SPIN-ORBIT FORCE OF HYPERON-NUCLEON INTERACTION IN THE CHIRAL SU(3) QUARK-MODEL

The spin-orbit (LS) force of the hyperon-nucleon interaction is studie d in the chiral SU(3) quark model. The symmetric LS terms from the one gluon exchange (OGE) and the scalar nonet exchange (OSE) are taken in to account. It is shown that two different treatments (the LS coupling from either OGE or OSE being artificially enhanced in order to reprod uce the P-3(J) phase shifts of the nucleon-nucleon scattering) lead to very similar LS couplings in the Sigma N(I = 3/2) channel but give qu ite different results in the Lambda N - Sigma N(I = 1/2) coupled-chann el system. A prominent resonance occurs in the P-1(1) state of the Lam bda N channel mainly due to the stronger LS(-) couplings in the Lambda N - Sigma N(I = 1/2) coupled-channel system in the OGE enhanced case. Comparatively the Lambda N P-1(1) phase shift curve exhibits a rather smooth behaviour in the OSE enhanced case. Comparing our theoretical results with the experimental data available, and considering the requ irement of the baryon spectrum, one can deduce that a stronger color-i ndependent LS coupling is preferred in the chiral quark model. (C) 199 8 Elsevier Science B.V.