Breakdown of QCD factorization at large Feynman<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi fontweight="bold">x</mml:mi></mml:mrow></mml:math>

Recent measurements by the BRAHMS Collaboration of high-${p}_{T}$ hadron production at forward rapidities at the BNL Relativistic Heavy Ion Collider found the relative production rate $(d\text{\ensuremath{-}}\mathrm{Au})/(p\text{\ensuremath{-}}p)$ to be suppressed rather than enhanced. Examining other known reactions (forward production of light hadrons, the Drell-Yan process, heavy flavor production, etc.), one notes that all of these display a similar property, namely, their cross sections in nuclei are suppressed at large ${x}_{F}$. Since this is the region where ${x}_{2}$ is minimal, it is tempting to interpret this as a manifestation of coherence or of a color glass condensate, whereas it is actually a simple consequence of energy conservation and takes place even at low energies. We demonstrate that in all these reactions there is a common suppression mechanism that can be viewed, alternatively, as a consequence of a reduced survival probability for large rapidity gap processes in nuclei, a Sudakov suppression, an enhanced resolution of higher Fock states by nuclei, or an effective energy loss that rises linearly with energy. Our calculations agree with the data.