Small x resummations confronted with F_2(x,Q^2) data

Abstract

It has been observed recently that a consistent LO BFKL gluon evolution leads to a steep growth of F_2(x,Q^2) for x -> 0 almost independently of Q^2. We show that current data from the DESY HERA collider are precise enough to finally rule out a pure BFKL behaviour in the accessible small x region. Several attempts have been made by other groups to treat the BFKL type small x resummations instead as additions to the conventional anomalous dimensions of the successful renormalization group ``Altarelli-Parisi'' equations. We demonstrate that all presently available F_2 data, in particular at lower values of Q^2, can not be described using the presently known NLO (two-loop consistent) small x resummations. Finally we comment on the common reason for the failure of these BFKL inspired methods which result, in general, in too steep x-dependencies as x -> 0.

Comments: Revised, to be published in Phys. Lett. B., 18 pages, LaTeX2e, 3 figures, uses amssymb and epsfig styles