Accurate Test of Chiral Dynamics in the boldmath$vec{gamma} p rightarrow pi^0p$ Reaction

A precision measurement of the differential cross sections $dsigma/dOmega$ and the linearly polarized photon asymmetry $Sigma equiv (dsigma_perp - dsigma_parallel) slash (dsigma_perp + dsigma_parallel)$ for the $vec{gamma} p rightarrow pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first time and provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of agreement with experiment.