Berlin 2005 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 15: Hauptvortr
äge

HK 15.1: Invited Talk

Monday, March 7, 2005, 10:15–10:45, TU MA001

Meson Production and Decay Studies at CELSIUS-WASA^∗ — •H. Clement — Physikalisches Institut, Universität Tübingen

At the CELSIUS cooler ring pp and pd collisions with the emission of γs, πs, η and ω have been measured using the WASA 4π detector with hydrogen and deuterium pellet targets. The WASA detector containing magnetic field, tracking detectors and calorimeters allows the detection of both charged and neutral particles.
One major aspect in the research program is the production and the decay of the η. The decay studies are being pursued in particular by use of the newly installed zero-degree spectrometer, which provides very clean η tagging in the production reaction pd → ³He η. High-statistics runs are currently being carried out.
Another focal point are multi-pion production processes. Whereas close to threshold the data for the ppπ⁺π⁻ channel exhibit features of Roper excitation and/or dynamic formation of the σ meson, at higher energies the formation of the ΔΔ system becomes increasingly important. Surprisingly the π⁰π⁰ channel shows a systematic enhancement at small invariant masses, in ³Heπ⁰π⁰ this is even much larger than expected from Bose-Einstein correlations - pointing possibly to (dynamic) isospin breaking due to ππ rescattering. Also, in the invariant mass spectrum M_γγ a small, narrow line has been observed at M_γγ=2m_π. In search of the nature of this line we pursue a variety of scenarios.
^∗ supported by BMBF (06 TU 201), DFG (Europ. Graduiertenkolleg) and Landesforschungsschwerpunkt (Quasiteilchen)