The pp→K+nΣ+ reaction near threshold

Inclusive K+ production in proton-proton collisions has been measured at a beam energy of 2.16 GeV using the COSY-ANKE magnetic spectrometer. The resulting spectrum, as well as those corresponding to K+p and K+π+ correlated pairs, can all be well described using consistent values of the total cross sections for the pp→K+pΛ, pp→K+pΣ0, and pp→K+nΣ+ reactions. While the resulting values for Λ and Σ0 production are in good agreement with world data, our value for the total Σ+ production cross section, σ(pp→K+nΣ+)=(2.5±0.6stat±0.4syst) μb at an excess energy of ε=129 MeV, could only be reconciled with other recently published data if there were a highly unusual near threshold behaviour.