Mechanism of " I=1/2 Enhancement" in the Relativistic Quark Model

Abstract

In the analysis of weak non-leptonic decays (abbreviated as NLD's) of hadrons various ingredients and effects should be taken into consideration, even when the theory provides the fundamental form of the weak interaction among the constitu­ ents. It is necessary to clarify the respective roles of these ingredients in order to make a correct estimation of the physical transition amplitudes. Now it is widely believed that the fundamental weak interaction of non-lepton­ lC decay of ordinary hadrons at lower energies is given by the New-Nagoya-GIM modelll (or its extension to six-quark KM model)) with the left-handed charged currents. Then the main problems concerning NLD of ordinary hadrons can be summarized as follows: (a) to understand what is called enhancement of the LII = 1/2 amplitudes and suppression of the LII = 3/2 ones; (b) to understand consistently the observed features of the S and P waves of hyperon decays as well as kaon decays. It has long been pointed outJ that, as far as the non-leptonic weak interac­ tion H wNL is a product of color-singlet V-A currents, only the flavor-anti­ symmetric component contributes to the one- (low-lying) baryon matrix elements (B' IHwNL[B) leading to the JJ = 1/2 rule for hyperon decays in the framework of PCAC and current-algebra technique. For the recent few years some progress has been made from two different sides. First the strong interaction effects at short distances are investigated on the effective weak Hamiltonian where we meet the operators containing a certain kind of right-handed current.'J Secondly, the mag­ nitude of (B' IHnlC[B) has been discussed by using the composite model and the effect of the confinement has been argued to be large enough to account for the observed magnitude of the LII = 1/2 amplitude of hyperon decays. 5)