Münster 2002 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 40: Electromagnetic and Hadronic Probes V

HK 40.2: Talk

Thursday, March 14, 2002, 14:30–14:45, D

First results of the CB-ELSA experiment — •Volker Credé — ISKP, University of Bonn

Constituent quark models predict far more states in the baryon spectrum than have been experimentally observed up to now. As nearly all results stem from πN scattering, photoproduction experiments seem to have a large discovery potential. The search for missing resonances is a topical aim of the CB-ELSA experiment. A large amount of data has been taken with a new setup since December 2000 at the e⁻ accelerator ELSA in Bonn. In a first series of experiments, the Crystal Barrel Detector was used in a combination with Time-Of-Flight walls in the forward direction. This setup almost forms a 4π arrangement and was used to measure a variety of multi-photon final states. Almost 200 000 events of the type γp→pπ⁰π⁰ and 40 000 events of the type γp→pπ⁰η could be identified and reconstructed. First hints for resonance production is given and cascades of the type N^**→N^*→ π⁰π⁰(π⁰η)p are observed. Indications for a P₃₃(1940)Δ are seen. Furthermore, differential cross sections for η photoproduction up to 2.8 GeV could be extracted from the data. Good consistency is found for η→γγ as well as for η→ 3π⁰. In addition, reactions of the type γp→pω and γp→pπ⁰ω are being analysed. The combined investigation of all these channels will help to answer questions as to what the relevant degrees of freedom and effective forces in hadrons are.

Supported by DFG.