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Two-photon-exchange effects in the electro-excitation of the $Δ$ resonance

Vladimir Pascalutsa·Carl E. Carlson·Marc Vanderhaeghen
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Abstract

We evaluate the two-photon exchange contribution to the $e N \to e Δ(1232) \to e πN$ process at large momentum transfer with the aim of a precision study of the ratios of electric quadrupole (E2) and Coulomb quadrupole (C2) to the magnetic dipole (M1) $γ^* N Δ$ transitions. We relate the two-photon exchange amplitude to the $N \to Δ$ generalized parton distributions and obtain a quantitative estimate of the two-photon effects. The two-photon exchange corrections to the C2/M1 ratio depend strongly on whether this quantity is obtained from an interference cross section or from the Rosenbluth-type cross sections, in similarity with the elastic, $e N \to e N$, process.

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Vladimir Pascalutsa, Carl E. Carlson, Marc Vanderhaeghen. 2005-09-06. Two-photon-exchange effects in the electro-excitation of the $Δ$ resonance. https://doi.org/10.1103/physrevlett.96.012301

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