Anomaly in the KS0Σ+ photoproduction cross section off the proton at the K⁎ threshold

The γ+p→K0+Σ+ photoproduction reaction is investigated in the energy region from threshold to Eγ=2250 MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the K⁎ threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the K⁎Λ and K⁎Σ thresholds.