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Science

How Pentaquarks May Lead To the Discovery of New Fundamental Physics 65

Posted by samzenpus from the that-looks-new dept.
StartsWithABang writes: Over 100 years ago, Rutherford's gold foil experiment discovered the atomic nucleus. At higher energies, we can split that nucleus apart into protons and neutrons, and at still higher ones, into individual quarks and gluons. But these quarks and gluons can combine in amazing ways: not just into mesons and baryons, but into exotic states like tetraquarks, pentaquarks and even glueballs. As the LHC brings these states from theory to reality, here's what we're poised to learn, and probe, by pushing the limits of quantum chromodynamics.
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How Pentaquarks May Lead To the Discovery of New Fundamental Physics More

How Pentaquarks May Lead To the Discovery of New Fundamental Physics

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  • Actually, you CAN'T do that (Score:5, Interesting)

    by wonkey_monkey ( 2592601 ) on Thursday July 23, 2015 @04:12AM (#50166361) Homepage

    At higher energies, we can split that nucleus apart into protons and neutrons, and at still higher ones, into individual quarks

    In one sense that seems to be something you really can't do. The force between free quarks increases with distance to about 10,000N, then remains constant (no, I have no idea how this makes any sense, but it's what I read). Any force sufficient to tear two quarks apart is sufficient to generate new quarks which then bind with the "free" quarks. So you never see quarks by themselves.

    IANAP, though. Does the above really mean that if you had two free quarks separated by a kilometre or a light year, that there would still be that constant 10,000N force between them?

    • Re:Actually, you CAN'T do that (Score:5, Interesting)

      by Carewolf ( 581105 ) on Thursday July 23, 2015 @04:18AM (#50166377) Homepage

      At higher energies, we can split that nucleus apart into protons and neutrons, and at still higher ones, into individual quarks

      In one sense that seems to be something you really can't do. The force between free quarks increases with distance to about 10,000N, then remains constant (no, I have no idea how this makes any sense, but it's what I read). Any force sufficient to tear two quarks apart is sufficient to generate new quarks which then bind with the "free" quarks. So you never see quarks by themselves.

      IANAP, though. Does the above really mean that if you had two free quarks separated by a kilometre or a light year, that there would still be that constant 10,000N force between them?

      Plus that we are not even sure quarks are individual things. They might just be eigenvalues of particle properties, nice to calculate on, but not necessarily anything real in themselves.

      • Re: (Score:3, Interesting)

        by Anonymous Coward

        The top quark can exist without hadronizing, so the properties of "naked" quarks can be studied. Not sure if just an eigenvector can explain that.

      • What is a real individual thing? In the end, if we can model it and we can measure it, it's about as real as anything in our world can be.

    • Any force sufficient to tear two quarks apart is sufficient to generate new quarks which then bind with the "free" quarks.

      Sounds like the War on Terrorism in a microscopic edition. Fractal universe confirmed!

    • Re:Actually, you CAN'T do that (Score:4, Informative)

      by fizassist ( 4194645 ) on Thursday July 23, 2015 @06:36AM (#50166719)

      In one sense that seems to be something you really can't do. The force between free quarks increases with distance to about 10,000N, then remains constant (no, I have no idea how this makes any sense, but it's what I read).

      IAAP, and you can "separate" a nucleon into constituent quarks in a sense. You're right in that you can't take them a kilometer apart because of the range behavior of the strong nuclear force that you cite. Instead, you create extremely high energy density region that makes the nucleons lose their identity, and the constituent quarks are free to interact with each other (a Quark-Gluon Plasma). This is done by colliding heavy ions, which creates a high energy density region that has some extent to it (as opposed to proton-proton collisions). The quarks can then "condense" out of this plasma into exotic things like pentaquarks.

    • Re:Actually, you CAN'T do that (Score:5, Informative)

      by ceoyoyo ( 59147 ) on Thursday July 23, 2015 @08:47AM (#50167397)

      You can't ever get two quarks very far apart. That property arises because the gluon, the force carrier for the strong force, has a strong charge of it's own. That's as if photons were electrically charged. When two quarks exchange virtual gluons the gluons exchange virtual gluons with everything around as well. The bigger the distance between the quarks, the more space for colour charged gluons between them, so the stronger the force.

      When you pull two quarks further and further apart, at some point it's energetically favourable for a couple of virtual quarks to pop into existence and you end up with a couple of mesons instead of two free quarks. That's what happens in accelerators: nobody ever sees quarks, they see sprays of particles that indicate a hadron was blown apart and the constituent quarks then reformed into hadrons.

      It's called colour confinement: https://en.wikipedia.org/wiki/... [wikipedia.org]

      • Re:Actually, you CAN'T do that (Score:4, Funny)

        by Anonymous Coward on Thursday July 23, 2015 @09:29AM (#50167749)

        "You can't ever get two quarks very far apart. That property arises because the gluon, the force carrier for the strong force, has a strong charge of it's own. "

        If you tried to separate "it" from "is", will the force generate new apostrophes?

        • Re: (Score:2)

          by hawkfish ( 8978 )

          "You can't ever get two quarks very far apart. That property arises because the gluon, the force carrier for the strong force, has a strong charge of it's own. "

          If you tried to separate "it" from "is", will the force generate new apostrophes?

          Pedantry AND wit - what is /. coming to?

    • The force between free quarks increases with distance to about 10,000N, then remains constant (no, I have no idea how this makes any sense, but it's what I read).

      According to Wikipedia [wikipedia.org] it's because gluons, which mediate the Strong Force interaction between quarks, also feel said force themselves (that is, they carry color charge(. So rather than disperse with distance like, say, photons do, they tend to stick together and form "ropes".

      So it's analogous to how a flashlight loses power faster than a laser.

    • IAAP and your mostly correct. However the force is no where near 10kN. However lets assume 1N, with 1m of seperation that is 1J of energy. Or enough energy to produce about a billion protons. So yea true separation distance are small before more quarks are created.

  • Not a summary (Score:5, Informative)

    by dinfinity ( 2300094 ) on Thursday July 23, 2015 @04:21AM (#50166389)

    This is not a summary, but a teaser. Let's keep that kind of bullshit off Slashdot.

    Actual summary:
    "Recently, the existence of pentaquarks, predicted by quantum chromodynamics, was confirmed. This sortof validates quantum chromodynamics. [Intro to quantum chromodynamics]. We could find many more particles predicted by quantum chromodynamics in the future!"

  • ..but I have no idea what any of it means.
  • Early discoveries and hypotheses on small stuff have led to immense improvements in chemistry and electronics, and the development of nuclear power. Is there even a hint of a notion that this sort of work is going to lead to something practical? If so, what?

  • TFS lost me right there. There is No Such Thing(tm)

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