Large-x Parton Distributions
S. Kuhlmann, J. Huston, J. Morfin, F. Olness, J. Pumplin, J. F. Owens, W. K. Tung, J. J. Whitmore
TL;DR
This paper assesses the status of parton distributions at large x, focusing on gluon and quark uncertainties that become sizable beyond x ~ 0.1. It compares major global analyses (CTEQ5 and MRST), highlighting how data choices and k_T corrections drive divergent large-x gluon distributions, and outlines potential future measurements (Drell-Yan, Tevatron dijets, and HERA CC) to tighten constraints. The authors review various quark-distribution issues, including potential modifications to u and d at high x and higher-twist effects, showing current data do not mandate drastic changes but allow small corrections. They also analyze the d/u ratio and discuss how W asymmetry and NMC data can be reconciled with or without nuclear corrections, emphasizing the need for high-luminosity HERA data to settle the issue. The work emphasizes an experimental-theoretical program to reduce large-x PDF uncertainties before the LHC era.
Abstract
Reliable knowledge of parton distributions at large x is crucial for many searches for new physics signals in the next generation of collider experiments. Although these are generally well determined in the small and medium x range, it has been shown that their uncertainty grows rapidly for x > 0.1. We examine the status of the gluon and quark distributions in light of new questions that have been raised in the past two years about large-x parton distributions, as well as recent measurements which have improved the parton uncertainties. We perform several specific global fits to answer the outstanding questions, and to investigate the potential of future experiments, particularly at HERA, which may provide critical constraints on parton distributions at large x.