Publications associated with Particle Theory

Parton distributions and lattice QCD calculations: A community white paper

Progress in Particle and Nuclear Physics Elsevier 100 (2018) 107-160

AM Cooper-Sarkar, M Constantinou, L Del Debbio, M Engelhardt, A Accardi, K Orginos, J-W Chen, G Bozzi, J Rojo, I Schienbein, G Schierholz, W Vogelsang, RS Thorne, S Collins, J-W Qiu, J Green, P Nadolsky, T Ishikawa, ER Nocera, F Olness, H-W Lin, A Kusina, R Gupta, LA Harland-Lang, C Alexandrou

In the framework of quantum chromodynamics (QCD), parton distribution functions (PDFs) quantify how the momentum and spin of a hadron are divided among its quark and gluon constituents. Two main approaches exist to determine PDFs. The first approach, based on QCD factorization theorems, realizes a QCD analysis of a suitable set of hard-scattering measurements, often using a variety of hadronic observables. The second approach, based on first-principle operator definitions of PDFs, uses lattice QCD to compute directly some PDF-related quantities, such as their moments. Motivated by recent progress in both approaches, in this document we present an overview of lattice-QCD and global-analysis techniques used to determine unpolarized and polarized proton PDFs and their moments. We provide benchmark numbers to validate present and future lattice-QCD calculations and we illustrate how they could be used to reduce the PDF uncertainties in current unpolarized and polarized global analyses. This document represents a first step towards establishing a common language between the two communities, to foster dialogue and to further improve our knowledge of PDFs.

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