  Inspired by the recent measurements of the CMS collaboration, we report a QCD
study of dijet production in proton+lead collisions at the LHC involving
large-transverse-momentum jets, $p_T \gtrsim 100$ GeV. Examining the inherent
uncertainties of the next-to-leading order perturbative QCD calculations and
their sensitivity to the free proton parton distributions (PDFs), we observe a
rather small, typically much less than 5% clearance for the shape of the dijet
rapidity distribution within approximately 1.5 units around the midrapidity.
Even a more stable observable is the ratio between the yields in the positive
and negative dijet rapidity, for which the baseline uncertainty can be made
negligible by imposing a symmetric jet rapidity acceptance. Both observables
prove sensitive to the nuclear modifications of the gluon distributions, the
corresponding uncertainties clearly exceeding the estimated baseline
uncertainties from the free-proton PDFs and scale dependence. From a
theoretical point of view, these observables are therefore very suitable for
testing the validity of the collinear factorization and have a high potential
to provide precision constraints for the nuclear PDFs.
