Heidelberg 2015 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 28: Hadron Structure and Spectroscopy 6

HK 28.1: Group Report

Tuesday, March 24, 2015, 14:30–15:00, T/SR25

Analysis of η-Meson Decays from the WASA Campaign at COSY — •Daniel Lersch for the WASA-at-COSY collaboration — Forschungszentrum Jülich, Germany

A pp→ ppη data sample has been acquired with the WASA-at-COSY facility at Forschungszentrum Jülich. A proton beam is accelerated with 1.4 GeV kinetic energy within the COSY storage ring towards a liquid hydrogen pellet target producing η-mesons. The η-decay products as well as the forward-scattered projectiles are detected within the 4π WASA-at-COSY detector. A first round of experiments was done with the pd→³Heη reaction used for the study of the more abundant η decay channels and to set up the framework for a common analysis. In order to address also rare decays ∼10⁹ η-mesons have been collected in the pp→ ppη reaction.

The study of η-decays allows to probe symmetry-breaking phenomena (e.g. C- and CP-violation), to test theoretical calculations and to explore the anomalous sector of QCD. The current analysis of the pp→ ppη data set is related to the charged decay modes of the η-meson: η→ π⁺π⁻π⁰ allows to probe quark mass ratios, η→ e⁺e⁻γ and η→ e⁺e⁻e⁺e⁻ serve to determine the electromagnetic transition form factor, the C-violating decay η→π⁰e⁺e⁻, or the radiative decay η→π⁺π⁻γ which is (in the chiral limit) sensitive to the box anomaly.

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