  We examine the uncertainty of perturbative QCD factorization for hadron
structure functions in deep inelastic scattering at a large value of the
Bjorken variable xB. We analyze the target mass correction to the structure
functions by using the collinear factorization approach in the momentum space.
We express the long distance physics of structure functions and the leading
target mass corrections in terms of parton distribution functions with the
standard operator definition. We compare our result with existing work on the
target mass correction. We also discuss the impact of a final-state jet
function on the extraction of parton distributions at large fractional momentum
x.
