Two-photon exchange from intermediate state resonances in elastic electron-proton scattering

Abstract

We use a recently developed dispersive approach to compute the two-photon exchange (TPE) correction to elastic electron-proton scattering, including contributions from hadronic $J^P=1/2^{\pm }$ and $3/2^{\pm }$ resonant intermediate states below~1.8~GeV. For the transition amplitudes from the proton ground state to the resonant excited states we employ new exclusive meson electroproduction data from CLAS at $Q^2\lesssim 5$~GeV${}^2$, and we explore the effects of both fixed and dynamic widths for the resonances. Among the resonant states, the $N(1520)3/2^{-}$ becomes dominant for $Q^2\gtrsim 2$~GeV${}^2$, with a sign opposite to the comparably sized $\Delta (1232)3/2^{+}$ contribution, leading to an overall increase in the size of the TPE correction to the cross section relative to the nucleon only contribution at higher $Q^2$ values. The results are in good overall agreement with recent $e^{+}p$ to $e^{-}p$ cross section ratio and polarization transfer measurements, and provide compelling evidence for a resolution of the electric to magnetic form factor ratio discrepancy.

arXiv comment40 pages, 15 figures

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