  The assumption of factorization lies at the core of calculations of medium
effects on observables computable in perturbative Quantum Chromodynamics. In
this work we examine this assumption, for which we propose a setup to study
hard processes and bulk nuclear matter in heavy-ion collisions on the same
footing using the Glauber modelling of heavy nuclei. To exemplify this
approach, we calculate the leading-order corrections to azimuthal decorrelation
in Drell-Yan and boson-jet processes due to cold nuclear matter effects, not
considering radiation. At leading order in both the hard momentum scale and the
nuclear size, the impact-parameter dependent cross section is found to
factorize for both processes. The factorization formula involves a convolution
of the hard cross section with the medium-modified parton distributions, and,
for boson-jet production, the medium-modified jet function.
