Determination of Parton Distribution Functions, Impact of HERA Data and Consequences for the LHC

Parton distribution functions are non-perturbative inputs necessary to calculate cross-sections for scattering processes involving hadrons in the initial state. They are obtained by fitting theoretical predictions to various sets of experimental measurements, many of which come from Deep Inelastic Scattering experiments. Among those, the experiments at the HERA electron-proton collider have played a crucial role, from the beginning of the data-taking, with the surprising observation of the strong rise of the structure function F2 at low Bjorken x in 1993, to its end, with the direct measurement of the structure function FL in 2008. This paper presents an overview of HERA measurements which constrain most the proton structure, and of our current knowledge of parton distribution functions (pdf) in the proton. The impact of the current pdf uncertainties on predictions for cross-sections at the LHC collider is also discussed. (author)