Mainz 2012 – wissenschaftliches Programm

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HK: Fachverband Physik der Hadronen und Kerne

HK 38: Hadronenstruktur und -spektroskopie

HK 38.7: Vortrag

Donnerstag, 22. März 2012, 18:30–18:45, RW 1

Measurement of the Rare Decay η→π+πe+e with WASA-at-COSY — •Daniel Coderre1,2 and James Ritman1,21Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich — 2Institut für Experimentalphysik I, Ruhr-Universität-Bochum

One focus of the WASA-at-COSY physics program is the testing of fundamental symmetries by measuring decays of light mesons. The decay η→π+πe+e has been measured with two main goals. First, to use a high-statistics sample of events to determine the branching ratio and second, to probe possible violation of CP-symmetry. It has been suggested that interference terms involving the CP-violating E1 transition could contribute to the decay rate. This would induce an asymmetry in the angle between the electron and π decay planes that could be an observable for CP-violation outside of the standard model. The theoretical upper limit for this asymmetry is  1%.

At WASA η mesons are produced in the pd3Heη and pppp η reactions. Preliminary results for the branching ratio and the CP-violating asymmetry term have been obtained from the proton-deuteron data, which features relatively low backgrounds but limited rates of η production. In the proton-proton data, which features significantly higher rates of η production but also higher backgrounds, the signal decay has been identified with improved statistics and extraction of the physics observables is in progress. This presentation will describe the analysis process with a focus on current and future results.

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