Chiral symmetry and the reaction γp → π0p

We analyze the new threshold data for neutral pion photoproduction off protons in the framework of heavy baryon chiral perturbation theory. We show that large loop corrections are needed to understand the S-wave multipole E0+ and that all pertinent low-energy constants can be understood within the framework of resonance exchange saturation. Previous inconsistencies in the description of this reaction in the threshold region are resolved.