Nucleon EM form factors computed in instanton vacuum model with parameters fixed by saddle-point equation yield proton charge radius 0.841 fm matching muonic hydrogen and good agreement on Q2 dependence of ratios.
Punjabi et al., Phys
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abstract
The ratio of the proton elastic electromagnetic form factors, $G_{Ep}/G_{Mp}$, was obtained by measuring $P_{t}$ and $P_{\ell}$, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic $\vec e p \to e\vec p$ ~reaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV$^2$. In the single-photon exchange approximation, the ratio $G_{Ep}/G_{Mp}$ is directly proportional to the ratio $P_t/P_{\ell}$. The simultaneous measurement of $P_{t}$ and $P_{\ell}$ in a polarimeter reduces systematic uncertainties. The results for the ratio $G_{Ep}/G_{Mp}$ show a systematic decrease with increasing $Q^2$, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been re-analyzed and systematic uncertainties have become significantly smaller than previously published results.
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A contact interaction model in the Dyson-Schwinger/Bethe-Salpeter framework produces elastic form factors for axial-vector mesons, with the electric form factor crossing zero at lower momentum than for vector mesons and charge radii decreasing with increasing dressed quark mass.
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Electromagnetic form factors of the nucleon from the instanton vacuum
Nucleon EM form factors computed in instanton vacuum model with parameters fixed by saddle-point equation yield proton charge radius 0.841 fm matching muonic hydrogen and good agreement on Q2 dependence of ratios.
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Elastic Form Factors of Axial-Vector Mesons: A Contact Interaction Exploration
A contact interaction model in the Dyson-Schwinger/Bethe-Salpeter framework produces elastic form factors for axial-vector mesons, with the electric form factor crossing zero at lower momentum than for vector mesons and charge radii decreasing with increasing dressed quark mass.