Mainz 2012 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 38: Hadronenstruktur und -spektroskopie

HK 38.6: Talk

Thursday, March 22, 2012, 18:15–18:30, RW 1

In search of the box anomaly by studying η → π⁺ π⁻ γ — •Daniel Lersch¹ and Frank Goldenbaum^1,2 — ¹Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich — ²Bergische Universität Wuppertal FB C

The decay channel η→ π⁺ π⁻ γ provides the opportunity to study QCD anomalies at the chiral limit. The decay width and the shape of the E_γ-distribution of this channel are sensitive to the box anomly term which is part of the Wess-Zumino-Witten-(WZW) Lagrangian. However, the theoretically predicted decay width and E_γ-distribution do not agree with the experimental results, if final state interactions are not included by unitarized extensions of the WZW-Lagrangian.The experimental observables for testing these extensions are (i) the branching (done by CLEO and KLOE) or (ii) the distribution of the single photon energy.

Recently, the reaction pd→ ³He[η→ π⁺π⁻γ] has been measured with WASA-at-COSY.

The aim of this work is to measure the branching ratio and the single photon energy distribution in one experiment using the reaction: pp→ pp[η→ π⁺π⁻γ], using the data acquired during spring 2010.

As a first step in the recent analysis the channel η→ π⁺π⁻π⁰ has been investigated, because it is important for determining the relative branching ratio Γ(η→ π⁺π⁻γ)/Γ(η→ π⁺π⁻π⁰) and also because it contributes to the background of the decay η→ π⁺π⁻γ.
First results will show how the channel of interest is extracted from data and how the remaining background is determined.