Observation of spin-parity 2+ dominance in the reactionγγ→ρ0ρ0 near threshold

The reactionγγ→π+π−π+π− has been studied with the ARGUS detector. The rate in the invariant mass region below 1.8 GeV/c2 is found to be largely due toρ0ρ0 production. A spin-parity analysis shows a dominance of the partial wave (J P ,J z )=(2+, 2) with a small admixture fromJ P =0+. The contribution of negative parity states is consistent with zero. The large ratio of cross sectionsσ(γγ→ρ0ρ0)/σ(γγ→ρ+ρ−)≃4, and the dominance of theJ P =2+ wave in the reactionγγ→ρ0ρ0 is a signature consistent with the production of an exotic (I=2) resonance.