Transition from hadronic to partonic interactions for a composite spin-1/2 model of a nucleon
A simple model of a composite nucleon is developed in which a fermion and a boson, representing quark and diquark constituents of the nucleon, form a bound state owing to a contact interaction. Photon and pion couplings to the quark provide vertex functions for the photon and pion interactions with the composite nucleon. By a suitable choice of cutoff parameters of the model, realistic electromagnetic form factors are obtained for the proton. When a pseudoscalar pion-quark coupling is used, the pion-nucleon coupling is predominantly pseudovector. A virtual photopion amplitude is considered in which there are two types of contributions: hadronic contributions where the photon and pion interactions have an intervening propagator of the nucleon or its excited states, and contactlike contributions where the photon and pion interactions occur within a single vertex. At large Q, the contactlike contributions are dominant. The model nucleon exhibits scaling behavior in deep-inelastic scattering and the normalization of the parton distribution provides a rough normalization of the contactlike contributions. Calculations for the virtual photopion amplitude are performed using kinematics appropriate to its occurrence as a meson-exchange current in electron-deuteron scattering. The results suggest that the contactlike terms can dominate the meson-exchange current for Q>1GeV/c. There is a direct connection of the contactlike terms to the off-forward parton distributions of the model nucleon.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40206109
- Journal Information:
- Physical Review C, Vol. 62, Issue 6; Other Information: DOI: 10.1103/PhysRevC.62.065202; Othernumber: PRVCAN000062000006065202000001; 064011PRC; PBD: Dec 2000; ISSN 0556-2813
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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