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How Pentaquarks May Lead To the Discovery of New Fundamental Physics
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.
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!"
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.
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/...