Modified Analysis of Nucleon Electromagnetic Form-Factor Data

Abstract

We suggest that the usual procedure for analyzing nucleon electromagnetic form-factor data be modified by retaining in a suitable manner the dispersion-integral contributions present even after removal of known vector-meson contributions. This allows a more general analysis consistent with all known restrictions on the form factors. The form factors are parametrized and the parameters determined by comparison with experimental data. It is possible to obtain reasonable fits to all of the data with a total of two parameters. The resulting form factors are suitable for the extraction of useful numbers, including the residues at the known vector-meson poles. In addition, analytic continuation to the annihilation region is well-defined and allows meaningful comparison with data there. It is not necessary to make statements about the existence of vector mesons other than $\rho$, $\omega$, $\varphi$. We use our results to discuss the $\rho$ dominance of the isovector form factor and to estimate the vector-meson-nucleon coupling constants.