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  • richardmitnick 1:30 pm on December 17, 2014 Permalink | Reply
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    From Symmetry: “LHC filled with liquid helium” 

    Symmetry

    December 17, 2014
    Sarah Charley

    The Large Hadron Collider is now cooled to nearly its operational temperature.

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

    The Large Hadron Collider isn’t just a cool particle accelerator. It’s the coldest.

    Last week the cryogenics team at CERN finished filling the eight curved sections of the LHC with liquid helium. The LHC ring is now cooled to below 4 kelvin (minus 452 degrees Fahrenheit).

    ice
    Photo by Maximilien Brice, CERN

    This cool-down is an important milestone in preparing the LHC for its spring 2015 restart, after which physicists plan to use it to produce the highest-energy particle collisions ever achieved on Earth.

    “We are delighted that the LHC is now cold again,” says Beate Heinemann, the deputy leader of the ATLAS experiment and a physicist with the University of California, Berkeley, and Lawrence Berkeley National Laboratory. “We are getting very excited about the high-energy run starting in spring next year, which will open the possibility of finding new particles which were just out of reach.”

    The LHC uses more than 1000 superconducting dipole magnets to bend high-energy particles around its circumference. These superconducting magnets are made from a special material that, when cooled close to absolute zero (minus 460 degrees Fahrenheit), can maintain a high electrical current with zero electrical resistance.

    “These magnets have to produce an extremely strong magnetic field to bend the particles, which are moving at very close to the speed of light,” says Mike Lamont, the head of LHC operations. “The magnets are powered with high electrical currents whenever beam is circulating. Room-temperature electromagnets would be unable to support the currents required.”

    To get the 16 miles of LHC magnets close to absolute zero, engineers slowly inject helium into a special cryogenic system surrounding the magnets and gradually reduce the temperature over the course of several months at a rate of one sector cooled per month. As the temperature drops, the helium becomes liquid and acts as a cold shell to keep the magnets at their operational temperature.

    “Helium is a special element because it only becomes a liquid below 5 kelvin,” says Laurent Tavian, the group leader of the CERN cryogenics team. “It is also the only element which is not solid at very low temperature, and it is naturally inert—meaning we can easily store it and never have to worry about it becoming flammable.”

    The first sector cool-down started in May 2014. Engineers first pre-cooled the helium using 9000 metric tons of liquid nitrogen. After the pre-cooling, engineers injected the helium into the accelerator.

    “Filling the entire accelerator requires 130 metric tons of helium, which we received from our supplier at a rate of around one truckload every week,” Tavian says.

    In January CERN engineers plan to have the entire accelerator cooled to its nominal operating temperature of 1.9 kelvin (minus 456 degrees Fahrenheit), colder than outer space.

    See the full article here.

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  • richardmitnick 1:29 pm on December 11, 2014 Permalink | Reply
    Tags: , INFN Gran Sasso, , Symmetry Magazine   

    From Symmetry: “ICARUS hits the road” 

    Symmetry

    December 11, 2014
    Kathryn Jepsen

    A giant neutrino detector is traveling by truck from the Italian Gran Sasso laboratories to CERN to get ready for a new life.

    On Tuesday night a 600-metric-tonne particle detector became the world’s largest neutrino experiment currently on an international road trip.

    The ICARUS T600 neutrino detector—the world’s largest liquid-argon neutrino experiment—is on its way from the INFN Gran Sasso laboratories in Italy to European research center CERN on the border of France and Switzerland. Once it arrives at CERN, it will undergo upgrades to prepare it for a second life.

    INFN Gran Sasso ICARUS
    INFN Gran Sasso ICARUS T600
    INFN Gran Sasso ICARUS T600

    “ICARUS is presently the state-of-the-art technology,” says Nobel Laureate Carlo Rubbia, the leader of the ICARUS experiment. “Its success has demonstrated the enormous potentials of this detector technique… Most of the ICARUS developments have become part of the liquid-argon technology that is now being used is most of the other, more recent projects.”

    Since 2010, the ICARUS experiment has studied neutrinos streaming about 450 miles straight through the Earth from CERN to Gran Sasso. Neutrinos come in three types, called flavors, and they switch flavors as they travel. The ICARUS experiment was set up to study those flavor oscillations. Its detector, which works like a huge, three-dimensional camera that visualizes subatomic events, has recorded several thousand neutrino interactions.

    Scientists see more experiments in the detector’s future, possibly using a powerful beam of neutrinos already in operation at Fermi National Accelerator Laboratory near Chicago.

    The detector is 6 meters wide, 18 meters long and 4 meters high. When in operation, it is filled with ultra-pure liquid argon and about 52,000 wires, which collect signals from particles and can reconstruct 3-D images of a what happens when a neutrino knocks an electron off of an atom of argon.

    To prepare the sensitive detector for transport, workers moved its inner chamber on sleds into a shipping container, says Chiara Zarra, the ICARUS movement and transportation coordinator. But getting the experiment out of its home was a challenge, she says. The laboratory layout had changed since ICARUS was first installed, and there were multiple other experiments to maneuver through. A team from CERN helped with planning by creating 3-D simulations of the operation.

    t
    Over the course of about a week, the detector will travel on a special equipment transporter through Rome, Genoa and Turin. After that it will cross the Alps through the Mont Blanc tunnel on its way to Geneva.
    Courtesy of: INFN

    See the full article here.

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  • richardmitnick 5:22 pm on December 10, 2014 Permalink | Reply
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    From Symmetry: “First LHC magnets prepped for restart” 

    Symmetry

    December 10, 2014
    Sarah Charley

    A first set of superconducting magnets has passed the test and is ready for the Large Hadron Collider to restart in spring.

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

    This week, one-eighth of the LHC dipole magnets reached the energy they’ll need to operate in 2015.

    m
    Photo by Anna Pantelia, CERN

    Engineers at CERN powered 154 superconducting magnets to a current of around 11,000 amps. This is about a thousand times greater than an average household appliance and is required to make the 50-foot-long electromagnets powerful enough to bend particles moving close to the speed of light around the curves of the LHC.

    “Over the summer we plan to ramp up the LHC to the highest energy ever achieved in a collider experiment,” says Mirko Pojer, an LHC engineer-in-charge and co-leader of the magnet re-commissioning team. “But before we do that, we need to make sure that our magnets are primed and ready for the job.”

    From 2010 to 2013, the LHC produced proton-proton collisions of up to 8 trillion electronvolts. This first run allowed physicist to probe a previously inaccessible realm of physics and discover the Higgs boson. But the LHC is designed to operate at even higher energies, and physicists are eager to see what might be hiding just out of reach.

    “We had a very successful first run and made a huge discovery, but we want to keep probing,” says Greg Rakness, a UCLA researcher and CMS run coordinator. “The exciting thing about the next run is that we have no idea what we could find, because we have never been able to access this energy realm before.”

    To prepare the LHC for 13 trillion electronvolt proton-proton collisions, CERN shut down the machine for almost two years for upgrades and repairs. This involved reinforcing almost 1700 magnet interconnections, including more than 10,000 superconducting splices.

    Now that that work is completed, engineers are putting the LHC magnets through a strenuous training program. Like Rocky Balboa prepping for a big fight, the magnets must be pushed repeatedly to the limits of their operation. This will prime them for the strenuous running conditions of the LHC.

    The LHC magnets are superconducting, which means that when they are cooled down, current passes through them with zero electrical resistance. During powering, current is gradually increased in the magnetic coils, which sometimes generates tiny movements in the superconductor. These movements create friction, which in turn locally heats up the superconductor and makes it quench—or suddenly return to a non-superconducting state. When this occurs, the circuit is switched off and its energy is absorbed by huge resistors.

    “By purposefully making the magnets quench, we can literally ‘shake out’ any unresolved tension in the coils and prep the magnets to hold a high current without losing their superconducting superpowers,” says Matteo Solfaroli, an LHC engineer-in-charge and co-leader of the commissioning team. “This is a necessary part of prepping the accelerator for the restart so that the magnets don’t quench while we are running the beam.”

    The magnets in all the other sectors will undergo similar training before being ready for operation. Many other tests will follow before beams can circulate in the LHC once more, next spring.

    See the full article here.

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  • richardmitnick 2:57 pm on December 5, 2014 Permalink | Reply
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    From Symmetry: “Einstein papers go digital” 

    Symmetry

    December 05, 2014
    Kathryn Jepsen

    In a single year of his 20s, Albert Einstein published papers explaining the photoelectric effect, Brownian motion, special relativity and E=mc2. In his 30s, he lived through World War I and came up with the theory of general relativity. In his early 40s, he won a Nobel Prize.

    ae

    Today a new window opened into this early period of Einstein’s life.

    Princeton University Press, working with The Einstein Papers Project hosted at Caltech, has made freely available online more than 5000 documents from Einstein’s first 44 years.

    The annotated documents are available in their original language and translated into English. They include his scientific papers but also professional letters to and from colleagues and personal notes to and from friends and family between the years 1879 to 1923.

    “It’s one of the most exciting periods in modern science,” says Professor Diana Kormos-Buchwald, director of the Einstein Papers Project. “It was probably one of the most vibrant periods to be a scientist.”

    The field of physics was different then, Kormos-Buchwald says. In 1900, there were only about 1000 physicists on the planet. Today that number makes up only about a third of a single experiment at the Large Hadron Collider.

    Those physicists wrote to one another. But it’s not just the professional letters that allow one to follow Einstein’s thinking over the years, Kormos-Buchwald says.

    “Einstein wrote a lot about his work in his private correspondence,” she says. “If you only look at his letters with [Neils] Bohr and [Erwin] Schrodinger and [Max] Planck, you don’t get an idea of his day-to-day activities and his impressions of other people.”

    Kormos-Buchwald is especially fond of the long-lasting correspondence between Einstein and fellow theoretical physicist Paul Ehrenfest, who made contributions to the field of statistical mechanics and its relationship to quantum mechanics.

    “The two would switch easily between important scientific topics and personal ones, within one paragraph,” she says. “Very few people wrote this way to Einstein.”

    In one May 1912 letter, Ehrenfest wrote to Einstein of a decision to take a position in Munich after hoping to find one in Zurich: “I must confess that I had lost myself very deeply in the dream of being able to work near you, and that it has by no means been easy for me to cut myself loose from this thought.”

    He begins the very next sentence, “Regarding your remark about the Ritz-Doppler effect, I have the following to say…”

    Similarly, Einstein ends a letter inviting Ehrenfest to visit with the unrelated post-script: “P.S. Abraham’s theory of gravitation is totally untenable.”

    The papers give insight into Einstein’s scientific ideas but also other details of his life.

    In 1895, his father Hermann Einstein wrote in a letter to Jost Winteler, family friend and the head of the special high school Einstein attended in Zurich: “I am taking the liberty of returning the enclosed school report; to be sure, not all of its parts fulfill my wishes and expectations, but with Albert I got used a long time ago to finding not-so-good grades along with very good ones, and I am therefore not disconsolate about them.”

    Other documents of interest include a high school French essay Einstein wrote about his future plans (“young people especially like to contemplate bold projects”); a letter to his eventual first wife Mileva Maric celebrating the birth of their daughter Lieserl; Einstein’s first job offer; a telegram informing him he had won the Nobel Prize; and a letter to physicist Max Planck about receiving death threats from an increasingly hostile Berlin.

    Also available are Einstein’s paper on the photoelectric effect (for which he won the Nobel Prize); his paper on special relativity; his paper on general relativity; and four lectures on relativity Einstein famously delivered at Princeton on his first trip to the United States.

    This is only the first installment. Princeton University Press and the Einstein Papers Project plan to continue the project, adding new documents from their collection of about 30,000.

    See the full article here.

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  • richardmitnick 2:09 pm on December 2, 2014 Permalink | Reply
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    From Symmetry: “Muon versus the volcano” 

    Symmetry

    December 02, 2014
    Glenn Roberts Jr.

    Particles produced by cosmic rays enter volcanoes and live to tell the tale.

    Exploring the innards of Mount Vesuvius, the active volcano that once destroyed the ancient town of Pompeii, sounds like a risky endeavor. Unless you’re a muon.

    Scientists from institutions in Italy, France, Japan and the United States are using muons, the big brothers of electrons, to study the structure of Mount Vesuvius and other volcanoes in Italy, France, Japan and the Caribbean.

    Muons are particles produced in the constant shower of cosmic rays that interact with Earth’s atmosphere. If you hold out your hand, a muon will pass through it about once per second—and it will keep on going. The highest-energy muons can travel more than a mile through solid rock.

    “[Studying volcanoes with muons] should help in giving information on how an eruption would develop,” says scientist Giulio Saracino of INFN, Italy’s National Institute for Nuclear Physics, who is a member of the MU-RAY experiment at Mount Vesuvius. Researchers say the measurements could be used in conjunction with other methods to identify areas of greatest risk based on concentrations of lower-density rock susceptible to fracture in an eruption.

    In May 2013 MU-RAY scientists took a 1-square-meter prototype of a muon detector to a research station at the foot of Mount Vesuvius for a technical run. The detector is an advanced version of technology used in physics experiments at Fermi National Accelerator Laboratory and Gran Sasso National Laboratory. A handful of researchers, assisted by local high school students in the delivery and setup of equipment, completed the installation in about three workdays.

    m
    Courtesy of: MU-RAY collaboration

    Vesuvius is considered the most dangerous volcano on the planet, owing to its well-documented history of incredibly explosive eruptions and the half a million people living in its high-risk “red zone.”

    “If you live in Naples, you feel the presence of Mount Vesuvius as a sleeping giant that could suddenly awaken with tremendous effects,” says MU-RAY scientist Paolo Strolin, also of INFN. “A better understanding of its dangers is worth any challenge.”

    Geologists and volcanologists have amassed an array of tools to study aspects of volcanoes: satellites, seismic readers, laser surveying kits and equipment to monitor gases, gravity fluctuations and electrical and electromagnetic signals.

    Nobel Laureate Luis Alvarez of the University of California, Berkeley, pioneered the muon radiography technique used on volcanoes in the late 1960s when he used it to look for hidden chambers in the Great Pyramid of Chephren in Egypt. In 2007, scientists used it to image the interior of an active volcano, Japan’s Mount Asama, for the first time.

    “This is quite unique compared to other survey methods,” says Valentin Niess of CNRS, the French National Center for Scientific Research, and a member of the TOMUVOL collaboration, a group of about 30 scientists studying the long-dormant Puy de Dôme in France.

    Volcano researchers hope using muons will pay off by helping to identify areas prone to particular risk from eruptions, says TOMUVOL scientist Cristina Cârloganu of CNRS: “That could significantly reduce the volcanic hazards.”

    See the full article here.

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  • richardmitnick 7:25 pm on November 24, 2014 Permalink | Reply
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    From Symmetry: “Creating a spark” 

    Symmetry

    November 24, 2014

    ec
    Photo by Fabricio Sousa, SLAC
    Eric Colby, US Department of Energy, Office of High Energy Physics

    A principle of 18th century mechanics holds that if a physical system is symmetric in some way, then there is a conservation law associated with the symmetry. Mathematician Emmy Noether generalized this principle in a proof in 1918. Her theorem, in turn, has provided a very powerful tool in physics, helping to describe the conservation of energy and momentum.

    Science has a long history of creativity generated through this kind of collaboration between fields.

    In the process of sharing ideas, researchers expose assumptions, discern how to clearly express concepts and discover new connections between them. These connections can be the sparks of creativity that generate entirely new ideas.

    In 1895, physicist Wilhelm Roentgen discovered X-rays while studying the effects of sending an electric current through low-pressure gas. Within a year, doctors made the first attempts to use them to treat cancer, first stomach cancer in France and later breast cancer in America. Today, millions of cancer patients’ lives are saved each year with clinical X-ray machines.

    A more recent example of collaboration between fields is the Web, originally developed as a way for high-energy physicists to share data. It was itself a product of scientific connection, between hypertext and Internet technologies.

    In only 20 years, it has transformed information flow, commerce, entertainment and telecommunication infrastructure.

    This connection transformed all of science. Before the Web, learning about progress in other fields meant visiting the library, making a telephone call or traveling to a conference. While such modest impediments never stopped interdisciplinary collaboration, they often served to limit opportunity.

    With the Web have come online journals and powerful tools that allow people to search for and instantly share information with anyone, anywhere, anytime. In less than a generation, a remarkable amount of the recorded history of scientific progress of the last roughly 3600 years has become instantly available to anyone with an Internet connection.

    Connections provide not only a source of creativity in science but also a way to accelerate science, both by opening up entirely new ways of formulating and testing theory and by providing direct applications of the fruits of basic R&D. The former opens new avenues for understanding our world. The latter provides applications of technologies outside their fields of origin. Both are vital.

    High-energy physics is actively working with other fields to jointly solve new problems. One example of this is the Accelerator Stewardship Program, which studies ways that particle accelerators can be used in energy and the environment, medicine, industry, national security and discovery science. Making accelerators that meet the cost, size and operating requirements of other applications requires pushing the technology in new directions. In the process we learn new ways to solve our own problems and produce benefits that are widely recognized and sought after. Other initiatives aim to strengthen intellectual connections between particle physics itself and other sciences.

    Working in concert with other fields, we will gain new ways of understanding the world around us.

    See the full article here.

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  • richardmitnick 2:29 pm on November 6, 2014 Permalink | Reply
    Tags: , , Astrostatistics, , , Symmetry Magazine   

    From Symmetry: “The rise of astrostatistics” 

    Symmetry

    November 04, 2014
    Lori Ann White

    Astrophysicists and cosmologists are turning to statisticians to help them analyze an ever-increasing deluge of data.

    graph
    Artwork by Sandbox Studio, Chicago with Kimberly Boustead

    In late 1801 the orbit of the newly discovered asteroid Ceres carried it behind the sun, and astronomers worried they had lost it forever. A young mathematical prodigy named Carl Friedrich Gauss developed a new statistical technique to find it. Called “least squares regression,” that technique is now a fundamental method of statistical analysis.

    For about 200 years after that, however, astronomers and statisticians had little to do with one another. But in the last decade or so, astronomy and statistics have finally begun to formalize a promising relationship. Together they are developing the new discipline of astrostatistics.

    Jogesh Babu, a Pennsylvania State professor and the director of the Penn State Center for Astrostatistics, remembers when the new age of astrostatistics dawned for him. Twenty-five years ago, when Babu’s focus was statistical theory, astronomy professor Eric Feigelson asked to meet with him to talk about a problem. At the end of the conversation, Babu says, “we realized we both speak English but we didn’t understand a word the other said.”

    To address that disconnect, the statistician and the astrophysicist organized a continuing series of conferences at Penn State. They also wrote a book, Astrostatistics, which effectively christened the new field. But collaborations between astrophysicists and statisticians remained small and scattered, only really starting to pick up in 2006, says Babu.

    “The development of statistical techniques useful to advanced astronomical research progressed very slowly, and until recently most all analyses had to be done by hand,” says statistician Joseph Hilbe, a statistics professor Arizona State University. Before the advent of computers with sufficient capacity to do the work, certain useful calculations could take statisticians weeks to months to complete, he said.

    In addition, says Tom Loredo, an astrostatistician at Cornell University, “astrophysicists are some of the more mathematically literate scientists, and we thought we could do it on our own.”

    Other fields had already embraced statistics. Statistics is vital to all branches of biology—especially epidemiology, medical research, and public health—and geology. In fact, in the 1990s Hilbe developed some of the first advanced statistical tools used to analyze Medicare data. Statisticians also contribute to the social sciences, economics, environmental and ecological sciences, and to the insurance and risk analysis industries.

    Slowly, though, astronomers began to realize that they might be able to benefit from the expert help of a statistician.

    “I believe the large surveys shocked astronomers with how much data there is,” Hilbe says. “The Sloan Digital Sky Survey [one of the first automated and digitized comprehensive astronomical sky surveys] told them they needed statistics.”

    Although he was aware of Babu’s and Feigelson’s nascent community, Hilbe decided to go bigger. He founded the International Statistical Institute’s Astrostatistics Interest Group, the first interest group or committee authorized by an astronomical or statistical association, in 2008. The formation of working groups within the American Astronomical Society and the International Astronomical Union followed in 2012. In the same year Hilbe was elected the first president of the newly formed International Astrostatistical Association.

    All told, about 700 scientists belong to the various groups, which have been gathered together under the umbrella of the Astrostatistics and Astroinformatics Portal, hosted by Penn State and with Feigelson and Hilbe as co-editors. The IAA also sponsors the new Cosmostatistics Consortium.

    One of the recently formed groups is the LSST Informatics and Statistical Science collaboration, organized in preparation for the Large Synoptic Survey Telescope, which, beginning in 2022, will photograph the entire southern sky every three days for 10 years. Babu and his collaborator Feigelson are members, as is Loredo.

    LSST Exterior
    LSST Telescope
    LSST

    “One of the virtues of big data is that it gives you access to rare events,” Loredo says. He likens it to sifting through the trillions of bytes of Large Hadron Collider data to find a handful of Higgs bosons.

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

    “Now that we have a billion galaxies, what are the rare events that we wouldn’t ever see in only a million galaxies? Studying those will require statistical methods that are as good with small data sets as with big data sets.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 3:18 pm on October 28, 2014 Permalink | Reply
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    From Symmetry: “Scientists mull potential gamma-ray study sites” 

    Symmetry

    October 28, 2014
    Kelen Tuttle

    An international panel is working to determine the two locations from which the Cherenkov Telescope Array will observe the gamma-ray sky.

    Cherenkov Telescope Array
    Cherenkov Telescope Array

    Somewhere in the Southern Hemisphere, about 100 state-of-the-art telescopes will dot the otherwise empty landscape for half a kilometer in every direction. Meanwhile, in the Northern Hemisphere, a swath of land a little over a third the size will house about 20 additional telescopes, every one of them pointing toward the heavens each night for a full-sky view of the most energetic—and enigmatic—processes in the universe.

    This is the plan for the Cherenkov Telescope Array Observatory, the world’s largest and most sensitive gamma-ray detector. The first of the two arrays is scheduled to begin taking data in 2016, with the other coming online in by 2020. At that point, CTA’s telescopes will observe gamma rays produced in some of the universe’s most violent events—everything from supernovas to supermassive black holes.

    Yet where exactly the telescopes will be built remains to be seen.

    Scientists representing the 29-country CTA consortium met last week to discuss the next steps toward narrowing down potential sites in the Northern Hemisphere: two in the United States (both in Arizona) and two others in Mexico and the Canary Islands. Although details from that meeting remain confidential, the CTA resource board is expected to begin negotiations with the potential host countries within the next few months. That will be the final step before the board makes its decision, says Rene Ong, co-spokesperson of CTA and a professor of physics and astronomy at UCLA.

    “Whichever site it goes to, it will be very important in that country,” Ong says. “It’s a major facility, and it will bring with it a huge amount of intellectual capital.”

    Site selection for the Southern Hemisphere is a bit further along. Last April, the CTA resource board narrowed down that list to two potential sites: one in Southern Namibia and one in Northern Chile. The board is now in the process of choosing between the sites based on factors including weather, operating costs, existing infrastructure like roads and utilities, and host country contributions. A final decision is expected soon.

    sites
    Artwork by: Sandbox Studio, Chicago

    “The consortium went through an exhaustive 3-year process of examining the potential sites, and all of the sites now being considered will deliver on the science,” says CTA Project Scientist Jim Hinton, a professor of physics and astronomy at the University of Leicester. “We’re happy that we have so many really good potential sites. If we reach an impasse with one, we can still keep moving forward with the others.”

    Scientists do not completely understand how high-energy gamma rays are created. Previous studies suggest that they stream from jets of plasma pouring out of enormous black holes, supernovae and other extreme environments, but the processes that create the rays—as well as the harsh environments where they are produced—remain mysterious.

    To reach its goal of better understanding high-energy gamma rays, CTA needs to select two sites—one in the Northern Hemisphere and one in the Southern Hemisphere—to see the widest possible swath of sky. In addition, the view from the two sites will overlap just enough to allow experimenters to better calibrate their instruments, reducing error and ensuring accurate measurements.

    With 10 times the sensitivity of previous experiments, CTA will fill in the many blank regions in our gamma-ray map of the universe. Gamma-rays with energies up to 100 gigaelectronvolts have already been mapped by the Fermi Gamma-ray Space Telescope and others; CTA will cover energies up to 100,000 gigaelectronvolts. It will survey more of the sky than any previous such experiment and be significantly better at determining the origin of each gamma ray, allowing researchers to finally understand the astrophysical processes that produce these energetic rays.

    NASA Fermi Telescope
    NASA/Fermi

    CTA may also offer insight into dark matter. If a dark matter particle were to naturally decay or interact with its antimatter partner to release a flash of energy, the telescope array could theoretically detect that flash. In fact, CTA is one of very few instruments that could see such flashes with energies above 100 gigaelectronvolts.

    “I’m optimistic that we’ll see something totally new and unexpected,” Ong says. “Obviously I can’t tell you what it will be—otherwise it wouldn’t be unexpected—but history tells us that when you make a big step forward in capability, you tend to see something totally new. And that’s just what we’re doing here.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 1:51 pm on October 15, 2014 Permalink | Reply
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    From Symmetry: “Top quark still raising questions” 

    Symmetry

    October 15, 2014
    Troy Rummler

    Why are scientists still interested in the heaviest fundamental particle nearly 20 years after its discovery?

    “What happens to a quark deferred?” the poet Langston Hughes may have asked, had he been a physicist. If scientists lost interest in a particle after its discovery, much of what it could show us about the universe would remain hidden. A niche of scientists, therefore, stay dedicated to intimately understanding its properties.

    tq
    Photo by Reidar Hahn, Fermilab

    Case in point: Top 2014, an annual workshop on top quark physics, recently convened in Cannes, France, to address the latest questions and scientific results surrounding the heavyweight particle discovered in 1995 (early top quark event pictured above).

    Top and Higgs: a dynamic duo?

    A major question addressed at the workshop, held from September 29 to October 3, was whether top quarks have a special connection with Higgs bosons. The two particles, weighing in at about 173 and 125 billion electronvolts, respectively, dwarf other fundamental particles (the bottom quark, for example, has a mass of about 4 billion electronvolts and a whole proton sits at just below 1 billion electronvolts).

    Prevailing theory dictates that particles gain mass through interactions with the Higgs field, so why do top quarks interact so much more with the Higgs than do any other known particles?

    Direct measurements of top-Higgs interactions depend on recording collisions that produce the two side-by-side. This hasn’t happened yet at high enough rates to be seen; these events theoretically require higher energies than the Tevatron or even the LHC’s initial run could supply. But scientists are hopeful for results from the next run at the LHC.

    “We are already seeing a few tantalizing hints,” says Martijn Mulders, staff scientist at CERN. “After a year of data-taking at the higher energy, we expect to see a clear signal.” No one knows for sure until it happens, though, so Mulders and the rest of the top quark community are waiting anxiously.

    A sensitive probe to new physics

    Top and anti-top quark production at colliders, measured very precisely, started to reveal some deviations from expected values. But in the last year, theorists have responded by calculating an unprecedented layer of mathematical corrections, which refined the expectation and promise to realigned the slightly rogue numbers.

    Precision is an important, ongoing effort. If researchers aren’t able to reconcile such deviations, the logical conclusion is that the difference represents something they don’t know about—new particles, new interactions, new physics beyond the standard model.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The challenge of extremely precise measurements can also drive the formation of new research alliances. Earlier this year, the first Fermilab-CERN joint announcement of collaborative results set a world standard for the mass of the top quark.

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

    Such accuracy hones methods applied to other questions in physics, too, the same way that research on W bosons, discovered in 1983, led to the methods Mulders began using to measure the top quark mass in 2005. In fact, top quark production is now so well controlled that it has become a tool itself to study detectors.
    Forward-backward synergy

    With the upcoming restart in 2015, the LHC will produce millions of top quarks, giving researchers troves of data to further physics. But scientists will still need to factor in the background noise and data-skewing inherent in the instruments themselves, called systematic uncertainty.

    “The CDF and DZero experiments at the Tevatron are mature,” says Andreas Jung, senior postdoc at Fermilab. “It’s shut down, so the understanding of the detectors is very good, and thus the control of systematic uncertainties is also very good.”

    FNALTevatron
    Tevatron at Fermilab

    FNAL CDF
    CDF experiment at the Tevatron

    FNAL DZero
    DZero at the Tevatron

    Jung has been combing through the old data with his colleagues and publishing new results, even though the Tevatron hasn’t collided particles since 2011. The two labs combined their respective strengths to produce their joint results, but scientists still have much to learn about the top quark, and a new arsenal of tools to accomplish it.

    “DZero published a paper in Nature in 2004 about the measurement of the top quark mass that was based on 22 events,” Mulders says. “And now we are working with millions of events. It’s incredible to see how things have evolved over the years.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 1:38 pm on October 3, 2014 Permalink | Reply
    Tags: , , , , LIGO, , Symmetry Magazine   

    From Symmetry: “To catch a gravitational wave” 

    Symmetry

    October 03, 2014
    Jessica Orwig

    Advanced LIGO, designed to detect gravitational waves, will eventually be 1000 times more powerful than its predecessor.

    Thirty years ago, a professor and a student with access to a radiotelescope in Puerto Rico made the first discovery of a binary pulsar: a cosmic dance between a pair of small, dense, rapidly rotating neutron stars, called pulsars, in orbit around one another.

    Scientists noticed that their do-si-do was gradually speeding up, which served as indirect evidence for a phenomenon predicted by Albert Einstein called gravitational waves.

    Today in Livingston, Louisiana, and Hanford, Washington, scientists are preparing the next stage of a pair of experiments that they hope will detect gravitational waves directly within the next five years. They’re called the Laser Interferometer Gravitational-Wave Observatory, or LIGO.

    Distorting the fabric of spacetime

    Gravitational waves are faint ripples in the fabric of spacetime thought to propagate throughout the universe. According to the theory of general relativity, objects with mass—and therefore gravitational pull—should emit these waves whenever they accelerate. Scientists think the stars in the binary pulsar that Russell Hulse and Joseph Taylor discovered in 1974 are being pulled closer and closer together because they are losing miniscule amounts of energy each year through the emission of gravitational waves.

    If a gravitational wave from a binary pulsar passes through Livingston or Hanford, the LIGO experiments will be waiting. In summer 2015, scientists will begin collecting data with Advanced LIGO, the next stage of LIGO, with more powerful lasers and attuned sensors. Advanced LIGO will by 2020 become 1000 times more likely than its predecessor to detect gravitational waves.

    “We’ll be able to see well beyond the local group, up to 300 megaparsecs away, which includes thousands of galaxies,” says Mario Diaz, a professor at the University of Texas at Brownsville and director of the Center for Gravitational Wave Astronomy. ”That’s the reason why pretty much everyone agrees if gravitational waves exist then Advanced LIGO has to see them.”

    Eventually joining LIGO in its attempt to catch a gravitational wave will be the VIRGO Interferometer at the European Gravitational Observatory in Italy and the Kamioka Gravitational Wave Detector at the Kamioka Mine in Japan. VIRGO started its search in 2007 and is currently undergoing upgrades. KAGRA is expected to begin operations in 2018. By the time KAGRA comes online, all three instruments should have similar levels of sensitivity.

    Advanced LIGO

    LIGO is made up of two identical laser interferometers, one in Louisiana and the other in Washington.

    ligo
    Courtesy of LIGO Laboratory

    At a laser interferometer, scientists take a single, powerful laser beam and split it in two. The two beams then travel down two equally long tunnels. At the end of each tunnel, each beam hits a mirror and reflects back.

    The tunnels are perpendicular to one another, creating a giant “L.” Because of this, the reflected beams return to the same spot and cancel each other out. That is, unless a gravitational wave intervenes.

    inter
    The light path through a Michelson interferometer. The two light rays with a common source combine at the half-silvered mirror to reach the detector. They may either interfere constructively (strengthening in intensity) if their light waves arrive in phase, or interfere destructively (weakening in intensity) if they arrive out of phase, depending on the exact distances between the three mirrors.

    If a gravitational wave passes through, it will distort the fabric of spacetime in which the observatory sits. This will warp the physical distance between the mirrors, giving one of the laser beams the advantage in reaching its final destination first. Because the beams will not cancel one another out, they will produce a signal in the detector.

    Advanced LIGO isn’t any bigger than LIGO, says Fred Raab of Caltech, head of the LIGO Hanford Observatory. Scientists are transforming the experiment from the inside. “That was part of the strategy for building LIGO… it’s the upgrades to technology that really counts.”

    The impressive part, says Gabriela Gonzalez, LIGO spokesperson and professor at Louisiana State University, is the miniscule size of the change in distance and the technology’s capability to detect it.

    “The [tunnels] are 4 kilometers long, and we have sensitivities to about 10-18 meters,” Gonzalez says. “We can tell how 4 kilometers one way differs from 4 kilometers the other way by a change that is a thousandth the size of a proton diameter.”

    Scientists built two identical machines 1865 miles apart because the wavelength of the gravitational waves they’re looking for should be about that long; if they measure the same signal in both detectors simultaneously, it will be a good indication that the signature is genuine.

    One of the new features of Advanced LIGO will be an additional mirror that will enable scientists to enhance sensitivity to different frequencies of gravitational waves. With different frequencies come different levels of spacetime distortion and hence different changes in the distance between the two mirrors. The different signals will tell scientists something about the properties of gravitational waves and their sources.

    “The extra mirror allows us to apply a boost in sensitivity to a smaller range of frequencies in the search band,” Raab says. “It works kind of like the treble/bass adjustment in your car stereo. You still hear the music, but with different frequencies enhanced.”

    Straight to the source

    Scientists at Advanced LIGO would like to identify the sources of gravitational waves.

    They most likely come from binary neutron stars like the one Hulse and Taylor discovered. But they could also originate in systems that right now exist only in theory, such as black hole binaries and neutron star-black hole binary systems.

    Christopher Berry, a research fellow at the University of Birmingham, is part of a team that is designing a way to quickly estimate where in the sky the source of a gravitational wave might originate in order to share that information with astronomers around the world, who could take a closer look.

    “You can analyze the data to determine quantities like mass, orientation and location,” he says. “One of the things we want to do with parameter estimation is quickly estimate where in the sky a source came from and then tell people with telescopes to point there.”

    Gravitational waves could also come from the same systems that produce gamma-ray bursts, the brightest known electromagnetic events in the universe. Scientists think that gamma-ray bursts may come from merging binary neutron stars, a hypothesis LIGO could investigate.

    Determining a link between gamma-ray bursts and binary neutron stars would be one outstanding achievement for Advanced LIGO, but the future observatory has potential for more, Berry says.

    “We can see inside the sun using neutrinos, and gravitational waves are yet another way to look at the universe,” he says. “We can make discoveries we weren’t expecting.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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