Instantons and η meson production near threshold in NN collisions

An enhancement for the η production in proton–neutron collisions as compared with that in proton–proton scattering has been recently observed. We present a calculation for the production cross section, in proton–neutron collisions near threshold, within instanton model for the QCD vacuum and show that a specific flavor dependent nonperturbative quark–gluon interaction related to instantons is able to explain the observed enhancement.