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  • richardmitnick 1:40 pm on February 27, 2020 Permalink | Reply
    Tags: "‘Flash photography’ at the LHC", , , , , , , , Symmetry Magazine   

    From Symmetry: “‘Flash photography’ at the LHC” 

    Symmetry Mag
    From Symmetry<

    Sarah Charley

    Photo by Tom Bullock

    An extremely fast new detector inside the CMS detector will allow physicists to get a sharper image of particle collisions.

    Some of the best commercially available high-speed cameras can capture thousands of frames every second. They produce startling videos of water balloons popping and hummingbirds flying in ultra-slow motion.

    But what if you want to capture an image of a process so fast that it looks blurry if the shutter is open for even a billionth of a second? This is the type of challenge scientists on experiments like CMS and ATLAS face as they study particle collisions at CERN’s Large Hadron Collider.

    When the LHC is operating to its full potential, bunches of about 100 billion protons cross each other’s paths every 25 nanoseconds. During each crossing, which lasts about 2 nanoseconds, about 50 protons collide and produce new particles. Figuring out which particle came from which collision can be a daunting task.

    “Usually in ATLAS and CMS, we measure the charge, energy and momentum of a particle, and also try to infer where it was produced,” says Karri DiPetrillo, a postdoctoral fellow working on the CMS experiment at the US Department of Energy’s Fermilab. “We’ve had timing measurements before—on the order of nanoseconds, which is sufficient to assign particles to the correct bunch crossing, but not enough to resolve the individual collisions within the same bunch.”

    Thanks to a new type of detector DiPetrillo and her collaborators are building for the CMS experiment, this is about to change.

    CERN/CMS Detector

    Physicists on the CMS experiment are devising a new detector capable of creating a more accurate timestamp for passing particles. The detector will separate the 2-nanosecond bursts of particles into several consecutive snapshots—a feat a bit like taking 30 billion pictures a second.

    This will help physicists with a mounting challenge at the LHC: collision pileup.

    Picking apart which particle tracks came from which collision is a challenge. A planned upgrade to the intensity of the LHC will increase the number of collisions per bunch crossing by a factor of four—that is from 50 to 200 proton collisions—making that challenge even greater.

    Currently, physicists look at where the collisions occurred along the beamline as a way to identify which particular tracks came from which collision. The new timing detector will add another dimension to that.

    “These time stamps will enable us to determine when in time different collisions occurred, effectively separating individual bunch crossings into multiple ‘frames,’” says DiPetrillo.

    DiPetrillo and fellow US scientists working on the project are supported by DOE’s Office of Science, which is also contributing support for the detector development.

    According to DiPetrillo, being able to separate the collisions based on when they occur will have huge downstream impacts on every aspect of the research. “Disentangling different collisions cleans up our understanding of an event so well that we’ll effectively gain three more years of data at the High-Luminosity LHC. This increase in statistics will give us more precise measurements, and more chances to find new particles we’ve never seen before,” she says.

    The precise time stamps will also help physicists search for heavy, slow moving particles they might have missed in the past.

    “Most particles produced at the LHC travel at close to the speed of light,” DiPetrillo says. “But a very heavy particle would travel slower. If we see a particle arriving much later than expected, our timing detector could flag that for us.”

    The new timing detector inside CMS will consist of a 5-meter-long cylindrical barrel made from 160,000 individual scintillating crystals, each approximately the width and length of a matchstick. This crystal barrel will be capped on its open ends with disks containing delicately layered radiation-hard silicon sensors. The barrel, about 2 meters in diameter, will surround the inner detectors that compose CMS’s tracking system closest to the collision point. DiPetrillo and her colleagues are currently working out how the various sensors and electronics at each end of the barrel will coordinate to give a time stamp within 30 to 50 picoseconds.

    “Normally when a particle passes through a detector, the energy it deposits is converted into an electrical pulse that rises steeply and the falls slowly over the course of a few nanoseconds,” says Joel Butler, the Fermilab scientist coordinating this project. “To register one of these passing particles in under 50 picoseconds, we need a signal that reaches its peaks even faster.”

    Scientists can use the steep rising slopes of these signals to separate the collisions not only in space, but also in time. In the barrel of the detector, a particle passing through the crystals will release a burst of light that will be recorded by specialized electronics. Based on when the intense flash of light arrives at each sensor, physicists will be able to calculate the particle’s exact location and when it passed. Particles will also produce a quick pulse in the endcaps, which are made from a new type of silicon sensor that amplifies the signal. Each silicon sensor is about the size of a domino and can determine the location of a passing particle to within 1.3 millimeters.

    The physicists working on the timing detector plan to have all the components ready and installed inside CMS for the start-up of the High Luminosity LHC in 2027

    “High-precision timing is a new concept in high-energy physics,” says DiPetrillo. “I think it will be the direction we pursue for future detectors and colliders because of its huge physics potential. For me, it’s an incredibly exciting and novel project to be on right now.”


    CERN map

    CERN LHC Maximilien Brice and Julien Marius Ordan

    CERN LHC particles



    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS


    CERN/ALICE Detector

    CERN CMS New

    CERN LHCb New II

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 1:54 pm on February 11, 2020 Permalink | Reply
    Tags: Although scientists have yet to find the spooky stuff they aren’t completely in the dark., , , , It all adds up to 85% of the universe., It shaped entire galaxies without touching a thing., It’s built to last., Natalia Toro, Symmetry Magazine,   

    From Symmetry: “What we know about dark matter” 

    Symmetry Mag
    From Symmetry<

    Jim Daley

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

    Although scientists have yet to find the spooky stuff, they aren’t completely in the dark.

    There are a lot of things scientists don’t know about dark matter: Can we catch it in a detector? Can we make it in a lab? What kinds of particles is it made of? Is it made of more than one kind of particle? Is it even made of particles at all?

    In short, dark matter is still pretty mysterious. The term is really just the name scientists gave to an ingredient that seems to be missing from our understanding of the universe.

    But there are some things scientists can definitively say about the stuff.

    Natalia Toro is a theoretical physicist at the US Department of Energy’s SLAC National Accelerator Laboratory and a member of the Light Dark Matter Experiment (LDMX) and the Beam Dump Experiment (BDX) dark matter search. She gave a talk at the 2019 meeting of the American Physical Society’s Division of Particles and Fields about the short list of things we do know about dark matter.

    Light Dark Matter Experiment (LDMX).https://www.researchgate.net/figure/The-LDMX-experiment-layout_fig4_330726206

    Beam Dump Experiment. https://www.jlab.org/accel/ops/ops_liaison/BDX/BDX.html

    1. It’s built to last.

    Dark matter formed very early on in the universe’s history. The evidence of this is apparent in the cosmic microwave background, or CMB—the ethereal layer of radiation left over from the universe’s searingly hot first moments.

    The fact that so much dark matter still seems to be around some 13.7 billion years later tells us right away that it has a lifetime of at least 1017 seconds (or about 3 billion years), Toro says.

    But there is another, more obvious clue that the lifetime of dark matter is much longer than that: We don’t see any evidence of dark matter decay.

    The heaviest particles in the Standard Model of particle physics break down, releasing their energy in the form of lighter particles. Dark matter doesn’t seem to do that, Toro says. “Whatever dark matter is made of, it lasts a really long time.”

    This property isn’t unheard of—electrons, protons and neutrinos all have extremely long lifespans—but it would be unusual, especially if dark matter turns out to be heavier than those light, stable particles.

    “One possibility is that there’s some kind of charge in nature, and dark matter is the lightest thing that carries that charge,” Toro says.

    In particle physics, charge must be conserved—meaning it cannot be created or destroyed. Take the decay of a muon, a heavier version of an electron. A muon often decays into a pair of neutrinos, one positively charged and one negatively charged, and an electron, which shares the muon’s negative charge. The charges of the neutrinos cancel one another out. So even though the muon has fallen apart into three other particles, its electromagnetic charge is conserved overall in the results of the decay.

    The electron is the lightest particle with a negative electromagnetic charge. Since there’s nothing with a smaller mass for it to decay into, it remains stable.

    But the electromagnetic charge is not the only type of charge. Protons, for example, are the lightest particle to carry a charge called the baryon number, which is related to the fact that they’re made of particles called quarks (but not anti-quarks). Quarks and gluons have what physicists call color charge, which seems to be conserved in particle interactions.

    It could be that dark matter particles are the most stable particles with a new kind of charge.

    2. It shaped entire galaxies without touching a thing.

    Dark matter’s apparent stability seems to have been key to another of its qualities: its ability to influence the evolution of the universe. Astrophysicists think that most galaxies would probably not have formed as they did without the help of dark matter.

    In the 1930s Swiss astrophysicist Fritz Zwicky noted that something seemed to be causing galaxies in the Coma Cluster to behave as if they were 400 times heavier than they would if they contained only luminous material. That discrepancy has today been calculated to be smaller, but it still exists. Zwicky coined the term “dark matter” to describe whatever could be giving the galaxies their extra mass.

    In the 1970s Vera Rubin, an astronomer at the Carnegie Institution in Washington, used spectrographic evidence to determine that spiral galaxies such as our own also seemed to be acting more massive than they appeared. They were rotating far more quickly than expected, something that could happen if they were, for example, sitting in invisible halos of dark matter.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

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

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

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

    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

    Dark Matter Research

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

    Scientists studying the cosmic microwave background [CMB]hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    [caption id="attachment_73741" align="alignnone" width="632"] CMB per ESA/Planck

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    Scientists have seen another effect of dark matter on luminous material. Clusters of dark matter act as cosmic potholes on the path that light travels through the cosmos, bending and distorting it in a process called “gravitational lensing.” Astronomers can map the distribution of otherwise invisible dark matter by studying this lensing.

    Just like regular matter, dark matter isn’t evenly distributed across the universe. Astrophysicists think that when the galaxies first formed, areas of the universe that had slightly more dark matter (and thus more gravitational pull) attracted more matter, leading to the distribution of galaxies that we now see.

    Had there been a different pattern of dark matter throughout the universe—or slightly more or less of it—then galaxies might have formed later, formed with different densities or never formed at all, Toro says. “Galaxies become a lot denser, and you could end up in a situation where lots of black holes form, or you could end up with much more dark matter.”

    Despite being massively (forgive the pun) influential, dark matter is famously standoffish, avoiding most of the kinds of interactions that Standard Model particles commonly undergo from the very beginning. “One thing that we know concretely from looking at the CMB is that there was a component of that plasma that was not interacting with the electrons and protons,” she says. “That’s one very clear constraint—that the constituents of dark matter interacted less than electrons and protons.”

    Dark matter is so nonreactive that it may not even interact with itself; when two galaxies merge, their respective dark matter halos simply pass through one another like ghosts.

    3. It all adds up to 85%.

    Amazingly, despite being unclear on precisely what dark matter is, astrophysicists do know pretty well how much of it there is—which is why we can say that it accounts for 85% of the known matter in the universe. Physicists call that amount the “cosmological abundance” of dark matter.

    Cosmological abundance can tell us a great deal about the makeup of the universe, Toro says—particularly in its earliest days, when it was much smaller and denser. During the evolution of the early universe, “average density was very representative” of the actual dark matter present in any area of it, she says.

    Currently, Toro says, dark matter’s cosmological abundance is “the only number physicists can hang our hat on.” Scientists have proposed—and are actively searching for—a number of different possible dark matter candidates. Whether dark matter is made up of a smaller number of heavy WIMPs or a larger number of light axions, its total mass must add up to the measure of the cosmological abundance.

    Toro says it’s important to take that number as far as it can be taken and to try to extrapolate different strategies for looking for dark matter from it.

    Quantifying anything else about dark matter—its interaction strength, its scattering rate and a laundry list of other potential properties—would be “amazing,” she says. “Having any confirmation, finding one more property of dark matter that we could actually quantify, would be a huge jump.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 10:33 am on February 4, 2020 Permalink | Reply
    Tags: "On background", , , , Symmetry Magazine   

    From Symmetry: “On background” 

    Symmetry Mag
    From Symmetry

    Jim Daley

    Physicists deal with background in their experiments in two ways: by reducing it and by rejecting it.

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

    One site where “background” is well blocked.

    To some degree, scientists on all of today’s particle physics experiments share a common challenge: How can they pick out the evidence they are looking for from the overwhelming abundance of all the other stuff in the universe getting in their way?

    Physicists refer to that stuff—the unwelcome clamor of gamma rays, cosmic rays and radiation crowding particle detectors—as background.

    “You’re trying to find a signal that is small and that has a lot of stuff around it that could fake it,” says Rupak Mahapatra, an experimental particle physicist at Texas A&M University, who battles background while developing next-generation dark matter detectors for the Super Cryogenic Dark Matter Search, or SuperCDMS.

    SLAC SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    Mahapatra sums up the strategies for mitigating background in two words: reduction and rejection. To reduce backgrounds, physicists build shielding around detectors and construct them from materials that are as unreactive as possible. To reject background, they use complex analyses to filter signal from noise.

    Shielding often comes in the form of lead or water—or even a mile or so of rock. Detectors looking for hard-to-spot targets such as neutrinos or dark matter are often built far underground to protect them from cosmic rays. That works pretty well. For SuperCDMS, going underground results in a reduction of background events in the detector each day from around a billion to about one.

    A scientist’s dream is to design experiments that have no background at all, says Lindley Winslow, an experimental nuclear and particle physicist at MIT. She works on the Cryogenic Underground Observatory for Rare Event Neutrinos (CUORE) experiment, which uses tellurium dioxide crystals to search for evidence of a phenomenon called neutrinoless double-beta decay.

    CUORE experiment,at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS) in located in the Abruzzo region of central Italy,a search for neutrinoless double beta decay

    Finding neutrinoless double-beta decay would be a sign that neutrino particles are their own antiparticles. Like SuperCDMS, CUORE is located deep underground to shield it from cosmic rays. The main background for CUORE is gamma rays, which can be produced by cosmic rays. But gamma rays don’t only rain down from interactions between cosmic rays and Earth’s atmosphere. They are also emitted by the materials that make up the CUORE detector itself.

    The main background for CUORE is gamma rays, which can be produced by cosmic rays. But gamma rays don’t only rain down from interactions between cosmic rays and Earth’s atmosphere. They are also emitted by the materials that make up the CUORE detector itself.

    Winslow works on both CUORE and a dark matter experiment with the especially long name “A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus,”—or ABRACADABRA for short.

    “At some level, you can’t get rid of all the background,” she says. “What you need, then, is to get smarter” about designing the experiment.

    For Michelle Dolinski, an experimental particle physicist at Drexel University, background includes anything that can deposit similar levels of energy in detectors as the kinds of particles she and her colleagues are looking for. She works with the EXO-200 and nEXO detectors, liquid xenon detectors used to search for neutrinoless double-beta decay. “We’re very sensitive to even tiny backgrounds that wouldn’t make a difference to many other experiments,” Dolinski says.

    “Even though we strive to find materials with some of the lowest radioactivity content anywhere, there’s still a tiny bit of radioactivity that can deposit energy in our detector,” Dolinski says.

    For its part, EXO-200 uses innovations both in how the detector is designed and built and in how researchers analyze the data. “We’ve developed a number of metrics that help us distinguish signal from background,” Dolinski says.

    For one thing, a signal coming from neutrinoless double-beta decay would most likely come from a single site in the detector, whereas background signals often come from multiple sites. Scientists can use this distinction to roughly identify each. “It’s not a perfect discriminator, but it gives us some ability to distinguish signal and background,” Dolinski says.

    Any gamma rays that do sneak in are most likely to come from the walls of the detector, which gives the researchers a clue to identify them. “We can look at the distribution of events, and if they’re concentrated more towards the wall, that’s more likely to be background than signal,” Dolinski explains.

    Dolinski and her colleagues plug all of these clues into a neural network for analysis. “We construct an optimal discriminator that says, on an event-by-event basis, what looks more like signal or background,” she says. “And we use that as a parameter when we do our final analysis.”

    As physicists continue to search for dark matter and rare physics events that could change our understanding of the Standard Model, the challenge of dealing with background will always be there. The good news is that scientists continue to get better and better at filtering it out.

    Until they discover what they’re looking for, “particle physicists will never stop building the next generation of detectors,” Mahapatra says. “We’ll always have to come up with new technologies to bypass what appears to be irreducible background.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 1:19 pm on January 21, 2020 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine,   

    From Symmetry: “The other dark matter candidate” 

    Symmetry Mag
    From Symmetry<

    Laura Dattaro

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    CERN CAST Axion Solar Telescope

    As technology improves, scientists discover new ways to search for theorized dark matter particles called axions.

    In the early 1970s, physics had a symmetry problem. According to the Standard Model, the guiding framework of particle physics, a symmetry between particles and forces in our universe and a mirror version should be broken.

    Standard Model of Particle Physics

    It was broken by the weak force, a fundamental force involved in processes like radioactive decay.

    This breaking should feed into the interactions mediated by another fundamental force, the strong force. But experiments show that, unlike the weak force, the strong force obeys mirror symmetry perfectly. No one could explain it.

    The problem confounded physicists for years. Then, in 1977, physicists Roberto Peccei and Helen Quinn found a solution: a mechanism that, if it existed, would cause the strong force to obey this symmetry and right the Standard Model.

    Shortly after, Frank Wilczek and Steven Weinberg—both of whom went on to win the Nobel Prize—realized that this mechanism creates an entirely new particle. Wilczek ultimately dubbed this new particle the axion, after a dish detergent with the same name, for its ability to “clean up” the symmetry problem.

    Several years later, the theoretical axion was found not only to solve the symmetry problem, but also to be a possible candidate for dark matter, the missing matter that scientists think makes up 85% of the universe but the true nature of which is unknown.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

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

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

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

    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

    Dark Matter Research

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

    Scientists studying the cosmic microwave background [CMB]hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    [caption id="attachment_73741" align="alignnone" width="632"] CMB per ESA/Planck

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    Despite its theoretical promise, though, the axion stayed in relative obscurity, due to a combination of its strange nature and being outshone by another new dark matter candidate, called a WIMP, that seemed even more like a sure thing.

    But today, four decades after they were first theorized, axions are once again enjoying a moment in the sun, and may even be on the verge of detection, poised to solve two major problems in physics at once.

    “I think WIMPs have one last hurrah as these multiton experiments come online,” says MIT physicist Lindley Winslow. “Since they’re not done building those yet, we have to take a deep breath and see if we find something.

    “But if you ask me the thing we need to be ramping up, it’s axions. Because the axion has to be there, or we have other problems.”

    Around the time the axion was proposed, physicists were developing a theory called Supersymmetry, which called for a partner for every known particle.

    Standard Model of Supersymmetry via DESY

    The newly proposed dark matter candidate called a WIMP—or weakly interacting massive particle—fit beautifully with the theory of Supersymmetry, making physicists all but certain they’d both be discovered.

    Even more promising was that both the supersymmetric particles and the theorized WIMPs could be detected at the Large Hadron Collider at CERN.


    CERN map

    CERN LHC Maximilien Brice and Julien Marius Ordan

    CERN LHC particles



    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS


    CERN/ALICE Detector

    CERN CMS New

    CERN LHCb New II

    “People just knew nature was going to deliver supersymmetric particles at the LHC,” says University of Washington physicist Leslie Rosenberg. “The LHC was a machine built to get a Nobel Prize for detecting Supersymmetry.”

    Experiments at the LHC made another Nobel-worthy discovery: the Higgs boson. But evidence of both WIMPS and Supersymmetry has yet to appear.

    Peter Higgs

    CERN CMS Higgs Event May 27, 2012

    CERN ATLAS Higgs Event

    Axions are even trickier than WIMPs. They’re theorized to be extremely light—a millionth of an electronvolt or so, about a trillion times lighter than the already tiny electron—making them next to impossible to produce or study in a traditional particle physics experiment. They even earned the nickname “invisible axion” for the unlikeliness they’d ever be seen.

    But axions don’t need to be made in a detector to be discovered. If axions are dark matter, they were created at the beginning of the universe and exist, free-floating, throughout space. Theorists believe they also should be created inside of stars, and because they’re so light and weakly interacting, they’d be able to escape into space, much like other lightweight particles called neutrinos. That means they exist all around us, as many as 10 trillion per cubic centimeter, waiting to be detected.

    In 1983, newly minted physics professor Pierre Sikivie decided to tackle this problem, taking inspiration from a course he had just taught on electromagnetism. Sikivie discovered that axions have another unusual property: In the presence of an electromagnetic field, they should sometimes spontaneously convert to easily detectable photons.

    “What I found is that it was impossible or extremely difficult to produce and detect axions,” Sikivie says. “But if you ask a less ambitious goal of detecting the axions that are already there, axions already there either as dark matter or as axions emitted by the sun, that actually became feasible.”

    When Rosenberg, then a postdoc working on cosmic rays at the University of Chicago, heard about Sikivie’s breakthrough—what he calls “Pierre’s Great Idea”—he knew he wanted to dedicate his work to the search.

    “Pierre’s paper hit me like a rock in the head,” Rosenberg says. “Suddenly, this thing that was the invisible axion, which I thought was so compelling, is detectable.”

    Rosenberg began work on what’s now called the Axion Dark Matter Experiment, or ADMX. The concept behind the experiment is relatively simple: Use a large magnet to create an electromagnetic field, and wait for the axions to convert to photons, which can then be detected with quantum sensors.

    When work on ADMX began, the technology wasn’t sensitive enough to pick up the extremely light axions. While Rosenberg kept the project moving forward, much of the field has focused on WIMPs, building ever-larger dark matter detectors to find them.

    But neither WIMPs nor supersymmetric particles have been discovered, pushing scientists to think creatively about what happens next.

    “That’s caused a lot of people to re-evaluate what other dark matter models we have,” says University of Michigan theorist Ben Safdi. “And when people have done that re-evaluation, the axion is the natural candidate that’s still floating around. The downfall of the WIMP has been matched exactly by the rise of axions in terms of popularity.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:46 pm on January 9, 2020 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine,   

    From Symmetry: “Expanding a neutrino hunt in the South Pole” 

    Symmetry Mag
    From Symmetry<

    Diana Kwon

    Photo by Martin Wolf, IceCube/NSF

    A forthcoming upgrade to the IceCube detector will provide deeper insights into the elusive particles.

    Underneath the vast, frozen landscape of the South Pole lies IceCube, a gigantic observatory dedicated to finding ghostly subatomic particles called neutrinos. Neutrinos stream through the Earth from all directions, but they are lightweight, abundant and hardly interact with their surroundings.

    The IceCube detector consists of an array of 86 strings festooned with more than 5000 sensors, like round, basketball-sized Christmas lights. They reach more than 2 kilometers (more than 1 mile) down through layers of Antarctic ice that have accumulated over hundreds of thousands of years.

    A small fraction of the neutrinos that pass through the ice collide with its atoms and spit out showers of particles, some of which can be spotted by IceCube’s sensors as sparks of blue light. By probing the light patterns, scientists can identify and assess the elusive particles, some of which originate beyond our solar system.

    In July 2019 the IceCube collaboration announced that the US National Science Foundation had granted it $23 million to put toward a $37 million upgrade, with additional financial support coming from Michigan State University, the University of Wisconsin–Madison, and agencies in Germany and Japan.

    The upgrade will add seven more strings of sensors to the detector, along with new instruments meant to characterize the ice. This extension will allow physicists to better understand how neutrinos oscillate between their three flavors: electron, muon and tau. Scientists also plan to make more precise measurements of IceCube’s icy interior to get a closer look at neutrinos from far out in the universe.

    U Wisconsin IceCube neutrino observatory

    U Wisconsin ICECUBE neutrino detector at the South Pole

    U Wisconsin IceCube experiment at the South Pole

    U Wisconsin ICECUBE neutrino detector at the South Pole

    IceCube Gen-2 DeepCore PINGU

    IceCube reveals interesting high-energy neutrino events

    When cosmic neutrinos crash into the IceCube detector, the interactions generate secondary particles that travel faster than the speed of light through the ice, producing a detectable faint blue glow. Courtesy of Nicolle R. Fuller/NSF/IceCube

    Extraterrestrial signals

    One of the main aims of IceCube, which is run by an international group of more than 300 scientists from 12 different countries, is to identify cosmic neutrinos. They know which neutrinos come from afar by the extraordinarily high levels of energy they have when they crash into the Earth, compared to their more local counterparts. By studying these alien particles, physicists hope to identify the powerful cosmic accelerators that form beams of ultra-high energy particles.

    IceCube had its first major breakthrough in 2013 when it identified two ultra-high energy neutrinos from outside the solar system. These events, dubbed Bert and Ernie, became the first of many cosmic neutrino detections, says Olga Botner, a physicist at Uppsala University in Sweden and former spokesperson of IceCube.

    “We knew we were in business,” she says. “We could observe not only the atmosphere but also neutrinos from outside our own galaxy. That was huge.”

    Four years later, IceCube physicists made a detection of an extraterrestrial neutrino that sparked a search for a glimpse of its source by scientists at astronomical observatories around the globe. This worldwide hunt allowed scientists to pinpoint the particle’s birthplace: an extremely luminous galaxy called a blazar. A blazar acts like a cosmic accelerator, spitting out a constant stream of particles from its core.

    “Working on IceCube is very exciting,” says Delia Tosi, an assistant scientist at the Wisconsin IceCube Particle Astrophysics Center (WIPAC). “There is no space for boredom.”

    Where most cosmic neutrinos come from remains a mystery. But IceCube’s scientific repertoire has expanded since those first discoveries. Scientists also use IceCube to examine how neutrinos change from one type to another—which could help determine whether there are new types of neutrinos that we don’t yet know about—as well as to search for dark matter and characterize how light travels though Antarctic ice.

    “When we started IceCube, we were 90% focused on finding point sources of astrophysical neutrinos,” says Kael Hanson, a physicist and director of WIPAC. “We really had no idea, when we were designing the experiment, how rich the science program would eventually become.”

    An upgrade on ice

    With the forthcoming upgrade, more than 700 new sensors spread across seven strings will be added to the center of IceCube.

    The core is already more densely packed with strings than the rest of the detector, which makes it better able to detect particles at low energies. The new sensors will push that sensitivity even further. “We’re pushing the energy threshold down by a factor of 10,” Hanson says.

    The denser core will make it possible for the scientists to examine the hundreds of thousands of atmospheric neutrinos that bombard the detector each year in more detail. This will allow physicists to make more accurate measurements of the tau neutrino, which can then be used to better understand neutrino oscillations—specifically, how muon neutrinos convert to tau neutrinos.

    “We don’t quite understand how neutrinos can spontaneously morph from one flavor to another,” Botner says. “If discrepancies exist between our predictions and what we observe, this would be a hint of unknown neutrino kinds—the so-called sterile neutrino.”

    To insert new strings into the detector, scientists must drill deep holes into the ice using a high-pressure stream of hot water. During the upgrade, scientists will deploy additional calibration instruments, such as cameras and light sources, along with the detectors to help them characterize the ice.

    When water refreezes around the strings—a process that can take several weeks—the ice that forms can contain dust and bubbles. These imperfections make it more difficult to see signs of neutrinos.

    Not only will characterizing the ice make it possible for scientists to more accurately assess future observations, researchers will also be able to apply this new knowledge to previously collected data. “In principle, we can recalibrate all the data and improve our ability to point back to a source,” says Dawn Williams, a particle astrophysicist at the University of Alabama.

    The IceCube collaboration plans to start drilling in late 2022. In the meantime, the group is preparing the sensors and other components of the upgrade as well as the software that will be used to run the upgraded detector. The team expects to start collecting data in the spring of 2023.

    The upgrade also serves an additional purpose: to test new sensor designs that scientists hope might be deployed in IceCube-Gen2, a proposed detector that would be 10 times the size of the current one. The super-sized observatory would allow scientists to conduct even more precise measurements of neutrinos and detect more ultra-high-energy particles from outer space, heightening the possibly of pinpointing their sources.

    See the full article here .


    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 9:24 am on January 7, 2020 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine, ,   

    From Symmetry: Women in STEM -“Vera Rubin, giant of astronomy” 

    Symmetry Mag
    From Symmetry<

    Kathryn Jepsen

    Illustration by Sandbox Studio, Chicago with Ana Kova

    The Large Synoptic Survey Telescope will be named for an influential astronomer who left the field better than she found it.

    The LSST Vera C. Rubin Observatory

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

    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

    The Large Synoptic Survey Telescope, a flagship astronomy and astrophysics project currently under construction on a mountaintop in Chile, will be named for astronomer Vera Rubin, a key figure in the history of the search for dark matter.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

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

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    Dark Matter Research

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

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA

    Inside the ADMX experiment hall at the University of Washington Credit Mark Stone U. of Washington. Axion Dark Matter Experiment

    The LSST collaboration announced the new name at the 235th American Astronomical Society meeting in Honolulu on Monday evening, in conjunction with US funding agencies the Department of Energy and the National Science Foundation.

    Scheduled to begin operation in late 2022, the Vera C. Rubin Observatory will undertake a decade-long survey of the sky using an 8.4-meter telescope and a 3200-megapixel camera to study, among other things, the invisible material Rubin is best known for bringing into the realm of accepted theory.

    Rubin was a role model, a mentor, and a boundary-breaker fueled by a true love of science and the stars. “For me, doing astronomy is incredibly great fun,” she said in a 1989 interview with physicist and writer Alan Lightman. “It’s just an incredible joy to get up every morning and come to work and, in some much larger framework, not even really quite know what it is I’m going to be doing.”

    Between the Lightman interview and An Interesting Voyage, a biography she wrote in 2010 for the Annual Review of Astronomy and Astrophysics, among other things, she left behind a detailed record of the story of her life.

    A curious child

    Rubin’s father, Pesach Kobchefski (later known as Philip Cooper), was born in Lithuania. Her mother, Rose Applebaum, was a second-generation American born to Bessarabian parents in Philadelphia. Rubin’s parents met at work at the Bell Telephone Company. They married and raised two children, Vera and her older sister, Ruth.

    Rubin was born in 1928. She wrote that she remembered growing up “amid a cheery scatter of grandparents, aunts, uncles and cousins… largely shielded from the financial difficulties” of the Great Depression. Ruth and Vera shared a room, with Vera’s bed against a window with a clear view of the north sky. “Soon it was more interesting to watch the stars than to sleep,” Rubin wrote.

    Her parents encouraged her curiosity. Her mother gave her written permission at an early age to check out books from the “12 and over” section of the library, and her father helped her build a (rather so-so) homemade telescope. “My parents were very, very supportive,” Rubin said in the interview with Lightman, “except that they didn’t like me to stay up all night.”

    Rubin’s teachers were not universally as encouraging. Her high school physics teacher, she wrote, “did not know how to include the few young girls in the class, so he chose to ignore us.” Still, Rubin knew she wanted to go into astronomy. “I didn’t know a single astronomer,” she said, “but I just knew that was what I wanted to do.”

    She did know about at least one female astronomer: Maria Mitchell, the first female professional astronomer in the United States. From 1865 to 1888, Mitchell taught at Vassar College in New York and served as director of Vassar College Observatory.

    Looking to follow in her footsteps, Rubin applied to Vassar. She was accepted with a necessary scholarship. Rubin said that when she told the high school physics teacher about it, he replied, “‘As long as you stay away from science, you should be okay.’”

    She graduated in three years as the only astronomy major in her class.

    A family effort

    Rubin spent summers in Washington, DC, working at the Naval Research Laboratory. The summer of 1947, her parents introduced her to Robert (Bob) Rubin. He was training to be an officer in the US Navy and studying chemistry at Cornell University.

    The two married in 1948. She was 19 and he was 21. Vera had been accepted to Harvard University, which was well known for its astronomy department, but she decided to join her husband at Cornell instead.

    Rubin completed her master’s thesis just before giving birth to her first child, and she gave a talk on her research at the 1950 meeting of the American Astronomical Society just after. Her adviser had said it made more sense for him to give the talk, as he was already a member of AAS and she would be a new mother, but Rubin insisted she would do it.

    “We had no car,” Rubin wrote. “My parents drove from Washington, DC, to Ithaca, then crossed the snowy New York hills with Bob, me and their first grandchild, ‘thereby aging 20 years,’ my father later insisted.”

    She gave a 10-minute talk on her study of the velocity distribution of the galaxies that at that time had published velocities. It solicited replies from several “angry-sounding men,” along with pioneering astronomer Martin Schwarzschild, who, Rubin wrote, kindly “said what you say to a young student: ‘This is very interesting, and when there are more data, we will know more.’”

    For a few months after the experience, Rubin stayed home with her newborn son. But she couldn’t keep away from the science. “I would push David to the playground, sit him in the sandbox, and read The Astrophysical Journal,” Rubin wrote.

    With her husband’s encouragement, she enrolled in the astronomy PhD program at Georgetown University. Her classes took place at night, twice per week. Those nights, between 1952 and 1954, Rubin’s mother babysat David (and, not long after, also her daughter, Judy) while Bob drove her to the observatory and waited to take her back home, eating his dinner in the car. In astronomy, “women generally required more luck and perseverance than men did,” Rubin wrote. “It helped to have supportive parents and a supportive husband.”

    PhD and beyond

    Theoretical physicist and cosmologist George Gamow—known for his contributions to developing the Big Bang theory, among other foundational work—heard about Rubin’s AAS talk and began asking her questions, Rubin wrote. One question—“Is there a scale length in the distribution of galaxies?”—so intrigued her that she decided to take it on for her thesis. Gamow served as her advisor.

    Rubin wrote that when she sent her research to The Astrophysical Journal in 1954, then-editor and later Nobel Laureate Subrahmanyan Chandrasekhar rejected it, saying he wanted her to wait until his student finished his work on the same subject. She did not wait, publishing in the Proceedings of the National Academy of Sciences instead. (A later editor of Astrophysical Journal asked her to send him Chandrasekhar’s letter as proof, and she wrote, “I refused, telling him to look it up in his files.”)

    In 1955, Georgetown offered Rubin a research position, which soon became a teaching position as well. She stayed there for 10 years.

    In 1962, Rubin taught a graduate course in statistical astronomy with six students, five who worked for the US Naval Observatory and one who worked for NASA. “Due to their jobs, the students were experts in star catalogs,” Rubin wrote, “so I gave the students (plus me as a student) a research problem: Can we use cataloged stars to determine a rotation curve for stars distant from the center of our [g]alaxy?”

    The group completed the paper, “some of it finished by seven of us working around my large kitchen table, long into the night,” Rubin wrote, and they submitted it to The Astrophysical Journal.

    The editor called to say he would accept the paper but that he would not take the then-unusual step of publishing the names of the students, Rubin wrote. When Rubin replied that she would then withdraw the paper, however, he changed his mind.

    Rubin wrote that she received many negative “and some very unpleasant” responses to the paper, but that it continued to be referenced every few years, even as she was writing in 2010. As she pointed out in her article, “[t]his was my first flat rotation curve”—a result she would see repeated in what would become her most famous publication.

    During the 1963-1964 school year, Bob took a sabbatical so Vera could move the family to San Diego and work with married couple Margaret and Geoffrey Burbidge. With two other scientists, they had in 1957 published the seminal paper explaining how thermonuclear reactions in stars could transform a universe originally made up only of hydrogen, helium and lithium into one that could support life. With the Burbidges, Rubin traveled to both Kitt Peak National Observatory in Arizona and McDonald Observatory in Texas.

    More than three decades later, in letter to Margaret Burbidge on her 80th birthday, Rubin described what the scientist had meant to her: “Did the words ‘role model’ and ‘mentor’ exist then? I think they did not. But for most of the women that followed you into astronomical careers, these were the roles you filled for us.”

    What Rubin best remembers from when she first arrived in San Diego, she wrote, “was my elation because you took me seriously and were interested in what I had to say…

    “From you we have learned that a woman too can rise to great heights as an astronomer, and that it’s all right to be charming, gracious, brilliant, and to be concerned for others as we make our way in the world of science.”

    The view from Palomar

    Caltech Palomar Hale Telescope, located in San Diego County, California, US, at 1,712 m (5,617 ft)

    In 1964, Rubin and her family (which now included four children, between ages 4 and 13) returned home. Shortly thereafter, Vera and Bob took off again for the meeting of the International Astronomical Union in Hamburg. (“Fortunately, my parents enjoyed being with their grandchildren,” Rubin wrote.)

    On the last evening of the conference, influential astronomer Allan Sandage, who in 1958 had published the first good estimate of the Hubble constant, asked Rubin if she were interested in observing on Palomar Mountain at the Carnegie Institution’s 200-inch telescope. It was a telescope, located on a mountain northeast of San Diego, that women had officially been prohibited from using (though it was a “known secret” that both Margaret and Geoffrey Burbidge had observed there together as postgraduate students). “Of course, I said yes,” Rubin wrote.

    Rubin would be observing on the same mountain where, in 1933, astronomer Fritz Zwicky [above] made a startling discovery. He noticed that the galaxies in the Coma Cluster were moving too quickly—so quickly that they should have broken apart. Judging by the mass of their visible matter, they should not have had the gravitational pull to hold together.

    He concluded that the cluster must be more massive than it appeared, and that most of this mass must come from matter that could not be seen. The Swiss astronomer called the source of the missing mass dunkle Materie, or dark matter. He presented this idea to the Swiss Physical Society, but it did not catch on. (He made several other big splashes in astronomy, though.)

    On Rubin’s first night at Palomar in December 1965, clouds prevented anyone from observing, so another observer took her on an unofficial tour of the facilities. The tour included the single available toilet, labeled “MEN.”

    On Rubin’s next visit, “I drew a skirted woman and pasted her up on the door,” she wrote. The third time she came to observe, heating had been added to the observing room, along with a gender-neutral bathroom.

    The world’s best spectrograph

    In 1965, Rubin decided to prioritize observing over teaching. She asked her colleague Bernie Burke—famous for co-discovering the first detection of radio noise from another planet, Jupiter—for a job at the Carnegie Institution’s Department of Terrestrial Magnetism. Burke invited her to the DTM’s community lunch. And that’s where she met astronomer Kent Ford.

    Working over the previous decade, Ford had pioneered the use of highly sensitive light detectors called photomultiplier tubes for astronomical observation. “Kent Ford had built a very exceptional spectrograph,” Rubin said. “He probably had the best spectrograph anywhere. He had a spectrograph that could do things that no other spectrographs could do.”

    Rubin got the job at DTM, becoming the first female scientist on its staff. Using Ford’s spectrograph on the telescope at Lowell Observatory in Arizona [above], Ford and Rubin could observe objects that were not otherwise detectable. Among the astronomers who noticed was Jim Peebles, winner of the 2019 Nobel Prize for Physics.

    By 1968, Rubin and Ford had published nine papers. “It was an exciting time,” Rubin wrote, “but I was not comfortable with the very rapid pace of the competition. Even very polite phone calls asking me which galaxies I was studying (so as not to overlap) made me uncomfortable.”

    So she decided to go back to a subject she had previously dabbled in: the velocity of stars and regions of ionized hydrogen in Messier 31, the Andromeda galaxy. “I decided to pick a problem that I could go observing and make headway on, hopefully a problem that people would be interested in, but not so interested [in] that anyone would bother me before I was done,” Rubin said.

    Astronomers had been studying the spectra of light from Andromeda since at least January 1899, but no one had taken a look with an instrument as advanced as Ford’s.

    One astronomer had gotten a better look than most, though. In the 1940s, astronomer Walter Baade had taken advantage of wartime blackout rules—meant to make it difficult for enemy planes to hit targets during World War II—to observe Andromeda from Mount Wilson Observatory northeast of Los Angeles.

    Mt Wilson 100 inch Hooker Telescope, perched atop the San Gabriel Mountains outside Los Angeles, CA, USA, Mount Wilson, California, US, Altitude 1,742 m (5,715 ft)

    He resolved the stars at the center of the galaxy for the first time and identified 688 emission regions worthy of study.

    Not knowing this, Rubin and Ford set out to do the same for themselves. They spent a frustrating night taking turns at the US Naval Observatory telescope in Arizona, huddled next to a small heater in negative 20 degree cold, before deciding they needed a new tactic.

    US Naval Observatory telescope in Arizona

    On their way out in the morning, they ran into Naval Observatory Director Gerald Kron. “He took us into his warm office, opened a large cabinet and showed us copies of Baade’s many plates of stars in Messier 31!” Rubin wrote. Rubin and Ford obtained copies of the images from the Carnegie Institute and went to work.

    A rotation curveball

    Rubin and Ford made their observations at Lowell Observatory[above] and Kitt Peak.

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

    “On a typical clear night we would obtain four to five spectra,” Rubin wrote. “The surprises came very quickly.”

    In our solar system, planets closest to the center are the fastest-moving, as they are most affected by the gravitational pull of the sun. Mercury, the closest, moves about 1.6 times as rapidly as Earth, whereas Neptune, the farthest, moves at less than 0.2 times Earth’s speed.

    “The expectation was that galaxies behaved the same way, in that stars farthest from the massive center would be moving most slowly,” Rubin wrote.

    But that’s not what they found. The rotation curves were flat, meaning that objects closer to the center of Andromeda were moving at the same speed as objects closer to the outskirts. “This was discovered over the course of about 4 ice cream cones that first night,” Rubin wrote, “as I alternated between developing the plates and eating (Kent would be starting the next observation).”

    This time, Rubin said, people believed the data. “It just piled up too fast. Soon there were 20, then 40, then 60 rotation curves, and they were all flat… And it was just a joy to have that kind of a program, after a program where you had to go through deep analysis and everybody doubted the answer.”

    But what did the flat rotation curves mean? The popularly accepted answer is that the way the galaxies in Andromeda move is influenced by dark matter.

    If a galaxy is formed in the center of a disk of invisible dark matter, the gravitational pull of the dark matter will affect how quickly each of its parts moves, flattening the rotation curves.

    Theorists Peebles, Jeremiah P. Ostriker, Amos Yahil and others had predicted the existence of dark matter independent of Rubin and Ford’s findings, Rubin said. “The ideas had been around for a while… But the observations fit in so well, [since] there was already a framework, so some people embraced the observations very enthusiastically.”

    Rubin was agnostic about the idea of dark matter and wrote that she would be delighted if the explanation actually came in the form of a new understanding of how gravity works on the cosmic scale. “One needs to keep an open mind in seeking solutions,” she wrote.

    A scientific legacy

    Rubin continued her work, receiving recognition for her contributions in various ways.

    From 1972 to 1977 she served as associate editor of The Astronomical Journal, and from 1977 to 1982 she served as associate editor of Astrophysical Journal Letters. In 1993, she received the National Medal of Science from President Bill Clinton. In 1994 she received the Dickson Prize in Science from Carnegie-Mellon University and the Henry Norris Russell Lectureship from the American Astronomical Society. In 1996 she became the second woman to receive the Gold Medal of the Royal Astronomical Society in London (168 years after the first, Caroline Herschel in 1828). In 1996 President Clinton nominated her to provide input to Congress as a member of the National Science Board for a term of six years.

    In 1997 she and a few other members of the board were invited to visit the McMurdo research station at the South Pole. Rubin wrote that she was asked if she would spend her time at McMurdo with the astronomers. “With a little embarrassment, I asked if that meant that I would miss everything else, the penguins, the mountains and all the other events,” she wrote. “Without much difficulty, I voted for the penguins.”

    In 2004 the National Academy of Sciences awarded Rubin the James Craig Watson Medal for “her seminal observations of dark matter in galaxies… and for generous mentoring of young astronomers, men and women.”

    Rubin made it a priority to listen to and encourage students and up-and-coming astronomers, and she was especially interested in improving the chances for women in science.

    Asked by Lightman, “Do you think that your experience in science has been different because you are a woman rather than a man?” she replied, “Of course. Yes, of course. But I’m the wrong person to ask that question. The tragedy in that question is all the women who would have liked to have become astronomers and didn’t.”

    Rubin shared her love of astronomy far and wide. “We are fortunate to live in an era when it is possible to learn so much about the [u]niverse,” she wrote. “But I envy our children, our grandchildren, and their children. They will know more than any of us do now, and they may even be able to travel there!”

    All four of the Rubin children have gone into science.

    Her son Allan, quoted in the 2010 article, remembered his parents often spent evenings “with their work spread out along the very long dining room table, which wasn’t used for eating unless a lot of company was expected,” he said. “At some point I grew old enough to realize that if what they really wanted to do after dinner was the same thing they did all day at work, then they must have pretty good jobs.”

    Rubin’s daughter followed Vera into the field of astronomy, initially hooked by a lesson her mother taught on black holes. Over several decades, Judy has collaborated on numerous publications and attended meetings around the world with her mom.

    Rubin died in 2016 at the age of 88. Her name lives on in the AAS Vera Rubin Early Career Prize, Vera Rubin Ridge on the planet Mars, Asteroid 5726 Rubin and, now, the Vera C. Rubin Observatory on Cerro Pachón

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:23 pm on December 17, 2019 Permalink | Reply
    Tags: "New physics- naughty and nice", , , Symmetry Magazine   

    From Symmetry: “New physics, naughty and nice” 

    Symmetry Mag
    From Symmetry<

    Sarah Charley


    ‘Twas the night before vacay, and all through the lab, not a physicist was stirring, not even an undergrad. To their warm homes they went with laptops in hand, to discuss all their searches and see where they stand.

    We all know by now the Standard Model is incomplete, and filling its gaps has been quite the feat.

    Standard Model of Particle Physics

    Gravity, for instance, is a fundamental force, but at the quantum level there’s no apparent source. Many theories propose to solve this and more, so let’s take a look and settle the score.

    Supersymmetry is the first to pass through our test, as mathematically speaking, it’s by far the best. It takes our equations and makes them quite lean by adding new particles to our treasured 17. While SUSY might come with a heart full of gold, it’s from the 1970s and is starting to get old. Its simplest forms have all been ruled out, and its continued absence gives many physicists doubt.

    Dark matter’s discovery is long overdue, though in terms of physics, it’s hardly new. Astronomers see it through gravitational pull, and its direct detection is the ultimate goal. Dark matter particles might pass undetected, or leave energy or sound in the data collected. It’s quite a challenge to find what cannot be seen, especially when particle collisions are more chaotic than clean.

    Antimatter is a topic straight from sci fi, and we want to measure how the laws of physics apply. Matter and antimatter are like yin and yang; they should have been equal just after the Big Bang. Because they are the perfect peers, we can’t explain why the antimatter disappeared. There must be some differences that are still unknown, though equal and opposite is what the data has shown. There are a few hints that could explain just why matter won and antimatter waned. But maybe neutrinos could hold the key, with their mysterious oscillations between flavors of three.

    Then there are extra dimensions, which sound very cool, and provide our theorists a clever new tool. They would be curled up inside of our own, hidden from forces that are commonly known. This could be the place that gravity hides, protected and snuggled on all of its sides. It leaks into spacetime and weakly interacts, a tiny force—with huge impacts. But extra dimensions have never been seen, nor given any hints on the experimental scene.

    The idea of long-lived particles has become quite popular; these particles could go far, even a kilometer! This could be why new physics hasn’t been found—they’d pass through a detector and be absorbed by the ground. Physicists have devised many a way to look for those particles that interact with delay. They could be from SUSY, or entirely new—just finding these particles would give quite the clue!

    As physicists lie warm in their beds, with images of quarks dancing in their heads, they wonder where all the new physics might be, and dream of making the next big discovery. To some it might seem that nature hasn’t been kind, giving so few clues when there is still so much to find. But others consider all of the questions that remain, and see that there is much for humanity to gain. There are still many places for physics to bloom, whether it’s direct searches at the LHC or neutrinos at DUNE. So here’s to the future and good science as well; there are still many secrets nature has yet to tell!

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 11:40 am on December 14, 2019 Permalink | Reply
    Tags: , , Femtoscopy, , Hyperons, , , , Symmetry Magazine   

    From Symmetry: “Neutron star particles go under the LHC microscope” 

    Symmetry Mag
    From Symmetry<

    Mordechai Rorvig


    Researchers on the ALICE experiment are uncovering the properties of elusive hyperon particles hypothesized to be found inside neutron stars.

    CERN/ALICE Detector

    Scientists know a thing or two about neutron stars, the compacted remains of massive stars that have burned out.

    They know that they’re about 95% made up of neutrons. They know that they’re generally 13 to 16 miles in diameter. Scientists know that, even though neutron stars are a thousandth the size of the Earth, they’re more massive than the sun. And the closest one they know of is about 500 light-years away.

    There’s also a lot they don’t know.

    “Neutron stars are the most dense objects in the universe,” says Laura Fabbietti, a physicist on the ALICE experiment and a professor at Technische Universität München in Germany. “And we don’t know what’s inside because we cannot fly there and look inside.”

    But scientists at CERN have found a way to learn more about the interior of neutron stars from a location that is much safer and easier to access: the Large Hadron Collider, right here on Earth.

    CERN/LHC Map

    Formed under pressure

    For neutron stars, gravity becomes extremely strong, approaching that of black holes. The force of it packs their matter down to high density.

    Neutron stars must be composed of matter that can withstand this pressure. And nature rearranges any matter that can’t into new matter that can.

    Iron, for example, is thought to be a component of the neutron star’s crust, where the pressure is lightest. Slightly deeper in, scientists think that iron atoms get crushed into heavier atoms. Even deeper, the electrons and protons that hold together atoms get crushed into neutrons. In the very interior of the star, those neutrons might get crushed into particles called hyperons.

    Hyperons are akin to heavier versions of neutrons, both of which are composed of quarks.

    Standard Model of Particle Physics

    There are six types of quarks in total. Most of the matter humans interact with, except for electrons, is built with the lightest of these quarks: up and down quarks. Neutrons, for example, are made of one up quark and two down quarks.

    The next heaviest quark is called the strange quark. Replacing an up or down quark in a neutron with a heavier strange quark yields a hyperon.

    Luckily for scientists who want to study this form of matter, all the different kinds of hyperons—different combinations of up, down and strange quarks—are produced in collisions in the Large Hadron Collider.

    Their lives are different there. In experiments at the LHC, hyperons last for less than a billionth of a second before decaying into other, lighter particles. In neutron stars, however, hyperons should be stable. Because they would be pressed in so close together, there would be no room for their decay products to form.

    Their short laboratory lifespans have made hyperons historically difficult to identify and study. But the unique capabilities of the ALICE detector at the LHC allowed Fabbietti and her research team to accurately identify the hyperon decay products and track those products back to their hyperon source. An upgrade of the ALICE detector will soon allow researchers to collect even more hyperon data.

    “We’re hungry for statistics, hungry for data,” says Bernhard Hohlweger, who led analysis to identify the Xi- (pronounced zai-minus) hyperon, a hyperon with a negative electric charge. “We use everything we can get our hands on.”

    Moving in pairs

    Fabbietti’s group didn’t want just to find hyperons, though; they wanted to learn more about what they do. If they could understand hyperon motion in the ALICE detector, then they could hypothesize the way that hyperons might behave while inaccessibly buried in the universe’s densest stars.

    The chief unknown for the ALICE researchers was the way that hyperons interact with the strong force, which binds quarks together and controls particle motion at small scales. Each kind of hyperon has its own unique mathematical function called a “potential” that explains how the hyperon interacts with the strong force to move.

    “For different particle interactions, there are different potentials,” says Anthony Timmins, a member of the ALICE collaboration and a professor at the University of Houston. Timmins recently presented results on proton Xi- hyperon interactions at the annual Division of Particles & Fields meeting in Boston in July.

    To figure out the Xi- hyperon potential, Fabbieti’s group first looked at a different kind of particle that comes from collisions in the LHC: the proton. Protons have never been observed to decay like short-lived LHC hyperons—and may not decay at all—making them easier to understand by comparison. On top of that, researchers already knew the proton potentials, and that those potentials cause protons to attract or repel each other based on how far apart they are.

    The scientists observed that pairs of protons coming out of collisions tend to be pulled into parallel trajectories by their strong-force potentials. They used that observation and a method called femtoscopy to infer the approximate size of the particles’ collision zone.

    Using femtoscopy, which relates particle motions and particle potentials to the size of collision zones, is like watching debris fly out of an explosion to figure out how big an explosive device must have been. (Only in this case, the debris also interact through the strong force.)

    Having analyzed the proton pairs, the researchers then looked at pairs of protons and hyperons coming out of particle collisions. They again observed parallel motions, indicating an attractive strong-force potential at work. Because they knew the size of the collision zone from the proton pairs, the they could solve for the only unknown: the hyperon potential.

    To understand and quantify this measured potential, next they needed a prediction from theory.

    Stiffening stars

    As it turned out, scientists had recently predicted what these potentials would be. They did it theoretically through simulations of quarks.

    These simulation models are general in nature, relying only on knowledge of quarks, with no specific customizations for the LHC experiments. To the researchers’ surprise and excitement, the simulation results and the measurements from Fabbietti’s group matched.

    “If we do some honest calculations and we get the result, then this result should be realized in nature,” says Tetsuo Hatsuda, a program director at the RIKEN institute in Japan, who helped lead the simulation program. And in this case, “the result was realized in nature.”

    Using these precisely calculated potentials, Takashi Inoue from Hatsuda’s HAL QCD collaboration showed how Xi- hyperons should interact with neutrons in neutron star matter. Hyperons and neutrons were found to repel, unlike hyperons and protons measured in the ALICE detector. This repulsion would make neutron stars stiffer and more resistant to gravitational forces if hyperons were present.

    The baton now goes to astrophysicists, who can compare predicted neutron star stiffness with their observations to help answer the question whether hyperons do indeed exist inside stars.

    Fabbietti and her group plan to continue analyzing more data for different kinds of hyperons, with better precision. Fabbietti says that now “this is a factory of results,” results that show how the 17-mile, underground ring of the LHC can act as a microscope into the stars.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 10:27 am on November 19, 2019 Permalink | Reply
    Tags: "A new view into the history of the universe", , , , Symmetry Magazine   

    From Symmetry: “A new view into the history of the universe” 

    Symmetry Mag
    From Symmetry<


    Diana Kwon

    With an upgrade to the Super-Kamiokande detector, neutrino physicists will gain access to the supernovae of the past.

    Super-Kamiokande experiment. located under Mount Ikeno near the city of Hida, Gifu Prefecture, Japan

    In 1987, the explosion of a gigantic star created a brilliant light show within the Large Magellanic Cloud, a small, satellite galaxy orbiting the Milky Way. The cataclysmic event, also known as a supernova, was visible from telescopes on Earth.

    Large Magellanic Cloud. Adrian Pingstone December 2003

    This is an artist’s impression of the SN 1987A remnant. The image is based on real data and reveals the cold, inner regions of the remnant, in red, where tremendous amounts of dust were detected and imaged by ALMA. This inner region is contrasted with the outer shell, lacy white and blue circles, where the blast wave from the supernova is colliding with the envelope of gas ejected from the star prior to its powerful detonation. Image credit: ALMA / ESO / NAOJ / NRAO / Alexandra Angelich, NRAO / AUI / NSF.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    But before the light from the stellar blast reached our planet, three observatories, including the Kamiokande neutrino observatory in Japan, picked up signals from another type of particle produced in the blast: neutrinos.

    Neutrino particles, though elusive, carry away almost all of the energy released by these exploding stars. By examining them, physicists can better understand the properties of neutrinos and probe the inner workings of supernovae.

    “There’s really no way to look inside the heart of a dying star except via neutrinos,” says Mark Vagins, an experimental physicist at University of Tokyo’s Kavli Institute for the Physics and Mathematics of the Universe.

    For the last three decades, physicists have patiently waited for the next nearby supernova. Luckily, waiting is no longer the only option.

    The successor to Kamiokande, called Super-Kamiokande, is about to get an upgrade. Adding the rare earth element gadolinium to Super-K will allow scientists to search for neutrinos not only from future supernovae, but also from stellar explosions in our universe’s history.

    “Every few seconds, a supernova happens somewhere in the universe, and they are all producing neutrinos,” says Masayuki Nakahata, the spokesperson for Super-K. “By using this new technology, we will be able to detect those neutrinos.”

    Separating signal from noise

    The Super-K observatory lies under Mount Ikeno, in a mine 3300 feet below the ground in central Japan. The detector is encased within a cylindrical stainless-steel tank as tall as the Statue of Liberty. Its interior is filled with 50,000 tons of ultra-pure water and lined with approximately 13,000 photosensors—golden bulbs that detect the flashes of light produced as neutrinos pass through.

    In the early 2000s, the Super-K collaboration tried to detect neutrinos from past supernovae, which are collectively known as the diffuse supernova neutrino background. In theory, Super-K was large enough to find these particles. But the signal was being concealed by “background noise” produced by other processes.

    Neutrinos come in three different “flavours”: electron neutrino, muon neutrino and tau neutrino. Supernovae release both neutrinos and their antimatter counterparts, antineutrinos, in various flavors, but the ones that most commonly interact within detectors like Super-K are electron antineutrinos. When one these particles comes in contact with hydrogen molecules in the Super-K detector, it releases a positron, along with another particle. This process creates a flash of light that Super-K’s sensors can identify.

    The problem is, a number of other particles—including the electron neutrinos that constantly stream from the sun and pass through Super-K far more often than electron antineutrinos from supernovae—produce the same signal.

    While at a neutrino conference in Munich in 2002, Vagins and his colleague John Beacom, a theoretical physicist now at the Ohio State University, came up with a solution to this problem. “John and I decided that there had to be a way to see these darn things,” Vagins says. “We talked about many different approaches and pretty quickly realized that we were going to have to use gadolinium.”

    The duo realized that gadolinium, a rare earth metal, would be a valuable addition to Super-K due to a certain property. Gadolinium is uniquely effective at gobbling up the other kind of particle an electron antineutrino produces when it hits the purified water in Super-K detector: a neutron.

    If gadolinium were added to the Super-K detector, it would interact with a neutron released by an electron antineutrino to generate a second pulse of light.

    Dual light flashes, which Vagins and Beacom have dubbed “gadolinium heartbeats,” would come only from electron antineutrinos—they would not be produced by electron neutrinos from the sun or in interactions with other particles that until now have obscured the detection of supernova electron antineutrinos.

    “We expect the background to be reduced by a factor 10,000,” Vagins says. “It’s a tremendous gain.”

    Convincing the crowd

    When Beacom and Vagins initially pitched the idea of adding gadolinium to Super-K to the collaboration, it was not greeted with the level of enthusiasm they expected. Their colleagues were impressed by the capability of this technique, but they worried that gadolinium could harm the multi-million-dollar detector.

    Researchers worried that gadolinium might corrode the steel, alter the transparency of the water, or introduce radioactivity into the detector. “There was a huge list of issues, and we had to go through those one at a time and show that no, it was not a problem,” Vagins says.

    There were also other challenges to overcome, such as figuring out how to dissolve the gadolinium into the water. This doesn’t happen naturally. (The answer: Combine it with sulfate to make gadolinium sulfate, a salt.)

    To test the feasibly of their plan, Super-K scientists built a miniature version of the detector called Evaluating Gadolinium’s Action on Detector Systems, or EGADS. This scaled-down version of the detector was lined with 240 photosensors and had room for 200 tons of water. The team filled the prototype tank with gadolinium-loaded ultrapure water, then left it closed for around two-and-a-half years while running tests to assess the detector’s capabilities.

    Meanwhile, Beacom and his team have been gearing up for the forthcoming upgrade by conducting theoretical assessments, such as examining the details of the background signals within the gadolinium-loaded detector and the signals that can be seen within it.

    The Super-K collaboration approved the gadolinium upgrade in June 2015. But the final test came in 2017, when a group of scientists, including Vagins, donned protective bunny suits (as human skin is highly radioactive, at least in comparison to ultrapure water) and opened EGADS up to assess whether there were any signs of damage.

    “That was a pretty nervous moment,” Vagins recalls. “But when we opened up, everything was still shiny and pretty. That was pretty much the final selling point for everybody.”

    Upgrading the detector

    The Super-K collaboration will start loading the detector with gadolinium next spring. They plan to start at 0.01% gadolinium and gradually add more. At a concentration of 0.01%, gadolinium will already be able to capture around half of the neutrons that appear in the detector.

    Illustration by Sandbox Studio, Chicago with Steve Shanabruch

    To prepare for the addition of gadolinium, last year, scientists opened up Super-K for the first time in 12 years to do some repairs. This included replacing broken phototubes, adding new piping, cleaning the interior, and sealing a leak. Since it first started running, Super-K has been losing around 1 ton of water per day, Nakahata says. This was not a problem when the tank was filled with water. Now that gadolinium is being added, however, they will need to make sure the liquid does not seep into the environment.

    Gadolinium poses about the same health risk as table salt, Vagins says. “A typical individual would have to directly consume ounces of gadolinium to have problems, and since at full loading the water in Super-K will be just 0.1% gadolinium, one could drink a gallon a day right out of the tank without trouble,” he says. “Even though gadolinium is relatively harmless, we don’t want to potentially be leaking that into the mountain range or the community.”

    Gadolinium-loaded Super-K will search for neutrinos from all past supernovae in the universe at once. Each supernova makes a tremendous number of neutrinos, but the chances of detecting one from supernovae outside the Milky Way are tiny, Beacom explains. But by looking at the entire diffuse supernova neutrino background, it’ll be possible to identity around two to six neutrinos per year.

    Those neutrinos will allow physicists to address some of the many unsolved mysteries about supernovae. For example, by making it possible to examine neutrinos from supernovae throughout our universe’s history, the upgraded detector will help scientists better identify the characteristics of a typical stellar explosion.

    Gadolinium will also make Super-K much more sensitive to proton decay—a phenomena which has yet to be observed—and better able to separate neutrinos from antineutrinos.

    “I think the gadolinium loading of Super-K is a very exciting development,” says André de Gouvêa, a theoretical particle physicist at Northwestern University who is not involved with the upgrade. “I am confident we will learn something interesting about the history of the universe, supernova explosions, and the properties of neutrinos.”

    Eventually, Vagins hopes the Hyper-Kamiokande collaboration—which in 2018 was granted seed funding toward the construction of a successor to Super-K that will hold a whopping 260,000 tons of water—will also add gadolinium to its detector.

    In the meantime, there are already a number of other detectors that are planning to use gadolinium in a similar way. These include the XENONnT experiment at Gran Sasso National Laboratory in Italy, which searches for dark matter particles, and the Water Cherenkov Monitor of Antineutrinos (WATCHMEN), a US- and UK-funded experiment based in UK’s Boulby mine that will test the feasibility of identifying nuclear reactors by monitoring the telltale antineutrinos they produce.

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

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

    Vagins expects to see even more enthusiasm for gadolinium once Super-K scientists prove its worth. “I think once we’re running Super-K with gadolinium, and people get used to the physics advantages, it’ll be hard to stop future experiments from doing it,” he says.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:43 pm on November 12, 2019 Permalink | Reply
    Tags: "Transitions into medical physics", , , , Symmetry Magazine   

    From Symmetry: “Transitions into medical physics” 

    Symmetry Mag
    From Symmetry<

    Catherine N. Steffel

    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    Scientists who moved from particle physics or astrophysics to medical physics sit down with Symmetry to talk about life, science and career changes.

    “I wasn’t one of those people who grew up knowing that they wanted to be a scientist,” says Jennifer Pursley.

    Pursley found her way to physics through enthusiastic and supportive instructors. She conducted research in experimental atomic, nuclear and particle physics before finally discovering medical physics.

    Medical physicists use their knowledge of physics to develop and improve medical diagnoses and treatments. Some medical physicists create better and safer radiation therapies for cancer patients, others more accurate imaging technologies. Some work exclusively in radiation protection as health physicists, a profession often (but not always) distinguished from medical physics.

    Many particle physicists and astrophysicists like Pursley have transitioned into medical physics, taking a variety of paths to get there. To learn more, Symmetry writer Catherine Steffel spoke with five individuals, ranging from those still in training to established professionals, who entered medical physics at different stages in their careers.

    Hunter Stephens

    Current position: Medical physics PhD student at Duke University, Durham, North Carolina, United States

    Education: BS in mathematics from Tennessee Technological University; MS in theoretical particle astrophysics from North Carolina State University, both in the United States

    Year he entered medical physics: 2018

    How he came to medical physics: I finished my coursework and written PhD qualifying exams and was only doing research when I thought, is research something I want to do long-term? I started looking into other options. I had heard of medical physics, but I didn’t know what it was. I started talking to people and meeting with people.

    My main love is still research. I considered just doing a certificate program and looking for a residency, but it wasn’t going to cost me much time to make the switch [to a medical physics PhD].

    Current area of research: Optimization and fast photon dose calculations.

    Most surprising part of the job: Seeing the broad reach of a field that’s almost unrecognized. I’m surprised that I didn’t hear about it before.

    Whether he misses astrophysics: Sure, but it’s one of those things where I know I’m going to love either one, and I’d miss the other.

    Future plans: I plan to do a clinical residency and become board-certified.

    Advice for future medical physicists: Know yourself well. In physics, it’s like everything and everybody outside is less than. If you really enjoy something and you see yourself fitting in better somewhere else, don’t let that stigma or what people think change that.

    Laza Rakotondravohitra

    Current position: Radiation therapy resident at Duke University, Durham, North Carolina, United States

    Education: MS in nuclear physics from University of Antananarivo in Madagascar; PhD in experimental particle physics at Fermi National Accelerator Laboratory in the United States; post-doctoral certificate in medical physics from Wayne State University in the United States

    Year he entered medical physics: 2016

    How he came to medical physics: Every two years, scientists from the US, Europe and Africa hold the African School of Physics, where selected students from underdeveloped countries, such as Madagascar, meet for a month of training. That’s how I discovered experimental particle physics and medical physics.

    Two years later, I got an offer for the Fermilab International Fellow Scholarship. I thought that I could switch to medical physics while doing experimental particle physics research, but it didn’t happen that way. After I was accepted to the medical physics certificate program at Wayne State University, I did research at Henry Ford Health System on the MRLinac while taking classes. Doing those simultaneously made the transition relatively easy.

    Most challenging part of going into medical physics: As an international student, I had a lot of questions and had to second-guess everything. I worked really hard to come to the US, and now I want to share my experience with my students. Maybe that saves them half a year, you know?

    Most rewarding part of the job: I do the same amount of coding as I did in experimental physics, except the input data and output goal are different. It’s very rewarding because I’m doing physics like I’ve done all my life, but now someone benefits immediately.

    Future plans: Become an ABR-certified academic clinical physicist. The more time you spend in the clinic, the more you want to improve things, and improvement requires research. I also want to work together with people to bring medical physics to my country, like I did with high-energy physics.

    Advice for future medical physicists: Be prepared to humble yourself. When I finished my PhD with my friends, they went into post-doc while I went back to class. Also, be patient. If you want to have a good future, you have to invest in what you have right now.

    Jennifer Pursley

    Current position: Clinical and academic medical physicist at Massachusetts General Hospital, Boston, Massachusetts, United States

    Education: BS in physics from Gonzaga University; MA and PhD in physics from Johns Hopkins University; postdoctoral research position at the University of Wisconsin-Madison; post-graduate certificate in medical physics and residency in the Harvard Medical Physics Residency Program, all in the United States

    Other careers considered: Science and technology policy

    Year she entered medical physics: 2010

    How she came to medical physics: Going from particle physics to medical physics is not as common as it used to be. Now that we have medical physics graduate programs, more people will be coming from that pathway. But my progression since residency is pretty typical for an academic clinical physicist in the United States.

    I did two summer Research Experiences for Undergraduates programs, one in atomic and the other in nuclear physics. Job prospects pushed me to the thing that seemed most similar to nuclear physics, which was particle physics. By the end of my second year of post-doc, I wanted a job that was more satisfying, in the sense of having an immediate impact.

    Most challenging part of the job: Balancing responsibilities. It’s easy to let clinic take all of your time because it’s satisfying and there’s always something to do. I really had to figure out what I wanted and how to balance clinical work and research.

    On the job: My clinical responsibilities have shifted. As a resident, I learned how to do treatment planning and machine QA. As a junior physicist, I did that stuff. Now, I’m moving into a leadership, mentoring, and teaching role and spending more time on research.

    What she misses about particle physics: I miss having a big, collaborative group. Medical physics research often happens in a vacuum, since every institution has different software environments and commercial products. The field is starting to realize this is an issue, but there’s a long way to go.

    On the future of the field: Early on, research was primarily technology development. More recently, it’s software driven. Now, I see research going in two directions. There’s big data, artificial intelligence, and machine learning, which I think will provide some efficiency savings. There’s also radiation biology, which I’m most interested in. Namely, how do we personalize treatments, rather than just saying, “Because this works for most people, that’s what everyone gets”? Physicists can tease out information from data we already have.

    Advice for future medical physicists: Make sure you will enjoy whatever field you go into. Talk to people who are in the field, and if they’re people who have come from your current field, even better.

    Ane Appelt

    Current position: Academic and part-time clinical medical physicist at Leeds University, Leeds, England

    Education & training: BS in physics from University of Southern Denmark; MS in elementary particle physics from University of Durham in England; PhD in medical physics and radiation oncology from University of Southern Denmark; postdoctoral research position at Rigshospitalet in Denmark and MD Anderson Cancer Center in the United States

    Other careers considered: Science communication

    Year she entered medical physics: 2009

    How she came to medical physics: My theoretical [particle physics] research—for long-baseline neutrino experiments—became very demotivating because whatever came out of my project, it would be decades before anybody built the experiments. I applied to a couple of medical physics positions by chance, and I started doing research after I worked at a hospital in Denmark for about three months.

    In Denmark, you train for three years and complete modules that combine self-study, on-the-job training, and official courses. A training supervisor signs off on your progress reports, which are then approved by a central board.

    In contrast, training in the UK is directly connected to the university with on-the-job training, modules, an MSc [master of science] project, and a final review [exam]. In both Denmark and the UK, we are registered, not board-certified like in the US.

    On the job: Clinically, I’m in radiotherapy treatment planning. From a research perspective, I’m interested in reducing and predicting side effects of treatment. I also work on optimizing when we deliver a second course of radiotherapy.

    Similarities between particle and medical physics: You have large amounts of messy data that you need to clean and analyze.

    Most rewarding part of the job: You get to use your high-level skills, all your intellectual capacity, on something that matters.

    Most challenging part of the job: Because I’m not a clinician, I’m always relying on other people, which is amazing but also super frustrating at times. Sometimes I wonder if I can do an MD part time!

    Magdalena Bazalova-Carter

    Current position: Academic medical physicist at University of Victoria, BC, Canada

    Education: MS (or BS, depending on who you talk to) in physics from the Czech Technical University; PhD from McGill University in Canada; postdoctoral research position at Stanford University in the United States

    Year she entered medical physics: 2005

    How she came to medical physics: I studied dosimetry rather than medical physics in college so that I could work at CERN. When I moved to Canada, they would not recognize my MS degree from the Czech Republic, so I took medical physics courses at McGill University. Then I went to the US, where, when I was applying for the clinical board exam, my MS from the Czech Republic was recognized!

    On the job: My ideal job would be a mix of clinical and research, which is why I pursued board certification, but when I moved to Canada, I could only do academic work and research because of my visa. After I got permanent residency, I had my daughter and wanted to spend time with her. So, right now, I do not do clinical work or use my board certification.

    I am an assistant professor and a Canada Research Chair, which gives me a decreased teaching load. I supervise four graduate and two undergraduate students in my lab, the X-ray Cancer Imaging and Therapy Experimental (XCITE) lab, and I’m on too many committees. Saying “no” is increasingly important to me.

    Differences between particle and medical physics: I had to rely on too many people to make progress on ATLAS, to the point where I wasn’t sure I would finish my PhD. In medical physics, we are the only ones responsible for a project, and it’s on us whether or not we finish.

    Most surprising part of the job: The composition of conference attendees. I was used to being the only woman and one of the few young people at conferences. When I went to my first medical physics conference, the energy was very different—there were lots of young people, lots of women, and they were presenting.

    Most rewarding part of the job: Supervising students. I graduated my first two students this year.

    Another rewarding part of the job: Every new idea we have is beneficial. It would be great if more people were coming to medical physics from high-energy physics and fields like engineering. In Czech, we have a saying that “the bread will not be cheaper.” A discovery or new treatment modality won’t make the bread cheaper, but you will be saving patients’ lives or improving their quality of life.

    Future plans: The minimum goal I have is to get my students good positions. I have a proposal on FLASH radiotherapy with TRIUMF. We don’t know whether our work will be clinically translatable, but we’ll see if we can make a difference.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

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