  Top-quark pair production at the LHC is directly sensitive to the gluon PDF
at large x. While total cross-section data is already included in several PDF
determinations, differential distributions are not, because the corresponding
NNLO calculations have become available only recently. In this work we study
the impact on the large-x gluon of top-quark pair differential distributions
measured by ATLAS and CMS at $\sqrt{s}=8$ TeV. Our analysis, performed in the
NNPDF3.0 framework at NNLO accuracy, allows us to identify the optimal
combination of LHC top-quark pair measurements that maximize the constraints on
the gluon, as well as to assess the compatibility between ATLAS and CMS data.
We find that differential distributions from top-quark pair production provide
significant constraints on the large-x gluon, comparable to those obtained from
inclusive jet production data, and thus should become an important ingredient
for the next generation of global PDF fits.
