Extraction of the Proton Parton Density Functions from the Combined HERA I Data using NLO QCD Fit

The precise combined HERA-I data set, of neutral and charged current inclusive crosssections for ep and e−p scattering, is 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 and the use of an improved theoretical model that takes into account the quark masses result in a new HERA PDF set. Model uncertainties, including those arising from parametrisation dependence, are also carefully considered. The resulting HERAPDF0.2 parton distributions have impressive precision compared to the global fits.