The production of the Sigma+ hyperon through the pp->K+nSigma+ 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 that 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 the 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+ nSigma+ total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].
The K+ double-differential cross section at each of the 5 beam energies intgerated over momentum bins of width +- 12 MeV/c. Note the errors do not include the 7 PCT systematic uncertainty coming from the normalization.
Total cross section for the P P --> K+ P LAMBDA.
Total cross section for the P P --> K+ P SIGMA0.
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+ pi+ correlated pairs, can all be well described using consistent values of the total cross sections for the pp->K+ p Lambda, pp->K+ p Sigma0, and pp->K+ n Sigma+ reactions. While the resulting values for Lambda and Sigma0 production are in good agreement with world data, our value for the total Sigma+ production cross section, sigma(pp->K+ n Sigma+) = 2.5+/-0.6(stat)+/-0.4(syst) mkb at an excess energy of epsilon=129 MeV, could only be reconciled with other recently published data if there were a highly unusual near--threshold behaviour.
Total cross section for the reaction P P --> K+ N SIGMA+.
Total cross section for the reaction P P --> K+ P LAMBDA.
Total cross section for the reaction P P --> K+ P SIGMA0.
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