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

    From Symmetry: “The $100 muon detector” 

    Symmetry Mag

    Symmetry

    08/19/16
    By Laura Dattaro

    1
    Spencer Axani

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

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

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

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

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

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

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

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

    FNAL/MiniBooNE
    FNAL/MiniBooNE

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

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

    IceCube PINGU
    IceCube PINGU

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


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

    From Symmetry: “Five facts about the Big Bang” 

    Symmetry Mag

    Symmetry

    08/23/16
    Matthew R. Francis

    1
    Illustration by Sandbox Studio, Chicago with Corinne Mucha

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

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

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

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

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

    The Big Bang happened everywhere at once.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    4

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

    It seems nobody likes the name “Big Bang.”

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


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

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

    Symmetry Mag

    Symmetry

    08/10/16
    Manuel Gnida

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

    1
    Hitomi collaboration; NASA/CXC; Greg Stewart

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

    JAXA/Hitomi telescope
    JAXA/Hitomi telescope

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

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

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

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

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

    ESA/XMM Newton
    ESA/XMM Newton

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

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

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

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

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

    NASA/Chandra Telescope
    NASA/Chandra Telescope

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:58 am on August 5, 2016 Permalink | Reply
    Tags: blip washes out- no new particle found, , , Symmetry Magazine   

    From Symmetry: “LHC bump fades with more data” 

    Symmetry Mag

    Symmetry

    08/05/16
    Sarah Charley

    1
    ATLAS detector. Claudia Marcelloni, CERN

    Possible signs of new particle seem to have washed out in an influx of new data.

    A curious anomaly seen by two Large Hadron Collider experiments is now looking like a statistical fluctuation.

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

    The anomaly—an unanticipated excess of photon pairs with a combined mass of 750 billion electronvolts—was first reported by both the ATLAS and CMS experiments in December 2015.

    CERN/CMS Detector
    CERN/CMS Detector

    Such a bump in the data could indicate the existence of a new particle. The Higgs boson, for instance, materialized in the LHC data as an excess of photon pairs with a combined mass of 125 billion electronvolts.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    However, with only a handful of data points, the two experiments could not discern whether that was the case or if it were the result of normal statistical variance.

    After quintupling their 13-TeV dataset between April and July this year, both experiments report that the bump has greatly diminished and, in some analyses, completely disappeared.

    What made this particular bump interesting is that both experiments saw the same anomaly in completely independent data sets, says Wade Fisher, a physicist at Michigan State University.

    “It’s like finding your car parked next to an identical copy,” he says. “That’s a very rare experience, but it doesn’t mean that you’ve discovered something new about the world. You’d have to keep track of every time it happened and compare what you observe to what you’d expect to see if your observation means anything.”

    Theorists predicted that a particle of that size could have been a heavier cousin of the Higgs boson or a graviton, the theoretical particle responsible for gravity. While data from more than 1000 trillion collisions have smoothed out this bump, scientists on the ATLAS experiment still cannot completely rule out its existence.

    “There’s up fluxes and down fluxes in statistics,” Fisher says. “Up fluctuations can sometimes look like the early signs of a new particles, and down fluctuations can sometimes make the signatures of a particle disappear. We’ll need the full 2016 data set to be more confident about what we’re seeing.”

    Scientists on both experiments are currently scrutinizing the huge influx of data to both better understand predicted processes and look for new physics and phenomena.

    “New physics can manifest itself in many different ways—we learn more if it surprises us rather than coming in one of the many many theories we’re already probing,” says Steve Nahn, a CMS researcher working at Fermilab. “So far the canonical Standard Model is holding up quite well, and we haven’t seen any surprises, but there’s much more data coming from the LHC, so there’s much more territory to explore.”

    See the full article here .

    See also this article from New Scientist.

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:11 pm on July 28, 2016 Permalink | Reply
    Tags: , , Symmetry Magazine, The Standard Model   

    From Symmetry: “The deconstructed Standard Model equation” 

    Symmetry Mag

    Symmetry

    07/28/16
    Rashmi Shivni

    1
    Yvonne Tang, SLAC National Accelerator Laboratory

    The Standard Model is far more than elementary particles arranged in a table.

    The Standard Model of particle physics is often visualized as a table, similar to the periodic table of elements, and used to describe particle properties, such as mass, charge and spin.

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

    The table is also organized to represent how these teeny, tiny bits of matter interact with the fundamental forces of nature.

    But it didn’t begin as a table. The grand theory of almost everything actually represents a collection of several mathematical models that proved to be timeless interpretations of the laws of physics.

    Here is a brief tour of the topics covered in this gargantuan equation.

    The whole thing

    This version of the Standard Model is written in the Lagrangian form. The Lagrangian is a fancy way of writing an equation to determine the state of a changing system and explain the maximum possible energy the system can maintain.

    Technically, the Standard Model can be written in several different formulations, but, despite appearances, the Lagrangian is one of the easiest and most compact ways of presenting the theory.

    3

    Section 1

    These three lines in the Standard Model are ultraspecific to the gluon, the boson that carries the strong force. Gluons come in eight types, interact among themselves and have what’s called a color charge.

    3

    Section 2

    Almost half of this equation is dedicated to explaining interactions between bosons, particularly W and Z bosons.

    Bosons are force-carrying particles, and there are four species of bosons that interact with other particles using three fundamental forces. Photons carry electromagnetism, gluons carry the strong force and W and Z bosons carry the weak force. The most recently discovered boson, the Higgs boson, is a bit different; its interactions appear in the next part of the equation.

    3

    Section 3

    This part of the equation describes how elementary matter particles interact with the weak force. According to this formulation, matter particles come in three generations, each with different masses. The weak force helps massive matter particles decay into less massive matter particles.

    This section also includes basic interactions with the Higgs field, from which some elementary particles receive their mass.

    Intriguingly, this part of the equation makes an assumption that contradicts discoveries made by physicists in recent years. It incorrectly assumes that particles called neutrinos have no mass.

    4

    Section 4

    In quantum mechanics, there is no single path or trajectory a particle can take, which means that sometimes redundancies appear in this type of mathematical formulation. To clean up these redundancies, theorists use virtual particles they call ghosts.

    This part of the equation describes how matter particles interact with Higgs ghosts, virtual artifacts from the Higgs field.

    5

    Section 5

    This last part of the equation includes more ghosts. These ones are called Faddeev-Popov ghosts, and they cancel out redundancies that occur in interactions through the weak force.

    6

    Note: Thomas Gutierrez, an assistant professor of Physics at California Polytechnic State University, transcribed the Standard Model Lagrangian for the web. He derived it from Diagrammatica, a theoretical physics reference written by Nobel Laureate Martinus Veltman. In Gutierrez’s dissemination of the transcript, he noted a sign error he made somewhere in the equation. Good luck finding it!

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:59 pm on July 26, 2016 Permalink | Reply
    Tags: , , inSPIRE - HEP High-Energy Physics Literature Database, , , Symmetry Magazine   

    From Symmetry: “The most important website in particle physics” 

    Symmetry Mag

    Symmetry

    07/26/16
    Matthew R. Francis

    The first website to be hosted in the US has grown to be an invaluable hub for open science.

    1
    Sandbox Studio, Chicago with Lexi Fodor

    With tens of thousands of particle physicists working in the world today, the biggest challenge a researcher can have is keeping track of what everyone else is doing. The articles they write, the collaborations they form, the experiments they run—all of those things are part of being current. After all, high-energy particle physics is a big enterprise, not the province of a few isolated people working out of basement laboratories.

    Particle physicists have a tool that helps them with that. The INSPIRE database allows scientists to search for published papers by topic, author, scholarly journal, what previous papers the authors cited and which newer papers have used it as a reference.

    2

    “I don’t know any other discipline with such a central tool as INSPIRE,” says Sünje Dallmeier-Tiessen, an information scientist at CERN who manages INSPIRE’s open-access initiative. If you’re a high-energy physicist, “everything that relates to your daily work-life, you can find there.”

    Researchers in high-energy physics and related fields use INSPIRE for their professional profiles, job-hunting and promotional materials. They use it to keep track of other people’s research in their disciplines and for finding good resources to cite in their own papers.

    INSPIRE has been around in one form or another since 1969, says Bernard Hecker, who is in charge of SLAC’s portion of INSPIRE. “So we have a high level of credibility with people who use the service.” It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970s.

    INSPIRE contains up-to-date information about over a million papers, including those published in the major journals. INSPIRE’s database also interacts with the arXiv, a free-access site that hosts papers independently of whether they’re published in journals or not. “We text-mine everything [on the arXiv], and then provide search to the content, and search based on specific algorithms we run,” Dallmeier-Tiessen says.

    In that way, INSPIRE is a powerful addition to the arXiv, which itself provides access to many articles that would otherwise require expensive journal subscriptions or exorbitant one-time fees.

    A lot of human labor is involved. The arXiv, for example, doesn’t distinguish between two people with the same last name and same first initial. “We have a strong interest in keeping dynamic profiles and disambiguating different researchers with similar names,” Hecker says.

    To that end, the INSPIRE team looks at author lists on published papers to match individual researchers with their correct institutions. This includes collaborating with the Institute of High Energy Physics in China, as well as cross-checking other databases.

    The goal, Hecker says, is “trying to find the stuff that’s directly relevant and not stuff that’s not relevant.” After all, researchers will only use the site if its useful, a complicated challenge that INSPIRE has met consistently. “We’re trying to optimize the time researchers spend on the site.”

    Now That’s What I Call Physics

    Every January, the INSPIRE team releases a list of the top 40 most cited articles in high-energy physics that year.

    Looking over the list for 2015, you might be forgiven for thinking it was a slow year. The most commonly referenced articles were papers from previous years, some just a few years old, a few going back several decades.

    But even in years without a blockbuster discovery such as the Higgs boson or gravitational waves, INSPIRE’s list is still useful a snapshot of where the minds of the research community are focused.

    In 2015, researchers prioritized studying the Higgs boson. The two most widely referenced articles of 2015 were the papers announcing its discovery by researchers at the ATLAS and CMS detectors at the Large Hadron Collider. The INSPIRE “top 40” for 2015 also includes the original 1964 theoretical papers by Peter Higgs, François Englert, and Robert Brout predicting the existence of the Higgs.

    Another topic that stood out in 2015 was the cosmic microwave background, a pattern of light that could tell us about conditions in the universe just after the Big Bang. Four highly cited papers, including the third most-referenced, came from the Planck cosmic microwave background experiment, with a fifth devoted to the final WMAP cosmic microwave background data.

    It seems that cosmology was on physicists’ minds. Two more top papers were the first measurements of dark energy from the late ’90s, while yet two more described results from the dark matter experiments LUX and XENON100.

    Open science, open data, open code

    INSPIRE grew out of the Stanford Public Information Retrieval System (SPIRES), a database started at SLAC National Accelerator Laboratory in 1969 when the internet was in its infancy.

    After Tim Berners-Lee developed the World Wide Web at CERN, SPIRES was the first US-hosted website.

    Like high-energy physics itself, the database is international and cooperative. SLAC joined with Fermi National Accelerator Laboratory in the United States, DESY in Germany, and CERN in Switzerland, which now hosts the site, to create the modern version of INSPIRE. The newest member of the collaboration is IHEP Beijing in China. Institutions in France and Japan also collaborate on particular projects.

    INSPIRE has changed a lot since its inception, and a new version is coming out soon. The biggest change will extend INSPIRE’s database to include repositories for data and computer code.

    Starting later this year, INSPIRE will integrate with the HEPDATA open-data archive and the github code-collaboration system to increase visibility for both data and code that scientists write. The INSPIRE team will also roll out a new interface, so it looks “less like something from 1995,” Hecker says.

    From its inception as a way to share printed articles by mail, INSPIRE continues to be a valuable resource to the community. With more papers coming out every year and no sign of decrease in the number of particle physicists working, the need to build on past research—and construct collaborations—is more important than ever.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:20 pm on July 12, 2016 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “Scientists salvage insights from lost satellite” 

    Symmetry Mag

    Symmetry

    07/06/16
    Manuel Gnida

    Before Hitomi died, it sent X-ray data that could explain why galaxy clusters form far fewer stars than expected.

    1
    Hitomi. A. Ikeshita, JAXA

    Working with information sent from the Japanese Hitomi satellite, an international team of researchers has obtained the first views of a supermassive black hole stirring hot gas at the heart of a galaxy cluster. These motions could explain why galaxy clusters form far fewer stars than expected.

    2
    This image created by physicists at Stanford’s SLAC National Accelerator Laboratory illustrates how supermassive black holes at the center of galaxy clusters could heat intergalactic gas, preventing it from cooling and forming stars. (Image credit: SLAC National Accelerator Laboratory)

    The data, published today in Nature, were recorded with the X-ray satellite during its first month in space earlier this year, just before it spun out of control and disintegrated due to a chain of technical malfunctions.

    “Being able to measure gas motions is a major advance in understanding the dynamic behavior of galaxy clusters and its ties to cosmic evolution,” said study co-author Irina Zhuravleva, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology. “Although the Hitomi mission ended tragically after a very short period of time, it’s fair to say that it has opened a new chapter in X-ray astronomy.” KIPAC is a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    Galaxy clusters, which consist of hundreds to thousands of individual galaxies held together by gravity, also contain large amounts of gas. Over time, the gas should cool down and clump together to form stars. Yet there is very little star formation in galaxy clusters, and until now scientists were not sure why.

    “We already knew that supermassive black holes, which are found at the center of all galaxy clusters and are tens of billions of times more massive than the sun, could play a major role in keeping the gas from cooling by somehow injecting energy into it,” said Norbert Werner, a research associate at KIPAC involved in the data analysis. “Now we understand this mechanism better and see that there is just the right amount of stirring motion to produce enough heat.”

    Plasma bubbles stir and heat intergalactic gas

    About 15 percent of the mass of galaxy clusters is gas that is so hot – tens of millions of degrees Fahrenheit – that it shines in bright X-rays. In their study, the Hitomi researchers looked at the Perseus cluster, one of the most massive astronomical objects and the brightest in the X-ray sky.

    4
    Perseus cluster. NASA Chandra.

    Other space missions before Hitomi, including NASA’s Chandra X-ray Observatory, had taken precise X-ray images of the Perseus cluster. These snapshots revealed how giant bubbles of ultrahot, ionized gas, or plasma, rise from the central supermassive black hole as it catapults streams of particles tens of thousands of light-years into space. At the same time, streaks of cold gas appear to be pulled away from the center of the galaxy cluster, according to additional images of visible light. Until now, it has been unclear whether these two actions were connected.

    To find out, the researchers pointed one of Hitomi’s instruments – the soft X-ray spectrometer (SXS) – at the center of the Perseus cluster and analyzed its X-ray emissions.

    6
    Perseus cluster. Hitomi Collaboration/JAXA, NASA, ESA, SRON, CSA

    “Since the SXS had 30 times better energy resolution than the instruments of previous missions, we were able to resolve details of the X-ray signals that weren’t accessible before,” said co-principal investigator Steve Allen, a professor of physics at Stanford and of particle physics and astrophysics at SLAC. “These new details resulted in the very first velocity map of the cluster center, showing the speed and turbulence of the hot gas.”

    By superimposing this map onto the other images, the researchers were able to link the observed motions of the cold gas to the hot plasma bubbles.

    According to the data, the rising plasma bubbles drag cold gas away from the cluster center. Researchers see this in the form of stretched filaments in the optical images. The bubbles also transfer energy to the gas, which causes turbulence, Zhuravleva said.

    “In a way, the bubbles are like spoons that stir milk into a cup of coffee and cause eddies,” she said. “The turbulence heats the gas, and it appears that this is enough to work against star formation in the cluster.”

    Hitomi’s legacy

    Astrophysicists can use the new information to fine-tune models that describe how galaxy clusters change over time.

    One important factor in these models is the mass of galaxy clusters, which researchers typically calculate from the gas pressure in the cluster. However, motions cause additional pressure, and before this study it was unclear if the calculations need to be corrected for turbulent gas.

    “Although the motions heat the gas at the center of the Perseus cluster, their speed is only about 100 miles per second, which is surprisingly slow considering how disturbed the region looks in X-ray images,” said co-principal investigator Roger Blandford, the Luke Blossom Professor of Physics at Stanford and a professor for particle physics and astrophysics at SLAC. “One consequence is that corrections for these motions are only very small and don’t affect our mass calculations much.”

    Although the loss of Hitomi cut most of the planned science program short – it was supposed to run for at least three years – the researchers hope their results will convince the international community to plan another X-ray space mission.

    “The data Hitomi sent back to Earth are just beautiful,” Werner said. “They demonstrate what’s possible in the field and give us a taste of all the great science that should have come out of the mission over the years.”

    Hitomi is a joint project, with the Japan Aerospace Exploration Agency (JAXA) and NASA as the principal partners. Led by Japan, it is a large-scale international collaboration, boasting the participation of eight countries, including the United States, the Netherlands and Canada, with additional partnership by the European Space Agency (ESA). Other KIPAC researchers involved in the project are Tuneyoshi Kamae, Ashley King, Hirokazu Odaka and co-principal investigator Grzegorz Madejski.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:06 pm on July 12, 2016 Permalink | Reply
    Tags: A primer on particle accelerators, , , Symmetry Magazine   

    From Symmetry: “A primer on particle accelerators” 

    Symmetry Mag

    Symmetry

    07/12/16
    Signe Brewster

    1
    Illustration by Sandbox Studio, Chicago with Jill Preston

    Research in high-energy physics takes many forms. But most experiments in the field rely on accelerators that create and speed up particles on demand.

    What follows is a primer on three different types of particle accelerators: synchrotrons, cyclotrons and linear accelerators, called linacs.

    Synchrotrons: the heavy lifters
    2

    Synchrotrons are the highest-energy particle accelerators in the world. The Large Hadron Collider currently tops the list, with the ability to accelerate particles to an energy of 6.5 trillion electronvolts before colliding them with particles of an equal energy traveling in the opposite direction.

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

    Synchrotrons typically feature a closed pathway that takes particles around a ring. Other variants are created with straight sections between the curves (similar to a racetrack or in the shape of a triangle or hexagon). Once particles enter the accelerator, they travel around the circular pathway over and over again, always enclosed in a vacuum pipe.

    Radiofrequency cavities at intervals around the ring increase their speed. Several different types of magnets create electromagnetic fields, which can be used to bend and focus the particle beams. The electromagnetic fields slowly build up as the particles are accelerated. Particles pass around the LHC about 14 million times in the 20 minutes they need to reach their intended energy level.

    Researchers send beams of accelerated particles through one another to create collisions in locations surrounded by particle detectors. Relatively few collisions happen each time the beams meet. But because the particles are constantly circulating in a synchrotron, researchers can pass them through one another many times over—creating a large number of collisions over time and more data for observing rare phenomena.

    “The LHC detectors ATLAS and CMS reached about 400 million collisions a second last year,” says Mike Lamont, head of LHC operations at CERN. “This is why this design is so useful.”

    CERN/ATLAS detector
    CERN ATLAS Higgs Event
    CERN/ATLAS detector; CERN ATLAS Higgs Event

    CERN/CMS Detector
    CERN CMS Higgs Event
    CERN/CMS detector; CERN CMS Higgs Event

    Synchrotrons’ power makes them especially suited to studying the building blocks of our universe. For example, physicists were able to witness evidence of the Higgs boson among the LHC’s collisions only because the collider could accelerate particles to such a high energy and produce such high collision rates.

    The LHC primarily collides protons with protons but can also accelerate heavy nuclei such as lead. Other synchrotrons can also be customized to accelerate different types of particles. At Brookhaven National Laboratory [BNL] in New York, the Relativistic Heavy Ion Collider [RHIC] can accelerate everything from protons to uranium nuclei.

    BNL RHIC Campus
    BNL/RHIC

    It keeps the proton beams polarized with the use of specially designed magnets, according to RHIC accelerator physicist Angelika Drees. It can also collide heavy ions such as uranium and gold to create quark-gluon plasma—the high-temperature soup that made up the universe just after the Big Bang.

    Cyclotrons: the workhorses
    3
    Synchrotrons are the descendants of another type of circular collider called cyclotrons. Cyclotrons accelerate particles in a spiral pattern, starting at their center.

    Like synchrotrons, cyclotrons use a large electromagnet to bend the particles in a circle. However, they use only one magnet, which limits how large they can be. They use metal electrodes to push particles to travel in increasingly large circles, creating a spiral pathway.

    Cyclotrons are often used to create large amounts of specific types of particles, such as muons or neutrons. They are also popular for medical research because they have the right energy range and intensity to produce medical isotopes.

    The world’s largest cyclotron is located at the TRIUMF laboratory in Vancouver, Canada.

    4
    INSIDE the TRIUMF 520 MeV CYCLOTRON Inside the Cyclotron with the lid raised for servicing

    At the TRIUMF cyclotron, physicists regularly accelerate particles to 520 million electronvolts. They can draw particles from different parts of their accelerator for experiments that require particles at different energies. This makes it an especially adaptable type of accelerator, says physicist Ewart Blackmore, who helped to design and build the TRIUMF accelerator.

    “We certainly make use of that facility every day when we’re running, when we’re typically producing a low-energy but high-current beam for medical isotope production,” Blackmore says. “We’re extracting at fixed energies down one beam for producing pions and muons for research, and on another beam line we’re extracting beams of radioactive nuclei to study their properties.”

    Linacs: straight and to the point
    6
    For physics experiments or applications that require a steady, intense beam of particles, linear accelerators are a favored design. SLAC National Accelerator Laboratory hosts the longest linac in the world, which measures 2 miles long and at one point could accelerate particles up to 50 billion electronvolts.

    SLAC Campus
    LINAC st SLAC

    Fermi National Accelerator Laboratory uses a shorter linac to speed up protons before sending them into a different accelerator, eventually running the particles into a fixed target to create the world’s most intense neutrino beam.

    While circular accelerators may require many turns to accelerate particles to the desired energy, linacs get particles up to speed in short order. Particles start at one end at a low energy, and electromagnetic fields in the linac accelerate them down its length. When particles travel in a curved path, they release energy in the form of radiation. Traveling in a straight line means keeping their energy for themselves. A series of radiofrequency cavities in SLAC’s linac are used to push particles on the crest of electromagnetic waves, causing them to accelerate forward down the length of the accelerator.

    Like cyclotrons, linacs can be used to produce medical isotopes. They can also be used to create beams of radiation for cancer treatment. Electron linacs for cancer therapy are the most common type of particle accelerator.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:59 pm on July 5, 2016 Permalink | Reply
    Tags: , , , Symmetry Magazine   

    From Symmetry: “Incredible hulking facts about gamma rays” 

    Symmetry

    07/05/16
    Matthew R. Francis

    2

    From lightning to the death of electrons, the highest-energy form of light is everywhere.

    Gamma rays are the most energetic type of light, packing a punch strong enough to pierce through metal or concrete barriers. More energetic than X-rays, they are born in the chaos of exploding stars, the annihilation of electrons and the decay of radioactive atoms. And today, medical scientists have a fine enough control of them to use them for surgery. Here are seven amazing facts about these powerful photons.

    Doctors conduct brain surgery using “gamma ray knives.”

    2

    Gamma rays can be helpful as well as harmful (and are very unlikely to turn you into the Hulk). To destroy brain cancers and other problems, medical scientists sometimes use a “gamma ray knife.” This consists of many beams of gamma rays focused on the cells that need to be destroyed. Because each beam is relatively small, it does little damage to healthy brain tissue. But where they are focused, the amount of radiation is intense enough to kill the cancer cells. Since brains are delicate, the gamma ray knife is a relatively safe way to do certain kinds of surgery that would be a challenge with ordinary scalpels.

    [My wife had gamma-knife brain surgery. Whn I asked her neursurgeon how they got gamma rays, he replied from cobalt.]

    3

    The name “gamma rays” came from Ernest Rutherford.

    French chemist Paul Villard first identified gamma rays in 1900 from the element radium, which had been isolated by Marie and Pierre Curie just two years before. When scientists first studied how atomic nuclei changed form, they identified three types of radiation based on how far they penetrated into a barrier made of lead. Ernest Rutherford named the radiation for the first three letters of the Greek alphabet. Alpha rays bounce right off, beta rays went a little farther, and gamma rays went the farthest. Today we know alpha rays are the same thing as helium nuclei (two protons and two neutrons), beta rays are either electrons or positrons (their antimatter versions), and gamma rays are a kind of light.

    4

    Nuclear reactions are a major source of gamma rays.

    When an unstable uranium nucleus splits in the process of nuclear fission, it releases a lot of gamma rays in the process. Fission is used in both nuclear reactors and nuclear warheads. To monitor nuclear tests in the 1960s, the United States launched gamma radiation detectors on satellites. They found far more explosions than they expected to see. Astronomers eventually realized these explosions were coming from deep space—not the Soviet Union—and named them gamma-ray bursts, or GRBs. Today we know GRBs come in two types: the explosions of extremely massive stars, which pump out gamma rays as they die, and collisions between highly dense relics of stars called neutron stars and something else, probably another neutron star or a black hole.

    6

    Gamma rays played a key role in the discovery of the Higgs boson.

    Most of the particles in the Standard Model of particle physics are unstable; they decay into other particles almost as soon as they come into existence. The Higgs boson, for example, can decay into many different types of particles, including gamma rays. Even though theory predicts that a Higgs boson will decay into gamma rays just 0.2 percent of the time, this type of decay is relatively easy to identify and it was one of the types that scientists observed when they first discovered the Higgs boson.

    NASA Fermi Gamma-ray Space Telescope  Gamma-ray Burst Monitor (GBM)
    NASA Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor

    To study gamma rays, astronomers build telescopes in space.

    Gamma rays heading toward the Earth from space interact with enough atoms in the atmosphere that almost none of them reach the surface of the planet. That’s good for our health, but not so great for those who want to study GRBs and other sources of gamma rays. To see gamma rays before they reach the atmosphere, astronomers have to build telescopes in space. This is challenging for a number of reasons. For example, you can’t use a normal lens or mirror to focus gamma rays, because the rays punch right through them. Instead an observatory like the Fermi Gamma-ray Space Telescope detects the signal from gamma rays when they hit a detector and convert into pairs of electrons and positrons.

    Some gamma rays come from thunderstorms.

    In the 1990s, observatories in space detected bursts of gamma rays coming from Earth that eventually were traced to thunderclouds. When static electricity builds up inside clouds, the immediate result is lightning. That static electricity also acts like a giant particle accelerator, creating pairs of electrons and positrons, which then annihilate into gamma rays. These bursts happen high enough in the air that only airplanes are exposed—and they’re one reason for flights to steer well away from storms.

    Gamma rays (indirectly) give life to Earth.

    Hydrogen nuclei are always fusing together in the core of the sun. When this happens, one byproduct is gamma rays. The energy of the gamma rays keeps the sun’s core hot. Some of those gamma rays also escape into the sun’s outer layers, where they collide with electrons and protons and lose energy. As they lose energy, they change into ultraviolet, infrared and visible light. The infrared light keeps Earth warm, and the visible light sustains Earth’s plants.

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:00 pm on June 29, 2016 Permalink | Reply
    Tags: , , , , , , Symmetry Magazine, Tetraquarks? For real?   

    From Symmetry: “LHCb discovers family of tetraquarks” 

    Symmetry Mag

    Symmetry

    06/29/16
    Sarah Charley

    1
    LHCb. Courtesy of CERN

    Researchers found four new particles made of the same four building blocks.

    It’s quadruplets! Syracuse University researchers on the LHCb experiment confirmed the existence of a new four-quark particle and serendipitously discovered three of its siblings.

    Quarks are the solid scaffolding inside composite particles like protons and neutrons. Normally quarks come in pairs of two or three, but in 2014 LHCb researchers confirmed the existence four-quark particles and, one year later, five-quark particles.

    The particles in this new family were named based on their respective masses, denoted in mega-electronvolts: X(4140), X(4274), X(4500) and X(4700). Each particle contains two charm quarks and two strange quarks arranged in a unique way, making them the first four-quark particles composed entirely of heavy quarks. Researchers also measured each particle’s quantum numbers, which describe their subatomic properties. Theorists will use these new measurements to enhance their understanding of the formation of particles and the fundamental structures of matter.

    “What we have discovered is a unique system,” says Tomasz Skwarnicki, a physics professor at Syracuse University. “We have four exotic particles of the same type; it’s the first time we have seen this and this discovery is already helping us distinguish between the theoretical models.”

    Evidence of the lightest particle in this family of four and a hint of another were first seen by the CDF experiment at the US Department of Energy’s Fermi National Accelerator Lab in 2009.

    FNAL/Tevatron CDF detector
    FNAL/Tevatron machine
    FNAL/Tevatron map
    CDF; Tevatron; Tevtron map

    However, other experiments were unable to confirm this observation until 2012, when the CMS experiment at CERN reported seeing the same particle-like bumps with a much greater statistical certainty.

    CERN/CMS Detector
    CERN/CMS Detector

    Later, the D0 collaboration at Fermilab also reported another observation of this particle.

    FNAL/Tevatron DZero detector
    D0/FNAL

    “It was a long road to get here,” says University of Iowa physicist Kai Yi, who works on both the CDF and CMS experiments. “This has been a collective effort by many complementary experiments. I’m very happy that LHCb has now reconfirmed this particle’s existence and measured its quantum numbers.”

    The US contribution to the LHCb experiment is funded by the National Science Foundation.

    LHCb researcher Thomas Britton performed this analysis as his PhD thesis at Syracuse University.

    “When I first saw the structures jumping out of the data, little did I know this analysis would be such an aporetic saga,” Britton says. “We looked at every known particle and process to make sure these four structures couldn’t be explained by any pre-existing physics. It was like baking a six-dimensional cake with 98 ingredients and no recipe—just a picture of a cake.”

    Even though the four new particles all contain the same quark composition, they each have a unique internal structure, mass and their own sets of quantum numbers. These characteristics are determined by the internal spatial configurations of the quarks.

    “The quarks inside these particles behave like electrons inside atoms,” Skwarnicki says. “They can be ‘excited’ and jump into higher energy orbitals. The energy configuration of the quarks gives each particle its unique mass and identity.”

    According to theoretical predictions, the quarks inside could be tightly bound (like three quarks packed inside a single proton) or loosely bound (like two atoms forming a molecule.) By closely examining each particle’s quantum numbers, scientists were able to narrow down the possible structures.

    “The molecular explanation does not fit with the data,” Skwarnicki says. “But I personally would not conclude that these are definitely tightly bound states of four quarks. It could be possible that these are not even particles. The result could show the complex interplays of known particle pairs flippantly changing their identities.”

    Theorists are currently working on models to explain these new results—be it a family of four new particles or bizarre ripple effects from known particles. Either way, this study will help shape our understanding of the subatomic universe.

    “The huge amount of data generated by the LHC is enabling a resurgence in searches for exotic particles and rare physical phenomena,” Britton says. “There’s so many possible things for us to find and I’m happy to be a part of it.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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