Study of the η → e⁺e⁻γ Decay Using WASA-at-COSY Detector System

¹ Institute of Physics, Jagiellonian University, PL-30059 Cracow, Poland
² Institut für Kernphysik and Jülich Center for Hadron Physics, D-52425 Jülich, Germany

^a e-mail: m.hodana@gmail.com

Abstract

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.