Seminario di Fenomenologia delle Particelle Elementari

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low-x and low-Q2 . A resolution of this tension incorporating ln(1/x)- resummation into the HERAPDF fits is investigated using the xFitter program. Such resummation not only gives a better description of the data, but it also results in a gluon PDF which is steeply rising at low x for low scales, contrary to the fixed-order result. Then, a new parametrization for PDFs designed to be flexible in the small-x region has been studied and new fits to HERA data have been performed. The new parametrization leads to a better fit quality, both at fixed order and at resummed level, and thus removes a signficant bias present in the previously used parametrizations. The benefits of including small-x resummation remains signficant also with the new more flexible parametrization, thus giving more robustness to the previous results.