Model-independent analysis of experimental baryon magnetic moments

The failure of simple constituent-quark models' to explain' the new experimental values of X and magnetic moments ' contrasts sharply with the remarkable success of the naive constituent-quark model in describing the nucleon and A magnetic moments"" and the hadron mass spectrum. " " The underlying dynamical reasons for this success are not understood and it all may be accidental, ' However, there may also be a simple explanation which awaits discovery from clues in the experimental data. This paper presents a model-independent analysis of the experimental data and precisely defines the frontier between the regions where the simple model works well and where it breaks down badly. The discrepancies in the X and magnetic moments are shown below to indicate a quenching of the magnetic moments of the nonstrange quarks in strange baryons. The magnetic moment of the strange quark, however, is not similarly quenched, thus ruling out scaling factors determined by hadron masses. 4 Furthermore, the successful mass relations" ' between mesons and baryons and the baryon magnetic moment suggests that no such quenching occurs in the color magnetic moments of the nonstrange quarks which are responsible for the hyperfine splitting in the simple models. The only proposed model with the qualitative features suggested by these regularities in the data is the pionexchange model of Brown et al." The two-body pion-exchange contribution affects only non'strange quarks since strange quarks are not coupled to the pion. Furthermore, the pion-exchange current carries electric charge but is color neutral and contributes to the electromagnetic moment without contributing to the color magnetic moment and spoiling the relations between hyperfine splittings. Previous attempts to explain the discrepancies by using linear combinations of baryon moments which project out individual quark contributions' have not given convincing results because of the large errors in the X moments, particularly the X . The present analysis chooses two functions of the baryon moments which approximately project out nonstrangeand strange-quark contributions while avoiding large contributions from poorly known moments with large errors: