Model-independent extraction of two-photon effects in elastic electron–proton scattering

We address the discrepancy between the Rosenbluth and polarization transfer data for the electromagnetic form factors of the nucleon. Assuming that the effect of two-photon corrections on the polarization transfer data is negligible, we obtain a model-independent estimate of the two-photon correction Δ2γΔ2γ. We analyze the polarization transfer data and the cross section data separately using dispersion relations. A central value as well as an error estimate for Δ2γΔ2γ is then obtained from a comparison of the two analyses. The resulting values for Δ2γΔ2γ are in good agreement with direct calculations available in the literature.