Energy dependence of thepp→K+nΣ+reaction close to threshold

Production of the ${\ensuremath{\Sigma}}^{+}$ hyperon through the $\mathit{pp}\ensuremath{\rightarrow}{K}^{+}n{\ensuremath{\Sigma}}^{+}$ reaction has been investigated at four energies close to threshold, $1.826,1.920,1.958$, and $2.020$ GeV. At low energies, correlated ${K}^{+}{\ensuremath{\pi}}^{+}$ pairs can only originate from ${\ensuremath{\Sigma}}^{+}$ production so their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the ${K}^{+}$-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive ${K}^{+}$ momentum distributions, also provide conservative upper limits on ${\ensuremath{\Sigma}}^{+}$ production rates. The measurements show a ${\ensuremath{\Sigma}}^{+}$ production cross section that varies roughly like phase space, and, in particular, none of the three experimental approaches used supports the anomalously high, near-threshold $\mathit{pp}\ensuremath{\rightarrow}{K}^{+}n{\ensuremath{\Sigma}}^{+}$ total cross section previously reported [T. Ro\ifmmode \dot{z}\else \.{z}\fi{}ek et al., Phys. Lett. B 643, 251 (2006)].