Münster 2002 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 32: Electromagnetic and Hadronic Probes IV
HK 32.1: Group Report
Wednesday, March 13, 2002, 14:00–14:30, D
Neutral meson photoproduction off nuclei — •M. Pfeiffer — II. Physikalisches Institut, Heinrich-Buff-Ring 16, 35392 Giessen
The photoproduction of mesons allows a detailed study of lower lying nucleon resonances. A series of experiments has been carried out with photon energies up to 820 MeV at the Mainz Microtron (MAMI) using different production targets.
The 3He experiment focuses on the coherent eta production. Former experiments on other light targets (2H, 4He) show small coherent contributions only. However, the quantum numbers of 3He suggest a larger coherent signal. Standard theoretical models of the coherent photoproduction fail to explain the cross section in the vicinity of the production threshold, but calculations by Shevchenko et. al. [1] take the possibility of so-called eta-mesic nuclei into account. These quasi bound states of η and nucleus might be responsible for the near threshold behaviour of the cross section.
In another experiment, the meson photoproduction off carbon was studied. This experiment offers the possibility to investigate in-medium modifications of the ω meson. On the proton, the ω (mω=782 MeV) is out of reach of the MAMI energy regime. But, assuming a modification of the omega mass and width in the carbon nucleus, the cross section for incident photon energies up to 882 MeV becomes measurable. First results are shown and compared to theoretical calculations [2].
[1] N. V. Shevchenko et.al., nucl-th/0108031
[2] W. Cassing, private communications