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arXiv · 2006.12543

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

Jaseer Ahmed·P. G. Blunden·W. Melnitchouk
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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 $Δ(1232)~\!3/2^+$ 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.

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Jaseer Ahmed, P. G. Blunden, W. Melnitchouk. 2020-06-22. Two-photon exchange from intermediate state resonances in elastic electron-proton scattering. https://doi.org/10.1103/physrevc.102.045205

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