Two photon exchange amplitude with \pi N intermediate states: P33 channel

TL;DR

This paper evaluates the two-photon exchange correction in elastic electron-proton scattering considering  N intermediate states, focusing on the P33 channel to include the (1232) resonance with realistic width, revealing significant corrections at higher momentum transfer.

Contribution

It provides a detailed calculation of TPE effects with  N states, including resonance width, improving upon previous zero-width resonance models.

Findings

TPE correction to electric form factor is the largest among corrections.

The correction increases with Q^2 and surpasses elastic contributions beyond 2.5 GeV^2.

Results agree with previous zero-width resonance calculations.

Abstract

We consider two-photon exchange (TPE) in the elastic electron-proton scattering and evaluate the effect of \pi N (pion + nucleon) intermediate hadronic states. Among different \pi N states, we concentrate on the P33 channel; thus we effectively include Delta(1232) resonance with realistic width and shape and corresponding background as well. In agreement with the previous result, obtained for the zero-width resonance, we observe that the TPE correction to the electric form factor is the largest one; it grows with Q^2 and at Q^2 > 2.5 GeV^2 exceeds the corresponding elastic contribution.