Parton Distributions for LO Generators

TL;DR

This paper evaluates the effectiveness of various parton distribution functions (PDFs) when used with leading-order (LO) matrix elements, proposing an improved LO* PDF set that performs well across multiple processes.

Contribution

The study introduces an optimized LO* PDF set tailored for LO matrix element calculations, outperforming standard LO and NLO PDFs in many cases.

Findings

LO* PDFs perform as well as or better than LO and NLO PDFs in most processes.

The LO* PDF set is now available in the LHAPDF package.

Modified LO PDFs improve predictions for LO matrix element calculations.

Abstract

We present a study of the results obtained combining LO partonic matrix elements with either LO or NLO partons distributions. These are compared to the best prediction using NLO for both matrix elements and parton distributions. The aim is to determine which parton distributions are most appropriate to use in those cases where only LO matrix elements are available, e.g. as in many Monte Carlo generators. Both LO and NLO parton distributions have flaws, sometimes serious, for some processes, so a modified optimal LO set is suggested. We investigate a wide variety of process, and the LO* pdf works at least as well as, and often better than, both LO and NLO pdfs in nearly all cases.The LO* pdf set is now available in the LHAPDF package.