Production of ρ0ω in 2-photon collisions

This thesis describes an experimental analysis of the reaction γγ→ρ0ω→2π+2π-π0. The data were taken with the CELLO detector at the PETRA ε+ε-storage ring with a beam energy of 17.5 GeV and correspond to an integrated luminosity of 86 pb -1 . After improvements of the photon reconstruction procedure, a signal of 50 ± 10 events of the type γγ→ωπ+π- can be selected, showing a complete π 0 ω correlation in the range of Wγγ < 2.5 GeV. Apart from σ γγ→π0ω (Wγγ) the topological cross section σ γγ→2π+2π-π0 (Wγγ) can be measured by making use of a second, independent selection. For the first time a spin-parity analysis of the reaction γγ→ωπ+π- is carried out by applying an extended maximum likelihood method. The inclusion of b1 π models allows to determine upper limits for the cross section σγγ→β1πxBR (β1→ωπ). In the W γγ range from 1.5 to 2.0 GeV the JP decomposition of the ρ0ω system leads to a mixture of several spin parity states. The absence of 2+ contributions establishes severe constraints on qqanti qanti q models. Present exchange models cannot provide a convivcing explanation for the experimental findings either. (orig.)