Possible interpretation of the ρ′(1600) as a threshold enhancement

The possibility that the ρ′(1600) is not a true resonance is examined. In the model considered the reactions γ p→ρπ+π-p and e+e-→ρπ+π- proceed through the production of a virtual ρ meson. The threshold factors associated with the opening of the ρππ channel are shown to combine with the virtual-ρ propagators to produce peaks in the ρπ+π- mass spectra, similar in mass and width to the experimental spectra. However, a comparison of the relative magnitudes of the two reactions, when combined with experimental limits on the reaction π+p→Δ++ρπ+π-, rules out this mechanism. The roles of final-state interactions and of the virtual-mass dependence of the γ p→ρ p production amplitude are considered. It is then assumed that the ρ′ is a real resonance. The ρ′-γ coupling and the ρ′ p total cross section are extracted. We find fρ′24π= 21±10 and σρ′ p=23±4 mb, as compared with the ρ-meson values of 2.1 ± 0.5 and 22.2 ± 2.6 mb. The background due to a ρ tail in the production of the recently reported ρ′(1250) is briefly discussed.