Production of K⁺K⁻ pairs in proton-proton collisions below the Φ meson threshold

The pp→ppK⁺K⁻ reaction was measured below the Φ threshold at a beam energy of 2.568 GeV using the COSY-ANKE magnetic spectrometer. By assuming that the four-body phase space is distorted only by the product of two-body final-state interactions, fits to a variety of one-dimensional distributions permit the evaluation of differential and total cross sections. The shapes of the distributions in the Kp and Kpp invariant masses are reproduced only if the K⁻p interaction is even stronger than that found at higher energy. The cusp effect in the K⁺K⁻ distribution at the K⁰K¯¯¯⁰ threshold is much more clear and some evidence is also found for coupling between the K⁻p and K¯¯¯⁰n channels. However, the energy dependence of the total cross section cannot be reproduced by considering only a simple product of such pairwise final-state interactions.