Studying

The η-meson is a unique tool in a way that it provides access to (rare) decay processes, which allow to probe symmetry breaking phenomena, determine transition form factors, or to explore the anomalous sector of QCD. Those decays have been studied with the WASA-at-COSY experiment. Two data sets with different η-production mechanisms have been acquired. The analysis of those data sets are restricted to: The investigation of the isospin violating decay η → π+π−π0; Exploring the box anomaly in η → π+π−γ; The determination of the electromagnetic transition form factor via the reactions: η → e+e− and η → e+e−e+e−; Testing the CP-violation in η → π+π−e+e−. An overview of the analysis of those decays will be given in the following