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Is this all the evidence for quarks?

  1. Mar 28, 2009 #1
    1-electron scattering
    2-collider data

    3- ? is there anything else which supports the quark model or is it just those 2. from what ive read so far its just those 2 but could be incorrect so correct me if my primative understandings off
  2. jcsd
  3. Mar 28, 2009 #2


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    Deep inelastisc scattering have used more probes than just electrons. One has used neutrinos and muons too for instance. (just deep inelastic scattering is enough to say that quarks exists)

    Just saying "Collider data" is quite non precise - there are a lot of different data, which measures different things, and also many different collider experiment. It is like saying that the only evidence we have for Z bosons are collider data.

    I would say the existence of the top quark as the strongest proofs of them all to call for the existence of quarks. The top quark does not hadronize, and the signal for top quarks is really interesting.

    So you should be beware of that these proves are really good and are quite astonishing, and also some of these explorations have been awarded Nobel Prize.

    Also when someone says "from what ive read", WHAT have you read? maybe there was a misunderstanding? etc.
  4. Mar 28, 2009 #3
    so basically anything that can enter the nucleus + can be measured when it deflects has been used then.... and the results of the paterns of deflections suggest theres 3 quarks per hadrun? that seems rather clever
  5. Mar 28, 2009 #4


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    oh, no, there are more than 3 quarks in a proton, there are sea quarks as well. I just gave that answer to you in the thread you created. https://www.physicsforums.com/showthread.php?t=302385

    I think you need to calm down, and get a good book on particle physics, and try to study it. You have again some misconceptions. First of all, there are hadrons which are made up on 2 valence quarks (one quark and one anti-quark).
  6. Mar 28, 2009 #5


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    The quark model was popular for five years before the first DIS experiments. This is because
    3- A large number of the static properties (mass, spin, charge, muliplicity, magnetic moment)
    of hadrons were correlated and predicted by assuming that baryons are composed of three quarks, and mesons of a quark-antiquark pair.
  7. Mar 28, 2009 #6
    Quite frankly to me the original question is not far from "what evidence do we have for quarks apart from physics ?". If you are clever enough to devise another experiment, please go ahead. But be aware that those two points you mention actually cover many different experiments. If only in DIS, historical measurements were done inclusively, by detecting only the scattered lepton. Nowadays we perform semi-inclusive measurements, where another particle at least is detected, and exclusive measurements, where all particles in the final state are detected. We find that all those phenomena are described by the same universal "wave functions" in terms of quark-gluon degrees of freedom.

    As for collider data, again there are many different observations. You may collide two leptons or two hadrons for instance. If you collide two hadrons, you have theorems to deal with phenomena at high transverse momenta, or you have lepton pair productions (Drell-Yann). In fact it is very difficult to make an exhaustive list.

    There is no definitive evidence that anything goes wrong with the partonic picture. On the contrary, the more we try to apply it to new situation, the more confident we become that our understanding is correct.
  8. Mar 28, 2009 #7
    Could you give more details or where to look?
  9. Mar 28, 2009 #8


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    what? you don't know what hadronization is or what the top-quark signal looks like?
  10. Mar 28, 2009 #9
    Yes, I am very stupid
    So you claim that t quark do not form any bound systems with other quarks or what?
  11. Mar 28, 2009 #10


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    no you are not stupid, I asked what you was asking for.

    No, the top quark does not form any bound states, it is too short-lived, it decays before reaching out of the "perturbative scale".
  12. Mar 28, 2009 #11
    I see... And what is so special about the signal?
    BTW I heard that there is a Higgs-less model where t-anti t pairs play the role of Higgs, does it make sense?
  13. Mar 28, 2009 #12


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    the signal is that you will have a b-quark etc which will give a invariant mass peak of about 170GeV for a fermion.

    I have not heard of it, so I let someone else answer about that model.
  14. Mar 28, 2009 #13
    It depends which model exactly you are talking about. Gribov tried to do this, but he passed away before he could convince the community, and now his specific views seem out of fashion. But in any case, people still think around those kind of ideas and we should have more to test with LHC.
    Electroweak symmetry breaking: to Higgs or not to Higgs
  15. Mar 28, 2009 #14


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    When talking about this time period, it's important to distinguish between quarks, the entities postulated by Gell-Mann and others, to account for the patterns of properties among hadrons, and partons, the hard point-like entities inside nucleons that were postulated by Feynman and others to account for the results of deep inelastic scattering experiments.

    In the 1970s, it was by no means certain that quarks and partons were the same thing. One of the main goals of deep inelastic scattering experiments of the time (including the neutrino experiments that I worked on as a graduate student), was to test what was then called the "quark-parton model," which is now a basic part of the "standard model." One of the professors in my research group warned me not to get too attached to the quark-parton model, because it might turn out to be wrong.
  16. Mar 29, 2009 #15
  17. Mar 29, 2009 #16
    alright, but now what im mainly wondering is how the DIS experiments support the quark model. i dont know how by shooting particle at the nucleus that it can differenciated that theres 3 quarks in a hadrun vs there being 9999. just by the paths of the deflections?
    Last edited: Mar 29, 2009
  18. Mar 29, 2009 #17
    This very same question you asked just a few hours earlier on this forum. It might be more constructive if you do not ignore the answers you were already given.

    It so happens that neutrinos respond differently to matter and anti-matter. So counting the difference between matter and antimatter inside a proton can be done by comparing the scattering of neutrinos and antineutrinos. It is by no means simple. But the observations agree with the theory.
  19. Mar 29, 2009 #18

    Vanadium 50

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    A few comments:

    As pointed out, there are a great many DIS experiments (including some at colliders - ZEUS and H1) and they clearly indicate the presence of three valance quarks - one type with charge +2/3 and the other with -1/3. It is, however, difficult to explain the details of how this can be extracted before someone understands (and by "understands", I mean "can calculate") the basics of DIS. Oh, and it's deeply inelastic scattering.

    While baryon magnetic moments are often touted as a success of the quark model, it's not the best example. Any theory that has SU(3) flavor symmetry will make the same predictions as the quark model. So while it's evidence in favor of the quark model (and evidence against alternatives), it's not as compelling as it's usually advertised.

    It's believed true that the top quark decays before it hadronizes, so one actually does observe a bare quark. However, there's no experimental evidence of this at the moment. One would need to study the angular correlations between polarized top quark pairs, and there just aren't enough of them out there to make a convincing measurement. We just have to wait.

    I have no idea what granpa is talking about with the Delta. It's a hadron, to be sure, and it's therefore made of quarks, but it was not a particularly important stepping stone on the road to the quark model. The better example was the Omega-minus baryon, which was a state predicted by the quark model and (at the time) was undiscovered. Nick Samios and collaborators looked for it, and discovered it with exactly the predicted properties.

    A powerful case for quarks is, in my mind, the energy levels of quarkonium - bound states of a heavy quark and an antiquark. These have energy levels similar to that of a hydrogen atom, and as such illustrate the dynamics of quark behavior. These measurements show that there are actual physical objects with the quark quantum numbers moving around inside the hadron.
  20. Mar 29, 2009 #19
    no i didnt
    thats impossible neutrinos go through protons
  21. Mar 29, 2009 #20

    Vanadium 50

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    So, JTBell, who worked on exactly these experiments (see above) is wrong? Or lying?

    What makes you think that you know better than someone who actually did the experiment?
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