Collinear and TMD Quark and Gluon Densities from Parton Branching Solution of QCD Evolution Equations

TL;DR

This paper introduces a method to derive collinear and TMD parton densities from QCD evolution equations at NLO accuracy, validated against existing data and providing new predictions for transverse momentum distributions.

Contribution

It presents a novel approach to construct both collinear and TMD parton densities from parton-branching solutions of QCD evolution equations at NLO accuracy.

Findings

Numerical agreement with existing evolution programs within 1%

Predictions for transverse momentum distributions

Set of NLO TMD distributions based on the approach

Abstract

We study parton-branching solutions of QCD evolution equations and present a method to construct both collinear and transverse momentum dependent (TMD) parton densities from this approach. We work with next-to-leading-order (NLO) accuracy in the strong coupling. Using the unitarity picture in terms of resolvable and non-resolvable branchings, we analyze the role of the soft-gluon resolution scale in the evolution equations. For longitudinal momentum distributions, we find agreement of our numerical calculations with existing evolution programs at the level of better than 1 percent over a range of five orders of magnitude both in evolution scale and in longitudinal momentum fraction. We make predictions for the evolution of transverse momentum distributions. We perform fits to the high-precision deep inelastic scattering (DIS) structure function measurements, and we present a set of NLO TMD distributions based on the parton branching approach.