Unitary symmetry in baryon-baryon scattering

Abstract

Motivated by a recent suggestion that an SU(3) selection rule may explain the narrow widths of some hypernuclear excitations in the Σ continuum, we re-examine the role of unitary symmetry in low energy baryon-baryon (BB) interactions. A direct examination of the BB scattering data indicates that SU(3) symmetry is broken, but leaves us with several alternative schemes for describing the mechanism of symmetry breaking. We study the one-boson exchange (OBE) model in some detail, and relate the usual spin-isospin representation of BB potentials/amplitudes to the quadratic and cubic SU(3) Casimir operators F 2 and G 3. For the long-range part of the BB interaction (pseudoscalar meson exchange), the G 3 amplitude is important, whereas the short-range part (quark-gluon or vector meson exchange) leads to the F 2 form. In the Nijmegen OBE model, which is very successful in reproducing the data, SU(3) symmetry is maintained at the level of coupling constants, and broken through the use of observed meson and baryon masses in the calculation of baryon-baryon potentials V BB. In spite of the sizable mass differences and the use of phenomenological hard cores at short distances in the OBE approach, certain SU(3) relations are still reasonably well satisfied. We also discuss other mechanisms of SU(3) breaking which involve an explicit hypercharge dependence of the BB amplitudes.