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  • richardmitnick 11:18 am on May 7, 2019 Permalink | Reply
    Tags: "A universe is born", , , , , , , , , , Quarks, , , The Planck epoch   

    From Symmetry: “A universe is born” 

    Symmetry Mag
    From Symmetry

    05/07/19
    Diana Kwon

    Take a (brief) journey through the early history of our cosmos.

    Timeline of the Inflationary Universe WMAP

    The universe was a busy place during the first three minutes. The cosmos we see today expanded from a tiny speck to much closer to its current massive size; the elementary particles appeared; and protons and neutrons combined into the first nuclei, filling the universe with the precursors of elements.

    By developing clever theories and conducting experiments with particle colliders, telescopes and satellites, physicists have been able to wind the film of the universe back billions of years—and glimpse the details of the very first moments in the history of our cosmic home.

    Take an abridged tour through this history:

    The Planck epoch
    Time: < 10^-43 seconds

    The Planck Epoch https:// http://www.slideshare.net ericgolob the-big-bang-10535251

    Welcome to the Planck epoch, named after the smallest scale of measurements possible in particle physics today. This is currently the closet scientists can get to the beginning of time.

    Theoretical physicists don’t know much about the earliest moments of the universe. After the Big Bang theory gained popularity, scientists thought that in the first moments, the cosmos was at its hottest and densest and that all four fundamental forces—electromagnetic, weak, strong and gravitational—were combined into a single, unified force. But the current leading theoretical framework for our universe’s beginning doesn’t necessarily require these conditions.

    The universe expands
    Time: From 10^-43 seconds to about 10^-36 seconds

    In this stage, which began either at Planck time or shortly after it, scientists think the universe underwent superfast, exponential expansion in a process known as inflation.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    Alan Guth’s notes:
    5

    Physicists first proposed the theory of inflation in the 1980s to address the shortcomings of the Big Bang theory, which, despite its popularity, could not explain why the universe was so flat and uniform, and why its different parts began expanding simultaneously.

    During inflation, quantum fluctuations could have stretched out to produce a pattern that later determined the locations of galaxies. It might have been only after this period of inflation the universe became a hot, dense fireball as described in the Big Bang theory.

    The elementary particles are born
    Time: ~10^-36 seconds

    When the universe was still very hot, the cosmos was like a gigantic accelerator, much more powerful than the Large Hadron Collider, running at extremely high energies. In it, the elementary particles we know today were born.

    Scientists think that first came exotic particles, followed by more familiar ones, such as electrons, neutrinos and quarks. It could be that dark matter particles came about during this time.

    3
    Quarks APS/Alan Stonebraker

    The quarks soon combined, forming the familiar protons and neutrons, which are collectively known as baryons. Neutrinos were able to escape this plasma of charged particles and began traveling freely through space, while photons continued to be trapped by the plasma.

    Standard Model of Particle Physics

    The first nuclei emerge
    Time: ~1 second to 3 minutes

    Scientists think that when the universe cooled enough for violent collisions to subside, protons and neutrons clumped together into nuclei of the light elements—hydrogen, helium and lithium—in a process known as Big Bang nucleosynthesis.

    Protons are more stable than neutrons, due to their lower mass. In fact, a free neutron decays with a 15-minute half-life, while protons may not decay at all, as far as we know.

    So as the particles combined, many protons remained unpaired. As a result, hydrogen—protons that never found a partner—make up around 74% of the mass of “normal” matter in our cosmos. The second most abundant element is helium, which makes up approximately 24%, followed by trace amounts of deuterium, lithium, and helium-3 (helium with a three-baryon core).

    Periodic table Sept 2017. Wikipedia

    Scientists have been able to accurately measure the density of baryons in our universe. Most of those measurements line up with theorists’ estimations of what the quantities ought to be, but there is one lingering issue: Lithium calculations are off by a factor of three. It could be that the measurements are off, but it could also be that something we don’t yet know about happened during this time period to change the abundance of lithium.

    The cosmic microwave background becomes visible
    Time: 380,000 years

    Hundreds of thousands of years after inflation, the particle soup had cooled enough for electrons to bind to nuclei to form electrically neutral atoms. Through this process, which is also known as recombination, photons became free to traverse the universe, creating the cosmic microwave background.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    Today, the CMB is one of the most valuable tools for cosmologists, who probe its depths in search of answers for many of the universe’s lingering secrets, including the nature of inflation and the cause of matter-antimatter asymmetry.

    Shortly after the CMB became detectable, neutral hydrogen particles formed into a gas that filled the universe. Without any objects emitting high-energy photons, the cosmos was plunged into the dark ages for millions of years.

    Dark Energy Camera Enables Astronomers a Glimpse at the Cosmic Dawn. CREDIT National Astronomical Observatory of Japan

    The earliest stars shine
    Time: ~100 million years

    The dark ages ended with the formation of the first stars and the occurrence of reionization, a process through which highly energetic photons stripped electrons off neutral hydrogen atoms.

    Reionization era and first stars, Caltech

    Scientists think that the vast majority of the ionizing photons emerged from the earliest stars. But other processes, such as collisions between dark matter particles, may have also played a role.

    At this time, matter began to form the first galaxies. Our own galaxy, the Milky Way, contains stars that were born when the universe was only several hundred million years old.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Our sun is born
    Time: 9.2 billion years

    3
    NASA

    The sun is one of a few hundred billion stars in the Milky Way. Scientists think it formed from a giant cloud of gas that consisted mostly hydrogen and helium.

    Today
    Time: 13.8 billion years

    Today, our cosmos sits at a cool 2.7 Kelvin (minus 270.42 degrees Celsius). The universe is expanding at an increasing rate, in a manner similar to (but many orders of magnitude slower than) inflation.

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

    Physicists think that dark energy—a mysterious repulsive force that currently accounts for about 70% of the energy in our universe—is most likely driving that accelerated expansion.

    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP)

    See the full article here .


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  • richardmitnick 11:26 am on May 5, 2019 Permalink | Reply
    Tags: 'Where Does A Proton’s Mass Come From?', 99.8% of the proton’s mass comes from gluons, , Antiquarks, Asymptotic freedom: the particles that mediate this force are known as gluons., , , , , , , , , Quarks, The production of Higgs bosons is dominated by gluon-gluon collisions at the LHC, , The strong interaction is the most powerful interaction in the entire known Universe.   

    From Ethan Siegel: “Ask Ethan: ‘Where Does A Proton’s Mass Come From?'” 

    From Ethan Siegel
    May 4, 2019

    1
    The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. The electrostatic repulsion and the attractive strong nuclear force, in tandem, are what give the proton its size, and the properties of quark mixing are required to explain the suite of free and composite particles in our Universe. (APS/ALAN STONEBRAKER)

    The whole should equal the sum of its parts, but doesn’t. Here’s why.

    The whole is equal to the sum of its constituent parts. That’s how everything works, from galaxies to planets to cities to molecules to atoms. If you take all the components of any system and look at them individually, you can clearly see how they all fit together to add up to the entire system, with nothing missing and nothing left over. The total amount you have is equal to the amounts of all the different parts of it added together.

    So why isn’t that the case for the proton? It’s made of three quarks, but if you add up the quark masses, they not only don’t equal the proton’s mass, they don’t come close. This is the puzzle that Barry Duffey wants us to address, asking:

    “What’s happening inside protons? Why does [its] mass so greatly exceed the combined masses of its constituent quarks and gluons?”

    In order to find out, we have to take a deep look inside.

    2
    The composition of the human body, by atomic number and by mass. The whole of our bodies is equal to the sum of its parts, until you get down to an extremely fundamental level. At that point, we can see that we’re actually more than the sum of our constituent components. (ED UTHMAN, M.D., VIA WEB2.AIRMAIL.NET/UTHMAN (L); WIKIMEDIA COMMONS USER ZHAOCAROL (R))

    There’s a hint that comes just from looking at your own body. If you were to divide yourself up into smaller and smaller bits, you’d find — in terms of mass — the whole was equal to the sum of its parts. Your body’s bones, fat, muscles and organs sum up to an entire human being. Breaking those down further, into cells, still allows you to add them up and recover the same mass you have today.

    Cells can be divided into organelles, organelles are composed of individual molecules, molecules are made of atoms; at each stage, the mass of the whole is no different than that of its parts. But when you break atoms into protons, neutrons and electrons, something interesting happens. At that level, there’s a tiny but noticeable discrepancy: the individual protons, neutrons and electrons are off by right around 1% from an entire human. The difference is real.

    3
    From macroscopic scales down to subatomic ones, the sizes of the fundamental particles play only a small role in determining the sizes of composite structures. Whether the building blocks are truly fundamental and/or point-like particles is still not known. (MAGDALENA KOWALSKA / CERN / ISOLDE TEAM)

    CERN ISOLDE

    Like all known organisms, human beings are carbon-based life forms. Carbon atoms are made up of six protons and six neutrons, but if you look at the mass of a carbon atom, it’s approximately 0.8% lighter than the sum of the individual component particles that make it up. The culprit here is nuclear binding energy; when you have atomic nuclei bound together, their total mass is smaller than the mass of the protons and neutrons that comprise them.

    The way carbon is formed is through the nuclear fusion of hydrogen into helium and then helium into carbon; the energy released is what powers most types of stars in both their normal and red giant phases. That “lost mass” is where the energy powering stars comes from, thanks to Einstein’s E = mc². As stars burn through their fuel, they produce more tightly-bound nuclei, releasing the energy difference as radiation.

    4
    In between the 2nd and 3rd brightest stars of the constellation Lyra, the blue giant stars Sheliak and Sulafat, the Ring Nebula shines prominently in the night skies. Throughout all phases of a star’s life, including the giant phase, nuclear fusion powers them, with the nuclei becoming more tightly bound and the energy emitted as radiation coming from the transformation of mass into energy via E = mc². (NASA, ESA, DIGITIZED SKY SURVEY 2)

    NASA/ESA Hubble Telescope

    ESO Online Digitized Sky Survey Telescopes

    Caltech Palomar Samuel Oschin 48 inch Telescope, located in San Diego County, California, United States, altitude 1,712 m (5,617 ft)


    Australian Astronomical Observatory, Siding Spring Observatory, near Coonabarabran, New South Wales, Australia, 1.2m UK Schmidt Telescope, Altitude 1,165 m (3,822 ft)


    From http://archive.eso.org/dss/dss

    This is how most types of binding energy work: the reason it’s harder to pull apart multiple things that are bound together is because they released energy when they were joined, and you have to put energy in to free them again. That’s why it’s such a puzzling fact that when you take a look at the particles that make up the proton — the up, up, and down quarks at the heart of them — their combined masses are only 0.2% of the mass of the proton as a whole. But the puzzle has a solution that’s rooted in the nature of the strong force itself.

    The way quarks bind into protons is fundamentally different from all the other forces and interactions we know of. Instead of the force getting stronger when objects get closer, like the gravitational, electric, or magnetic forces, the attractive force goes down to zero when quarks get arbitrarily close. And instead of the force getting weaker when objects get farther away, the force pulling quarks back together gets stronger the farther away they get.

    5
    The internal structure of a proton, with quarks, gluons, and quark spin shown. The nuclear force acts like a spring, with negligible force when unstretched but large, attractive forces when stretched to large distances. (BROOKHAVEN NATIONAL LABORATORY)

    This property of the strong nuclear force is known as asymptotic freedom, and the particles that mediate this force are known as gluons. Somehow, the energy binding the proton together, responsible for the other 99.8% of the proton’s mass, comes from these gluons. The whole of matter, somehow, weighs much, much more than the sum of its parts.

    This might sound like an impossibility at first, as the gluons themselves are massless particles. But you can think of the forces they give rise to as springs: asymptoting to zero when the springs are unstretched, but becoming very large the greater the amount of stretching. In fact, the amount of energy between two quarks whose distance gets too large can become so great that it’s as though additional quark/antiquark pairs exist inside the proton: sea quarks.

    6
    When two protons collide, it isn’t just the quarks making them up that can collide, but the sea quarks, gluons, and beyond that, field interactions. All can provide insights into the spin of the individual components, and allow us to create potentially new particles if high enough energies and luminosities are reached. (CERN / CMS COLLABORATION)

    Those of you familiar with quantum field theory might have the urge to dismiss the gluons and the sea quarks as just being virtual particles: calculational tools used to arrive at the right result. But that’s not true at all, and we’ve demonstrated that with high-energy collisions between either two protons or a proton and another particle, like an electron or photon.

    The collisions performed at the Large Hadron Collider at CERN are perhaps the greatest test of all for the internal structure of the proton. When two protons collide at these ultra-high energies, most of them simply pass by one another, failing to interact. But when two internal, point-like particles collide, we can reconstruct exactly what it was that smashed together by looking at the debris that comes out.

    7
    A Higgs boson event as seen in the Compact Muon Solenoid detector at the Large Hadron Collider. This spectacular collision is 15 orders of magnitude below the Planck energy, but it’s the precision measurements of the detector that allow us to reconstruct what happened back at (and near) the collision point. Theoretically, the Higgs gives mass to the fundamental particles; however, the proton’s mass is not due to the mass of the quarks and gluons that compose it. (CERN / CMS COLLABORATION)

    Under 10% of the collisions occur between two quarks; the overwhelming majority are gluon-gluon collisions, with quark-gluon collisions making up the remainder. Moreover, not every quark-quark collision in protons occurs between either up or down quarks; sometimes a heavier quark is involved.

    Although it might make us uncomfortable, these experiments teach us an important lesson: the particles that we use to model the internal structure of protons are real. In fact, the discovery of the Higgs boson itself was only possible because of this, as the production of Higgs bosons is dominated by gluon-gluon collisions at the LHC. If all we had were the three valence quarks to rely on, we would have seen different rates of production of the Higgs than we did.

    8
    Before the mass of the Higgs boson was known, we could still calculate the expected production rates of Higgs bosons from proton-proton collisions at the LHC. The top channel is clearly production by gluon-gluon collisions. I (E. Siegel) have added the yellow highlighted region to indicate where the Higgs boson was discovered. (CMS COLLABORATION (DORIGO, TOMMASO FOR THE COLLABORATION) ARXIV:0910.3489)

    As always, though, there’s still plenty more to learn. We presently have a solid model of the average gluon density inside a proton, but if we want to know where the gluons are actually more likely to be located, that requires more experimental data, as well as better models to compare the data against. Recent advances by theorists Björn Schenke and Heikki Mäntysaari may be able to provide those much needed models. As Mäntysaari detailed:

    “It is very accurately known how large the average gluon density is inside a proton. What is not known is exactly where the gluons are located inside the proton. We model the gluons as located around the three [valence] quarks. Then we control the amount of fluctuations represented in the model by setting how large the gluon clouds are, and how far apart they are from each other. […] The more fluctuations we have, the more likely this process [producing a J/ψ meson] is to happen.”

    9
    A schematic of the world’s first electron-ion collider (EIC). Adding an electron ring (red) to the Relativistic Heavy Ion Collider (RHIC) at Brookhaven would create the eRHIC: a proposed deep inelastic scattering experiment that could improve our knowledge of the internal structure of the proton significantly. (BROOKHAVEN NATIONAL LABORATORY-CAD ERHIC GROUP)

    The combination of this new theoretical model and the ever-improving LHC data will better enable scientists to understand the internal, fundamental structure of protons, neutrons and nuclei in general, and hence to understand where the mass of the known objects in the Universe comes from. From an experimental point of view, the greatest boon would be a next-generation electron-ion collider, which would enable us to perform deep inelastic scattering experiments to reveal the internal makeup of these particles as never before.

    But there’s another theoretical approach that can take us even farther into the realm of understanding where the proton’s mass comes from: Lattice QCD.

    10
    A better understanding of the internal structure of a proton, including how the “sea” quarks and gluons are distributed, has been achieved through both experimental improvements and new theoretical developments in tandem. (BROOKHAVEN NATIONAL LABORATORY)

    The difficult part with the quantum field theory that describes the strong force — quantum chromodynamics (QCD) — is that the standard approach we take to doing calculations is no good. Typically, we’d look at the effects of particle couplings: the charged quarks exchange a gluon and that mediates the force. They could exchange gluons in a way that creates a particle-antiparticle pair or an additional gluon, and that should be a correction to a simple one-gluon exchange. They could create additional pairs or gluons, which would be higher-order corrections.

    We call this approach taking a perturbative expansion in quantum field theory, with the idea that calculating higher and higher-order contributions will give us a more accurate result.

    11
    Today, Feynman diagrams are used in calculating every fundamental interaction spanning the strong, weak, and electromagnetic forces, including in high-energy and low-temperature/condensed conditions. But this approach, which relies on a perturbative expansion, is only of limited utility for the strong interactions, as this approach diverges, rather than converges, when you add more and more loops for QCD.(DE CARVALHO, VANUILDO S. ET AL. NUCL.PHYS. B875 (2013) 738–756)

    Richard Feynman © Open University

    But this approach, which works so well for quantum electrodynamics (QED), fails spectacularly for QCD. The strong force works differently, and so these corrections get very large very quickly. Adding more terms, instead of converging towards the correct answer, diverges and takes you away from it. Fortunately, there is another way to approach the problem: non-perturbatively, using a technique called Lattice QCD.

    By treating space and time as a grid (or lattice of points) rather than a continuum, where the lattice is arbitrarily large and the spacing is arbitrarily small, you overcome this problem in a clever way. Whereas in standard, perturbative QCD, the continuous nature of space means that you lose the ability to calculate interaction strengths at small distances, the lattice approach means there’s a cutoff at the size of the lattice spacing. Quarks exist at the intersections of grid lines; gluons exist along the links connecting grid points.

    As your computing power increases, you can make the lattice spacing smaller, which improves your calculational accuracy. Over the past three decades, this technique has led to an explosion of solid predictions, including the masses of light nuclei and the reaction rates of fusion under specific temperature and energy conditions. The mass of the proton, from first principles, can now be theoretically predicted to within 2%.

    12
    As computational power and Lattice QCD techniques have improved over time, so has the accuracy to which various quantities about the proton, such as its component spin contributions, can be computed. By reducing the lattice spacing size, which can be done simply by raising the computational power employed, we can better predict the mass of not only the proton, but of all the baryons and mesons. (LABORATOIRE DE PHYSIQUE DE CLERMONT / ETM COLLABORATION)

    It’s true that the individual quarks, whose masses are determined by their coupling to the Higgs boson, cannot even account for 1% of the mass of the proton. Rather, it’s the strong force, described by the interactions between quarks and the gluons that mediate them, that are responsible for practically all of it.

    The strong nuclear force is the most powerful interaction in the entire known Universe. When you go inside a particle like the proton, it’s so powerful that it — not the mass of the proton’s constituent particles — is primarily responsible for the total energy (and therefore mass) of the normal matter in our Universe. Quarks may be point-like, but the proton is huge by comparison: 8.4 × 10^-16 m in diameter. Confining its component particles, which the binding energy of the strong force does, is what’s responsible for 99.8% of the proton’s mass.

    See the full article here .

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    Please help promote STEM in your local schools.

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    “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 12:00 pm on August 8, 2018 Permalink | Reply
    Tags: , , , Could a new type of quark fix the “unnaturalness” of the Standard Model?, , , , , Quarks,   

    From CERN ATLAS: “Could a new type of quark fix the “unnaturalness” of the Standard Model?” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    From CERN ATLAS

    8th August 2018
    ATLAS Collaboration

    1
    Figure 1: One of the Feynman diagrams for T pair production at the LHC. (Image: ATLAS Collaboration © CERN 2018)

    While the discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012 confirmed many Standard Model predictions, it has raised as many questions as it has answered. For example, interactions at the quantum level between the Higgs boson and the top quark ought to lead to a huge Higgs boson mass, possibly as large as the Planck mass (>1018 GeV). So why is it only 125 GeV? Is there a mechanism at play to cancel these large quantum corrections caused by the top quark (t)? Finding a way to explain the lightness of the Higgs boson is one of the top (no pun intended) questions in particle physics.

    A wide range of solutions have been proposed and a common feature in many of them is the existence of vector-like quarks – in particular, a vector-like top quark (T). Like other quarks, vector-like quarks would be spin-½ particles that interact via the strong force. While all spin-½ particles have left- and right-handed components, the weak force only interacts with the left-handed components of Standard Model particles. However, vector-like quarks would have “ambidextrous” interactions with the weak force, giving them a bit more leeway in how they decay. While the Standard Model top quark always decays to a bottom quark (b) by emitting a W boson (t→Wb), a vector-like top can decay three different ways: T→Wb, T→Zt or T→Ht (Figure 1).

    2
    Figure 2: Lower limit (scale on right axis) on the mass of a vector-like top as a function of the branching ratio to Wb and Ht (bottom and left axes). (Image: ATLAS Collaboration © CERN 2018)

    The ATLAS collaboration uses a custom-built programme to search for vector-like top pairs in LHC data. It utilizes data from several dedicated analyses, each of them sensitive to various experimental signatures (involving leptons, boosted objects and/or large missing transverse momentum). This allows ATLAS to look for all of possible decays, increasing the chance of discovery.

    ATLAS has now gone one step further by performing a combination of all of the individual searches. While individual analyses are designed to study a particular sets of decays, combined results provide sensitivity to all possible sets of decays. These have allowed ATLAS to search for vector-like tops with masses over 1200 GeV. It appears, however, that vector-like tops are so far nowhere to be found. On the bright side, the combination allows ATLAS to set the most stringent lower limits on the mass of a vector-like top for arbitrary sets of branching ratios to the three decay modes (Figure 2).

    Between these limits on vector-like top quarks and those on other theories that could offer a solution (like supersymmetry), the case for a naturally light Higgs boson is not looking good… but Nature probably still has a few tricks up its sleeve for us to uncover.

    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

    See the full article here .


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    CERN map


    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN


    CERN Courier

    QuantumDiaries


    Quantum Diaries

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

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

    Symmetry Mag

    Symmetry

    06/30/17
    Sarah Charley

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

    1
    Wow!! ATLAS collaboration.

    The Large Hadron Collider is definitely large.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

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

    Hadrons are composite particles made up of quarks and gluons.

    The quark structure of the proton 16 March 2006 Arpad Horvath

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

    2
    SA

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

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

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

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

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

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

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

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

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

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

    See the full article here .

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    STEM Icon

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  • richardmitnick 10:31 am on October 9, 2015 Permalink | Reply
    Tags: , , , Quarks   

    From FNAL- “Frontier Science Result: CMS Why three?” 

    FNAL II photo

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

    Oct. 9, 2015
    FNAL Don Lincoln
    Don Lincoln

    Temp 1
    The Standard Model includes six types of quarks, arranged into three generations. Only generation I is necessary to make ordinary matter. So why are there three generations, and what message are the other four quarks telling us?

    There are a lot of mysteries in particle physics, but one of the most curious is called the flavour problem. Physicists use the word flavour to mean the different varieties of particles. As readers of this column will recall, there are six types of quarks: up and down, charm and strange, and top and bottom. Up and down quarks are found in ordinary matter and are called generation I. The other two generations are very similar in their properties compared to the first generation, but they have higher mass.

    So why are there these two other copies? Scientists have many ideas. One is that the quarks contain smaller particles within them. While these smaller particles have never been found, they already have a name — preons. Another idea is that there may be only one generation, but this generation exists in a higher dimensional space. In the same way that a football viewed end on looks like a circle while looking like, well, a football from the side, perhaps the different generations are just a single particle seen from different angles.

    Nobody knows the answer to the flavour problem, and, to share a personal note, this particular physics problem is the one that keeps me awake at night. The existence of these extra generations would tell us something profound about the universe if we just had the wits to understand what it is saying.

    Another interesting possibility is that there are other generations, say generation IV. We already have names for the quarks of that generation — t’ and b’, pronounced t prime and b prime. However, no evidence for the existence of this fourth generation has been found. Indeed, a measurement from experiments from back in the 1990s using the LEP accelerator at CERN suggests that there are only three generations.

    CERN LEP
    LEP at CERN

    There are possible loopholes in that measurement, but it might well be that there are but three generations.

    Yet another idea, generally based on the preon concept, is that the hypothetical constituents of the quarks can be given energy. Just as a slumbering beehive is different from one that was recently kicked, maybe enough energy can stir up the quarks’ constituents.

    In the simplest incarnation, this principle should be true of all quarks, but one could also imagine adding energy only to the constituents of the third-generation quarks. Scientists call such a configuration an excited quark and denote such a quark with an asterisk. So CMS scientists went looking for a b*.

    CERN CMS Detector
    CMS at CERN

    The idea is that the b* would be a very massive particle and could decay into a W boson and a top quark. No evidence was found for a b*, and physicists ruled out the existence of a b* with a mass below about 1,500 GeV. A particular peculiarity of this particle is that it wouldn’t get its mass from the Higgs field, but from the energy that excited the quark.

    A negative measurement isn’t as much fun as a positive one, but at least we know what’s not the answer for the flavor problem, and that’s progress. But it doesn’t help my insomnia, and so we keep looking, hoping to solve this thorniest of problems.

    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 5:35 am on March 17, 2015 Permalink | Reply
    Tags: , , , , , , Quarks   

    From New Scientist: “Quark stars: How can a supernova explode twice?” 2013 But Well Worth the Read 

    NewScientist

    New Scientist

    09 December 2013
    Anil Ananthaswamy

    What do you get when you melt a neutron star? An unimaginably dense lump of strange matter and a whole new celestial beast

    1
    (Image: Matt Murphy)

    ON 22 September last year, the website of The Astronomer’s Telegram alerted researchers to a supernova explosion in a spiral galaxy about 84 million light years away. There was just one problem. The same object, SN 2009ip, had blown up in a similarly spectacular fashion just weeks earlier. Such stars shouldn’t go supernova twice, let alone in quick succession. The thing was, it wasn’t the only one, the next year another supernova, SN 2010mc, did the same.

    One of the few people not to be bamboozled was Rachid Ouyed. “When I looked at those explosions, they were talking to me right away,” he says. Ouyed, an astrophysicist at the University of Calgary in Alberta, Canada, thinks that these double explosions are not the signature of a supernova, but something stranger. They may mark the violent birth of a quark star, a cosmic oddity that has only existed so far in the imaginations and equations of a few physicists. If so they would be the strongest hints yet that these celestial creatures exist in the cosmic wild.

    The implications would be enormous. These stars would take pride of place alongside the other heavenly heavyweights: neutron stars and black holes. They could help solve some puzzling mysteries related to gamma-ray bursts [GRBs] and the formation of the heftiest elements in the universe. Back on Earth, quark stars would help us better understand the fundamental building blocks of matter in ways that even machines like the Large Hadron Collider cannot.

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

    Astrophysicists can thank string theorist Edward Witten for quark stars. In 1984, he hypothesised that protons and neutrons may not be the most stable forms of matter.

    Both are made of two types of smaller entities, known as quarks: protons are comprised of two “up” quarks and one “down” quark, whereas neutrons are made of two downs and one up. Up and down are the lightest of six distinct “flavours” of quark. Add the third lightest to the mix and you get something called strange quark matter. Witten argued that this kind of matter may have lower net energy and hence be more stable than nuclear matter made of protons and neutrons.

    Quark nova

    If so, we might all start decaying into strange matter. But don’t fret. You either need to wait around longer than the age of the universe for the stuff to form spontaneously, or find somewhere with the right conditions to start the process. One place this could happen is inside neutron stars, the dense remnants of certain types of supernovae.

    When a star many times more massive than the sun runs out of fuel, its inner core implodes. The outer layers are cast off in a spectacular explosion. What’s left behind is a rapidly spinning neutron star, which as the name implies is made mainly of neutrons, with a crust of iron. Whirling up to 1000 times per second, a neutron star is constantly shedding magnetic fields. Over time, this loss of energy causes the star to spin slower and slower. As it spins down, the centrifugal forces that kept gravity at bay start weakening, allowing gravity to squish the star still further.

    In what is a blink of an eye in cosmic time, the neutrons can be converted to strange quark matter, which is a soup of up, down and strange quarks. In theory, this unusual change happens when the density inside the neutron star starts increasing. New particles called hyperons begin forming that contain at least one strange quark bound to others.

    However, the appearance of hyperons marks the beginning of the end of the neutron star. “Once you start to form hyperons, then you can start the nucleation of the first droplet of strange quark matter,” says Giuseppe Pagliara of the University of Ferrara in Italy. As the density in the core continues to increase, the star’s innards “melt”, freeing quarks from their bound state. In fact, a single droplet of strange matter is enough to trigger a runaway process that converts all the neutrons. What was a neutron star turns into a quark star.

    Of course, this assumes that Witten is correct about strange quark matter being more stable than neutrons. No one has yet proved him wrong, but it is a tough idea for some to swallow. “More conservative thinkers are just not open to the idea that free quarks exist in neutron stars,” says Fridolin Weber, an astrophysicist at the San Diego State University in California.

    Not so the daring ones. Ouyed, for instance, has been trying to convince his fellow astrophysicists of the existence of quark stars for more than a decade. Not only do these intrepid few think that quarks can exist freely inside neutron stars, they have even thought about what comes next. “We all agree that if quark stars exist, then the conversion of normal, ordinary matter into a quark star will be a very exothermic process, a lot of energy will be released,” says Pagliara. “How this energy is released is a matter of debate.”

    On one hand, Pagliara and his colleagues have done extensive simulations to show that this conversion will happen in a matter of milliseconds. In what he calls a “strong deflagration”, the neutron star burns up as it turns into a quark star. There is no explosion.

    Ouyed, on the other hand, begs to differ. His team’s simulations show that the conversion is most likely to be an extremely violent process. The seed of strange quark matter spreads until it reaches the outer crust of the neutron star. As the part of the star that has been turned into quark matter separates from the iron-rich crust, it collapses. The collapse halts when the inner core becomes incredibly dense and rebounds, creating a shock wave. Much as in a supernova, the iron-rich crust and leftover neutrons are ejected in another spectacular explosion – a “quark nova”.

    Hurtling through space, the quark nova ejecta then slam into the earlier supernova remnants, causing them to light up again, as they did after the explosion of the original, conventional star. What’s left behind is a quark star. “It was very hard to find solutions where the entire neutron star turned into a quark star, in just a puff with no explosion,” says Ouyed.

    Double explosion

    Depending on the mass of the star before its first explosion, the second blast could occur anywhere from seconds to years after the original supernova. Too soon, and the two explosions would merge, appearing as one blast, smeared out in time. Too late, and the supernova ejecta would have dispersed long before the detonation of the quark nova, and there would be no re-brightening.

    But if the timing is just right, the outcome should be observable. In 2009, Ouyed’s team predicted that if the quark nova goes off days or weeks after the supernova, there should be two peaks in energy: the first being the supernova explosion itself, and the second being the reheating of the supernova ejecta. The objects SN 2009ip and SN 2010mc matched predictions in ways almost too good to be true.

    SN 2009ip had its first major explosion in early August 2012, and 40 days later flared up again. SN 2010mc was eerily similar in its outbursts, showing a double explosion in which the peaks were about 40 days apart. While other researchers continue trying to explain these unusual observations using their tried-and-tested models of supernovae, Ouyed is convinced that we have witnessed quark stars being born.

    Oddly, it is the first peak in both events that convinces him. If these have all the characteristics of a regular supernova, it makes the second boom harder to explain using conventional arguments. “When you look at the first ejecta, it looks like a duck and walks like a duck: it’s a supernova,” says Ouyed. “Then what’s the second one?”

    He points the finger at quark novae. “We just applied our model of the dual shock quark nova, and it was actually easy to fit,” he says. “That’s the beauty of it.”

    While Pagliara and Ouyed’s teams disagree on whether the transition from a neutron star to a quark star is explosive, they do agree that space should be littered with quark stars. How should we look for them?

    We might be mistaking some of them for neutron stars, says Pagliara. Most neutron stars weigh as much as 1.4 suns or slightly more. The best studied examples, orbiting each other in systems called Hulse-Taylor binary pulsars, certainly follow this pattern. Both neutron stars involved weigh in at 1.4 solar masses. However, Pagliara is bothered by two discoveries of neutron stars that tip the scales at 2 solar masses each. “It’s difficult to reach this mass with normal particle components like neutrons, protons and hyperons,” he says.

    This has to do with a property of matter called its equation of state. Equations of state describe how matter behaves under changes in physical conditions, such as pressure and temperature. Hyperons, which are precursors to strange quark matter, have a “soft” equation of state. Their existence in the dense core of a neutron star makes the star more compressible, causing it to shrink in size.

    Astronomers estimate that neutron stars are about 10 kilometres across – but squeezing 2 solar masses into an object of such size would end up creating a black hole. Pagliara says that compact stars weighing 2 solar masses or more have to be bigger, or put another way, the matter has to be “stiffer” so that gravity cannot compress it as much. There is one candidate with a stiffer equation of state: strange quark matter.

    Pagliara and his colleague Alessandro Drago and others claim that the compact stars we have spotted come from two families. The smaller ones must be the run-of-the-mill neutron stars. The larger ones must be quark stars. The only way to verify this claim is to measure their masses and also measure their radii to the nearest kilometre. A proposed European satellite mission called the Large Observatory for X-ray Timing could do just that. Its aim is to measure the equation of state for compact objects – and thus differentiate between neutron stars and quark stars.

    ESA LOFT
    ESA/LOFT

    Meanwhile, Ouyed’s team is concentrating on predictions based on their quark nova model. One prediction has to do with the creation of heavy elements in the universe. Once a massive star goes supernova, weighty elements are synthesised in a matter of milliseconds, when neutrons are absorbed into iron nuclei. These neutron-rich nuclei are unstable and decay into elements further up in the periodic table when neutrons get converted to protons. “But the challenge with supernovae has always been to go to really heavy elements,” says Ouyed. The iron and neutrons needed for the process are in short supply because most of them are left behind in the remnant neutron star.

    The quark nova solves that problem. Its ejecta are a potent mix of neutrons and iron from the neutron star’s crust, providing just the laboratory for synthesising the heaviest elements. Ouyed is urging astronomers to study double explosions carefully. His team predicts that the second blast should show the presence of elements heavier than atomic mass 130, elements which should be missing from the first explosion.

    The conversion of a neutron star to a quark star could also solve another problem plaguing astrophysics: the source of some long-duration gamma-ray bursts, which are among the brightest events in the universe. On 9 July 2011, NASA’s SWIFT gamma-ray satellite saw a burst with two spectacular peaks of emission, spaced 11 minutes apart.

    NASA SWIFT Telescope
    NASA/Swift

    And the second was the stronger of the two. The traditional “collapsar” model of gamma-ray bursts relies on a star collapsing to a black hole. As the last remnants of the doomed star fall in, it is thought to result in such an emission. But 11 minutes is an eternity for a black hole – it’s hard to make sense of the second peak.

    Pagliara thinks his team has the answer. According to their model, a neutron star converts to a quark star without an explosion. Yet there is still a tremendous release of energy, which Pagliara suspects goes into gamma rays. This could explain the second peak. “At the moment, and it’s speculation, we think that this second event could be related to quark stars,” he says. “If you want to see a possible signature of formation of quark matter, you should probably look at those gamma-ray bursts that have an activity long after the main event.”

    Quark world

    Confirming the existence of quark stars and verifying their properties could have a huge impact on particle physics. Colliders like the LHC and the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory [BNL]in New York have been smashing heavy ions head-on to create a state of matter called a quark-gluon plasma, where quarks are essentially free.

    BNL RHIC Campus
    BNL RHIC
    RHIC at BNL

    The best way to study this phase of matter is using a method called lattice quantum chromodynamics [QCD]. But physicists have only been able to solve the equations of lattice QCD for high temperatures and low density – the conditions created at the LHC and the RHIC. The equations are intractable for other conditions. For instance, it is impossible to calculate the density at which protons and neutrons can melt into their constituent quarks at low temperatures.

    Enter quark stars. First, if their existence is confirmed, it proves that quarks can exist freely at high densities and low temperatures, rather than bound up in hadrons – the catch-all name given to any particle made of quarks. Second, for the explosive quark nova model Ouyed’s team has shown that the density at which quarks get freed is intimately linked to the time lag between the supernova and the quark nova. Measure the timing of the double explosion and you will glean important clues about conditions at the transition. “The quark nova is a very beautiful bridge that straddles the hadronic world and the quark world,” says Ouyed. “It’d be a very nice tool to use for physics and astrophysics.”

    Weber agrees that quark stars, if they exist, would be a unique astrophysical laboratory. They would help us probe properties of matter in ways that we cannot do with the best colliders on Earth – in the domain of high densities and low temperatures. “This is a regime that is only accessible to stars, and only stars can tell us what will happen.”

    See the full article here.

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  • richardmitnick 12:19 pm on December 29, 2014 Permalink | Reply
    Tags: , , , Quarks   

    From livescience: “7 Strange Facts About Quarks” 

    Livescience

    May 05, 2014
    Elizabeth Howell

    Teensy Particles

    1

    q
    A proton, composed of two up quarks, one down quark and the gluons “binding” them together. The color assignment of individual quarks is not important, only that all three colors be present.

    Quarks are particles that are not only hard to see, but pretty much impossible to measure. These teensy-tiny particles are the basis of subatomic particles called hadrons. With every discovery in this field of particle physics in the past 50 years, however, more questions arise about how quarks influence the universe’s growth and ultimate fate. Here are seven strange facts about quarks.

    Emerged just after Big Bang

    2
    NASA/WMAP

    NASA WMAP satellite
    NASA/ WMAP spacecraft

    NASA WMAP

    The first quarks appeared about 10^minus 12 seconds after the universe was formed, in the same era where the weak force (which today is the basis for some radioactivity) separated from the electromagnetic force. The antiparticles of quarks appeared around the same time.

    Discovered in an atom smasher

    3
    Credit: Brookhaven National Lab

    A mystery arose in the 1960s when researchers using the Stanford Linear Accelerator Center found that the electrons were scattering from each other more widely than calculations suggested. More research found that there were at least three locations where electrons scattered more than expected within the nucleon or heart of these atoms, meaning something was causing that scattering. That was the basis for our understanding of quarks today.

    Mentioned by James Joyce

    j
    Credit: Cornell Joyce Collection, Public Domain

    Murray Gell-Mann, the co-proposer for the quark model in the 1960s, drew inspiration for the spelling from the 1939 James Joyce book Finnegan’s Wake, which read: “Three quarks for Muster Mark! / Sure he has not got much of a bark / And sure any he has it’s all beside the mark.” (The book came out well before quarks were discovered and so their name has always been spelled in this way.)

    Come in flavors

    q
    Credit: MichaelTaylor | Shutterstock

    Physicists refer to the different types of quark as flavors: up, down, strange, charm, bottom, and top. The biggest differentiation between the flavors is their mass, but some also differ by charge and by spin. For instance, while all quarks have the same spin of 1/2, three of them (up, charm and top) have charge 2/3, and the other three (down, strange and bottom) have charge minus 1/3. And just because a quark starts out as a flavor doesn’t mean it will stay that way; down quarks can easily transform into up quarks, and charm quarks can change into strange quarks.

    Tricky to measure

    t

    Quarks can’t be measured, because the energy required produces an antimatter equivalent (called an antiquark) before they can be observed separately, among other reasons, according to a primer from Georgia State University. The mass of quarks is best determined by techniques such as using a supercomputer to simulate the interactions between quarks and gluons, with gluons being the particles that glue quarks together.

    Teach us about matter

    5
    Credit: Chukman So

    In 2014, researchers published the first observation of a charm quark decaying into its antiparticle, providing more information about how matter behaves. Because particles and antiparticles should destroy each other, one would think the universe should just have photons and other elementary particles. Yet antiphotons and antiparticles still exist, leading to the mystery of why the universe is made mostly of matter and not antimatter.

    May set the universe’s fate

    7

    Nailing down the mass of the top quark could reveal to researchers one of two ghastly scenarios: that the universe could end in 10 billion years, or that people could materialize out of nowhere. If the top quark is heavier than expected, energy carried through the vacuum of space could collapse. If it’s lower than expected, an unlikely scenario called “Boltzmann brain” could see self-aware entities come out of random collections of atoms. (While this isn’t a part of the Standard Model, the theory – framed as a paradox – goes that it would be more likely to see organized groups of atoms as the random ones observed in the universe.)

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    See the full article here.

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  • richardmitnick 12:04 pm on December 4, 2014 Permalink | Reply
    Tags: , , , , , , Quarks   

    From FNAL- “Frontier Science Result: CDF Wading through the swamp to measure top quark mass” 


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

    Thursday, Dec. 4, 2014
    edited by Andy Beretvas

    Even after the discovery of the Higgs boson, the top quark is still a focus of attention because of its peculiar position of being the heaviest quark in the Standard Model and for its possible role in physics beyond the Standard Model.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    If the Standard Model is correct, the stability of the vacuum strongly depends on the mass of the Higgs boson and the top quark mass. In this context, scientists favor the scenario that the universe is in a metastable state. A precision measurement of the top quark mass helps to better determine the relative stability of that state in this scenario.

    At the Tevatron, top quarks were produced, mostly in pairs, only once in about 10 billion collisions. They decayed right away into a W boson and a b quark. In the most abundant and yet most challenging scenario, the final state contains six collimated sprays of particles, called jets, two of which likely originated from the b quarks, with peculiar, identifiable characteristics (allowing them to be “b-tagged”). This decay mode is usually called the all-hadronic channel, for which the signal is swamped by a background associated to the production of uninteresting multijet events, which were about a factor of 1,000 more abundant than the signal events.

    FNAL Tevatron
    Tevatron

    This new analysis uses the full CDF Run II data set.
The set contains nearly twice the number of top quark pairs as seen in our previous measurement. The analysis uses an improved simulation and relies on there being at least one b-tagged jet. An important part of the analysis is to minimize the uncertainty in our measurement of jet scale energies. Exploiting the expected behavior of top-antitop signal events, the huge background can be tamed through finely tuned requirements, yielding about 4,000 events, where about one event out of three is expected from the signal. The all-hadronic final state can then be fully reconstructed using the energies of the six jets, and the mass of the top quark can be derived comparing the data to simulations produced for different input values of the top quark mass (see the [below] figure).

    i
    The black dots plot the distribution of the reconstructed top mass for events containing one or more b-tags. The distribution is compared to the expected yield for background and signal events, normalized to the best fit.

    FNAL CDF
    CDF

    This procedure yields a value of 175.1 ± 1.2 (stat) ± 1.6 (sys) GeV/c2 for the top quark mass, with a 1 percent relative precision. This measurement complements the results obtained by CDF in other channels. Our measurement is consistent with the current world average (which includes our previous measurement in the all-hadronic channel), obtained from measurements by ATLAS, CDF, CMS and DZero. The top quark mass world average is 173.3 ± 0.8 GeV/c2.

    CERN ATLAS New
    ATLAS

    CERN CMS New
    CMS

    FNAL DZero
    DZero

    See the full article here.

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    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.

     
  • richardmitnick 2:14 pm on November 29, 2014 Permalink | Reply
    Tags: , , , , , Quarks   

    From Daily Galaxy: “The Hunt for Colossal “Quark” Stars –Do They Exist?” 

    Daily Galaxy
    The Daily Galaxy

    November 29, 2014

    No Writer Credit

    “We haven’t found strange stars yet,” explains Prashanth Jaikumar from the Argonne National Laboratory. “But that doesn’t mean they don’t exist. Maybe we have found them. Maybe some of these neutron stars are really strange stars. According to our theory, it would be very difficult to tell a strange star from a neutron star.”

    Recent research suggests that neutron stars may gradually transform into ‘strange’ stars – i.e. in stars made up primarily from the ‘strange’ quark. The conventional wisdom is that the electric field of a such a hypothetical strange star (made up from strange matter) at its surface would be so huge and its luminosity so big that it would be impossible to confuse it with anything else.

    However, Jaikumar and his fellow researchers from the Argonne National Laboratory, and two colleagues from Los Alamos National Laboratory in New Mexico, have challenged that. The team developed a theory about what a strange star would look like.

    One of the most interesting aspects of neutron stars is that they are not gaseous like usual stars, but they are so closely packed that they are liquid. Strange stars should also be liquid with a surface that is solid.

    However, Jaikumar and his colleagues challenge that. Strange stars are usually assumed to exhibit huge electric fields on their surface precisely because they are assumed to have a smooth surface. But according to the scientists neither neutron stars nor strange stars have such a smooth solid-like surface.

    “It’s like taking water,” Jaikumar says, “with a flat surface. Add detergent and it reduces surface tension, allowing bubbles to form. In a strange star, the bubbles are made of strange quark matter, and float in a sea of electrons. Consequently, the star’s surface may be crusty, not smooth. The effect of surface tension had been overlooked before.”

    One consequence is that a strange star wouldn’t have large electrical field at surface or be super-luminous. It also allows for a strange star to be less dense than originally thought, although such stars are definitely unusually dense compared to regular stars.

    Much of the matter in our Universe may be made of a type of dark matter called weakly interacting massive particles, also known as WIMPs, . Although some scientists predict that these hypothetical particles possess many of the necessary properties to account for dark matter, until recently scientists have not been able to make any definite predictions of their mass. In a new study, physicists have derived a limit on the WIMP mass by calculating how these dark matter particles can transform neutron stars into stars made of strange quark matter, or “strange” stars.

    h

    WIMPs are thought to be largely located in the halos of galaxies. Although galaxy halos (image above) are not visible, they contain most of a galaxy’s mass in the form of the heavy WIMPs.

    Dr. M. Angeles Perez-Garcia from the University of Salamanca in Salamanca, Spain, along with Dr. Joseph Silk of the University of Oxford and Dr. Jirina R. Stone of the University of Oxford and the University of Tennessee showed that, when a neutron star gravitationally captures nearby WIMPs, the WIMPs may trigger the conversion of the neutron star into a strange star.

    One important issue is whether at high density ‘strange’ quark matter is more stable than regular matter (which is comprised of ‘up’ and ‘down’ quarks). Jaikumar and colleagues think that as a neutron star spins down and its core density increases, it may convert into the more stable state of strange quark matter, forming a strange star.

    Theorists cannot say with absolute certainty whether or not a neutron star gradually converts into a strange star. The conversion occurs, according to new research, as a result of the WIMPs seeding the neutron stars with long-lived lumps of strange quark matter, or strangelets. WIMPs captured in the neutron star’s core self-annihilate, releasing energy in the process.

    According to Jaikumar, making the distinction is rather tricky: “There might be a slight difference. You’d look at surface temperature and see how stars are cooling in time. If it is quark matter, the emission rates are different, so the strange star may cool a little faster.”

    It’s the astronomers’ job to discover whether strange stars exist or not. Either discovery will have important implications for the theory of Quantum Chromodynamics (QCD) — which is the fundamental theory of quarks. “Finding a strange star would improve our understanding of QCD, the fundamental theory of the nuclear force. And it would also be the first solid evidence of stable quark matter”, Jaikumar said.

    Elsewhere, Kwong-Sang Cheng of the University of Hong Kong, China, and colleagues have presented evidence that a quark star formed in a bright supernova called SN 1987A (above), which is among the nearest supernovae to have been observed.

    Observing a quark star could shed light on what happened just after the Big Bang, because at this time, the Universe was filled with a dense sea of quark matter superheated to a trillion °C. While some groups have claimed to have found candidate quark stars, no discovery has yet been confirmed.

    Now Kwong-Sang Cheng of the University of Hong Kong, China, and colleagues have presented evidence that a quark star formed in a bright supernova called SN 1987A (pictured), which is among the nearest supernovae to have been observed.

    The birth of a neutron star is known to be accompanied by a single burst of neutrinos. But when the team examined data from two neutrino detectors – Kamiokande II in Japan and Irvine-Michigan-Brookhaven in the US – they found that SN 1987A gave off two separate bursts.

    “There is a significant time delay between [the bursts recorded by] these two detectors,” says Cheng. They believe the first burst was released when a neutron star formed, while the second was triggered seconds later by its collapse into a quark star. The results appeared in The Astrophysical Journal (http://www.arxiv.org/abs/0902.0653v1).

    “This model is intriguing and reasonable,” says Yong-Feng Huang of Nanjing University, China. “It can explain many key features of SN 1987A.” However, Edward Witten of the Institute for Advanced Study in Princeton, New Jersey, is not convinced. “I hope they’re right,” he says. “My first reaction, though, is that this is a bit of a long shot.”

    High-resolution X-ray observatories, due to fly in space in the next decade, may have the final say. Neutron stars and quark stars should look very different at X-ray wavelengths, says Cheng.

    The image of SN 1987A at top of the page combines data from NASA’s orbiting Chandra X-ray Observatory and the 8-meter Gemini South infrared telescope in Chile, which is funded primarily by the National Science Foundation.

    The X-ray light detected by Chandra is colored blue. The infrared light detected by Gemini South is shown as green and red, marking regions of slightly higher and lower-energy infrared, respectively. The core remains of the star that exploded in 1987 is not visible here. The ring is produced by hot gas (largely the X-ray light) and cold dust (largely the infrared light) from the exploded star interacting with the interstellar region. Credit: Gemini/NASA

    “Supernova 1987A is changing right before our eyes,” said Dr. Eli Dwek, a cosmic dust expert at NASA Goddard Space Flight Center in Greenbelt, Md. For several years Dwek has been following this supernova, named 1987A for the year it was discovered in the Large Magellanic Cloud, a neighboring dwarf galaxy. “What we are seeing now is a milestone in the evolution of a supernova.”

    See the full article here.

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  • richardmitnick 3:17 pm on November 11, 2014 Permalink | Reply
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    From Symmetry: “The November Revolution” 

    Symmetry

    November 11, 2014
    Amanda Solliday

    Forty years ago today, two different research groups announced the discovery of the same new particle and redefined how physicists view the universe.

    On November 11, 1974, members of the Cornell high-energy physics group could have spent the lulls during their lunch meeting chatting about the aftermath of Nixon’s resignation or the upcoming Big Red hockey season.

    But on that particular Monday, the most sensational topic was physics-related. One of the researchers in the audience stood up to report that two labs on opposite sides of the country were about to announce the same thing: the discovery of a new particle that heralded the birth of the Standard Model of particle physics.

    tr
    Ting and Richter

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    “Nobody at the meeting knew what the hell it was,” says physicist Kenneth Lane of Boston University, a former postdoctoral researcher at Cornell. Lane, among others, would spend the next few years describing the theory and consequences of this new particle.

    It isn’t often that a discovery comes along that forces everyone to reevaluate the way the world works. It’s even rarer for two groups to make such a discovery at the same time, using different methods.

    One announcement would come from a research group led by MIT physicist Sam Ting at Brookhaven National Laboratory in New York. The other was to come from a team headed by physicist Burton Richter at SLAC National Accelerator Laboratory, then called the Stanford Linear Accelerator Center, in California. Word traveled fast.

    “We started getting all sorts of inquiries and congratulations before we even finished writing the paper,” Richter says. “Somebody told a friend, and then a friend told another friend.”

    Ting called the new particle the J particle. Richter called it psi. It became known as J/psi, the discovery that sparked the November Revolution.

    Independently, the researchers at Brookhaven and SLAC had designed two complementary experiments.

    Ting and his team had made the discovery using a proton machine, shooting an intense beam of particles at a fixed target. Ting was interested in how photons, particles of light, turn into heavy photons, particles with mass, and he wanted to know how many of these types of heavy photons existed in nature. So his team—consisting of 13 scientists from MIT with help from researchers at Brookhaven—designed and built a detector that would accept a wide range of heavy photon masses.

    “The experiment was quite difficult,” Ting says. “I guess when you’re younger, you’re more courageous.”

    In early summer 1974, they started the experiment at a high mass, around 4 to 5 billion electronvolts. They saw nothing. Later, they lowered the mass and soon saw a peak near 3 billion electronvolts that indicated a high production rate of a previously unknown particle.

    At SLAC, Richter had created a new type of collider, the Stanford Positron Electron Asymmetric Rings (SPEAR). His research group used a beam of electrons produced by a linear accelerator and stored the particles in a ring of magnets. Then, they would generate positrons in a linear accelerator and inject them in the other direction. The detector was able to look at everything produced in electron-positron collisions.

    The goal was to determine the masses of known elementary particles, but the researchers saw strange effects in the summer of 1974. They looked at that particular region with finer resolution, and over the weekend of November 9-10, discovered a tall, thin energy peak around 3 billion electronvolts.

    At the time, Ting visited SLAC as part of an advisory committee. The laboratory’s director, Pief Panofsky, asked Richter to meet with him.

    “He called and said, ‘It sounds like you guys have found the same thing,’” Richter says.

    Both researchers sent their findings to the journal Physical Review Letters. Their papers were published in the same issue. Other labs quickly replicated and confirmed the results.

    At the time, the basic pieces of today’s Standard Model of particle physics were still falling into place. Just a decade before, it had resembled the periodic table of the elements, including a wide, unruly collection of different types of particles called hadrons.

    Theorists Murray Gell-Mann and George Zweig were the first to propose that all of those different types of hadrons were actually made up of the same building blocks, called quarks. This model included three types of quark: up, down and strange. Other theorists—Sheldon Lee Glashow, James Bjorken, and then also John Iliopoulos and Luciano Maiani—proposed the existence of a fourth quark.

    On the day of the J/psi announcement, the Cornell researchers talked about the findings well into the afternoon. One of the professors in the department, Ken Wilson, made a connection between the discovery and a seminar given earlier that fall by Tom Appelquist, a physicist at Harvard University. Appelquist had been working with his colleague David Politzer to describe something they called “charmonium,” a bound state of a new type of quark and antiquark.

    “Only a few of us were thinking about the idea of a fourth quark,” says Appelquist, now a professor at Yale. “Ken called me right after the discovery and urged me to get our paper out ASAP.”

    The J/psi news inspired many other theorists to pick up their chalk as well.

    “It was clear from day one that J/psi was a major discovery,” Appelquist says. “It almost completely reoriented the theoretical community. Everyone wanted to think about it.”

    Less than two weeks after the initial discovery, Richter’s group also found psi-prime, a relative of J/psi that showed even more cracks in the three-quark model.

    “There was a whole collection of possibilities of what could exist outside the current model, and people were speculating about what that may be,” Richter says. “Our experiment pruned the weeds.”

    The findings of the J/psi teams triggered additional searches for unknown elementary particles, exploration that would reveal the final shape of the Standard Model. In 1976, the two experiment leaders were awarded the Nobel Prize for their achievement.

    In 1977, scientists at Fermilab discovered the fifth quark, the bottom quark. In 1995, they discovered the sixth one, the top.

    Today, theorists and experimentalists are still driven to answer questions not explained by the current prevailing model. Does supersymmetry exist? What are dark matter and dark energy? What particles have we yet to discover?

    Supersymmetry standard model
    Standard Model of Supersymmetry

    “If the answers are found, it will take us even deeper into what we are supposed to be doing as high-energy physicists,” Lane says. “But it probably isn’t going to be this lightning flash that happens on one Monday afternoon.”

    t&R
    Ting and Richter
    Courtesy of: SLAC National Accelerator Laboratory

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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