In this contribution we estimate the influence of the shadowing effect and initial state parton energy loss in the quarkonium production at HERA-B. We analyze the xF behavior of the effective exponent alpha(xF) and present a comparison with the preliminary HERA-B data for J/psi production. Moreover, we present our predictions for <FONT FACE=Symbol>¡</FONT> production at HERA-B. The magnitude of these effects in the J/psi production at RHIC is also analyzed.
Quarkonium production; Shadowing effects; Energy loss
