Experimental constraints on the ω –nucleus real potential

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 π0γ 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 π0γ pairs, which would indicate the population and decay of bound ω 11 B states, are not observed. The π0γ cross section of 0.3 nb MeV −1  sr −1 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 ω -meson. A comparison of the measured total energy distribution with calculations suggests the real part V0 of the ω 11 B potential to be small and only weakly attractive with V0(ρ=ρ0)=−15±35(stat)±20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100–150 MeV

The polarization observables T , P , and H and their impact on γp→pπ0 multipoles

Data on the polarization observables T , P , and H for the reaction γp→pπ0 are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction