Consequences of a QQQ¯ model for meson-baryon processes

Abstract

The consequences of a QQQ¯ model for meson-baryon processes, proposed recently by one of the authors (ANM), are examined in relation to vector-meson production in association with both the octet and the decuplet of baryons. As shown in that paper, the basic quark-meson amplitudes which represent the processes PQ→PQ and PQ→VQ (where P and V denote pseudoscalar and vector mesons, respectively) can be classified in terms of two sets A^(±), where A⁽⁺⁾ represents the transition amplitude between positive-parity QQQ¯ states, and A^(-) between negative-parity QQQ¯ states. The analysis of the data, which is made most conveniently in terms of density matrices for spin-1 and spin-3/2 final-state objects, shows that several of the experimental density matrices can be fitted in terms of either of the sets A⁽⁺⁾ and A^(-), though a dominance of A(-) seems to be favored by experiment. However, density matrices for certain processes like PB→VB are found to require both A⁽⁺⁾ and A^(-) for a proper fit to the experimental data. A sum rule of the form 4/3[ρ3,3^D+√3ρ3,-1^D]=ρ1,1^V+ρ1,-1^V, which is derived for the density matrices using both the amplitudes A^(±), is found to be identical with one obtained by other authors using the additivity assumption, thus extending the range of validity of this result beyond pure additivity. Using only A(-) amplitudes, certain results on the angular distribution of the density matrices for PB→VB^* processes, especially their zero-angle behavior, are found to agree rather well with experiment, the agreement being somewhat better than for SU(6)_W. From the experimental point of view, the QQQ¯ model also seems to work somewhat better than the additivity principle in respect of density matrices like ρ1,0, inasmuch as this model predicts them to be nonzero in nonforward directions, while the additivity assumption makes them identically zero for all angles. The main conclusions of this investigation are as follows: (1) Experiment is consistent with the dynamical assumption of dominance of the QQ¯ force over the QQ force, which implies a higher priority for multiple-scattering effects within the QQQ¯ system than for the scattering of the meson by the quark constituents of the baryon. (2) Experiment is also consistent with the SU(3) and spin independence of the quark forces. (3) While the precise mechanism of the quark forces cannot be studied in this model, it nevertheless suggests a general classification of the meson amplitudes in terms of two distinct types A⁽⁺⁾ and A^(-)of which the latter is favored most by experiment.