TheWASA-at-COSY experiment is, besides meson production processes, dedicated to studies on rare and forbidden decays of light mesons. In extensive η-production beam times, a high-statistics data set have been collected by means of proton-proton scattering which opens the door to studies on forbidden decays like the C-parity violating process η → π0e+e−. In this article, an optimized detector calibration leading to a significantly improved missing mass resolution and a preliminary decay analysis are presented
