Neutron charge radius and the neutron electric form factor

For nearly forty years, the Galster parametrization has been employed to fit existing data for the neutron electric form factor, GnE, vs the square of the four-momentum transfer, Q 2. Typically this parametrization is constrained to be consistent with experimental data for the neutron charge radius. However, we find that the Galster form does not have sufficient freedom to accommodate reasonable values of the radius without constraining or compromising the fit. In addition, the GnE data are now at sufficient precision to motivate a two-parameter fit (or three parameters if we include thermal neutron data). Here we present a modified form of a two-dipole parametrization that allows this freedom and fits both GnE (including recent data at both low and high four-momentum transfer) and the charge radius well with simple, well-defined parameters. Analysis reveals that the Galster form is essentially a two-parameter approximation to the two-dipole form but becomes degenerate if we try to extend it naturally to three parameters.