Cross section of the $pp\to K^{+}{\mathrm{\Sigma }}^{+}n$ reaction close to threshold

We have measured inclusive data on $K^{+}$-meson production in $pp$ collisions at COSY J"ulich close to the hyperon production threshold and determined the hyperon-nucleon invariant mass spectra. The spectra were decomposed into three parts: $\mathrm{\Lambda }p$, ${\mathrm{\Sigma }}^{0}p$ and ${\mathrm{\Sigma }}^{+}n$. The cross section for the ${\mathrm{\Sigma }}^{+}n$ channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence.