Anomaly in the K^0_S Sigma^+ photoproduction cross section off the proton at the K* threshold

The $γ+ p \rightarrow K^0 + Σ^+$ photoproduction reaction is investigated in the energy region from threshold to $E_γ= 2250$\,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. It is speculated whether this signals the turnover of the reaction mechanism from t-channel exchange below the $K^*$ production threshold to an s-channel mechanism associated with the formation of a dynamically generated $K^*$-hyperon intermediate state.