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Why are quarks fundamental particles?

  1. Apr 30, 2015 #1
    Are quarks really considered fundamental particles that cannot be divided further? If an up quark can transmute to a down quark and release a W+ boson which decays to a positron and a neutrino (for example) - doesn't this mean that there is substructure to a quark?

    What exactly is it that makes a particle fundamental and non divisible?
  2. jcsd
  3. Apr 30, 2015 #2
    In Standard Model, yes.

    No, it does not prove that.

    A particle is either fundamental or it is a bound state. Bound states have more degrees of freedom. A fundamental particle is completely described by its internal quantum numbers, position, momentum and spin. The internal quantum numbers must be discrete.
    In case of a bound state we have additional degrees of freedom related to the position and orientation of the constituents. These degrees of freedom are always continuous.
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