We analyze J/ψ− production in nucleon-nucleon collisions near threshold
in the framework of a general model independent formalism, which can be applied
to any reaction N+N→N+N+V0, where V0=ω, ϕ, or J/ψ. Such
reactions show large isotopic effects: a large difference for pp- and
pn-collisions, which is due to the different spin structure of the
corresponding matrix elements. The analysis of the spin structure and of the
polarization observables is based on symmetry properties of the strong
interaction. Using existing experimental data on the different decays of
J/ψ−meson, we suggest a model for N+N→N+N+J/ψ, based on
t−channel η+π-exchanges. We predict polarization phenomena for the
n+p→n+p+J/ψ-reaction and the ratio of cross sections for np and
pp-collisions. For the processes η(π)+N→N+J/ψ we apply two
different approaches: vector meson exchange and local four-particle
interaction. In both cases we find larger J/ψ-production in
np-collisions, with respect to pp-collisions.Comment: 17 pages, 6 figure