Study of the

At the turn of October and November 2008, the WASA-at-COSY collaboration performed an experiment to collect data on the η meson decays in pd → 3He η reactions. This report presents results of a study of the η → e+e−γ conversion decay. The desired feature of this decay is that the final state e+e− pairs come from the conversion of a virtual γ quantum and, therefore, they constitute a rich source of knowledge about the electromagnetic structure of decaying meson. This is a very important characteristic when it comes to study of a short-lived neutral particle like the η meson, because the classical methods of particle scattering are not applicable here. The analysis performed on one third of the p-d data sample collected using the WASA-at-COSY detector, lead to the extraction of the η transition form factor as a function of the e+e− mass and to the calculation of the slope parameter, related to the charge radius of the η meson