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HK: Fachverband Physik der Hadronen und Kerne

HK 8: Hadronenstruktur und -spektroskopie

HK 8.5: Vortrag

Montag, 17. März 2014, 18:15–18:30, HZ 1+2

Polarization Observables T and F in η-Photoproduction off Quasi-Free Protons and Neutrons — •Thomas Strub for the A2 collaboration — Departement of Physics, University of Basel, CH-4056 Basel, Switzerland

The study of the nucleons excitation spectrum by meson photoproduction has developed to a powerful tool in order to test QCD in the non-pertubative regime where effective quark models and lattice QCD become relevant. On the path towards a complete understanding also a minimal set of polarization observables has to be measured, from which one can deduce the J^P configurations of the resonances through partial wave analysis. Moreover, to decode the isospin decomposition of excited states it is necessary to measure on both the proton and the neutron. Eta-photoproduction is of special interest in two ways: First, since η has isospin I = 0, only N^* resonances can contribute. Second, the polarization observables can give further information about the narrow structure around 1670 MeV which has been observed in the cross section of the neutron channel in recent experiments.

Eta-photoproduction off a transversally polarized D-Butanol target has been measured using circularly polarized bremsstrahlung photons produced by the MAMI-C electron microtron with incident energies up to 1.5 GeV. Due to the nearly 4π acceptance of the combined Crystal Ball/TAPS setup it is possible to extract the double polarization observable F and the target asymmetry T for polarized, quasi-free protons and neutrons over a wide energy and angular range. Preliminary results for T and F are presented.