The energy dependence of the pp->K+ n Sigma+ reaction close to threshold

TL;DR

This study measures the Sigma+ hyperon production in proton-proton collisions near threshold energies, finding results consistent with phase space expectations and challenging previous reports of anomalously high cross sections.

Contribution

It provides new experimental data on Sigma+ production near threshold and refutes earlier claims of unexpectedly high cross sections.

Findings

Sigma+ production cross section varies with phase space

No evidence supporting previously reported high cross sections

Consistent results across multiple measurement methods

Abstract

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)].