Toward Understanding the Quark Parton Model of Feynman

W-Y. P. Hwang

《Chinese Journal of Physics》 30卷5期 (1992/10) Pp. 617-644

並列摘要

The quark parton model of Feynman, which has been used for analyses of high energy physics experiments, invokes a set of parton distributions in the description of the nucleon structure (the probability concept), contrary to the traditional use of wave functions in nuclear and medium ener,7 physics for structural studies (the amplitude concept). In this paper, I first review briefly how the various parton distributions of a nucleon may be extracted from high energy physics experiments. I then proceed to consider how the sea distributions of a free nucleon at low and moderate Q^2 (e.g., up to 20 GeV^2) may be obtained in the meson-baryon picture, a proposal made by Hwang, Speth, and Brown. Using the form factors associated with the couplings of mesons to baryons such as πNN, πNΔ, and KNΛ couplings which are constrained by the CCFR neutrino data, we find that the model yields predictions consistent with the CDHS and Fermilab E615 data on the sea-to-valence ratio. We also find that the recent finding by the New Muon Collaboration (NMC) on the violation of the Gottfried sum rule can be understood quantitatively. Finally, we consider, using the pion as the example, how valence quark distributions of a hadron may be linked to the hadron wave function written in the light-cone language. Specifically, we use the leading pion wave function that is constrained by the QCD sum rules, and find that, at Q^2 ≈ (0.5 Gev)^2, the leading Fock component accounts for about 40% of the observed valence quark distributions in the pion. The question of how to generate the entire valence quark distributions from the valence quark distribution calculated from the leading Fock component is briefly considered again using the specific proposal of Hwang, Speth, and Brown.