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The first measurement is reported of the double-polarization observable G in the photoproduction of neutral pions off protons, covering the photon energy range from 620 to 1120 MeV and the full solid angle. G describes the correlation between the photon polarization plane and the scattering plane for protons polarized along the direction of the incoming photon. The observable is highly sensitive to contributions from baryon resonances. The new results are compared to the predictions from SAID, MAID, and BnGa partial wave analyses. In spite of the long-lasting efforts to understand γp→pπ(0) as the simplest photoproduction reaction, surprisingly large differences between the new data and the latest predictions are observed which are traced to different contributions of the N(1535) resonance with spin parity J(P)=1/2(-) and N(1520) with J(P)=3/2(-). In the third resonance region, where N(1680) with J(P)=5/2(+) production dominates, the new data are reasonably close to the predictions.

New data on pion-photoproduction off the proton have been included in the partial wave analyses Bonn-Gatchina and SAID and in the dynamical coupled-channel approach Jülich-Bonn. All reproduce the recent new data well: the double polarization data for E, G, H, P and T in γp → π 0 p from ELSA, the beam asymmetry Σ for γp → π 0 p and π + n from Jefferson Laboratory, and the precise new differential cross section and beam asymmetry data Σ for γp → π 0 p from MAMI. The new fit results for the multipoles are compared with predictions not taking into account the new data. The mutual agreement is improved considerably but still far from being perfect.

In a search for ω mesic states, the production of ω-mesons in coincidence with forward going protons has been studied in photon induced reactions on 12 C for incident photon energies of 1250 -3100 MeV. The π 0 γ pairs from decays of bound or quasi-free ω-mesons have been measured with the CBELSA/TAPS detector system in coincidence with protons registered in the MiniTAPS forward array. Structures in the total energy distribution of the π 0 γ pairs, which would indicate the population and decay of bound ω 11 B states, are not observed. The π 0 γ cross section of 0.3 nb/MeV/sr observed in the bound state energy regime between -100 and 0 MeV may be accounted for by yield leaking into the bound state regime because of the large in-medium width of the ωmeson. A comparison of the measured total energy distribution with calculations suggests the real part V 0 of the ω 11 B potential to be small and only weakly attractive with V 0 (ρ = ρ 0 ) = −15± 35(stat) ±20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100 -150 MeV.