Threshold Neutral Pion Photoproduction on the Proton

TL;DR

This paper presents a covariant chiral perturbation theory calculation of neutral pion photoproduction on the proton near threshold, including the Delta(1232) resonance, improving agreement with experimental data.

Contribution

It introduces a fully covariant chiral perturbation theory calculation up to order p^3 with explicit Delta resonance inclusion for neutral pion photoproduction.

Findings

Convergence of the theory improves with Delta inclusion.

Better agreement with experimental data across energies.

Highlights importance of higher-order corrections.

Abstract

The neutral pion photoproduction on the proton near threshold has a very small scattering cross section when compared to the charged channels, which in ChPT is explained by strong cancellations between the lowest order pieces. Therefore it is very sensitive to higher-order corrections of chiral perturbation theory. We perform a fully covariant calculation up to chiral order p^3 and we investigate the effect of the inclusion of the Delta(1232) resonance as an explicit degree of freedom. We show that the convergence improves, leading to a much better agreement with data at a wide range of energies.