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  • richardmitnick 8:28 pm on November 25, 2015 Permalink | Reply
    Tags: ‘Material universe’ yields surprising new particle, , Physics,   

    From Princeton: “‘Material universe’ yields surprising new particle” 

    Princeton University
    Princeton University

    November 25, 2015

    A crystal of tungsten ditelluride is shown. Image courtesy of Wudi Wang and N. Phuan Ong, Princeton University.

    An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act as insulators for current applied in some directions and as conductors for current applied in other directions. This behavior suggests a range of potential applications, from low-energy devices to efficient transistors.

    The researchers theorize that the particle exists in a material known as tungsten ditelluride (WTe2), which the researchers liken to a “material universe” because it contains several particles, some of which exist under normal conditions in our universe and others that may exist only in these specialized types of crystals. The research appeared in the journal Nature this week.

    The new particle is a cousin of the Weyl fermion, one of the particles in standard quantum field theory. However, the type-II particle exhibits very different responses to electromagnetic fields, being a near perfect conductor in some directions of the field and an insulator in others.

    The research was led by Princeton University Associate Professor of Physics B. Andrei Bernevig, as well as Matthias Troyer and Alexey Soluyanov of ETH Zürich, and Xi Dai of the Chinese Academy of Sciences Institute of Physics. The team included Postdoctoral Research Associates Zhijun Wang at Princeton and QuanSheng Wu at ETH Zürich, and graduate student Dominik Gresch at ETH Zürich.

    The particle’s existence was missed by physicist Hermann Weyl during the initial development of quantum theory 85 years ago, say the researchers, because it violated a fundamental rule, called Lorentz symmetry, that does not apply in the materials where the new type of fermion arises.

    Particles in our universe are described by relativistic quantum field theory, which combines quantum mechanics with [Albert] Einstein’s theory of relativity. Under this theory, solids are formed of atoms that consist of a nuclei surrounded by electrons. Because of the sheer number of electrons interacting with each other, it is not possible to solve exactly the problem of many-electron motion in solids using quantum mechanical theory.

    Instead, our current knowledge of materials is derived from a simplified perspective where electrons in solids are described in terms of special non-interacting particles, called quasiparticles, that move in the effective field created by charged entities called ions and electrons. These quasiparticles, dubbed Bloch electrons, are also fermions.

    Just as electrons are elementary particles in our universe, Bloch electrons can be considered the elementary particles of a solid. In other words, the crystal itself becomes a “universe,” with its own elementary particles.

    In recent years, researchers have discovered that such a “material universe” can host all other particles of relativistic quantum field theory. Three of these quasiparticles, the Dirac, Majorana, and Weyl fermions, were discovered in such materials, despite the fact that the latter two had long been elusive in experiments, opening the path to simulate certain predictions of quantum field theory in relatively inexpensive and small-scale experiments carried out in these “condensed matter” crystals.

    These crystals can be grown in the laboratory, so experiments can be done to look for the newly predicted fermion in WTe2 and another candidate material, molybdenum ditelluride (MoTe2).

    “One’s imagination can go further and wonder whether particles that are unknown to relativistic quantum field theory can arise in condensed matter,” said Bernevig. There is reason to believe they can, according to the researchers.

    The universe described by quantum field theory is subject to the stringent constraint of a certain rule-set, or symmetry, known as Lorentz symmetry, which is characteristic of high-energy particles. However, Lorentz symmetry does not apply in condensed matter because typical electron velocities in solids are very small compared to the speed of light, making condensed matter physics an inherently low-energy theory.

    “One may wonder,” Soluyanov said, “if it is possible that some material universes host non-relativistic ‘elementary’ particles that are not Lorentz-symmetric?”

    This question was answered positively by the work of the international collaboration. The work started when Soluyanov and Dai were visiting Bernevig in Princeton in November 2014 and the discussion turned to strange unexpected behavior of certain metals in magnetic fields (Nature 514, 205-208, 2014, doi:10.1038/nature13763). This behavior had already been observed by experimentalists in some materials, but more work is needed to confirm it is linked to the new particle.

    The researchers found that while relativistic theory only allows a single species of Weyl fermions to exist, in condensed matter solids two physically distinct Weyl fermions are possible. The standard type-I Weyl fermion has only two possible states in which it can reside at zero energy, similar to the states of an electron which can be either spin-up or spin-down. As such, the density of states at zero energy is zero, and the fermion is immune to many interesting thermodynamic effects. This Weyl fermion exists in relativistic field theory, and is the only one allowed if Lorentz invariance is preserved.

    The newly predicted type-2 Weyl fermion has a thermodynamic number of states in which it can reside at zero energy – it has what is called a Fermi surface. Its Fermi surface is exotic, in that it appears along with touching points between electron and hole pockets. This endows the new fermion with a scale, a finite density of states, which breaks Lorentz symmetry.

    Left: Allowed states for the standard type-I Weyl fermion. When energy is tuned from below, at zero energy, a pinch in the number of allowed states guarantees the absence of many-body phenomena such as superconductivity or ordering. Right: The newly discovered type-II Weyl fermion. At zero energy, a large number of allowed states are still available. This allows for the presence of superconductivity, magnetism, and pair-density wave phenomena. Credit B. Andrei Bernevig et al.

    The discovery opens many new directions. Most normal metals exhibit an increase in resistivity when subject to magnetic fields, a known effect used in many current technologies. The recent prediction and experimental realization of standard type-I Weyl fermions in semimetals by two groups in Princeton and one group in IOP Beijing showed that the resistivity can actually decrease if the electric field is applied in the same direction as the magnetic field, an effect called negative longitudinal magnetoresistance. The new work shows that materials hosting a type-II Weyl fermion have mixed behavior: While for some directions of magnetic fields the resistivity increases just like in normal metals, for other directions of the fields, the resistivity can decrease like in the Weyl semimetals, offering possible technological applications.

    “Even more intriguing is the perspective of finding more ‘elementary’ particles in other condensed matter systems,” the researchers say. “What kind of other particles can be hidden in the infinite variety of material universes? The large variety of emergent fermions in these materials has only begun to be unraveled.”

    Researchers at Princeton University were supported by the U.S. Department of Defense, the U.S. Office of Naval Research, the U.S. National Science Foundation, the David and Lucile Packard Foundation and the W.M. Keck Foundation. Researchers at ETH Zurich were supported by Microsoft Research, the Swiss National Science Foundation and the European Research Council. Xi Dai was supported by the National Natural Science Foundation of China, the 973 program of China and the Chinese Academy of Sciences.

    The article, “Type II Weyl Semimetals,” by Alexey A. Soluyanov, Dominik Gresch, Zhijun Wang, QuanSheng Wu, Matthias Troyer, Xi Dai, and B. Andrei Bernevig was published in the journal Nature on November 26, 2015.

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    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 1:07 pm on November 24, 2015 Permalink | Reply
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    From Symmetry: “Charge-parity violation” 


    Photo by Reidar Hahn, Fermilab with Sandbox Studio, Chicago

    Manuel Gnida and Kathryn Jepsen

    Matter and antimatter behave differently. Scientists hope that investigating how might someday explain why we exist.

    One of the great puzzles for scientists is why there is more matter than antimatter in the universe—the reason we exist.

    It turns out that the answer to this question is deeply connected to the breaking of fundamental conservation laws of particle physics. The discovery of these violations has a rich history, dating back to 1956.

    Parity violation

    It all began with a study led by scientist Chien-Shiung Wu of Columbia University. She and her team were studying the decay of cobalt-60, an unstable isotope of the element cobalt. Cobalt-60 decays into another isotope, nickel-60, and in the process, it emits an electron and an electron antineutrino. The nickel-60 isotope then decays into a pair of photons.

    The conservation law being tested was parity conservation, which states that the laws of physics shouldn’t change when all the signs of a particle’s spatial coordinates are flipped. The experiment observed the decay of cobalt-60 in two arrangements that mirrored one another.

    The release of photons in the decay is an electromagnetic process, and electromagnetic processes had been shown to conserve parity. But the release of the electron and electron antineutrino is a radioactive decay process, mediated by the weak force. Such processes had not been tested in this way before.

    Parity conservation dictated that, in this experiment, the electrons should be emitted in the same direction and in the same proportion as the photons.

    But Wu and her team found just the opposite to be true. This meant that nature was playing favorites. Parity, or P symmetry, had been violated.

    Two theorists, Tsung Dao Lee and Chen Ning Yang, who had suggested testing parity in this way, shared the 1957 Nobel Prize in physics for the discovery.

    Charge-parity violation

    Many scientists were flummoxed by the discovery of parity violation, says Ulrich Nierste, a theoretical physicist at the Karlsruhe Institute of Technology in Germany.

    “Physicists then began to think that they may have been looking at the wrong symmetry all along,” he says.

    The finding had ripple effects. For one, scientists learned that another symmetry they thought was fundamental—charge conjugation, or C symmetry—must be violated as well.

    Charge conjugation is a symmetry between particles and their antiparticles. When applied to particles with a property called spin, like quarks and electrons, the C and P transformations are in conflict with each other.

    Physicists then began to think that they may have been looking at the wrong symmetry all along.

    This means that neither can be a good symmetry if one of them is violated. But, scientists thought, the combination of the two—called CP symmetry—might still be conserved. If that were the case, there would at least be a symmetry between the behavior of particles and their oppositely charged antimatter partners.

    Alas, this also was not meant to be. In 1964, a research group led by James Cronin and Val Fitch discovered in an experiment at Brookhaven National Laboratory that CP is violated, too.

    The team studied the decay of neutral kaons into pions; both are composite particles made of a quark and antiquark. Neutral kaons come in two versions that have different lifetimes: a short-lived one that primarily decays into two pions and a long-lived relative that prefers to leave three pions behind.

    However, Cronin, Fitch and their colleagues found that, rarely, long-lived kaons also decayed into two instead of three pions, which required CP symmetry to be broken.

    The discovery of CP violation was recognized with the 1980 Nobel Prize in physics. And it led to even more discoveries.

    It prompted theorists Makoto Kobayashi and Toshihide Maskawa to predict in 1973 the existence of a new generation of elementary particles. At the time, only two generations were known. Within a few years, experiments at SLAC National Accelerator Laboaratory found the tau particle—the third generation of a group including electrons and muons. Scientists at Fermi National Accelerator Laboratory later discovered a third generation of quarks—bottom and top quarks.
    Digging further into CP violation

    In the late 1990s, scientists at Fermilab and European laboratory CERN found more evidence of CP violation in decays of neutral kaons. And starting in 1999, the BaBar experiment at SLAC and the Belle experiment at KEK in Japan began to look into CP violation in decays of composite particles called B mesons

    By analyzing dozens of different types of B meson decays, scientists on BaBar and Belle revealed small differences in the way B mesons and their antiparticles fall apart. The results matched the predictions of Kobayashi and Maskawa, and in 2008 their work was recognized with one half of the physics Nobel Prize.

    “But checking if the experimental data agree with the theory was only one of our goals,” says BaBar spokesperson Michael Roney of the University of Victoria in Canada. “We also wanted to find out if there is more to CP violation than we know.”

    This is because these experiments are seeking to answer a big question: Why are we here?

    When the universe formed in the big bang 14 billion years ago, it should have generated matter and antimatter in equal amounts. If nature treated both exactly the same way, matter and antimatter would have annihilated each other, leaving nothing behind but energy.

    And yet, our matter-dominated universe exists.

    CP violation is essential to explain this imbalance. However, the amount of CP violation observed in particle physics experiments so far is a million to a billion times too small.

    Current and future studies

    Recently, BaBar and Belle combined their data treasure troves in a joint analysis (1). It revealed for the first time CP violation in a class of B meson decays that each experiment couldn’t have analyzed alone due to limited statistics.

    This and all other studies to date are in full agreement with the standard theory. But researchers are far from giving up hope on finding unexpected behaviors in processes governed by CP violation.

    The future Belle II, currently under construction at KEK, will produce B mesons at a much higher rate than its predecessor, enabling future CP violation studies with higher precision.

    And the LHCb experiment at CERN’s Large Hadron Collider is continuing studies of B mesons, including heavier ones that were only rarely produced in the BaBar and Belle experiments. The experiment will be upgraded in the future to collect data at 10 times the current rate.

    To date, CP violation has been observed only in particles like these ones made of quarks.

    “We know that the types of CP violation already seen using some quark decays cannot explain matter’s dominance in the universe,” says LHCb collaboration member Sheldon Stone of Syracuse University. “So the question is: Where else could we possibly find CP violation?”

    One place for it to hide could be in the decay of the Higgs boson. Another place to look for CP violation is in the behavior of elementary leptons—electrons, muons, taus and their associated neutrinos. It could also appear in different kinds of quark decays.

    “To explain the evolution of the universe, we would need a large amount of extra CP violation,” Nierste says. “It’s possible that this mechanism involves unknown particles so heavy that we’ll never be able to create them on Earth.”

    Such heavyweights would have been produced last in the very early universe and could be related to the lack of antimatter in the universe today. Researchers search for CP violation in much lighter neutrinos, which could give us a glimpse of a possible large violation at high masses.

    The search continues.

    1.First observation of CP violation in B0->D(*)CP h0 decays by a combined time-dependent analysis of BaBar and Belle data.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 12:11 pm on November 19, 2015 Permalink | Reply
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    From Physics: “Synopsis: LHC Data Might Reveal Nature of Neutrinos” 

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    November 18, 2015
    Michael Schirber


    As recognized by this year’s Nobel Prize in physics, evidence now points to neutrinos having mass (see 7 October 2015 Focus story). But this opens up new questions about why the neutrino mass is so much smaller than other particle masses. One solution is to assume that the neutrino is a different kind of particle—one that is its own antiparticle. A new theoretical study shows that observations of W boson decays at the Large Hadron Collider (LHC) in Geneva could potentially uncover the antiparticle nature of the neutrino.

    Electrons, protons, and other fermions are Dirac particles, meaning they have a separate antiparticle with the same mass, but opposite charge. Neutrinos could be Dirac particles, but because they have no electric charge, they could also be Majorana particles, for which particle and antiparticle are the same thing. Such Majorana models are attractive because they offer a fairly natural explanation for the extremely small neutrino mass.

    Experiments looking at extremely rare nuclear decays are trying to detect a possible Majorana or Dirac signature of the neutrino. To widen the search, Claudio Dib from Santa María University in Chile and Choong Sun Kim from Yonsei University in Korea propose looking at W boson decays. They considered decays that result in specific combinations of electrons, muons, and neutrinos. These decays have yet to be observed, but they are predicted in theories involving hypothetical sterile neutrinos. Taking into account current limits on the existence of sterile neutrinos, the team predicts that the next runs at the LHC could produce as many as a few thousand of the desired W boson decays. If this count is correct, then physicists should be able to discriminate Majorana from Dirac neutrinos by the shape of the energy spectrum of the outgoing muons.

    This research is published in Physical Review D.

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

  • richardmitnick 10:02 am on November 17, 2015 Permalink | Reply
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    From Kavli IPMU: “Yuji Tachikawa receives 2016 Fundamental Physics New Horizons Prize” 


    The Kavli Foundation

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    Yuji Tachikawa

    Kavli IPMU researcher Yuji Tachikawa was honored at the 2016 Breakthrough Prize ceremony, held at NASA’s Ames Research Center on November 9.

    Tachikawa was awarded the 2016 Fundamental Physics New Horizons Prize for his penetrating and incisive studies of supersymmetric quantum field theories.

    The Breakthrough Prizes in Physics were set up in 2012 by Russian entrepreneur Yuri Milner. They consist of three prizes: the Breakthrough Prize in Fundamental Physics, the Special Breakthrough Prize in Fundamental Physics, and the New Horizons Prize. Tachikawa’s prize recognizes junior researchers who have made significant contributions to their field.

    “I’d like to thank all the institutes and universities that have provided me with the best research environments; I am grateful and feel very fortunate to have been able to work with amazing mentors and colleagues; and I am especially thankful to my family for their continued support. I would like to consider this Prize as a stepping stone and promise to continue to do good research,” says Tachikawa.

    The 2016 Breakthrough Prize in Fundamental Physics was awarded to scientists in five experiments around the world for their studies in neutrino oscillations. Seven scientists representing the experiments, including Kavli IPMU’s Yoichiro Suzuki and Takaaki Kajita, received the award at the same ceremony of behalf of all the researchers.

    In 2010, Tachikawa collaborated with Luis Fernando Alday and Davide Gaiotto and developed the Alday-Gaiotto-Tachikawa correspondence: the trio had found that the partition functions of carefully chosen four-dimentional and two-dimensional quantum field theories are equal to one another. This discovery was a big step in the understanding of quantum field theory in various dimensions.

    To date, Tachikawa has also received the 2014 Nishinomiya-Yukawa Memorial Prize, and he was the first Japanese national to receive the Hermann Weyl Prize in 2014.

    See the full article here .

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    Kavli IPMU (Kavli Institute for the Physics and Mathematics of the Universe) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
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    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

  • richardmitnick 12:23 pm on October 22, 2015 Permalink | Reply
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    From NOVA: “Are the Laws of Physics Really Universal?” 



    21 Oct 2015
    Kate Becker

    Can the laws of physics change over time and space?

    As far as physicists can tell, the cosmos has been playing by the same rulebook since the time of the Big Bang. But could the laws have been different in the past, and could they change in the future? Might different laws prevail in some distant corner of the cosmos?

    “It’s not a completely crazy possibility,” says Sean Carroll, a theoretical physicist at Caltech, who points out that, when we ask if the laws of physics are mutable, we’re actually asking two separate questions: First, do the equations of quantum mechanics and gravity change over time and space? And second, do the numerical constants that populate those equations vary?

    An artist’s impression of the quasar 3C 279. Astrophysicists use light from quasars to look for variations in the fundamental constants. Credit: ESO/M. Kornmesser, adapted under a Creative Commons license.

    To see the distinction, imagine the whole universe as one big game of basketball. You can tweak certain parameters without changing the game: Raise the hoop a little higher, make the court a little bigger, change the way you score, and it’s still basketball. But if you tell the players to start running bases or kicking field goals, then you’re playing a different game.

    Most of the current research into the changeability of physical laws has focused on the numerical constants. Why? It’s the easier question to answer. Physicists can make solid, testable predictions about how variations in numerical constants should affect the results of their experiments. Plus, says Carroll, it wouldn’t necessarily blow physics wide open if it turns out that constants do change over time. In fact, some constants have changed: The mass of an electron, for instance, was zero until the Higgs field turned on a tiny sliver of a second after the Big Bang. “We have lots of theories that can accommodate changing constants,” says Carroll. “All you have to do to account for time-dependent constants is to add some scalar field to the theory that moves very slowly.”

    A scalar field, Carroll explains, is any quantity that has a unique value at every point in space-time. The celebrity-du-jour scalar field is the Higgs, but you can also think of less exotic quantities, like temperature, as scalar fields, too. A yet-undiscovered scalar field that changes very slowly could continue to evolve even billions of years after the Big Bang—and with it, the so-called constants of nature could evolve, too.

    Luckily, the cosmos has gifted us with some handy windows through which we can peer at the constants as they were in the deep past. One such window is located in the rich uranium deposits of the Oklo region of Gabon, in Central Africa, where, in 1972, workers serendipitously discovered a group of natural nuclear reactors—rocks that spontaneously ignited and managed to sustain nuclear reactions for hundreds of thousands of years. The result: “A radioactive fossil of what the rules of nature looked like” two billion years ago, says Carroll. (For perspective, the Earth is about 4 billion years old, and the universe is edging toward 14 billion.)

    The characteristics of that fossil depend on the value of a special number called the fine structure constant, which bundles up a handful of other constants—the speed of light [in a vacuum], the charge on an electron, the electric constant, and Planck’s constant—into a single number, about 1/137. It’s what physicists call a “dimensionless” constant, meaning that it’s really just a number: it’s not 1/137 inches, seconds, or coulombs, it’s just plain 1/137. That makes it an ideal place to look for changes in the constants embedded within it, says Steve Lamoreaux, a physicist at Yale University. “If the constants changed in such a way that the electron mass and the electrostatic interaction energies changed in different way, it would show up in the 1/137 unambiguously, independent of measurement system.”

    But interpreting that fossil isn’t easy, and over the years researchers studying Oklo have come to apparently conflicting conclusions. For decades, studies of Oklo seemed to show that the fine structure constant was absolutely steady. Then came a study suggesting that it had gotten bigger, and another that it had gotten smaller. In 2006, Lamoreaux (then at Los Alamos National Laboratory) and his colleagues published a fresh analysis that was, they wrote, “consistent with no shift.” But, they pointed out, it was still “model dependent”—that is, they had to make certain assumptions about how the fine structure constant could change.

    Using atomic clocks, physicists can search for even tinier changes in the fine structure constant, but they’re limited to looking at present-day variations that happen over just a year or so. Researchers at the National Institute of Standards and Technology in Boulder, Colorado, compared time kept by atomic clocks running on aluminum and mercury to put extremely tight limits on the present-day change in the fine structure constant. Though they can’t say for certain that the fine structure constant isn’t changing, if it is, the variation is tiny: just quadrillionths of a single percent each year.

    Today, the best limits on how the constants could be varying over the life of the universe come from observations of distant objects on the sky. That’s because, the farther into space you look, the farther back in time you can see. The Oklo “time machine” stops two billion years ago, but, using light from distant quasars, astronomers have dialed the cosmic time machine 11 billion years back.

    Quasars are extremely bright, ancient objects that astronomers believe are probably glowing supermassive black holes. As light from these quasars travels to us, some of it gets absorbed by the gas it travels through along the way. But it doesn’t get absorbed evenly: only very particular wavelengths, or colors, get plucked out. The specific colors that are “deleted” from the spectrum depend on how photons from the quasar light interact with atoms in the gas, and those interactions depend on the fine structure constant. So, by looking at the spectrum of light from distant quasars, astrophysicists can search for changes to the fine structure constant over many billions of years.

    “By the time that light has reached us here on Earth, it has collected information regarding several galaxies going back billions of years,” says Tyler Evans, who led some of the most rigorous quasar measurements to date while he was a PhD student at Swinburne University of Technology in Australia. “It is analogous to taking a core sample of ice or the Earth in order to tell how climate was behaving in previous epochs.”

    Despite some tantalizing hints, the latest studies all show that changes to the fine structure constant are “consistent with zero.” That doesn’t mean that the fine structure constant absolutely isn’t changing. But if it is, it’s doing so more subtly than these experiments can detect, and that seems unlikely, says Carroll. “It’s hard to squeeze a theory into the little daylight between not changing at all, and not changing enough that we can see it.”

    Astrophysicists are also looking for changes to G, the gravitational constant, which dials in the strength of gravity. In 1937, Paul Dirac, one of the pioneers of quantum mechanics, offered up the hypothesis that gravity gets weaker as the universe ages. Though the idea didn’t stick, physicists kept looking for changes in G, and today some exotic alternative theories of gravity embrace a shifting gravitational constant. While lab experiments here on Earth have returned confusing results, studies off Earth suggest that G isn’t changing much, if it all. Most recently, radio astronomers scoured 21 years of precise timing data from an unusually bright, stable pulsar to see if they could trace any changes in its regular “heartbeat” of radio emission to changes in the gravitational constant. The result—nothing.

    But back to the second, tougher half of our original question: Could the laws of physics themselves, and not just the constants sewn into them, be changing? “That’s much harder to say,” says Carroll, who points out that there are different degrees of disruption to consider. If the rules of some “sub-theory” of quantum mechanics, like quantum electrodynamics, turned out to be fluid, maybe existing theory could accommodate that. But if the laws of quantum mechanics itself are in flux, says Carroll, “That would be very bizarre.” No theory predicts how or why such a change might happen; there is simply no framework from which to investigate the question.

    As far as we can tell, the universe seems to be playing fair. But physicists will keep scouring the rulebook, looking for clues that the rules of the game could be changing at a level we haven’t yet perceived.

    Go Deeper
    Picks for further reading

    Discover: Is the Search for Immutable Laws of Nature a Wild-Goose Chase?
    Astrophysicist Adam Frank profiles four theorists who challenge the notion that there is one set of unchanging laws that perfectly describes the universe.

    Michael Murphy: Are Nature’s Laws Really Universal?
    Murphy, an astrophysicist at Swinburne University of Technology, provides a general-audience overview of the search for changes in the fundamental constants, with links to related articles and video.
    Natural History Magazine: On Earth As In The Heavens
    In this essay, astrophysicist Neil deGrasse Tyson explains why physicists think that the same laws that apply on Earth apply throughout the cosmos, and how we may one day use this knowledge to communicate with alien civilizations.

    See the full article here .

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

  • richardmitnick 10:33 am on October 11, 2015 Permalink | Reply
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    From Weizmann: “Getting to the Center” 

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    No Writer Credit

    The nucleus (red) in the cell center is surrounded by the disorganized actin network in the cytoplasm, on which the myosin-v motors move the vesicles around in the “active random motion” No image credit.

    Before an egg – whether mouse or human – can be fertilized, it must get its “internal affairs” in order. That includes moving its nucleus into position in the exact center of the cell. Under a microscope, the nucleus appears to do a little dance, jigging its way from the edge of the cell to the middle. What is really going on?

    “This is a question that physics can answer,” says Prof. Nir Gov of the Weizmann Institute’s Chemical Physics Department. “We examine the physics of the biological molecules in the cell to see whether the means of motion that are proposed are mechanically possible.” Gov, a theoretical physicist, worked with physicists and biologists led by Prof. Marie-Helen Verlhac at the College de France in Paris, observing what happens to the nuclei in mouse egg cells.

    The nucleus dance, they found, is the result of bumping: Tiny motorized sacs called vesicles continually collide with the nucleus. These vesicles run on tracks – the long, thin actin filaments that provide the cell with support – and they are transported by molecular motors made of a kind of myosin – a relative of the myosin that makes our muscles contract. (“The vesicles with their myosin motors underneath look like little people running on a track,” says Gov.)

    But the actin fibers form a disorganized network in the cell’s cytoplasm, and the movement of the vesicles is random as well. How does this random motion turn into the directed movement of the nucleus? This is where the physics came in. The mechanism that indeed explains the movement turned out to be subtle but effective.

    Prof. Nir Gov

    The researchers found that the motors carrying the vesicles move more vigorously at the cell’s outer edges and more slowly in its center. Since there is about the same number of vesicles everywhere, this means that the bumping is more intense from one side. As the nucleus moves in toward the center, however, the force of the vesicles striking it gradually drops until it reaches the point at which the pressure is equally low all around. The physical model for this motion also reveals that the myosin motors stir up the cytoplasm, making it more fluid so that the nucleus can slide through it more easily.

    Further investigations showed that, unlike the active motion of the vesicles, “random thermal motion” – the heat-induced movement that makes molecules “jumpy” – cannot give rise to this type of movement, and would not be able to direct the nucleus to the center of the cell.

    How does the differential velocity of the tiny motors arise in the cell? This open question is under further study. “This is the first time that we have seen such ‘active random motion’ perform work in biological systems,” says Gov. “Since almost all cells contain actin transport systems, we think it could play a role in other types of intracellular movements. As well as solving a biological puzzle, we have learned something new about basic physics by researching movement in cells,” he adds.

    See the full article here .

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    Weizmann Institute Campus

    The Weizmann Institute of Science is one of the world’s leading multidisciplinary research institutions. Hundreds of scientists, laboratory technicians and research students working on its lushly landscaped campus embark daily on fascinating journeys into the unknown, seeking to improve our understanding of nature and our place within it.

    Guiding these scientists is the spirit of inquiry so characteristic of the human race. It is this spirit that propelled humans upward along the evolutionary ladder, helping them reach their utmost heights. It prompted humankind to pursue agriculture, learn to build lodgings, invent writing, harness electricity to power emerging technologies, observe distant galaxies, design drugs to combat various diseases, develop new materials and decipher the genetic code embedded in all the plants and animals on Earth.

    The quest to maintain this increasing momentum compels Weizmann Institute scientists to seek out places that have not yet been reached by the human mind. What awaits us in these places? No one has the answer to this question. But one thing is certain – the journey fired by curiosity will lead onward to a better future.

  • richardmitnick 9:18 am on October 8, 2015 Permalink | Reply
    Tags: , , Physics   

    From FNAL: “Physics in a Nutshell – Is the universe getting bigger or am I getting smaller?” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Oct. 8, 2015
    Jim Pivarski

    Temp 1
    Alice knows she’s getting bigger only because the room isn’t.

    It is a well-established fact that the universe is expanding. It grows without center, like an inflating raisin cake, but an infinite raisin cake filling all of space in all directions. The raisins are the galaxies.

    A problem I’ve had with this explanation is that if everything were to double in size — galaxies, houses, you and me, rulers — then we’d never notice. I might be a towering giant, but if the room is equally huge, I wouldn’t know. We can only see relative differences in sizes.

    When scientists say the universe is expanding, they don’t mean that its occupants are expanding along with it. The raisins do not grow with the cake. Imagine cake batter so full of raisins that they’re pressed against each other when you first put the cake in the oven, but by the time it’s done, there’s only one raisin per mouthful. This would be a better analogy, but it raises another question: How do we know the raisins aren’t shrinking?

    Putting the question another way, what if the distances between galaxies are fixed, but everything except those distances are getting smaller? Or somewhere in between — the universe grows a little while we shrink a little. For that matter, where should we put the boundary line between the scales that grow relative to the scales that shrink?

    Fundamentally, the expansion of the universe is described by one ratio that relates lengths in space with durations in time, sometimes called the cosmic scale factor. As time passes, this ratio changes: the scale of space increases with each second. But since this ratio, length divided by time, is a speed, suppose we think of space as fixed and all speeds slowing down.

    What would happen if every object, from particles to planets, suddenly slowed down? Planets would fall in closer to the sun because they would have less angular momentum. Similarly, electrons would get closer to the nuclei of atoms. Molecular bonds would shorten. Every system bound by a force would shrink, but the distances between unconnected systems would stay the same.

    Alternatively, what would happen if particle speeds were left alone but everything expanded uniformly, like a plate of marshmallows in the microwave? Again, electron and planetary orbits would then shrink to their natural sizes, like marshmallows taken out of the microwave, but the gaps between them wouldn’t.

    Regardless of how we interpret the underlying theory, we have the same picture: Distances between bound systems increase relative to the sizes of those systems. But that shouldn’t be a surprise, since we’re talking about the same physics theory in two different ways. It’s all a matter of perspective.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

  • richardmitnick 3:25 pm on October 6, 2015 Permalink | Reply
    Tags: , , , Physics   

    From DESY: “Physicists shrink particle accelerator” 


    No Writer Credit

    Terahertz accelerator modules easily fit into two fingers. Credit: DESY/Heiner Müller-Elsner

    An interdisciplinary team of researchers has built the first prototype of a miniature particle accelerator that uses terahertz radiation instead of radio frequency structures. A single accelerator module is no more than 1.5 centimetres long and one millimetre thick. The terahertz technology holds the promise of miniaturising the entire set-up by at least a factor of 100, as the scientists surrounding DESY’s Franz Kärtner from the Center for Free-Electron Laser Science (CFEL) point out. They are presenting their prototype, that was set up in Kärtner’s lab at the Massachusetts Institute of Technology (MIT) in the U.S., in the journal Nature Communications. The authors see numerous applications for terahertz accelerators, in materials science, medicine and particle physics, as well as in building X-ray lasers. CFEL is a cooperation between DESY, the University of Hamburg and the Max Planck Society.

    In the electromagnetic spectrum, terahertz radiation lies between infrared radiation and microwaves. Particle accelerators usually rely on electromagnetic radiation from the radio frequency range; DESY’s particle accelerator PETRA III, for example, uses a frequency of around 500 megahertz.

    DESI Petra III interior

    The wavelength of the terahertz radiation used in this experiment is around one thousand times shorter. “The advantage is that everything else can be a thousand times smaller too,” explains Kärtner, who is also a professor at the University of Hamburg and at MIT, as well as being a member of the Hamburg Centre for Ultrafast Imaging (CUI), one of Germany’s Clusters of Excellence.

    For their prototype the scientists used a special microstructured accelerator module, specifically tailored to be used with terahertz radiation. The physicists fired fast electrons into the miniature accelerator module using a type of electron gun provided by the group of CFEL Professor Dwayne Miller, Director at the Max Planck Institute for the Structure and Dynamics of Matter and also a member of CUI. The electrons were then further accelerated by the terahertz radiation fed into the module. This first prototype of a terahertz accelerator was able to increase the energy of the particles by seven kiloelectronvolts (keV).

    “This is not a particularly large acceleration, but the experiment demonstrates that the principle does work in practice,” explains co-author Arya Fallahi of CFEL, who did the theoretical calculations. “The theory indicates that we should be able to achieve an accelerating gradient of up to one gigavolt per metre.” This is more than ten times what can be achieved with the best conventional accelerator modules available today. Plasma accelerator technology, which is also at an experimental stage right now, promises to produce even higher accelerations, however it also requires significantly more powerful lasers than those needed for terahertz accelerators.

    The physicists underline that terahertz technology is of great interest both with regard to future linear accelerators for use in particle physics, and as a means of building compact X-ray lasers and electron sources for use in materials research, as well as medical applications using X-rays and electron radiation. “The rapid advances we are seeing in terahertz generation with optical methods will enable the future development of terahertz accelerators for these applications,” says first author Emilio Nanni of MIT. Over the coming years, the CFEL team in Hamburg plans to build a compact, experimental free-electron X-ray laser (XFEL) on a laboratory scale using terahertz technology. This project is supported by a Synergy Grant of the European Research Council.

    So-called free-electron lasers (FELs) generate flashes of laser light by sending high-speed electrons from a particle accelerator down an undulating path, whereby these emit light every time they are deflected. This is the same principle that will be used by the X-ray laser European XFEL, which is currently being built by an international consortium, reaching from the DESY Campus in Hamburg to the neighbouring town of Schenefeld, in Schleswig-Holstein. The entire facility will be more than three kilometres long and will be the best and most modern of its kind after completion.

    The experimental XFEL using terahertz technology is expected to be less than a metre long. “We expect this sort of device to produce much shorter X-ray pulses lasting less than a femtosecond”, says Kärtner. Because the pulses are so short, they reach a comparable peak brightness to those produced by larger facilities, even if there is significant less light in each pulse. “With these very short pulses we are hoping to gain new insights into extremely rapid chemical processes, such as those involved in photosynthesis.”

    Developing a detailed understanding of photosynthesis would open up the possibility of implementing this efficient process artificially and thus tapping into increasingly efficient solar energy conversion and new pathways for CO2 reduction. Beyond this, researchers are interested in numerous other chemical reactions. As Kärtner points out, “photosynthesis is just one example of many possible catalytic processes we would like to investigate.” The compact XFEL can be potentially also used to seed pulses in large scale facilities to enhance the quality of their pulses. Also, certain medical imaging techniques could benefit from the enhanced characteristics of the novel X-ray source.

    „Terahertz-driven linear electron acceleration“; Emilio A. Nanni, Wenqian R. Huang, Kyung-Han Hong, Koustuban Ravi, Arya Fallahi, Gustavo Moriena, R. J. Dwayne Miller & Franz X. Kärtner; Nature Communications, 2015; DOI: 10.1038/NCOMMS9486

    See the full article here .

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    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

  • richardmitnick 9:43 am on October 2, 2015 Permalink | Reply
    Tags: , , Heisenberg's Uncertainty Principle, Physics,   

    From AAAS: “Physicists observe weird quantum fluctuations of empty space—maybe” 



    1 October 2015
    Adrian Cho

    The setup in which a long “pump” light pulse (red) changes the polarization of a short “probe” light pulse (green) also serves to measure the effect of vacuum fluctuations—just by turning off the pump beam. ADAPTED FROM C. RIEK ET AL., SCIENCE (2015)

    Empty space is anything but, according to quantum mechanics: Instead, it roils with quantum particles flitting in and out of existence. Now, a team of physicists claims it has measured those fluctuations directly, without disturbing or amplifying them. However, others say it’s unclear exactly what the new experiment measures—which may be fitting for a phenomenon that originates in quantum mechanics’ famous uncertainty principle.

    “There are many experiments that have observed indirect effects of vacuum fluctuations,” says Diego Dalvit, a theorist at Los Alamos National Laboratory in New Mexico who was not involved in the current work. “If this [new experiment] is correct, it would be the first direct observation of the field [of fluctuations] itself.”

    Thanks to the [Heisenberg’s] uncertainty principle, the vacuum buzzes with particle-antiparticle pairs popping in and out of existence. They include, among many others, electron-positron pairs and pairs of photons, which are their own antiparticles. Ordinarily, those “virtual” particles cannot be directly captured. But like some spooky Greek chorus, they exert subtle influences on the “real” world.

    For example, the virtual photons flitting in and out of existence produce a randomly fluctuating electric field. In 1947, physicists found that the field shifts the energy levels of an electron inside a hydrogen atom and hence the spectrum of radiation the atom emits. A year later, Dutch theorist Hendrik Casimir predicted that the field would also exert a subtle force on two closely spaced metal plates, squeezing them together. That’s because the electric field must vanish on the plates’ surfaces, so only certain wavelike ripples of the electric field can fit between the plates. In contrast, more ripples can push on the plates from the outside, exerting a net force. The Casimir effect was observed in 1997.

    But now, Claudius Riek, Alfred Leitenstorfer, and colleagues at the University of Konstanz in Germany say they have directly observed those electric field fluctuations by charting their influence on a light wave. The experiment riffs on a technique they developed to study a longer light pulse with a much shorter one by shooting them simultaneously through a crystal (see diagram). The longer “pump” pulse is polarized horizontally, meaning that the electric field in it oscillates sideways. The shorter “probe” pulse starts out polarized vertically. However, the properties of the crystal depend on the electric field in it, so the pump beam causes the polarization of the probe beam to change and emerge from the crystal tracing an elliptical pattern. By adjusting the timing of the pulses, researchers can use the polarization effect to map out the wiggles in the electric field in the pump wave.

    But vacuum fluctuations themselves will affect the crystal and hence the polarization of the probe pulse, Leitensdorfer says. So to measure the fluctuations of the vacuum field, “we only put in the probe pulse, nothing else.” On average the polarization of the lone probe pulse remained vertical. But over many repeated trials, it varied slightly, and that noise was the sign of the vacuum fluctuations, the team says.

    Spotting the effect is no mean feat, as the polarization also varies because of random variation in the number of photons in each pulse, or “shot noise.” To tease the two apart, the physicists vary the duration and width of the pulse, but not the number of photons in it. The shot noise should stay constant, whereas the noise from quantum fluctuations should shrink as the pulses become bigger. The researchers saw a change of a few percent in the noise, an effect they attribute to vacuum fluctuations.

    Some physicists question what the new experiment actually measures, however. The researchers assume that fluctuating optical properties of the crystal reflect the vacuum fluctuations, says Steve Lamoreaux, a physicist at Yale University and one of the first to observe the Casimir effect. But the variations in the crystal’s optical properties could have some other source, such as thermal fluctuations, he says. “The material properties will fluctuate on their own,” he says, so “how does one attribute these fluctuations to the vacuum alone?”

    Moreover, Leitenstorfer’s group is not the first to directly probe such fluctuations. In 2011, Christopher Wilson, a physicist now at the University of Waterloo in Canada, and colleagues reported in Nature that they had pumped up vacuum fluctuations and turned them into real photons. In principle, that can be done by accelerating a mirror back and forth at near light speed. Wilson used a more practical analog: a system in in which the effective length of a small superconducting cavity could be changed electronically. Leitenstorfer notes that the new experiment differs from Wilson’s in that it does not require amplifying the fluctuations. Wilson responds, “While I agree that that’s a difference, I don’t think that it’s fundamental.”

    Leitenstorfer contends that the new work makes a qualitative advance over previous efforts. “We clearly have gone a significant step further in comparison to anybody else by directly measuring the electric field amplitude of the vacuum as it fluctuates in space and time,” he says. Others seem less certain about that.

    See the full article here .

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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  • richardmitnick 3:40 pm on September 24, 2015 Permalink | Reply
    Tags: , , Physics,   

    From SLAC: “Mysterious Neutrinos Take the Stage at SLAC” 

    SLAC Lab

    Of all known fundamental particles, neutrinos may be the most mysterious: Although they are highly abundant in the universe and were discovered experimentally in 1956, researchers still have a lot left to learn about them. To find out more about the elusive particles and their potential links to cosmic evolution, invisible dark matter and matter’s dominance over antimatter in the universe, the Department of Energy’s SLAC National Accelerator Laboratory is taking on key roles in four neutrino experiments: EXO, DUNE, MicroBooNE and ICARUS.

    Neutrinos were also the central theme of the 43rd annual SLAC Summer Institute for particle physics and astrophysics. The tradition-rich educational event, held Aug. 10-21, attracted more than 150 scientists from around the globe and featured lectures by some of the world’s leading neutrino experts.

    “Neutrinos are a hot research topic and have become a major focus of U.S. high-energy physics,” said SLAC theorist Thomas Rizzo, one of the summer school’s organizers. “There are many things we want to know about neutrinos. For instance, what are the masses of the known neutrinos? Are there other types of neutrinos that we don’t know about? Do neutrinos and antineutrinos behave differently? Or are neutrinos their own antiparticles?”

    Francis Halzen, principal investigator of the international IceCube Neutrino Observatory at the South Pole and neutrino specialist at the University of Wisconsin, gave the summer institute’s opening lecture.

    ICECUBE neutrino detector
    IceCube neutrino detector interior

    He said neutrinos have a high potential for scientific discovery – and they are also never boring. As a matter of fact, the history of neutrino research has seen a few surprising twists and turns.

    Neutrinos were the central theme of the 43rd annual SLAC Summer Institute for particle physics and astrophysics, which featured lectures by some of the world’s leading neutrino experts. (SLAC National Accelerator Laboratory)

    Elusive and Mysterious Neutrinos

    Neutrinos are one of the most common fundamental particles in the universe. They are abundantly produced in supernova explosions, star-powering nuclear fusion and other nuclear processes, resulting in trillions of neutrinos passing through us every minute. Yet, they are very difficult to study because they rarely interact with their surroundings and easily evade detection. This explains why it took researchers nearly 30 years to catch a first glimpse of neutrinos, although their existence had been first postulated in 1930 to explain an apparent violation of the conservation of energy in the radioactive decay of unstable atomic nuclei known as beta decay.

    A few years after the initial discovery in 1956, researchers were caught by surprise when more than one type of neutrino showed up in their experiments. By the turn of the millennium, they had identified three different types, or flavors, each associated with another fundamental charged partner particle: the electron, muon and tau.

    For the longest time, neutrinos were thought to be massless. But in 1998, scientists discovered that neutrinos frequently change from one flavor into another – a process called neutrino oscillation that can only occur if neutrinos do, in fact, have mass. Although the exact masses remain unknown, researchers estimate neutrinos to be two million times lighter than the next heavier particle, the electron, and this large mass difference is one of the great puzzles of neutrino physics.

    Neutrinos are abundantly produced in nuclear processes in the universe, for instance inside the sun. This image shows the sun in “neutrino light” as seen by the Super-Kamiokande neutrino detector in Japan. (Kamioka Observatory, ICRR, University of Tokyo)

    Super-Kamiokande experiment Japan
    Super-Kamiokande neutrino detector

    EXO: The Origin of the Neutrino Mass

    The origin of neutrino masses could be different from the origin of the masses of other particles. This could explain why neutrinos are incredibly light. One sign that this is true would be if they were their own antiparticles. This is only possible for neutrinos, since they carry no electric charge. The Enriched Xenon Observatory (EXO) is searching for a theorized rare nuclear process – neutrinoless double beta decay – that would prove that neutrinos and antineutrinos are identical.

    EXO experiment
    Part of the EXO-200 underground detector used to search for a hypothesized radioactive decay that could reveal how neutrinos acquire their incredibly small mass. (EXO Collaboration)

    Located almost half a mile underground at the Waste Isolation Pilot Plant in New Mexico, protected from cosmic radiation, the sensitive EXO experiment uses 200 kilograms of enriched liquid xenon that could potentially undergo the sought-after decay. If it exists, it would be so rare that it would take billions of times longer than the age of the universe for half of the radioactive xenon nuclei to decay. Only the large number of xenon atoms in the experiment allows researchers to search for such a long-lived decay.

    “Neutrinoless double beta decay would not only tell us that neutrinos must be their own antiparticles,” said SLAC particle physicist and EXO team member Martin Breidenbach. “From the measured decay rate, we could also determine the effective neutrino mass.”

    SLAC co-led the construction of the experiment’s 200-kilogram version (EXO-200), which also serves as a test bed for a more sensitive future ton-scale version (nEXO) that would give researchers a much better chance of seeing neutrinoless double beta decay.

    DUNE: Trio of Neutrino Masses and Matter-Antimatter Imbalance

    SLAC researchers are also taking part in another neutrino experiment – the Deep Underground Neutrino Experiment (DUNE), which will be constructed by a new international collaboration hosted at the Long-Baseline Neutrino Facility (LBNF) as the centerpiece of the particle physics program in the U.S.

    As part of LBNF, neutrinos and antineutrinos will be sent 800 miles through the Earth from Fermi National Accelerator Laboratory in Illinois to the DUNE detector in South Dakota – an “eye” for neutrinos that will eventually consist of four 10,000-ton modules of liquid argon. Scientists will then track how the particles morph from one neutrino flavor into another along the way.

    By comparing the oscillations of antineutrinos with those of neutrinos, DUNE researchers will be able to determine if the matter-antimatter siblings behave differently. If they do, the difference could potentially help explain why our universe is made of matter rather than antimatter.

    “Since each neutrino flavor interacts differently with the material in the Earth, the experiment will also tell us which of the three neutrino types is the lightest and which is the heaviest,” said researcher Mark Convery, who heads SLAC’s LBNF/DUNE group.

    DUNE’s liquid argon detector may also make other experiments possible. It could be used, for instance, to catch a glimpse of neutrino bursts from supernova explosions, which could tell us more about the physics of collapsing stars. Scientists at the joint SLAC/Stanford University Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) are particularly interested in this research opportunity.

    The future DUNE experiment will send neutrinos and antineutrinos 800 miles through the Earth to determine the relative masses of the three known neutrino types and study whether neutrinos and antineutrinos behave differently. (Fermi National Accelerator Laboratory)

    MicroBooNE and ICARUS: Search for Unknown Neutrinos

    However, DUNE will not be ready until the mid-2020s. In the meantime, Convery and his team are also engaging in the current MicroBooNE and future ICARUS experiments at Fermilab. These are so-called short-baseline experiments with detectors just hundreds of yards away from the neutrino source, rather than hundreds of miles away.

    FNAL MicroBooNE
    MicroBooNE detector


    “MicroBooNE and ICARUS will help us prepare for DUNE, but they also have the potential to discover completely new physics,” Convery said. “They’ll follow up on previous short-baseline studies that observed anomalies in neutrino oscillations.”

    Researchers believe that these anomalies could hint at the existence of a fourth, “sterile” neutrino. This hypothetical particle could potentially be linked to dark matter, the invisible substance that is five times more prevalent in the universe than regular matter.

    MicroBooNE’s 170-ton liquid argon detector began collecting data in August 2015, while ICARUS, which is three-and-a-half times heavier, is being upgraded at the European particle physics laboratory CERN. Both experiments will eventually become part of a three-detector short-baseline neutrino program at Fermilab, scheduled to launch in 2018 and designed to clarify whether previous hints at sterile neutrinos are correct or not.

    See the full article here .

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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