  The CMS measurement of dijet pseudorapidity distributions in pPb versus pp
collisions at 5.02 TeV provides a direct probe on nuclear gluon PDFs. We show
that while the predicted pPb pseudorapidity distributions suffer from sizable
free-proton PDF uncertainties, the ratios of the pPb and pp distributions are
practically insensitive to scale and free-proton PDF choices. We find the CMS
data on pPb to pp ratios to be in good agreement with the EPPS16 nuclear
modifications. Using a non-quadratic extension of the Hessian PDF reweighting
method, we study the impact of these data on the EPPS16 nuclear PDFs. Relative
to EPPS16, we find stronger evidence for mid-x gluon antishadowing as well as
indication for larger gluon shadowing at small x. The data are also able to
further constrain the gluon PDF in the EMC region.
