Determination of the Strange Nucleon Form Factors

The strange contribution to the electric and magnetic form factors of the nucleon is determined at a range of discrete values of $Q^2$ up to $1.4{\mathrm{GeV}}^2$. This is done by combining a recent analysis of lattice QCD results for the electromagnetic form factors of the octet baryons with experimental determinations of those quantities. The most precise result is a small negative value for the strange magnetic moment: $G_M^s(Q^2=0)=-0.07\pm 0.03{\mu }_N$. At larger values of $Q^2$ both the electric and magnetic form factors are consistent with zero to within 2 standard deviations.

Figure 1

Loop diagrams which are included in the estimate of ${{}^{\ell }R}_d^s$ from effective field theory. Figure 1 is included for the electric form factor only. The solid, dashed and wavy lines denote octet baryons, mesons, and photons, respectively.

Figure 2

Estimate of ${{}^{\ell }R}_d^s$ from effective field theory with finite-range regularization for the electric (dashed green line) and magnetic (solid blue line) form factors.

Figure 3

Strange contribution to the magnetic [3] and electric [3] form factors of the proton, for strange quarks of unit charge. The blue circles and purple squares show the results of independent analyses based on lattice simulations with scales $a=0.074(2)\mathrm{fm}$ and 0.062(2) fm, respectively. The experimental results (red stars) are taken from Refs. [2, 4, 5, 8, 9, 12].

Figure 4

Comparison of the results of this work to $1\sigma$ (red ellipse) at $Q^2=0.26{\mathrm{GeV}}^2$ for $a=0.074(2)\mathrm{fm}$ and (orange ellipse) at $Q^2=0.17{\mathrm{GeV}}^2$ at 0.062(2) fm with available experimental results at similar values of $Q^2$. The dark and pale green ellipses show $1\sigma$ and $2\sigma$ results from the A4 Collaboration at $Q^2=0.23{\mathrm{GeV}}^2$ [11] while the blue ellipses show G0 Collaboration results close to $Q^2=0.23{\mathrm{GeV}}^2$ [1, 2].