The Structure of the Proton in the LHC Precision Era

Abstract

We review recent progress in the determination of the parton distribution functions (PDFs) of the proton, with emphasis on the applications for precision phenomenology at the Large Hadron Collider (LHC). First of all, we introduce the general theoretical framework underlying the global QCD analysis of the quark and gluon internal structure of protons. We then present a detailed overview of the hard-scattering measurements, and the corresponding theory predictions, that are used in state-of-the-art PDF fits. We emphasize here the role that higher-order QCD and electroweak corrections play in the description of recent highprecision collider data. We present the methodology used to extract PDFs in global analyses, including the PDF parametrization strategy and the definition and propagation of PDF uncertainties. Then we review and compare the most recent releases from the various PDF fitting collaborations, highlighting their differences and similarities. We discuss the role that QED corrections and photon-initiated contributions play in modern PDF analysis. We provide representative examples of the implications of PDF fits for high-precision LHC phenomenological applications, such as Higgs coupling measurements and searches for high-mass New Physics resonances. We conclude this report by discussing some selected topics relevant for the future of PDF determinations, including the treatment of theoretical uncertainties, the connection with lattice QCD calculations, and the role of PDFs at future high-energy colliders beyond the LHC.

Constraining the gluon PDF at large x with LHC data

“…Introduction. In a recent paper [1] the NNPDF Collaboration presented NNPDF3.1, a new set of parton distribution functions (PDFs) [2] which features several improvements with respect to the previous global analysis, NNPDF3.0 [3], both in terms of methodology and data. On the methodological side, the charm PDF was parametrised on the same footing as the other light quark and gluon PDFs.…”

The gluon and charm content of the deuteron

“…Now that we have the light-front distribution of the nucleon in the deuteron, we can derive the gluon PDF in the deuteron using the impulse approximation, by folding the gluon PDF of the nucleon [74][75][76][77][78][79][80][81] by N N/A (z). Since we are interested in the high-x behavior of the gluon PDF, we need a well behaved gluon PDF up to 1.…”

On the power divergence in quasi gluon distribution function

“…Because of the nonperturbative nature, the PDFs can not be calculated in QCD perturbation theory. Traditionally, PDFs are extracted using the experimental data for the processes in which the factorization theorem is established [1][2][3][4]. Another popular non-perturbative method is to use lattice QCD (LQCD).…”