In this proceedings, we discuss factorization of jet cross section in heavy-ion collisions based on fixed-order calculations. First, using Glauber modelling of heavy nuclei, a factorized formula for jet cross sections is derived, which involves defining jet functions in QCD medium. Then, we present our result of the jet function for producing a heavy quark-antiquark pair, denoted by $Q\bar{Q}$ at leading order in a static medium. The jet function is found to depend on the virtuality of the hard parton that initializes the jet, showing that the presence of QCD matter allows the production of $𝑄\bar{𝑄}$ at virtuality where it is kinematically forbidden in vacuum jets.