We explore production mechanism and final state interaction in the $pp to nK^ + Sigma ^ +$ channel based on the inconsistent experimental data published respectively by COSY-11 and COSY-ANKE. The scattering parameter $a> 0$ for $nSigma ^ +$ interaction is favored by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong $nSigma ^ +$ interaction comparable to $pp$ interaction is also indicated. Based on this analysis we calculate the contribution from resonance $Delta ^* (1920)$ through $pi ^ +$ exchange within resonance model, and the numerical result suggests a rather small near-threshold total cross section, which is consistent with the COSY-ANKE data. With an additional sub-threshold resonance $Delta ^*(1620)$, the model gives a much better description to the rather large near-threshold total cross section published by COSY-11.
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