Toward Understanding the Quark Parton Model of Feynmant

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 Q2 (e.g., up to 20 Ge?) 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 nNN, xNA, and KNA couplings which are constrained by the CCFR
neutrino data, we find that the model yields predictions consistent with the CDHS and Fermilab
E61S 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*
= (0.5 Gev2, 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.