The Upper Energy Limit of HBChPT in Pion Photoproduction

TL;DR

This paper evaluates the energy range where Heavy Baryon Chiral Perturbation Theory (HBChPT) accurately describes neutral pion photoproduction, finding it effective up to about 170 MeV before empirical methods outperform it.

Contribution

The study provides a detailed assessment of HBChPT's applicability limit in pion photoproduction using recent high-quality experimental data.

Findings

HBChPT agrees well with data up to ~170 MeV

Beyond 170 MeV, empirical parametrizations outperform HBChPT

The analysis sets a clear energy boundary for HBChPT validity

Abstract

We assess the energy limit up to which Heavy Baryon Chiral Perturbation Theory (HBChPT) can be applied to the process of neutral pion photoproduction from the proton by analyzing the latest data collected by the MAMI/A2 collaboration at Mainz. The high-quality differential cross section and the photon asymmetry measured data allow to test the theory at a level not previously achieved. We find that, within the current experimental status, the agreement between theory and experiment is excellent up to $\sim$170 MeV. Above this energy HBChPT fails to provide high-quality fits while an empirical parametrization of the multipoles still provides an excellent description of the data.