A Critical Appraisal and Evaluation of Modern PDFs

TL;DR

This paper critically reviews the current status of parton distribution functions (PDFs), comparing different sets, analyzing their uncertainties, and providing recommendations for their use in LHC predictions.

Contribution

It offers a comprehensive evaluation of existing PDF sets, analyzes differences in their predictions, and discusses uncertainties and averaging procedures relevant for LHC physics.

Findings

Differences in PDF predictions stem from specific theoretical assumptions.

PDF uncertainties are significant in the LHC kinematic region.

Recommendations are provided for using PDFs in collider predictions.

Abstract

We review the present status of the determination of parton distribution functions (PDFs) in the light of the precision requirements for the LHC in Run 2 and other future hadron colliders. We provide brief reviews of all currently available PDF sets and use them to compute cross sections for a number of benchmark processes, including Higgs boson production in gluon-gluon fusion at the LHC. We show that the differences in the predictions obtained with the various PDFs are due to particular theory assumptions made in the fits of those PDFs. We discuss PDF uncertainties in the kinematic region covered by the LHC and on averaging procedures for PDFs, such as advocated by the PDF4LHC15 sets, and provide recommendations for the usage of PDF sets for theory predictions at the LHC.