Reuber, A. G. (Corresponding author)

1995
Forschungszentrum Jülich GmbH Zentralbibliotek, Verlag Jülich

Report No.: JUEL-3117

Abstract: The exchange of two correlated pions or kaons provides the main part of the intermediate-range attraction between two baryons. In this work, a dynamical model for correlated two-pion and two-kaon exchange in the baryon-baryon interaction is presented, both in the scalar-isoscalar ($\sigma$) and the vector-isovector ($\rho$) channel. The contribution of correlated $\pi\pi$ and K$\overline{K}$ exchange is derived from the amplitudes for the transition of a baryon-antibaryon state (B$\overline{B}$') to a $\pi\pi$ or K$\overline{K}$ state in the pseudophysical region by applying dispersion theory and unitarity. For the B$\overline{B}$' $\rightarrow \pi\pi$, K$\overline{K}$ amplitudes a microscopic model is constructed, which is based on the hadron-exchange picture. The Born terms include contributions from baryon-exchange as well as $\rho$-pole diagrams. The correlations between the two pseudoscalar mesons are taken into account exactly by means of $\pi\pi$-K$\overline{K}$ amplitudes derived likewise from a meson-exchange model, which is in line with the empirical $\pi\pi$ data. The parameters of the B$\overline{B}$' $\rightarrow \pi\pi$,K$\overline{K}$ model, which are related to each other by the assumption of SU(3) symmetry, are determined by the adjustment to the quasiempirical N$\overline{N}$ $\rightarrow \pi\pi$ amplitudes in the pseudophysical region. It is found that correlated K$\overline{K}$ exchange being negligible in the N N interaction plays an important role in the $\sigma$-channel for baryon-baryon states with non-vanishing strangeness. The strength of correlated $\pi\pi$ plus K$\overline{K}$ exchange in the $\sigma$-channel decreases with the strangeness of the baryon-baryon system becoming more negative. Due to the admixture of baryon-exchange processes to the SU(3)-symmetric $\rho$-pole contributions the results for correlated $\pi\pi$-exchange in the vector-isovector channel deviate from what is expected in the naive SU(3) picture for genuine $\rho$-exchange. In present models of the hyperon-nucleon interaction contributions of correlated $\pi\pi$ and K$\overline{K}$ exchange are parametrized for simplicity by single $\sigma$ and $\rho$ exchange. Shortcomings of this effective description, e.g. the missing long-range contributions, are pointed out by comparison with the dispersiontheoretic results.

1. Institut für Kernphysik (IKP)