The reaction pp -→ pΛK⁺ near threshold

We analyze the recent total cross section data for pp → pΛK⁺ near threshold measured at COSY. Using an effective range approximation for the on-shell pΛ S-wave final state interaction we extract from these data the combination K = √2|K_s|² + |K_t|² = 0.38 fm⁴ of the singlet (K_s) and triplet (K_t) threshold transition amplitudes. We present an exploratory calculation of various (tree-level) vector and pseudoscalar meson exchange diagrams. Pointlike w-exchange alone and the combined (p⁰, w K*⁺)-exchange can explain the experimental value of K. The pseudoscalar meson exchanges based on a SU(3) chiral Lagrangian turn out to be too large. However, when adding π⁰-exchange in combination with the resonant πN → S₁₁ (1650) → K Λ transition and introducing monopole form factors with a cut-off A_c = 1.5 GeV one is again able to reproduce the experimental value of K. More exclusive measurements are necessary to reveal the details of the pp → pΛK⁺ production mechanism.