Low-energy vector-dominance-model description of reactions

The threshold enhancement of is reexamined. We claim that factorization, when explicitly evaluated for low energies, does account for most, if not all, of the reported cross-section data. Our analysis indicates an important low-energy isoscalar-photon contribution yielding a large production cross section. Our approach implies that the vector-dominance model is the major low-energy mechanism. This is supported by the preliminary available information on total cross sections.