Illuminating the photon content of the proton within a global PDF analysis



In previous NNPDF analyses, a model-independent parametrization of the photon PDF was constrained by LHC Drell-Yan measurements. In this work, the photon PDF is instead determined by the LUXqed formalism relating it to inclusive structure functions in lepton-proton scattering. Based on the same settings as the NNPDF3.1 global analysis, the NNPDF3.1luxQED set accounts for QED effects in the DGLAP evolution, the momentum sum rule, and deep-inelastic scattering coefficient functions. The resulting uncertainties on γ(x,Q) are now at the few-percent level, with photons carrying up to ≃ 0.5% of the total proton momentum. We also study the phenomenological implications for Drell-Yan, vector boson pair, top quark pair, and Higgs associated production at the LHC. For electroweak processes, photon-initiated corrections range between a few percent up to ≃ 30%.

Paper: arXiv:1712.07053

LHAPDF sets: 10.5281/zenodo.1119583

NNPDF3.1 QED sets NLO and NNLO with nf=4