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arXiv · 1407.2711

$\Delta(1232)$ Resonance Contribution to Two-Photon Exchange in Electron-Proton Scattering Revisited

Hai-Qing Zhou·Shin Nan Yang
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Abstract

We revisit the question of the contributions of two-photon exchange with $\Delta(1232)$ excitation to the electron-proton scattering in a hadronic model. Three improvements over the previous calculations are made, namely, correct vertex function for $\gamma N\rightarrow\Delta$, realistic $\gamma N\Delta$ form factors, and coupling constants. The discrepancy between the values of $R\equiv \mu_p G_E/G_M$ extracted from Rosenbluth technique and polarization transfer method can be reasonably accounted for if the data of Andivahis {\it et al.} \cite{Andivahis94} are analyzed. However, substantial discrepancy remains if the data of Qattan {\it et al.} \cite{Qattan05} are used. For the ratio $R^\pm$ between $e^\pm p$ scatterings, our predictions appear to be in satisfactory agreement with the preliminary data from VEPP-3. The agreement between our model predictions and the recent measurements on single spin asymmetry, transverse and longitudinal recoil proton polarizations ranges from good to poor.

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Hai-Qing Zhou, Shin Nan Yang. 2014-07-10. $\Delta(1232)$ Resonance Contribution to Two-Photon Exchange in Electron-Proton Scattering Revisited. https://doi.org/10.1140/epja/i2015-15105-1

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