Scattering Observables of NN Interaction in the SU6 Quark Model

Abstract

Scattering observables of the N N interaction are investigated in a recent quark model developed for a unified description of N N and hyperon-nucleon systems. Satisfactory agree­ ment with experiment is obtained for the total and differential cross sections, as well as the polarization observables of np and pp scattering. Since quantum chromodynamics (QCD) is widely accepted as the dynamics un­ derlying the strong interaction, 1) there have been many attempts to investigate the baryon-baryon interaction in terms of QCD-inspired quark models. The study of the nucleon-nucleon (N N) interaction is particularly important, not only because the N N system is most fundamental, but also because all the essential aspects and ingredients of this kind of approach are already involved in this system. The most successful quark-model study of the N N interaction is carried out within the frame­ work of the resonating-group method (RGM) applied to the (3q)-(3q) system, in which the gluon effect is incorporated through the color analog of the Fermi-Breit (FB) interaction in the one-gluon exchange approximation, and through a simple power-law confinement potential put in by hand. 2) The conclusion drawn from such calculations can be summarized as follows: The phase-shift equivalent local poten­ tials derived from the (3q)-(3q) model of N N scattering are short-ranged, strongly energy dependent and purely repulsive. The repulsive core of several hundred MeV is determined mainly by the color-magnetic term of the FB interaction (for even-parity states) and by the effect of the Pauli principle (for odd-parity states). Although the confinement potential strongly influences single-baryon properties (such as the ab­ solute values of baryon masses), it plays an insignificant role in the N N scattering. The most important conclusion of the simple (3q)-(3q) RGM is that it gives only the extreme short-range part of the N N interaction and fails to make a natural connec­ tion to the mesonic degree of freedom responsible for the medium- and long-range attractive part of this interaction. In recent quark-model studies for the N N inter­ action, various kinds of effective meson-exchange potentials (EMEP) are therefore introduced more or less phenomenologically, to achieve a realistic description of the experimental data. Recent interest in the hyperon-nucleon (Y N) interaction has motivated the reex­ amination of the EMEP employed in the quark model for the N N interaction. In our