The pp->K+n Sigma+ reaction near threshold

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 Sigma(0), and pp -> K+ n Sigma(+) reactions. While the resulting values for Lambda and Sigma(0) 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)) mu b 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. (c) 2007 Elsevier B.V. All rights reserved