Exact NNLO corrections vs K-factors in PDF fits

TL;DR

This paper compares the effects of using approximate K-factors versus exact NNLO corrections in PDF fits, focusing on top pair production at the LHC, and finds good agreement among different PDF sets.

Contribution

It introduces a new PDF fitting approach using exact NNLO corrections and compares it with traditional K-factor based methods.

Findings

Good agreement among K-factors from different PDF sets.

Exact NNLO corrections can be effectively incorporated into PDF fits.

K-factors vary depending on the PDF set used, affecting cross section predictions.

Abstract

Parton distribution functions (PDFs) often include datasets corresponding to processes whereby the theoretical predictions at next-to-next-to-leading order (NNLO) in peturbative QCD have to be approximated, and this approximation may be performed using K-factors, which in turn depend on the PDF set used to compute them. In this study, we investigate the impact of K-factors produced with various PDF sets, namely CT18, MSHT20 and NNPDF4.0 on (differential) cross sections of top pair production at the Large Hadron Collider (LHC). Furthermore, we perform a new fit (otherwise analogous to NNPDF4.0 with MHOUs) where the exact NNLO corrections are used in the fitting procedure and compare the K-factors obtained from this fit with those obtained from the above mentioned PDF sets. We find good agreement amongst K-factors obtained from these different PDF sets.