Effect of revised $R_n$ measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors

Abstract

The extended Gari-Krumpelmann (GK) model of nucleon electromagnetic form factors, in which the $\rho$, ${\rho }^{\prime }$, $\omega$, ${\omega }^{\prime }$ and $\varphi$ vector meson pole contributions evolve at high momentum transfer to conform to the predictions of perturbative QCD (pQCD), was recently shown to provide a very good overall fit to all the nucleon electromagnetic form factor (emff) data, including the preliminary $R_p$ and $R_n$ polarization data available in 2002, but excluding the older $G_{Ep}$ and $G_{En}$ differential cross section data that was inconsistent with the $R_p$ and $R_n$ data. The recently published final version of the polarization data of the electric to magnetic ratio $R_p$ differs little from the preliminary values for the former, but the new values of $R_n$ are midway between the preliminary values and those inferred from the differential cross section data and the Rosenbluth separation. A new fit of the parameters of the same model has been made with the final $R_p$ and $R_n$ data replacing the preliminary values and the addition of some new $R_n$ and $G_{Mn}$ data. Again there is a good fit to all the data when excluding the differentialcross section data that is inconsistent with the polarization data. This includes a very good fit of the $R_p$ data, which was not possible when the differential cross section $G_{(}En)$ data was used in place of the polarization $R_n$ data. Thus the change between the preliminary and final $R_n$ data, while substantial, has not impeded the good simultaneous fit to the neutron and proton data. The parameters, fit to the data and predictions of the new model are compared to those of the previous models. Low momentum structures that appear in some data analyses are partially reproduced by the model.

8 pages, 11 figures, BoxedEPS.tex included. An extra figure, 2b, has been added