Köln 2004 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 30: Electromagnetic and Hadronic Probes V
HK 30.7: Vortrag
Mittwoch, 10. März 2004, 15:45–16:00, B
η photoproduction on nuclei — •Th. Mertens — University of Basel, 4056 Basel, Klingelbergstr. 82, Switzerland
The in-medium behavior of nucleon resonances and mesons is a hotly debated topic. Measurements of total photoabsorption from nuclei show a strong suppresion of the peak corresponding to the excitation of the P11(1440) , D13(1520) and S11(1535) resonance.
Photoproduction of η mesons in this energy region is completely dominated by the excitation of the S11(1535) resonance and this allows a detailed study of this state. Previous measurements of quasifree η photoproduction found no unexplained suppression of the reaction although strong FSI effects have been seen.
However, those experiments did not cover the full excitation range of the resonance so that no final conclusion about in-medium effects on position and width could be drawn.
The present experiment on 12 C , 40 Ca , 93 Nb , Pb using the Crystall Barrel and Taps detector at the ELSA accelerator will overcome the problem with data up to 2.6 GeV. Furthermore, the investigation of the π0 η final state may allow for the first time the study of in-medium modification of the scalar meson a0(980) . First preliminary results will be discussed.