Pion-photon reactions and chiral dynamics in Primakoff processes at COMPASS

With the COMPASS experiment at CERN, pion-photon reactions are investigated via the Primakoff effect, implying that high-energetic pions react with the quasi-real photon field surrounding the target nuclei.The production of a single hard photon in such a pionscattering at lowest momentum transfer to the nucleus is related to pionCompton scattering. From the measured cross-section shape, the pion polarisability is determined. The COMPASS measurement is in contradiction to the earlier dedicated measurements, and rather in agreement with the theoretical expectation from chiralperturbation theory.In the same data taking, reactions with neutral and charged pions in the final state are measured and analyzed. At low energy in the pion-photon centre-of-momentum system, these reactions are governed by chiral dynamics and contain information relevant for chiralperturbation theory. At higher energies, resonances are produced and their radiative coupling is investigated.