On Nucleon Electromagnetic Form Factors

Abstract.

A Poincaré-covariant Faddeev equation, which describes baryons as composites of confined-quarks and -nonpointlike-diquarks, is solved to obtain masses and Faddeev amplitudes for the nucleon and Δ. The amplitudes are a component of a nucleon-photon vertex that automatically fulfills the Ward-Takahashi identity for on-shell nucleons. These elements are sufficient for the calculation of a quark core contribution to the nucleons’ electromagnetic form factors. An accurate description of the static properties is not possible with the core alone but the error is uniformly reduced by the incorporation of meson-loop contributions. Such contributions to form factors are noticeable for Q² ≲ 2 GeV² but vanish with increasing momentum transfer. Hence, larger Q² experiments probe the quark core. The calculated behaviour of G _E ^p(Q²)/G _M ^p(Q²) on Q² ∈ [2,6] GeV² agrees with that inferred from polarization transfer data. Moreover, $\sqrt{Q^2} F_2(Q^2)/F_1(Q^2)\hskip-1pt\approx$ constant on this domain. These outcomes result from correlations in the proton’s amplitude.