Münster 2011 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 43: Hadronenstruktur und -spektroskopie VIII
HK 43.8: Talk
Wednesday, March 23, 2011, 18:15–18:30, HS3
Analysis of the η → e+ e− e+ e− double Dalitz decay — •Patrick Wurm — Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, Germany
The Wide Angle Shower Apparatus detector (WASA) – operated at the Cooler Synchrotron (COSY-Jülich) – is a large-acceptance detector to study the decay channels of light mesons ranging up into the strange quark sector. A large number of η-mesons is being produced in proton-deuteron and proton-proton collisions. The huge amount of data permits the study of very rare η-decay channels. One of these channels is the double Dalitz decay, where the η-meson decays via two virtual photons into two electron-positron pairs. By introducing the Form Factor, this decay can be related to the QED process, where the η-meson decays into two real photons. The Form Factor depends on the squared invariant mass of the lepton pairs and allows one to study the structure of the decay mechanism.
Currently, there is only an experimental upper limit for the branching ratio. One objective of the WASA-at-COSY experiment is to reduce the upper limit for this decay channel or to determine a finite value of the branching ratio. The status of two independent analyses of this challenging decay based on an amount of in total 30 × 106 η-mesons from pd-interactions and preliminary results will be presented.