Energy dependence of the pp→K^{+}nΣ^{+} reaction close to threshold

Production of the Sigma(+) hyperon through the pp -> K(+)n 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+pi(+) pairs can only originate from 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 Sigma(+) production rates. The measurements show a 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 pp -> K(+)n Sigma(+) total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].