The effects of combined HERA and recent Tevatron W - > lepton neutrino charge asymmetry data on the MSTW PDFs

TL;DR

This paper assesses how incorporating combined HERA structure function data influences the MSTW PDFs and examines the consistency of Tevatron W charge asymmetry data with existing PDFs, finding small but notable effects and some tensions among data sets.

Contribution

It provides a detailed analysis of the impact of combined HERA data on PDFs and evaluates the compatibility of recent Tevatron charge asymmetry measurements with these PDFs.

Findings

HERA data causes up to 2-3% change in PDFs at NLO for certain processes.

D0 charge asymmetry data suggests significant adjustments to the down-quark distribution.

Some Tevatron W asymmetry data are inconsistent with the current PDFs.

Abstract

We examine the effect of including the `combined' HERA structure function data in the MSTW global fit for parton distribution functions (PDFs). The combined neutral-current HERA data have a significant, if not dramatic, effect, of up to 2--3% at NLO for Z boson and Higgs production at the Tevatron and LHC, and a generally slightly smaller effect, particularly on LHC processes, at NNLO. This is an amount comparable, or less than, the typical PDF uncertainties, and hence we do not intend to release an imminent update to the MSTW 2008 fit. We also investigate the consistency with the recent D0 data on electron and muon charge asymmetry from W decays and the direct CDF measurement of the W charge asymmetry. The D0 lepton charge asymmetry data imply a fairly large change to the down-quark distribution and/or large nuclear corrections to be applied when fitting to deuterium structure function data, while the CDF W charge asymmetry data are more consistent with the existing PDFs. However, it is difficult to reconcile all of the Tevatron W -> lepton neutrino charge asymmetry data sets with the fit, and to some extent, with each other.