QCD factorization at forward rapidities

We analyze particle production in several reactions on nuclear targets at forward rapidities and different energies. The forward kinematic region at high energies allows to access the smallest Bjorken x. Nuclear effects are then usually interpreted as a result of the coherence effects associated with shadowing or the Color Glass Condensate. QCD factorization of soft and hard interactions requires the nucleus to be an universal filter for different Fock components of the projectile hadron. We demonstrate, however, that this is not the case in the vicinity of the kinematic limit, x → 1, where sharing of energy between the projectile constituents becomes an issue. The rise of suppression of particle production with x is confirmed by the E772 and E886 data on Drell-Yan and heavy quarkonia. We show that this effect can also be treated alternatively as an effective energy loss proportional to initial energy. This leads to a nuclear suppression at any energy, and predicts Feynman xF scaling of the suppression. We demonstrate how the kinematic limit influences the high-p_T particle production at mid-rapidity where the Cronin enhancement at medium-high p_T switches to a suppression at larger p_T violating thus QCD factorization. Such an expectation seems to be confirmed by RHIC data for pion and direct photon production. We show that this effect as an additional large-p_T suppression significantly revises calculations for jet quenching in heavy ion collisons at RHIC.