Improved Tests of Relations for Baryon Isomultiplet Splittings

The least well-known octet baryon mass is MΞ0 = 1314.9 ± 0.6 MeV. The prospect of an improved measurement of its mass by the KTeV experimental program at Fermilab, and opportunities for improvements in charged and excited hyperon and ∆ mass measurements, makes it timely to re-examine descriptions of isospin splittings in baryons containing light quarks. By examining such relations as the Coleman-Glashow relation Mn −Mp +MΞ− −MΞ0 = MΣ− −MΣ+ one can distinguish between those models making use of oneor two-body effects involving quarks and those involving genuine three-body effects. A hierarchy based on an expansion in 1/Nc, where Nc is the number of quark colors, is useful in this respect. The present status of other quark-model mass relations involving Λ− Σ mixing and the baryon decuplet is also noted, and the degree to which one can determine parameters such as quark mass differences and individual electromagnetic contributions to splittings is discussed. Revised version submitted to Phys. Rev. D.