Proton-η′ interactions at threshold.

Abstract Recent data on photoproduction of η ′ mesons off protons have been included in the data base for the Bonn–Gatchina partial wave analysis. The real and imaginary parts of the S -wave η ′ p → η ′ p scattering amplitude in the threshold region were fit to yield the η ′ p scattering length and the interaction range. This new analysis found | a η ′ p | = (0.403 ± 0.015 ± 0.060) fm and a phase ϕ = (87 ± 2) ∘ , while the range parameter is not well-constrained. The striking behavior of the GRAAL data on the beam asymmetry in the threshold region suggests that a narrow proton- η ′ resonance might exist. However, the scattering length was found to be relatively insensitive to the possible existence of this narrow resonance. [ABSTRACT FROM AUTHOR]