CTEQ Parton Distributions and Flavor Dependence of Sea Quarks

TL;DR

This work presents a new generation of CTEQ parton distributions obtained from a comprehensive NLO QCD global analysis, incorporating high-precision DIS data to reveal detailed flavor structure in the sea. The best-fit CTEQ1M shows a strongly flavor-dependent sea, with a softer strange quark distribution that rises at small x and a sign change in the light sea asymmetry $ar{d}-ar{u}$ around x~0.06, while also reducing the gluon momentum fraction at low Q^2. The study demonstrates excellent overall agreement across diverse data sets and emphasizes the importance of relaxing conventional SU(2)/SU(3) assumptions for sea quarks. It also discusses uncertainties, including heavy-target corrections and charm mass effects, and outlines directions for incorporating additional data to further refine parton distributions and QCD consistency at small x.

Abstract

This paper describes salient features of new sets of parton distributions obtained by the CTEQ Collaboration based on a comprehensive QCD global analysis of all available data. The accuracy of the new data on deep inelastic scattering structure functions obtained by the very high statistics NMC and CCFR experiments provides unprecedented sensitivity to the flavor dependence of the sea-quark distributions. In addition to much better determination of the small x dependence of all parton distributions, we found: (i) the strange quark distribution is much softer than the non-strange sea quarks and rises above the latter at small-x; and (ii) the difference $\bar d-\bar u$ changes sign as a function of x. A few alternative sets of viable distributions with conventional assumptions are also discussed.