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  • richardmitnick 3:59 pm on July 11, 2017 Permalink | Reply
    Tags: A new model for standards, In an upcoming refresh particle physics will define units of measurement such as the meter the kilogram and the second, , Symmetry Magazine   

    From Symmetry: “A new model for standards” 

    Symmetry Mag

    Symmetry

    07/11/17
    Daniel Garisto

    1
    Artwork by Sandbox Studio, Chicago

    In an upcoming refresh, particle physics will define units of measurement such as the meter, the kilogram and the second.

    While America remains obstinate about using Imperial units such as miles, pounds and degrees Fahrenheit, most of the world has agreed that using units that are actually divisible by 10 is a better idea. The metric system, also known as the International System of Units (SI), is the most comprehensive and precise system for measuring the universe that humans have developed.

    In 2018, the 26th General Conference on Weights and Measures will convene and likely adopt revised definitions for the seven base metric system units for measuring: length, mass, time, temperature, electric current, luminosity and quantity.

    The modern metric system owes its precision to particle physics, which has the tools to investigate the universe more precisely than any microscope. Measurements made by particle physicists can be used to refine the definitions of metric units. In May, a team of German physicists at the Physikalisch-Technische Bundesanstalt made the most precise measurements yet of the Boltzmann constant, which will be used to define units of temperature.

    Since the metric system was established in the 1790s, scientists have attempted to give increasingly precise definitions to these units. The next update will define every base unit using fundamental constants of the universe that have been derived by particle physics.

    meter (distance):

    Starting in 1799, the meter was defined by a prototype meter bar, which was just a platinum bar. Physicists eventually realized that distance could be defined by the speed of light, which has been measured with an accuracy to one part in a billion using an interferometer (interestingly, the same type of detector the LIGO collaboration used to discover gravitational waves). The meter is currently defined as the distance traveled by light (in a vacuum) for 1/299,792,458 of a second, and will remain effectively unchanged in 2018.

    kilogram (mass):

    For over a century, the standard kilogram has been a small platinum-iridium cylinder housed at the International Bureau of Weights and Measures in France. But even its precise mass fluctuates due to factors such as accumulation of microscopic dust. Scientists hope to redefine the kilogram in 2018 by setting the value of Planck’s constant to exactly 6.626070040×1034 kilograms times meters squared per second. Planck’s constant is the smallest amount of quantized energy possible. This fundamental value, which is represented with the letter h, is integral to calculating energies in particle physics.

    second (time):

    The earliest seconds were defined as divisions of time between full moons. Later, seconds were defined by solar days, and eventually the time it took Earth to revolve around the sun. Today, seconds are defined by atomic time, which is precise to 1 part in 10 billion. Atomic time is calculated by periods of radiation by atoms, a measurement that relies heavily on particle physics techniques. One second is currently defined as 9,192,631,770 periods of the radiation for a Cesium-133 atom and will remain effectively unchanged.

    kelvin (temperature):

    Kelvin is the temperature scale that starts at the coldest possible state of matter. Currently, a kelvin is defined by the triple point of water—where water can exist as a solid, liquid and gas. The triple point is 273.16 Kelvin, so a single kelvin is 1/273.16 of the triple point. But because water can never be completely pure, impurities can influence the triple point. In 2018 scientists hope to redefine kelvin by setting the value of Boltzmann’s constant to exactly 1.38064852×10−23 joules per kelvin. Boltzmann’s constant links the movement of particles in a gas (the average kinetic energy) to the temperature of the gas. Denoted by the symbol k, the Boltzmann constant is ubiquitous throughout physics calculations that involve temperature and entropy.

    ampere (electric current):

    André-Marie Ampère, who is often considered the father of electrodynamics, has the honor of having the basic unit of electric current named after him. Right now, the ampere is defined by the amount of current required to produce of a force of 2×10−7 newtons for each meter between two parallel conductors of infinite length. Naturally, it’s a bit hard to come by things of infinite length, so the proposed definition is instead to define amperes by the fundamental charge of a particle. This new definition would rely on the charge of the electron, which will be set to 1.6021766208×10−19 amperes per second.

    candela (luminosity):

    The last of the base SI units to be established, the candela measures luminosity—what we typically refer to as brightness. Early standards for the candela used a phenomenon from quantum mechanics called “black body radiation.” This is the light that all objects radiate as a function of their heat. Currently, the candela is defined more fundamentally as 1/683 watt per square radian at a frequency of 540×1012 herz over a certain area, a definition which will remain effectively unchanged. Hard to picture? A candle, conveniently, emits about one candela of luminous intensity.

    mole (quantity):

    Different from all the other base units, the mole measures quantity alone. Over hundreds of years, scientists starting from Amedeo Avogadro worked to better understand how the number of atoms was related to mass, leading to the current definition of the mole: the number of atoms in 12 grams of carbon-12. This number, which is known as Avogadro’s constant and used in many calculations of mass in particle physics, is about 6 x 1023. To make the mole more precise, the new definition would set Avogadro’s constant to exactly 6.022140857×1023, decoupling it from the kilogram.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:21 pm on July 4, 2017 Permalink | Reply
    Tags: 1933 Italian physicist Enrico Fermi dubbed the hypothetical particle the neutrino, A definitive measurement would be potentially revolutionary, It might seem absurd that physicists don't know how much neutrinos weigh, It would elude detection for another 23 years, Karlsruhe Tritium Neutrino (KATRIN) experiment, , Neutrinos - what do they weigh?, Neutrinos first betrayed their existence through an absence: as if energy were disappearing, Symmetry Magazine, The upper limit now stands at about 2 eV—two-billionths the mass of the lightest atom—as experimenters in Mainz Germany and Troitsk Russia independently reported in 1999, To perform the experiment scientists need a supply of tritium, Working out the kinks took longer than expected putting the experiment roughly 7 years behind original plans   

    From Science via Symmetry: “Weighing the universe’s most elusive particle” 

    Symmetry Mag

    Symmetry

    AAAS
    Science Magazine

    Jun. 29, 2017
    Adrian Cho

    1
    The vacuum inside KATRIN’s spectrometer must be kept as airless as the surface of the moon. MICHAEL ZACHER.

    The silvery vacuum chamber resembles a zeppelin, the vaguely Art Deco lines of the welds between its stainless steel panels looking at once futuristic and old-fashioned. One tenth the size of the Hindenburg—but still as big as a blue whale—the vessel looms in a hangarlike building here at the Karlsruhe Institute of Technology (KIT), seemingly ready to float away. Although it is earthbound, the chamber has an ethereal purpose: weighing the most elusive and mysterious of subatomic particles, the neutrino.

    2
    Schematic view of the vessel. KIT.

    3
    Main spectrometer at MAN DWE in early August 2006, being prepared for vacuum tests. KIT.

    Physicists dreamed up the Karlsruhe Tritium Neutrino (KATRIN) experiment in 2001. Now, the pieces of the €60 million project are finally coming together, and KATRIN researchers plan to start taking data early next year. “This is really the final countdown,” says Guido Drexlin, a physicist at KIT and co-spokesperson for the roughly 140 researchers working on the project.

    It might seem absurd that physicists don’t know how much neutrinos weigh, given that the universe contains more of them than any other type of matter particle. Every cubic centimeter of space averages roughly 350 primordial neutrinos lingering from the big bang, and every second, the sun sends trillions of higher-energy neutrinos streaming through each of us. Yet no one notices, because the particles interact with matter so feebly. Spotting just a few of them requires a detector weighing many tons. There’s no simple way to weigh a neutrino.

    Instead, for the past 70 years, physicists have tried to infer the neutrino’s mass by studying a particular nuclear decay from which the particle emerges—the beta decay of tritium. Time and again, these experiments have set only upper limits on the neutrino’s mass. KATRIN may be physicists’ last, best hope to measure it—at least without a revolutionary new technology. “This is the end of the road,” says Peter Doe, a physicist and KATRIN member from the University of Washington (UW) in Seattle.

    KATRIN physicists have no guarantee that they’ll succeed. From very different kinds of experiments—such as giant subterranean detectors that spot neutrinos from space—they now know that the neutrino cannot be massless. But in recent years, data from even farther afield—maps of the cosmos on the grandest scales—suggest that the neutrino might be too light for KATRIN to grasp. Still, even cosmologists say the experiment is worth doing. If the neutrino mass does elude KATRIN, their current understanding of the cosmos will have passed another test.

    A definitive measurement, on the other hand, would be potentially revolutionary. “If KATRIN finds something,” says Licia Verde, a cosmologist at University of Barcelona in Spain, “cosmologists will be left scratching their heads and saying, ‘Where did we go wrong?'”

    Neutrinos first betrayed their existence through an absence. In 1914, U.K. physicist James Chadwick was studying beta decay, a form of radioactive decay in which a nucleus emits an electron, transforming a neutron into a proton. Conservation of energy suggested that the electrons from a particular nucleus, say lead-214, should always emerge with the same energy. Instead, Chadwick showed that they emerge with a range of energies extending down to zero, as if energy were disappearing.

    That observation caused a minor crisis in physics. The great Danish theorist Niels Bohr even suggested that energy might not be conserved on the atomic scale. However, in 1930, the puckish Austrian theorist Wolfgang Pauli solved the problem more simply. In beta decay, he speculated, a second, unseen particle emerges with the electron and absconds with a random fraction of the energy. The particle had to be light—less than 1% of the mass of a proton—and, to avoid detection, uncharged.

    Three years later, Italian physicist Enrico Fermi dubbed the hypothetical particle the neutrino. It would elude detection for another 23 years. But, in developing a fuller theory of beta decay, Fermi immediately realized that the electrons’ energy spectrum holds a clue to a key property of the neutrino: its mass. If the particle is massless, the spectrum should extend up to the same energy the electron would have if it emerged alone—corresponding to decays in which the neutrino emerges with virtually no energy. If the neutrino has mass, the spectrum should fall short of the limit by an amount equal to the mass. To weigh the neutrino, physicists had only to precisely map the upper end of the electron spectrum in beta decay.

    That measurement requires exquisite precision, however. For decades, physicists have striven to achieve it with tritium, the simplest nucleus to undergo beta decay. In 1949, a first study concluded that the neutrino weighed less than 500 electron volts (eV), 1/1000 the mass of the electron. Since then, successive experiments have cut the upper limit in half roughly every 8 years, says Hamish Robertson, a KATRIN physicist at UW. “There’s a sort of Moore’s Law for the neutrino mass,” he says, referring to the trend that, for many years, described the regular shrinking of transistors on microchips. The upper limit now stands at about 2 eV—two-billionths the mass of the lightest atom—as experimenters in Mainz, Germany, and Troitsk, Russia, independently reported in 1999.

    In 2001, those teams and others gathered in a castle high on a hill in the hamlet of Bad Liebenzell in Germany’s Black Forest and decided to push further, by mounting the definitive tritium beta decay experiment. “That was the point of origin, the big bang for KATRIN,” KIT’s Drexlin says. KATRIN experimenters hope to lower the mass limit by a factor of 10, to 0.2 eV—or, better yet, to come up with an actual measurement of the neutrino mass.

    To perform the experiment, scientists need a supply of tritium—a highly radioactive isotope of hydrogen produced in certain nuclear reactors that’s tightly regulated because of its potential health hazards and weapons applications. The search for it brought them to KIT, which already had a facility, unique in the Western Hemisphere, for processing and recycling tritium.

    With tritium in hand, physicists then have to collect the beta electrons it emits without altering their energies. They cannot, for example, put tritium gas in a container with a thin crystalline window, because passing through even the thinnest window would sap the electrons’ energy enough to ruin KATRIN’s measurement.

    Instead, KATRIN depends on a device called a windowless gaseous tritium source: an open-ended pipe 10 meters long that tritium enters from a port in the middle. Superconducting magnets surrounding the pipe generate a field 70,000 times as strong as Earth’s. Beta decay electrons from the tritium spiral in the magnetic field to the pipe’s ends, where pumps suck out the uncharged tritium molecules. Set it up right, with not so much tritium that the gas itself slows the electrons, and the source should produce 100 billion electrons per second.

    Finally, physicists must measure the electrons’ energies. That’s where KATRIN’s zeppelinlike vacuum chamber comes into play. Still riding the magnetic field lines from the source, the electrons enter the chamber from one end. The magnetic field, now supplied by graceful hoops of wire encircling the blimp, weakens to a mere six times Earth’s field as the field lines spread out. That spreading is key, as it forces the electrons to move along the lines, and not around them.

    Once the electrons are moving in precisely the same direction, physicists can measure their energies. Electrodes lining the chamber create an electric field that pushes against the onrushing electrons and opposes their motion. Only those electrons that have enough energy can push past the electric field and reach the detector at the far end of the chamber. So by varying the strength of the electric field and counting the electrons that hit the detector, physicists can trace the spectrum. KATRIN researchers will concentrate on the spectrum’s upper end, the all-important region mapped out by just one in every 5 trillion electrons from the decays.

    Everything has to be tuned perfectly. Additional coils of wire around the spectrometer must precisely cancel Earth’s magnetic field, or else the electrons will run into the zeppelin’s wall. The specific voltages of the myriad electrodes must be stable to parts per million. The vacuum within the spectrometer must be held at 0.01 picobar, a pressure as low as at the moon’s surface and an unprecedented level for such a big chamber. And the temperature of the tritium source must be kept at a frigid 30 kelvins to slow the molecules so their motion doesn’t affect the energy of the ejected electrons.

    KATRIN physicists have run into some nettlesome surprises. For example, to avoid stray magnetic fields, they had the concrete floor below the 200-metric-ton chamber reinforced not with rebar of ordinary steel, which is magnetic, but with nonmagnetic stainless steel. Still, magnetic fields from the ordinary steel in the concrete walls played havoc with the spectrometer, says Kathrin Valerius, a physicist at KIT. “We had to demagnetize the building,” she says, a painstaking process that required passing an electromagnet over every square meter of the walls.

    Working out the kinks took longer than expected, putting the experiment roughly 7 years behind original plans. No single issue slowed it down, says Johannes Blümer, KIT’s head of physics and mathematics. “Things turned out to be much more complex than we thought initially,” he says. “Everything has to be perfect and perfectly stable.”

    The wait is almost over. Last October, physicists fired electrons from an electron gun through the spectrometer. This summer, they will calibrate it with a sample of krypton-83, which emits electrons of a fixed energy. Later this year, they will connect the tritium works, ready for next year’s data taking. In a single week KATRIN should outperform all previous experiments, Drexlin says, but researchers will still need to take data for at least 5 years to make their ultimate measurement.

    The long way home

    The Karlsruhe Tritium Neutrino (KATRIN) experiment in Germany is the culmination of a 70-year-old quest to measure the mass of the neutrino, but the construction of the experiment involved an odyssey of its own. The heart of the experiment, a stainless steel vacuum chamber 23 meters long and nearly 10 meters wide, was fabricated by a company in Deggendorf, just a 400-kilometer drive from the KATRIN site at the Karlsruhe Institute of Technology (KIT). Yet with no direct road route that could accommodate such a big load, scientists couldn’t bring their baby straight home.

    Instead, in September 2006 the 200-metric-ton apparatus began a much longer journey, first sailing down the Danube River to the Black Sea. From there a ship carried it through the Aegean and Mediterranean seas, up Europe’s Atlantic coast, and up the Rhine River. Finally, after 2 months, it came ashore at Leopoldshafen, a village 7 kilometers north of KIT, where a special truck inched it through the center of town, at one moment with just 5 centimeters to spare. The 8800-kilometer journey cost €600,000, says Thomas Thuemmler, a physicist at KIT, and “the last 7 kilometers cost as much as all the previous stages.”

    4
    Passage. KIT.

    Physicists already know that neutrinos have some mass. For decades, they have known that neutrinos come in three types, or “flavors”—electron, muon, and tau—depending on the particle interactions in which they are born. In 1998, experimenters with Super-Kamiokande, a gigantic subterranean neutrino detector in western Japan, proved that muon neutrinos created when cosmic rays strike molecules in the atmosphere could change flavor as they zipped through Earth to the detector.

    Such flavor changing shows that neutrinos cannot be massless. Otherwise, according to relativity, they would have to travel at the speed of light, like photons. In that case, time for them would stand still, making change impossible. But such flavor changing depends on differences in the three neutrinos’ masses, not the exact values. So although physicists have studied the phenomenon in detail, they can say only that one of the neutrino types must have a mass of at least 0.05 eV. And they don’t know which type is heaviest or lightest.

    KATRIN may not be sensitive enough to provide an answer, results from cosmology suggest. The big bang created a sea of neutrinos that shaped the evolution of cosmic structures, slowing the formation of galaxies and galaxy clusters. By studying the cosmic microwave background, emitted when matter in the newborn universe was just beginning to clump, and the distribution of galaxies, cosmologists have inferred that the sum of the masses of all three types of neutrinos is less than 0.2 eV, right at the limit of KATRIN’s sensitivity. If so, the electron neutrino alone—the kind emitted by beta decay—is likely to be too much of a featherweight for KATRIN.

    That estimate comes with a caveat: It depends on the validity of cosmologists’ standard model, which assumes that the universe contains ordinary matter, mysterious “dark matter” that interacts only through gravity, and bizarre, space-stretching “dark energy,” which also slows the formation of galaxy clusters. So, turning things around, by measuring the neutrino mass, KATRIN physicists can test that model, particularly its assumptions about dark energy, says Kevork Abazajian, a cosmologist at the University of California, Irvine. “If they find something that’s not in agreement with what’s found in cosmology, they’re saying that something is broken in cosmology,” he says. “That would be profound.”

    And if the neutrino proves too light for KATRIN to measure? Physicists envision an upgrade to boost the experiment’s sensitivity to 0.1 eV. Beyond that, they would have to replace the ordinary tritium gas, which forms diatomic molecules, with atomic tritium, Drexlin says, because the splitting of the molecules when the tritium beta decays creates the biggest uncertainty in the electrons’ energies. But such an atomic source doesn’t yet exist and would be a major challenge to invent.

    Others are exploring even more radical approaches. At UW, Robertson is testing out a different way to measure the energies of electrons from beta decay. When an electron circles in a magnetic field it radiates energy—such as the x-ray synchrotron radiation that scientists use at accelerator light sources the world over. In KATRIN, the electrons are much lower energy, so they radiate radio waves—although not enough to spoil KATRIN’s energy measurements.

    The frequency of those radio waves corresponds to an electron’s energy, a signal that Robertson and his colleagues plan to take advantage of. In what they call Project-8, they have built a thumbnail-sized chamber that can measure the radiation from a single electron. They hope to scale it up to measure the radio emissions of billions of electrons at once. That would require a 200-cubic-meter chamber studded with a slew of small radio antennas.

    Others hope to pry out the neutrino’s mass by studying nuclei of holmium-163, a synthetic radioisotope, created with particle accelerators, that undergoes a process nearly the opposite of beta decay called electron capture. In it, the nucleus gobbles up one of the atom’s own electrons while spitting out a neutrino. By tallying up all the heat and other energy from such captures and looking for a small shortfall at the end of its spectrum, physicists should be able to infer the mass of the neutrino, just as in a tritium experiment.

    That’s the goal of the Electron Capture on Holmium (ECHo) experiment at the University of Heidelberg in Germany, which embeds holmium atoms in tiny gold “calorimeters.” Experimenters have made working arrays of dozens of detectors, says Loredana Gastaldo, an ECHo physicist. To produce enough decays to measure the neutrino mass, she says, “we need to go from 100 detectors to 100,000 detectors.”

    If KATRIN falls short of a definitive measurement and neither of the new approaches pans out, then directly weighing the neutrino could remain an unreachable goal. Physicists may have to content themselves with the indirect and uncertain mass estimates that come from the heavens. And the shy and retiring particle will have preserved its shroud of mystery once again.

    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 9:00 pm on July 3, 2017 Permalink | Reply
    Tags: , , , , , Joe Incandela, Symmetry Magazine, What comes next?   

    From Symmetry: “When was the Higgs actually discovered?” 

    Symmetry Mag

    Symmetry

    07/03/17
    Sarah Charley

    The announcement on July 4 was just one part of the story. Take a peek behind the scenes of the discovery of the Higgs boson.

    1
    Maximilien Brice, Laurent Egli, CERN

    Joe Incandela UCSB and Cern CMS

    Joe Incandela sat in a conference room at CERN and watched with his arms folded as his colleagues presented the latest results on the hunt for the Higgs boson. It was December 2011, and they had begun to see the very thing they were looking for—an unexplained bump emerging from the data.

    “I was far from convinced,” says Incandela, a professor at the University of California, Santa Barbara and the former spokesperson of the CMS experiment at the Large Hadron Collider.

    CERN CMS Higgs Event

    CERN/CMS Detector

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    For decades, scientists had searched for the elusive Higgs boson: the holy grail of modern physics and the only piece of the robust and time-tested Standard Model that had yet to be found.

    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 construction of the LHC was motivated in large part by the absence of this fundamental component from our picture of the universe. Without it, physicists couldn’t explain the origin of mass or the divergent strengths of the fundamental forces.

    “Without the Higgs boson, the Standard Model falls apart,” says Matthew McCullough, a theorist at CERN. “The Standard Model was fitting the experimental data so well that most of the theory community was convinced that something playing the role of Higgs boson would be discovered by the LHC.”

    The Standard Model predicted the existence of the Higgs but did not predict what the particle’s mass would be. Over the years, scientists had searched for it across a wide range of possible masses. By 2011, there was only a tiny region left to search; everything else had been excluded by previous generations of experimentation.

    FNAL in the Tevatron research had ruled out many of the possible levels of energy that could have been the home of Higgs.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    If the predicted Higgs boson were anywhere, it had to be there, right where the LHC scientists were looking.

    But Incandela says he was skeptical about these preliminary results. He knew that the Higgs could manifest itself in many different forms, and this particular channel was extremely delicate.

    “A tiny mistake or an unfortunate distribution of the background events could make it look like a new particle is emerging from the data when in reality, it’s nothing,” Incandela says.

    A common mantra in science is that extraordinary claims require extraordinary evidence. The challenge isn’t just collecting the data and performing the analysis; it’s deciding if every part of the analysis is trustworthy. If the analysis is bulletproof, the next question is whether the evidence is substantial enough to claim a discovery. And if a discovery can be claimed, the final question is what, exactly, has been discovered? Scientists can have complete confidence in their results but remain uncertain about how to interpret them.

    In physics, it’s easy to say what something is not but nearly impossible to say what it is. A single piece of corroborated, contradictory evidence can discredit an entire theory and destroy an organization’s credibility.

    “We’ll never be able to definitively say if something is exactly what we think it is, because there’s always something we don’t know and cannot test or measure,” Incandela says. “There could always be a very subtle new property or characteristic found in a high-precision experiment that revolutionizes our understanding.”

    With all of that in mind, Incandela and his team made a decision: From that point on, everyone would refine their scientific analyses using special data samples and a patch of fake data generated by computer simulations covering the interesting areas of their analyses. Then, when they were sure about their methodology and had enough data to make a significant observation, they would remove the patch and use their algorithms on all the real data in a process called unblinding.

    “This is a nice way of providing an unbiased view of the data and helps us build confidence in any unexpected signals that may be appearing, particularly if the same unexpected signal is seen in different types of analyses,” Incandela says.

    A few weeks before July 4, all the different analysis groups met with Incandela to present a first look at their unblinded results. This time the bump was very significant and showing up at the same mass in two independent channels.

    “At that point, I knew we had something,” Incandela says. “That afternoon we presented the results to the rest of the collaboration. The next few weeks were among the most intense I have ever experienced.”

    Meanwhile, the other general-purpose experiment at the LHC, ATLAS, was hot on the trail of the same mysterious bump.

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    Andrew Hard was a graduate student at The University of Wisconsin, Madison working on the ATLAS Higgs analysis with his PhD thesis advisor Sau Lan Wu.

    “Originally, my plan had been to return home to Tennessee and visit my parents over the winter holidays,” Hard says. “Instead, I came to CERN every day for five months—even on Christmas. There were a few days when I didn’t see anyone else at CERN. One time I thought some colleagues had come into the office, but it turned out to be two stray cats fighting in the corridor.”

    Hard was responsible for writing the code that selected and calibrated the particles of light the ATLAS detector recorded during the LHC’s high-energy collisions. According to predictions from the Standard Model, the Higgs can transform into two of these particles when it decays, so scientists on both experiments knew that this project would be key to the discovery process.

    “We all worked harder than we thought we could,” Hard says. “People collaborated well and everyone was excited about what would come next. All in all, it was the most exciting time in my career. I think the best qualities of the community came out during the discovery.”

    At the end of June, Hard and his colleagues synthesized all of their work into a single analysis to see what it revealed. And there it was again—that same bump, this time surpassing the statistical threshold the particle physics community generally requires to claim a discovery.

    “Soon everyone in the group started running into the office to see the number for the first time,” Hard says. “The Wisconsin group took a bunch of photos with the discovery plot.”

    Hard had no idea whether CMS scientists were looking at the same thing. At this point, the experiments were keeping their latest results secret—with the exception of Incandela, Fabiola Gianotti (then ATLAS spokesperson) and a handful of CERN’s senior management, who regularly met to discuss their progress and results.

    Fabiola Gianotti, then the ATLAS spokesperson, now the General Director of CERN

    “I told the collaboration that the most important thing was for each experiment to work independently and not worry about what the other experiment was seeing,” Incandela says. “I did not tell anyone what I knew about ATLAS. It was not relevant to the tasks at hand.”

    Still, rumors were circulating around theoretical physics groups both at CERN and abroad. Mccullough, then a postdoc at the Massachusetts Institute of Technology, was avidly following the progress of the two experiments.

    “We had an update in December 2011 and then another one a few months later in March, so we knew that both experiments were seeing something,” he says. “When this big excess showed up in July 2012, we were all convinced that it was the guy responsible for curing the ails of the Standard Model, but not necessarily precisely that guy predicted by the Standard Model. It could have properties mostly consistent with the Higgs boson but still be not absolutely identical.”

    The week before announcing what they’d found, Hard’s analysis group had daily meetings to discuss their results. He says they were excited but also nervous and stressed: Extraordinary claims require extraordinary confidence.

    “One of our meetings lasted over 10 hours, not including the dinner break halfway through,” Hard says. “I remember getting in a heated exchange with a colleague who accused me of having a bug in my code.”

    After both groups had independently and intensely scrutinized their Higgs-like bump through a series of checks, cross-checks and internal reviews, Incandela and Gianotti decided it was time to tell the world.

    “Some people asked me if I was sure we should say something,” Incandela says. “I remember saying that this train has left the station. This is what we’ve been working for, and we need to stand behind our results.”

    On July 4, 2012, Incandela and Gianotti stood before an expectant crowd and, one at a time, announced that decades of searching and generations of experiments had finally culminated in the discovery of a particle “compatible with the Higgs boson.”

    Science journalists rejoiced and rushed to publish their stories. But was this new particle the long-awaited Higgs boson? Or not?

    Discoveries in science rarely happen all at once; rather, they build slowly over time. And even when the evidence overwhelmingly points in a clear direction, scientists will rarely speak with superlatives or make definitive claims.

    “There is always a risk of overlooking the details,” Incandela says, “and major revolutions in science are often born in the details.”

    Immediately after the July 4 announcement, theorists from around the world issued a flurry of theoretical papers presenting alternative explanations and possible tests to see if this excess really was the Higgs boson predicted by the Standard Model or just something similar.

    “A lot of theory papers explored exotic ideas,” McCullough says. “It’s all part of the exercise. These papers act as a straw man so that we can see just how well we understand the particle and what additional tests need to be run.”

    For the next several months, scientists continued to examine the particle and its properties. The more data they collected and the more tests they ran, the more the discovery looked like the long-awaited Higgs boson. By March, both experiments had twice as much data and twice as much evidence.

    “Amongst ourselves, we called it the Higgs,” Incandela says, “but to the public, we were more careful.”

    It was increasingly difficult to keep qualifying their statements about it, though. “It was just getting too complicated,” Incandela says. “We didn’t want to always be in this position where we had to talk about this particle like we didn’t know what it was.”

    On March 14, 2013—nine months and 10 days after the original announcement—CERN issued a press release quoting Incandela as saying, “to me, it is clear that we are dealing with a Higgs boson, though we still have a long way to go to know what kind of Higgs boson it is.”​

    To this day, scientists are open to the possibility that the Higgs they found is not exactly the Higgs they expected.

    “We are definitely, 100 percent sure that this is a Standard-Model-like Higgs boson,” Incandela says. “But we’re hoping that there’s a chink in that armor somewhere. The Higgs is a sign post, and we’re hoping for a slight discrepancy which will point us in the direction of new physics.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:04 pm on June 30, 2017 Permalink | Reply
    Tags: , , Gluons, , Symmetry Magazine, What really hapens?   

    From Symmetry: “What’s really happening during an LHC collision?” 

    Symmetry Mag

    Symmetry

    06/30/17
    Sarah Charley

    It’s less of a collision and more of a symphony.

    1
    Wow!! ATLAS collaboration.

    The Large Hadron Collider is definitely large.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    With a 17-mile circumference, it is the biggest collider on the planet. But the latter fraction of its name is a little misleading. That’s because what collides in the LHC are the tiny pieces inside the hadrons, not the hadrons themselves.

    Hadrons are composite particles made up of quarks and gluons.

    The quark structure of the proton 16 March 2006 Arpad Horvath

    The gluons carry the strong force, which enables the quarks to stick together and binds them into a single particle.

    2
    SA

    The main fodder for the LHC are hadrons called protons. Protons are made up of three quarks and an indefinable number of gluons. (Protons in turn make up atoms, which are the building blocks of everything around us.)

    If a proton were enlarged to the size of a basketball, it would look empty. Just like atoms, protons are mostly empty space. The individual quarks and gluons inside are known to be extremely small, less than 1/10,000th the size of the entire proton.

    “The inside of a proton would look like the atmosphere around you,” says Richard Ruiz, a theorist at Durham University. “It’s a mixture of empty space and microscopic particles that, for all intents and purposes, have no physical volume.

    “But if you put those particles inside a balloon, you’ll see the balloon expand. Even though the internal particles are microscopic, they interact with each other and exert a force on their surroundings, inevitably producing something which does have an observable volume.”

    So how do you collide two objects that are effectively empty space? You can’t. But luckily, you don’t need a classical collision to unleash a particle’s full potential.

    In particle physics, the term “collide” can mean that two protons glide through each other, and their fundamental components pass so close together that they can talk to each other. If their voices are loud enough and resonate in just the right way, they can pluck deep hidden fields that will sing their own tune in response—by producing new particles.

    “It’s a lot like music,” Ruiz says. “The entire universe is a symphony of complex harmonies which call and respond to each other. We can easily produce the mid-range tones, which would be like photons and muons, but some of these notes are so high that they require a huge amount of energy and very precise conditions to resonate.”

    Space is permeated with dormant fields that can briefly pop a particle into existence when vibrated with the right amount of energy. These fields play important roles but almost always work behind the scenes. The Higgs field, for instance, is always interacting with other particles to help them gain mass. But a Higgs particle will only appear if the field is plucked with the right resonance.

    When protons meet during an LHC collision, they break apart and the quarks and gluons come spilling out. They interact and pull more quarks and gluons out of space, eventually forming a shower of fast-moving hadrons.

    This subatomic symbiosis is facilitated by the LHC and recorded by the experiment, but it’s not restricted to the laboratory environment; particles are also accelerated by cosmic sources such as supernova remnants. “This happens everywhere in the universe,” Ruiz says. “The LHC and its experiments are not special in that sense. They’re more like a big concert hall that provides the energy to pop open and record the symphony inside each proton.”

    See the full article here .

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  • richardmitnick 2:07 pm on June 27, 2017 Permalink | Reply
    Tags: , , , , , Symmetry Magazine,   

    From Symmetry: “The rise of LIGO’s space-studying super-team” 

    Symmetry Mag

    Symmetry

    06/27/17
    Troy Rummler

    The era of multi-messenger astronomy promises rich rewards—and a steep learning curve.

    NASA/Fermi LAT

    Sometimes you need more than one perspective to get the full story.

    Scientists including astronomers working with the Fermi Large Area Telescope have recorded brief bursts of high-energy photons called gamma rays coming from distant reaches of space. They suspect such eruptions result from the merging of two neutron stars—the collapsed cores of dying stars—or from the collision of a neutron star and a black hole.

    But gamma rays alone can’t tell them that. The story of the dense, crashing cores would be more convincing if astronomers saw a second signal coming from the same event—for example, the release of ripples in space-time called gravitational waves.

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

    “The Fermi Large Area Telescope detects a few short gamma ray bursts per year already, but detecting one in correspondence to a gravitational-wave event would be the first direct confirmation of this scenario,” says postdoctoral researcher Giacomo Vianello of the Kavli Institute for Particle Astrophysics and Cosmology, a joint institution of SLAC National Accelerator Laboratory and Stanford University.

    Scientists discovered gravitational waves in 2015 (announced in 2016). Using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, they detected the coalescence of two massive black holes.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


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

    ESA/eLISA the future of gravitational wave research

    LIGO scientists are now sharing their data with a network of fellow space watchers to see if any of their signals match up. Combining multiple signals to create a more complete picture of astronomical events is called multi-messenger astronomy.​

    Looking for a match

    “We had this dream of finding astronomical events to match up with our gravitational wave triggers,” says LIGO scientist Peter Shawhan of the University of Maryland. ​

    But LIGO can only narrow down the source of its signals to a region large enough to contain roughly 100,000 galaxies.

    Searching for contemporaneous signals within that gigantic volume of space is extremely challenging, especially since most telescopes only view a small part of the sky at a time. So Shawhan and his colleagues developed a plan to send out an automatic alert to other observatories whenever LIGO detected an interesting signal of its own. The alert would contain preliminary calculations and the estimated location of the source of the potential gravitational waves.

    “Our early efforts were pretty crude and only involved a small number of partners with telescopes, but it kind of got this idea started,” Shawhan says. The LIGO Collaboration and the Virgo Collaboration, its European partner, revamped and expanded the program while upgrading their detectors. Since 2014, 92 groups have signed up to receive alerts from LIGO, and the number is growing.

    LIGO is not alone in latching onto the promise of multi-messenger astronomy. The Supernova Early Warning System (SNEWS) also unites multiple experiments to look at the same event in different ways.

    Neutral, rarely interacting particles called neutrinos escape more quickly from collapsing stars than optical light, so a network of neutrino experiments is prepared to alert optical observatories as soon as they get the first warning of a nearby supernova in the form of a burst of neutrinos.

    National Science Foundation Director France Córdova has lauded multi-messenger astronomy, calling it in 2016 a bold research idea that would lead to transformative discoveries.​

    The learning curve

    Catching gamma ray bursts alongside gravitational waves is no simple feat.

    The Fermi Large Area Telescope orbits the earth as the primary instrument on the Fermi Gamma-ray Space Telescope.

    NASA/Fermi Telescope

    The telescope is constantly in motion and has a large field of view that surveys the entire sky multiple times per day.

    But a gamma-ray burst lasts just a few seconds, and it takes about three hours for LAT to complete its sweep. So even if an event that releases gravitational waves also produces a gamma-ray burst, LAT might not be looking in the right direction at the right time. It would need to catch the afterglow of the event.

    Fermi LAT scientist Nicola Omodei of Stanford University acknowledges another challenge: The window to see the burst alongside gravitational waves might not line up with the theoretical predictions. It’s never been done before, so the signal could look different or come at a different time than expected.

    That doesn’t stop him and his colleagues from trying, though. “We want to cover all bases, and we adopt different strategies,” he says. “To make sure we are not missing any preceding or delayed signal, we also look on much longer time scales, analyzing the days before and after the trigger.”

    Scientists using the second instrument on the Fermi Gamma-ray Space Telescope have already found an unconfirmed signal that aligned with the first gravitational waves LIGO detected, says scientist Valerie Connaughton of the Universities Space Research Association, who works on the Gamma-Ray Burst Monitor. “We were surprised to find a transient event 0.4 seconds after the first GW seen by LIGO.”

    While the event is theoretically unlikely to be connected to the gravitational wave, she says the timing and location “are enough for us to be interested and to challenge the theorists to explain how something that was not expected to produce gamma rays might have done so.”

    From the ground up

    It’s not just space-based experiments looking for signals that align with LIGO alerts. A working group called DESgw, members of the Dark Energy Survey with independent collaborators, have found a way to use the Dark Energy Camera, a 570-Megapixel digital camera mounted on a telescope in the Chilean Andes, to follow up on gravitational wave detections.​


    Dark Energy Camera [DECam], built at FNAL


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

    “We have developed a rapid response system to interrupt the planned observations when a trigger occurs,” says DES scientist Marcelle Soares-Santos of Fermi National Accelerator Laboratory. “The DES is a cosmological survey; following up gravitational wave sources was not originally part of the DES scientific program.”

    Once they receive a signal, the DESgw collaborators meet to evaluate the alert and weigh the cost of changing the planned telescope observations against what scientific data they could expect to see—most often how much of the LIGO source location could be covered by DECam observations.

    “We could, in principle, put the telescope onto the sky for every event as soon as night falls,” says DES scientist Jim Annis, also of Fermilab. “In practice, our telescope is large and the demand for its time is high, so we wait for the right events in the right part of the sky before we open up and start imaging.”

    At an even lower elevation, scientists at the IceCube neutrino experiment—made up of detectors drilled down into Antarctic ice—are following LIGO’s exploits as well.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    Lunar Icecube

    IceCube DeepCore

    IceCube PINGU

    DM-Ice II at IceCube

    “The neutrinos IceCube is looking for originate from the most extreme environment in the cosmos,” says IceCube scientist Imre Bartos of Columbia University. “We don’t know what these environments are for sure, but we strongly suspect that they are related to black holes.”

    LIGO and IceCube are natural partners. Both gravitational waves and neutrinos travel for the most part unimpeded through space. Thus, they carry pure information about where they originate, and the two signals can be monitored together nearly in real time to help refine the calculated location of the source.

    The ability to do this is new, Bartos says. Neither gravitational waves nor high-energy neutrinos had been detected from the cosmos when he started working on IceCube in 2008. “During the past few years, both of them were discovered, putting the field on a whole new footing.”

    Shawhan and the LIGO collaboration are similarly optimistic about the future of their program and multi-messenger astronomy. More gravitational wave detectors are planned or under construction, including an upgrade to the European detector Virgo, the KAGRA detector in Japan, and a third LIGO detector in India, and that means scientists will home in closer and closer on their targets.​


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    IndIGO LIGO in India

    IndIGO in India

    See the full article here .

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  • richardmitnick 3:09 pm on June 24, 2017 Permalink | Reply
    Tags: , CERN ProtoDUNE, , , , , Symmetry Magazine   

    From Symmetry: “World’s biggest neutrino experiment moves one step closer” 

    Symmetry Mag

    Symmetry

    06/23/17
    Lauren Biron

    1
    Photo by Maximilien Brice, CERN

    The startup of a 25-ton test detector at CERN advances technology for the Deep Underground Neutrino Experiment.

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


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    In a lab at CERN sits a very important box. It covers about three parking spaces and is more than a story tall. Sitting inside is a metal device that tracks energetic cosmic particles.

    CERN Proto DUNE Maximillian Brice

    This is a prototype detector, a stepping-stone on the way to the future Deep Underground Neutrino Experiment (DUNE). On June 21, it recorded its first particle tracks.

    So begins the largest ever test of an extremely precise method for measuring elusive particles called neutrinos, which may hold the key to why our universe looks the way it does and how it came into being.

    A two-phase detector

    The prototype detector is named WA105 3x1x1 (its dimensions in meters) and holds five active tons—3000 liters—of liquid argon. Argon is well suited to interacting with neutrinos then transmitting the subsequent light and electrons for collection. Previous liquid argon neutrino detectors, such as ICARUS and MicroBooNE, detected signals from neutrinos using wires in the liquid argon. But crucially, this new test detector also holds a small amount of gaseous argon, earning it the special status of a two-phase detector.

    INFN Gran Sasso ICARUS, since moved to FNAL

    FNAL/ICARUS

    FNAL/MicrobooNE

    As particles pass through the detector, they interact with the argon atoms inside. Electrons are stripped off of atoms and drift through the liquid toward an “extraction grid,” which kicks them into the gas. There, large electron multipliers create a cascade of electrons, leading to a stronger signal that scientists can use to reconstruct the particle track in 3D. Previous tests of this method were conducted in small detectors using about 250 active liters of liquid argon.

    “This is the first time anyone will demonstrate this technology at this scale,” says Sebastien Murphy, who led the construction of the detector at CERN.

    The 3x1x1 test detector represents a big jump in size compared to previous experiments, but it’s small compared to the end goal of DUNE, which will hold 40,000 active tons of liquid argon. Scientists say they will take what they learn and apply it (and some of the actual electronic components) to next-generation single- and dual-phase prototypes, called ProtoDUNE.

    The technology used for both types of detectors is a time projection chamber, or TPC. DUNE will stack many large modules snugly together like LEGO blocks to create enormous DUNE detectors, which will catch neutrinos a mile underground at Sanford Underground Research Facility in South Dakota. Overall development for liquid argon TPCs has been going on for close to 40 years, and research and development for the dual-phase for more than a decade. The idea for this particular dual-phase test detector came in 2013.

    “The main goal [with WA105 3x1x1] is to demonstrate that we can amplify charges in liquid argon detectors on the same large scale as we do in standard gaseous TPCs,” Murphy says.

    By studying neutrinos and antineutrinos that travel 800 miles through the Earth from the US Department of Energy’s Fermi National Accelerator Laboratory [FNAL] to the DUNE detectors, scientists aim to discover differences in the behavior of matter and antimatter. This could point the way toward explaining the abundance of matter over antimatter in the universe. The supersensitive detectors will also be able to capture neutrinos from exploding stars (supernovae), unveiling the formation of neutron stars and black holes. In addition, they allow scientists to hunt for a rare phenomenon called proton decay.

    “All the R&D we did for so many years and now want to do with ProtoDUNE is the homework we have to do,” says André Rubbia, the spokesperson for the WA105 3x1x1 experiment and former co-spokesperson for DUNE. “Ultimately, we are all extremely excited by the discovery potential of DUNE itself.”

    2
    One of the first tracks in the prototype detector, caused by a cosmic ray. André Rubbia

    Testing, testing, 3-1-1, check, check

    Making sure a dual-phase detector and its electronics work at cryogenic temperatures of minus 184 degrees Celsius (minus 300 degrees Fahrenheit) on a large scale is the primary duty of the prototype detector—but certainly not its only one. The membrane that surrounds the liquid argon and keeps it from spilling out will also undergo a rigorous test. Special cryogenic cameras look for any hot spots where the liquid argon is predisposed to boiling away and might cause voltage breakdowns near electronics.

    After many months of hard work, the cryogenic team and those working on the CERN neutrino platform have already successfully corrected issues with the cryostat, resulting in a stable level of incredibly pure liquid argon. The liquid argon has to be pristine and its level just below the large electron multipliers so that the electrons from the liquid will make it into the gaseous argon.

    “Adding components to a detector is never trivial, because you’re adding impurities such as water molecules and even dust,” says Laura Manenti, a research associate at the University College London in the UK. “That is why the liquid argon in the 311—and soon to come ProtoDUNEs—has to be recirculated and purified constantly.”

    While ultimately the full-scale DUNE detectors will sit in the most intense neutrino beam in the world, scientists are testing the WA105 3x1x1 components using muons from cosmic rays, high-energy particles arriving from space. These efforts are supported by many groups, including the Department of Energy’s Office of Science.

    The plan is now to run the experiment, gather as much data as possible, and then move on to even bigger territory.

    “The prospect of starting DUNE is very exciting, and we have to deliver the best possible detector,” Rubbia says. “One step at a time, we’re climbing a large mountain. We’re not at the top of Everest yet, but we’re reaching the first chalet.”

    See the full article here .

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  • richardmitnick 1:51 pm on June 20, 2017 Permalink | Reply
    Tags: , , , , , Micro-X rocket experiment—an X-ray space telescope, Symmetry Magazine   

    From Symmetry: “A speed trap for dark matter, revisited” 

    Symmetry Mag

    Symmetry

    06/20/17
    Manuel Gnida

    1
    NASA, JPL-Caltech, Susan Stolovy (SSC/Caltech) et al.

    A NASA rocket experiment could use the Doppler effect to look for signs of dark matter in mysterious X-ray emissions from space.

    Researchers who hoped to look for signs of dark matter particles in data from the Japanese ASTRO-H/Hitomi satellite suffered a setback last year when the satellite malfunctioned and died just a month after launch.

    JAXA Hitomi ASTRO-H instruments

    Now the idea may get a second chance.

    In a new paper, published in Physical Review D, scientists from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory, suggest that their novel search method could work just as well with the future NASA-funded Micro-X rocket experiment—an X-ray space telescope attached to a research rocket.

    2
    Micro-X rocket schematic. http://inspirehep.net/record/1258362/plots

    The search method looks for a difference in the Doppler shifts produced by movements of dark matter and regular matter, says Devon Powell, a graduate student at KIPAC and lead author on the paper with co-authors Ranjan Laha, Kenny Ng and Tom Abel.

    The Doppler effect is a shift in the frequency of sound or light as its source moves toward or away from an observer. The rising and falling pitch of a passing train whistle is a familiar example, and the radar guns that cops use to catch speeders also work on this principle.

    The dark matter search technique, called Dark Matter Velocity Spectroscopy, is like setting up a speed trap to “catch” dark matter.

    “We think that dark matter has zero averaged velocity, while our solar system is moving,” says Laha, who is a postdoc at KIPAC. “Due to this relative motion, the dark matter signal would experience a Doppler shift. However, it would be completely different than the Doppler shifts from signals coming from astrophysical objects because those objects typically co-rotate around the center of the galaxy with the sun, and dark matter doesn’t. This means we should be able to distinguish the Doppler signatures from dark and regular matter.”

    Researchers would look for subtle frequency shifts in measurements of a mysterious X-ray emission. This 3500-electronvolt (3.5 keV) emission line, observed in data from the European XMM-Newton spacecraft and NASA’s Chandra X-ray Observatory, is hard to explain with known astrophysical processes.

    ESA/XMM Newton

    NASA/Chandra Telescope

    Some say it could be a sign of hypothetical dark matter particles called sterile neutrinos decaying in space.

    “The challenge is to find out whether the X-ray line is due to dark matter or other astrophysical sources,” Powell says. “We’re looking for ways to tell the difference.”

    The idea for this approach is not new: Laha and others described the method in a research paper last year[Physical Review Letters], in which they suggested using X-ray data from Hitomi to do the Doppler shift comparison. Although the spacecraft sent some data home before it disintegrated, it did not see any sign of the 3.5-keV signal, casting doubt on the interpretation that it might be produced by the decay of dark matter particles. The Dark Matter Velocity Spectroscopy method was never applied, and the issue was never settled.

    In the future Micro-X experiment, a rocket will catapult a small telescope above Earth’s atmosphere for about five minutes to collect X-ray signals from a specific direction in the sky. The experiment will then parachute back to the ground to be recovered. The researchers hope that Micro-X will do several flights to set up a speed trap for dark matter.

    4
    Jeremy Stoller, NASA

    “We expect the energy shifts of dark matter signals to be very small because our solar system moves relatively slowly,” Laha says. “That’s why we need cutting-edge instruments with superb energy resolution. Our study shows that Dark Matter Velocity Spectroscopy could be successfully done with Micro-X, and we propose six different pointing directions away from the center of the Milky Way.”

    Esra Bulbul from the MIT Kavli Institute for Astrophysics and Space Research, who wasn’t involved in the study, says, “In the absence of Hitomi observations, the technique outlined for Micro-X provides a promising alternative for testing the dark matter origin of the 3.5-keV line.” But Bulbul, who was the lead author of the paper that first reported the mystery X-ray signal in superimposed data of 73 galaxy clusters, also points out that the Micro-X analysis would be limited to our own galaxy.

    The feasibility study for Micro-X is more detailed than the prior analysis for Hitomi. “The earlier paper used certain approximations—for instance, that the dark matter halos of galaxies are spherical, which we know isn’t true,” Powell says. “This time we ran computer simulations without this approximation and predicted very precisely what Micro-X would actually see.”

    The authors say their method is not restricted to the 3.5-keV line and can be applied to any sharp signal potentially associated with dark matter. They hope that Micro-X will do the first practice test. Their wish might soon come true.

    “We really like the idea presented in the paper,” says Enectali Figueroa-Feliciano, the principal investigator for Micro-X at Northwestern University, who was not involved in the study. “We would look at the center of the Milky Way first, where dark matter is most concentrated. If we saw an unidentified line and it were strong enough, looking for Doppler shifts away from the center would be the next step.”

    See the full article here .

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  • richardmitnick 2:20 pm on June 12, 2017 Permalink | Reply
    Tags: But it’s not a perfect vacuum, , Creating secondary electrons, How to clean inside the LHC, Self-healing feature, Symmetry Magazine   

    From Symmetry: “How to clean inside the LHC” 

    Symmetry Mag

    Symmetry

    06/12/17
    Sarah Charley

    1
    Daniel Dominguez, CERN

    The beam pipes of the LHC need to be so clean, even air molecules count as dirt.

    The Large Hadron Collider is the world’s most powerful accelerator.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Inside, beams of particles sprint 17 miles around in opposite directions through a pair of evacuated beam pipes that intersect at collision points surrounded by giant particle detectors.

    The inside of the beam pipes need to be spotless, which is why the LHC is thoroughly cleaned every year before it ramps up its summer operations program.

    It’s not dirt or grime that clogs the LHC. Rather, it’s microscopic air molecules.

    “The LHC is incredibly cold and under a strong vacuum, but it’s not a perfect vacuum,” says LHC accelerator physicist Giovanni Rumolo. “There’s a tiny number of simple atmospheric gas molecules and even more frozen to the beam pipes’ walls.”

    Protons racing around the LHC crash into these floating air molecules, detaching their electrons. The liberated electrons jump after the positively charged protons but quickly crash into the beam pipe walls, depositing heat and liberating even more electrons from the frozen gas molecules there.

    This process quickly turns into an avalanche, which weakens the vacuum, heats up the cryogenic system, disrupts the proton beam and dramatically lowers the efficiency and reliability of the LHC.

    But the clouds of buzzing electrons inside the beam pipe possess an interesting self-healing feature, Rumolo says.

    “When the chamber wall is under intense electron bombardment, the probability of it creating secondary electrons decreases and the avalanche is gradually mitigated,” he says. “Before ramping the LHC up to its full intensity, we run the machine for several days with as many low-energy protons as we can safely manage and intentionally produce electron clouds. The effect is that we have fewer loose electrons during the LHC’s physics runs.”

    In other words, accelerator engineers clean the inside of the LHC a little like they would unclog a shower drain. They gradually pump the LHC full of more and more sluggish protons, which act like a scrub brush and knock off the microscopic grime clinging to the inside of the beam pipe. This loose debris is flushed out by the vacuum system. In addition, the bombardment of electrons transforms simple carbon molecules, which are still clinging to the beam pipe’s walls, into an inert and protective coating of graphite.

    Cleaning the beam pipe is such an important job that there is a team of experts responsible for it (officially called the “Scrubbing Team”).

    “Scrubbing is essential if we want to operate the LHC at its full potential,” Rumolo says. “It’s challenging, because there is a fine line between thoroughly cleaning the machine and accidentally dumping the beam. When we’re scrubbing, we work around the clock in the CERN Control Center to make sure the accelerator is safe and the scrubbing is working properly.”

    See the full article here .

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  • richardmitnick 3:28 pm on June 6, 2017 Permalink | Reply
    Tags: , , CERN unveils new linear accelerator, Symmetry Magazine   

    From Symmetry: “CERN unveils new linear accelerator” 

    Symmetry Mag

    Symmetry

    05/09/17 [Don’t know how I missed this one]
    No writer credit found

    1
    Photo by CERN

    Linac 4 will replace an older accelerator as the first step in the complex that includes the LHC.

    At a ceremony today, CERN European research center inaugurated its newest accelerator.

    Linac 4 will eventually become the first step in CERN’s accelerator chain, delivering proton beams to a wide range of experiments, including those at the Large Hadron Collider.

    After an extensive testing period, Linac 4 will be connected to CERN’s accelerator complex during a long technical shutdown in 2019-20. Linac 4 will replace Linac 2, which was put into service in 1978. Linac 4 will feed the CERN accelerator complex with particle beams of higher energy.

    “We are delighted to celebrate this remarkable accomplishment,” says CERN Director General Fabiola Gianotti. “Linac 4 is a modern injector and the first key element of our ambitious upgrade program, leading to the High-Luminosity LHC. This high-luminosity phase will considerably increase the potential of the LHC experiments for discovering new physics and measuring the properties of the Higgs particle in more detail.”

    “This is an achievement not only for CERN, but also for the partners from many countries who contributed in designing and building this new machine,” says CERN Director for Accelerators and Technology Frédérick Bordry. “We also today celebrate and thank the wide international collaboration that led this project, demonstrating once again what can be accomplished by bringing together the efforts of many nations.”

    The linear accelerator is the first essential element of an accelerator chain. In the linear accelerator, the particles are produced and receive the initial acceleration. The density and intensity of the particle beams are also shaped in the linac. Linac 4 is an almost 90-meter-long machine sitting 12 meters below the ground. It took nearly 10 years to build it.

    Linac 4 will send negative hydrogen ions, consisting of a hydrogen atom with two electrons, to CERN’s Proton Synchrotron Booster, which further accelerates the negative ions and removes the electrons. Linac 4 will bring the beam up to an energy of 160 million electronvolts, more than 3 times the energy of its predecessor. The increase in energy, together with the use of hydrogen ions, will enable doubling the beam intensity delivered to the LHC, contributing to an increase in the luminosity of the LHC by 2021.

    Luminosity is a parameter indicating the number of particles colliding within a defined amount of time. The peak luminosity of the LHC is planned to be increased by a factor of 5 by the year 2025. This will make it possible for the experiments to accumulate about 10 times more data over the period 2025 to 2035 than before.

    See the full article here .

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  • richardmitnick 1:27 pm on May 30, 2017 Permalink | Reply
    Tags: , , Symmetry Magazine   

    From Symmetry: “A brief etymology of particle physics” 

    Symmetry Mag

    Symmetry

    05/30/17
    Daniel Garisto

    1
    Illustration by Sandbox Studio, Chicago

    Over the years, physicists have given names to the smallest constituents of our universe.

    This pantheon of particles has grown alongside progress in physics. Anointing a particle with a name is not just convenient; it marks a leap forward in our understanding of the world around us.

    The etymology of particle physics contains a story that connects these sometimes outlandish names to a lineage of scientific thought and experiment.

    So, without further ado, Symmetry presents a detailed guide to the etymology of particles—some we’ve found and others we have yet to discover.

    Editor’s note: PIE, referenced throughout, refers to proto-Indo-European, one of the earliest known languages.

    [NOTE: IN THE FULL ARTCLE THESE ARE ALL HOT LINKS. TOO MANY FOR ME, GO TO THE FULL ARTICLE FOR THE LINKS.]

    Discovered particles
    Expand all
    ion ion
    fermion Fermi + on
    lepton leptos + on
    electron electric + on
    muon mu-meson (contraction)
    tau triton
    neutrino neutro (diminutive)
    quark quark
    boson Bose + on
    photon photo + on
    Higgs boson Higgs + boson
    W boson weak + boson
    Z boson zero + boson
    gluon glue + on
    hadron hadros + on
    baryon barys + on
    proton protos + on
    neutron neutral + on
    meson mesos + on
    antimatter anti + matter

    Hypothetical particles
    Expand all
    axion Axion
    chameleon chameleon
    graviton gravity + on
    majoron Majorana + on
    tachyon tachy + on
    supersymmetric particles super + symmetry

    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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