Abstract
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 \simeq0.5\%≃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\%20%. Our results represent a state-of-the-art determination of the partonic structure of the proton including its photon component.
Highlights
We find that photon-initiated corrections computed with NNPDF3.1luxQED can be significant for many processes, leading to corrections of up to 20% depending on the kinematics
Parton distributions with QED effects and a photon parton distribution functions (PDFs) are an essential component in highprecision calculations of many LHC processes
|y | h driven strategy to determine the photon PDF, independently parametrising γ(x, Q0) and fitting it using constraints from Drell-Yan measurements at the LHC. While this strategy minimised the theoretical bias due to model assumptions, the lack of a precise experimental handle to constrain the photon PDF led to large uncertainties
Summary
Recent progress in the computation of higher-order QCD corrections to LHC processes is such that the current state-of-the-art accuracy is NNLO, with even N3LO calculations available in some relevant cases (see Ref. [1] for a review). The photon PDF is parametrised in a model-independent way using an artificial neural network and constrained by LHC Drell-Yan measurements This procedure was adopted in the NNPDF2.3/3.0QED determinations [23, 37,38,39]. Building upon the recent NNPDF3.1 fit [16], the goal of this paper is to perform a global PDF analysis including QED corrections where the LUXqed calculation is used to constrain the photon PDF. The resulting PDF set, NNPDF3.1luxQED, represents a state-of-the-art determination of the partonic content of the proton including its photon component. We find that photon-initiated corrections computed with NNPDF3.1luxQED can be significant for many processes, leading to corrections of up to 20% depending on the kinematics These PI contributions are consistent with previous estimates based on NNPDF3.0QED within uncertainties in the kinematic region Q >∼ MZ , with larger differences in processes for which Q < MZ. The full breakdown of the χ2/Ndat values in NNPDF3.1luxQED and its comparison with those in NNPDF3.1 is collected in Appendix A
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