  Achieving the highest precision for theoretical predictions at the LHC
requires the calculation of hard-scattering cross-sections that include
perturbative QCD corrections up to (N)NNLO and electroweak (EW) corrections up
to NLO. Parton distribution functions (PDFs) need to be provided with matching
accuracy, which in the case of QED effects involves introducing the photon
parton distribution of the proton, $x\gamma(x,Q^2)$. In this work a
determination of the photon PDF from fits to recent ATLAS measurements of
high-mass Drell-Yan dilepton production at $\sqrt{s}=8$ TeV is presented. This
analysis is based on the xFitter framework, and has required improvements both
in the APFEL program, to account for NLO QED effects, and in the aMCfast
interface to account for the photon-initiated contributions in the EW
calculations within MadGraph5_aMC@NLO. The results are compared with other
recent QED fits and determinations of the photon PDF, consistent results are
found.
