Di-electrons from $\eta$ meson Dalitz decay in proton-proton collisions

The reaction $pp \to pp \eta \to pp \gamma e^+ e^-$ is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction $pp \to pp \eta$. Our focus is on di-electrons from Dalitz decays of $\eta$ mesons, $\eta\to \gamma \gamma^* \to\gamma e^+e^-$, and the role of the corresponding transition form factor $F_{\eta \gamma \gamma^*}$. Numerical results are presented for the intermediate energy kinematics of HADES experiments.