  We discuss the implications of the preliminary CMS dijet data from 5.02 TeV
pp and pPb collisions for gluon PDFs of the proton and nuclei. The preliminary
pp data show a discrepancy with NLO predictions using for example the CT14
PDFs. We find that this difference cannot be accommodated within the associated
scale uncertainties and debate the possible changes needed in the gluon PDF. A
similar discrepancy is found between the CMS pPb data and NLO predictions e.g.
with the EPPS16 nuclear modifications imposed on the CT14 proton PDFs. When a
nuclear modification ratio of the pp and pPb data is constructed, the
uncertainties in the scale choices and in proton PDFs effectively cancel and a
good agreement between the data and EPPS16 is found, except in some bins at
backward rapidities corresponding to large x of the nucleus. To assess the
impact of these data on the EPPS16 nuclear PDFs, we use a non-quadratic
extension of the Hessian PDF reweighting method. A significant reduction in
EPPS16 uncertainties is obtained with the fit supporting strong nuclear
shadowing and valence-like antishadowing for gluons. We also indicate the
possible extensions needed in the EPPS16 parametrization at large x.
