The ?? in the reaction ?p? ?+???0?0 p at photon energies of 20?70 GeV

The reactionγp→π + π − π 0 π 0 p (excludingωπ 0 production) has been studied for photon energies in the range 20–70 GeV. A peak is seen in the 4π mass spectrum at ∼1.66 GeV with a width of ∼0.3 GeV which is identified with theρ′(1600). Maximum likelihood fits show that the peak is dominantly inρ ± π ∓ π 0 withB(ρ′→ρ 0 π 0 π 0)/B(ρ′→ρ ± π ∓ π 0)<0.1. This indicates anI=1ρπ final-state interaction. However, no evidence is found for any resonant ρπ state such as anA 1 orπ′.