Strangeness Production Process $pp \to nK^ + \Sigma ^ +$ within Resonance Model

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 $n\Sigma ^ +$ interaction is favored by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong $n\Sigma ^ +$ 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.