Threshold open charm production in nucleon-nucleon collisions

The associative charm particles production in nucleon-nucleon collisions $N+N\to \Lambda_c(\Sigma_c)+\bar{D}+N$, 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 ($\Lambda K$)-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 order of magnitude smaller than for strange particle production.