Small–x Resummation and HERA Structure Function Data

We apply our systematic NLO small x resummation of singlet splitting functions to the scaling violations of structure functions and compare the results with data. We develop various theoretical tools which are needed in order to relate resummed parton distributions to measurable structure functions, and we present results from a variety of fits to HERA data for the structure functions F2 and FL using the resummation. The behaviour of the singlet splitting functions at small x and fixed Q is effectively parametrized as x. We find that, for λ small or negative, the resummed description of scaling violations may be phenomenologically as good as or even better than the standard next-to-leading order treatment. However, the best fit gluon density and value of αs can be significantly modified by the resummation. CERN-TH/2000-252 November 2000 † On leave from INFN, Sezione di Torino, Italy