Bonn 2010 – wissenschaftliches Programm
HK 26.7: Vortrag
Dienstag, 16. März 2010, 18:15–18:30, HG IV
Measuring η→ π+ π− e+ e− with WASA-at-COSY — •Daniel Coderre and James Ritman — Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, Germany and Institut für Experimentalphysik, Ruhr Universität Bochum, Germany
The analysis of η → π+ π− e+ e− has two purposes: measurement of the branching ratio and probing of possible non Standard Model CP Violation in this decay. The existing experimental results on the branching ratio are not conclusive, but the higher 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. To probe the CP-Violating contribution the asymmetry between the electron and pion decay planes in the η reference frame will be measured. Currently, the upper limit for this asymmetry is about 1%.
We have on disk roughly 3x107 η decays produced with the reaction pd → 3He η just above threshold energy. The analysis focuses on proper track identification and efficient background rejection. Particle identification is particularly important not only for mass assignments, but for proper measurements of the decay plane angle. This presentation will show both the analysis methods and the first sample of candidates for this decay.