beginning of uncovering this era in the history of our universe, Liu says. “I would say that one of the most fun things about working in this field is that we don’t know exactly what happened.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

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