LO, NLO, and NNLO Parton Distributions for LHC Event Generators

TL;DR

This paper introduces the NNPDF4.0MC set of parton distribution functions tailored for Monte Carlo event generators at LO, NLO, and NNLO, emphasizing constraints like positivity and stability across phase space.

Contribution

It develops a new PDF set optimized for MC generators, incorporating additional constraints and comparing it to previous sets for improved LHC phenomenology.

Findings

NNPDF4.0MC PDFs satisfy positivity and stability criteria.

Comparison shows differences with baseline NNPDF4.0 and NNPDF2.3LO sets.

Phenomenological impact on LHC cross-sections is briefly assessed.

Abstract

We present NNPDF4.0MC, a variant of the NNPDF4.0 set of parton distributions (PDFs) at LO, NLO and NNLO, with and without inclusion of the photon PDF, suitable for use with Monte Carlo (MC) event generators, which require PDFs to satisfy additional constraints in comparison to standard PDF sets. These requirements include PDF positivity down to a low scale $Q\sim 1$ GeV, smooth extrapolation in the very small and large $x$ regions, and numerically stable results even in extreme regions of phase space for all PDFs. We compare the NNPDF4.0MC PDFs to their baseline NNPDF4.0 counterparts, and to the NNPDF2.3LO set entering the Monash tune of the Pythia8 event generator. We briefly assess the phenomenological impact of these PDFs on the cross-sections for hard and soft QCD processes at the LHC.