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  • richardmitnick 2:57 pm on March 20, 2018 Permalink | Reply
    Tags: , BaBar experiment at SLAC National Accelerator Laboratory, , , KEK Belle detector at the High Energy Accelerator Research Organisation (KEK) in Tsukuba Ibaraki Prefecture Japan, LHCb experiment operating at CERN, Symmetry Magazine, The bottom quark may lead physicists on a path to new discoveries   

    From Symmetry: “Starting from the bottom” 

    Symmetry Mag


    Sarah Charley

    The bottom quark may lead physicists on a path to new discoveries.

    Bottom Quark

    The Standard Model of particle physics has been developed over several decades to describe the properties and interactions of elementary particles.

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

    Standard Model of Particle Physics from Symmetry Magazine

    The model has been extended and modified with new information, but time and again, experiments have bolstered physicists’ confidence in it.

    And yet, scientists know that the model is incomplete. It cannot predict the masses of certain particles, nor can it explain what most of the universe is made of. To discover what lies beyond the Standard Model, scientists are searching for its flaws—untenable assumptions and phenomena that it does not predict. A growing set of results from the study of bottom quarks may offer physicists a welcome chance to do just that.

    “The Standard Model is very rigid,” says Marco Nardecchia, a theorist from Italy, “so the best way to break it is by precisely testing its predictions.”

    The Standard Model makes many detailed predictions about how particles should interact or decay. Some subatomic processes are so complicated that even theorists aren’t quite sure exactly how they are supposed to work. For one: quarks—the constituents that make up elementary particles—should interact in the same way with the electron as with its heavier cousins, the muon or tau lepton.

    There are six types of quarks. The lightest and most common are the up and down quarks, which together make up protons and neutrons. Particles carrying a bottom quark—which is much heavier—are short-lived. In their decays, the bottom quark transitions into a lighter quark, preferentially a charm quark and rarely an up quark, forming another known particle.

    The remaining energy is carried by a charged lepton: an electron, a muon or a tau, each accompanied by its associated neutrino. According to the Standard Model, the rates of producing electrons, muons and taus differ only due to the very different masses of these three charged leptons. (The tau mass, for example, exceeds the electron mass by a factor of about 3500.)

    “These predictions are straightforward and precise,” says Vera Lüth, a scientist on the Babar experiment, “which is why we decided to pursue these measurements in the first place.”


    Scientists working on three different experiments are testing these predictions by examining specific decays of particles that carry a bottom quark.

    The first hint of an unexpected tau enhancement appeared in 2012 at the BaBar experiment at SLAC National Accelerator Laboratory, which studied close to 500 million events produced in electron-position collisions, and reconstructed less than 2000 decays involving taus. In 2015, the Belle experiment in Japan reported a similar enhancement in the tau rate in data collected from electron-position collisions at the same energy.

    KEK Belle detector, at the High Energy Accelerator Research Organisation (KEK) in Tsukuba, Ibaraki Prefecture, Japan

    KEK Belle 2 detector

    “A friend working on another experiment was sure that we had done something wrong,” Lüth says. “Then they observed the same effect.”

    In 2015, scientists working on the LHCb experiment operating at CERN saw signs of the same phenomenon in very large samples of proton-proton collisions at much higher energy and collision rates.

    CERN/LHCb detector

    CERN LHCb chamber, LHC

    “All these results point in the same direction,” says Hassan Jawahery, a professor at the University of Maryland working on LHCb. “That’s what puzzles everyone.”

    On their own, these individual results have a significance below the level that would raise an eyebrow. But together, they are “intriguing,” according to Tom Browder, the spokesperson of the Belle experiment and its successor, Belle II. “We are pretty sure that something new is out there. Proving even a tiny deviation from the Standard Model could lead to a revolution in our field.”

    The results accumulated so far have already inspired theorists to speculate about what kind of new physics processes might cause these enhancements.

    Some theories suggest that perhaps there is a yet undiscovered charged Higgs boson which favors the heavy tau over the much lighter muon and electron. Other models predict the existence of at least one new particle outside the Standard Model. “We may need something which interacts with quarks and leptons simultaneously,” Nardecchia says.

    Scientists won’t know what’s happening without further study, and gathering enough data to allow more detailed and precice studies will be a crucial step toward to find out.

    Scientists at the LHCb experiment are only at the beginning of this study. They plan to analyze about four times as many events in the next few years. They hope to complete new and updated measurements by this summer. The LHC accelerator complex program foresees major upgrades that will enlarge the experiments’ datasets over the next decade. In parallel, Belle II is scheduled to start collecting data in 2019 and is expected to record enough to shed light on this query in a few years.

    Physicists around the globe are eagerly waiting to compare notes.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 5:35 pm on March 6, 2018 Permalink | Reply
    Tags: , fields, , , Subatomic Smackdown, Symmetry Magazine   

    From Symmetry: “Subatomic Smackdown” 

    Symmetry Mag


    Kristen Coyne, National High Magnetic Field Laboratory


    When it comes to talent, versatility and the power to change the world, which atomic particle is the champ? Read what our four contenders have to say—then you decide.

    Physics fans, are you ready to rumble?

    Of course you are — and you’ve come to the right place. In the text that follows, you will have a ringside seat to perhaps the most anticipated skirmish in science history, as four atomic adversaries duke it out for the coveted title of Most Awesome Subatomic Particle of the Millennium.

    More rousing than the Rumble in the Jungle, more chilling than the Thrilla in Manila, we present to you, ladies and gentlemen, the (drumroll, please) Subatomic Smackdown.

    There will be no messy blood, sweat or other bodily fluids involved in this brainy battle. This is a war of words, ideas and wit based in science, from which one, and only one, of these four deserving combatants will emerge as victor. Introducing:

    In the blue corner, championed by CERN (the European Organization for Nuclear Research) near Geneva, Switzerland, and weighing in at 938.27231 megaelectronvolts (MeV), is the proton.

    In the red corner, supported by SLAC National Accelerator Laboratory in Menlo Park, California, USA, and weighing in at—well, nothing, really—is the photon.

    In the purple corner, championed by the National High Magnetic Field Laboratory in Tallahassee, Florida, USA, and weighing in at 0.51099906 MeV, is the electron.

    Finally, in the green corner, rooted on by the Institute for Quantum Matter at Johns Hopkins University in Baltimore, Maryland, USA, and weighing in at 939.56563 MeV, is the neutron.

    This epic physics feud will take place over four rounds, as each challenger (with a little help from their supporters) will argue why it, and it alone, deserves to hold the title of Most Awesome Subatomic Particle.

    So … electronvolt for electronvolt, which particle packs the most impressive punch? Read on, award points as you go, then weigh in on who you believe emerges as champion of this quantum quarrel.

    Round 1: The Proton
    Pay heed to this smashing subatomic celebrity, used in medicine and to produce neutrinos, antiprotons and, of course, the God particle.
    Round 2: The Photon
    Lighter than a butterfly, faster than a bee (by far) — no other particle can compete with me!
    Round 3: The Electron
    It might look like wizardry, but racking up a shelf of Nobel Prizes is all skill, ingenuity and inherent greatness.
    Round 4: The Neutron
    We’re neutral, not unbiased: Revealing science secrets as we scatter, neutrons are worth our weight in the gold we create.

    [See the full article for the complete story of this epic battle played out.]

    So … who wins the Subatomic Smackdown?
    We’re moving the final round out of the ring and into the social sphere. Which particles will go down for the count and which one will take the prize? You decide.
    On March 30, follow the blow-by-blow on Twitter at #SubatomicSmackdown and join a corner to support your favorite particle. But remember: We want a good clean fight, so let’s keep those tweets above the belt, everyone.

    Tally your points and submit your scorecard on Smackdown Day via a Twitter poll hosted by @NationalMagLab. The champion will be selected by majority decision.

    Check out our printable poster
    for the Subatomic Smackdown.

    Editor’s Note: Subatomic Smackdown is a co-production of Symmetry magazine and fields magazine, a publication about high magnetic field research produced at the National High Magnetic Field Laboratory.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 2:56 pm on March 4, 2018 Permalink | Reply
    Tags: , , , , , , , , Symmetry Magazine   

    From Symmetry: “At LIGO, three’s a trend” 

    Symmetry Mag

    Kathryn Jepsen

    The third detection of gravitational waves from merging black holes provides a new test of the theory of general relativity.

    Aurore Simonnet, LIGO/Caltech/MIT/Sonoma State
    For the third time, the LIGO and Virgo collaborations have announced directly detecting the merger of black holes many times the mass of our sun. In the process, they put general relativity to the test.

    On January 4, the twin detectors of the Laser Interferometer Gravitational-Wave Observatory stretched and squeezed ever so slightly, breaking the symmetry between the motions of two sets of laser beams.

    This barely perceptible shiver, lasting a fraction of a second, was the consequence of a catastrophic event: About 3 billion light-years away, a pair of spinning black holes with a combined mass about 49 times that of our sun sank together into a single entity.

    UC Santa Cruz

    UC Santa Cruz


    A UC Santa Cruz special report

    Tim Stephens

    Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.


    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.

    A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.


    It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

    A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

    Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

    According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.


    Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

    Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

    The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

    “This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”


    Neutron stars
    A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

    “We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

    David Coulter, graduate student

    The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

    “I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

    “Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

    Charles Kilpatrick, postdoctoral scholar

    Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

    Ariadna Murguia-Berthier, graduate student

    “In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

    At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

    Matthew Siebert, graduate student

    “It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

    Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

    It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

    César Rojas Bravo, graduate student

    Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

    Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

    Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

    Yen-Chen Pan, postdoctoral scholar

    “There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

    Enia Xhakaj, graduate student


    Scientific Papers from the 1M2H Collaboration

    Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

    Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

    Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

    Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

    Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

    Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

    Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

    Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

    Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

    Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger


    Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

    Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

    New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

    Science – Merging neutron stars generate gravitational waves and a celestial light show

    CBS News – Gravitational waves – and light – seen in neutron star collision

    CBC News – Astronomers see source of gravitational waves for 1st time

    San Jose Mercury News – A bright light seen across the universe, proving Einstein right

    Popular Science – Gravitational waves just showed us something even cooler than black holes

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

    National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

    Associated Press – Astronomers witness huge cosmic crash, find origins of gold

    Science News – Neutron star collision showers the universe with a wealth of discoveries

    UCSC press release
    First observations of merging neutron stars mark a new era in astronomy


    Writing: Tim Stephens
    Video: Nick Gonzales
    Photos: Carolyn Lagattuta
    Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development: Rob Knight
    Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

    Dark Energy Survey

    Dark Energy Camera [DECam], built at FNAL

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

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Noted in the video but not in the article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    CTIO PROMPT telescope telescope built by the University of North Carolina at Chapel Hill at Cerro Tololo Inter-American Observatory in Chilein the Chilean Andes.

    PROMPT The six domes at CTIO in Chile.

    NASA NuSTAR X-ray telescope

    See the full UCSC article here .

    The merger produced more power than is radiated as light by the entire contents of the universe at any given time. “These are the most powerful astronomical events witnessed by human beings,” says Caltech scientist Mike Landry, head of the LIGO Hanford Observatory.

    When the black holes merged, about two times the mass of the sun converted into energy and released in the form of ripples in the fabric of existence. These were gravitational waves, predicted by Albert Einstein’s theory of general relativity a century ago and first detected by LIGO in 2015.

    “Gravitational waves are distortions in the medium that we live in,” Landry says. “Normally we don’t think of the nothing of space as having any properties of all. It’s counterintuitive to think it could expand or contract or vibrate.”

    It was not a given that LIGO would be listening when the signal from the black holes arrived. “The machines don’t run 24-7,” says LIGO research engineer Brian Lantz of Stanford University. The list of distractions that can sabotage the stillness the detectors need includes earthquakes, wind, technical trouble, moving nitrogen tanks, mowing grass, harvesting trees and fires.

    When the gravitational waves from the colliding black holes reached Earth in January, the LIGO detectors happened to be coming back online after a holiday break. The system that alerts scientists to possible detections wasn’t even fully back in service yet, but a scientist in Germany was poring over the data anyway.

    “He woke us up in the middle of the night,” says MIT scientist David Shoemaker, newly elected spokesperson of the LIGO Scientific Collaboration, a body of more than 1000 scientists who perform LIGO research together with the European-based Virgo Collaboration.

    The signal turned out to be worth getting out of bed for. “This clearly establishes a new population of black holes not known before LIGO discovered them,” says LIGO scientist Bangalore Sathyaprakash of Penn State and Cardiff University.

    The merging black holes were more than twice as distant as the two pairs that LIGO previously detected, which were located 1.3 and 1.4 billion light-years away. This provided the best test yet of a second prediction of general relativity: gravitons without any mass.

    Gravitons are hypothetical particles that would mediate the force of gravity, just as photons mediate the force of electromagnetism. Photons are quanta of light; gravitons would be quanta of gravitational waves.

    General relativity predicts that, like photons, gravitons should have no mass, which means they should travel at the speed of light. However, if gravitons did have mass, they would travel at different speeds, depending on their energy.

    As merging black holes spiral closer and closer together, they move at a faster and faster pace. If gravitons had no mass, this change would not faze them; they would uniformly obey the same speed limit as they traveled away from the event. But if gravitons did have mass, some of the gravitons produced would travel faster than others. The gravitational waves that arrived at the LIGO detectors would be distorted.

    “That would mean general relativity is wrong,” says Stanford University Professor Emeritus Bob Wagoner. “Any one observation can kill a theory.”

    LIGO scientists’ observations matched the first scenario, putting a new upper limit on the mass of the graviton—and letting general relativity live another day. “I wouldn’t bet against it, frankly,” Wagoner says.

    Like a pair of circling black holes, research at LIGO seems to be picking up speed. Collaboration members continue to make improvements to their detectors. Soon the complementary Virgo detector is expected to come online in Italy, and in 2024 another LIGO detector is scheduled to start up in India. Scientists hope to eventually see new events as often as once per day, accumulating a pool of data with which to make new discoveries about the goings-on of our universe.

    See the full Symmetry article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:53 pm on February 27, 2018 Permalink | Reply
    Tags: , Gravity-Looking for nothing, , Symmetry Magazine   

    From Symmetry: “Looking for nothing to test gravity” 

    Symmetry Mag


    Matthew R. Francis

    Gravity. NASA.

    When they look for violations of Einstein’s general relativity, physicists deliberately plan experiments to find nothing at all.

    In 1887, physicists Albert Michelson and Edward Morley performed one of physics’ most famous experiments (at Case Western Reserve University, coincidentally, across the street from where this article was written). Unlike other important experiments, they didn’t find what they were looking for, but unexpectedly their “null” result prepared the way for the theory of relativity.

    Sometimes researchers deliberately set out to generate null results—while on the lookout for something new. One type of experiment is looking for deviations from Einstein’s general theory of relativity.

    “General relativity has been the staple of gravitational understanding for 100 years,” says Katie Chamberlain, a physics student at Montana State University. “We have to rule out the potential for other existing theories to come in and replace [it].”

    Many alternative theories of gravity are out there, designed to explain various phenomena or fix general relativity’s famous incompatibility with quantum theory. Some of these predict differences in the behavior of gravity that can be tested in the lab.

    One experiment examined precision measurements of the distance between Earth and the moon. Another recent test involved superconducting gravimeters, which measure how strong gravity is in various places on Earth’s surface. If there are gravitational effects not described by general relativity, they might show up in those experiments: the highly coveted results known as “new physics.”

    The null result tells us where new physics is not. That limits the places that one can continue to look for new physics.

    In these cases, everything was perfectly in line with general relativity, but that doesn’t mean the experiments were failures.

    “It isn’t especially a disappointment,” says Jay Tasson of Carleton College, who worked on the superconducting gravimeter analysis. “The null result tells us where new physics is not. That limits the places that one can continue to look for new physics.”

    In other words, even an experiment in line with general relativity tells us something, in this case that any theory—including theories not yet born—with results at odds with these results (as long as they hold up) must be wrong.

    “Progress in this field is often measured by [looking] with better sensitivity than anyone has looked before,” Tasson says.

    Einstein’s happiest thought

    Though general relativity is mathematically complicated, it’s based on some simple concepts. Among those: Objects experiencing only gravity don’t feel any force acting on them. That’s how someone aboard the International Space Station can float as freely as if there were no gravity at all, even though the force of gravity at that orbit is only about 10 percent less than it is on the surface of Earth. Einstein called this realization “the happiest thought” of his life.

    A consequence of this happy thought is “local Lorentz invariance.” “Local” means “approximately at a single point in space,” and “invariance” means two experiments performed under equivalent conditions should return the same results. “Local Lorentz invariance” means (for example) two experiments at the same position should be the same if one is rotated by 90 degrees compared with the other. While real experiments take up more than a single point in space, researchers compensate for that through precision measurements and understanding how the size of their experiment affects results.

    Several theories of gravity predict violations of local Lorentz invariance, including string theory and other quantum theories of gravity. Most of these violations occur at smaller length scales than current experiments can reach, but some effects might “leak” into testable regimes.

    Rather than test a particular alternative theory, gravitational physicists worked out a general framework for modeling deviations. The framework consists of numbers that are all zero in general relativity but take on various values depending on which alternative theory is doing the predicting.

    “Currently there are a lot of constraints on different modified theories of gravity,” Chamberlain says. “As we’re able to explore more relativistic spacetimes with higher sensitivities from our instruments, we’ll be able to place much tighter constraints.”

    Testing, testing

    Astronauts starting with Apollo 11 left “retroreflectors” on the surface of the moon that reflect light directly back toward the source. Astronomers on Earth send laser beams through telescopes at those retroreflectors and time how long it takes the light to come back to the observatory. These “lunar-ranging” experiments are some of the best tests of general relativity we have.

    “The usefulness of the lunar laser ranging experiment is mainly due to its very precise data,” says Adrien Bourgoin of the University of Bologna. He points out that these experiments are precise on the level of centimeters, compared with the 400,000 kilometer distance between Earth and the moon. That’s good enough to see possible deviations from general relativity.

    For example, if gravity violates local Lorentz invariance, it might affect the travel time of light differently when the moon is aligned with the sun (full and new moon) than when the moon and sun are at right-angles with respect to Earth (half-moon). That’s a large-scale version of rotating the experimental apparatus.

    The first lunar distance test began in 1969, with many follow-up experiments. Bourgoin and his colleagues looked at 13 tests involving five different observatories.

    The lunar retroreflectors were intended to test relativity, but the Earth-bound superconducting gravimeters that Jay Tasson and his colleagues used in their relativity tests are primarily there to study variations in our planet’s gravity due to rock density, earthquakes, the moon’s pull, and so forth. These instruments consist of metal spheres cooled until they become superconducting, which means they can be levitated using electromagnets. By keeping them levitating at precisely the same height, the instruments can measure the gravitational field at that position.

    As with lunar ranging, these gravimeters provide a lot of precise data, some going back over a decade. Tasson and his collaborators compared results between multiple groupings of gravimeters around the world to look for any variations that can’t be explained by ordinary phenomena.

    Both sets of researchers concluded there are no violations of general relativity that can be detected at this level of precision. In both cases, though, these data are improvements over what came before, with the lunar-range experiment showing as much as a thousandfold increase in precision over prior measurements.

    “Any set of experiments that you can do to test general relativity are going to be complementary to each other,” Chamberlain says.

    In particular, her research looks at how future gravitational-wave observatories might spot deviations from general relativity—including Lorentz invariance violations. Unlike the Earth and moon tests, these gravitational waves come from the strongest gravity we know: colliding black holes and neutron stars.

    “We need very strong signals to be able to tell the difference between a Lorentz-violating gravitational-wave form and a gravitational-wave form that looks like it should in general relativity.”

    In the meantime, nobody is terribly surprised to see experiments perfectly in line with Einstein’s theory.

    “I’m pleased that the measurements are null,” Bourgoin says. “If not, I’ll still be working on the subject wondering if the measurements come from computational errors or if it is real.”

    He recalls the experiment from 2011 that deceptively appeared to show neutrinos traveling faster than the speed of light, a result that vanished under later analysis. A seeming violation of local Lorentz invariance would also likely mean measurement snafus rather than a fundamental discovery.

    But there’s always that chance. And, like the Michelson-Morley experiment, the “nothing” results tell us where new physics may or may not be hiding.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:18 pm on February 20, 2018 Permalink | Reply
    Tags: , , DarkMatter, , , , , Symmetry Magazine   

    From Symmetry: “The secret life of Higgs bosons” 

    Symmetry Mag


    Sarah Charley

    Are these mass-giving particles hanging out with dark matter?

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    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 Higgs boson has existed since the earliest moments of our universe. Its directionless field permeates all of space and entices transient particles to slow down and burgeon with mass. Without the Higgs field, there could be no stable structures; the universe would be cold, dark and lifeless.

    Many scientists are hoping that the Higgs boson will help them understand phenomena not predicted by the Standard Model, physicists’ field guide to the subatomic world. While the Standard Model is an ace at predicting the the properties of all known subatomic particles, it falls short on things like gravity, the accelerating expansion of the universe, the supernatural speeds of spinning galaxies, the absurd excess of matter over antimatter, and beyond.

    “We can use the Higgs boson as a tool to look for new physics that might not readily interact with our standard set of particles,” says Darin Acosta, a physicist at the University of Florida.

    In particular, there’s hope that the Higgs boson might interact with dark matter, thought to be a widespread but never directly detected kind of matter that outnumbers regular matter five to one. This theoretical massive particle makes itself known through its gravitational attraction. Physicists see its fingerprint all over the cosmos in the rotational speed of galaxies, the movements of galaxy clusters and the bending of distant light. Even though dark matter appears to be everywhere, scientists have yet to find a tool that can bridge the light and dark sectors.

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

    If the Higgs field is the only vendor of mass in the cosmos, then dark matter must be a client. This means that the Higgs boson, the spokesparticle of the Higgs field, must have some relationship with dark matter particles.

    “It could be that dark matter aids in the production of Higgs bosons, or that Higgs bosons can transform into dark matter particles as they decay,” Acosta says. “It’s simple on paper, but the challenge is finding evidence of it happening, especially when so many parts of the equation are completely invisible.”

    The particle that wasn’t there

    To find evidence of the Higgs boson flirting with dark matter, scientists must learn how to see the invisible. Scientists never see the Higgs boson directly; in fact, they discovered the Higgs boson by tracing the particles it produces as it decays. Now, they want to precisely measure how frequently the Higgs boson transforms into different types of particles. It’s not easy.

    “All we can see with our detector is the last step of the decay, which we call the final state,” says Will Buttinger, a CERN research fellow. “In many cases, the Higgs is not the parent of the particles we see in the final state, but the grandparent.”

    The Standard Model not only predicts all the different possible decays of Higgs bosons, but how favorable each decay is. For instance, it predicts that about 60 percent of Higgs bosons will transform into a pair of bottom quarks, whereas only 0.2 percent will transform into a pair of photons. If the experimental results show Higgs bosons decaying into certain particles more or less often than predicted, it could mean that a few Higgs bosons are sneaking off and transforming into dark matter.

    Of course, these kinds of precision measurements cannot tell scientists if the Higgs is evolving into dark matter as part of its decay path—only that it is behaving strangely. To catch the Higgs in the act, scientists need irrefutable evidence of the Higgs schmoozing with dark matter.

    “How do we see invisible things?” asks Buttinger. “By the influence it has on what we can see.”

    For example, humans cannot see the wind, but we can look outside our windows and immediately know if it’s windy based whether or not trees are swaying. Scientists can look for dark matter particles in a similar way.

    “For every action, there is an equal and opposite reaction,” Buttinger says. “If we see particles shooting off in one direction, we know that there must be something shooting off in the other direction.”

    If a Higgs boson transforms into a visible particle paired with a dark matter particle, the solitary tracks of the visible particles will have an odd and inexplicable trajectory—an indication that, perhaps, a dark matter particle is escaping.

    The Higgs boson is the newest tool scientists have to explore the uncharted terrain within and beyond the Standard Model. The continued research at the LHC and its future upgrades will enable scientists to characterize this reticent particle and learn its close-held secrets.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:56 pm on February 6, 2018 Permalink | Reply
    Tags: , , , , , Symmetry Magazine   

    From Symmetry: “Learning to speak quantum” 

    Symmetry Mag


    Laura Dattaro

    Artwork by Sandbox Studio, Chicago with Ana Kova

    Particle physicists are studying ways to harness the power of the quantum realm to further their research.

    In a 1981 lecture, the famed physicist Richard Feynman wondered if a computer could ever simulate the entire universe. The difficulty with this task is that, on the smallest scales, the universe operates under strange rules: Particles can be here and there at the same time; objects separated by immense distances can influence each other instantaneously; the simple act of observing can change the outcome of reality.

    “Nature isn’t classical, dammit,” Feynman told his audience, “and if you want to make a simulation of nature, you’d better make it quantum mechanical.”

    Quantum computers

    Feynman was imagining a quantum computer, a computer with bits that acted like the particles of the quantum world. Today, nearly 40 years later, such computers are starting to become a reality, and they pose a unique opportunity for particle physicists.


    “The systems that we deal with in particle physics are intrinsically quantum mechanical systems,” says Panagiotis Spentzouris, head of Fermilab’s Scientific Computing Division. “Classical computers cannot simulate large entangled quantum systems. You have plenty of problems that we would like to be able to solve accurately without making approximations that we hope we will be able to do on the quantum computer.”

    Quantum computers allow for a more realistic representation of quantum processes. They take advantage of a phenomenon known as superposition, in which a particle such as an electron exists in a probabilistic state spread across multiple locations at once.

    Unlike a classical computer bit, which can be either on or off, a quantum bit—or qubit—can be on, off, or a superposition of both on and off, allowing for computations to be performed simultaneously instead of sequentially.

    This not only speeds up computations; it makes currently impossible ones possible. A problem that could effectively trap a normal computer in an infinite loop, testing possibility after possibility, could be solved almost instantaneously by a quantum computer. This processing speed could be key for particle physicists, who wade through enormous amounts of data generated by detectors.

    In the first demonstration of this potential, a team at CalTech recently used a type of quantum computer called a quantum annealer to “rediscover” the Higgs boson, the particle that, according to the Standard Model of particle physics, gives mass to every other fundamental particle.

    Standard Model of Particle Physics from Symmetry Magazine

    Scientists originally discovered the Higgs boson in 2012 using particle detectors at the Large Hadron Collider at CERN research center in Europe.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    They created Higgs bosons by converting the energy of particle collisions temporarily into matter. Those temporary Higgs bosons quickly decayed, converting their energy into other, more common particles, which the detectors were able to measure.

    Scientists identified the mass of the Higgs boson by adding up the masses of those less massive particles, the decay products. But to do so, they needed to pick out which of those particles came from the decay of Higgs bosons, and which ones came from something else. To a detector, a Higgs boson decay can look remarkably similar to other, much more common decays.

    LHC scientists trained a machine learning algorithm to find the Higgs signal against the decay background—the needle in the haystack. This training process required a huge amount of simulated data.

    Physicist Maria Spiropulu, who was on the team that discovered the Higgs the first time around, wanted to see if she could improve the process with quantum computing. The group she leads at CalTech used a quantum computer from a company called D-Wave to train a similar machine learning algorithm. They found that the quantum computer trained the machine learning algorithm on a significantly smaller amount of data than the classical method required. In theory, this would give the algorithm a head start, like giving someone looking for the needle in the haystack expert training in spotting the glint of metal before turning their eyes to the hay.

    “The machine cannot learn easily,” Spiropulu says. “It needs huge, huge data. In the quantum annealer, we have a hint that it can learn with small data, and if you learn with small data you can use it as initial conditions later.”

    Some scientists say it may take a decade or more to get to the point of using quantum computers regularly in particle physics, but until then they will continue to make advances to enhance their research.

    Quantum sensors

    Quantum mechanics is also disrupting another technology used in particle physics: the sensor, the part of a particle detector that picks up the energy from a particle interaction.

    In the quantum world, energy is discrete. The noun quantum means “a specific amount” and is used in physics to mean “the smallest quantity of energy.” Classical sensors generally do not make precise enough measurements to pick up individual quanta of energy, but a new type of quantum sensor can.

    “A quantum sensor is one that is able to sense these individual packets of energy as they arrive,” says Aaron Chou, a scientist at Fermilab. “A non-quantum sensor would not be able to resolve the individual arrivals of each of these little packets of energy, but would instead measure a total flow of the stuff.”

    Chou is taking advantage of these quantum sensors to probe the nature of dark matter. Using technology originally developed for quantum computers, Chou and his team are building ultrasensitive detectors for a type of theorized dark matter particle known as an axion.

    “We’re taking one of the qubit designs that was previously created for quantum computing and we’re trying to use those to sense the presence of photons that came from the dark matter,” Chou says.

    For Spiropulu, these applications of quantum computers represent an elegant feedback system in the progression of technology and scientific application. Basic research in physics led to the initial transistors that fed the computer science revolution, which is now on the edge of transforming basic research in physics.

    “You want to disrupt computing, which was initially a physics advance,” Spiropulu says. “Now we are using physics configurations and physics systems themselves to assist computer science to solve any problem, including physics problems.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 2:00 pm on January 23, 2018 Permalink | Reply
    Tags: , , , Neural networks for neutrinos, , , , Symmetry Magazine   

    From Symmetry: “Neural networks for neutrinos” 

    Symmetry Mag


    Diana Kwon

    Artwork by Sandbox Studio, Chicago

    Scientists are using cutting-edge machine-learning techniques to analyze physics data.

    Particle physics and machine learning have long been intertwined.

    One of the earliest examples of this relationship dates back to the 1960s, when physicists were using bubble chambers to search for particles invisible to the naked eye. These vessels were filled with a clear liquid that was heated to just below its boiling point so that even the slightest boost in energy—for example, from a charged particle crashing into it—would cause it to bubble, an event that would trigger a camera to take a photograph.

    Female scanners often took on the job of inspecting these photographs for particle tracks. Physicist Paul Hough handed that task over to machines when he developed the Hough transform, a pattern recognition algorithm, to identify them.

    The computer science community later developed the Hough transform for use in applications such as computer vision, attempts to train computers to replicate the complex function of a human eye.

    “There’s always been a little bit of back and forth” between these two communities, says Mark Messier, a physicist at Indiana University.

    Since then, the field of machine learning has rapidly advanced. Deep learning, a form of artificial intelligence modeled after the human brain, has been implemented for a wide range of applications such as identifying faces, playing video games and even synthesizing life-like videos of politicians.

    Over the years, algorithms that help scientists pick interesting aberrations out of background data have been used in physics experiments such as BaBar at SLAC National Accelerator Laboratory and experiments at the Large Electron-Positron Collider at CERN and the Tevatron at Fermi National Accelerator Laboratory.


    CERN LEP Collider

    FNAL Tevatron

    FNAL/Tevatron map

    FNAL/Tevatron DZero detector

    FNAL/Tevatron CDF detector

    More recently, algorithms that learn to recognize patterns in large datasets have been handy for physicists studying hard-to-catch particles called neutrinos.

    This includes scientists on the NOvA experiment, who study a beam of neutrinos created at the US Department of Energy’s Fermilab near Chicago.

    FNAL NOvA Near Detector

    FNAL/NOvA experiment map

    The neutrinos stream straight through Earth to a 14,000-metric-ton detector filled with liquid scintillator sitting near the Canadian border in Minnesota.

    When a neutrino strikes the liquid scintillator, it releases a burst of particles. The detector collects information about the pattern and energy of those particles. Scientists use that information to figure out what happened in the original neutrino event.

    “Our job is almost like reconstructing a crime scene,” Messier says. “A neutrino interacts and leaves traces in the detector—we come along afterward and use what we can see to try and figure out what we can about the identity of the neutrino.”

    Over the last few years, scientists have started to use algorithms called convolutional neural networks (CNNs) to take on this task instead.

    CNNs, which are modelled after the mammalian visual cortex, are widely used in the technology industry—for example, to improve computer vision for self-driving cars. These networks are composed of multiple layers that act somewhat like filters: They contain densely interconnected nodes that possess numerical values, or weights, that are adjusted and refined as inputs pass through.

    “The ‘deep’ part comes from the fact that there are many layers to it,” explains Adam Aurisano, an assistant professor at the University of Cincinnati. “[With deep learning] you can take nearly raw data, and by pushing it through these stacks of learnable filters, you wind up extracting nearly optimal features.”

    For example, these algorithms can extract details associated with particle interactions of varying complexity from the “images” collected by recording different patterns of energy deposits in particle detectors.

    “Those stacks of filters have sort of sliced and diced the image and extracted physically meaningful bits of information that we would have tried to reconstruct before,” Aurisano says.

    Although they can be used to classify events without recreating them, CNNs can also be used to reconstruct particle interactions using a method called semantic segmentation.

    When applied to an image of a table, for example, this method would reconstruct the object by tagging each pixel associated with it, Aurisano explains. In the same way, scientists can label each pixel associated with characteristics of neutrino interactions, then use algorithms to reconstruct the event.

    Physicists are using this method to analyze data collected from the MicroBooNE neutrino detector.


    “The nice thing about this process is that you might find a cluster that’s made by your network that doesn’t fit in any interpretation in your model,” says Kazuhiro Terao, a scientist at SLAC National Accelerator Laboratory. “That might be new physics. So we could use these tools to find stuff that we might not understand.”

    Scientists working on other particle physics experiments, such as those at the Large Hadron Collider at CERN, are also using deep learning for data analysis.


    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    “All these big physics experiments are really very similar at the machine learning level,” says Pierre Baldi, a computer scientist at the University of California, Irvine. “It’s all images associated with these complex, very expensive detectors, and deep learning is the best method for extracting signal against some background noise.”

    Although most of the information is currently flowing from computer scientists to particle physicists, other communities may also gain new tools and insights from these experimental applications as well.

    For example, according to Baldi, one question that’s currently being discussed is whether scientists can write software that works across all these physics experiments with a minimal amount of human tuning. If this goal were achieved, it could benefit other fields, such a biomedical imaging, that use deep learning as well. “[The algorithm] would look at the data and calibrate itself,” he says. “That’s an interesting challenge for machine learning methods.”

    Another future direction, Terao says, would be to get machines to ask questions—or, more simply, to be able to identify outliers and try to figure out how to explain them.

    “If the AI can form a question and come up with a logical sequence to solve it, then that replaces a human,” he says. “To me, the kind of AI you want to see is a physics researcher—one that can do scientific research.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 5:11 pm on January 18, 2018 Permalink | Reply
    Tags: , , , , , Symmetry Magazine   

    From Symmetry: “The biggest little detectors” 

    Symmetry Mag


    Leah Hesla

    Photo by Maximilien Brice, CERN

    The ProtoDUNE detectors for the Deep Underground Neutrino Experiment are behemoths in their own right.

    In one sense, the two ProtoDUNE detectors are small. As prototypes of the much larger planned Deep Underground Neutrino Experiment, they are only representative slices, each measuring about 1 percent of the size of the final detector. But in all other ways, the ProtoDUNE detectors are simply massive.

    CERN Proto DUNE Maximillian Brice

    Once they are complete later this year, these two test detectors will be larger than any detector ever built that uses liquid argon, its active material. The international project involves dozens of experimental groups coordinating around the world. And most critically, the ProtoDUNE detectors, which are being installed and tested at the European particle physics laboratory CERN, are the rehearsal spaces in which physicists, engineers and technicians will hammer out nearly every engineering problem confronting DUNE, the biggest international science project ever conducted in the United States.

    Gigantic detector, tiny neutrino

    DUNE’s mission, when it comes online in the mid-2020s, will be to pin down the nature of the neutrino, the most ubiquitous particle of matter in the universe. Despite neutrinos’ omnipresence—they fill the universe, and trillions of them stream through us every second—they are a pain in the neck to capture. Neutrinos are vanishingly small, fleeting particles that, unlike other members of the subatomic realm, are heedless of the matter through which they fly, never stopping to interact.

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    FNAL DUNE Argon tank at SURF

    Surf-Dune/LBNF Caverns at Sanford

    SURF building in Lead SD USA

    Well, almost never.

    Once in a while, scientists can catch one. And when they do, it might tell them a bit about the origins of the universe and why matter predominates over antimatter—and thus how we came to be here at all.

    A global community of more than 1000 scientists from 31 countries are building DUNE, a megascience experiment hosted by the Department of Energy’s Fermi National Accelerator Laboratory. The researchers’ plan is to observe neutrinos using two detectors separated by 1300 kilometers—one at Fermilab outside Chicago and a second one a mile underground in South Dakota at the Sanford Underground Research Facility. Having one at each end enables scientists to see how neutrinos transform as they travel over a long distance.

    The DUNE collaboration is going all-in on the bigger-is-better strategy; after all, the bigger the detector, the more likely scientists are to snag a neutrino. The detector located in South Dakota, called the DUNE far detector, will hold 70,000 metric tons (equivalent to about 525,000 bathtubs) of liquid argon to serve as the neutrino fishing net. It comprises four large modules. Each will stand four stories high and, not including the structures that house the utilities, occupy a footprint roughly equal to a soccer field.

    In short, DUNE is giant.

    Lots of room in ProtoDUNE

    The ProtoDUNE detectors are small only when compared to the giant DUNE detector. If each of the four DUNE modules is a 20-room building, then each ProtoDUNE detector is one room.

    But one room large enough to envelop a small house.

    As one repeatable unit of the ultimate detector, the ProtoDUNE detectors are necessarily big. Each is an enormous cube—about two stories high and about as wide—and contains about 800 metric tons of liquid argon.

    Why two prototypes? Researchers are investigating two ways to use argon and so are constructing two slightly different but equally sized test beds. The single-phase ProtoDUNE uses only liquid argon, while the dual-phase ProtoDUNE uses argon as both a liquid and a gas.

    “They’re the largest liquid-argon particle detectors that have ever been built,” says Ed Blucher, DUNE co-spokesperson and a physicist at the University of Chicago.

    As DUNE’s test bed, the ProtoDUNE detectors also have to offer researchers a realistic picture of how the liquid-argon detection technology will work in DUNE, so the instrumentation inside the detectors is also at full, giant scale.

    “If you’re going to build a huge underground detector and invest all of this time and all of these resources into it, that prototype has to work properly and be well-understood,” says Bob Paulos, director of the University of Wisconsin–Madison Physical Sciences Lab and a DUNE engineer. “You need to understand all the engineering problems before you proceed to build literally hundreds of these components and try to transport them all underground.”

    A crucial step for ProtoDUNE was welding together the cryostat, or cold vessel, that will house the detector components and liquid argon. Photo by CERN.

    Partners in ProtoDUNE

    ProtoDUNE is a rehearsal for DUNE not only in its technical orchestration but also in the coordination of human activity.

    When scientists were planning their next-generation neutrino experiment around 2013, they realized that it could succeed only by bringing the international scientific community together to build the project. They also saw that even the prototyping would require an effort of global proportions—both geographically and professionally. As a result, DUNE and ProtoDUNE actively invite students, early-career scientists and senior researchers from all around the world to contribute.

    “The scale of ProtoDUNE, a global collaboration at CERN for a US-based megaproject, is a paradigm change in the way neutrino science is done,” says Christos Touramanis, a physicist at the University of Liverpool and one of the co-coordinators of the single-phase detector. For both DUNE and ProtoDUNE, funding comes from partners around the world, including the Department of Energy’s Office of Science and CERN.

    The successful execution of ProtoDUNE’s assembly and testing by international groups requires a unity of purpose from parties that could hardly be farther apart, geographically speaking.

    Scientists say the effort is going smoothly.

    “I’ve been doing neutrino physics and detector technology for the last 20 or 25 years. I’ve never seen such an effort go up so nicely and quickly. It’s astonishing,” says Fermilab scientist Flavio Cavanna, who co-coordinates the single-phase ProtoDUNE project. “We have a great collaboration, great atmosphere, great willingness to make it. Everybody is doing his or her best to contribute to the success of this big project. I used to say that ProtoDUNE was mission impossible, because—in the short time we were given to make the two detectors, it looked that way in the beginning. But looking at where we are now, and all the progress made so far, it starts turning out to be mission possible.”

    The anode plane array (APA) [STFC] is prepped for shipment at Daresbury Laboratory in the UK. Christos Touramanis.

    Inside the liquid-argon test bed

    The first signal emerges as a streak of ionization electrons.

    To record the signal, scientists will use something called an anode plane array, or APA. An APA is a screen created using 24 kilometers of precisely tensioned, closely spaced, continuously wound wire. This wire screen is positively charged, so it attracts the negatively charged electrons.

    Much the way a wave front approaches the beach’s shore, the particle track—a string of the ionization electrons—will head toward the positively charged wires inside the ProtoDUNE detectors. The wires will send information about the track to computers, which will record its properties and thus information about the original neutrino interaction.

    A group in the University of Wisconsin–Madison Physical Sciences Lab led by Paulos designed the single-phase ProtoDUNE wire arrays. The Wisconsin group, Daresbury Laboratory in the UK and several UK universities are building APAs for the same detector. The first APA from Wisconsin arrived at CERN last year; the first from Daresbury Lab arrived earlier this week.

    “These are complicated to build,” Paulos says, noting that it currently takes about three months to build just one. “Building these 6-meter-tall anode planes with continuously wound wire—that’s something that hasn’t been done before.”

    The anode planes attract the electrons. Pushing away the electrons will be a complementary set of panels, called the cathode plane. Together, the anode and cathode planes behave like battery terminals, with one repelling electron tracks and the other drawing them in. A group at CERN designed and is building the cathode plane.

    The dual-phase detector will operate on the same principle but with a different configuration of wire arrays. A special layer of electronics near the cathode will allow for the amplification of faint electron tracks in a layer of gaseous argon. Groups at institutions in France, Germany and Switzerland are designing those instruments. Once complete, they will also send their arrays to be tested at CERN.

    Then there’s the business of observing light.

    The flash of light is the result of a release of energy from the electron in the process of getting bumped from an argon atom. The appearance of light is like the signal to start a stopwatch; it marks the moment the neutrino interaction in a detector takes place. This enables scientists to reconstruct in three dimensions the picture of the interaction and resulting particles.

    On the other side of the equator, a group at the University of Campinas in Brazil is coordinating the installation of instruments that will capture the flashes of light resulting from particle interactions in the single-phase ProtoDUNE detector.

    Two of the designs for the single-phase prototype—one by Indiana University, the other by Fermilab and MIT—are of a type called guiding bars. These long, narrow strips work like fiber optic cables: they capture the light, convert it into light in the visible spectrum and finally guide it to an external sensor.

    A third design, called ARAPUCA, was developed by three Brazilian universities and Fermilab and is being partially produced at Colorado State University. Named for the Guaraní word for a bird trap, the efficient ARAPUCA design will be able to “trap” even very low light signals and transmit them to its sensors.

    The ARAPUCA array, designed by three Brazilian universities and Fermilab, was partially produced at Colorado State University. D. Warner, Colorado State University.

    “The ARAPUCA technology is totally new,” says University of Campinas scientist Ettore Segreto, who is co-coordinating the installation of the light detection systems in the single-phase prototype. “We might be able to get more information from the light detection—for example, greater energy resolution.”

    Groups from France, Spain and the Swiss Federal Institute of Technology are developing the light detection system for the dual-phase prototype, which will comprise 36 photomultiplier tubes, or PMTs, situated near the cathode plane. A PMT works by picking up the light from the particle interaction and converting it into electrons, multiplying their number and so amplifying the signal’s strength as the electrons travel down the tube.

    With two tricked-out detectors, the DUNE collaboration can test their picture-taking capabilities and prepare DUNE to capture in exquisite detail the fleeting interactions of neutrinos.

    Bringing instruments into harmony

    But even if they’re instrumented to the nines inside, two isolated prototypes do not a proper test bed make. Both ProtoDUNE detectors must be hooked up to computing systems so particle interaction signals can be converted into data. Each detector must be contained in a cryostat, which functions like a thermos, for the argon to be cold enough to maintain a liquid state. And the detectors must be fed particles in the first place.

    CERN is addressing these key areas by providing particle beam, innovative cryogenics and computing infrastructures, and connecting the prototype detectors with the DUNE experimental environment.

    DUNE’s neutrinos will be provided by the Long-Baseline Neutrino Facility, or LBNF, which held an underground groundbreaking for the start of its construction in July. LBNF, led by Fermilab, will provide the construction, beamline and cryogenics for the mammoth DUNE detector, as well as Fermilab’s chain of particle accelerators, which will provide the world’s most intense neutrino beam to the experiment.

    CERN is helping simulate that environment as closely as possible with the scaled-down ProtoDUNE detectors, furnishing them with particle beams so researchers can characterize how the detectors respond. Under the leadership of scientist Marzio Nessi, last year the CERN group built a new facility for the test beds, where CERN is now constructing two new particle beamlines that extend the lab’s existing network.

    The recently arrived anode plane array (hanging on the left) is moved by a crane to its new home in the ProtoDUNE cryostat. Photo by CERN.

    In addition, CERN built the ProtoDUNE cryostats—the largest ever constructed for a particle physics experiment—which also will serve as prototypes for those used in DUNE. Scientists will be able to gather and interpret the data generated from the detectors with a CERN computing farm and software and hardware from several UK universities.

    “The very process of building these prototype detectors provides a stress test for building them in DUNE,” Blucher says.

    CERN’s beam schedule sets the schedule for testing. In December, the European laboratory will temporarily shut off beam to its experiments for upgrades to the Large Hadron Collider. DUNE scientists aim to position the ProtoDUNE detectors in the CERN beam before then, testing the new technologies pioneered as part of the experiment.

    “ProtoDUNE is a necessary and fundamental step towards LBNF/DUNE,” Nessi says. “Most of the engineering will be defined there and it is the place to learn and solve problems. The success of the LBNF/DUNE project depends on it.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 2:52 pm on January 16, 2018 Permalink | Reply
    Tags: , , , , , , , Symmetry Magazine, The Dark Sector   

    From Symmetry: “Voyage into the dark sector” 

    Symmetry Mag


    Sarah Charley

    Artwork by Sandbox Studio, Chicago with Ana Kova

    A hidden world of particles awaits. [We hope!]

    We don’t need extra dimensions or parallel universes to have an alternate reality superimposed right on top of our own. Invisible matter is everywhere.

    For example, take neutrinos generated by the sun, says Jessie Shelton, a theorist at the University of Illinois at Urbana-Champaign who works on dark sector physics. “We are constantly bombarded with neutrinos, but they pass right through us. They share the same space as our atoms but almost never interact.”

    As far as scientists can tell, neutrinos are solitary particles. But what if there is a whole world of particles that interact with one another but not with ordinary atoms? This is the idea behind the dark sector: a theoretical world of matter existing alongside our own but invisible to the detectors we use to study the particles we know.

    “Dark sectors are, by their very definition, built out of particles that don’t interact strongly with the Standard Model,” Shelton says.

    The Standard Model is a physicist’s field guide to the 17 particles and forces that make up all visible matter.

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

    Standard Model of Particle Physics from Symmetry Magazine

    It explains how atoms can form and why the sun shines. But it cannot explain gravity, the cosmic imbalance of matter and antimatter, or the disparate strengths of nature’s four forces.

    CERN ALPHA Antimatter Factory

    On its own, an invisible world of dark sector particles cannot solve all these problems. But it certainly helps.

    Artwork by Sandbox Studio, Chicago with Ana Kova

    The main selling point for the dark sector is that the theories comprehensively confront the problem of dark matter. Dark matter is a term physicists coined to explain bizarre gravitational effects they observe in the cosmos. Distant starlight appears to bend around invisible objects as it traverses the cosmos, and galaxies spin as if they had five times more mass than their visible matter can explain. Even the ancient light preserved in cosmic microwave background seems to suggest that there is an invisible scaffolding on which galaxies are formed.

    Some theories suggest that dark matter is simple cosmic debris that adds mass—but little else—to the complexity of our cosmos. But after decades of searching, physicists have yet to find dark matter in a laboratory experiment. Maybe the reason scientists haven’t been able to detect it is that they’ve been underestimating it.

    “There is no particular reason to expect that whatever is going on in the dark sector has to be as simple as our most minimal models,” Shelton says. “After all, we know that our visible world has a lot of rich physics: Photons, electrons, protons, nuclei and neutrinos are all critically important for understanding the cosmology of how we got here. The dark sector could be a busy place as well.”

    According to Shelton, dark matter could be the only surviving particle out of a similarly complicated set of dark particles.

    “It could even be something like the proton, a bound state of particles interacting via a very strong dark force. Or it could even be something like a hydrogen atom, a bound state of particles interacting via a weaker dark force,” she says.

    Even if terrestrial experiments cannot see these stable dark matter particles directly, they might be sensitive to other kinds of dark particles, such as dark photons or short-lived dark particles that interact strongly with the Higgs boson.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    “The Higgs is one of the easiest ways for the Standard Model particles to talk to the dark sector,” Shelton says.

    As far as scientists know, the Higgs boson is not picky. It may very well interact will all sorts of massive particles, including those invisible to ordinary atoms. If the Higgs boson interacts with massive dark sector particles, scientists should find that its properties deviate slightly from the Standard Model’s predictions. Scientists at the Large Hadron Collider are precisely measuring the properties of the Higgs boson to search for unexpected quirks that could open a gateway to new physics.


    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    At the same time, scientists are also using the LHC to search for dark sector particles directly. One theory is that at extremely high temperatures, dark matter and ordinary matter are not so different and can transform into one another through a dark force. In the hot and dense early universe, this would have been quite common.

    “But as the universe expanded and cooled, this interaction froze out, leaving some relic dark matter behind,” Shelton says.

    The energetic particle collisions generated by the LHC imitate the conditions that existed in the early universe and could unlock dark sector particles. If scientists are lucky, they might even catch dark sector particles metamorphosing into ordinary matter, an event that could materialize in the experimental data as particle tracks that suddenly appear from no apparent source.

    But there are also several feasible scenarios in which any interactions between the dark sector and our Standard Model particles are so tiny that they are out of reach of modern experiments, according to Shelton.

    “These ‘nightmare’ scenarios are completely logical possibilities, and in this case, we will have to think very carefully about astrophysical and cosmological ways to look for the footprints of dark particle physics,” she says.

    Even if the dark sector is inaccessible to particle detectors, dark matter will always be visible through the gravitational fingerprint it leaves on the cosmos.

    “Gravity tells us a lot about how much dark matter is in the universe and the kinds of particle interactions dark sector particles can and cannot have,” Shelton says. “For instance, more sensitive gravitational-wave experiments will give us the possibility to look back in time and see what our universe looked like at extremely high energies, and could maybe reveal more about this invisible matter living in our cosmos.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 4:30 pm on December 19, 2017 Permalink | Reply
    Tags: , , CERN Large Hadron Collider, , , , , Large Electron-Positron Collider, , , , , , Symmetry Magazine   

    From Symmetry: “Machine evolution” 

    Symmetry Mag

    Amanda Solliday

    Courtesy of SLAC

    Planning the next big science machine requires consideration of both the current landscape and the distant future.

    Around the world, there’s an ecosystem of large particle accelerators where physicists gather to study the most intricate details of matter.

    These accelerators are engineering marvels. From planning to construction to operation to retirement, their lifespans stretch across decades.

    But to get the most out of their investments of talent and funding, laboratories planning such huge projects have to think even longer-term: What could these projects become in their next lives?

    The following examples show how some of the world’s big physics machines have evolved to stay at the forefront of science and technology.

    Same tunnel, new collisions

    Before CERN research center in Geneva, Switzerland, had its Large Hadron Collider, it had the Large Electron-Positron Collider. LEP was the largest electron-positron collider ever built, occupying a nearly 17-mile circular tunnel dug beneath the border of Switzerland and France. The tunnel took three years to completely excavate and build.

    The first particle beam traveled around the LEP circular collider in 1989. Long before then, the international group of CERN physicists and engineers were already thinking about what CERN’s next machine could be.

    “People were saying, ‘Well, if we do build LEP, then we should make it compatible with the [then-proposed] Large Hadron Collider,’” says James Gillies, a senior communications advisor and member of the strategic planning and evaluation unit at CERN. “If you want to have a future facility, you often have to engage the people who just finished designing one machine to start thinking about the next one.”

    LEP’s designers chose an energy for the collider that would mass-produce Z bosons, fundamental particles discovered by earlier experiments at CERN. The LHC would be a step up from LEP, reaching higher energies that scientists hoped could produce the Higgs boson. In the 1960s, theorists proposed the Higgs as a way to explain the origin of the mass of elementary particles. And the new machine to look for it could be built in the same 17-mile tunnel excavated for LEP.

    Engineers began working on the LHC while LEP was still running. The new machine required enlargements to underground areas—it needed bigger detectors and new experimental halls.

    “That was challenging because these caverns are huge. As they were being excavated, the pressure on the LEP tunnel was reduced and the LEP beamline needed realignment,” Gillies says. “So you constantly had to realign the collider for experiments as you were digging.”

    After LEP reached its highest energy in 2000, it was switched off. The tunnel remained the same, says Gillies, but there were many other changes. Only one of the LEP detectors, DELPHI, remains underground at CERN as a visitors’ point.

    In 2012, LHC scientists announced the discovery of the long-sought Higgs boson. The LHC is planned to continue running until at least 2035, gradually increasing the intensity of its particle collisions. The research and development into the accelerator’s successor is already happening. The possibilities include a higher energy LHC, a compact linear collider or an even larger circular collider.


    Large Electron-Positron Collider
    Location: CERN—Geneva, Switzerland
    First beam: 1989
    Link to LEP Timeline: Timeline
    Courtesy of CERN


    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Large Hadron Collider
    Location: CERN—Geneva, Switzerland
    First beam: 2008
    Link to LHC Timeline: Timeline
    Courtesy of CERN

    High-powered science
    Decades before the LHC came into existence, a suburb of Chicago was home to the most powerful collider in the world: the Tevatron. A series of accelerators at Fermi National Accelerator Laboratory boosted protons and antiprotons to nearly the speed of light. In the final, 4-mile Tevatron ring, the particles reached record energy levels, and more than 1000 superconducting magnets steered them into collisions. Physicists used the Tevatron to make the first direct measurement of the tau neutrino and to discover the top quark, the last observed lepton and quark, respectively, in the Standard Model.

    The Tevatron shut down in 2011 after the LHC came up to speed, but the rest of Fermilab’s accelerator infrastructure was still hard at work powering research in particle physics—particularly on the abundant, mysterious and difficult-to-detect neutrino.

    Starting in 1999, a brand-new, 2-mile circular accelerator called the Main Injector was added to the Fermilab complex to increase the number of Tevatron particle collisions tenfold. It was joined in its tunnel by the Recycler, a permanent magnet ring that stored and cooled antiprotons.

    But before the Main Injector was even completed, scientists had identified a second purpose: producing powerful beams of neutrinos for experiments in Illinois and 500 miles away in Minnesota.

    FNAL/NOvA experiment map

    By 2005, the proton beam circulating in the Main Injector was doing double duty: sending ever-more-intense beams to the Tevatron collider and smashing into a target to produce neutrinos. Following the shutdown of the Tevatron, the Recycler itself was recycled to increase the proton beam power for neutrino research.

    “I’m still amazed at how we are able to use the Recycler. It can be difficult to transition if a machine wasn’t originally built for that purpose,” says Ioanis Kourbanis, the head of the Main Injector department at Fermilab.

    Fermilab’s high-energy neutrino beam is already the most intense in the world, but the laboratory plans to enhance it with future improvements to the Main Injector and the Recycler, and to build a brand-new neutrino beamline.

    Neutrinos almost never interact with matter, so they can pass straight through the Earth on their way to detectors onsite and others several hundred miles away. Scientists hope to learn more about neutrinos and their possible role in shaping our early universe.

    The new beamline will be part of the Long-Baseline Neutrino Facility, which will send neutrinos 800 miles underground to the massive, mile-deep detectors of the Deep Underground Neutrino Experiment.

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    FNAL DUNE Argon tank at SURF

    Surf-Dune/LBNF Caverns at Sanford

    SURF building in Lead SD USA

    Scientists from around the world will use the DUNE data to answer questions about neutrinos, thanks to the repurposed pieces of the Fermilab accelerator complex.


    FNAL Tevatron

    FNAL/Tevatron map

    FNAL/Tevatron DZero detector

    FNAL/Tevatron CDF detector

    Location: Fermilab—Batavia, Illinois
    First beam: 1983
    Link to Tevatron Timeline: Timeline
    Courtesy of Fermilab


    Neutrinos at the Main Injector (NuMI) beam
    Location: Fermilab—Batavia, Illinois
    First beam: 2004
    Link to Fermilab Timeline: Timeline
    Courtesy of Fermilab

    A monster accelerator

    When physicists first came up with the idea to build a two-mile linear accelerator at what is now called SLAC National Accelerator Laboratory, managed by Stanford University, they called it “Project M” for “Monster.” Engineers began building it from hand-drawn designs. Once completed, the machine was able to accelerate electrons to near the speed of light, producing its first particle beam in May 1966.

    SLAC Campus

    The accelerator’s scientific purpose has gone through several iterations of particle physics experiments over the decades, from fixed-target experiments to the Stanford Linear Collider (the only electron-positron linear collider ever built) to an injector for a circular collider, the Positron-Electron Project.

    These experiments led to the discovery that protons are made of quarks, the first evidence that the charm quark existed (through observations of the J/psi particle, co-discovered with researchers at MIT) and the discovery of the tau lepton.

    In 2009, the lab used the accelerator as the backbone for a different type of science machine—an X-ray free-electron laser, the Linac Coherent Light Source.

    “Looking around, SLAC was the only place in the world with a linear accelerator capable of driving a free-electron laser,” says Claudio Pellegrini, a distinguished professor emeritus of physics at the University of California, Los Angeles and a visiting scientist and consulting professor at SLAC. Pellegrini first proposed the idea to transform SLAC’s linear accelerator.

    The new machine, a DOE Office of Science user facility, would be the world’s first laser of its kind that could produce extremely bright hard X-rays, the high-energy X-rays that let scientists take snapshots of atoms and molecules.

    “Much of the physics and many of the tools learned and developed during the operation of the Stanford Linear Collider were directly applicable to the free electron laser,” says Lia Merminga, head of the accelerator directorate at SLAC. “This was a big factor in the LCLS being commissioned in record time. Without the Stanford Linear Collider experience, this significant body of work would have to be reinvented and reproduced almost from scratch.”

    Little about the accelerator itself needed to change. But to create a free-electron laser, scientists needed to design a new part: an electron gun, a device that generates electrons to be injected into the accelerator. A collaboration of several national labs and UCLA created a new type of electron gun for LCLS, while other national labs helped build undulators, a series of magnets that would wiggle the electrons to create X-rays.

    LCLS used only the last third of SLAC’s original linear accelerator. In part of the remaining section, scientists are developing plasma wakefield and other new particle acceleration techniques.

    For the X-ray laser’s next iteration, LCLS-II, scientists are aiming for an even brighter laser that will fire 1 million pulses per second, allowing them to observe rare and exceptionally transient events.


    To do this, they will need to replace the original copper structures with superconducting technology. The technology is derived from designs for a large International Linear Collider [ILC] proposed to be built in Japan.

    ILC schematic

    “I’m in awe of the foresight of the original builders of SLAC’s linear accelerator,” Merminga adds. “We’ve been able to do so much with this machine, and the end is not yet in sight.”


    Fixed target and collider experiments

    Location: SLAC—Menlo Park, California
    First beam: 1966
    Link to SLAC Timeline: Timeline
    Courtesy of SLAC


    Linac Coherent Light Source
    Location: SLAC—Menlo Park, California
    First beam: 2009
    Link to SLAC Timeline: Timeline
    Courtesy of SLAC

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

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