Speaker
Description
The study of the internal spin structure of the proton in terms of the contributions from quarks, anti-quarks and gluons, is a key focus of modern particle physics. These contributions can be described in terms of the longitudinally polarized parton distribution functions (pPDFs) or helicity PDFs, which are probed in high-energy scattering processes involving polarized nucleons.
In this talk I will present the results of our recent next-to-next-to-leading order (NNLO) fully-global QCD analysis of the proton's helicity PDFs. To obtain the distributions, we use data for longitudinal spin asymmetries in inclusive and semi-inclusive lepton-nucleon scattering as well as in weak-boson and hadron or jet production in proton-proton scattering. We analyze the data using QCD perturbation theory at NNLO accuracy, employing approximations provided by the threshold resummation formalism in cases where full NNLO results for partonic hard-scattering functions are not readily available. Our numerical results suggest a remarkable perturbative stability of the extracted helicity parton distribution functions.