Abstract
The η -meson is a unique tool in a way that it provides access to (rare) decay processes, which allow to probe symmetry breaking phenomena, determine transition form factors, or to explore the anomalous sector of QCD. Those decays have been studied with the WASA-at-COSY experiment. Two data sets with different η -production mechanisms have been acquired. The analysis of those data sets are restricted to: The investigation of the isospin violating decay η → π + π − π 0 ; Exploring the box anomaly in η → π + π − γ ; The determination of the electromagnetic transition form factor via the reactions: η → e + e − and η → e + e − e + e − ; Testing the CP-violation in η → π + π − e + e − . An overview of the analysis of those decays will be given in the following.
Highlights
The WASA-at-COSY FacilityThe different η-decays are measured and reconstructed within the 4π wide angle shower apparatus (WASA) (see Fig. 1), which is located at the cooler synchrotron (COSY) at the Jülich Research Center in Germany
The η-meson is a unique tool in a way that it provides access to decay processes, which allow to probe symmetry breaking phenomena, determine transition form factors, or to explore the anomalous sector of QCD
The different η-decays are measured and reconstructed within the 4π wide angle shower apparatus (WASA), which is located at the cooler synchrotron (COSY) at the Jülich Research Center in Germany
Summary
The different η-decays are measured and reconstructed within the 4π wide angle shower apparatus (WASA) (see Fig. 1), which is located at the cooler synchrotron (COSY) at the Jülich Research Center in Germany. A proton beam, provided by COSY, is impinged on a liquid deuterium / hydrogen target producing η-mesons via: pd → 3Heη and pp → ppη. The scattered projectiles are detected in the forward part of WASA, where the angular information is provided by tracking detectors and the kinetic energy is reconstructed by a range hodoscope (see Fig. 1). The decay products are detected in the central part of WASA. Charged particles are reconstructed within a drift chamber in combination with a ∼ 1 T magnetic solenoid field. Additional plastic scintillators and an electromagnetic calorimeter allow for the distinction between pions and electrons. Neutral particles are reconstructed within the electromagnetic calorimeter
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