NNLO PDFs for the LHC

TL;DR

This paper reviews the progress and remaining challenges in precisely determining parton distribution functions (PDFs) at NNLO, emphasizing theoretical frameworks, experimental data, and the impact of higher-order QCD corrections for LHC predictions.

Contribution

It provides an overview of the current status of NNLO PDF determinations, highlighting the fixed flavor number scheme and the role of new collider data in refining PDFs.

Findings

Good agreement of heavy-quark contributions with experimental data

Drell-Yan data helps disentangle quark flavors at various x

No significant changes in PDFs when including higher-order corrections

Abstract

We consider some trends, achievements and a series of remaining problems in the precision determination of parton distribution functions. For the description of the scaling violations of the deep-inelastic scattering data, forming the key ingredients to all PDF fits, a solid theoretical framework is of importance. It is provided by the fixed flavor number scheme in describing the heavy-quark contributions which is found in good agreement with the present experimental data in a very wide range of momentum transfers. In this framework also a consistent determination of the heavy-quark masses is possible at high precision. The emerging Drell-Yan data measured at hadron colliders start to play a crucial role in disentangling the quark species, particularly at small and large values of $x$. These new inputs demonstrate a good overall consistency with the earlier constraints on the PDFs coming from fixed-target experiments. No dramatic change is observed in the PDFs in case of a consistent account of the higher-order QCD corrections and when leaving enough flexibility in the PDF shape parameterization.}