Extracting Nucleon Strange and Anapole Form Factors from World Data

The complete world set of parity-violating electron scattering data up to $Q^2\sim 0.3{\mathrm{GeV}}^2$ is analyzed. We extract the current experimental determination of the strange electric and magnetic form factors of the proton, as well as the weak axial form factors of the proton and neutron, at $Q^2=0.1{\mathrm{GeV}}^2$. Within experimental uncertainties, we find that the strange form factors are consistent with zero, as are the anapole contributions to the axial form factors. Nevertheless, the correlation between the strange and anapole contributions suggest that there is only a small probability that these form factors all vanish simultaneously.

Figure 1

The strange electric and magnetic form factors. The solid curve shows the leading-order fit, with $1\mathrm{\text{−}}\sigma$ bound shown by the dotted curves. The dashed and dash-dotted curves show the fit and error of the next-to-leading-order fit.

Figure 2

The contours display the 68% and 95% confidence intervals for the joint determination of $G_M^s$ and $G_E^s$ at $Q^2=0.1{\mathrm{GeV}}^2$. The solid ellipse shows the theoretical results of Leinweber et al. [22, 23].

Figure 3

The contours display the 68% and 95% confidence intervals for the joint determination of the form factors (defined on the axes) at $Q^2=0.1{\mathrm{GeV}}^2$. The horizontal and vertical bands in the left panel show the theory results of Leinweber et al. [22] and Zhu et al. [11], respectively. The disk in the right panel displays the theoretical result of Zhu et al. [11], with the white star indicating the zero anapole origin. [The same dipole behavior as Eq. (7) is assumed.]