Speaker
Description
A powerful tool to investigate the properties of nucleon resonances is the detailed study of the excitation spectrum of the nucleons. It consists of many resonances which contribute with different strength to distinct decay channels. To obtain information about the contributing resonances,
the experimental measurement of several well chosen single
and double polarization observables is needed in different decay channels.
These observables are used as input for Partial Wave Analyses (PWA) which identify the resonances and characterize their properties.
The polarization observables are measured at the Crystal Ball experiment at MAMI in Mainz, using polarized photons and polarized nucleons. The setup covers nearly 4$\pi$ of the solid angle and has a high detection efficiency for neutral and charged final states.
The preliminary results of the double polarization observable G and E in the reactions $\gamma p \to p \pi^0$ and $\gamma p \to n \pi^+$ are presented.
They have been determined in a beam energy range starting from 266 MeV to 860 MeV for G and from 266 MeV to 1400 MeV for E , using a linearly/circularly polarized photon beam in combination with a longitudinally polarized butanol target.
Supported by the Deutsche Forschungsgemeinschaft (SFB1044), Schweizerischer Nationalfonds and Hadron Physics 3 under the 7$^{th}$ Framework Program of the EU.
