Comparison of results for the electromagnetic form factors of the proton at low $Q^2$

Abstract

The goal in this work is the comparison of five parameterisations of the Sachs form factors of the proton $G^p_E$ (electric) and $G^p_M$ (magnetic) at low $4$-momentum transfer $Q^2$. It will be shown that a simple model, based on two dipoles which admit as parameters the rms electric charge radius $r_{E;p}$ and the rms magnetic radius $r_{M;p}$ of the proton, suffices for the purposes of the phase-shift analyses (PSAs) of the low-energy pion-nucleon ($\pi N$) data. The replacement of the electromagnetic form factors, currently used in the ETH model of the $\pi N$ interaction, by the parameterisation of this work will enable the removal from the PSAs of this research programme of the largest part of the dependence on extraneous sources.