Search for C violation in the decay η → π0e+e− with WASA-at-COSY

Abstract

We report on the search for the rare decay η→π0e+e−which is of interest to study Cviolation in the electromagnetic interaction which would indicate contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The ex-periment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Jülich, Germany. In total 3 ×107events of the reaction pd→3Heηhave been recorded at an excess energy of Q=59.8MeV. Based on this data set the Cparity violating decay η→π0γ∗→π0e+e−via a single-photon intermediate state has been searched for, resulting in new upper limits of η→π0e+e− / η→π+π−π0 <3.28 ×10−5and η→π0e+e− / (η→all)<7.5 ×10−6(CL=90%), respectively.