Chiral dynamics in the gamma p --> p pi0 reaction

TL;DR

This paper studies neutral pion production on protons near threshold using covariant chiral perturbation theory with Delta resonances, showing improved convergence and agreement with precise experimental data.

Contribution

It introduces the explicit inclusion of Delta degrees of freedom in covariant chiral perturbation theory for this reaction, enhancing convergence and data agreement.

Findings

Including Delta resonances improves theoretical convergence.

The model aligns well with Mainz microtron data.

Chiral dynamics are effectively described near threshold.

Abstract

We investigate the neutral pion photoproduction on the proton near threshold in covariant chiral perturbation theory with the explicit inclusion of Delta degrees of freedom. This channel is specially sensitive to chiral dynamics and the advent of very precise data from the Mainz microtron has shown the limits of the convergence of the chiral series for both the heavy baryon and the covariant approaches. We show that the inclusion of the Delta resonance substantially improves the convergence leading to a good agreement with data for a wider range of energies.