Darmstadt 2016 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 47: Hadron Structure and Spectroscopy VIII

HK 47.1: Group Report

Thursday, March 17, 2016, 14:00–14:30, S1/01 A5

Study of η-Meson Decays with the WASA-at-COSY experiment — •Daniel Lersch for the WASA-at-COSY collaboration — Forschungszentrum Juelich, Germany

The study of η-decays allows to probe symmetry-breaking phenomena (e.g. C- and CP-violation), to measure the electromagnetic transition form factor and to explore the anomalous sector of QCD.

In order to perform those studies two data samples have been acquired with the WASA-at-COSY facility at Forschungszentrum Jülich. A proton beam, provided by COSY, is impinged upon a liquid deuterium / hydrogen pellet target producing η-mesons via: pd→³Heη / pp→ ppη. The η-decay products as well as the forward-scattered projectiles are detected within the 4π WASA-at-COSY detector.

A first iteration of measurements was done using the pd→³Heη reaction for the study of the more abundant η decay channels (such as η→π⁺π⁻π⁰) and to set up the framework for a common analysis. In order to address the rare η-decays (e.g. η→ π⁺π⁻e⁺e⁻) a high-statistics data set has been collected using the reaction pp→ ppη.

The current analysis of the pp→ ppη data set is dedicated to the isospin violating decay η→ π⁺π⁻π⁰; The determination of the electromagnetic transition form factor via the decays η→ e⁺e⁻γ and η→ e⁺e⁻e⁺e⁻; Testing C- and CP-violation by investigating η→π⁰e⁺e⁻ and η→ π⁺π⁻e⁺e⁻; Exploring the box anomaly via the radiative decay η→π⁺π⁻γ.

This talk will give an overview about the status of the analyses.