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arXiv · 1312.0310

Meson exchange effects in elastic $ep$ scattering at loop level and the electromagnetic form factors of the proton

Hong-Yu Chen·Hai-Qing Zhou
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Abstract

A new form of two-photon exchange(TPE) effect is studied to explain the discrepancy between unpolarized and polarized experimental data in elastic $ep$ scattering. The mechanism is based on a simple idea that apart from the usual TPE effects from box and crossed-box diagrams, the mesons may also be exchanged in elastic $ep$ scattering by two-photon coupling at loop level. The detailed study shows such contributions to reduced unpolarized cross section ($σ_{un}$) and polarized observables ($P_t,P_l$) at fixed $Q^2$ are only dependent on proton's electromagnetic form factors $G_{E,M}$ and a new unknown universal parameter $g$. After combining this contribution with the usual TPE contributions from box and crossed-box diagrams, the ratio $μ_pG_E/G_M$ extracted from the recent precise unpolarized and polarized experimental data can be described consistently.

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Hong-Yu Chen, Hai-Qing Zhou. 2014-10-21. Meson exchange effects in elastic $ep$ scattering at loop level and the electromagnetic form factors of the proton. https://doi.org/10.1103/physrevc.90.045205

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