Parton distributions and lattice QCD calculations: A community white paper

Journal article

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.

Authors: Lin, H; Nocera, E; Olness, F; Orginos, K; Rojo, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Progress in Particle and Nuclear Physics
• Volume: 100
• Pages: 107-160
• Publication date: 2018-01-31
• Acceptance date: 2018-01-31
• DOI: 10.1016/j.ppnp.2018.01.007
• EISSN: 1873-2224
• ISSN: 0146-6410
• Keywords: lattice QCD; unpolarized/polarized parton distribution functions (PDFs); global QCD fits