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  • richardmitnick 12:49 pm on August 8, 2018 Permalink | Reply
    Tags: , , , , Symmetry Breaking   

    From Ethan Siegel: “What Was It Like When The Higgs Gave Mass To The Universe?” 

    From Ethan Siegel
    Aug 8, 2018

    1
    A candidate Higgs event in the ATLAS detector. Note how even with the clear signatures and transverse tracks, there is a shower of other particles; this is due to the fact that protons are composite particles. This is only the case because the Higgs gives mass to the fundamental constituents that compose these particles. (THE ATLAS COLLABORATION / CERN)

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    One moment, every particle in the Universe was massless. Then, they weren’t anymore. Here’s how it happened.

    In the earliest stages of the hot Big Bang, the Universe was filled with all the particles, antiparticles, and quanta of radiation it had the energy to create. As the Universe expanded, it cooled: the stretching fabric of space also stretched the wavelengths of all the radiation within it to longer wavelengths, which equates to lower energies.

    If there are any particles (and antiparticles) that exist at higher energies that are yet to be discovered, they were likely created in the hot Big Bang, so long as there was enough energy (E) available to create a massive (m) particle via Einstein’s E = mc². It’s possible that a slew of puzzles about our Universe, including the origin of the matter-antimatter asymmetry and the creation of dark matter, are solved by new physics at these early times. But the massive particles we know today are foreign to us. At these early stages, they have no mass.

    The particles and antiparticles of the Standard Model are easy to create, even as the Universe cools and the fractions-of-a-second ticked by. The Universe might start of at energies as large as 10¹⁵ or 10¹⁶ GeV; even by time it’s dropped to 1000 (10³) GeV, no Standard Model particle is threatened. At the energies achievable by the LHC, we can create the full suite of particle-antiparticle pairs that are known to physics.

    But at this point, unlike today, they’re all massless. If they have no rest mass, they have no choice but to move at the speed of light. The reason particles are in this strange, bizarre state that’s so different from how they exist today? It’s because the fundamental symmetry that gives rise to the Higgs boson — the electroweak symmetry — has not yet broken in the Universe.

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    The particles and antiparticles of the Standard Model have now all been directly detected, with the last holdout, the Higgs Boson, falling at the LHC earlier this decade. Today, only the gluons and photons are massless; everything else has a non-zero rest mass. (E. SIEGEL / BEYOND THE GALAXY)

    When we look at the Standard Model today, it’s arranged as follows:

    six quarks, each of which come in three colors, and their antiquark counterparts,
    three charged leptons (e, μ, τ) and three neutral ones (ν_e, ν_μ, ν_τ), and their antimatter counterparts,
    the eight massless gluons that mediate the strong force between the quarks,
    the three heavy, weak bosons (W+, W-, and Z_0) that mediate the weak nuclear force,
    and the photon (γ), the massless mediator of the electromagnetic force.

    But there’s a symmetry that’s broken at today’s low-energy scale: the electroweak symmetry. This symmetry was restored in the early days of the Universe. And when it’s restored versus when it’s broken, it fundamentally changes the Standard Model picture.

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


    Standard Model of Particle Physics from Symmetry Magazine

    Instead of the weak and electromagnetic bosons (W+, W-, Z_0, γ), where the first three are very massive and the last is massless, we have four new bosons for the electroweak force (W_1, W_2, W_3, B), and all of them have no mass at all. The other particles are all the same, except for the fact that they, too, have no mass yet. This is what’s floating around in the early Universe, colliding, annihilating, and spontaneously being created, all in motion at the speed of light.

    As the Universe expands and cools, all of this continues. So long as the energy of your Universe is above a certain value, you can think about the Higgs field as floating atop the liquid in a soda (or wine) bottle. As the level of the liquid drops, the Higgs field remains atop the liquid, and everything stays massless. This is what we call a restored-symmetry state.

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    When a wine bottle is either completely or partially filled, a drop of oil or a ping pong ball will float on the wine’s surface inside the bottle. At any location, the wine-level, and hence what’s floating atop it, will remain at the same level. This corresponds to a restored-symmetry state. (EVAN SWIGART FROM CHICAGO, USA)

    But below a certain liquid level, the bottom of the container starts to show itself. And the field can no longer remain in the center; more generally, it can’t take on simply any old value. It has to go to where the liquid level is, and that means down into the divot(s) at the bottom of the bottle. This is what we call a broken-symmetry state.

    When this symmetry breaks, the Higgs field settles into the bottom, lowest-energy, equilibrium state. But that energy state isn’t quite zero: it has a finite, non-zero value known as its vacuum expectation value. Whereas the restored-symmetry state yielded only massless particles, the broken symmetry state changes everything.

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    When a wine bottle is completely empty, any ball or drop of oil inside will slide all the way down to the lowest-level ‘ring’ at the bottom. This corresponds to a broken symmetry state, since all values (i.e., locations) are no longer equivalent. (PATRICK HEUSSER, X8ING.COM)

    Once the symmetry breaks, the Higgs field has four mass-containing consequences: two are charged (one positive and one negative) and two are neutral. Then, the following things all happen at once:

    The W_1 and W_2 particles “eat” the charged, broken-symmetry consequences of the Higgs, becoming the W+ and W- particles.
    The W_3 and B particles mix together, with one combination eating the uncharged broken-symmetry consequence of the Higgs, becoming the Z_0, and with the other combination eating nothing, to remain the massless photon (γ).
    The last neutral broken-symmetry consequence of the Higgs gains mass, and becomes the Higgs boson.
    At last, the Higgs boson couples to all the other particles of the Standard Model, giving mass to the Universe.

    This is the origin of mass in the Universe.

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    When the electroweak symmetry is broken, the W+ gets its mass by eating the positively charged Higgs, the W- by eating the negatively charged Higgs, and the Z_0 by eating the neutral Higgs. The other neutral Higgs becomes the Higgs boson, detected and discovered earlier this decade at the LHC. The photon, the other combination of the W3 and the B boson, remains massless. (FLIP TANEDO / QUANTUM DIARIES)

    This whole process is called spontaneous symmetry breaking. And for the quarks and leptons in the standard model, when this Higgs symmetry is broken, every particle gets a mass due to two things:

    The expectation value of the Higgs field, and
    A coupling constant.

    And this is kind of the problem. The expectation value of the Higgs field is the same for all of these particles, and not too difficult to determine. But that coupling constant? Not only is it different for every particle, but — in the standard model — it’s arbitrary.

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    The Higgs boson, now with mass, couples to the quarks, leptons, and W-and-Z bosons of the Standard Model, which gives them mass. That it doesn’t couple to the photon and gluons means those particles remain massless. (TRITERTBUTOXY AT ENGLISH WIKIPEDIA)

    We know that the particles have mass; we know how they get mass; we’ve discovered the particles responsible for mass. But we still have no idea why the particles have the values of the masses they do. We have no idea why the coupling constants have the couplings that they do. The Higgs boson is real; the gauge bosons are real; the quarks and leptons are real. We can create, detect, and measure their properties exquisitely. Yet, when it comes to understanding why they have the values that they do, that’s a puzzle we cannot yet solve. We do not have the answer.

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    The masses of the fundamental particles in the Universe, once the electroweak symmetry is broken, spans many orders of magnitude, withe the neutrinos being the lightest massive particles and the top quark being the heaviest. We do not understand why the coupling constants have the values they do, and hence, why the particles have the masses they do. (FIG. 15–04A FROM UNIVERSE-REVIEW.CA)

    Before the breaking of the electroweak symmetry, everything that is known to exist in the Universe today is massless, and moves at the speed of light. Once the Higgs symmetry breaks, it gives mass to the quarks and leptons of the Universe, the W and Z bosons, and the Higgs boson itself. Suddenly, with huge mass differences between light particles and heavy ones, the heavy ones spontaneously decay into the lighter ones on very short timescales, especially when the energy (E) of the Universe drops below the mass equivalent (m) needed to create these unstable particles via E = mc².

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    A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. Without the Higgs giving mass to the particles in the Universe at a very early, hot stage, none of this would have been possible. (NASA / CXC / M. WEISS)

    Without this critical gauge symmetry associated with electroweak symmetry breaking, existence wouldn’t be possible, as we do not have stable, bound states made purely of massless particles. But with fundamental masses to the quarks and charged leptons, the Universe can now do something it’s never done before. It can cool and create bound states like protons and neutrons. It can cool further and create atomic nuclei and, eventually, neutral atoms. And when enough time goes by, it can give rise to stars, galaxies, planets, and human beings. Without the Higgs to give mass to the Universe, none of this would be possible. The Higgs, despite the fact that it took 50 years to discover, has been making the Universe possible for 13.8 billion years.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    See the full article here .

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 9:06 am on February 11, 2014 Permalink | Reply
    Tags: , , , , , Symmetry Breaking   

    From Symmetry: “Quarks in the looking glass” 

    February 10, 2014
    Kandice Carter

    A recent experiment at Jefferson Lab probed the mirror symmetry of quarks, determining that one of their intrinsic properties is non-zero—as predicted by the Standard Model.
    sm
    Standard Model of Particle Physics

    From matching wings on butterflies to the repeating six-point pattern of snowflakes, symmetries echo through nature, even down to the smallest building blocks of matter. Since the discovery of quarks, the building blocks of protons and neutrons, physicists have been exploiting those symmetries to study quarks’ intrinsic properties and to uncover what those properties can reveal about the physical laws that govern them.

    A recent experiment carried out at Jefferson Lab has provided a new determination of an intrinsic property of quarks that’s five times more precise than the previous measurement.

    jlab
    Courtesy of Jefferson Lab

    The result has also set new limits, in a way complementary to such as the Large Hadron Collider at CERN, for the energies that researchers would need to access physics beyond the Standard Model. The Standard Model is a well-tested theory that, excluding gravity, describes the subatomic particles and their interactions, and physicists believe that peering beyond the Standard Model may help resolve many unanswered questions about the origins and underlying framework of our universe. The result was published in the February 6 edition of Nature.

    CERN

    CERN LHC New
    LHC

    The experiment probed properties of the mirror symmetry of quarks. In mirror symmetry, the characteristics of an object remain the same even if that object is flipped as though it were reflected in a mirror.

    The mirror symmetry of quarks can be probed by gauging their interactions with other particles through fundamental forces. Three of the four forces that mediate the interactions of quarks with other particles—gravity, electromagnetism and the strong force—are mirror-symmetric. However, the weak force—the fourth force—is not. That means that the intrinsic characteristics of quarks that determine how they interact through the weak force (called the weak couplings) are different from, for example, the electric charge for the electromagnetic force, the color charge for the strong force, and the mass for gravity.

    jlab
    Info-Graphic by: Jefferson Lab

    In Jefferson Lab’s Experimental Hall A, experimenters measured the breaking of the mirror symmetry of quarks through the process of deep-inelastic scattering. A 6.067 billion-electronvolt beam of electrons was sent into deuterium nuclei, the nuclei of an isotope of hydrogen that contain one neutron and one proton each (and thus an equal number of up and down quarks).

    “When it’s deep-inelastic scattering, the momentum carried by the electron goes inside the nucleon and breaks it apart,” says Xiaochao Zheng, an associate professor of physics at the University of Virginia and a spokesperson for the collaboration that conducted the experiment.

    To produce the effect of viewing the quarks through a mirror, half of the electrons sent into the deuterium were set to spin along the direction of their travel (like a right-handed screw), and the other half were set to spin in the opposite direction. Researchers identified about 170,000 million electrons that interacted with quarks in the nuclei through both the electromagnetic and the weak forces over a two-month period of running.

    “This is called an inclusive measurement, but that just means that you only measure the scattered electrons. So, we used both spectrometers, but each detecting electrons independently from the other. The challenging part is to identify the electrons as fast as they come,” Zheng says.

    The experimenters found an asymmetry, or difference, in the number of electrons that interacted with the target when they were spinning in one direction versus the other. This asymmetry is due to the weak force between the electron and quarks in the target. The weak force experienced by quarks has two components. One is analogous to electric charge and has been measured well in previous experiments. The other component, related to the spin of the quark, has been clearly isolated for the first time in the Jefferson Lab experiment.

    Specifically, the present result led to a determination of the effective electron-quark weak coupling combination 2C2u–C2d that is five times more precise than previously determined. This particular coupling describes how much of the mirror-symmetry breaking in the electron-quark interaction originates from quarks’ spin preference in the weak interaction. The new result is the first to show that this combination is non-zero, as predicted by the Standard Model.

    The last experiment to access this coupling combination was E122 at SLAC National Accelerator Laboratory. Data from that experiment were used to establish the newly theorized Standard Model more than 30 years ago.

    The good agreement between the new 2C2u–C2d result and the Standard Model also indicates that experimenters must reach higher energy limits in order to potentially find new interactions beyond the Standard Model with respect to the violation of mirror symmetry due to the spin of the quarks. The new limits, 5.8 and 4.6 trillion electronvolts, are within reach of the Large Hadron Collider at CERN, but the spin feature provided by this experiment cannot be identified cleanly in collider experiments.

    In the meantime, the researchers plan to extend this experiment in the next era of research at Jefferson Lab. In a bid to further refine the knowledge of quarks’ mirror-symmetry breaking, experimenters will use Jefferson Lab’s upgraded accelerator to nearly double the energy of the electron beam, reducing their experimental errors and improving the precision of the measurement by five to 10 times the current value. The experiment will be scheduled following completion of the upgrade in 2017.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.



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  • richardmitnick 7:15 pm on March 20, 2012 Permalink | Reply
    Tags: , , , , Symmetry Breaking   

    From Symmetry/Breaking: “More physics for your funding” 

    Sarah Charley
    March 20, 2012

    “The decommissioning of the Tevatron represented the end of an era, but it also is ushering in the next generation of physics by providing valuable equipment to other experiments.

    ‘We don’t have enough funding to buy things new, so when we want to improve our experiments, we must search for and reuse equipment,’ said Bogdan Wojtsekhowski, a staff scientist at Jefferson Lab. ‘Scientists share equipment all the time. It’s the best way to get more physics for your budget.’

    Fermilab’s CDF experiment is donating photomultiplier tubes, computers, electronics racks and other equipment to experiments located all over the world,’ said Jonathan Lewis of Fermilab’s Particle Physics Division, who is organizing the decommissioning of the detector.

    ‘These computers are going to a lab in Korea,’ Lewis said during a tour of the building. ‘And we’re sending those electronics racks to Italy.’

    Jefferson Lab received more than 600 of the Tevatron experiment’s photomultiplier tubes for an experiment measuring the charge distribution inside protons. New, these photomultiplier tubes would have cost $700,000, but because they came from Fermilab, J-Lab had to pay only roughly $1,000 for disassembly and shipping costs.

    ‘We could not have afforded these photomultiplier tubes new, so we are very appreciative that we could get them from Fermilab,’ Wojtsekhowski said. ‘They will significantly enhance this experiment’s detection capabilities – by 30 percent, which means we will get more accurate data for the same beam time and stay within our budget. It was amazing luck.’

    The equipment swap is not limited to just national labs. Many universities, which often have tight research budgets, have placed claims on old Tevatron material.”

    See the article here.

    Symmetrybreaking is a joint Fermilab/SLAC publication

     
  • richardmitnick 10:35 am on January 24, 2012 Permalink | Reply
    Tags: , , , , , , , Symmetry Breaking   

    From ALICE at CERN via Symmetry/Breaking: “Scientists finish installation of 80-ton ‘particle thermometer’ at ALICE detector” 

    “Scientists on the ALICE experiment at the Large Hadron Collider just completed the installation of a crucial component for tracking high-energy particle jets. Without it, physicists would be lacking crucial tools to select which events out of billions to store and analyze.

    Engineers and physicists around the world worked intensively over five years to complete the electromagnetic calorimeter, or EMCal. The United States, supported by the Department of Energy’s Nuclear Physics Office, contributed 70 percent of the project costs. Scientists installed the last two pieces of the 80-ton device on Jan. 18.

    The EMCal’s heft comes from its many sheets of lead absorbers, which it needs to stop particles coming from collisions in the detector in order to measure their energy. “The calorimeter measures the energy of individual photons and electrons,” said ALICE physicist Peter Jacobs. “It’s a sort of particle thermometer.”

    EMCal

    i3
    Scientists install the electromagnetic calorimeter at the ALICE detector. Image: CERN

    See the full post here.

     
  • richardmitnick 10:11 am on December 15, 2011 Permalink | Reply
    Tags: , , , , Symmetry Breaking   

    From The Sanford Undergorund Laboratory via Symmetry/Breaking: “First physics experiments soon to move into former Homestake mine” 

    December 15, 2011
    Bill Harlan, Sanford Underground Laboratory
    Guest author

    “Construction of a 12,000-square-foot research campus a mile underground is nearing completion in the Black Hills of South Dakota, and scientists will begin to move the first physics experiments underground this spring.

    i1
    Rick Labahn, project engineer (left) and Ben Sayler, director of education and outreach at Sanford Lab, check out the almost-finished Davis Cavern, located about a mile underground in the former Homestake mine. Photo by Matt Kapust, Sanford Underground Laboratory

    ‘We’re on schedule for occupancy in March 2012, but it’s quite a little process,’ said Project Engineer Rick Labahn, understating the complexity of his job. Labahn is directing the outfitting of the Davis Campus, which comprises two large underground halls at the 4,850-foot level of the Sanford Underground Laboratory in the former Homestake gold mine. Early next spring researchers will begin installing two experiments there—both of them at the leading edge of 21st-century physics. The Large Underground Xenon experiment, which already is taking test run data in a building on the surface, aims to become the world’s most sensitive detector to look for a mysterious substance called dark matter. Thought to comprise 80 percent of all the matter in the universe, dark matter remains undetected so far. The second experiment, the Majorana Demonstrator, will search for one of the rarest forms of radioactive decays—neutrinoless double-beta decay. Majorana could help determine whether subatomic particles called neutrinos can act as their own anti-particles, a discovery that could help physicists better explain how the universe evolved.”

    See the full article here.

     
  • richardmitnick 7:25 am on November 18, 2011 Permalink | Reply
    Tags: , , , , , , Symmetry Breaking   

    From Symmetry/Breaking – Hey, Higgs, Come Out, Come Out, Wherever You Are 

    Favored Higgs hiding spot remains after most complete search yet

    Kathryn Grim
    November 18, 2011

    “The CMS and ATLAS experiments at the Large Hadron Collider have backed the Standard Model Higgs boson, if it exists, into a corner with their first combined Higgs search result.

    The study, made public today, eliminates several hints the individual experiments saw in previous analyses but leaves in play the favored mass range for the Higgs boson, between 114 and 141 GeV. ATLAS and CMS ruled out at a 95 percent confidence level a Higgs boson with a mass between 141 and 476 GeV.

    The new result combines eight studies of predicted decays of the Higgs boson using data the experiments collected up to July. Physicists expected to be able to rule out an even wider mass range, between 125 and 500 GeV, based on the amount of data used and the sensitivities of the different search modes. But small excesses that could be the result of statistical fluctuations or could indicate the presence of a hidden particle reduced the range of masses that could be excluded.

    i1
    The Standard Model Higgs boson is excluded at a 95 percent confidence level everywhere the thick black line drops below the red line. Image: ATLAS and CMS experiments

    ‘I think it could be an interesting message the data is telling us,’ said physicist Eilam Gross of the Weizmann Institute of Science, who shares leadership of the ATLAS experiment’s Higgs group. ‘Any discovery starts with the inability to exclude.”

    Several related measurements indirectly suggest a Standard Model Higgs boson exists at the lower end of the mass range.’ ”

    See the full article here.

    Symmetrybreaking is a joint Fermilab/SLAC publication

     
  • richardmitnick 3:32 pm on November 15, 2011 Permalink | Reply
    Tags: , , , , , , , Symmetry Breaking   

    More on Heavy Ion Physics from Symmetry/Beaking 

    The making and tending of heavy ion beams for the LHC

    November 15, 2011
    Amy Dusto

    “This week the Large Hadron Collider began heavy ion physics, the process of colliding lead ions to learn about conditions in the primordial universe.

    The accelerator is expected to perform five to 10 times better than it did in its first run of these collisions last November. Although the heavy ion program will last only from now until CERN’s annual winter shutdown just after the first week of December, operators started preparations months in advance. Here symmetry breaking examines what it really takes to put lead beams in the LHC.

    The source

    Making heavy ions is more complicated than preparing the protons used in regular LHC collisions, which come from hydrogen gas. Since hydrogen atoms have only one proton and one electron each, applying a voltage to them is sufficient to rip off their electrons, leaving a load of beam-ready, positively charged protons. But the source for heavy ions, enriched lead, starts with 82 electrons. Physicists do not have miracle flypaper to grab that many subatomic particles at once, so the process takes a few steps.

    Meet Detlef Kuchler, a heavy-ion expert who tends the lead source, the first part of the heavy-ion acceleration process, by hand. He helped develop the method of extracting lead ions decades ago and can explain from memory its hundreds of associated, unlabeled diagrams. Although several people work on the source, a flowchart of what to do when things go wrong at this stage dead-ends everywhere with, ‘Call the expert.’ It may as well say, ‘Call Detlef.’ He spends a lot of nights and weekends at CERN during heavy ion season.”

    i1
    Heavy-ion expert Detlef Kuchler holds a container of lead. Image: CERN

    i2
    Kuchler prepares the oven. Image: Amy Dusto

    i3
    Operators test beams of lead ions in this linear accelerator. Image: CERN

    i4
    Operators declared “stable beams” today, which means the LHC is ready for heavy ion physics. Image: John Jowett

    See the full article here.

     
  • richardmitnick 4:07 pm on November 14, 2011 Permalink | Reply
    Tags: , , , , , , , Symmetry Breaking   

    From Symmetry/Breaking: “LHCb uses charm to find asymmetry” 

    Antonella Del Rosso at CERN Bulletin

    “According to theory, matter and antimatter should have been created in equal parts during the big bang. But somehow, the balance of the two skewed in the universe’s first moments. Now, matter dominates nature.

    Scientists from the LHCb collaboration at CERN recently saw curious possible evidence [take the time to look at this very cool piece] of this asymmetry: The difference between the decay rates of certain particles in their detector, D and anti-D charm mesons, was higher than expected.

    This anomaly is evidence of charge-parity violation, a more precise descriptor of nature’s preference for matter. Other LHC experiments have seen such symmetry breaking, but this is a first sighting in these charm particles.

    ‘CP violation is expected to be very small in charm physics,’ LHCb member Bolek Pietrzyk said. ‘This is a really surprising result.’

    The preliminary findings, which the collaboration presented Monday night in Paris, have a significance measured at 3.5 sigmas. Statistically speaking, this indicates an interesting observation. But scientists will need more certainty before they can declare a discovery.

    In this study, the group used data they collected in the first half of 2011. LHCb’s next steps will be to look at the rest of the 2011 data and see whether they can make sense of the observations within the Standard Model theory, or if they’ll need a new explanation.

    View the presentation about the LHCb result [same link as above, so you have another chance if you skipped by the first link].

    i2
    7 TeV collision event seen by the LHCb detector. The LHCb experiment at the LHC will be well-placed to explore the mystery of antimatter. Image courtesy CERN

    Symmetrybreaking is a joint Fermilab/SLAC publication

     
  • richardmitnick 9:14 am on September 20, 2011 Permalink | Reply
    Tags: , , , Symmetry Breaking   

    From SLAC News Center via SymmetryBreaking: “How Slow is Slow? EXO Knows!” 

    September 8, 2011
    by Lori Ann White

    “Cooks think of watched pots. Handymen grumble about drying paint. Kids dread the endless night before Christmas morning.

    Turns out physicists have their own expression to convey the concept of “slow,” and now, thanks to the Enriched Xenon Observatory (EXO), they know how slow “slow” really is: The flurry of activity during the 13.75 billion years from the Big Bang to us was positively hasty in comparison.

    The expression is “2nubb” and it stands for two-neutrino double-beta decay, a rare type of particle decay undergone by certain forms of radioactive elements. In this type of decay, two neutrons, the neutral subatomic particles in the nucleus of an atom, spontaneously decay into two protons, two electrons, and two antineutrinos, which are the antimatter twins of the tiny, nearly massless mystery particles called neutrinos. The EXO team announced yesterday at a conference in Munich that, according to their measurements of two-neutrino double-beta decay in Xe-136, an isotope of xenon, the half-life of the process clocks in at 2.11 x 10^21 years. In other words, it would take 100 billion times longer than the universe has even existed for half of a sample of this radioactive isotope to decay via the 2nubb decay pathway.

    ‘This represents the slowest Standard Model process ever measured,’ said Giorgio Gratta, Stanford University physicist and member of the joint SLAC-Stanford Kavli Institute for Particle Astrophysics and Cosmology , who leads the team. The Standard Model is the best description scientists have for the way all the building blocks of matter, like the aforementioned neutrons, protons and electrons, fit together, and why two-neutrino double-beta decay happens in the first place.”

    See the full article here.

    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. i1

     
  • richardmitnick 5:23 pm on July 26, 2011 Permalink | Reply
    Tags: , , , Symmetry Breaking   

    From SymmetryBreaking: “More than one way to search for SUSY” 

    July 26, 2011 | 11:44 am
    Kathryn Grim

    “Experiments at the Large Hadron Collider have yet to find signs of supersymmetric particles, scientists announced at the European Physical Society conference this week in Grenoble.

    But physicists will significantly improve their knowledge of SUSY in the coming year through indirect methods, which could include the discovery of the Higgs boson.

    ‘ For supersymmetry, this is a decisive moment in time,’ said theorist Lars Bergstrom of Stockholm University.

    Supersymmetry is a model that solves some significant problems of the Standard Model of particle physics. SUSY doubles the zoo of elementary particles by adding a partner for each of the particles we already know. It handily relates different types of particles in the Standard Model and offers an appealing candidate for dark matter. So far, scientists have found no evidence of SUSY particles at the LHC.

    Discovering the mass of the Higgs boson, which scientists could do by next year, will reveal something about the likelihood that supersymmetry exists. Members of the ATLAS and CMS collaborations both displayed at the EPS conference tiny hints of a Higgs boson with a mass within the interval of 115-150 GeV.

    ‘ If it were higher than 140 GeV, you would have to twist things in weird ways to make supersymmetry work,’ Bergstrom said. He added, ‘ But one should never underestimate theorists.’ ”

    Symmetrybreaking is a joint Fermilab/SLAC publication

     
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