Monday, August 5, 2013

A QCD fit analysis to the combined HERA-I inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for $e^\pm p$ scattering resulting into a competitive NLO PDF set, HERAPDF1.0 is presented. HERAPDF at NNLO fits are presented as well, resulting, however, in a worse description of the combined HERA data. In addition, a preliminary analysis including the HERA II measurements of lower proton-beam energies is performed. The effect of including the new data on the determination of HERA parton distribution functions is analysed, using fits similar to those performed for HERAPDF1.0. Some tension of the QCD fit with respect to the data is identified in the kinematic region of low $Q^2$ and low x. Finally, the QCD fit analysis of the combined HERA-I inclusive deep inelastic cross sections has been extended to include combined HERA II measurements at high $Q^2$. The effect of including these data on the determination of parton distribution functions is analysed, resulting into HERAPDF1.5. The precision of the new PDFs at high-x is considerably improved, particularly in the valence sector.