Dresden 2013 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 6: Hadronenstruktur und -spektroskopie

HK 6.7: Talk

Monday, March 4, 2013, 12:45–13:00, HSZ-304

Measuring the relative branching ratio and the E_γ-distribution of η → π⁺ π⁻ γ with WASA-at-COSY — Daniel Lersch¹ and •Frank Goldenbaum^1,2 — ¹Jülich 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 (relative) branching ratio (done by CLEO and KLOE) and (ii) the distribution of the photon energy E_γ.

In order to measure both observables in one experiment, the WASA-at-COSY collaboration has measured the reaction pp→ pp[η→ π⁺π⁻γ]. The status on reconstructing this channel will be presented together with results on the channel η→ π⁺π⁻π⁰ which is a major component of the background to the channel of interest, and is needed to normalise the measured partial width. In this presentation the methods and preliminary results will be presented.