München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 9: Elektromagnetische und Hadronische Sonden

HK 9.1: Gruppenbericht

Montag, 20. März 2006, 16:30–17:00, G

Physics with WASA at COSY — •Magnus Wolke — Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich, Germany

The physics programme for WASA at COSY focuses on the fate of fundamental symmetries and symmetry breaking patterns in hadronic systems, to extend our knowledge of aspects of QCD in the non–perturbative regime. Precision studies of η and η^′ decays and dedicated production experiments in isospin filtering reactions provide proper tools, and will be the key experiments of the new experimental facility at COSY Jülich.

Isospin symmetry breaking is probed by pseudoscalar decays that vanish in the chiral limit, i.e. decays η^′→ 3 π allow to derive the light up–down quark mass difference. Charge symmetry breaking few–nucleon reactions like d d → α π⁰ involve the same quark mass term, and can be studied exclusively at COSY. Radiative η and η^′ decays to γ γ and π⁺ π⁻ γ are determined by the anomalous behaviour of the QCD effective action under chiral transformation, reproduced in the Wess–Zumino–Witten Lagrangian. Higher order terms are expected to contribute to the non–resonant part of the π⁺ π⁻ γ decay modes, but have not been unequivocally confirmed experimentally. CP symmetry in flavour conserving processes will be probed in the semileptonic decay η → π⁺ π⁻ e⁺ e⁻, and a search sensitivity of the Standard Model prediction is aimed at in a test of C violation for η → π⁰ e⁺ e⁻.

The physics programme with WASA at COSY is introduced and the road map of the project towards first data taking beginning of 2007 is outlined.