Threshold open charm production in nucleon-nucleon collisions

The associative charm particles production in nucleon-nucleon collisions N + N --> Lambda(c) (Sigma(c)) + (D) over bar + N, is described in a general way and the spin and isospin structure of the corresponding matrix elements are derived. Using an analogy with strange-particle (LambdaK) production, the D-meson exchange model is considered in detail. Estimations of the energy behavior of the threshold cross-sections show a large dependence on the form of the phenomenological hadron form factors and indicate that, at threshold, the cross-section is three orders of magnitude smaller than for strange-particle production.