  Precision phenomenology at the LHC requires accounting for both higher-order
QCD and electroweak corrections as well as for photon-initiated subprocesses.
Building upon the recent NNPDF3.1 fit, in this work the photon content of the
proton is determined within a global analysis supplemented by the LUXqed
constraint relating the photon PDF to lepton-proton scattering structure
functions: NNPDF3.1luxQED. The uncertainties on the resulting photon PDF are at
the level of a few percent, with photons carrying up to 0.5% of the proton's
momentum. We study the phenomenological implications of NNPDF3.1luxQED at the
LHC for Drell-Yan, vector boson pair, top quark pair, and Higgs plus vector
boson production. We find that photon-initiated contributions can be
significant for many processes, leading to corrections of up to 20%. Our
results represent a state-of-the-art determination of the partonic structure of
the proton including its photon component.
