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How does fragmentaton occur?

  1. Consider

    e+e* -> q+q* in the centre of mass frame. Where I am using star for antiparticle.

    the quark and anti quark pair cannot exist alone due to color confinement so they form 2 jets that will go in opposite directions (to conserve momenta). Where do these jets come from? Do the quarks emit gluons that then form more quarks? Or are they spontaneously produced from the vaccum or something?

    Also the jets can be mesons or baryons but if they form baryons then one jet has to be baryons and the other has to be anti-baryons to conserve baryon number correct?
  2. jcsd
  3. mfb

    Staff: Mentor

    Both options are possible, but once you get to hadronization the perturbative description (in particular, everything you can write down as Feynman diagram) becomes problematic.
    A single particle is not a jet, but in total, the baryon number is conserved, sure.
  4. Bill_K

    Bill_K 4,159
    Science Advisor

    Yes. Jets are primarily due to gluon emission, and arise from the acceleration of a color-charged particle, (a parton, either a quark or gluon), analogous to the bremsstrahlung emitted by an accelerating electromagnetically charged particle.

    Jets are side effects, useful to the experimenter because they reveal the presence of the intermediate high-energy parton. But the original parton is not part of the jet. The jet itself is colorless. The original parton is pulled back.
  5. Ok so when the qq* pair are produced they will emit 2 gluons that will each turn to jets (in the case of 2 jet events)? Also these gluons must be very energetic to conserve energy of all the particles created in the jet right?
  6. mfb

    Staff: Mentor

    No, the quarks initiate the jets. If you just get two jets, all the additional gluons and quarks go (roughly) in the same direction as one of the initial quarks.
    Very energetic gluons, not aligned with a quark, would lead to additional jets.
  7. A single quark can radiate multiple gluons.

    In the system you are talking about, the important thing is conserving the quantum numbers.

    So baryon, lepton, colour bla bla bla.

    This conservation is overall. So in fact, this means that the two jets of energetic bunches of particles have to know about one another. This is required to totally conserve the colourless state originated by the e e* beams.
  8. Bill_K

    Bill_K 4,159
    Science Advisor

    No, each jet by itself is colorless.
  9. Yes. If you mean the reconstructed object of colourless particles is colourless, I agree.

    I am talking about the formation of the colourless objects. Which is what the question is about. To form the colourless hadrons, the two quark initiated jets must know about one another.

    In analogy with jets initiated by a colour octet (q q* pair from tree level gluon exchange) at a hadron collider. This must know about the rest of the colliding beams else colour confinement doesn't work.
  10. Bill_K

    Bill_K 4,159
    Science Advisor

    Again, no. The original quarks are correlated, but the jets are both colorless and completely uncorrelated. I don't know how else to say this.

    Suppose the original reaction produces a red quark and an antired antiquark, and let's follow what happens to the quark. Suppose it emits a red antiblue gluon. Typically this gluon will simply be reabsorbed. But suppose the quark (which is now blue) then emits a second gluon, one which is blue antired. The gluons taken together are colorless, and together they can separate a macroscopic distance, going on to create a jet by fragmenting into a number of hadrons. Again, the quark does not require "knowledge" of what color gluons it must emit to produce the jet, since any other choice will be reabsorbed.

    The quark (which is now red) is pulled back, and reinteracts with the original antiquark, which in the meantime has done something which I don't know or care about.
  11. You are just repeating what I said.

    "The quark (which is now red) is pulled back, and reinteracts with the original antiquark, which in the meantime has done something which I don't know or care about."

    This interaction is what I am talking about and is important - without this interaction colour confinement would not work and the string/cluster models would make no sense. Also, local parton hadron duality (which is observed) says that the hadrons formed from the quarks should have the same quantum numbers and energy-momentum flow. So your suggestion that the quark spits off the colour singlet jets via gluons doesn't make sense to me.
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