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HK: Fachverband Hadronen und Kerne

HK 34: Hadron Structure and Spectroscopy I

HK 34.7: Talk

Tuesday, March 17, 2009, 18:15–18:30, H-ZO 20

Analysis of the η→ e⁺e⁻e⁺e⁻ decay WASA-at-COSY — •Leonid Yurev — Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 — Joint Institute for Nuclear Research, Dzhelepov Laboratory of Nuclear Problems, 141980 Dubna, Russia

The decay η→ e⁺e⁻e⁺e⁻ is closely related to the channels with real photons: η→γγ, η→π⁺π⁻γ, η→ e⁺ e⁻γ which are driven by the chiral anomaly of Quantum Chromodynamics. The extended interaction region of the electromagnetic processes of the η meson is parameterized by a so-called transition form factor – a scalar function of the invariant masses squared of the photons. The decay η→ e⁺e⁻e⁺e⁻ allows to study the form factor in the domain where there are two virtual photons with positive invariant masses squared.

We have recorded 10⁷ η events in the reaction pd→³Heη at 1 GeV during a four weeks run in October 2008. The experimental method is similar to that used recently by the CELSIUS/WASA collaboration where two η→ e⁺e⁻e⁺e⁻ decay candidates were identified and an upper limit BR(η→ e⁺e⁻e⁺e⁻)<9.7· 10⁻⁵ (90% CL) was determined. Since the number of the η decays collected by the WASA-at-COSY collaboration is forty times larger, we expect to extract a statistically significant data sample of η→ e⁺e⁻e⁺e⁻ decays for the first time. In this presentation the status of the analysis of the η→ e⁺e⁻e⁺e⁻ decay channel and preliminary results will be discussed.

* Supported by FZ Jülich, BMBF, Wallenberg Foundation and DAAD