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

TL;DR

This paper revisits the contribution of $232$ resonance to two-photon exchange in electron-proton scattering, improving the hadronic model with better vertex functions, form factors, and coupling constants, and compares predictions with experimental data.

Contribution

It introduces three key improvements to previous models of two-photon exchange involving the $232$ resonance, enhancing accuracy in scattering predictions.

Findings

Reasonably explains the discrepancy in $R$ from Rosenbluth and polarization methods for certain data.

Predictions for $e^\u00b1 p$ scattering ratios agree with VEPP-3 data.

Model predictions for spin asymmetries and recoil polarizations vary in agreement with recent measurements.

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.