Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Behind the quark theory

  1. Feb 18, 2005 #1
    What's some of the maths and experiment that supports the theory that neutrons and protons and elctrons are made up of 3 or 2 quarks, why not 8 5 or 4 or 100, what tells us that they exists and that there are so many flavours, what masses do these quarks have and does this tally with the masses of a neutron say or an electron? why do we say 3 in a neturton but 2 in the bosons?

    Since we can't force them apart how can we be sure there is anything at all,could it just as easily be an infinite sea of quasi quarks that only come into existence when enough energy is supplied, what is it in the theories that now leads QM to be more accepted, please if you're gonna use alot of maths a good description of what your showing would be nice, assume I have a pre degree but well informed quantum understanding :smile: any answers greatly appreciated
  2. jcsd
  3. Feb 18, 2005 #2
    Baryons and mesons are consited out of 3 and 2 quarks respectively because of several conservation laws that are at hand. Conservation of energy, baryon and letpon number and so on...also the Pauli-exclusion principle plays a determining role in the distinction between baryons and mesons...

    On a more grouptheoretical level, the baryons are made up of three quarks because the tensor product of three fundamental SU(3)-colour representations (ie the quark colours) will cover they entire eightfold way. Same goes for the mesons (2 terms in the tensor product here, representing the two constituent quarks).

    The last explanaition requires some knowledge on group theory so i don't know whether you got the last part

  4. Feb 18, 2005 #3


    User Avatar

    Staff: Mentor

    1. By the early to mid 1960s, particle physicists had discovered a whole zoo of supposedly "elementary" particles besides protons, neutrons, and electrons: pions, kaons, lambdas, sigmas. xis, omegas, rhos, etas... they were getting close to running out of Greek letters! :rofl:

    They observed particles that had certain combinations of properties (charge, spin, etc.) but no particles that had certain other combinations. So Gell-Mann and Zweig proposed that these particles are actually combinations of more fundamental "things" with certain properties. They predicted that new particles should exist with certain properties, corresponding to quark combinations that hadn't been observed yet, and those particles were found. I think the omega-minus was the most important one.

    As I recall, Gell-Mann in particular was vague about whether he thought these "things" were particles in the usual sense, or something more abstract and mathematical.

    2. In the late 1960s, some physicists were scattering high-energy electrons off of protons and neutrons, and studying the characteristics of the particles that come out (scattering angle, momentum, etc.) They found some interesting regularities in their data, which Feynman explained by assuming that protons and neutrons have point-like "partons" inside them.

    Further investigation with electron-scattering and neutrino-scattering experiments, continuing through the 1970s and into the 1980s, convinced physicists that Feynman's "partons" had the properties of Gell-Mann's "quarks." When I was in graduate school during this period, one of the major goals of many experiments (including the ones that I worked on) was to test or verify this "quark-parton model."

    The Gell-Mann / Feynman quark-parton model explained preceding experiments and successfully predicted the results of many new experiments. Nobody has come up with anything better, in terms of agreement with experimental data on particle-scattering experiments and other experiments that measure the basic properties of "elementary" particles. That's why we believe in it.
  5. Feb 18, 2005 #4

    Thanks for that, looking for understanding of the fundamentals, I've read that this is true just wondering why we believe these things; much apreciated cheers guys :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook