The total cross section of the reaction \(pp\to ppK^+K^-\) has been determined for proton--proton reactions with \(p_{beam}=3.67 GeV/c\). This represents the first cross section measurement of the ...\(pp \to ppK^-K^+\) channel near threshold, and is equivalent to the inclusive \(pp\to ppK^-X\) cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive \(pp\to ppK^+X\) meson production at the same CM energy above the corresponding threshold. This large difference in the \(K^+\) and \(K^-\) meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.
We report the first polarization transfer measurements for exclusive hyperon production reactions. The normal spin transfer coefficient DNN for pp -> p K+ Lambda is large and negative for forward ...Lambda production at a beam momentum of 3.67 GeV/c, a result qualitatively consistent with expectations for a mechanism dominated by kaon-exchange and rescattering. The sign of DNN is opposite to that observed in the fragmentation regime for inclusive Lambda production at much higher energies.
