Paper
MSTW PDFs and impact of PDFs on cross sections at Tevatron and LHC
Authors
Graeme Watt
Abstract
We briefly summarise the "MSTW 2008" determination of parton distribution functions (PDFs), and subsequent follow-up studies, before reviewing some topical issues concerning the PDF dependence of cross sections at the Tevatron and LHC. We update a recently published study of benchmark Standard Model total cross sections (W, Z, gg->H and t-tbar production) at the 7 TeV LHC, where we account for all publicly available PDF sets and we compare to LHC data for W, Z, and t-tbar production. We show the sensitivity of the Higgs cross sections to the gluon distribution, then we demonstrate the ability of the Tevatron jet data, and also the LHC t-tbar data, to discriminate between PDF sets with different high-x gluon distributions. We discuss the related problem of attempts to extract the strong coupling alpha_S from only deep-inelastic scattering data, and we conclude that a direct data constraint on the high-x gluon distribution is required to obtain a meaningful result. We therefore discourage the use of PDF sets obtained from "non-global" fits where the high-x gluon distribution is not directly constrained by data.