New Generation of Parton Distributions with Uncertainties from Global QCD Analysis

TL;DR

This paper delivers a new generation of parton distribution functions (CTEQ6M) with quantified uncertainties by integrating full correlated systematic errors into a global NLO QCD analysis and employing a Hessian-eigenvector framework to propagate uncertainties to physical predictions. The analysis yields a harder gluon distribution at moderate to large x, driven largely by inclusive jet data, and provides 40 eigenvector PDF sets for robust uncertainty estimates of collider observables. The work demonstrates improved fits to diverse datasets (DIS, Drell-Yan, jets) and presents uncertainties for parton luminosities at the Tevatron and LHC, including predicted cross-section uncertainties for W/Z production and a light Higgs. It also compares its methodology and results to MRST2001 and prior uncertainty studies, highlighting the importance of flexible parametrization and the limitations of current theory in reducing systematic uncertainties. Overall, this study establishes a practical, uncertainty-quantified framework for using PDFs in precision SM phenomenology and new-physics searches at high-energy colliders, with clear avenues for future refinement (NNLO, heavy-quark dynamics, resummation, and additional data).

Abstract

A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work significantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errors for both new and old data sets; (ii) a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the Hessian method. The new gluon distribution is considerably harder than that of previous standard fits. A number of physics issues, particularly relating to the behavior of the gluon distribution, are addressed in more quantitative terms than before. Extensive results on the uncertainties of parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are presented. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, based on current knowledge of the parton distributions. In particular, the uncertainties on the production cross sections of the $W,Z$ at the Tevatron and the LHC are estimated to be $\pm 4%$ and $\pm 5%$ respectively, and that of a light Higgs at the LHC to be $\pm 5%$.