Münster 2011 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 43: Hadronenstruktur und -spektroskopie VIII
HK 43.7: Vortrag
Mittwoch, 23. März 2011, 18:00–18:15, HS3
Measuring η → π+π−e+e− with WASA-at-COSY — •Daniel Coderre1,2 and James Ritman1,2 — 1Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, Germany — 2Institut für Experimentalphysik, Ruhr Universität Bochum, Germany
The analysis of the rare decay η → π+π−e+e− has two purposes: measurement of the branching ratio and probing of a possible non standard model CP violation observable in the decay system. Existing experimental results on the branching ratio are not in agreement with modern theories, but the high rates of η production at WASA-at-COSY will allow a statistically significant sample to be identified and a precise determination of the branching ratio to be made. Additionally, it has been postulated that the asymmetry between the electron and π decay planes in the η reference frame may be an observable for CP violation outside the standard model. Currently the upper limit for this asymmetry is about 1%.
We have recorded about 3x107 η-mesons produced with the reaction pd → 3Heη as well as about 108 η-mesons produced with the reaction pp → ppη just above the kinematic threshold. A clean sample of signal event candidates has been identified in the proton-deuteron data allowing a preliminary determination of the total branching ratio. The decay has also been observed in higher-statistic proton-proton data though the analysis of this data is in its early stages. The presentation will focus on the current results as well as on the analysis techniques.
Supported by COSY-FFE