Few-Body Systems

, Volume 37, Issue 1, pp 1-31

First online:

On Nucleon Electromagnetic Form Factors

  • R. AlkoferAffiliated withInstitut für Theoretische Physik, Universität Tübingen
  • , A. HöllAffiliated withPhysics Division, Argonne National Laboratory
  • , M. KlokerAffiliated withInstitut für Theoretische Physik, Universität Tübingen
  • , A. KrassniggAffiliated withPhysics Division, Argonne National Laboratory
  • , C. D. RobertsAffiliated withPhysics Division, Argonne National LaboratoryFachbereich Physik, Universität Rostock

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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 Q 2 ≲ 2 GeV2 but vanish with increasing momentum transfer. Hence, larger Q 2 experiments probe the quark core. The calculated behaviour of G E p (Q 2)/G M p (Q 2) on Q 2 ∈ [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.