Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 16: Elektromagnetische und Hadronische Proben
HK 16.7: Vortrag
Montag, 7. März 2005, 15:30–15:45, TU MA001
η photoproduction on nuclei — •Thierry Mertens — Universität Basel, CH-4056 Basel, Klingelbergst. 82
Total photo-absorption cross sections on nuclei show a clear disappearance of the second resonance region. Theoritical models predict such a depletion caused by a large increase of the D13(1520) width. The η photoproduction on nuclei is a very powerful tool to investigate properties and possible in-medium modification of the S11(1535) resonance. It allows us to select one particular resonance since η photoproduction in this energy range is completely dominated by the excitation of the S11(1535). The Experiments have been carried out using the combined Crystall Barrel and Taps detectors at the ELSA accelerator facility in Bonn with an incident photon beam up to 2.2 GeV. The inclusive η cross section covering the entire lineshape of the S11(1535) has been measured on four nuclear targets: carbon, calcium, nyobium and lead. Furthermore the final state interaction of η mesons in nuclear matter was analysed in view of the η -mean free path. Previous experiments extracted an average value of ≈ 2 fm using incident photons up to 800 MeV. This is the region where the η - nucleon interaction is dominated by the excitation of the S11(1535). The present experiment extends to much larger momenta of the η meson.