Universality and Evolution of TMDs

TL;DR

This paper discusses how QCD evolution enhances the treatment of TMD parton distribution and fragmentation functions, enabling more accurate predictions across all transverse momentum ranges, especially for spin-sensitive observables.

Contribution

It introduces methods to convert non-perturbative TMD fits into fully evolved TMDs consistent with TMD-factorization formalism.

Findings

Evolution improves the predictive power of TMD-based calculations.

Fully evolved TMDs are consistent with the complete TMD-factorization formalism.

Evolution is crucial for accurate TMD predictions, especially for transverse spin observables.

Abstract

In this talk, we summarize how QCD evolution can be exploited to improve the treatment of transverse momentum dependent (TMD) parton distribution and fragmentation functions. The methods allow existing non-perturbative fits to be turned into fully evolved TMDs that are consistent with a complete TMD-factorization formalism over the full range of kT. We argue that evolution is essential to the predictive power of calculations that utilize TMD parton distribution and fragmentation functions, especially TMD observables that are sensitive to transverse spin.