Combination of H1 and ZEUS Inclusive Deep Inelastic e±p Scattering Cross Section Measurements and Extraction of the Proton Parton Density Functions using a NLO-QCD Fit

A new averaging method is used to combine previously published HERA-I data by the H1 and ZEUS Collaborations of neutral and charged current inclusive cross sections for e±p scattering. The combination procedure takes into account the systematic error correlations in a coherent approach, leading to a significantly reduced overall cross section uncertainty. This precise combined HERA-I data set is then used as the sole input for a next-to-leading order (NLO) QCD parton distribution function (PDF) fit. The consistent treatment of systematic uncertainties in the combined data results in PDFs with greatly reduced experimental uncertainties compared to the separate analyses of the H1 and ZEUS experiments. Model uncertainties, including those arising from parametrisation dependence, are also carefully considered. The resulting HERAPDFs have impressive precision compared to the global fits.