Investigation into the limits of perturbation theory at low Q2 using HERA deep inelastic scattering data

A phenomenological study of the final combined HERA data on inclusive deep inelastic scattering has been performed. The data are presented and investigated for a kinematic range extending from values of the four-momentum transfer, Q(2), above 10(4) GeV2 down to the lowest values observable at HERA of Q(2) = 0.045 GeV2 and Bjorken x, x(Bj) = 6 x 10(-7). The data are well described by fits based on perturbative quantum chromodynamics (QCD) using collinear factorisation and evolution of the parton densities encompassed in the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi formalism from the highest Q(2) down to Q(2) of a few GeV2. The Regge formalism with the soft Pomeron pole can describe the data up to Q(2) approximate to 0.65 GeV2. The complete data set can be described by a new fit using the Abramowicz-LevinLevy-Maor parametrization. The region between the Regge and the perturbative QCD regimes is of particular interest.