Dresden 2013 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 6: Hadronenstruktur und -spektroskopie

HK 6.1: Group Report

Monday, March 4, 2013, 11:00–11:30, HSZ-304

Measurement of charged decays of the η meson with WASA-at-COSY — •Daniel Coderre — Forschungszentrum Jülich, Germany

The WASA-at-COSY experiment is a 4-π detector installed at the COSY storage ring at the Jülich Research Center. The detector is designed to measure decays of light mesons in hadronic interactions and is capable of measuring both charged and neutral decay products. This presentation will focus on a data sample of 3× 10⁷ η-mesons which were collected in the pd →  ³He η reaction.

Precision studies of decays of the η meson allow probes of symmetry-breaking reactions as well as precise tests of theoretical calculations. The current analysis is focused on charged decays of the η, including the anomalous decays η→π⁺π⁻γ and η→π⁺π⁻e⁺e⁻ as well as the leptonic reactions η→ e⁺e⁻γ and η→ e⁺e⁻e⁺e⁻. The primary goal of the analysis is a precise and consistent measurement of the branching ratios of these channels. Additionally the electromagnetic transition form factor in the reaction η→ e⁺e⁻γ and the dihedral angle in η→ π⁺π⁻e⁺e⁻, which is an observable for possible CP-violation outside the standard model, are measured. The C-violating reaction η→π⁰e⁺e− is also analyzed in an attempt to improve the experimental upper limit on its branching ratio. Results of these analyses will be presented.

This work is supported by COSY-FFE.